EPA-600/1-77-053
November 1977
Airborne Particles
by
Subcommittee on Airborne Particles
Committee on Medical and Biologic Effects of
Environmental Pollutants
National Research Council
National Academy of Sciences
Washington, B.C.
Contract No. 68-02-1226
Project Officer
Orin Stopinski
Criteria and Special Studies Office
Health Effects Research Laboratory
Research Triangle Park, N.C. 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
HEALTH EFFECTS RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, N.C. 27711
-------
DISCLAIMER
This report has been reviewed by the Health Effects Research
Laboratory, I'.S. Environmental Protection Agency, ,HH) approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
NOTICE
The project that is the subject of this report was approved by the
Governing Board of the National Research Council, whose members are
drawn from the Councils of the National Academy of Sciences, the National
Academy of Engineering, and the Institute of Medicine. The members of
the Committee responsible for the report were chosed for their special
competences and with regard for apropriate balance.
This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee consisting
of members of the National Academy of Sciences, the National Academy of
Engineering, and the Institute of Medicine.
ii
-------
FOREWORD
The many benefits of our modern, developing, industrial society are
accompanied by certain hazards. Careful assessment of the relative risk
of existing and new man-made environmental hazards is necessary for the
establishment of sound regulatory policy. These regulations serve to
enhance the quality of our environment in order to promote the public
health and welfare and the productive capacity of our Nation's population.
The Health Effects Research Laboratory, Research Triangle Park,
conducts a coordinated environmental health research program in toxicology,
epidemiology, and clinical studies using human volunteer subjects. These
studies address problems in air pollution, non-ionizing radiation,
environmental carcinogenesis and the toxicology of pesticides as well as
other chemical pollutants. The Laboratory develops and revises air quality
criteria documents on pollutants for which national ambient air quality
standards exist or are proposed, provides the data for registration of new
pesticides or proposed suspension of those already in use, conducts research
on hazardous and toxic materials, and is preparing the health basis for
non-ionizing radiation standards. Direct support to the regulatory function
of the Agency is provided in the form of expert testimony and preparation of
affidavits as well as expert advice to the Administrator to assure the
adequacy of health care and surveillance of persons having suffered imminent
and substantial endangerment of their health.
To aid the Health Effects Research Laboratory to fulfill the functions
listed above, the National Academy of Sciences (NAS) under EPA Contract
No. 68-02-1226 prepares evaluative reports of current knowledge of selected
atmospheric pollutants. These documents serve as background material for
the preparation or revision of criteria documents, scientific and technical
assessment reports, partial bases foi EPA decisions and recommendations
for research needs. "Airborne Particles" is one of these reports.
John H. Knelson, M.D.
Director
Health Effects Research Laboratory
-------
SUBCOMMITTEE ON AIRBORNE PARTICLES
IAN T. T. HIGGINS, University of Michigan, Ann Arbor, Michigan, Chairman
ROY E. ALBERT, New York University Medical Center, New York, New York
ROBERT J. CHARLSON, University of Washington, Seattle, Washington
ELLIS F. DARLEY, University of California, Riverside, California
BENJAMIN G. FERRIS, JR., Harvard University School of Public Health, Boston,
Massachusetts
ROBERT FRANK, University of Washington, Seattle, Washinqton
KENNETH T. WHITBY, University of Minnesota, Minneapolis, Minnesota
JOHN REDMOND, JR., Division of Medical Sciences, National Research Council,
Washington, D.C., Staff Officer
IV
-------
CONTENTS .
CHAPTER
1 Introduction ............. , ............... 1
2 Aerosols: Characteristics, Behavior, and Measurement ....... 3
3 Aerosol Cycles ........................... 31
4 Measurements of Size Distribution and Concentration ........ 57
5 Chemical and Trend Data ...................... 97
5 Effects on Atmospheric Processes .................. Ill
7 Effects of Inhaled Particles on Humans and Animals: Deposition,
Retention, and Clearance . . . .x ............... 155
8 Effects of Sulfur Dioxide and Aerosols, Alone and Combined, on
Lung Function ......................... 213
9 Epidemiologic Studies on the Effects of Airborne Particles on
Human Health ......................... 243
10 Effects on Vegetation ....................... 289
11 Effects on Building Materials ................... 315
12 Summary, Conclusions, and Recommendations ............. 397
References ............................. 427
VI
-------
COMMITTEE ON MEDICAL AND BIOLOGIC EFFECTS OF ENVIRONMENTAL POLLUTANTS
REUEL A. STALLONES, University of Texas, Houston, Texas, Chairman
MARTIN ALEXANDER, Cornell University, Ithaca, New York
ANDREW A. BENSON, University of California, La Jolla, California
RONALD F. COBURN, University of Pennsylvania School of Medicine, Philadelphia,
Pennsylvania
CLEMENT A. FINCH, University of Washington School of Medicine, Seattle,
Washington
EVILLE GORHAM, University of Minnesota, Minneapolis, Minnesota
ROBERT I. HENKIN, Georgetown University Medical Center, Washington, D.C.
IAN T. T. HIGGINS, University of Michigan, Ann Arbor, Michigan
JOE W. HIGHTOWER, Rice University, Houston, Texas
HENRY KAMIN, Duke University Medical Center, Durham, North Carolina
ORVILLE A. LEVANDER, Agricultural Research Center, Beltsville, Maryland
ROGER P. SMITH, Dartmouth Medical School, Hanover, New Hampshire
T. D. BOAZ, JR., Division of Medical Sciences, National Research Council,
Washington, D.C., Executive Director
-------
ACKNOWLEDGMENTS
This document was prepared by the Subcommittee on Airborne Particles under
the chairmanship of Dr. Ian T. T. Higgins. Although the initial drafts of
the various sections were prepared by individuals, the entire document was
extensively reviewed by the entire Subcommittee and represents a group effort.
The Introduction was written by Dr. Higgins. Chapters 2 through 6, which
define particulates and describe their characteristics, measurements, sources,
and effects on atmospheric processes were written by Dr. Kenneth T. Whitby and
Dr. Robert J. Charlson with assistance from Dr. M. B. Baker, Dr. S. S. Butcher,
Dr. D. S. Covert, and Dr. T. V. Larson. Special credit for these five chapters
should go to Dr. Larson who coordinated the material and shaped it into its
final form.
The effects of inhaled particles on both humans and animals are described
in Chapter 7 by Dr. Morton Lippmann and Dr. Roy E. Albert, who were assisted
by Dr. D. B. Yeates.
Chapter 8, which covers the effects on lung function of sulfur dioxide
and aerosols, both alone and combined, was written by Dr. Robert Frank.
Epidemiologic studies on the effects of airborne particles on human health
are reviewed in Chapter 9 by Dr. Higgins and Dr. Benjamin G. Ferris, Jr.
Dr. Shimshon L. Lerman and Dr. Ellis F. Darley collaborated on Chapter 10,
in which the effects of particulate air pollutants on vegetation are discussed.
Extensive material on the effects of atmospheric particulate matter on
building materials is summarized in Chapter 11. This section was prepared by
the Building Research and Advisory Board, a unit of the National Research
Council.
vii
-------
Summaries of these chapters and the conclusions and recommendations of
the Subcommittee are contained in the final chapter, to which all Subcommittee
members contributed.
The preparation of the document was assisted by the comments from anonymous
reviewers designated by the Assembly of Life Sciences and from members of the
Committee on Medical and Biologic Effects of Environmental Pollutants. The
Subcommittee is particularly indebted to Dr. Joe W. Hightower who served as
Associate Editor.
Dr. Robert J. M. Horton of the Environmental Protection Agency gave inval-
uable assistance by providing the Subcommittee with various documents and trans-
lations. Informational assistance was obtained from the National Research
Council Advisory Center on Toxicology, The National Academy of Sciences Library,
The Library of Congress, the Department of Commerce Library, and the Air Pol-
lution Technical Information Center.
The staff officer for the Subcommittee on Airborne Particles was Mr. John
Redmond, Jr. Special recognition is given to Mrs. Louise Mulligan who verified
the many references. The document was edited by Mrs. Frances M. Peter.
viii
-------
CHAPTER 1
INTRODUCTION
The air we breathe contains many particles. In the unpolluted country-
side there may be mass concentrations of up to 50 pg/m3, while at the height
of pollution episodes concentrations have sometimes reached several mg/m ,
roughly 100 times as high. These particles may result from natural pro-
cesses (dust, spray, natural decay, etc.) or from the activities of man
(combustion or comminution). An important source is conversion of a gas
to an aerosol either from cooling or from oxidation. Particles come in
all shapes and sizes. They may be of animal, vegetable, or mineral origin.
They may be living or inanimate. They can affect plants, animals, or mate-
rials. Particles may affect a person's health in a variety of ways: some
are inert, producing changes in the body only by their passive accumula-
tion and evoking little or no tissue reaction; others are intensely irritant
or toxic causing changes that may result in serious illness—even death,
when inhaled in sufficient quantity. Some particles are known to produce
cancer. Evidence indicates that the action of particles may be modified
by the presence of other particles. Particles may also interact with gases
that may be present in the air. These interactions may either enhance or
moderate the effect of either substance when inhaled alone.
The purpose of this report is to consider those particles that are
most often associated with general types of air pollution. Specific Par-
ticles such as lead, arsenic, or asbestos, which may often contaminate the
air, are not discussed. These substances have been the subject of other
-------
MAS publications. Nor will living particles be considered. Bacterial and
viral particles are excluded and the infections resulting therefrom are men-
tioned incidentally and only in very general terms. Similarly, vegetable
particles such as pollens are considered, if at all, only in relation to
their importance in pollution-evoked asthmatic attacks. Possibly the most
important source of airborne particles from the standpoint of health is
,tobacco smoking. Cigarette smoking in particular should be considered care-
fully in any health effects study. Full allowance must be made for any ef-
fects of smoking before conclusions can be drawn about the effects of air
pollution. No attempt, however, is made here to deal specifically with
aerosols arising from cigarette smoke.
The emphasis of this report, then, is on particles that result from
man's activities. The types of particles and their distribution are con-
sidered. The origins, behavior, and fate of such particles, their physical
and chemical characteristics, their interactions, transport, and removal
from the ambient air are discussed in Chapters 2 through 5. Routine and
special monitoring and trends are reviewed in Chapter 6. In Chapters 7 and
8, there is detailed discussion of the deposition, clearance, and retention
of particles, their effects on man and on other animals. Chapter 9 is de-
voted to the available epidemiologic evidence from which conclusions can
be drawn about the effects of particulate pollution on man. It indicates
the gaps in our knowledge about exposure/response relationships and sug-
gests studies that should be conducted to remedy these deficiencies.
Chapters 10 and 11 consider the effects of particulate matter on vegetation
and materials. Summaries, conclusions, and recommendations, prepared by
the authors of the individual chapters, are consolidated in Chapter 12.
-------
CHAPTER 2
AEROSOLS: CHARACTERISTICS, BEHAVIOR, AND MEASUREMENT
ATMOSPHERIC AEROSOLS
Atmospheric aerosols, consisting of solid or liquid particles suspended
in the air, range in size from a few tens of angstroms to several hundred
micrometers. They may be described by their size range, composition, origin,
effects, or in terms of what is measured by a particular technique. Special
names such as fog, dust, smoke, and Aitken nuclei have arisen from various
disciplines. However, because most of these names are imprecise, they are
used sparingly in this report. Some of these names and their relation to
the more fundamental physical and chemical terminology are tabulated in
Table 2-1.
All aerosol particles are formed either by condensation of gases or
vapors or by mechanical or comminutive processes. Aerosol particles may
then be transformed by coagulation and condensation at the same time that
they are transported by air movement and dilution. All aerosol particles
eventually disappear from the atmosphere to some surface that acts as a
sink. Because aerosol concentrations are ordinarily very small (tens of
yg/m3) compared to the mass of the surfaces that serve as their sinks,
aerosols only have effects on surfaces under conditions where a very small
mass can produce a large effect because of chemical composition. In con-
trast, large in situ effects such as visibility reduction can result from
very small aerosol mass concentrations.
-------
I
CN
W
J
CO
CO
CU
H
O
•H
•P
O
W
o
CO
O
•H
•P
CO
cu
•p
o
to
o
tO
CO
CU
10
-p
C
to
c
•H
E
o
o
£j
cu
rH
rd
o
•H
C/)
^1
f~*t
Cu
Q)
•H
C
3
E
3.
CU
bO
C
o§
cu
•H
CO
C
•H
bO
•H
£^
O
co
4~>
O
CU
1{_I
WH
w
CO
CJ
•H
.p
co
•H
£4
0)
•p
o
(0
1
o
CN CN rH
A V A
CO 1
CO fc
CU CU
0 ft
o co
Ll -H
ft c Td
o
rH -H rH
fd -p td
0 rd O
*H u} tO *H
C C co C
td cu cu id
rC Td O £ C
o co o o
CU O Li CU -H
S O ft S CO
•H
cu
H
0
c
cu
o
•H
ft
cu
o
c
td
co
•H
3
2;
Td
•H
•H
o
w
rH
V
C
O
•H
•P
id
to
c
cu
c
o
CJ
•p
•H
H
•H
f)
•H
CO
•H
^>
T)
c
(0
[~]
-p
H
rd
CU
a:
Td
•H
;3
CT1
•H
rH
h
O
Td
•H
rH
O
CO
rH
V
C
O
•H
•P
id
w
C
cu
Td
c
0
a
-p
•H
H
•H
,£)
•H
CO
•H
J>
Td
c
(0
co
f~l ^_j
•P O
H CU
rO 4n
CU 4n
K OJ
Td
•H
H
O
CO
O
CO
1
CN
C
O
•H
-P
CO
C
CU
c
o
o
c
o
•rH
•P
O
Td
Q)
£_|
^
4_i
•H
H
•H
•H
to
•H
>
to
•p
cu
rH
O
Td
r^
•P
ts
o
o
o
A
H
1
LO
Ll
o
c
0 C
•H O
•P -H
10 -P
co td
C N
CU -H
Td E
C 0
0 -P
o td
cT
0
•H
•P
O
j3
Td
cu
r_j
Li
-P tfl
•H
H CU
•H CO
£> G
•H tO
CO CU
•H H
> O
CO
-P
CU
H
ft
O
C3
^,
0)
1
rH
V
G
O
•H
-P
CJ
T3
cu
r^
^t
4_j
•H
rH
•H
•H
CO
•H
>
£C
S
cu
^5
o
rH
-P
to
to
•p
co
•H
X
w
0
•H
ft
O
o
w
o
&>
>>
I
bO
O
C
rO
-p
rH
O
V
1 >,
O Li
e -p
-p co
td -H
6
•>
td
•H CO
CU Li
H CU
33^
25 CO
rH
A
CO
•P
CO
3
rH
(C
3
-p
tO
25
1
£•4
cu w
ft 4->
3 0)
tt) H
ft
MH O
O fn
bO
G L<
•H CU
N +J
0) rd
CO S
£(
MH bO
C
CU 'i-t
CO rH
ffl O
O 0
rH CU
10 Lt
•H 3
0 -P
CU O
ft 3
CO C,
>, w
CU rH
> td
•p
CU CO
fO Lt
X 0
0
o
o
A
CO
cu
o
3
o
CO
H
H
"*
o
•H
0)
rC
ft
CO >-,
0 -P
B -H
-P O
rd 'H
>, -P
f-i O
Li CU
(0 H
CJ CU
f,
•p
•H CU
S bO
CU 10
H f.
O O
•H
•P 0
Li -H
tfl Li
ft -P
O
CU CU
1 — 1 1 — 1
rP CU
to
-P C
CO rd
1
rH
o
cu
rd
c
rH
rd
•rH
0
ft
CO
rH
A
CU
td
c
rH
fd
•rH
o
CO
ft
CO
O
•H
•P
P
10
ft
CU
CO
Ll
id
o
o
o
•H
-p
Ll
tO
ft
CU
C
•H
•P
W
Q
CU
,X
O
CO
hO to
O -H
CM S
CU
N
rd
c
o
•H
•P
(0
CO
c
cu
c
o
o
£^
o
c
cu
^
•p
•H
/*~N
25
CJ
•H
CU
H
O
P
-— •
rH
^^
•H
CU
rH
O
3
C
cu
o
to
G
O
•H
H
rH
E
co
cu
o
•H
ft
CU
bO
< G M
CO
to
CU
H
O
•H
•P
•P
fO
•H
O
-------
The residence time of aerosol particles in the atmosphere varies
tremendously from a few minutes, for either 0.005 or 100 ym die particles
near the earth's surface in the troposphere, to years,for 0.5 ym dia par-
ticles in the stratosphere. The significance of these different lifetimes
is that for equal masses of small and large particles emitted into a given
large volume of air per unit time, the effective suspended mass of the small
particles is as much as 10 to 100 times that of the large ones. For this
reason emission inventories or formation rates expressed in tonnages without
regard to particle size, composition, or point of origin in the atmosphere
have little utility for judging effect. A million tons of sand blowing along
the desert surface is not as significant as a few milligrams of plutonium
smoke emitted from a fuel reprocessing plant stack.
It has been known for years that toxic materials such as lead and as-
bestos are health hazards when high concentrations are breathed by indus-
trial workers. A relatively new realization is that low concentrations of
such compounds as sulfate in the form of fine particles may also be potential
health hazards. Sulfate is now known to be quite extensively distributed in
the atmosphere because of the ubiquitous emission of sulfur dioxide and sul-
770
fates into the atmosphere from the combustion of sulfur-containing fuels.
The rising concern over the potential health hazards of sulfate aero-
sols has focused new attention on the mechanism of formation, distribution,
transport, effects, and health hazards of secondary aerosols formed from
chemical reactions in the atmosphere.
During the past five years there has been a revolution in both our
knowledge and understanding of atmospheric aerosols as a result of both
328,330
monitoring and special aerosol characterization studies. Large
-------
monitoring efforts such as those carried out by the Environmental Protection
Agency (EPA), although they have used relatively simple total particulate
sampling techniques, have enhanced our understanding of the distribution of
353
aerosols at the surface even though the absolute accuracy can be questioned.
The development of automatic physical, chemical, and gas analyzers and
automatic aerosol-particle-sizing instruments has permitted the construction
and extensive use of several large mobile laboratories on the earth's surface
as well as the more recent application of aircraft to the three-dimensional
study of the physical and chemical properties of atmospheric aerosols and
gases. These new tools are accumulating a large amount of data which are
only now just being analyzed and understood. However, the early results
have already upset many old ideas.
Sophisticated collaborative research efforts on aerosols, such as those
328,330 143,808
conducted in California and more recently in St. Louis, have
provided much good data on the complete physical and chemical size distri-
butions of atmospheric aerosols at a great variety of sites.
Because atmospheric sciences, particle technology, industrial hygiene,
and health effects studies of pollutants are separate fields, the latest
information and understanding about aerosols has not been transferred from
one field to another as rapidly as it should. It is hoped that this report,
because it has been compiled by an interdisciplinary team, will aid in this
diffusion of knowledge.
DEFINITIONS AND BASIC PROPERTIES
Atmospheric aerosols can best be described within the framework of
the most recent concepts concerning their physical and chemical size
distributions.
-------
Particle; Any minute piece of solid or liquid. Many particles that
are important in studies of air pollution are unstable; they can change or
even disappear on contact with a surface. Examples are a raindrop striking
a surface and coalescing, a loose aggregate of carbon black disintegrating
on contact with a surface, and an ion losing its charge after contact with
a surface or an oppositely charged particle.
Aerosol; A mixture of gases and particles that exhibits some stability
332
in a gravitational field. In atmospheric aerosol, this gravitational
stability excludes particles with a diameter greater than several hundred
micrometers.
Other Names for Particles and Aerosols
Because aerosols are important in many fields of study, a great variety
of identifying terms have come into use describing unique physical charac-
teristics of the particles, effects caused by the particles, and features
related to the origin or size of the particles. Particle names and their
derivations are given in Table 2-1.
The definition of coarse and fine particles as larger and smaller than
1 pm radius, respectively, originated from the fact that atmospheric aero-
sol size distributions are bimodal: one mode occurs above 1 ym radius, the
other below 1 wn (Figure 2-1). In atmospheric distributions, coarse par-
ticles are produced by mechanical processes whereas fine particles result
almost entirely from condensation and coagulation.
Certain particles serve as nuclei to initiate further processes.
Aitken or condensation nuclei, cloud condensation nuclei, and ice nuclei
are named for their effects.
-------
180
80
4=60
O>
040
020
Seal* Chang*
Run Concentration Percent
No. iQ/m3 < T
4-14
14
.03
I 3 10
Particle Diameter -
30
too
300
FIGURE 2-1. Bimodal mass distributions measured with a set of special
impactors and a cascade impactor. Run 14 contains many more
coarse particles than the average because of construction
activity upwind. Note the negligible effect of this in-
creased concentration of coarse particles on the fine par-
ticle mode. Fran Whitby, 1975, p. 111-21.798
-------
Small and large ions carry electrical charges. Small ions are clusters
of molecules around a charge. Their stability depends on their having a
charge. Large ions are merely particles that carry an electric charge.
Large particles (0.1 to 1.0 ym dia) and giant particles (>1.0 urn dia) are
terms also applied by atmospheric physicists.
Particle Properties
Particles may be classified
tion methods. For example, primary
emission. Examples are road dust
In contrast, a substantial fract
formed by in situ chemical react
produced sulfate and photochemical
Particles and aerosols may
scattering, chemical composition
sphericity or other particle shape
Because of the almost explosive
years, many of the references are
being published. During the past:
size distributions have also begi)n
resulting from field studies.
Until the last two decades
by individual investigators who
in only a few locations. Despite
these studies elucidated the
by a variety of their properties or forma-
particles do not change form after
, salt spray from oceans, and cement dust.
on of the mass of secondary particles is
ons involving gases. Photochemically
smog are examples of secondary aerosols.
be classified by size, area, mass, light
and by such geometric characteristics as
character istics.
growth in data during the past few
to reports and papers that are new or just
five years, methods for describing aerosol
to change in keeping with the new data
THE PHYSICAL AND CHEMICAL SIZE DISTRIBUTION OF ATMOSPHERIC AEROSOLS
nost atmospheric aerosol data were obtained
collected limited data during a short time
the snapshot nature of most of this work,
features of atmospheric aerosols.
size>-dependent
-------
5
In the 19th century, Aitken showed that most particles in the atmosphere
were smaller than 0.1 pm dia and that their concentration varied from a few
hundred per cubic centimeter over the ocean to millions per cubic centimeter
740
in cities. Payleigh's 19th century work showed that most light scattering
by atmospheric aerosols was caused by 0.1 to 1.0 vim dia particles. These
early workers also discovered that the origin of particles smaller than
about 1.0 ym dia is different than the origin of larger particles. The
smaller particles were called smokes, fumes, or hazes; the larger ones,
dusts, mists, fogs, or ashes. These early hints of the multimodal nature
of atmospheric aerosols remained dormant for a long period because most size
distribution data were obtained simply by counting particles with the light
microscope. The overwhelming number of small particles compared to the
larger particles hid the modal nature of the aerosol.
399,402,403
After the Second World War, Junge began a series of studies
using a variety of measurement methods. He elucidated the continuous nature
of the atmospheric aerosol number size distribution and concentration in
urban and nonurban locations as functions of altitudes and location. From
Junge's work came the standard form for plotting size distribution data:
log of dN/dD vs log D , where N = number and EL = particle diameter.
398 P P T
Junge observed that this plot was a straight line that could be described
by the equation: dN/dD = A D "^ where A and K were constants. He also
noted that in the range from 0.1 to 10.0 pm dia, k was approximately equal
to 4.0.
This distribution model, known variously as the Junge distribution or
the power law distribution, has been widely used. Its acceptance was fur-
259
thered by Friedlander who showed that by balancing aerosol source and
10
-------
removal rates, a portion of the resultant theoretical number distribution
steady state could be fitted reasonably well by the Junge distribution.
153
Clark and Whitby, by fitting the Junqe distribution to 52 atmospheric
distributions, found that the constant A was equal to 0.4 multiplied by
the aerosol volume concentration in ym3/cm3. This agrees with the value
259
predicted by Friedlander.
805
In 1972, Whitby and his colleagues, while analyzing smog size dis-
tribution data from Pasadena, found that although the Junge distribution was
a reasonable fit to the number distribution, it was not a good model for the
surface or volume distributions. They found that the mass size distribution
of Los Angeles smog was normally bimodal with one mode at about 0.3 ym dia
and the other from 5.0 to 15.0 ym dia.
517
In 1947, May developed the cascade impactor. Although aerosol mass
concentration had been measured by filtration long before, this instrument
was the first to measure directly the aerosol mass size distribution over
the range of approximately 0.5 ym dia to over 10 ym dia. Unfortunately most
investigators using impactors adopted the powder technology method to plot
their data in cumulative form on log probability paper. This method is
useful for determining the geometric mean and geometric standard deviation
of unimodal distributions having no sampling or measurement biases.
However, the impactor's sampling biases affect the value of the integral
204,802
used to normalize the data. As a result, the true bimodal nature
of the mass distribution is often hidden, and characteristics of the impactor,
such as particle bounce and sampling bias, may be interpreted as significant
characteristics of the mass size distribution.
11
-------
506,627,794
Recent studies have made it possible to apply the cascade
impactor under many conditions to validate the measured mass size distri-
495
butions. For example, Lundgren has used inpactors to verify directly the
bimodal nature of atmospheric aerosol mass distributions (Figure 2-1).
Figure 2-2 is a conventional plot of the particle size distribution of
805
the total average aerosol measured in Log Angeles in 1969. Figure 2-3
presents the same data, but in such a manner that the apparent area under
the curves is proportional to the number, surface area, or volume in a
given size range. These curves were constructed assuming uniformly dense,
spherical particles. This is a fairly typical urban distribution (see
Chapter 4). The following important observations can be made from this
figure.
• Most particles are approximately 0.01 pm dia. Most of the sur-
face area is provided by particles averaging 0.2pm dia. The
volume (or mass) distribution is bimodal; one mode is about
0.3 um dia, the other is about 10.0pm dia.
• The mass of fine particles (<2 pm) is almost equal to the mass
of coarse particles (>2 vim).
• The dN/d log D vs D plot on log coordinates (Figure 2-2) shows
that the number of particles decreases sharply with increasing
size.
• Atmospheric aerosol size distributions consist basically of three
797,801
separate modes: nuclei (<0.1 pro dia), accumulation (<2.0 pm
but >_0.1 pm dia), and coarse particle (>2.0 pm dia). Depending on
their source there may be from one to three distinct maxinums in
the surface or volume distributions.
12
-------
1969 L.A. GRAND AVERAGE
.001 .01 .1 I 10 100
FIGURE 2-2. Grand average number aerosol size distribution from the 1969 Los
Angeles smog experiment805 compared with a Junge power law distri-
bution calculated with the constants of Clark and Whitby.153
Agreement is reasonably good from 0.1 to 10 ym dia but not above
or below these sizes.
13
-------
ID
'o
x
0*
o
o
OL
O
^ 3.6
. CO
-8
«
.4
.01 .1 I 10
Particle diameter, vim
FIGUEE 2-3. Normalized frequency plots of number, surface, and volume
(particle volume times particle density) distributions for
the grand average 1969 Pasadena smog aerosol. Note the
bimodal distribution of mass. Each weighting shows features
of the distribution not shown by the other plots. From
Whitby, 1975, p. 11-11.798
14
-------
Figure 2-4 shows the surface distribution, assuming spherical particles,
of an aerosol measured in Ft. Collins, Colorado under conditions in which
all three modes are distinct and separate. Washout by rain greatly reduced
the nuclei and coarse particle mode but had little effect on the accumulation
mode.
A distinct trimodal volume distribution was measured during the General
Motors Sulfate Study in Milford, Michigan during October 1975 (Figure 2-5).
The nuclei mode was distinct because the background concentration of aerosol
in the accumulation mode was low and because the catalyst-equipped cars on
the test track emitted nuclei-mode-sized aerosols.
The origin of each mode of atmospheric aerosol size distribution can be
associated with various aerosol formation mechanisms (Figure 2-6). (See
Chapter 3 for further discussion of these mechanisms.)
An important transformation mechanism for fine particles is the Brownian
motion of particles smaller than a few tenths of a micrometer in diameter.
This Brownian motion, resulting from gas-molecule impact, causes the par-
ticles to diffuse. If the number concentration is high enough, this diffusion
results in collision and coagulation to larger sizes.
Diffusion-caused coagulation has several important effects on atmos-
pheric aerosols. It limits the maximum concentration to less than a few
million per cubic centimeter at distances further than a few hundred feet
from sources, and it causes particles smaller than approximately a few
hundredths of a micrometer in diameter to coagulate rapidly with particles
a few tenths of a micrometer in diameter. This tends to generate multimodal
distributions near strong sources of submicrometer primary aerosols. Coag-
ulation can also affect the shape and chemical composition of particles.
15
-------
O BEFORE
A START
D DURING
RUNS
168-169
170-171
172-173
NT-no/cm3
44,620
4960
6615
89.7
36.1
123
12.
114
25.3
33.4
S-ft'/cm8
11
86.6
81.7
83 O
72.6
30.4
9.03
200 ~
100 -
001
O.I 10
PARTICLE OIAVETER, Op, fim
FIGURE 2-4.
Surface area aerosol size distributions measured before, at
the beginning, and during a rain on August 14, 1970 in Ft.
Collins, Colorado. The three aerosol node peaks (nuclei
[0.015 \m dia], accumulation [0.3 ym dia], and coarse par-
ticle [>10 pro dia] ) are visible. As the rain continued,
the nuclei and coarse particle nodes were removed but the
accumulation node was unchanged. From Whitby, 1975, p.
II-12.798
16
-------
.1 i ic
Particle diameter, \ig/m6
FIGURE 2-5.
Computer-prepared volume size distribution measured during
the General Motors Sulfate Study in Milford, Michigan in the
fall of 1975. The range of measurement of the three instru-
ments used to obtain the size distribution from which the dis-
tribution was calculated is shown. The distinct trimodal nature
of this distribution is the result of the low aerosol concentra-
tion (<6 yg/m3) and the strong nuclei mode size emissions from
catalyst-equipped cars. From Whitby et al., 1976.806
17
-------
CHEMICAL CONVERSION
OF GASES TO LOU
VOLATILITY VAPORS
J_
.1 1 2
PARTICLE DIAMETER. MICROMETER
TRANSIENT NUCLEI OR
AITKEN NUCLEI RANGE
ACCUMULATION
RANGE
-FINE PARTICLES
MECHANICALLY GENERATED
AEROSOL RANGE
COARSE PARTICLES
FIGURE 2-6. Schematic of an atmospheric aerosol surface area distribution
showing principal modes, main sources of mass for each mode,
and the principal processes involved in inserting mass in each
mode and the principal removal mechanisms. From Whitby and
Cantrell, 1976.801
18
-------
Nuclei or Aitken Nuclei Mode
814
The nuclei or Aitken nuclei mode accounts for most of the Aitken
nuclei count and originates primarily from the condensation and coagulation
of hot, highly supersaturated vapors during combustion.
There is evidence that a prominent nuclei mode in the size distribu-
tion indicates the presence of substantial amounts of fresh combustion
198,803,806
aerosol. Many particles in the nuclei mode raise the Aitken
nuclei count. Usually, however, they do not greatly increase the aerosol
mass concentration because the nuclei mode rarely accounts for more than
a few percent of the total mass.
An important exception is aerosol near heavily traveled multiple-lane
803
roadways. Whitby et al. found that in regions bordering the Harbor Freeway
in Los Angeles the nuclei mode may contain over 25 pg/m3 of aerosol. More
recently, investigators studying emissions from catalyst-equipped cars ob-
served distributions in which the nuclei mode contained more volume than
806
the accumulation mode.
Since particles may serve as nuclei for the condensation of water vapor,
condensation is an important growth mechanism for submicrometer aerosols.
Examples are fogs and hazes formed when the humidity exceeds 60%.
Accumulation Mode
The twin mechanisms of coagulation and heterogeneous nucleation (conden-
sation of one material on another) tend to accumulate submicrometer aerosol
801,814
mass in this mode. However, because of the sham decrease in par-
ticles larger than 0.3 ym dia, little mass is transferred from the accumulation
332,738
mode to the coarse particle size range. Sedimentation and impaction
19
-------
tend to increase the relative concentration of the smallest mechanically
produced particles. Therefore, these smallest particles also accumulate
in this mode.
Coarse Particle Mode
In the arbitrarily named coarse particle mode, practically all aerosol
particles at relative humidities below 100% originate from mechanical
328,382,814
processes. Most fine particles originate from condensation
processes occurring both in the atmosphere and in source processes; coarse
particles are produced from natural and anthropogenic mechanical processes.
The origin, behavior, and removal processes of fine particles are almost
entirely independent from those of coarse particles. Therefore, the control
measures for each group are quite different and the effects on health,
visibility, and meteorology can be segregated.
The multimodal nature of the size-mass distribution is also supported
by evidence from the size distribution of chemical elements or compounds
in aerosols. (See Chapter 5.)
Figure 2-7 shows the chemical-size distribution of several elements
measured in San Jose, California. Such elements as lead, which are emitted
212
as smokes or fumes, exist mostly in the fine particle size range. These
aerosols eventually coagulate and become mixed throughout the accumulation
mode. Table 2-2 illustrates that the geometric mean size of lead and sulfate
aerosol is nearly equal to the mass or volume geometric mean size of the
accumulation mode. Most chemical elements are found in the fine or coarse
particle modes and are only rarely distributed between them. Elements in
the soil, such as silicon, calcium, and iron, are mostly in the coarse
particle range; such elements as sulfur and lead, which are produced by
20
-------
CO
fi1
s.o
2.0
1.0
800
100
50
ao
10
•
500
200
100
<
«
1000
500
>00
100
so
SAM JOSE 8/25/72
h V
Stick;
Dry Teflon
Sticky
Dry Teflon
Dry Mylar
Sticky
Dry Mylar
Dry Teflon
10
100
Particle Diameter, \m
FIGURE 2-7. Comparison of the chemical size distributions determined with
the Lundgren Impactor in San Jose, California using different
surfaces. The vanadium distribution is bimodal; the fine par-
ticles probably result from combustion and the large ones from
another, unknown source. The bromine distribution found in
this study is typical of lead and bromine in automobile emis-
sions. These particles were all in the fine particle range.
The sodiun distribution is uninodal and is probably from sea
salt. The unimodal aluminum distribution comes from soil dust.
From Wesolowski et al., 1975.m
21
-------
TABLE 2-2
Comparison of the Geometric Mean Diameter of the Fine Particle
Mass Distribution Mode with Chemical Distribution of Lead and Sulfate
Geometric Geometric Stan-
Distribution Mean, urn dard Deviation Reference
7Q 7
Average of 11 volume distri- 0.34 2.05
butions of atmospheric aerosols
Lundgren mass distribution by 0.35 1.90 lf95
impactor, average of 10 dis-
tributions
Lead—Wind from freeway 0.27 2.46 803
Lead—Wind away from freeway 0.29 2.62 803
Sulfate—Average four cities 0.39 2.03 777
22
-------
condensation processes from anthropogenic combustion-related sources, are
205,207
principally in the fine particle range. The size of such chemical
elements as silicon from soil dust found in the mechanically generated
807
mode is similar to the mass distribution of the coarse particle mode.
INTEGRAL PROPERTIES OF SIZE DISTRIBUTIONS
Any property that is a size-dependent function of a size distribution
is called an integral property of the distribution. These are classified
arrl discussed below.
System Integral Properties (SIP)
Three important integral properties of aerosol size distributions are
called system integral properties because they depend only on the size dis-
tribution. These are the total aerosol number, surface, and volume or mass
concentration. In a perfect sampling system, an Aitken nuclei counter would
count number concentration, and a high efficiency filter sampler, evaluated
by weighing, would measure the mass concentration.
weighted Integral Properties (WIP)
When a size distribution is multiplied by a size-dependent function of
the distribution, and then integrated, the resultant value is a weighted
integral property. An important WIP is light scattering where the light scat-
tering cross section per volume is integrated with the volume distribution to
obtain the total particle scattering coefficient, b . Assuming uniformly
^ * sp
dense spherical particles, the average normalized surface and volume distri-
butions and the computed particle light scattering coefficient for Los Angeles
aerosol are shown in Figure 6-1, page 115. (See Chapter 6 for further dis-
cussion of the optical properties of aerosols.)
23
-------
Pulmonary deposition is another WIP property. Fine particles are more
efficiently deposited in the lung than coarse particles. Deposition is dis-
cussed in greater detail in Chapter 7.
Another significant WIP is the value reported by the filter stain mea-
surement in which a stain, left on a filter after a known quality of aerosol
has been filtered, is measured by optical transmission or reflectance.
800 603
Whitby et al. and Pedace and Sansone have shown that the stain test
essentially measures the optically absorbing particles but does not respond
to the transparent or liquid particles in the air.
Dustfall is another WIP in which the settling velocity of particles is
sufficient to allow them to reach the ground from the height at which they
are launched into the atmosphere.
AEROSOL SAMPLING AND MEASUREMENT METHODS
Because of the great diversity of application, the size range of atmos-
pheric aerosol physical and chemical concentration variations, and the wide
variety of measurement principles available, there are literally thousands
of usable combinations of application and measurement methods and procedures.
Because it is impossible to review all these different methods and studies
in one report, this document concentrates on the most important methods in
use and cites the most recent references on each. Because of the breadth
of this field and the specific interests of its investigators, the literature
usually reflects the specializations of the authors. The best general re-
views of aerosol measurement techniques and technology appear in conference
proceedings.
24
-------
Recent Literature
293
Green and Lane have reviewed work prior to 1955. More recently,
534 111
Mercer and Cadle have discussed aerosol sanpling and measurement tech-
niques in considerable detail and breadth. Mercer's 1973 book emphasizes
the techniques used to assess radioactive aerosols for biologic studies.
Cadle's 1975 book stresses such classical methods as the microscope that are
used to assess general atmospheric aerosols. Both books were written before
the recent revolution in the understanding of atmospheric aerosols. The pro-
ceedings of the 1972 symposium, Assessment of Airborne Particles, edited by
535
Mercer et al., contain detailed reviews of many of the methods mentioned
in Mercer's earlier work.
The proceedings of several conferences contain good discussions of impor-
tant aerosol measurement techniques. The Illinois Institute of Technology
376
in Chicago sponsored several particle technology conferences that were
slanted toward powder technology. A National Bureau of Standards conference
129
on aerosol measurement produced some good papers on recent developments
in optical measurement of aerosols. The proceedings of a recent conference
478
on fine particles at the University of Minnnesota constitute a most com-
prehensive recent review on fine particle measurement. During an inter-
378
national conference on environmental assessment a number of papers re-
viewed developments in aerosol measurement. These proceedings are especially
valuable for their information on international developments. The pro-
ceedings of the Gesellschaft fur Aerosol Forschung (GAP) conferences, held
75
annually in Bad Soden, Germany since 1973, also contain useful information
on aerosol measurement techniques.
25
-------
Important Character1stics of Aerosol Measurement Methods
Before discussing the characteristics of the many different methods,
the suitability of a method for a given purpose must be assessed.
In Situ vs. Collection. Such methods as filters and cascade impactors
collect the aerosol onto a surface. The collected sample must then be eval-
uated for size and composition. Other methods, such as optical techniques,
sense the aerosol in situ without collecting it. Since accumulation mode
aerosols (fine particles) contain a substantial fraction of liquid at normal
temperatures and humidities, these fine particles must be sized in situ with-
out precipitation. In some extreme cases, such as Los Angeles smog, the
344
liquid content may be as high as 75% or 80% of the total mass. Further-
more, evaluation techniques such as electron microscopy, which subject the
aerosol particles to a high vacuum, may yield extremely misleading results
when used on fine atmospheric aerosols that contain significant quantities
of liquid in situ.
Integral vs. Differential Measurement of Particle Size. Many aerosol-
measuring methods, such as the condensation nuclei counter, integrating
nephelometer, and filter collectors, integrate some response function of
the instrument with the particle size distribution. The weighting of the
size distribution that the integral method senses can give greatly different
results. For example, although a filter collects all particles, the results
obtained depend greatly on the method of evaluation. If particle counting
is used, the response is essentially equal to the integral of the number
distribution weighting. On the other hand, if the filter is weighed, then
the integral measurement is the integral of the mass weighting of the
26
-------
distribution. Furthermore, integral methods are always sensitive to the
modification of the size distribution by the sampling inlets and transport
495
lines used in the technique. To illustrate, Lundgren, using impactors
designed with inlet cutoffs well above those usually used for atmospheric
sampling, showed that particles up to several hundred micrometers in diameter
were present in the atmosphere under certain conditions. However, most
726
mass sampling methods, including the high-volume sampler, truncate the
distribution thereby giving concentrations less than those actually existing.
Table 2-3 lists the most important integral sampling and measurements with
their characteristics and a recent key reference. Table 2-4 gives the most im-
portant differential, size-resolving methods used to sample and measure atmos-
spheric aerosols. The Remarks column indicates the part of the size distribution
and the modes that dominate the sensitivity of the method. The upper and lower
size limits are nominal values for the most commonly used forms of the technique.
Practical Considerations
Cost, complexity, operational requirements, calibration problems, and
the demands of the particular evaluation to be used also affect the choice of
methods. For example, chemical analysis usually requires that a sample be
collected, then taken to the evaluation device. This normally requires a
collection-type method, such as the high-volume filter collectors used in
the National Air Sampling Network. Simplicity during sampling may mandate
/
the use of a collection method despite its other problems.
The rapid development of modem electronics and inexpensive dat^t acqui-
sition systems has led to j.n situ, automatic, and complex monitoring techniques.
Collection methods are being replaced with both physical and chemical analysis
with in situ, automatic methods.
27
-------
3
3
a
H -H
ElS
a
!•'
5
I
'U
I
I
i* *
g
o
o
***
!
in
CM
in
o
in
eg
o o
iH 01
CM
•H
0)
I
W
in
H
*
o
CO
28
-------
en
CCJ 5fi^43
•H -H 4J O -H
& | 8) fj S
gj m O P 9 VH
to w 3
-------
30
-------
CHAPTER 3
AEROSOL CYCLES
The production and disposition of aerosol particles are outlined in
Figure 3-1. When studying the sources, transformations, transport, and sinks
of particles, the nuclei (<0.1 ym dia) and accumulation (between 0.1 and 2.0
ym dia) modes, which together comprise fine particles, should be considered
separately from the coarse (>2.0 ym dia) mode. The distinction between coarse
and fine particles is shown in Figure 2-6 of the previous chapter.
PARTICLE PBQDDCTION PROCESSES
Coarse Particles
Most particles with a radius larger than 1.0 ym are produced from me-
chanical processes. Natural, mechanically originated aerosols arise from
windblown dust and sea spray. Manmade mechanical aerosols are produced by
a wide variety of industrial processes, for example, the grinding of coal
and cement dust and the handling of powdered materials.
Fine Particles
Most fine particles are formed in the nuclei made by various condensa-
tion processes. Coagulation and gas-particle interactions (heterogeneous
nucleation) are intimately linked with fine particle formation (especially
in the accumulation mode). (See the section on TRANSFORMATICN PROCESSES on
page 39.) Nucleation phenomena can be broadly defined as processes in which
aerosol particles are formed in the same size range as large molecules from
reactant gases. Nucleation implies the genesis of new particles. Two types
31
-------
OJ
o
CO
a.
c c
•r- -i—
U- «/>
3 3
O O
_c c
«/) T-
(O (O
2 a:
-or
r—
U
•r~
•U
IO C
O ••-
O IO
c
o
rO C
4-> O
C T- -M
-r- S
10
(U
O)
•1- rtj
U- CL
0) U
U1 •!-
J- 4->
n> $-
o 10
c_> a.
O)
to O
C U •!-
(U T- 4->
-O E U
C OJ to
O J= (U
uus-
-r-
4-> (- in
O
O o
(U
c
£ a»
i— 10
+J O V-
J- I- 3
•r- (O O
a a. v>
0)
u
3
a>
to
S-
to
O C «O «/>
O OJ •• X >> O O)
r— to O IO -r- ««
4-> O (U r— S. C W)
O -i- O ^3 OL «J O)
QJ 4-> I- T3 W> J= O
t- I- 3 C « O O
•r- tt) s-
O Q. to Vt g O.
•o
A
+J
«0
t/>
c:
t-
o
to
o>
I/I
«0
CT>
32
-------
of nucleation phenomena are important in the atmosphere. The formation of
aerosols from the condensation of a hot, supersaturated vapor is exemplified
by the particles resulting from condensation of metallic vapors, low vapor
pressure oils, and other low vapor pressure materials formed by combustion.
Most aerosols formed from the condensation of cold, supersaturated vapors
result from _in situ conversions of high vapor pressure gases into low vapor
pressure reaction products. Examples are the formation of photochemical
smogs from hydrocarbons and of sulfuric acid aerosol from the oxidation
of sulfur dioxide.
Condensation of Hot, Supersaturated Vapors. The rapid cooling of many
hot, supersaturated vapors produces fine particles (Figure 2-6). For ex-
ample, metallic vapor leaving the vicinity of a hot source cools rapidly
when mixed with air. Under these conditions homogeneous nucleation of the
supersaturated vapor occurs. This leads to the formation of high concentrations
of fine particles.
Condensation of Cold, Supersaturated Vapors. Oils and other low vapor
pressure materials do not provide enough vapor by evaporation at ambient
temperatures to form any detectable quantities of aerosol. However, _in situ
chemical processes that convert high vapor pressure gases to low pressure
reaction products can result in supersaturation of the vapor. The vapor
then condenses into an aerosol. The two most important examples in the
atmosphere are the photochemical smog formed from the reaction of hydrocarbons
with nitrogen oxides and the sulfuric acid droplets and sulfate particles
resulting from the oxidation of sulfur dioxide.
33
-------
Theoretical treatment of the condensation growth of fine atmospheric
aerosols is difficult because condensation and coagulation usually occur
simultaneously in natural conditions. Only recently has much attention
89
been given to this problem. Brock has shown that the main features of
783
the size distribution can be predicted. Walter has shown that the fluc-
tuation in the number of particles in a chamber that is initially particle-
free can be predicted qualitatively. However, quantitative prediction of
production rates in laboratory experiments requires further knowledge of
the complex transformation processes.
Figure 3-2 shows the development of various aerosol parameters over time
during photooxidation of sulfur dioxide in a laboratory. In Period 1, the
photooxidation converts sulfur dioxide to sulfuric acid vapor. This rapidly
results in supersaturation because the vapor pressure of sulfuric acid is only
approximately 10~8 mm of mercury. Homogeneous nucleation occurs, resulting
in a rapid growth in the number concentration of the aerosol. As the number
concentration of particles increases, more and more of the vapor condenses on
existing particles. In Period 2, the number concentration reaches a maximum
where the rate of new nuclei formation equals the rate of coagulation. At
this point, nucleation, coagulation, and condensation all proceed simul-
taneously. In Period 3, nucleation decreases to a low value and the primary
mechanisms of aerosol change are coagulation and condensation. Little light
is scattered before the particles grow into the accumulation mode (>0.15 ym).
The laboratory studies of photochemically produced aerosols fall into
two general categories. Smog chamber studies emphasize the formation and
growth of light scattering aerosols. Most of these investigations entail
detailed knowledge of the initial chemical species involved in the reaction.
34
-------
UJJ
i iNUCLEATION.
8'CONDENSATION,
^m I
CONDENSATION,
COAGULATION
TOTAL NUCLEI
CONCENTRATION
LIGHT SCATTERING
TIME
FIGURE 3-2.
Time development of condensation nuclei concentration and light
scattering in an initially particle-free chamber containing an
aerosol produced by a photochemically reacting mixture.
35
-------
Early investigators concentrated on measuring the increase in light scat-
tering resulting from irradiating automobile exhaust with ultraviolet light
for a variety of engine conditions and fuel compositions. In recent smew
chamber studies attempts have been made to determine the influence on aerosol
formation of specific hydrocarbons in the urban atmosphere. Most of these
studies have centered on one or two hydrocarbons with various proportions
of nitric oxide, nitrogen dioxide, sulfur dioxide, and water vapor. Smog
chamber studies on automobile exhaust and individual hydrocarbons have
818
been reviewed by Wilson et al. for the American Petroleum Institute.
101 ~~ 21
Bufalini and Altshuller and Bufalini have written extensive reviews
of the literature concerning the photochemistry of the atmosphere, with
discussions of photochemically produced aerosols.
In addition to smog chamber studies, investigators have studied the
formation of aerosols resulting from the irradiation of particle-free
ambient air. These experiments have emphasized the formation of condensation
nuclei from ambient air, including natural and manmade trace gases, from
which only particles had been filtered. These studies have not generally
included detailed analyses of all the trace gases involved.
641 618 728
Renzetti and Doyle, Prager et al., and Stevenson et al. stud-
ied systems in which hydrocarbons, ND, and sulfur dioxide were irradiated
Jv
and the various gases, nuclei, and light scattering aerosols monitored.
Irradiation in the reaction chamber causes the condensation nuclei count to
rise rapidly to a maximum value and then to decrease (Figure 3-2). Ini-
tially, homogeneous nucleation occurs, but eventually the coagulation rate
equals the aerosol formation rate and the Aitken nuclei number concentration
decreases.
36
-------
641
An extensive series of experiments was conducted by Renzetti and Doyle
to establish which specific hydrocarbons could produce a light scattering
aerosol in the presence of nitric oxide and in the presence and absence of
sulfur dioxide. For the conditions selected, only branched-chain internal
olefins, cycloolefins, and diolefins produced light scattering aerosol in
the absence of sulfur dioxide. In the presence of sulfur dioxide light
scattering was greater for the olefins and diolefins, and about the same for
cyclohexene. For some hydrocarbons the addition of sulfur dioxide to the
system had little or no effect on the aerosol formation.
22
Altshuller et al. monitored the formation of photochemical aerosols
for a number of hydrocarbon/nitric oxide reactions during a study of the
products and biologic effects resulting from irradiation of nitric oxide
with hydrocarbons or aldehydes. These investigators found that 4-carbon
olefins in mixtures with nitric oxide produced condensation nuclei but no
light scattering aerosols, and that mixtures of olefin-aromatic hydrocarbons
and nitric oxide produced very little condensation nuclei and no aerosols.
On the other hand, aromatic hydrocarbons in mixtures with nitric oxide pro-
duced both condensation and light scattering aerosols.
817
Wilson and Levy observed that the addition of sulfur dioxide to the
reaction system produced little effect on the light scattering aerosols
formed by aromatic compounds. However, for alkanes and olefins, the amount
of light scattering was greater when sulfur dioxide was present but was less
than that obtained from the same amount of sulfur dioxide irradiated in clean,
humid air. This discrepancy in earlier studies was attributed to differences
in air circulation and residence times.
37
-------
819
In 1971, Wilson et al. reported that stirring the reactions in a
smog chamber during irradiation significantly reduced the formation of light
scattering aerosols. The effect of stirring depended on the composition of
the reactants under study as well as the stirring rate. The authors con-
cluded that the difference in sensitivity to stirring found for olefins and
aromatic hydrocarbons and for systems that included or excluded sulfur
dioxide accounted for many of the discrepancies in previous smog chamber
studies.
419
The 1973 studies by Kocmond et al., which extend the 1971 studies by
819
Wilson et al. at Battelle Institute, and the 1975 unpublished work by
Kittelson et al. (unpublished data), suggest that the reaction products of
sulfur dioxide photooxidation (possibly sulfuric acid) passivate the
chamber walls and thereby reduce the effects on the walls.
Aerosols resulting from the irradiation of filtered ambient air have
88 772 373
been studied by Bricard et al., Vohra et al., and Husar et al. Evans
221 ~~
and Roddy also added sulfur dioxide to the filtered ambient air before
studying its Aitken nuclei number concentrations. These studies all show
that ambient air, even in relatively pollution-free locations, contains
enough gaseous precursers to form a large number of Aitken nuclei. In 1971,
371
Husar measured the aerosol volume as well as the Aitken nuclei. He showed
that the volume of aerosol (and whether it is likely to grow into the light
scattering range) depends greatly on the amount and kinds of reactants ores-
ent. Relatively clean urban air will produce only a few vm3/cm3/hr.
In most urban atmospheres photochemical conversion rates should rarely
exceed a few wn3/cm3/hr. Also, some photochemical conversion probably occurs
throughout much of the lower trooosphere and perhaps even in the stratosphere.
38
-------
However, the converted mass is usually so small compared to the existing mass
of the aerosol that the amount of growth is undetectable.
TRANSFORMATION PROCESSES
Aerosol transformation can be generally classified into two categories:
gas-particle interactions and particle-particle interactions (coagulation).
These processes are discussed below for both coarse and fine particles.
Coarse Particles
These particles are not greatly transformed in the atmosphere. The
surface distribution reaches a maximum in the accumulation mode (at about
0.3 urn). Gas-particle interactions are not significant in the coarse mode
in which only a small fraction of the particle surface is available. (See
Figure 2-3, Chapter 2.) The surface distribution also limits the mass
transfer by coagulation from the accumulation mode to the coarse mode.
The small coagulation rates within the coarse mode are attributed to the
decreasing number and mobility of these larger particles.
Fine Particles
In contrast, fine particles undergo significant gas-particle and
particle-particle interactions.
Gas-particle Interactions. In this process, particulate mass is pro-
duced by accretion of reactive gases. The total number of atmospheric par-
ticles remains constant, unlike nucleation or coagulation. The mass concen-
trations of typical aerosol-producing gases usually far exceed that of the
mass concentration of the particles or other substances formed from the
gas. For example, 0.1 ppn» of sulfur dioxide (a frequently encountered
39
-------
concentration) is approximately 285 Ug/m ; if oxidized to ammonium sulfate,
it would make about 590 vg/m3 of aerosol. Thus, the particles produced by
only 5% to 10% of these gases are a significant addition to the mass
concentration.
In liquid phase reactions reactant gases are dissolved in aqueous or
organic aerosol droplets including cloud droplets. Most submicrometer atmos-
pheric aerosols, whether formed by direct emission or by secondary conversion,
are deliquescent or hygroscopic; thus, their particles contain substantial
144 " 825 344
amounts of water. Charlson et al., Winkler, and Ho et al. have
shown that urban submicrometer aerosols usually contain large quantities
of water. Further, there is always abundant water vapor to provide sources
for this condensation; at 80% relative humidity the aerosol particles con-
tain as much as 70% water. Therefore, submicrometer atmospheric aerosols
must be modeled as liquid droplets rather than as dry solid particles.
The submicrometer aerosols that comprise most of the atmospheric aerosol
surface have sufficient water under most atmospheric conditions to present
a liquid surface to the gas phase. Consequently, the dry surface chemistry
is often probably unimportant.
The relationship between the pressure of a gas in equilibrium with a
liquid solution containing the gas and the mole fraction of the gas in solu-
tion is approximately linear for many gases. This relationship, known as
Henry's Law, applies to gases present at low concentrations in the solution
and surrounding medium. This constant of proportionality is discussed ex-
tensively in the literature. For water vapor pressure over dilute solu-
tions, the constant of proportionality is the saturation water vapor pressure,
which is also a function of temperature. However, for such gases as carbon
40
-------
dioxide, sulfur dioxide, and ammonia, the amount of gas dissolved in the
liquid phase also depends on the degree of dissociation of the dissolved
species. For these particular gases, the dissociation is regulated by the
pH of the liquid, which can be governed by the gases themselves, by the
chemical composition of the original particle, or by reaction products
formed in the liquid. Therefore, the extent of gas-liquid interaction
is regulated not only by the amount of liquid available and the temperature
but also by the chemical composition and reactivity of the various aerosol
components.
152 154
Clark and Clark and Whitby obtained considerable insight into
sane of the mechanisms of secondary aerosol transformation through their
studies of aerosols formed in a smog chamber. In the classical smog chamber
experiment, an initially particle-free gas mixture is irradiated, resulting
in the formation of reaction products and aerosol. Although the number of
particles rises and then decreases, the surface area first increases, then
becomes relatively constant. However, when sulfur dioxide is used, the aerosol
volume increases at a nearly linear rate indicating that the conversion rate
is practically constant.
154
Clark and Whitby concluded that in most photochemical systems stud-
ied, the chemical conversion process and the physical behavior of the par-
ticles formed are essentially separate. For example, Clark and Whitby found
a unique relationship between the equilibrium surface of the aerosol and
the volume conversion rate that is independent of the chemical system. This
relationship suggests that if the surface area of an aerosol for a given
volumetric conversion rate is greater than the value shown in Figure 3-3,
then the low vapor pressure products from chemical conversion in the
41
-------
(M
'o
x 100
10
u 60
40
uT 2°
u
If 10
— 2
CD
s
I I I I I I III I I I I Mil] I I I Mill
oRHOTOOXIDATION OF SOE
ATERPENE VAPOR AND AMBIENT AIR
o FILTERED AMBIENT AIR IN SUNLIGHT
I III!
11111
111
1 1 _J I 1 I 1 ll
i i i i 11 rl
•575
t i i
1111
.01 .02 .04
1.0 2.0 40
10
20 40
100
dV/dt, /im3/ctn3hr
FIGURE 3-3. Variation of the apparent equilibrium surface area with
volumetric conversion rate. From Clark and Whittoy, 1975.151*
42
-------
atmosohere will condense on existing particles rather than form many new
particles by homogeneous nucleation. Even relatively "clean" sources of
combustion, such as gas-fired burners, are prolific sources of condensation
nuclei. In all urban areas, therefore, the nuclei and surface area orovided
by combustion aerosols are probably sufficient to preclude significant aerosol
mass formation by homogeneous nucleation of photochemically or chemically
373
converted vapors. Husar et al. concluded that if the surface area of
aerosols exceeds approximately 2,000 vm2/cm3, homogeneous nucleation is
unlikely.
628
Rasmussen and Went have observed a blue haze over vegetation where
terpene vapors are released to the atmosphere. Under these circumstances,
where there are few combustion nuclei present, ishotochemical or chemical
conversion of terpene vapors could result in homogeneous nucleation of the
products. However, this condition could be transient, disappearing as soon
as the surface of the aerosol increases sufficiently to accommodate all of
the condensible vapors.
Solid phase reactions are defined as the reactions and sorption of gas
molecules on surfaces of dry solid particles. The ratio of grams of adsor-
bate (gas) to grains of adsorbent (X) depends on gas pressure (P) for a given
temperature. This is a complicated thermodynamic function of both solid and
liquid phases and, in such cases as hygroscopic growth of nitrate aerosols,
their history. For many substances, the relationship is illustrated by the
Langmuir isotherm in Figure 3-4 where a and b are temperature-dependent
constants. Although adsorption of typical atmospheric gas mixtures have
not been studied extensively, Figure 3-4 plots the expected adsorption of
all atmospheric gases except water vapor, whose values of P/P may be as
high as 0.5 to 1.0. Thus, adsorption on aerosols may be extremely complex.
43
-------
P/P (dimenslonless)
FIGURE 3-4. Ratio of grams of adsorbate to grains of adsorbent (X) versus
relative vapor pressure (P/P ).
44
-------
For comparison, consider the liquid and solid phase takeup of atmospheric
sulfur dioxide. The concentration of sulfur dioxide dissolved in water at
a given partial pressure is a function of the partial pressures of certain
other gases, mainly ammonia and the water content of the air. For 0.1 ppm
(285 yg/m3) sulfur dioxide, 0.1 ppb (76 ug/m3) ammonia, and a water concen-
tration of 0.5 g/fo3 (fog), the concentration of dissolved sulfur dioxide
is 5.5 vg/m3. Solid takeup of sulfur dioxide, at the same partial pressure
611
and at 10 pg/in3 of airborne particles, is estimated to be 0.005 yg/m3.
Particle-particle Interactions (Coagulation). Aerosol coagulation is
an important mechanism by which the large number concentration of Aitken
nuclei produced by homogeneous nucleation is transferred to larger particles.
This transfer is governed by, Brownian diffusion. Aerosol coagulation has
261 333
been discussed by many authors, including Fuchs and Hidy and Brock.
There are two types of coagulation: homogeneous and heterogeneous.
Homogeneous coagulation, which occurs between like-sized particles, is
of special importance in or near fine particle sources. Number concentra-
tions of primary particles may approach 1010/cm3. Since the monodisperse
coagulation coefficient is on the order of 10~9cm3/sec, the coagulation rate
is very rapid at concentrations exceeding about 108/cm3- See Equation 1,
where dn/dt = coagulation rate (number/time/volume); K = coagulation coef-
ficient (homogeneous or heterogeneous, volume/time); and n = particle number
concentration (number/volume).
dn/dt = -Kn2 (1)
45
-------
In integral form (from n to n), this becomes
o
n
Kn t + 1
o
The result is that within milliseconds, aggregates of these small
primary particles are formed. The very small aggregates or primary particles
contribute to a surface area mode that usually occurs at around 0.02 um.
The larger aggregates, resulting from high concentrations of primary emis-
sions, can contribute significantly to the accumulation mode of surface
area or of mass.
Figure 3-5 shows the normalized surface area size distribution of a
number of combustion aerosols. Note that clean flames, such as those from
methanol, give particles predominantly in the transient nuclei range approx-
imately a few hundredths of a micrometer. In contrast, dirty flames, such
as those from a candle or from acetone which provide more massf result in a
distinct mode in the accumulation range at a few tenths of a micrometer.
Heterogeneous coagulation refers to the coagulation of two or more sizes
of aerosol particles. The rate of heterogeneous coagulation may be consid-
261
erably greater than that of homogeneous coagulation.
If the initial concentration times the time during which coagulation
has occurred is much greater than the coagulation coefficient, then the con-
centration becomes a function only of time and independent of the initial
concentration. (See Equation 2.) That is why the maximum Aitken nuclei
count in the atmosphere rarely exceeds a few million even near sources.
Also, the observed Aitken counts in the atmosphere»are poor indicators of
46
-------
SAIogDp
FT. COLLINS
200
.005 0.01
0.05 0.1
Dp-
05
FIGURE 3-5. The sutadcrometer surface distribution of several aerosols pro-
duced by combustion compared with a distribution observed in
Colorado.801* Ccnbustion produces an average primary particle
mode of 0.01 pm and an agglomerated accumulation mode between
0.2 and 0.8 ym. The figures are the surface area in
for each of the aerosols.
47
-------
the initial Aitken counts in the sources, since the concentration is usually
coagulation limited before measurement.
The aerosols from real sources and in the real atmosphere are rarely
monodispersed enough so that monodisperse coagulation theory applies.
Naturally occurring size distributions are quite varied so that heterogeneous
coagulation occurs.
The heterogeneous coagulation coefficient can be one or more orders of
magnitude greater than the monodisperse coagulation rate. For example, the
rate at which 0.01 ym nuclei coagulate with particles in the accumulation
mode (0.2 ym) has a coefficient of about 3 x 10~8 compared to 10~9 for 0.1 ym
particles coagulating with themselves. Since coagulation of small particles
with larger ones can be very rapid, substantial quantities of mass can be
transferred by coagulation directly from the smallest sizes to the accumulation
mode. '.?he volume transferred by coagulation is relatively constant up to
approximately 0.3 ym after which it decreases sharply, thus producing the
cutoff iietween the two upper modes.
Th';» form of an aerosol size distribution resulting from pure coagula-
tion of a relatively monodisperse aerosol has been studied extensively.
259
Friedlander has calculated that a unimodal size distribution with a geo-
metric standard deviation of approximately 1.3 results from the coagulation
of a monodisperse aerosol. This so-called self-preserving size distribution
371
preserves its shape and spread as it grows in size by coagulation. Husar
obtained similar results by measuring size distribution of coagulating aero-
sols in the 0.01 to 0.1 ym range. No good experimental measurements of
coagulating heterodisperse aerosols have been made.
48
-------
PARTICLE TRANSPORT
Coarse Particles
The dispersion of large and/or dense particles, whose settling velocities
equal or exceed the vertical component of the wind velocity, is affected by
sedimentation. However, such theoretical treatments of their diffusion as
840 707
reported by Yudine and Smith require extensive knowledge of particle
size, shape, and density distributions, since settling velocity is a complex
function of these variables.
Most anthropogenic coarse particles are emitted close to the surface
where they will be removed before they travel very far. Steady, high concen-
trations of coarse particles larger than about 25 pm can be observed only near
309
the source or during unusual conditions such as dust storms.
Convective transport of these particles is also important. Increasing
evidence indicates that significant concentrations (10 to 30 yg/fa3) of coarse
particles can be transported over long distances after being injected high
383
into the troposphere over dry deserts. Jaenicke et al. observed concen-
trations of Sahara dust exceeding 100 pg/ft3 on the island of Barbados.
622
Prospero and Bonatti found dust in the eastern Pacific that apparently
94
traveled from the Asian mainland. Bryscn observed concentrations of that
same dust exceeding several hundred micrograms per cubic meter at 4.5 km
802
over northwest India. Whitby et al. observed the steady concentrations
of coarse particles near Ft. Collins, Colorado that were apparently trans-
ported long distances and mixed well enough so that the characteristic rapid
fluctuations of locally generated dust were smoothed out. (See Chapter 4.)
49
-------
Fine Pat tides
Since sedimentation velocities of particles <1 gm radii are nenerally
I0~?cm/sec, sedimentation does not affect their atmospheric disnersion.
The dispersion of fine Particles, which most efficiently scatter and absorb
liqht, is governed mainly by eddy diffusion and advection. It may therefore
tie assumed that this class of particles behaves as a gas.
Atmospheric particles are largely confined to a 2 to 3 km layer near
the earth's surface. Since particle residence time is short (a few days at
•oost) and their vertical transport is slow, particle concentrations drop
•mickly above 2 km and are very small at 5 km. (See Figures 6-13 and 6-14,
Chapter b.) The low altitude concentrations are controlled by the stability
of lower atmospheric layers and the conseouent disparity of mixing times
and lifetimes. Clouds affect fine particles that form cloud condensation
nuclei by causing them to have finite fall speeds. Thus, the volume of
atmosphere actually available for dumping waste particles is limited.
SINKS FOR ATMOSPHERIC PARTICLES
Coarse Particles
Sedimentation and washout are the most important sinks for coarse par-
ticles. These sinks limit the maximum particle size in the atmosphere under
a oacticular set of atmospheric conditions as well as the maximum mass concen
trations of large particles as a function of condition.
!•'in*-; 1',• 11 ides
cv igulation >us already been discussed as a sink for the nurlpj merit*;
is another. (See Figure 2-4 in Chapter 2.) Accumulation mode L-
s have fewer efficient atmospheric sinks; their motion is ooverned
50
-------
totally by air movement. Minor removal mechanisms include fallout, impaction
with objects at the surface, and washout by impaction processes during pre-
cipitation. Of greater importance are incorporation into cloud droplets
647
(nucleation processes) and subsequent rainout. In Europe, Rodhe and Grandell
estimated the lifetimes of accumulation mode sulfate aerosol to be 100 to
300 hr in summer and 35 to 80 hr in winter based on the actions of the removal
mechanisms in the European climate.
The importance of natural compared to manmade aerosols must be under-
stood to develop realistic control strategies. Control measures cannot bring
concentrations below natural levels. In many locations natural aerosols may
even dominate those produced by humans. The presence of sea salt aerosol
in maritime regions, terpene hazes in forested regions, natural windblown
dust in the plains areas, etc., must be quantified if practicable control
measures are to be designed.
AEROSOL BUDGETS
There are several estimates of global aerosol budgets, but they cannot
be applied directly to urban regions. Also, they do not distinguish between
coarse and fine particles. They do, however, illustrate the role of human
377
activity in the aerosol cycles. Table 3-1 provides examples of global
646 333
aerosol budgets. Estimates by Robinson and Robbins and Hidy and Brock
are similar. These budgets show that, on a global scale, anthropogenic
aerosol sources constitute from perhaps 5% to 50% of the total, regardless
of particle size and lifetime. Since human activity is confined to a small
portion of the Northern Hemisphere, and since most human-produced aerosol
is limited to approximately 1,000 km from the source (residence time times
average tropospheric wind velocity), most aerosol in urban regions is clearly
51
-------
TABLE 3-1
Estimates of Particles Smaller than 20 ym Radius
Emitted into or Formed in the Atmosphere*7
Type of particle
Natural
Soil and rock debris0
Forest fires and slash-burning debris
Sea salt
Volcanic debris
Particles formed from gaseous emissions
Sulfate from H2S
Ammonium salts frcm NHs
Nitrate from NOX
Hydrocarbons frcm plant exudations
Nunber in atmosphere,
109 kg/yr
100-500
3-150
(300)
25-150
130-200
80-270
60-430
75-200
Subtotal:
773-2,200
Manmade
Particles (direct emissions)
Particles formed from gaseous emissions
Sulfate from SOz
Nitrate from NOX
Hydrocarbons
Subtotal:
TOTAL:
10- 90
130-200
30- 35
15- 90
185-415
958-2,615
From Report of the Study of Man's Impact on the Climate, 1971, p. 189.377
Includes unknown amounts of indirect manmade contributions.
52
-------
dominated by human activity, particularly by the production of sulfur dioxide
from the combustion of oil and coal.
Few assessments have been made of the aerosol budget on an urban or a
543
regional basis. Miller et al. developed an approach to this subject for
the Los Angeles basin showing the relative importance of human and naturally
produced particulate matter. They included both direct and gas-particle
production in their model.
No carefully prepared budgets exist showing particle size and vertical
distribution, although these are important factors. As a result, it is not
possible to derive exposures (concentration times time in the atmosphere)
at the surface from these budgets. However, it is safe to conclude that the
fractional concentrations of fine particles in the lower troposphere are at
least as great as their fractional concentrations at their sources. They
may even be up to 100 or more times greater due to their relative longevity.
Because aerosol residence time depends strongly on particle size, the
budget in Table 3-1 forecasts that the future aerosols may be increasingly
333
dominated by the lower mode, especially in urban areas. Hidy and Brock
projected that the anthropogenic aerosol contribution would be dominated by
sulfate and direct production.
SULFUR; AN EXAMPLE OF AEROSOL CYCLE PROCESSES
In general, aerosol particles are an important part of the life cycles of
many chemical substances such as sulfur (Figure 3-6). The study of one such
substance enables one to see this explicity. Although there are thousands of
detectable compounds in the atmosphere, knowledge is sufficiently limited to
preclude assessment of their contribution to observed atmospheric phenomena.
53
-------
-<]-
Gases - nonaerosol
precursors
Stses - aerosol precursors
Low RH aerosol
High RH aerosol
Warm Clouds
Ice Clouds
Key:
I—| Recognizable entitles In the
1—' atmosphere
jf\ Processes having single
direction of material flow
A Reversible processes
FIGURE 3-6. The tropospheric sulfur cycle, (a) Sources, (b) Sinks.
(c) Gas-to-particle conversions, (d) Sorption. (e) Deli-
quescence, (f) Efflorescence, (g) Raoult's equilibriun.
(h) Reaction in concentrated solution droplet, (i) Nucle-
ation and condensation of water, (j) Evaporation, (k) Cap-
ture of aerosol by cloud drops. (1) Reaction in dilute
solution, (m) Rain, (n) Freezing of supercooled drop by
ice nucleus, (o) Melting, (p) Direct Sublimation of ice
on ice nucleus, (q) Precipitation. R = organic radical.
54
-------
There is, however, growing awareness of the role of sulfur compounds in
19
determining the characteristics of aerosol and sufficient data do exist
on sulfur for it to serve as an example. As in total aerosol budgets, most
260
sulfur data are given as global averages. Since approximately 30% to 50%
of the atmospheric sulfur is anthropogenic and since man populates only a
small percentage of the earth, the role of sulfur compounds in the atmosphere
can only be understood by studying local or regional sulfur cycles. Although
quantitative data are so far lacking, man may dominate the regional cycles
in the Eastern United States, Europe, and in a few other places.
In the troposphere the total atmospheric burden is approximately
2 x 1012 g. Atmospheric sulfur exists largely in such reduced forms as
hydrogen sulfide, methyl sulfide, etc., and in the oxidized forms of sulfur
dioxide and sulfate ions by a variety of gas phase and liquid surface reactions.
The most important reactions are listed in Table 3-2. Sulfate ions combine
with available cations (e.g., hydrogen, ammonium, etc.) in both liquid and
solid particles. Sulfur is transported in the atmosphere largely through its
gaseous compounds and sulfate-containing particles. Thus, sulfur transport
has a spatial scale of -103 km. The sinks are dry deposition of sulfur di-
oxide gas and sulfate particles and removal by precipitation. The average
residence time is roughly estimated to be a few days.
55
-------
B
S
x
m
Sr-
O
A ;
CM 1—1
5. 5
,
M-l
s
a
01
fl
Is
U fc«
I
I
«• r
ft ot cl pj i» <"* O
" S - 5 2 ~ «
n
§, 1 s.
in "oSgu o u
a *x.2 s's-2
. Q o in o O
fj | 1
£ ""N +
° o 5* 9 56 S* o
(S C4 C4 rJ
-------
CHAPTER 4
MEASUREMENTS OF SIZE DISTRIBUTION AND CONCENTRATION
Before comparing results from the many studies of tropospheric aerosols
or particulates, a scheme for classification should be devised. Considera-
tion should be given to:
• Type of study
• Location of study
• The method and purpose of measurement
• Average sampling time
There are three general types of studies. The first includes data from
federal and state sampling networks that monitor aerosol concentrations in
primarily urban areas. Most of these data have been obtained with the high-
volume filter sampler, with the results expressed as total suspended par-
ticulate (TSP) mass. The second category of data, such as that obtained
662
in the California Tri-City Project and the Environmental Protection
455
Agency Cascade Impactor Network, contains some information on particle
size distributions and chemistry. Finally, intensive research studies use
the latest and most advanced equipment to obtain detailed data. However,
because of the complexity of these intensive studies, the number of sites
and time over which measurements can be made is limited. Examples are the
805
1969 Pasadena smog experiment and the most recent aerosol character-
ization experiment (ACHEX) 331 sponsored by the California Air Resources
331 , 808
Board, the Regional Air Pollution Study (RAPS) Program in St. Louis,
and the Midwest Interstate Sulfur Transport and Transformation Study (MISTTS)
(Cantrell and Whitby, unpublished data).
57
-------
The second method of categorizing tropospheric aerosol data is by the
location of the study. Studies may be categorized as urban, nonurban, or
whether their goal is to determine the characteristics of the natural global
background. Most air pollution studies have been conducted in areas having
pollution problems, such as urban or downwind of urban areas. In studies
of the natural background, however, investigators consciously seek the
cleanest possible air, such as that over oceans, icecaps, or other remote
areas.
In studies of the long distance transport of tropospheric aerosols, the
vertical distribution of the aerosols and the variations in their size dis-
tribution with altitude are important. These data can be further categorized
by altitude above the earth's surface.
Particulate data can also be classified by the kind of measurement used,
e.g., concentration, size distribution, chemical distribution, or other
special characteristics"! Because of the great variety of measurable charac-
teristics, as well as the inevitable compromises that must be made in field
work, few investigators have measured a complete list of physical and chem-
ical parameters in any given study. The most complete attempt to measure
all relevant chemical and physical parameters was made during the ACHEX study
330,331
in California.
Another method for classifying aerosol data is by average sampling time.
Monitoring networks often make limited measurements of concentration over
long periods. These monitoring methods usually provide only limited data on
size distribution and chemical composition. Because of the difficulties of
mobilizing a large array of measurement methods to measure many chemical and
physical parameters, comprehensive measurements have usually been limited
58
-------
to short intensive studies. However, as the duration of the study is de-
creased, the validity of the time averages also decreases. This inevitable
trade-off between depth and validity of the time averages is one of the
facets of field and monitoring research that deserves very careful attention
during the planning phase of such efforts.
In the following discussions of tropospheric aerosol data, location is
used as the primary method of classification, with measurement and time-
average characteristics adopted as the subordinate methods of classification.
The order in which locations are discussed progresses from the cleanest,
most natural background locations to the most polluted.
BACKGROUND MEASUREMENTS
Global Background Over the Oceans
Concentration Measurements. Because oceans occuoy a large portion of
the earth's surface and play an important role in the earth's radiation bal-
ance, the global background over the oceans has been studied intensively for
402,403
a long time by atmospheric scientists from many countries.
The altitude above the ocean surface can be divided into four regions:
• Close to the surface, that is, within a few meters above the
surface, is a region where salt spray aerosols occur in relatively
624
high concentrations depending on sea conditions. Pueschel et al.
measured coarse particle concentrations from 10 to 50 yg/m3
several meters above the surface in the Pacific near the coast
of Washington.
• The second region extends from the upper edge of the surface layer
to the top of the mixing layer. Concentrations averaging 5 Vg/m
of salt aerosol are found in this second reaion. Condensation in
59
-------
clouds at the upper edge of the mixing layer is an effective
barrier to the transport of salt aerosols to the region between
the upper edge of the mixing layer and the lower edge of the
stratospherer the tropopause.
• This region between the mixing layer and the tropopause has ex-
tremely clean air. Data obtained from the Mauna Loa background
monitoring station indicate that the average concentration of
aerosol is very low, with Aitken nuclei counts averaging a few
623
hundred/cm3. Prosper© measured sea salt concentrations of
2 to 3 yg/m3 in this layer over the mid-Atlantic.
• Above the tropopause in the stratosphere, the aerosol concentra-
tion is essentially the same over both sea and land, because the
removal rate is slow compared to the transport rate by stratospheric
401 612
winds. Measurements by Junge, Podzimek, and other investi-
gators have indicated that typical particle concentrations in the
stratosphere range from 1 to 20 Aitken nuclei/cm3, corresponding
to mass concentrations from 0.001 to 0.01 yg/m3. These concen-
trations are subject to large changes due to occasional injection
of high aerosol concentrations into the stratosphere from volcanoes
or from atomic tests.
There is also evidence of a sulfate aerosol layer just above the tropo-
pause but it is not known whether this originates from sulfur diffusing
upward through the tropopause, or from volcanic injections into the strato-
sphere. Figure 4-1 shows a typical variation in Aitken nuclei count and
calculated mass concentration with altitude based on a summary of available
data.
60
-------
25
* 2°
l
® l*
•O 13
3
< 10
5
0
h
.001
Aitken Nuclei
Accumulation Mode Volume,
based on DGV=0.3/im and
10 100 I03
Aitken Nuclei - No./cm3
I04
H-
.01
10
100
Volume Concentration - /i.m3/cnv
FIGURE 4-1. Typical variation of Aitken nuclei counts with altitude. The
two solid lines above and below the central solid line represent
the upper and lower boundaries as duduced from the available
literature. The accumulation mode volume has been calculated
assuming a nuclei count to volume ratio of 1,000 nuclei/on3:
1 ymVcm3. From Whitby, 1975.798
61
-------
Size Distribution Measurements. Global background aerosols over the
oceans tend to be dominated by aerosols in the surface layer that have been
mechanically produced by the sea surface, and by the coarse particle and
fine particle aerosols above the mixing layer that have been transported
from land. Aged particles are those that have had enough time to coagulate
and settle for at least a few hours. They tend to be unimodal, the nuclei
mode having been removed by coagulation and the coarse particles by settling,
unless large amounts of dust are present. These unimodal distributions have
a geometric mean size by volume or mass ranging from 0.4 to 1 um, with an
383,402
average geometric standard deviation of 2. Some typical number
distributions are shown in Figure 4-2.
250
In 1976, Flyger et al. reported finding very small nuclei mode-sized
aerosols (<0.01 ym) above Greenland. They interpreted this to indicate that
chemical or photochemical production of new nuclei is occurring. On occasion,
they found Aitken nuclei counts of 10,000/on3 at altitudes of several km.
Surface and background counts are normally between 200 and 500/cm3.
666
In a recent comprehensive report, Schaefer has summarized many years
of measurement of fine particles, especially of condensation nuclei. The
results agree well with the modal concepts discussed in Chapter 2. He has
categorized his condensation nuclei count data into seven categories ranging
from 50 to 10 million particles/cm3.
Long Distance Transport of Coarse Particles. As discussed in Chapter 3,
96,97,124,383,623
recent evidence indicates that dust advected above the
mixing layer into the mid-tropospheric altitudes over hot, dry desert areas
is then tr?nsported long distances over the ocean. For example, studies
62
-------
io2
10
10'
RADIUS r
cm
FIGURE 4-2.
Mean aerosol size distribution from all data obtained during
Spring, 1969, on the R. V. Meteor. From Jaenicke et al., 1971. 383
A: Below 2 x 10~5 cm radius. Data obtained with diffusion
battery and electrostatic precipitators.
B: Data obtained with double state impactors.
C: Composite data obtained with the impactor, plus an optical
counter, and free air impactor plate.
63
-------
over the Atlantic have shown that dust from the Sahara Desert is transported
in measurable quantities across the entire South Atlantic. Concentrations
exceeding 100pg/fa3 above the mixing layer at several km altitude were mea-
sured during the Global Atmospheric Research Program's Atlantic Tropical
Experiment (GATE).
The average concentration of dust during the dry season over the island
of Barbados is 10 vg/m3. During the rainy season, it is less than 1 yg/m3.
This Saharan dust layer is bounded on the bottom by the oceanic mixing layer
623
at 1.2 to 1.8 km, and at the upper edge by an inversion at about 3.7 km.
The sea salt concentration in this dust layer averages 2 to 3 vg/m3.
Similar dust plumes have been observed downwind of the desert areas of
north India and Pakistan, and over the China Sea downwind of some deserts
on the mainland. These dust plumes may play a substantial role in the earth's
meteorology and cloud physics, but conclusive results are not yet available.
Clean Background Over Land
Clean background conditions over land are more complex than over the
oceans. Over land, variations in surface albedo, topography, and precipita-
tion can cause very large variations in the rates of generation by the surface
and of removal. Thus, there is no single set of parameters for the background
aerosol concentration and size distribution over land.
The following locations and conditions have been selected to illustrate
the possible range of concentrations and the general effect of different
surface and location characteristics on observed aerosol concentrations and
size distributions.
64
-------
354
Remote Areas with Snow and Ice Surfaces. Studies over Antarctica
and the Arctic show the aerosol concentration to be as low or lower than over
the oceans. Aitken nuclei counts of 100/cm3 are common. Most of the aerosol
in these locations has been transported over lonq distances such as the a^ro-
249
sol observed by Flyger et al. over the Greenland ice cap. On occasion,
nuclei counts as high as 10,000/cm3 were observed at altitudes of 1 km,
with accompanying accumulation mode mass concentrations of 10 yg/m3. Al-
though these high nuclei counts imply in_ situ production of new particles,
the majority of the aerosol mass was found in the accumulation mode. It
was probably transported from the North American continent.
Remote Dry or Desert Areas. As indicated earlier, these areas may be
the source of large quantities of dust advected to high altitudes. Such
aerosols are produced by mechanical processes and modified by sedimentation
removal of the larger particles. In their measurement of dusts over the
682
Sahara, Schutz and Jaenicke found geometric mean sizes by volume to be
3 to 6 urn dia and geometric standard deviations from 2.0 to 2.5 ym dia.
o
Concentrations can range to several hundred yg/m .
275
Gillette et al. found that the distribution of coarse particle aero-
sols generated by wind erosion over land in the Midwest was similar to that
found by Schutz and Jaenicke over the Sahara. Figure 4-3 shows a typical
size distribution observed in the Midwest studies.
688 323
Sehmel and Heinsohn et al. have studied the dust produced by cars
and trucks on roadways. This source of coarse particles is important since
few areas of the United States are free from vehicles traveling on roadways.
While most roads are paved, many in desert areas are not.
65
-------
10
?r-
10
en
o
10
-2
10
-3
• 1.5m
Q 1.5 km
A 2.4 km
O 3.5 km
• 6.1 km
• 11.9 km
0.10
1.0 10
RADIUS (urn)
100
FIGURE 4-3. Coarse particle size distributions measured at various
altitudes over the Midwest on April 30, 1971. If these
number distributions are transformed to volume distribu-
tions, the coarse particle mode sizes are in yeneral agree-
ment with those given in Table 4-3. Gillette et al.27S
66
-------
796
Whitby found evidence of such particles settling as a steady rain in
the western United States. These particles were possibly carried to high
altitudes by thunderstorms.
In dry areas, these particles provide a substantial coarse particle mode
background. Since these are measured by such filter techniques as the stan-
dard high-volume filter method for total suspended particulates, they affect
the significance of such integral mass measurements. In the western United
States, these fugitive dusts often account for most of the total suspended
323
particulates.
747
Sverdrup et al. reported measurements made at the Goldstone tracking
station in the Mojave Desert as part of the California ACHEX study. One day
after rain, when the winds were from the northwest, the total aerosol volume
was 1.85, the submicrometer volume was 1.03 vm3/cm3, and the Aitken nuclei
666
count was less than 1,000/cm3. Although Schaefer reported somewhat lower
Aitken nuclei counts in very clean locations such as Yellowstone National
Park during winter, the Goldstone measurement on October 31, 1972 is probably
the lowest that could occur in most dry areas.
Areas of Average Precipitation and'Vegetative Cover. The precipitation
and vegetative cover such as that found over the eastern two-thirds of the
United States provide a quite different background aerosol situation than in
the dry areas of the western United States.
First, because the area over which dust can be suspended is limited,
the source of coarse particles, and, therefore, the coarse particle mode,
is usually much smaller. In many cases, measurements as small as 5 or 10
yg/m3 have Heen recorded. However, during periods of high wind or near dry,
67
-------
bare fields, the amount of coarse particles in a particular location can be
increased temporarily to several hundred micrograms per cubic meter.
The amount of natural accumulation-mode-sized aerosol that exists during
true background conditions is not clear. Evidence suggests that most areas
in the United States are affected at some time by anthropogenic aerosol
sources.
Natural accumulation mode aerosol concentrations were studied by Whitby
806
et al. during the General Motors Sulfate Study. On several days when
the wind was out of the northwest over essentially uninhabited regions of
Canada and the United States, they measured aerosol accumulation mode
volume concentrations from 1 to 2 ymVcm3, corresponding to 1 to 3 vg/fo3.
In early morning, coarse particle volume was only 2 to 5 ym3/cm3. This
increased to 5 to 15 ym3/cm3 later in the day, as the relative humidity de-
creased and the traffic in the area increased. These observations suggest
that most of these coarse particles had a local, anthropogenic origin, even
though they were not emitted from a stack. This air transversed vegetated,
but relatively uninhabited, areas of Canada and the United States, indicating
the possible accumulation mode background in that area prior to man's arrival
and his subsequent pollution.
Measurements during the RAPS study in the St. Louis area, and during
the General Motors Sulfate Study in central Michigan when the wind was from
the southwest, south, or east, indicate that accumulation mode volume concen-
trations ordinarily ranged from 5 to 20 ymVcm3. This suggests that most of
this aerosol was aged and had been transported from anthropogenic sources.
20
Altshuller, by using the concentrations of various chemicals measured
in impactor and NASN Hi-Vol studies, has recently calculated the concentration
68
-------
of fine particles that should exist in different parts of the country. He
calculated fine particle mass concentrations (FPF) for various urban and non-
urban areas in the United States (Table 4-1). The lowest value of FPF is
2.7 yg/m3.
The differences in FPF and coarse particle mass concentrations (CPF)
between the eastern and western United States can be clearly seen by com-
paring the ratios of the average eastern concentrations to the average
western concentrations. ("East" includes East Coast, Southeast, and Mid-
west [E]). The ratio for urban FPF is 1.7:1, nonurban FPF is 2.2:1, urban
CPF is 1.2:1, and nonurban CPF is 1.3:1. While the average concentrations
of coarse particles in the East and West are similar, the East has nearly
twice as much fine particle mass in both urban and nonurban areas as the
West. This is evidence that the fine particle concentrations, both in urban
and nonurban areas, are much more directly related to man's activity than
are coarse particle concentrations.
MEASUREMENTS OF ANTHROPOGENIC INFLUENCE
Evidence from the many measurements of aerosols throughout the world
indicates that most places on earth are influenced at some time by anthro-
pogenic activity. In any meaningful discussion of anthropogenic influence,
one must first specify which aerosol characteristics are to be discussed;
then the significance of specific concentrations should be defined.
To present the data, the amounts by particle size will be broken down
either into fine, coarse, or, where available, into the an»unts in the
nuclei, accumulation, or coarse particle modes. The data will be further
categorized in a number of different ways, since there is no general agree-
ment as to what constitutes an urban aerosol or a background aerosol.
69
-------
a
PQ
CO
3
o
•H
C i
rd
C
•H
CO
cu
4-*
•H
C/3
c
rQ
jj
rO
c
rd
C
»-Q
fi
•p
rrf
'U
W
CU
•H
O
cu
co
cu
4->
rd
H
3
O
•H
4->
PM
V
a
•H
fa
(^
o
co
C
0
•H
•P
rd
C
CU
O
C
O
O
^.
v?
^*\
•O
CU
4-1
Q
C
cu
£l
CU
-d
Jl
n
CD
CO
CD
H
1
CO
CD
i-l
£•<
o
o
CD
H
I
CO
CD
r~^
bO
e
•rH
3
t)
to
0>
•p
rd
•P
CO
Tl
w
cu
•p
•H
5
nj
u*
-p
P3
•H
W
C
o
•a
bO
0)
v{
to
o
•H
••> C
CO rd
CO bO
(0 £|
E O
CU CU
•P H
H 3
3 H
O 0
•H CO
•P 1
S-i CU
rd C
ft cu
N
"S m
CU II
ft,
CO O
3 W)
CO PQ
H •«
rd <~^
•p r* i
O PL.
1
ii CM
0, H
CO ^~-
£-H
G
.«> O
C -H
O -P
•H rd
•P P
rd -P
k C
-p cu
C 0
cu c
o o
C 0
o
o w
W rd „
WE e
6 3 M
cu o ^
, 1 ,,_!
<•> ^ C
38 §
f-t ft I]
&. 2
co £
cm 0
••-i n ^
tZ u °
U-, CJ c
n
II II ru>
\-J
fl , ^1^
&H DH
K. O
CM
Pk
CJ
falfa
P-4 ICO
f
P-)
fc
C
*t^^
^ CD
* to
•H CD
55 H
" 1
C c**
S3 ID
* CD
r-l [
;_) ' — 1
CJ «—
/^*s
CD
CO
CD
H
jl
to
CD
Q) j~'j
^\
£
^.
i — i
CM
1
CO
O J-
*-^ *T"
1^4 M^H
I— J &
O
PQ
+
r— i
V^
O-*
-J
jCO K
C
O
•H
(0
O
Q
^
c
o
•H
bO
CO
ez
in
CD
^
in
CM
0
in
in
CM
in
f~
o
*
0
o
H
J-
,-1
O
CO
H
to
H
q
£4
^
•p
co
rd
O
O
•P
co
rd
M
0
Jt
CM
H
CO
o
00
0
H
in
H
o
in
o
0
00
0
o
t>
o
to
H
3-
00
c
JH
I
0
*
00 CN
CO CO
00 CO
00 CM
H CM
0 0
J- CM
00 0
H iH
in
CO H
0 O
00
J- O
0 0
C""*
0 0
H O
00 OO
rH 0
r- co
in H
H t-
CD r-
pj
tfl
X)
C fc
L Q
a
•p
co
rd
cu
*c
•p
^
0
CO
t~- CO
00 CD
O CM
H
en oo
H CM
0 0
m d-
in H
CM H
in
CO CN
o o
d- co
CO H
o o
oo
i-l O
H 0
H C--
CN 0
to r--
in H
CD O
J- CD
, — 1
c
m
XI
C h
?-( O
D S5
-p
CO
CO
5
T3 ^-»
•H W
s «->
O 00
co m
CD H
co d-
H CN
o o
en o
co in
in
CM H
o o
,3-
d" O
0 0
CO
t- o
0 0
d- d-
.H 0
d" CN
d" H
t~ CM
CO CO
c
1 g
^ 0
_!_>
co
cu
»
'& >"V
•rH S
CO H CO
O J- CO
C~- CM C^
in co CM
H CM H
0 O 0
J- CM 3-
CM C^ O
H i-l
in in
H H CM
00 0
in d- in
CN O CN
o o o
J-
O O 00
HO O
to r^ CN
MO r-i
in in co
d- H zf
CD 00 CO
J- J- co
rj
JS
c fj a
rd 3 rd
XI G X)
& O fc
D s n
1)
w c
CU -H
S rd
rC 4-1
•P C
3 3
o o
CO 2
o
CD
co
CM
o
£•>•
CM
H
o
H
0
0
o
o
o
in
H
0
00
0
CO
H
c
i
*
CO O
.d- in
CO &
CO O
CM rH
O 0
CN O
CD in
H
in
CN rH
o o
in co
CM O
o o
o
r- o
H 0
in
O CO
CO O
in
tO t-l
co d-
f» CO
a
II
5 a
co
nj
o
o
4J
CO
0)
o
-------
Urban Aerosols
Since aerosols in urban areas differ greatly in size, source, meteorology,
and other aspects, only the most general characteristics will be discussed
here. Since urban areas have many aerosol sources, various sections or
individual sampling stations can be strongly influenced by local sources.
Only data thought to be relatively uninfluenced by local sources have been
included below.
In Table 4-2, the fine and coarse particle concentrations in several
urban areas are compared to very clean values. The results of Table 4-2 com-
pared with Table 4-1 indicate that the concentrations determined by the two
different methods are in reasonable agreement. These tables also indicate
that fine particle concentration in urban areas is considerably higher than
in clean areas. During polluted conditions, the fine particle concentration
in St. Louis reached 296 vg/m3 on one day. In 1973, a concentration approach-
ing 300 yg/hi3 was observed in Los Angeles. Under normal conditions fine
particle concentrations in urban areas seem to average 20 to 30yg/m3.
At a rural site 40 km from St. Louis and at an urban site in St. Louis,
207
Dzubay et al. observed that sulfur and lead dominated the fine particles
and were an insignificant fraction of the coarse particles. The composition of
the rural and urban aerosols were similar indicating that the rural sample
was transported from the city. Chemical composition as a function of aerosol
size will be discussed in greater detail in Chapter 5.
Urban vs. Nonurban Aerosols
Aerosol size distribution data from a variety of locations are listed by
distribution modes in Table 4-3. These data show that the volume of aerosol
in the nuclei mode is usually quite small (<1 um3/cm3), except very near
71
-------
TABLE 4-2
Fine and Coarse Aerosol Concentrations from
Some
Urban Measurements Compared to Clean Areas
Concentration, yg/m3 (p =1)
Location
St. Louis
Los Angeles
Los Angeles freeway
Denver
Goldstone
Milford, Mich.
Pt. Arguello
Condition
Very polluted
Grand average
Wind from freeway
Grand average
Clean
Very clean
Marine air
Fine
particles
296.0
37.0
77.0
16.6
1.5
1.03
1.1
Coarse
particles
94.0
30.0
59.0
232.0
3.0
0.82
53.0
Reference
a
805
803
815
71*7
806
331
(seaside)
Cantrell and Whitby, unpublished data from 1975 EPA MISTTS Program, St. Louis.
72
-------
W
J
CQ
CD
CO
£_l
(0
0
O
CO
c
o
•rH
P
•H
T)
q
o
o
T3
C
(0
CO
C
O
•H
P
cO
O
o
•P
c
0)
r^j
0)
<4n
M-t
•H
Q
£_,
O
IP,
CO
CD
-j-J
CD
E
CO
£_(
CO
p ,
H
(0
13
O
S
LL.J
0
£?
E
E
P
cv3
C
o
•rH
-P
cO
H
3
0
|3
O
0
<
c
O
ro
E
*
>
r~l
•
[--.
*> — '
CD
ID
CO
^
^
•
>
0
Q
ro
E
O
no
E
1
£>
CM
.H
N— '
C^-
•
in
Jf_^
00
•
CN
iH
*^
J-
•
rH
^J-
g
^
*
>
O
O
/— N
t£)
O
•
o
^s
in
oo
•
0
•H
CD
i — |
O
|3
^y
r>
E
O
r)
e
ri
>
en
H
*
O
^^s
CN
C^
0
*k
E
tj
n
>
Q
\J
H
O
•
0
v^
CN
jj-
O
•
o
CO
CD
rH -P
0) -H
f") Q/)
S 0
Ol
rH
O
CO
O
£_j
Q)
(0
MH
O
0)
P,
[>^
,p
^
c
(0
C
0
•H
P
cO
O
O
CO
CD
bO
<0
CD
>
rrj
a
cO
bO
^i
rH
P
CO
o
1
c
(0
^
£4
ID
L^
•
t —
^*s
to
^
ct-
^^
CO
oo
> — f
t-^
•
Id
s_^
CN
•
jj-
CN
s ^
CD
•
(£>
CN
/ — \
H
•3~
O
•
0
•*^s
CD
CN
•
O
^^
in
•
CN
H
\^_s
CN
OO
^
00
o
0
•
o
*• — '
00
oo
o
•
o
•*
0)
CO
o
CJ
r-*^
rQ
r^
Q)
o
c
Q)
3
H
13
•H
1
0)
C CJ
CO k
rQ d
^ O
O CO
—i
•
LO
00
\ s
oo
UD
IT)
^
0
in
^.^
QO
•
t^
^_^
cn
•
CM
\^s
J-
•
jj-
^-~*
CN
CO
O
•
o
^^
oo
00
•
o
,_,
^
o
•
o
^ — ^
LO
oo
o
o
CO
o
o
•
o
^^
LO
CO
o
•
0
t>
d
CO
,Q
JLj
13
CD
rH
P
4-i
•H
H
1
T)
c
^
0
£_j
bO
O
cO
CO
CD
O
C
CD
|3
rH
IP,
C
•H
d)
O
^3
0
w
f^J
o
V- '
CO
^
X"N
rH
H
^_x
to
•
^
/«\
CD
»
^
\^^x
CO
•
CO
/ — s
J-
rH
0
•
o
*^s
CN
CN
•
O
f S
CN
03
•
O
\_ ,
[ —
t>
o
'P
rH
O
•
O
°*^s
CN
OO
O
•
O
CN
CO
CD
O
fn
O
CO
£_j
(0
CD
C
1
T3
G
O
C_)
bb
^
O
m
PQ
-j
•
LO
^ — /
H
-j!
rH
H
CO
0
V •
oo
CN
•
*
^
CN
•
CN
00
•« — ^
CN
•
CN
J-
s-~*
H
rH
•
O
^^
r-
oo
•
o
rH
CO
O
•
O
«^_/
t^
J-
o
o
1
1
oo
^>
A
id
CD
o
C
CD
P
H
(4-1
C
•rH
t
T)
C
^
0
^)
bO
^
O
(0
PQ
CO
CO
CO
C
O
•H
P
CO
•H
CD
C
cO
+J
CO
0)
P
(0
CO
•H
CO
(V
,c
P
CD
CO
-------
intense sources of condensation nuclei such as a freeway or roadway. In most
urban areas, the accumulation mode contains upwards of 30 urn3/cm3. The
amount in the coarse particle mode is quite variable. The highest values are
obtained in dry areas where windblown dust may dominate the coarse particles.
Table 4-3 summarizes the modal parameters of a large amount of data col-
lected in a variety of locations in the country. Those sites classified as
urban were all within cities. At the urban sites, the nuclei mode average
was 0.72 wif/cm3; the accumulation mode average was 41.4 wn3/cm3; and the
coarse particle mode average was 36.9 vmVcm3.
An example of "urban influenced by close source" would be an urban site
within 50 m of a road or freeway. In this case there is a relatively large
volume in the nuclei mode, as compared to the general urban aerosol. The
volume in the accumulation mode is less than the urban average. Because
these data apply only to a particular site they have no great significance.
The background sites were divided into three groups. The first group,
obtained from averaging data from seven sites, showed little urban or source
influence. In this group, the nuclei mode concentration was very low. At four
of the seven sites, it was essentially equal to 0. The average for the accu-
mulation mode was 4.4 wn3/cm3, roughly one-tenth of that for the urban areas.
Some of the background sites had accumulation mode volumes as low as 1 ym3/cm3.
However, the volume in the coarse particle mode was essentially the same as
for the urban sites.
The second group consisted of two background sites that had nearby sources
of clean combustion aerosol. In this case the nuclei mode was about the same
as the urban. However, the accumulation mode volume was much less. There
was a very low volume in the coarse particle mode (7.8 vm3/cm3) because these
measurements were made on days when there was very little windblown dust.
74
-------
A third group consisted of background sites at which there was ample
evidence of incursions of urban aerosol from as far as 150 km.
Figure 4-4 shows an incursion of accumulation mode air in substantial
747
volume as measured by Sverdrup et al. at the Goldstone tracking station
in 1972. There is a large increase in volume in the accumulation mode with
little increase in the coarse particle mode.
Figure 4-5 shows two size distributions measured at Hunter-Liggett
Military Reservation during the 1972 ACHEX experiment, in which local anthro-
pogenic activity caused significant brief fluctuations in the coarse particle
mode without affecting the accumulation mode.
In general, the coarse particle mode is influenced mostly by local sources
of coarse particles. The accumulation mode is affected by secondary aerosols
which are formed over large areas and which can be transported over distances
of hundreds of kilometers.
Long Distance Transport of Accumulation Mode Aerosols
As discussed in Chapter 3, fine particles can be transported over long
distances. Evidence outlined above shows that accumulation mode aerosols
have been transported from 100 to 150 km. Recent evidence indicates that
accumulation mode aerosols can be transmitted at even greater distances—
perhaps up to several thousand km.
90
Brosset et al. and others in Europe have shown that sulfate and soot-
containing accumulation-mode-sized aerosols are frequently transported from
776
northern Europe to Norway and Sweden. Waggoner et al. have reported a
significant correlation between sulfate mass concentrations and particle
scattering coefficient measured at 1 to 2 km over Norway.
75
-------
GOLDSTONE
11-4-72
O 05:00
05:40
D 07:50
PARTICLE DIAMETER,
FIGURE 4-4. Incursion of aged smog aerosol from Los Angeles at the Goldstone
tracking station in the Mojave Desert in California. Note the
buildup in the accumulation mode. Sverdruo et al_.
76
-------
60
50
« 40
o
o
E
Qa3°
O>
_O
-------
372
In June 1975, Husar et al. observed a large, hiqh pollution eoisode
that wandered around many states in the eastern half of the United States.
They measured the light scattering and sulfate in St. Louis during June and
July 1975 (Figure 4-6). The light scattering and sulfate values are highly
correlated. The peak aerosol concentrations probably correspond to 60 to 70
yg/m3 of total aerosol and 35 to 40 yg/fa3 of sulfate.
Figure 4-7 shows visibility isopleths calculated from Weather Service
visibility data on June 30, 1975. Figure 4-8 shows a Synchronous Meteor-
ological Satellite (SMS) photograph obtained on that same day. Figures 4-7
and 4-8 show that the region of haziness covers multiple-state areas consistent
500
with earlier satellite observations. From Figure 4-7, it can be estimated
that these hazy areas contain sulfate aerosol concentrations aoproximately
35 yg/m3. Figure 4-9 shows the correlation between sulfur content and fine
particle mass measured near St. Louis for a 20-day period starting August 18,
1975. From these various measurements it is apparent that an accumulation
mode aerosol containing a large proportion of sulfate frequently covers a
large portion of the eastern third of the United States. ,
Simultaneous Measurements of Light Scattering and Fine Particle
Mass Concentration"
Because of its importance, the relationship between light scattering and
either total suspended particulate mass concentration or fine particle mass
concentration has been examined by a number of investigators. Chapter 6 con-
tains a more detailed discussion of aerosol optical properties in general, and
135
the particle scattering coefficient (b ) in particular. Charlson, in
scat
a review paper, gave a relationship between total aerosol mass concentration,
c, and b : c (yg/m3) = 4.5 x 10 b (nT1). If the fine particle mass
scat scat
78
-------
— STATION 4
— STATION 6
— STATION 9
(ii
2
OT
(O
6/23 6/24 6/25 6/26 6/27 6/28 6/29 . 6/30 7/1 7/2 7/3 7/4 7/5
FIGURE 4-6.
Light scattering and sulfate measurements in St. Louis during
a long episode of haziness. The upper graph shows the fc>scat
and sulfate data and the lower one the extinctions calculated
from visibility data. From Husar et al. 372
79
-------
FIGURE 4-7. Visibility isopleths for June 30, 1975 showing a large area of
haziness over the Midwest of the United States. The peak values
of bgcat' corresponding to the lowest visibilities, correspond
to the peak values of sulfate in Figure 4-6 and the roost hazy
areas in Figure 4-8. From Lyons and Husar, 1976. *
80
-------
FIGURE 4-8. Photograph from the SMS satellite on June 30, 1975 showing the large
area of air pollution haziness shown in Figure 4-7. This hazy air
mass was transported from the east and south. From Lyons and Husar,
1976.""
81
-------
RURAL PARTICULATE MASS AND SULFUR FRACTION
80i-
60
.£
o>
8
<
40
20
Fine Fraction
Rural (124)
I I I I I 1
I I I I I I I
3
QC
CO
18
21
24
27
30
AUG
2
SEPT
FIGURE 4-9. Correlation of fine particle fraction and the sulfur content of
aerosol measured on a rural site in St. louis in the sunroer of
1975. Data of Dzubay and Stevens.206
82
-------
is 50% of the total average mass concentration, the fine particle mass
concentration to b ratio would be 22.5:1.
scat 598
Recently, Patterson and Wagman obtained samples at four different
visibility levels in separate Anderson impactors. (See Table 4-4.) By
log-normal fitting, they determined the mass median diameter (MMD) in both
the fine particle and coarse particle fractions, corresponding approximately
to the accumulation and coarse particle modes. The MMD's in both fractions
agree with those in Table 4-3, which were obtained by entirely different
methods. As the visibility decreased or, in other words, b increased,
scat
the percent of the mass in the fine particle fraction, or accumulation mode,
increased (Table 4-4). At the lowest visibility, 61% of the mass was in
the fine particle fraction.
In Table 4-4, the fine particle mass to b . ratio has been calculated
scat
from the data of Patterson and Wagman. The ratio varies from 12.2 to 16.8,
but is relatively constant considering the range of visibility conditions
sampled.
746
Recently, Sverdrup and Whitby examined the relationship of conden-
sation nuclei count to the ratio of fine particle volume to b for the
scat
data collected during the ACHEX Program in California. (See Figure 4-10.)
The ratio varies from around 5:1 at very low concentrations to about 35:1
at the highest concentrations near strong sources of aerosol.
662
Samuels et al. made a detailed study of the relationship between
particle mass concentration smaller than 3 vm dia, and prevailing visibility
and b . They obtained ratios of particle mass concentration < 3 vro to
scat
b ranging from 22.7:1 to 31:1.
scat
83
-------
I
H
•H
o
10
H
0)
w
O
•H
I
•P
It)
•P
0)
bO
fj
0)
+J
Id
O
•r4
•J
1
•H
CO
CJ
•H
•P
fc
ffl
a,
4-1
O
O -P
•H m
•p o
& (0
(3 Xl rH
ft CO |
-IB
0) W S-*
C to \ 1
•H id t»o o
fM 6 3- H
00
•
(O
H
CN
•
CN
H
"8
•p
id
o
H
(ti
O
O
W
O C
o o
•Hen
w -p e
CO (0
IT3 ^
a -p
TJ
0)
I
id
Q>
I
•P cu 6
id bW-
O C I
co id o
•p
•H
•H a)
w >
•H Q)
> H
oo
en
•
CO
cu
H
O
•H
•P
h
id*c>
ft c
0
0) -H
M -P
& 0
id id
o p
O MH
O 00 CN
S3
3S f- co
1 0 00
cjp| r^ m
CO H
• •
oo oo
r-~ en
co co
ao 10 in CN
d- d- * d-
• • • •
o o o o
o
CO
oo
CM
in
•
00
CO
(O
(O
o o
• •
d- CN
H H
H CN
IT)
CO
I
tn
o
A
C
§
O
•xs
m
o
00
4->
id
&
6
0
tl
C
« .
c
o
•H
•P
id
o
o
id
0)
fi
i \
T-*
C
•H
(0
CU
CO
10
f=
CU
X!
•P
O
+J
>i
H
Q)
•P
6
•H
X
O
p
CU
a
id
T3
c
o
ft
CO
0)
h
b
0
o
co
c
o •
•H >>
•P H
0 0)
id >
•ft 3
o
CO CU
H ft
O CO
•H 0
•P b
fo Co •
^^ s
CD 0 -P
W 8 *
(o 4) fg
O -M -H
O O T3
•H
•e f 5
sa-5
CO CO
H !
b
rd
fn
•P
•H
f)
h
Id
C
O
•8
CO
Jl
CO
CO
•H
1
0)
•p
id
o
>>
4->
•H
H
•H
.a
•H
co
•H
tf
84
-------
o
o"
o
1 I 1 rTTTT| |—
STRONGLY SOURCE INFLUENCED f
SOURCE INFLUENCED E
URBAN D
AGED POLLUTED URBAN C
URBAN INFLUENCED B
CLEAN NONUR8AN A
, A 6
i A
A
A A
bsxIO4, cm3
FIGURE 4-10.
Relation of Aitken nuclei concentration (CNC) to the ratio of
the aerosol (<1 ]jm dia) volume concentration (V3-) to bgcat
(bs) for the sites in California that were measured during
ACHEX I. From Sverdrup and Whitby, 1976.
85
-------
The above studies all show a good correlation between fine particle
135
concentration and light scattering, and hence, visibility. Charlson
obtained correlation coefficients of 0.9 between light scattering and sub-
micrometer volume. They also indicate a relationship between the absolute
concentration and the ratio of b . to aerosol mass. The ratio of fine
particle mass concentration to b __. ranges from 10:1 to over 30:1, depending
SCctu
on concentration and site. An average ratio, for levels at which visibility
degradation is important, would be approximately 20:1. Figure 4-10 shows
that much of the urban data from California clusters near the ratio of 20:1.
86
-------
CHAPTER 5
CHEMICAL AND TREND DATA
There are both routine monitorinq programs and specific research efforts
designed to collect information on the composition of atmospheric particles.
By far the largest volume of data over the longest period has been accumu-
lated by the routine monitoring operation of the National Air Sampling Net-
work (NASN) and other federal programs. However, the analyses performed on
these samples are limited to the determination of a few ionic and atomic
species and to extraction with solvents such as benzene to indicate the pres-
ence of organic material. There are no routine analyses for silica, silicates,
or oxygen in various substances, nor for high molecular weight organic mate-
rials that are benzene insoluble, nor is elemental carbon measured. Because
of the incompleteness of these routine chemical analyses, it is not possible
19
to obtain an anion-cation balance or specific molecular information. An
average of 25% to 30% of the weighable substances on the NASN filters are
routinely analyzed. Further, filterable mass is usually less than suspended
particulate mass due to volatility of a fraction of the aerosol. In certain
situations, however, where gas to particle reactions occur on the filter
(e.g., where sulfur dioxide is converted to sulfate), the filterable mass
may be larger than the suspended mass.
Many, perhaps most, of the important chemical properties of particulate
matter are due to the molecular rather than the ionic or atomic character.
Toxicity, water solubility, hygroscopicity or the lack of it, deliquescence
and efflorescence, refractive index, particle shape and state, acidity,
87
-------
basicity, and several other properties depend on the molecular nature
rather than on the presence of a single atomic or ionic species. However,
the ionic composition of a highly hydrated droplet aerosol that is composed
of a large number of anions and cations clearly dominates the system behavior.
At low humidity this same aerosol may have some definable molecular charac-
teristics such as deliquescence if adequate amounts of the necessary ions
are present in the particles. For example, sulfuric acid, ammonium sulfate,
calcium sulfate (or gypsum), and magnesium sulfate (or epsom salts) are all
sulfates but grow differently at high relative humidity (RH), appear in
different size classes, and have different sources and, presumably, different
effects.
More complete and molecular analyses by the large scale routine networks
in the United States are not feasible. Attempts made in various intensive
research programs have been limited in time and scope. (See Chapter 4.)
Consequently, definitive molecular composition as a function of particle
size, time, and location have yet to be determined. Since existing data are
limited, it is seldom possible to relate particle properties to effects, nor
is it possible to identify the predominant sources of the various particle
classes.
Hie composition of gases can be measured specifically. Ihese measure-
ments provide a scientifically defensible basis for cause-effect studies. In
contrast most particulate matter is measured by its total suspended particu-
late content, which includes all filterable particles. Molecular and ionic
species are often lumped together, precluding cause-effect studies where
chemical composition is important. To understand the behavior and effects
of particulate matter, analyses must be as specific as those currently
used for gases.
88
-------
OVERVIEW OF DATA
National Air Sampling Network (NASN)
The typical composition data from the NASN summarized in Table 5-1 show
only one of the many ways in which these data can be presented. For example,
the distribution of specific ions in rural areas may be mapped. From the map
in Figure 5-1 the differences in concentration and distribution of sulfate
and nitrate ions are immediately evident. Given the number of sampling
sites, their spatial distribution in both urban and rural areas, and the lon-
gevity of the NASN, it is evident that a large variety of data presentations
can be made. Available data from the Environmental Protection Agency (EPA),
consist mainly of statistical tables containing raw data. Some publications
494
on trends have been developed from these data. Further such work is in
progress both in the EPA and in various research groups. Unfortunately, the
decentralization of the EPA has resulted in great delays in processing NASN
samples and data so that the newest facts in this report are several years
old. Chemical analyses are currently at a near standstill.
Composition Data from Intensive Studies
Some of the first intensive studies of atmospheric particle composition
397
were conducted by Junge at Frankfurt, Germany; Round Hill, Massachusetts;
Mauna Kea, Hawaii; and various sites in Florida in the early 1950's. His
analyses showed that sulfate and ammonium ions were frequently predominant,
although only a few ions were analyzed and no mass or ionic balance was
attained.
Data collected at Round Hill show the daily variation of these ions for
fine particles (0.08 to O.Sum radius) and coarse particles (0.8 to 8.0 Mm
radius). (See Figures 5-2 and 5-3.) The terms "large" and "giant" were used
89
-------
TABLE 5-1
Arithmetic Mean and Maximum Urban Particulate Concentrations
in the United States, Biweekly Samplings, 1960-1965"
Pollutant
Suspended particulates
Fractions:
Benzene-soluble organic s
NO 3
Sb
As
Be
Bi
Cd
Cr
Co
Cu
Fe
Pb
Mn
Mo
Ni
Sn
Ti
V
Zn
Gross beta radioactivity
Number of
stations
291
218
96
96
56
35
133
100
35
35
103
35
103
104
104
103
35
103
85
104
99
99
323
Concentration, ug/m3
Arith. average^ Maximum
105
6.8
2.6
10.6
1.3
0.001
0.02
< 0.0005
< 0.0005
0.002
0.015
< 0.0005
0.09
1.58
0.79
0.10
< 0.005
0.034
0.02
0.04
0.050
0.67
(0.8 p_Ci/m3)
1,254
39.7
101.2
75.5
0.160
a
0.010
0.064
0.420
0.330
0.060
10.00
22.00
8.60
9.98
0.78
0.400
0.50
1.10
2.200
58.00
( 12.4 p_Ci/m3)
16.
768
a From USDHEW, 1969, p
Arithmetic averages are presented to permit comparable expression of averages
derived from quarterly composite samples; as such they are not directly com-
parable to geometric means calculated for previous years* data. The geometric
mean for all urban stations during 1964-1965 was yg/m3, for the nonurban
stations, 28 ug/m3.
No individual sample analyses performed.
90
-------
FIGURE 5~1. Isopleths of nitrate and sulfate concentrations drawn from
measurements taken at nonurban sites by the Environmental
Protection Agency (unpublished data).
91
-------
e
6
4
2
6
4
co 2
31 12
'o 10
X
4
2
4
2
4
2
00 O.I O.I O.I 0.0 0.0 0.0
00 0.3 04 0.3 Of 00 O.I
T» M
m ffl
'hi »«
1
'•' f ^ " i p
l.» 1 T 14
• 0.9 m m 09 'o •
mvAm m mm 1*
•
O.t O.t O.t 01 0.0 00 OO
Cl MEAN VALUE '0.022
0.0 0.0 0.0 00 0.0 0.0 0.0
Nd^MEAN VALUE'O.IO y|
01 00 00 0.0 O.I 0.0 0.0
S04~~MEAN VALUE- 3.00 V
ss
%
\
// I0 OT °» m L4
0i BE EH o-1 m m Wt
NH4 MEAN VALUE «O.T2 }i <
o» 04
rrn O.I Ol 0.0 O.I "•*
N03~MEAN VALUE- 005 \
0.0 OO OO 0.0 OO OO OO
yg/
'n.3
0.0 0.1 0.0 OO O.t
/m-
l».4
)
00 0.0
g/n
1
i/nrt^
OT
!3
1.0
1
*
1
7
^
0.0
/OO 0.1
8.4
,.
J
. . or o.» m
0.0
0.0
Cl"
\-
,
MEAN VALUE- 0.031 W9/[
-
o.i o.o oo ao o.o o.o
NO MEANVALUE-0.03I4J9/I
0.2
TO
I
1
is
M
o.o
10 «
1
I/I
?
(Wl
0.0 0.0 0.0
II 2
1
I
so;
NH,
tra
1
m
+
»
D«
0.0 0.0 O.I
"MEAN VALUE -6 15 PQ/1
ra '••> IZ
vA m M
MEAN VALUE «0.931)g/i
'
m v^ m m m m m m ^i m M ^ M
tg/r
,3
0.1 OO 0.0 O.I' 0.1
O.I
OO
NO
3~
O.J o.o oo
MEANVALUE-0.062 U8
?
2
6
^3
2
8
6
4
2
«u
^
'IF
0.0 0.0 0.1 1
E
i
4 55 6 7 8 9 10 II 12 13 14 15 IB 26 27 28 29 3O I 2 3456 T «
f JUNE | | JUNE (
SEA FOG SEA FOG SEA FOG SEA FOG
FIGURE 5-2. Ofoe daily variation in the chemical composition of fine parti-
cles (0.08 to 0.8 um radius) at Round Hill, Massachusetts.
From Junge, 1954 J*69
92
-------
8
6
4
2
6
4
2
O)
^3- A
**
0 10
X
8
6
4
2
4
2
4
2
_
30 j ,
' 0.7
y//i
1
m
58
10
Pfl
00
%
!
J7Z
1
//I
««
!
4
^
w
oz °4 °4
i
<
t
i
5S
p
j
17
1
7
mj
w,
n
0 2
0, Q|
[/^
n 01
2 1
KJJj
CJJJ73 r//l
J 5
1
/n
^
7!
01 o, o
Cl MEAN VALUE = 171 '
§0,
rvz
T
NCI MEAN VALUE* 1.61 |K
01 °002 ™ ^ ra 05
jg/m3
09
ra If °
.
Cl MEAN VALUE'073 ^9/r
i e 13
O'osf^O.S^ °*04
WA I777L \//\ 777\ Y/A T7/A
-------
extensively in these studies. These figures indicate that there are few
sodium or chlorine ions in the smaller particles and many more in the larger
ones. The opposite is true of the ammonium and sulfate ions which are
usually <1 urn dia. These and similar data have formed the basis for the
concept of a background of sulfate aerosol in some regions. The origin of
this aerosol containing sulfate, ammonium, and hydrogen ions is not known.
It may be dominated by man's activities such as the oxidation of sulfur di-
oxide from fossil fuel combustion. Further, as discussed in Chapter 4 and
as indicated in Figure 4-2, this aerosol is widespread in the eastern half
of the United States. At the very least, this indicates that care must be
taken in interpreting rural data on particle composition in terms of a natural
background versus large spatial scale pollution.
One of the earliest and still most complete urban analyses was reported
110
by Cadle in Los Angeles. He noted the presence of sulfate and signifi-
cantly higher amounts of nitrate ions. The lack of size segregation limited
the conclusions to be drawn from these analyses. Perhaps the most useful
results came from the separation of mineral and other inorganic substances
( ^60%), of which 45% are water-soluble, and organic compounds, which com-
prised approximately 25% of the mass. Although these are analyses of just
one sample from one, perhaps unique, city, the insight provided by this sort
of a separation aids the understanding of the sources and physical properties
of the particulate. It also crudely indicates the molecular nature.
From their analyses of intensive studies in Pasadena, California, Miller
543
et al. (Table 5-2) reported compositional features similar to those found
in Los Angeles. The dominant substance analyzed was noncarbonate carbon (by
94
-------
TABLE 5-2
Percentages of Chemical Elements in Pasadena Particulate Matter1"
(Total
Element
Al
Ba
Br
C (noncarbcnate)
Ca
Cl (dry analysis)
Cu
Fe
mass
at
%
0.8
0.04
0.6
19.0
0.99
0.07
0.03
3.2
loading = 101.5 ug/m3, measured
50% relative humidity)
Element
I
K
Mg
Mn
Na
Pb
V
Zn
%
0.006
0.32
1.1
0.03
1.0
3.3
0.01
0.18
Miller et al., 1972.51*3
95
-------
combustion analysis). Sulfate, not given in this table, is typically in the
range of 1 to 10 yg/n^when the total mass concentration is approximately
100 yg/m3.
After measuring the effects of humidity on light scattering in St. Louis,
144
Charlson et al. concluded that the light scattering aerosol both inside
and outside the city was dominated by one or more sulfates such as sulfuric
acid, ammonium bisulfate, and ammonium sulfate. The lack of correlation
with local wind direction, which might be expected from such maps as Figure
5-1, appears to be due to the long distance (103 km) transport of those
sulfates. Sulfates in Southern California, on the other hand, might have
local sources.
Data from Independent Investigators
Large amounts of useful data have been acquired over the years by inde-
pendent investigators studying individual substances in aerosols. Notable
820,821
among these is the work of Winchester and his colleagues on sub-
681
stances detectable by various nuclear techniques. Schuetzle et al.
studied the molecular nature of both organic and inorganic materials in
482
size-fractionated samples by high resolution mass spectroscopy. Lodge
deduced from electron microscopy that fine particles often contained free
sulfuric acid.
Since space limitations preclude the inclusion of an exhaustive list of
composition measurements, only a few examples from recent studies are
mentioned.
96
-------
SIZE DEPENDENCE OF COMPOSITION
Before the recent intensive studies of composition versus particle size
and prior to the understanding of the bimodal volume distribution, it was
common to assume a chemically well-mixed system. Current control strategies
for particles are based itnplicity on this as well as on the frequent assump-
tion "that all particles come directly from sources and not from production
or condensation in the air. Optical models of aerosol frequently assume
422
a uniform composition/size dependence. Health effects models such as
pulmonary deposition often use a similar approach.
Recent data suggest that a chemically well-mixed aerosol that has a
similar composition at all sizes is probably rare or nonexistent. Rather,
certain classes of substances appear to dominate above the 1 to 2 ym dia
205
range, and others below. Dzubay and Stevens analyzed urban aerosol
samples using a 2-stage dichotomous filter, with a separation at a particle
diameter (D ) of ^2 pirn. (See Figures 5-4 and 5-5.) They found that at least
75% of the sulfur, zinc, bromine, arsenic, selenium, and lead occur in the
fine particles and at least 75% of the silicon, calcium, titanium, and iron
in the coarse ones (Table 5-3).
The fine particles between 0.1 and 1.0 ym dia consist mainly of sulfates
from sulfur dioxide oxidation, nitrates from NO reactions, ammonium from
x
ammonia reactions, condensed organic matter (partially oxygenated), and
primary emitted particles such as lead and carbon. The coarse particles,
from 2.0 to 50.0 ym dia, consist largely of mechanically produced substances
such as soil or rock dust, road and tire dust, fly ash, and sea salt. (See
also Figure 2-7.)
97
-------
1 1/ta
TO puirp
FIGURE 5-4. Schematic view of a dichotcntous sampler which contains a
virtual inpactor. The flow rate at the inlet is 50 liters/
min, and the flow rates at the outlets are 49 and 1 liters/
min. Fran Drubay and Stevens, 1975.205 With permission from
Environmental Science and Technology. Copyright by the
American Chemical Society!
98
-------
S, Zn, Br, Pb
SMMjLER THAN 2 ym
1.8 - mg DEPOSIT
Al, SI, Ca, Tl, Fe
LARGER THAN 2 yin
1.3 - mg DEPOSIT
5 L
FIGURE 5-5.
Filters used in dichotonous sampler for the 23-hr
period beginning at 1015 hr, August 30, 1973 in a St. Louis
residential neighborhood. The air volume sampled was 68 m3.
From Dzubay and Stevens, 1975.205 With permission from Environ-
Science and Technology. Copyright by the American
99
Chemical Society.
-------
r-
CT)
,-1
co
0)
H
O
CO
I
en
W
10
bO
.5
.1
bO
(U
O,
I
CO
CM
TJ
CP
•M
O
0)
H
H
O
O
CO
0)
a
0)
COCO
§
O
Q
«M
0)
C
•rt
g
bO
C
CO
a
x^
$
CM
H
+1
0
H
H
V
O
IT)
+1
O
CO
H
V
O
O
CM
+1
O
o
CO
o
0
co
+1
o
0
r-
*
CO
O CM
O
C--
+1 -H
o d-
o
o
CM •> 4-
CM H
V V
CM O
CO
f—^
+\ -H
r> o
0
CO
3- CM
H
V V
0
co
+1
o
1-1
CM
+1
^
CO
CM
+1
in
H
CO
V
CM CO
+1 +1
J- LO
^
O
o
00
-{-I
0
o
CM
on
H
O
O
oo
-f.j
o
o
CO
•t
co
CM
g
§
H
W
-Q
CD
Cflco
C. C
nJ "^
O bO
0 G
d- o
o
co
+1 +1
0 0
CO O
|X*
A O "CO
CO H H
V V V
O O CM
d- co
+1 +1 +1
O O CO
o d-
3- CM
CM CO CO CM
V V V V
0
6
s
o
H
-H
O
CM
O
CO
V
CM
H
41
d-
H
H
O
•*
+1
O
fw]
f~\
CO
H
V
;J-
H
+1
0
CO
H
CM CO CO
V V V
o
(O
+1
o
CO
H
CM
+1
in
CM
V
V
C
0)
H
W
CM
c
o
•H
CO
CO
0) •
& Pi
.C CD
•H -H
•H CJ
* O
W
3 «
M O
.•H
"> §
rv. 0)
CO o
C-H
a> &
>
-------
Table 5-4 shows similar results that are further classified by urban
207
and rural location. "Hie percentage of fine sulfur particles is almost the
same in both locations, consistent with the theory of long distance transport
144
of sulfates discussed in Chapter 4. The optical studies of Charlson et a_l.
showed that the acid sulfate species sulfuric acid and/or ammonium bisulfate
frequently occur in the fine particle mode, confirming the classic results
397 575
of Junge. Natusch et al. showed that arsenic, antimony, cadmium, lead,
selenium, and thoriun emitted from coal-fired power plants occurred primarily
in the fine particle mode. A size-segregating elemental analysis network is
currently being operated by the State of California Air Resources Board Moni-
toring Program. Preliminary results confirm the 1976 studies of Flocchini
245
et al.
Some of the elements mentioned above can affect human health. Size-
segregating chemical analysis coupled with information regarding the molecular
state of these elements should aid the understanding of these effects (see
Chapter 7).
Two types of particle mixtures can be defined:
• External mixtures, in which the individual particles are pure or
nearly pure compounds and composition varies from particle to
particle.
• Internal mixtures, in which each particle contains all the sub-
stances in the same proportions.
The small Brownian displacement and collision frequencies of coarse
particles and their shorter atmospheric lifetime suggest that the coarse
particles of the mechanical mode probably exist as discrete particles of
identifiable substances. The larger Brownian displacement and high
101
-------
d-
1
in
a
<
H
C
(0
43
k
3
q
m
•H
(0
CO
cu
1
^n
O
•H
•)->
f^
(0
P-,
0)
(0
&
ro
0
0
•O
C
ro
0)
c
•H
CM
!J_i
m
o
o
•H
•H
•r(
CO
O
&
§
a
0)
bO
(0
•H
q
0)
9
H
0)
CX,
(U
bO
n)
p
S
>
<
i
£
f—4
00
H
0)
.C
4-1
MH
O
g
Vj
CO
•rl
(U
rt
|
s.
JJ
31
rH
ft
t^
fc
0)
43
0)
4-)
O4
Q)
CO
rr~4
T3
C
tti
00
H
+J
CO
g)
Of
3
<
C
0)
0)
s
•M
0)
m
T3
C; H
Sw^
/*~N
CO
6
<
bo
c a
•H CO f- O CO IT)
O CN CO ID CTI iH IT)
o o o co oo o o
CN 00 CN ID 3- O O
00 J- rH O rH 00 CN
f- J- J- CN in O rH
O rH O CN CN H H
H
ITJ 0) rd -H -H
O CM X pj CO CO E->
P«.
O
CM
[•^
[-,
cn
rH
A
•
Hi
ml
$
>,
a)
A
g
O
£
o
102
-------
collision frequencies of fine particles suggest that this mass mode is
internally mixed. Since the interaction between these two modes is rela-
tively weak, they form an external mixture.
HYGROSCOPICITY AND DELIQUESCENCE
Several effects of atmospheric particulates depend on the growth of the
particles at high RH. Growth and impaction in the respiratory tract, visi-
bility degradation, and cloud condensation are notable examples. In turn,
the properties controlling such growth are controlled by the molecular com-
position. Most of the hygroscopic and deliquescent substances present in
atmospheric particles appear in particles <1 wm dia, with the notable ex-
ception of sea salt particles which may be larger.
Deliquescent salts undergo a sudden phase transition from a dry crystal
to a solution droplet when the RH exceeds that of the saturated solution of
the highest hydrate of the salt.
The deliquescence points of several atmospheric substances are: ammonium
sulfate, 80%; sodium sulfate, 86%; sodium chloride, 75%; and ammonium nitrate,
62%.
Because of their polar molecular nature, hygroscopic compounds absorb
water until they became solutions at equilibrium with the ambient humidity.
They exhibit nonotonic growth in size as RH is increased, in contrast to the
deliquescent salts. Examples of hygroscopic atmospheric substances are
sulfuric acid, glycols, sugars, organic acids, and alcohols.
Internal mixing affects the hygroscopic and deliquescent growth charac-
teristics of fine particles. Clear cut deliquescent orowth has been observed
167
optically for two atmospheric substances: sea salt and ammonium sulfate.
Frequently, interval mixing masks the deliquescence of minor substances.
103
-------
The quantitative aspects of this qrowth with RH can be studied optically,
by weighing techniques, and with microwave absorption. Atmospheric fine par-
ticles are almost always sufficiently hygroscopic or deliquescent to exhibit
growth below 100% RH. The amount of growth that occurs as RH is raised from
a low of 20% to 30% to 95+% depends on the fraction of the material that is
hygroscopic or deliquescent and on its composition. For specific pure sub-
stances, such as sodium chloride or sulfuric acid, it is possible to calculate
the size increase with RH assuming the solution behavior is known. The ratio
of particle radius (r) at the given RH to that of the dry particle, r(RH)/r(0),
assuming ideal solution behavior, is typically 2 at ^ 90% RH for a hygro-
scopic salt. The nonideality of solutions actually alters the real behavior
slightly? however, the magnitude of the growth is adequately demonstrated.
Measurement of impure atmospheric particles by optical, mass, or micro-
wave techniques indicates that in most urban locations, the fine particles
are often hygroscopic, occasionally deliquescent, and only rarely hydrophobic.
167
Covert's data from eight sites in California, three sites in and near
St. Louis, and two sites in Denver demonstrate these three behavior classi-
fications. In California the aerosol was rarely deliquescent. A comparative
study of optical and microwave techniques produced the results shown in
Figure 5-6 for the mass of water in submicrometer aerosol versus RH. At 80%
RH, approximately 50% of the mass of the fine particles is water. Further,
the particles clearly contain water at 50% RH and below. The fact that
such particles are usually wet suggests that it is necessary to consider
the presence of the water for studies of aerosol chemisorption, such as
526
sulfur dioxide-particle synergism. It must also be concluded that the
fine particles are often composed of hygroscopic or deliquescent substances.
104
-------
1.0
Pomona 10/24 Charlson Humidified Nephelometer
• Pasadena 9/15 (RH Decreasing)
• Pasadena 9/9
A Pasadena 9/20
A Pomona 10/4-10/5
Goldstone 11/2
50 , 75
RELATIVE HUMIDITY (%)
100
FIGURE 5-6. Weight fraction of liquid water as a function of relative
humidity for the Los Angeles Basin area. The data points
are results obtained with a microwave technique and the
dotted curves are the results obtained optically with a
nephelometer. Fran Ho et al., 1974. 3l*4
105
-------
A notable exception to this observation that fine particles are usually
wet occurred in Denver where, from 5% to 10% of the time, limited growth
occurred at humidities tp to 93%. That aerosol was probably composed of
water-insoluble, hydrophobia substances. An aerosol of carbon, certain
metal oxides, or partially burned oil would behave in this manner. From
90% to 95% of the time, the dominant behavior was simple hyqroscopic growth.
If the fine particles are uniform in composition with size, it is pos-
sible to calculate the change in mass or volume distribution as they equili-
brate at some increased humidity. Figure 6-7 shows the calculated distri-
bution of aerosol volume as a function of particle size, as the particle
grows hygroscopically to 1.5 and 2.0 times its initial size.
The effect of hygroscopic/deliquescent growth of particles < 1 w» dia
dramatically increases the mass median diameter of these particles and the
total amount of material in the condensed phase.
The final aspect of hygroscopic/deliquescent growth is the response time
410 44
of the particles. Keith and Arons and Azarniouch et al. have calculated
the time required for such particles to attain various fractions of their
equilibrium size when a step increase of humidity is imposed. Table 5-5
illustrates this response time, suggesting that growth is sufficiently
rapid to occur in the upper airways of humans. However, the response time
for particles >1 Mm dia and for humidities approaching 100% becomes suffi-
ciently long that complete equilibrium may not be attained in the breathing
cycle.
106
-------
TABLE 5-5
Growth Rates of Sea Salt Aerosol
Time to reach 97% of
Dry aerosol equi.libri.LEti radius
radius, ym at 90% RH, sec
0.1 - 0.0022
1.0 0.22
5.0 5.4
TRENDS IN DATA ON PARTICULATE MATTER
Although the measurement methodologies of the past decades have many
shortcomings, they do indicate significant trends. Notable among these long-
term data are the measurements of "settleable dust" or "dust fall" made in
some cases since 1925 and in many cities since 1955, and of the total filter-
able particulate matter obtained by high-volume samplers in 58 urban and 20
494
nonurban sites since 1957.
Calculations of dust fall ( mass ) show that Pittsburgh, Cincinnati,
area . time
Chicago, and New York in particular have enjoyed decreases in settleable
dust nearing a factor of two between 1925 to 1964 (Figure 5-7). The data of
494
Ludwig et al. on the composition of the coarse particle mode indicate that
settleable dust consists mainly of mechanically produced substances, some of
which are amenable to simple control measures. However, decreased dust fall
should not be attributed to control alone since oiling or paving of roads,
changes in agricultural practices, and location could produce the same result.
Much of the decrease in dust fall is no doubt due to the control of industrial
emissions of very large particles (> 1 pm dia), but no quantitative relation-
ship can be deduced from the data and from the lack of analysis of long-term
composition records.
107
-------
200
ISO
100
i »
I
NEW YORK
N PITTSBURGH
X
CINCINNATI
PHILADELPHIA
1925 1930 1935 1940 y 1945 1950 1955 1960 1965
FIGURE 5-7. Trends in settleable dust in six cities. From Ludwig et al.,
1974.^
108
-------
Statistical analysis of measurements of the total filterable particulate
matter (TFP) suggests that urban values have decreased approximately 20%
between 1960 and 1971. The most recent data available from the EPA were
collected in 1973. From their analyses of these same data minus the year
494
1971, Ludwig et al. suggested that the filterable mass concentration in
nonurban areas increased slightly over the period of record in spite of
the improvement in cities.
In view of the bimodal mass or volume distribution and of the usual lo-
cation of the NASN high-volume sampler on dusty roofs, the decrease in urban
TFP cannot be uniquely interpreted in terms of decreases in emissions from
man's activities. The lack of size resolution and chemical composition pre-
cludes a detailed understanding of the trends.
109
-------
110
-------
CHAPTER 6
EFFECTS ON ATMOSPHERIC PROCESSES
Participate matter influences atmospheric physical processes in two
basic ways. First, it scatters and absorbs light. This results occasionally
in dramatic reduction of visual range, colored hazes, decreased sunlight at
the ground, and other related effects. These optical effects are probably
the only effects of air pollution that are directly perceived by most people.
These may therefore be the most socially or politically important.
Second, the interaction of particulates with water in condensation and
cloud processes implies that particulates may cause changes in the amount
and composition of precipitation. This section will summarize the state of
knowledge concerning both processes.
RELEVANT OPTICAL PROPERTIES
Basic Principles
The angular distribution (6) of light scattered by a unit volume of
aerosol can be described by the function 3 ,(<{>). This is called the volume
Sp,A
phase function. The fraction of light of wavelength A scattered into all
directions per unit pathlength is called the scattering component of the
particulate extinction coefficient and is denoted b ..
sp,X
The total extinction coefficient of a real atmosphere is the sum of two
terms:
b = b + b
ext,A scat,A abs,A
= b + b +b +b
Rg,A sp,A ap,A ag,A
111
-------
where
b ., = extinction coefficient at the wavelength
GXu f A --
b = scattering component of extinction
scat -
b = absorption component of extinction
abs ™"
b = Rayleigh scattering component of extinction due to g_as molecules
Rg
b = scattering component of extinction due to particles
b = absorption component of extinction due to particles
ap - *-
b = absorption component of extinction due to erases
ag —
For brevity, the subscript X is omitted in the following discussion,
but wavelength dependence is an important measurement consideration. Both
b and b define the role of atmospheric particulate matter in light ex-
sp ap
tinction processes. Ihe scattering of light by atmospheric particles is
maximum at angles () near 0°. In other words, most of the scattered light
energy is redirected only slightly and only from ^10% to 20% of the scattered
light is reflected in the backward hemisphere (90° l 1 180°). We can de-
fine a hemispheric backscatter coefficient b , where
JDSJp
= 2* 10 sin*d*
The amount of light scattered out of the atmosphere depends on the solar
zenith angle; but, where the earth is flat and the sun is directly overhead,
the reflected intensity of light reflected by particles contained in a layer
of air of thickness Ax is proportional to b Ax.
Other and more complex optical variables can also be identified such as
those related to angular scattering dependence, polarization, etc.; however,
much more data exists on quantities b , b , and b , which are most directly
sp ap bsp
related to atmospheric effects.
112
-------
b - The Light Scattering Coefficient due to Particles
-sp- a *
b is a relevant integral property of the atmosphere that usually con-
trols both the transmission of sunlight and the visual range. It is also
often highly correlated with the volume concentration of particles between
0.1 and 1.0 urn dia. Since the submicrometer volume mode contains a large
portion of the respirable particles and contains substances that have the
potential to affect health, the measurement of bg should provide a useful
index for health-related studies, b is easily measured with an integrating
nephelometer.
b depends on the following aerosol properties:
• Fine particle mass concentration
• Total mass concentration
• Particle size distribution
• Refractive index (which is determined by the chemical composition)
• Particle shape
• Relative humidity
• Relative humidity history (regarding hysteresis)
• Wavelength of light
While it is difficult to assign an absolute order of dominance of the
aerosol properties in determining b , the order in which they are listed
reflects their dominance under such conditions as low relative humidity (RH)
137
in urban atmospheres. The effects of nonspherical particle shape and, to
some extent, the effects of refractive index on the value of b , are rela-
sp,A
tively small. The main factor controlling b , for atmospheric size dis-
Sp, A
tributions is the mass or volume, or particles between 0.1 and 1.0pm dia for
* ^ 0.5 vm. Values of bs at 550 nm as low as 1 x 10~7m"i have been measured
113
-------
with the integrating nephelometer in clean upper troposphetic air at the
74 -3 -1
Mauna Loa Observatory and as high as 2 x 10 m in Los Angeles smog.
167
Still higher values occur when the FH exceeds about 80%, demonstrating
that b is an extremely variable atmospheric property.
b as a Function of Particle Mass Concentration. There is a signifi-
•*P
cant relationship between light scattering and both the size and volume or
mass concentration of particles. This is apparent in studies of the depen-
dence of light scattering on particle size. Figure 6-1 shows the calculated
805
size dependence of scattering for an average measured size distribution,
assuming uniformly dense spherical particles, a real part of the particulate
refractive index equal to 1.5, and an imaginary part equal to 0.001. Also
shown are the volume and surface area distribution functions Av/& log D and
AS/Alog D vs log D .
P P
Figure 6-1 also shows that both light scattering and the volume concen-
tration are dominated by particles between 0.1 and 1.0 pro dia. This suggests
a correlation between light scattering and fine particle volume or mass con-
centrations. This figure also shows that the upper size limit for light scat-
tering is governed by the surface area. Therefore, a correlation of light
scattering with the concentration of particles > 1.0 ym dia or with total mass
concentration is not expected unless the fine mode correlates with the coarse
volume mode. It is somewhat surprising, in view of this, that the measured
correlation coefficient between b and total aerosol mass concentration is
sp
as high as the observed range between 0.5 and 0.9. While the former value
is not impressive nor particularly useful, the latter is sufficiently high
to allow inference of mass concentration from b . Aerosol Characterization
330 sp
Experiment (ACHEX) II data (Figure 6-2) yield a correlation coefficient
114
-------
400.00
380.00
320.00
280.00
3z« JB
iZDO.OO
1180.00
120.00
00.00
40.00
lff-;
6 1CT1 2 E 10° 2 4
Diameter, vtn
S ID"1 2 6
Diameter, ym
FIOJKE 6-1. Comparison of the computed particle light scattering coefficient
(A) with the surface (B) and volume (C) distributions of the 1969
Los Angeles grand average aerosol size distribution.805 The
light scattering coefficient was coroputed assuming a real part of
the refractive index (1.5) and an imaginary part (0.001) at a
wavelength of 552 nanometers. The particle light scattering is
limited at the lower end by transition to Rayleigh scattering
and at the upper end by a sharply decreasing surface area of
the distribution.
115
-------
£UD/£Ulrt
o
m
7
ro
o o
in a.
VO
-------
of 0.865 between b and total particle volume (b <\, b under the
scat scat ^ sp
conditions of these measurements). Table 6-1 summarizes the various pub-
lished correlations of b and mass. The ratio of v to b is relatively
sp sp
insensitive to variations in modal particle diameter, D , in the range from
219
0.3 to 0.8 ym (Figure 6-3), which largely accounts for the observed high
correlations between v and b .
sp
There are few extensive measurements relating the mass concentration of
fine particles to light scattering. Measurement of bscat and submicrometer
volume concentration as part of the ACHEX II program (Figure 6-4 and 6-5)
(Clark, 1974, personal communication) yielded correlation coefficients of
0.94 for t> . and total submicrometer volume and 0.95 for b and volume
in the size range of 0.1 to 1.0 um dia. Results in other types of locations
produced somewhat different values of the ratio v to b and of the correla-
tion coefficient due mainly to variations in the nuclei mode. Locations
near Aitken nuclei concentration (CNC) sources such as freeways may show
poorer and/or different correlations of fine particle mass and light scat-
tering (Figure 6-6). These measurements are discussed in more detail in
Chapter 4.
Compounds that Dominate b . Classes of compounds that dominate the
£ gp
accumulation mode (0.1 and 2.0 wn dia) are far more important in determining
b than compounds that occur in the coarse particle mode ( >2 wn dia).
t>P
Sulfates (sulfuric acid, ammonium bisulfate, ammonium sulfate, and perhaps
others), nitrates (ammonium nitrate), and organic compounds (condensed hydro-
carbons and oxidized organic matter) appear to be important. In contrast,
soil dust, tire dust, and road debris, airborne rock-crushing products, fly
117
-------
. #1
c
to
to
10
•o
c
tO
c
o
•H
•P
Ifl
0
o
>)
W
0)
•H
•X3
p
c
o
•H
•P
C,
p
c
o
c
o
H C_)
1
ID tO
to
W to
PQ
H
bO
C
•H
c.
Q)
•P
•P
10
O
CO
•p
JC
•H
, "\
O
•H
C|
P
Ci)
£
0
H
.C
04
0)
3
o
^t
c.
flj
£
CO
0
H
p
tO
§H
(1)
c
H
to
^J
C
0)
H
CJ
H
t-l
J_j
O
O
O
n
o
H
to
to
c^
bfl
0)
C_j
II
PQ
«*
rf
• ft
•P
C
CO
•H
U
•H
lp
01
0
o
c
o
•p
tO
H
£_j
£4
O
o
£-,
m
_C
1— j
n
Pi
• A
T)
0
•P
0)
£
bO
C
•H
,— j
ft
5
CO
d)
o
c
it
CD
*«
OS
CM cvj CM U) ID )
H »J O
MH
T) W
W C -H
w «H e.
to ,<= C
H tt) (0
pq
r- CN j-
I I I I
co co j- 1 1 1 1
^j
CO d" CO
CO CO H
• •III!
O 0 O 1 1 1 1
c.
CO CT> 00
oo t«» cn
• • • I I I I
0001 1 1 1
0)
E CO
3 H
H CU
o e
> tO
1 M
fC
bO ^
*H *H
tC rO
PQ
CN d" 00 ID O '
•••II • •
CN CN CN 1 1 CO CN
<^
CD i — 1 ID ^D in
O ID in CM H
... . *
O O O 1 1 O O
1 1 1 1 1 1
L
CO ID CO CO UD
in co en r-» co
... I I . .
0001 1 O 0
^
fn 0),
(U -P
•P H
(U *H
£ UH
(0
•H 0)
T3 f-t
0
E O.
O 0)
i — i
in tj
. ^j
CN C
PQ
o t>
III • 1 1
1 1 1 co H 1 1
^
CO
co in
• •
1 1 1 0 H 1 1
1 1 1 1 II
h
CM ID
a> in
i I I « • „ I
1 1 1 0 0 <3 |
M
^ W
tt) tO
P H
Q) bO p
E cp
tO « -P
•H 0) H
T3 O -H
03 MH
E 4-i
O ^
c a)
in (1) rQ
• pij >r^
CM O IP
PQ
j- co CN in
... i I . i
CM r-| CN 1 1 CO 1
<
t- O CO
ID d- O O
• • • •
O O O 1 1 O 1
1 1 1 1 1
c.
co en in co
CO ID CD CO
... 1 1 . 1
O O O 1 1 O 1
^^
c
0
•p
tO
o
o
**«
0 <
W < " & O <
a> o o se <
iH -P •> •> S
d> « C A! CO *
bO T3 - "-3 -P O
-H fc -P -P
W ,X O * C (0 W
O 10 10 0) tO CO O
J O CO S CO CO PQ
rO
0)
W
3
Q)
&
s
to
£4
(U
•p
H
•H
MH
ip
O
to
0)
ft
4->
.C
•P
O
t>
118
-------
(XGMEHKIC
ffBUCARD
DEVIATION, J.
INDEX * 1.50
I£NGTH OF LIGHT = 550 ntl
I I I Illlll 1 ill Hill I i l i nut i i i i mil
10-2
1(T2
10-1
GEOMETRIC MASS MEAN RADIUS, r ,
9*
FIGURE 6-3. The ratio V/bg as a function of the lognorraal size distri-
bution parameters for a white aerosol. From Ensor and
Pilat, 1971, p. 500.219
119
-------
CM
CO
o
CM
3
§
7
vo
120
-------
s
o o
o
o
m
o
o
CM
oo
OD •
s *
o "
X g
-------
= V3[ym3/cm3]
FRESNO |b = V3°'/]8
HARBOR FREEWAY
POMONA
POINT ARGUELLO
DENVER, 1971
GOLDSTONE
HUNTER-LIGGETT
Log V3-(iiin3/OT3)
200 300
FIGURE 6-6. Correlation of b vs V3~ (volume < 1 von) for ACHEX I data.
sp
From Hidy et al., 1974, p. 3-32.33°
122
-------
ash, etc., contribute little to b except in the relatively rare situation
of dust storms.
Substances of most importance to atmospheric light scattering occur
predominantly in the fine particles that dominate optical effects. Many of
these same compounds (sulfuric acid, ammonium sulfate, etc.) are hygroscopic
or deliquescent. They cause more light scattering at elevated RH than they
would if they were hydrophobic, like silica and some soil dust.
One approach to estimating the importance of various substances is to
calculate the effect of various substances via a combination of measurements
267
and theory. Gartrell and Friedlander estimate that in Pasadena and Pomona
smog, visibility deterioration can be largely ascribed to nitrates, sulfates,
organics, ammonium ions, and water, converted from the gas phase to a condensed
598
phase. Patterson and Wagman measured aerosol composition, mass, and size
distributions for four different ranges of b . Their results suggested
SC3. t
an important role for carbon compounds.
Shape Effects. Light scattering may be influenced by particle shape.
Although several theoretical approaches have been attempted, very few experi-
mental efforts have been made to isolate shape effects in atmospheric scat-
tering. Such atmospheric particles as, for example, sea salt at high FH, are
nearly homogeneous and spherical; in other cases, a particle sample resembles
a bowl of popcorn, and may be impossible to analyze theoretically. One effect
of nonspherical particle shape and lack of homogeneity is to deform the phase
function B ,(<(>)• This is particularly important for scattering angles over
sp'A 356
•n/2. Holland and Gagne show such results for silica dust. A more defin-
itive statement regarding particle shape effects must await the results of
current research.
123
-------
b as a Function of Relative Humidity. Also of importance are the
~sp
changes that occur in the light scattering to mass or volume relationships
167
with hygroscopic aerosol growth (Figures 4-4 and 4-5). Figures 6-7 and 6-8
illustrate in another way the calculated changes in the distributions due to
increasing radii by 1.5 and 2.0 times. The normalized distributions of
AV/Alog D and Ab /Alog D were calculated (using refractive index m = 1.33)
and plotted vs the original, i.e., low humidity, diameter, on a semilogarithmic
graph. This illustrates clearly the particle size intervals that are respon-
sible for these changes. Changes in light scattering are due primarily to
the growth of the particles which were initially in the optical subrange (0.1
to 1.0 ym dia) and not due to growth of particles whose initial diameters
were <0.1 ym. Measurement of hygroscopic aerosol growth by optical tech-
niques senses primarily the size increase of particles between 0.1 and 1.0
ym dia.
An extensive theoretical investigation of the relationships between the
parameters of aerosol light scattering, volume, and mass as a function of RH
315-317
has been made by Hanel. His calculations of the ratio bsp(RH)/1:)Sp
(RH = 30%) agree closely with results of direct measurements.
By preconditioning the aerosol sample to regulate the RH of the aerosol
before entry into an integrating nephelometer, then measuring the temperature
and dew point inside the nephelometer, this instrument was modified to monitor
167"
b as a function of RH. A summary of measured curves is shown in Figure
6-9.
b as a Function of Wavelength. The scattering coefficient of a medium
-SP
depends on the wavelength of the incident light. If the light is polychromatic
(like sunlight), this may result in vivid coloration of the scattered light,
124
-------
0.01
1.0
PARTICLE DIAMETER, D j, ^m, at 30% RH
10.0
FIGURE 6-7. Change in volume distribution with change in particle diameter.
From Covert, 1974.167
125
-------
(%oo lda
rds
(%oo - qv
id _
(HH) a BQIV
i'ds
126
-------
s
B-
3-
2-
ii
en
1-
1 i • i r r ^ i • 1
0 50%
100%
Relative Humidity
FIGURE 6-9.
Range of variability in Humidogram data averaged by site;
vertically hatched area includes strongly deliquescent
aerosol at Pt. Reyes, California and Tyson, Missouri.
From Covert, 1974. 167
127
-------
depending on scattering anqle and size distribution. For single scatter ers
and a Junge size distribution [dn/dr = Cr , where dn/dr is the number
of particles per unit volume with radii between r and r -t- dr], it can be
shown that b % A where a = 2 - v. The results of atmospheric measurements
sp
regarding the wavelength dependence of b fall into two cateqories.
• Normal wavelength dependence where 0.5 £ a <_ 2, with a mean value
of approximately 1.2. Figure 6-10 shows the frequency of occurrence
138
of a measured in Pasadena, California, by Charlson et al.
• Anomalous wavelength dependence where a < 0.
Normal wavelength dependence results in the attenuation of blue light
from a direct beam and its scattering into 4ir steradians around the scattering
volume. Of course, Rayleigh scattering always occurs simultaneously and has
a wavelength dependence that is similar:
b
Rq
For both normal wavelength dependence and Rayleigh scattering, blue scattered
light against a dark background or red traasmitted light (fron the sun or a
bright white object) is observed. Whether b or bn dominates is determined
sp Kg
by the amount of particulate matter that is present. Anomalous wavelength
dependence results in such rare phenomena as the blue sun or moon, usually
614
attributable to very well-aged aerosol.
Blue hazes, such as those found in mountainous areas, may or may not be
due tc scattering by particles, deoending on viewing conditions (e.g., dark
T light background) and the distance from the observer to the background.
Since b^ 55Q = 0.1S x 10~''nr! , if bc. .% - 0, mountains should not aooear to be
behind a haze if they are within 10 tar,. They will, however, appear hazy if
128
-------
35
30
25
20
in
$
8
U-l
0
1 15
10
5
0
i-o-i
—
—
_
0
o ID.J
0 0
0 0
0 0
0 6
0 0
0 0
0 0
0 0
0 0.
0 0
O 0
0 0
Jo-' o o
000
o o b
0000
0000
f
-O pOJ 0
o-
o
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
OOOOO 000
OOOOO 000
— ooooo ooo
OOOOO 000
OOOOO 000
OOOOO 000
JCrOOOOO OOO
OOOOOO 000
o o o o o o oLcr ooo
ooooooooooo
ooooooooooo
ooooooooooo
1 1 1 1 1 I 1 1 1 1 1 1 1 1
•O-i
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
o
0
0
0
0
1
•o
o
0
o
o
0
o
o
0
0
o
0
0
o
0
•-O-
0
0
0
pO 0
0 0
0 0
oLo o
-oJ o o oLo.|
OOOOOO
OOOOOO
ooooo oLo.
0 O 0 0 0 0 0
0000000
oooooo oLo
00000000
oooooooo
III 1 i 1 1 1 I
0.5
1.0
1.5
2.0
2.5
FIGURE 6-10.
Histogram showing frequency of occurrence of the Angstrom
exponent, a, during Period 13 to September 3, 1969, Pasadena,
California. From Charlson et al., 1972.138
129
-------
the distance is much more than 100 km due to the omnipresent scatterinq by
gas molecules. Conversely, if a mountain at such a distance is not visible
at all, b » bn and the haze is due to particles.
sp Kg
When viewing bright objects such as the sun, moon, sunlit snowcapped
peaks and cumulous clouds, hazes with 1 £ a ^2 or sufficient optical depth
538,774
cause reddening of the color. Because this color is remarkably similar
363
to that observed through an optically thin layer of nitrogen dioxide, its
presence is no proof of the existence of nitrogen dioxide. To further oom-
374
plicate this issue, Husar and White have shown that light scattered in the
backward hemisphere calculated from typical measured size distribution is en-
riched in the red wavelengths also causing the haze itself to appear reddened.
In forward scatter (0° ^_ <}> 1 90°) this same haze appears white. Charlson
138
et al. showed that in perhaos 20% of the measured cases during August 1969
in Pasadena, there was enough nitrogen dioxide to influence the coloration of
the haze and that in the remaining cases particles dominated the wavelength
dependence of total extinction (b ,). Figure 6-11 shows a plot of b vs
GJCt- " ^P
nitrogen dioxide in which the conditions dominated by particles and nitrogen
dioxide, respectively, are shown. This figure applies only to the coloration
of bright white objects viewed through haze.
— ~ Light Absorption by Particles
aP "
Light absorption by particles is a well recognized but rarely measured
467 239,240
quantity. Results to date with the method of Lin et al., Fischer,
468
and Lindberg and Laude indicate that the imaginary part, n. • , of the
complex refractive index, n , (which determines the light absorbing orop-
ccrnplex ^ ^
erty of the particles), of a sample of urban particles is frequently in the
range from 0.004 to 0.05, where n n = n ., - in . . and n , =
^ ' complex real imaginary real
130
-------
20 30 40 50 70
ND2, pphn
FIGURE 6-11. Light scattering, bscat, plotted against nitrogen dioxide
in pphm showing the ratio of bscatA3N02 ~ 6 at 546 nm for
color effect of NOz to appear in transmitted light. Shaded
region covers approximate 90% confidence intervals for the
extra ordinate scales, mass concentration, and visible range
(LV) . The lines ^scat/^abs = 2 and 18 are limiting cases
vrtiere NO 2 can be said to dominate and be totally unimportant
respectively. From Charlson et al., 1972.138
131
-------
teal part of refractive index i = /^TT Also, the aosorption coefficient is
typically up to 30% of the total extinction, i.e., 0 <_ b^g <_ 0.3 bext«
Measurement programs are currently underway to establish the generality of
this result and of the value of the imaginary part of the refractive index
for a variety of locations. Size dependence of the refractive index is an
important factor due to the size dependence of chemical composition. It makes
the relationship between an averaae index of refraction and the integral
property b very tenuous.
RELATIONSHIP TO VISIBILITY
Having discussed the relationship of b and b to the other properties
of the particles, it is logical to relate these correlations to visual range
423,424
and associated quantities. According to Koschmieder's visibility
theory, the following quantities are closely related:
• Prevailing visibility or visual range, V(km)
• Meteorologic range, L (km)
• Light extinction coefficient, b (m"1)
" X L
And in light of our previous discussion, these correlations should also be
related to:
• Particle mass concentration (uq/m3), especially in the fine particle
mode.
The Koschmieder theory relates the distance at which an ideal black
object, viewed against the horizon sky, can barely be oerceived in sunlight
by a normal human observer. If the atmosphere is homogeneous and the
illumination is uniform, this relationship is:
132
-------
L = 3.9
v
bext
where L is the meteorologic range. Definitions of prevailing visibility,
visual range, and related terms are given in standard handbooks (see, for ex-
375
ample, the Glossary of Meteorology), but for our purposes they are nearly
identical to meteorologic range.
There are published data with which these relationships can be checked
with the exception of simultaneous visibility observations and fine particle
mass concentration. Only total and < 5 ym particle mass concentrations have
been measured in simultaneous field observations to date.
364
Horvath and Noll conducted a study in Seattle relating total light
scattering, b , measured with an integrating nephelometer, and prevailing
scat
visibility determined by two separate observers. Their results agreed with
423,424
the theoretical expression of Koschmieder, when only data for FH <65%
were included. This limitation apparently resulted from the location of the
nephelometer in a heated room which caused reduced RH in the light scattering
measurements. At < 65% HH, the correlations between b^=. and prevailing
SGcl u
visibility were 0.89 and 0.91 with a coefficient in the Koschmieder expression
of 3.5 ± 0.36 and 3.2 ± 0.25, respectively, for the two observers. This can
be compared with the theoretical value of 3.9, indicating a slightly lower
prevailing visibility than meteorologic range, assuming b +. = bQ . . Since
SC3.L. GXu
no ideal black targets were used (only trees, buildings, and other objects
that reflect some wavelengths of liaht), these would have caused just such
a deviation. Alternatively, 10% to 20% light absorption would yield this
result.
133
-------
580
Noll et al. studied prevailing visibility, mass concentration, and
soiling index in Oakland, California. They concluded that the prevailing
visibility was inversely proportional to total mass concentration determined
via 4-hr samples taken with 2.5 cm dia glass fiber filters. The product of
mass concentration and prevailing visibility was near 1.4 g/m2. This compares
137
well with a value of 1.8 gytn2 determined with a nephelometer. The cor-
relation in Oakland between prevailing visibility and mass was approximately
0.9 indicating a good relationship between these variables.
662
Samuels et al. have conducted the most extensive tests of the rela-
tionship of prevailing visibility to light scattering and various mass con-
centration measures. They conclude that b as measured with the integrating
SCcl U
nephelometer is a good predictor of prevailing visibility and that the regres-
sion analysis is in basic agreement with Koschmieder's theory.
EFFECTS OF TURBIDITY ON SOLAR RADIATION
Besides visibility degradation, one of the most pronounced effects of
man-made or man-caused particles is the diminution of the intensity of direct
sunlight in urban regions. However, the main portion of scattered light is
in the forward direction, and this reaches the surface of the earth along with
the direct beam, where it is used in such processes as photosynthesis, heating
142
of soil, or evaporation of water. Most data on the optical properties of
the atmosphere concern direct solar radiation which must be weighed in terms
of the actual fractions reaching the ground and being rejected upward. Clearly,
data are needed on the actual amounts of radiation reaching the ground and
not just that in the direct beam.
134
-------
Extinction of the direct beam can be measured with the Volz sun photo-
meter, pyrheliometer, and astronomical telescopes. The extinction coefficient
is reported in various forms.
The extinction vertically through the whole atmosphere may be given by
the Beer Lambert law in integrated form:
oo
I = e~ (/obext dx> = e-T
T
where T (2 /Obext dx) is the optical depth.
Another form of this expression results in a definition of decadic
turbidity, B:
Km) _ in-(a 4- a + B)m
10 eg Rg
where a is the extinction due to light absorption by gases per unit air
ag
mass, m, and a is the extinction due to Rayleiqh scatter. Another quantity
Kg
is astronomical extinction, K:
^-=10-^5-m
where K is given in units of star magnitudes per air mass. Even though bext,
a, B, and K are closely related, they are seldom compared and used together
for studies of the effects of atmospheric particles.
Much of the data available for appraisal of extinction effects comes
from the network of Volz sun photometers which was reported by Flowers
247
et al. They interpolated the data into turbidity units, B. More recently,
135
-------
351
astronomical data have been used. Four general features of the data are
immediately apparent:
• There is usually a turbid air mass centered over the eastern part
of the United States. The turbidity (or extinction coefficient)
in this air mass is about a factor of two higher than in the less
247
turbid air found in the rural west. (See Figure 6-12. Urban
values are shown in oarenthesis.)
• There is a seasonal variation in the turbidity with a maximum in
summer and minimum in winter, with exceptions in some urban lo-
247,648
cations where the opposite is found.
523
• In and near cities there has been a trend of increasing turbidity,
350 360
increasing astronomical extinction, and decreasing visibility
over the past half century.
• In remote locations there is not yet a proven global trend over
214
similar time scales. Such a trend may exist, but the data
quality and period of record are insufficient to detect it.
Losses of direct radiation of up to 50% have been measured in the rural
247
Midwest in summer. Of this decrease, assuming b =0.2 b . and b^ =
0.1 b , we can estimate that up to 20% of the radiation may be unavailable at
GiXTl
the earth surface. This decrease along with the atmospheric heating caused by
b ttiqht be important, for example, to agricultural production or to local or
regional climate.
The few systematic studies of total (solar plus sky) radiation reaching
the ground, which have been conducted simultaneously in cities and in rural
523
areas, show reductions of this magnitude. Much more extensive studies are
needed to provide a more quantitative estimate of the possible reduction and
fate of useable solar radiation over large rural areas.
136
-------
FIGURE 6-12. Msan annual turbidity over the United States. Urban station
values are in parentheses. From Flowers et al., 1969, p. 957.
137
-------
Notable among these optical data are the long-term records of the
Smithsonian Institution in Washington, D.C. and in Davos, Switzerland. These
operations were started around 1900 as part of the determination of the
solar constant. Almost by chance these operations continued and are among
our only long-term records. The Volz photometer network, which was started
in 1962, has grown steadily both in the United States and abroad.
In 1910, the late Charles Abbott of the Smithsonian Institution con-
cluded that Mt. Wilson, California was not useful for solar photometry because
350
of the hazes that emanated from the Los Angeles basin below. Hodge noted
that this effect has continued to develoo there, virtually stopping photometric
measurements at that observatory.
CLIMATE; DIRECT EFFECTS
In recent years there has been a great deal of speculation regarding the
role of aerosol in determining regional or even global scale climate. The
main concern is the possibility that aerosol might be responsible for the
548
cooling trend noted globally in meteorologic data in recent years. How-
ever, controversies have arisen largely because of insufficient data on
relevant properties of particulate matter on both regional and global scales.
Even if the particulate mass or number concentration were known, its clima-
tologically important radiative effects would not be easily understood.
Such radiative effects may be searegated into direct and cloud-related cases.
The latter is due to the influence of the aerosol on cloud formation or on
the optical properties of the clouds into which the aerosol is incorporated.
In the simplest case of direct radiative effect of aerosol without cloud
involvement, disagreement exists on even the sign of tenroerature change to
expect from secular changes in aerosol concentration on regional to global
138
-------
79,140 676 629
scales. Schneider and Rasool and Schneider suggested that
aerosols would uniquely cool the earth's surface given one set of assumptions
141 139
which were disputed by Charlson and Pilat and by Charlson et al.
In spite of the lack of detailed data it is clear that the regional and
global effects of particulate matter due to scattering and sunlight absorption
95 645 " 422 99
may not be disregarded. Bryson, Robinson, Kondratyev, Budyko,
523 395
McCormick and Ludwig, Joseph and Manes, the Study of Critical Environ-
512 377
mental Problems (SCEP), the Study of Man's Impact on Climate (SMIC),
and other reports have all echoed the potential importance of this statement
and the need for measurements and theoretical calculations. In many of these
papers particulate matter is implicated via statistical correlation with past
climate changes. The importance of volcanic debris is frequently mentioned.
There is also interest in the current or future role of anthropogenic particles.
Various theoretical models have been used to aid in judging the impor-
629
tance of particles to radiative transfer. Rasool and Schneider, Ensor
220 43 149 832
et al., Atwater, Chylek and Coakley, Yamamoto and Tanaka,
548,549 784
Mitchell, Wang and Domoto, and others have explored a variety of
optical calculations, different approaches to the radiative transfer, and
atmospheric models over a range of complexity. Virtually all models depended
on assumed values for the relevant optical constants of the atmospheric par-
ticles, notably, complex refractive index as a function of particle size and
the size distribution. The lack of data and the complexity of the climate
problems render the results of such calculations extremely tenuous.
548
As an example of one of the simplest models, the sensible heating,
H, of both an optically thin aerosol layer and the underlying surface is
given by:
139
-------
H = SQ C(l-A)e~(a + b)[l + A (1 - e~b)]
sensible surface heating
j. c 'i ~a\ TT , * ~b "(a + b)-,
+S ^ 1 - e ) L1 + Ae e 1
o
aerosol heating
where S is the incident solar flux, A is the surface albedo, a is the absorp-
o
tion optical depth, and b is the backscatter optical depth defined as that
fraction of the scattered light rejected into space. C = B/(B + 1), where B
is the ratio of sensible heating to latent (or evaporative heating) known as
the Bowen ratio.
The temperature rise in this system is proportional to H, and the
quantities a and b define the role of aerosol; if we assume they are both
small, then H depends on the ratio a:b. At H = 0, a/b = (a/bV , where
(a/b)Q = c(i-A)2
1 + A - C(l-A)
so that the critical ratio depends on both the albedo and the Bowen ratio.
If a/b > (a/b) , then the aerosol would be expected to cause heating of the
o
atmosphere; if a/b < (a/b) , cooling would be expected. In either case the
surface of the earth might cool due to a decrease of radiation.
A chief part of the controversy mentioned earlier was due to the fact
that a/b, or its equivalent in other models, is unknown. It was estimated or
calculated from assumed refractive indices or assumed size distributions and
composition/size dependence. Depending on the assumptions, the value of the
ratio a:b ranges fron values well above to well below (a/b) , giving rise to
0 549
the questions of heating vs cooling due to oar tides. As Mitchell con-
cluded, "...it is of the utmost importance to measure the backscattering,
140
-------
absorption, and other optical properties of each type (each combination of
chemical constituents) of aerosol layer commonly encountered in the atmosphere.1
Among the factors that are important to climate studies are the spatial
dependence of aerosol properties and the role of RH in determining these prop-
erties as humidity increases.
The horizontal spatial extent of turbid air masses typically spans 1,000
647
km, as expected from calculation of removal rates and from turbidity data
(Figure 6-12). The vertical distribution is important since there is a pos-
sibility that the particles exist below, between, or above clouds, which them-
selves have high albedos. Thus,1 heating is very much more probable for a given
aerosol over clouds than over oceans, or other low A surfaces. Data on the
vertical distribution of particles outside of urban locations is fairly sparse.
Figure 6-13 shows integrating nephelometer data at different altitudes and
142,215
locations along with searchlight data from New Mexico. Figure 6-14
shows optical depth data from astronomical telescopes compared to those cal-
142
culated from the searchlight data. In both cases it appears that most
of the optical effects of the particles occur below 3 km altitude. Because
these data are limited in quantity, location, and period of record they should
be expanded.
The effect of humidity on bc_ has been measured, as oointed out above.
t>p
The effects on a/b have not yet been measured, and their calculation is even
more tentative than the estimation of a/b at low RH.
CLIMATE; CLOUD-RELATED EFFECTS
Over the past 15 years increasing evidence indicates that major urban
and industrial complexes are significantly modifying the downwind climate and,
in oarticular, changing levels of precipitation. While there are certainly a
141
-------
41.1
33.8
12 15 18 21 24 27 30
sp
FIGURE 6-13.
Altitude dependence of light extinction due to aerosols by
nephelometer and astronomical telescope, with searchlight
data of Elterman (1973) for comparison. Nephelometer data
with 90% interval for bsp at 500 ran ( ) compared to search-
light data ( ) at 550 nm of Elterman (1973).215 From
Char 1 son et_ aJL., 1974, p. 354.
142
-------
10 15 20 25 30 35 ' 40 45 50 55 60 65 70 75
/*bsp(z)dz(xi63)
FIGURE 6-14.
Mean aerosol optical depth vs altitude via astronomical tele-
scope (data points) at 500 nm, the integral / ™ bSp(z) for the
geometric mean nephelometer data in Figure 6-13 ( ) and the
same integral for the searchlight data ( }. The astronomical
data compared here can be regarded as typical for remote loca-
tions, and were taken over varying time periods by many dif-
ferent observers. A value of Tozone - 0.004 was assumed in the
telescopic data. Observations are by number, with altitude
(meters) in parentheses: (1) Royal, Cape of Good Hope (10);
(2) Boyden, Republic of South Africa (1,387); (3) Radcliff,
Republic of South Africa (1,542); (4) Mt. Bingor, Australia
(460); (5) Mt. Stromol, Australia (768); (6) Siding Spring,
Australia (1,164); (7) Mt. John, New Zealand (1,029); (8) Europ
South, Chile (2,400); (9) Cerro Tololo, Chile (2,195) (10) Lo
Houga, France (146); (11) Naini Tal, India (1,927); (12) Mauna
Loa, Hawaii (3,370); (13) Mauna Kea, Hawaii (4,170); (14) Rattle-
snake Ridge, Washington (1,080); (15) Lick, California (1,283);
(16) Kitt Peak, Arizona (2,064); (17) McDonald, Texas (2,081).
From Charlson et al., 1974, p. 355.lif2
143
-------
number of operative mechanisms involved in the modifications, the concentration
and chemical nature of the pollution aerosol play an important role.
This atmospheric interaction occurs because the transformation of water
vapor into water droplets and ice crystals is a nucleation phenomenon re-
quiring the presence of specific nuclei. The nuclei that are "weather active"
usually constitute only a very small fraction of the total aerosol population.
The nuclei involved in cloud droplet formation, cloud condensation nuclei
(CCN), comprise approximately 1% of the total aerosol. Generally, the CCN
outnumber the ice nuclei by a factor of 105 to 10s. The relatively rare ice
nuclei either freeze supercooled droplets or serve as sublimation sites for
the direct deposition of vapor.
The concentration of these nuclei directly influences the concentration
of cloud droplets and ice crystals. This in turn influences the cloud dy-
namics and the probability and amount of rainfall. Since, under normal cir-
cumstances, the concentrations of these nuclei are quite small in comparison
to the total aerosol concentration, and because relatively small increases
will produce significant effects, the concentration of weather-active nuclei
is clearly a most sensitive environmental parameter.
Warm Cloud Processes
Cloud formation is due almost entirely to the expansion and subsequent
coolinq of ascending air. When the air is cooled to the saturation point
(100% RH), condensation on the largest and most hygroscopic of the CCN
accelerates. (Some of these particles may experience limited growth well
below 100% RH.) The number of droplets that ultimately form in a ctiven cloud
depends on a complex feedback mechanism depending on temperature, uplift
velocity, the concentration of CCN, and the supersaturation required for
144
-------
each available CCN to act as a nucleating site. This mechanism generally
limits the RH to less than 101% in clouds. Further, it has been established
that measurements of CCN concentration as a function of activation super-
saturation and estimates of the uplift velocity enable prediction of the
764,765
approximate droplet concentration throughout the cloud.
While a direct relationship exists between CCN and droplet concentra-
tions, the relationship between these factors and precipitation probability
is less well understood. Theory indicates that raindrops cannot be formed
231
by condensation alone in a reasonable period. Indeed, it shows that in
the early stages of cloud development the assembly of droplets forms a rather
368,762
size-stable array of nearly uniform 5 to 10 pirn dia drops. This array
becomes unstable if droplet-droplet coalescence occurs. This will happen only
349
if a significant number of the droplets grow larger than ~20 jjm radius.
Warm clouds that fail to produce a reasonable number of large drops will
719,763
remain stable and not produce precipitation.
Observation and theory suggest that the population of CCN can affect
warm cloud stability and hence precipitation probability in several ways.
First, if there is a large number of effective CCN (103 to lO1* cm3) having
nearly the same activation supersaturation and size, then a cloud of high
droplet concentration consisting of very small uniform droplets will result.
Since the available water is spread among many droplets, the chance that
any will grow large enough to initiate the coalescence process is relatively
small, as is the probability of precipitation. Conversely, if there are
relatively few CCN (10 to 102 on3), the available water shared among the
resulting few droplets is far more likely to produce rainfall. Further, if
there are more than a few per liter of very large hygroscopic nuclei (larger
145
-------
than a few micrometers) in either polluted or unpolluted cloud masses, these
nuclei may become large enouqh droplets to promote the coalescence mechanism
787,831
regardless of the population of less effective CCN. This destabilizing
technique provides the basis for most of the warm cloud modification schemes
that have been tried to date.
Cold Cloud Processes
Ice particles appear in clouds once the droplets are cooled to below the
freezing point. On the basis of ice nucleus measurements, the increase in ice
crystal concentration is approximately an order of magnitude for every 4°C of
244
cooling. At about -40°C all of the remaining supercooled cloud droplets
freeze spontaneously irrespective of the ice nucleus activity-temperature
spectrum.
Unfortunately, the relationship between the measured concentrations of
ice nuclei and of cloud ice particle concentrations is not understood. There
is generally a large and highly variable difference between the two measure-
421,560
ments, with usually more ice crystals than nuclei. In addition, the
ice nucleus concentration has a much larger spatial and time variation than
does the CCN concentration. Some short-term variations may be traced to local
sources, but the general distribution of ice nuclei in the atmosphere is
not clearly understood. Typical concentrations of ice nuclei measured at
-20°C are from 0.1 to 1.0 per liter.
Once ice particles are present among supercooled droplets, the cloud
stability is substantially decreased; the ice particles will always grow
at the expense of the surrounding droplets. These growing ice crystals soon
acquire a differential velocity compared to their surrounding droplets, which
they collect by impaction. This provides a destabilizing mechanism similar
146
-------
to coalescence that, depending on ice nucleus concentration, can have a
powerful influence on cloud precipitation probability. Mast rainmaking pro-
jects proceed on the assumption that the natural concentration of ice nuclei
is too low for optimally efficient precipitation and that the addition of
ice nuclei will increase precipitation. However, this is not always the
case. Rainmaking efforts have apparently decreased rainfall by providing
too many ice nuclei and increasing the cloud stability similar to the effect
248
caused by too many OCN. While there is considerable variation for dif-
ferent cloud types, a few ice nuclei per liter are probably optimal for
precipitation.
Observed Effects
The addition of ice nuclei and CCN to clouds affects the cloud's micro-
physical structure. This, in turn, may either increase or decrease the prob-
ability of precipitation. The probable effects and the approximate concentra-
tions of nuclei to promote these effects are outlined in Table 6-2.
The literature indicates that the effects of urban areas on precipitation
are often stronger than those of the most effectively planned weather modifi-
437
cation projects. Landsberg reported that many large urban areas show
downwind precipitation increases of 5% to 15%. The now famous La Porte
132
anomaly appeared to show an increase of 31%. Moreover, a recent clima-
369
tologic study of eight major U.S. cities confirms Landsberg's results
showing precipitation increases of 9% to 17% with only one city showing no
effect. Other studies downwind of nuclei sources have indicated, variously,
584 786
no effect, decreased precipitation of 25%, and increases from 10%
348
to 30%.
147
-------
TABLE 6-2
Expected Effects on Precipitation Probability Due
to the Addition of Ice Nuclei and Cloud Condensation Nuclei
Precipitation
Probability
Increase
Ice Nuclei (IN)
Decrease
The addition of sufficient
ice nuclei active at the
cloud temperature so that
the total concentration
becomes 1 to 10 per liter.
Increase the ice nucleus
concentration beyond a
few hundred per liter.
Produce
uncertain
effects
Cloud Condensation Nuclei
(CCN)
The addition of sufficient
giant hygroscopic nuclei
so that the total concen-
tration becomes 1 to 10
per liter.
Increase the CCN concen-
tration beyond a few
hundred per cubic centi-
meter.
The combination of high
CCN concentrations to-
gether with optimal
numbers of large hygro-
scopic particles.
148
-------
Unfortunately, despite ample evidence that there are many significant
346-348,
urban-industrial and agricultural sources of weather-active nuclei,
420,625,711,720,751,788
the link directly relating these sources with
observed changes in cloud microphysics and in precipitation remains tenuous.
Much of this uncertainty has been due to the lack of a program to make
simultaneous measurements of nucleus concentrations, inputs of heat and
water vapor, cloud microphysical changes, and rainfall patterns.
133
The Metromex study, conducted around St. Louis, was the first attempt
690
to make these measurements. Semonin indicates that there is evidence of
a direct link between nuclei emission and precipitation. A few other obser-
786
vations also strengthen this link. In Australia, Warner reported de-
creased rainfall downwind of agricultural burning of sugarcane refuse. This
waste material, when formed, proved to be a copious source of CCN, which was
traced in turn to substantial increases in cloud droplet concentrations in
the area downwind. This case provides reasonable evidence linking a nuclei
source with increased cloud stability and decreased precipitation.
Significant sources of CCN have also been associated with increased rain-
348
fall. A study was made of many of the major sources of CCN in the north-
western United States and of the downwind winter rainfall patterns before and
after the emitting industries were established. The strong sources showed a
208
clear pattern of increased rainfall. Recent measurements support the
original hypothesis that the increases are not primarily due to the copious
CCN emission, but to the simultaneous emission of moderate numbers of large
(> 1 wn) and very hygroscopic particles. These particles apparently form
the large, destabilizing droplets necessary in the coalescence mechanism.
149
-------
Evidence for inadvertent weather modification h>y the known urban-
industrial ice nucleus sources must be largely argued from their similarity
to planned programs of ground-based cloud-seeding since direct observations
667
are lacking. Some indirect observations have been made, such as Schaefer's
report of dramatic increases in ice crystal concentrations downwind of major
urban-industrial areas.
Thus, a limited, but growing body of evidence suggests that the urban-
industrial aerosol significantly effects local downwind climate and cloud
structure.
PRECIPITATION SCAVENGING AND RAIN CHEMISTRY
Precipitation scavenging is one of the major removal processes of aerosol
from the atmosphere. It is therefore one of the important links in the cycle
of many elements. Scavenging can be divided into two major categories:
washout, or removal below the cloud layer; and rainout, or removal within the
clouds. For particles <1 pm dia, rainout is the dominant scavenging mech-
anism. For larger particles (>lwn dia), washout is important; it competes with
rainout and gravitational settling as the dominant removal mechanism. Since
the removal efficiencies of both washout and rainout are functions of particle
size, the amount and frequency of precipitation events, both regionally and
globally, have a pronounced effect on the size distribution of the regional
and global "background" aerosols, respectively.
Of these two general types of scavenging, the below cloud processes have
217
been more extensively studied. Impaction efficiencies integrated over
both particle and droplet size have been related to a "washout coefficient,"
the characteristic decay time of aerosol concentration during precipitation.
This treatment generally ignores other phoretic forces that dominate within
150
-------
the cloud. Since these phoretic processes ate more difficult to quantify,
the lainout mechanism has not been extensively studied. Some theoretical
woik on rainout has been done; however, the contributions of electrical
706
interactions and ice nucleation require further investigation.
The fact that atmospheric turbidity often decreases after precipitation
does not necessarily imply that precipitation scavenging has cleaned the air.
247
Flowers et al. have shown that the turbidity change is more strongly re-
lated to the presence of unstable air (and thus greater mixing) associated
with the precipitation than to precipitation scavenging. Thus, a majority
of the aerosol has merely been diluted and not removed from the atmosphere.
The effect of precipitation scavenging of aerosols on the chemical com-
position of rainwater has received recent attention. It is complicated by
the fact that some gases can contribute to the same chemical species in
71
solution as the aerosol. Bielke and Georgii have estimated that the aero-
sol contribution can be as low as 25%. In a well^nixed atmosphere, however,
564
rainout undoubtedly predominates.
The inorganic chemistry of precipitation has been extensively studied
over the past 60 years in both Eurooe and North America. A good bibliographic
review of the literature on inorganic chemistry of precipitation has been
183
published by Dana et al. Most of the precipitation in these studies has
been sampled at ground level over one-month collection periods. Therefore,
there have been relatively few attempts, if any, to relate the short-term
( ^< 3 day) chemistry of precipitation to the equally short-term synoptic
meteorology, or to determine the relative contribution of rainout and washout
to the precipitation chemistry.
151
-------
Perhaps the most reported chemical variable in rain is the hydrogen ion.
Both hydrogen and sulfate ions have shown marked geographic variations and
systematic changes in time, with both acidity and sulfate increasing most
78
notably in Scandinavia. A Swedish report concludes that increased sulfate
and acid is due to sulfur emissions associated with fossil fuel combustion
in Germany, Holland, Belgium, and Great Britain, and that these increases
have significant biospheric effects. The most notable effects attributable
to the increased acidity are decreases in the pH of lakes and rivers and
the leaching of calcium from forest soils. The pH has become sufficiently
low in affected lakes to cause some fish to cease production. The thin forest
soils show important changes in nutrient balance. There is also evidence
of decreases in growth rate of trees.
FOGS
As the RH in the lowest atmospheric layer approaches 100%, water vapor
will condense on airborne particles, thereby forming fog. At a given PH a
certain fraction of the droplets thus formed grow until they reach an equil-
ibrium radius, typically 1 to 3 ym, while other droplets continue to grow
until they begin to fall, at 15 ym radius. The former are called unactivated,
and the latter, activated droplets.
Both stability and visibility in fogs depend on the numbers of unacti-
vated vs activated droplets. Large droplets tend to collide with smaller
ones as they fall, thus providing a relatively efficient removal mechanism
for water. Therefore, fog stability is enhanced by the presence of small,
unactivated droplets and is decreased by the formation of large ones. Visi-
bility varies inversely as the light-scattering coefficient, which is dom-
266
inated by the smaller droplets even when many of the droplets are activated.
152
-------
Thus, visibility is decreased in fogs containing large numbers of small
droplets and is improved as a relatively large number of the droplets are
activated.
The factors that determine the activation efficiencies of different kinds
of small droplets are not precisely known. Laboratory experiments show that
the application of organic surface films to the droplets at some intermediate
418 459,739
stage of growth or to the dry particles can suppress droplet growth,
thus increasing stability and lowering visibility. The possible role of
anthropogenic organic compounds in the atmosphere is unknown.
153
-------
CHAPTER 7
EFFECTS OF INHALED PARTICLES ON HUMANS AND ANIMALS:
DEPOSITION, RETENTION, AND CLEARANCE
The major regions of the respiratory tract differ markedly in structure,
size, function, and sensitivity or reactivity to deposited particles. Some
regions also have different mechanisms for particle elimination. Thus, a com-
plete determination of dose from an inhaled aerosol depends on the pattern of
deposition, the retention times at the deposition sites and along the elimina-
tion pathways, and the physical, chemical, and biologic properties of the
particles.
This chapter begins with a discussion of the factors that determine the
amounts and patterns of particle deposition within the various regions compris-
ing the respiratory tract. Following that is a discussion of the pathways and
dynamics of particle translocation and elimination. Both discussions emphasize
the normal patterns of particle behavior and transport that are applicable to
most atmospheric aerosol that is not acutely toxic. This material provides a
basic background for the sections on epidemiologic studies, on dose-response
relationships, and on laboratory studies designed to produce toxic or functional
effects on animals and humans.
As discussed in Chapter 2, most of the particles in the accumulation mode
(0.1 to 2.0 ym dia) of atmospheric aerosol contain water and are hygroscopic.
Thus, their size can change as they travel through the warm and humid atmosphere
in the conductive airways. These droplet aerosols also contain dissolved ma-
terials that can rapidly diffuse within and through the fluid lining of the
airways. On the other hand, inert and insoluble particles or components of
155
-------
liquid particles that are deposited within the conductive airways undergo
passive transport determined by the motion of the raucous layer. Consequently,
the fate of inert, insoluble particles during the bronchial clearance phase can
be discussed more generally than that of rapidly soluble or highly irritating
particles. To study the soluble particles that deposit in any part of the
respiratory tract or the insoluble particles that are deposited within the
nonciliated alveolar zone, the chemical composition of each aerosol must first
be considered.
FUNCTIONAL ZONES FOR PARTICLE DEPOSITION
The respiratory tract (Figure 7-1) can be divided into zones on the basis
that the insoluble particles that deposit therein contact or affect different
cell populations and/or have substantially different retention times and clear-
ance pathways. Each zone includes one or more anatomic regions. In each zone,
the retention of soluble or reactive particles usually differs from that of
inert, insoluble particles because they diffuse within the fluid layer at the
surface, then through it into the underlying cells and circulating blood. The
clearance kinetics for particles deposited in each region are discussed under
PARTICLE RETENTION, page 186.
Anterior Nares
Particles deposited in the unciliated anterior portion of the nose remain
at the deposition sites for a variable and usually indeterminate period until
they are removed mechanically by nose wiping, blowing, sneezing, etc. The
effect of particle solubility on retention in this zone is not known.
156
-------
OLFACTORY AREA
CONCHAE
VESTIBULE
TRACHEA, 20mm
LUNG
BRONCHUS 6mm
BRONCHIAL
ARTERY
PULMONARY
ARTERY
LYMPHATICS
PULMONARY
VEIN
LYMPHATICS
LUNG LOBULE
NASOPHARYNX
ORAL PHARYNX
EPIGLOTTIS
LUNG
TRACHEO -BRONCHIAL
LYMPH NODES
0.5 TO 1.5 cm
CONDUCTING
BRONCHIOLE, 0.6mm
TERMINAL
BRONCHIOLE, 0.6mm
RESPIRATORY
BRONCHIOLE, 0.5mm
ALVEOLAR
DUCT, 0.2mm
ALVEOLAR
SAC, 0.3mm
ALVEOLUS
FIGURE 7-1. Structure of the respiratory tract.
157
-------
Ciliated Nasal Passages
After leaving the nares, or nostrils, the inspired air passes through a
web of nasal hairs, than flows through the narrow passages around the turbi-
nates. It is warmed, moistened, and partially depleted of particles with aero-
dynamic diameters > 1.0 ym by sedimentation and by impaction on the nasal hairs
and on the passage walls at the bends in the air path. Particles <0.1 ym dia
can be deposited in this zone by diffusion. The surfaces of the nasal passages
ace coveted by mucus, most of which is propelled toward the pharynx by the beat-
inq of the cilia. Deposited insoluble particles are transported by the mucus;
soluble particles may dissolve in it. Some mucus moves toward the anterior
nares, carrying inhaled whole or dissolved particles into the zone of inter-
mittent mechanical clearance.
Nasopharynx, Dial Passages, Larynx (Nonciliated Large Airways)
Paitides inhaled through the nose and deposited in the nasopharynx or
particles inhaled through the mouth and deposited in the mouth and orooharynx
aie swallowed within minutes. They pass through the esophagus to the gastro-
intestinal tract. Particles inhaled by either route can also be deposited on
the larynx where they are transported rapidly to the esophagus in or on the
mucus coming up from the trachea.
Although the residence times for particles in these zones may be very
short, local deposition is important. Concentration buildup on some of these
surfaces can be very high and may exceed the capacity for clearance. This
2,551
may account for cancers of the anterior nares in furniture workers and
342,723
for laryngeal cancers in cigarette smokers.
158
-------
Tiacheobionchial Tree
The tracheobronchial or conductive airways have the appearance of an in-
verted tree, with the trachea analogous to the trunk and subdividing bronchi
to the limbs. The airway diameter decreases distally, but because of the in-
creasing number of tubes the total cross section for flow increases and the
air velocity decreases. In the larger airways, particles too massive to follow
the bends in the air path are deposited by imoaction. At the low velocities
in the smaller airways, particles deposit by sedimentation and diffusion.
Ciliated and secretory cells are found throughout the tracheobronchial tree.
Inert nonsoluble particles deposited on normal ciliated airways are cleared
13
within one day by transport on the moving mucus to the larynx. Soluble
836
particles are cleared much faster, presumably via bronchial blood flow.
Alveolar Zone
Gas exchange occurs in the alveoli beyond the ciliated airways. Ihe epi-
thelium there is very thin, permitting soluble particles to enter the pulmonary
blood within minutes. Insoluble particles deposited in this zone by sedimenta-
tion and diffusion are removed at a very slow rate, with clearance half-times
measured in days, months, or years. The mechanisms for clearance of insoluble
particles from the alveolar zone are only partly understood, and their relative
importance is a subject of debate. (See section on ALVEOLAR CLEARANCE,
page 205.)
FACTORS AFFECTING PARTICLE DEPOSITION
Particles are deposited in the various zones of the respiratory tract by
a variety of physical mechanisms. Deoosition efficiency depends on the aero-
dynamic properties of the particles, the anatomy of the airways, and the geo-
metric and temporal patterns of flow.
159
-------
Deposition Mechanisms
There are five mechanisms by which significant particle deposition can
occur within the respiratory tract: interception, impaction, sedimentation,
diffusion, and electrostatic precipitation. Of these, impaction, sedimenta-
tion, and diffusion are the most important.
Interception. Interception is usually significant only with fibrous par-
ticles. It takes place when the trajectory of a particle brings it so close
to a surface that an edge of the oar tide contacts that surface; thus, the
larger the particle, the greater the chances for interception. The prob-
ability of deposition by impaction and sedimentation is determined by aero-
dynamic diameter (D), which is the diameter of a unit density sphere having
the same terminal settling velocity of the oarticle under study. Nonfibrous
particles with D > 5 ym are usually deposited in large airways by impaction
or sedimentation rather than by interception. In his studies of asbestos and
755
other fibrous particles, Timbrell found that D averaged ~3 times the fiber
diameter for fibers with a length to diameter ratio >10:1. Consequently, a
fiber with length of 200 urn and a diameter of 1 ym would have an aerodynamic
diameter of ~3 urn. Such fibers have a low probability of deposition in the
conductive airways by impaction or sedimentation. However, the probability
of their deposition by interception is higher because of the fiber length.
756
Some 200-mn-long fibers have been observed in human lung samples. Such
straight fibers as amphibole asbestos are more,likely to oenetrate to the
alveoli than the similarly sized, but curly, chrysotile asbestos because the
straight fibers assume orientations more parallel to the flow streamlines.
Impaction. Inhaled air follows a tortuous path through the nose or
mouth, then into the branching airways in the lung. Each time the air changes
160
-------
direction, the momentum of particles tends to keep them on their preestablished
trajectories. This can cause them to impact on airway surfaces. Impaction
probability is determined by stop distance d = \JT, where v = air velocity and
s
T is the relaxation time. It also depends on the location of the particle with-
in the airway. For example, in a bifurcating airway, deposition probability on
inhalation is much higher for a particle traveling along the centerline of the
parent tube than for particles moving nearer to the walls. The most likely
deposition sites are at or near the carina of the bifurcation.
No adequate mathematical model exists for impaction deposition in the
bronchial tree. The periodic air flow can change from turbulent in the trachea
to laminar in deeper airways. In the larger airways, where most impaction
occurs, the flow pattern is never fully developed since the Reynolds number* is
362,792
high and the length of each segment is only about 3 times the diameter.
Sedimentation. Gravitational sedimentation is an important mechanism for
deposition in the smaller bronchi, the bronchioles, and the alveolar spaces
where the airways are small and the air velocity is low.
Sedimentation becomes less effective than diffusion when the terminal
settling velocity of the particles falls below -0.001 cm/sec, which for unit
density spheres is equivalent to a diameter of 0.5 urn.
Diffusion. Submicrometer particles in air undergo a random motion caused
by the impact of gas molecules surrounding the particles. This Brownian motion
increases with decreasing particle size and becomes an effective mechanism
*The Reynolds number (Re) is dimensionless. It is equal to the oroduct (DVp)
y
where D is the diameter of the airway, V is the velocity of the air, p is the
density of the air, and v is the viscosity of the air.
161 > >
-------
for particle deposition in the lung as the root-mean-square displacement
approaches the size of the ait spaces.
Diffusional deposition is important in small airways and alveoli and at
airway bifurcations for particles less than ~0.5 pm dia. The diffusional
efficiency of radon and thoron daughters, whose particle sizes are molecular,
can be high, especially in the head and in large airways such as the trachea.
Electrostatic Precipitation. Particles with high electric mobility can
have an enhanced respiratory tract deposition even though no external field is
applied across the chest. Deposition results from the image charges induced
on the surface of the airways by the charged particles. Test aerosols, produced
from the evaporation of aqueous droplets, can have substantial mobility. The
results of deposition studies using such aerosols without charge neutralization
are accordingly suspect. Since most ambient aerosols have reached charge equi-
librium, their charge levels are much lower. Thus, the deposition due to this
mechanism is usually small compared to that due to the mechanisms discussed
above.
Aerosol Factors
Particle size is always an important variable in regional deposition.
There are a number of ways of expressing particle size. Usually, particle size
is expressed in terms of actual or equivalent diameters, although some scien-
tific literature uses particle radius. When particle size is measured by one
parameter and expressed in terms of another or "equivalent" size, the basis
for the conversion must be clearly established. Nonspherical particles are
frequently characterized in terms of equivalent spheres, e.a., on the basis
of equal volumes, equal masses, or aerodynamic drag. The aerodynamic diameter,
162
-------
discussed above, is used with increasing frequency. This measurement incor-
porates both particle density and drag.
Aerodynamic diameter is the best measurement to use in studies of particle
deposition by impaction and sedimentation, which usually account for most of
the deposition by mass in the head and lunqs. Interception also depends on
both the linear dimensions of the particle and its aerodynamic drag, which can
affect the particle's orientation within the airway. On the other hand, dif-
fusional displacement, which is the dominant mechanism for particles < 0.5 ym,
depends only on particle size and not on density or shape.
The conversion of linear or projected area microscopic measurements of
nonspherical particles to aerodynamic diameters requires assumptions about the
relationship between projected area and volume, about density, and about aero-
dynamic shape factors. Sometimes these conversions have been made accurately,
but more often they have not. An alternative is to measure aerodynamic size
425,730,755
directly with an aerosol spectrometer.
A complicating factor for water-soluble particles is the change in size
that may occur in humid atmospheres. Furthermore, dry aerosols of materials
such as sodium chloride, sulfuric acid, and glycerol will take up water vapor
and grow in size within the warm and nearly saturated atmosphere in the
539,615
lungs. Since total and regional deposition depend on particle size,
droplet growth could significantly change deposition pattern and efficiency.
Respiratory and Flow Factors
Increasing air velocity increases impaction deposition but decreases
sedimentation and diffusion by decreasing residence time. The calculation of
deposition at a constant velocity is relatively simple but cannot be applied
to normal breathing during which velocity is continuously variable and reverses
163
-------
direction twice in each cycle. During exhalation, the flow profiles within the
airways differ from those durinq inhalation thereby affectina particle deposi-
tion probabilities, especially for the impaction mechanism.
The velocity profiles in the larger conducting airways are quite different
from those normally encountered in fluid-filled conduits. Because the average
362,792
length of a bronchial airway is only about 3 times its diameter, the
flow therein never achieves a fully developed flow profile. Moreover, since
each segment terminates in a bifurcation, the entering flow profile is asymmet-
rical, i.e., the maximum velocity is close to the carinal ridge. Such profiles
586 604
have been demonstrated by Olson et al. and Pedley et al., who also have
shown that the asymmetrical entry results in a secondary swirling motion that
is imposed on the bulk flow. Finally, the flow is cyclical and reverses many
times per minute. At its peak rate, it may be turbulent in the trachea. Be-
cause the Reynolds number decreases with increasing lung depth, the flow is
always laminar in the smaller conducting airways and viscous in the alveolar
186
region.
The flow is laminar in the more distal bronchioles, which contain most of
the volume of the conductive airway system. In these distal segments of the
anatomic dead space, the central core velocity is almost twice the average
velocity. Even during very shallow breathing, a substantial fraction of the
inhaled air penetrates beyond the anatomical dead space. Particles with ap-
preciable sedimentation rates ( > 2 pm) or large diffusional displacements
( <0.1 urn) are deposited efficiently in peripheral airways.
Tidal volume is an important respiratory parameter. The air inhaled at
the start of each breath goes deeper into the lung and remains there longer
than the air inhaled later in the breath. The deeoer the air goes and the
164
-------
longer it stays, the greater its depletion of inhaled particles. During
quiescent breathing, when the air velocity is low, mixing is minimal, and the
tidal volume is only 2 to 3 times the dead soace volume, a large portion of the
inhaled particles can be exhaled.
Anatomical Factors
Intrasubject variations in airway anatomy affect particle deposition in
several ways:
• The diameter of the airway influences the displacement required by the
particle before it contacts the airway surface.
• The cross section of the airway determines the flow velocity for a
given volumetric flow rate. Velocity affects particle deposition,
as discussed under respiratory factors.
• The variations in diameter and branching patterns along the bronchial
tree affect the mixing characteristics between the tidal and reserve
air in the lunqs. Such convective mixing can be the single most
important factor determining deposition efficiency of particles
with aerodynamic diameters <~2 \en.
There are also significant intersubject differences in respiratory tract
anatomy. For example, the average dimension of alveolar zone air space has a
substantial coefficient of variation when measured either post-mortem on lung
sections or in vivo by aerosol persistence during breath holding. In the for-
513
mer case, Matsuba and Thurlbeck reported a mean size and variation of 0.678
438
mm ± 0.236; in the latter, Laop et al. found values of 0.535 nrn ± 0.211.
Physiologic Factors
The effective diameters of the conductive airways for airflow are defined
by the surface of the mucous layer. In healthy subjects, where the mucous layer
165
-------
180
on the conductive airways is believed to be approximately 5 ym thick, the
reduction in air oath cross section by the mucus is neqliqible. In individuals
with bronchitis, the mucous layer can be much thicker; it can accumulate and
partially or completely cccljde some of the airway. Air flowing throuqh par-
tially occluded airways forms jets. This orobably increases small airway par-
ticle deposition by impaction and turbulent diffusion.
An important function of the conductive airways is to warm and humidify
the inspired air. Air inhaled throuqh the nose is already saturated at body
temperature before it reaches the pharynx. Air inhaled through the mouth may
not reach saturation before the major or segmental bronchi. The warming and
humidifying of the insoired air within the upper airways will cause hygroscopic
539,615
particles to grow in size, thereby affecting their regional deposition.
Environmental Factors
There is relatively little information on the effects of natural environ-
mental factors (e.g., temperature and humidity) on particle deposition. While
low ambient humiditv may dry the tracheal mucus durinq mouth breathing, it does
not appear to affect the mucous transport of particles in the nose in normal
nose-breathing humans, even at a relative humidity (RH) level as low as 10% at
621
23'C. However, ambient humidity can greatly affect the size of many ool-
lutant particles thereby affecting their total and regional deposition
efficiencies.
Most of the attiospheric aerosol in the accumulation mode contains water-
soluble acids and/or salts that are formed from gaseous orecursors. As dis-
cussed in Chapter 5, as much as 50% or more of the atmospheric aerosol mass may
be composed of sulfuric acid, ammonium bisulfate, and/or ammonium sulfate.
Sulfuric acid and ammonium bisulfate are aqueous solution droplets at all
166
-------
relative humidities from 30% to 100%, while ammonium sulfate undergoes a tran-
143,588
sition from the dry crystal to a solution droplet at an RH of -80%.
Sodium chloride, potassium chloride, and sodium bromide also undergo sudden
transitions from dry crystals to aqueous droplets at -70%, 75%, and 40% RH,
163,588
respectively. However, when the humidity then decreases, these droplets
retain water at humidities considerably lower than that at which they originally
143,163,588
changed to their aqueous state.
Effects of Pollutant Gases and Aerosols
When discussing the deposition of inhaled atmospheric aerosols, the in-
fluence of airborne cocontaminants on the lungs of the people inhaling the
particles should be considered. Such inhaled irritants can affect the fate
and toxicity of the inhaled particles by altering airway caliber, respiratory
function, clearance function, and/or the function, survival, and distribution
of the cells lining the airways.
A large portion of the overall pollution aerosol, and the dominant portion
of the aerosol in the accumulation mode, is formed within the atmosphere from
gaseous precursors associated with combustion sources. Thus, any atmosphere
containing elevated sulfate and nitrate aerosol concentrations may also contain
elevated sulfur dioxide and nitrogen dioxide gas concentrations. Elevated
gaseous oxidant is associated with elevated hydrocarbon aerosols.
The effects of pollutant gases and aerosols on lung function are discussed
in Chapter 8. Increased pulmonary flow resistance reflects the bronchoconstric-
tive effects of some pollutants. Any reduction in airway cross section in the
larger bronchial airways results in increased flow velocities. This should
increase particle deposition by impaction. Increased bronchial deposition of
inhaled particles was observed in two healthy young men who had been exposed
167
-------
to sulfur dioxide. One subject, exposed 7 min to 34 mgA\3 (13 ppm), showed
decreased alveolar zone deposition of 4.6-ym aerodynamic diameter particles
from 10% to 2%. It also produced a marked proximal shift in the bronchial
deposition pattern. The second subject, exposed 6 min to 31 mg/m3 (12 ppm),
showed decreased alveolar deposition of 5.9 ym dia particles from 18% to 4%.
Tests on two other healthy subjects at exposures of 13 and 24 mg/m3 (5 and 9
474
ppm) did not produce any significant shift in regional deposition.
Effects of Chronic Lung Disease
While some healthy cigarette smokers have increased bronchial deposition,
the increase is small conroared to that in individuals with clinically defined,
473
chronic bronchitis. Greatly increased tracheobronchial particle deposition
473
has also been seen in some asymptomatic asthmatics who did not smoke.
Among 58 working coal miners, total respiratory tract deposition of 1 urn
particles was significantly correlated with lung function measurements charac-
terizing airway obstruction. The increased deposition was observed among
smokers in the group. The presence of simple pneumoconiosis was not associated
488
with the degree of aerosol deposition.
EXPERIMENTAL DEPOSITION DATA
Total Deposition
Few measurements of regional particle deposition in humans have beer.
attempted. In most studies, total deposition has been explored. For parti-
cles between ~0.1 and 2 m. aerodynamic diameter, deposition in the conductive
airways is generally small compared to deposition in the alveolar regions.
Thus, total deposition is close to that of alveolar deposition alone. Total
deposition as a function of particle size and respiratory parameters has been
168
-------
measured experimentally by numerous investigators. Many reviews of deposi-
tion studies have called attention to the very larqe difference in the re-
185,319,470,741,749
ported results.
Much of the discrepancy can be attributed to uncontrolled experimental
variables and poor laboratory technique. The major sources of error have been
186
described by Davies. Figure 7-2 shows data from studies that were performed
with good techniques and precision. All were done with mouth breathing at
respiration frequencies of from 12 to 16 breaths/min. Tidal volumes varied
from 0.5 to 1.5 liter. All appear to show the same trend with a minimum of
deposition at ~0.5 Mm dia. All four studies in which di(2-ethylhexyl)sebacate
187,326,327,562
(DBS) was used appear to have somewhat lower absolute values.
In most studies involving more than one subject, there was considerable
187
individual variation among the subjects. Davies et aL. showed that some of
this variation could be eliminated by standardizing the expiratory reserve
volume (ERV) and thereby the size of the air soaces. They found that deposi-
326,327
tion decreases as ERV increases. This was confirmed by Heyder et al_. who
reported little intrasubject variation among six subjects when their deposition
tests were performed at their normal ERV's.
The data of Heyder and his colleagues aopear to represent minimum deposi-
tion for healthy men. Their test procedures were orecisely controlled. There
were no electrical charges on particles. With more natural aerosol and respi-
ratory parameters, higher deposition efficiencies would be expected. The data
435,436 18 269
of Landahl et al., Altshuler et al., Giacomelli-Maltoni et al., and
507
Martens and Jacobi, which are higher and agree quite well with each other,
provide the best available data for total deposition in normal humans.
169
-------
1.0
.9 -
.7
.6
0
± .5
S
a
1 1—I ! I I I I
Sourc
No. of
Subfrcti
Tidal l«p
Vol fat*
O
Lippmann
Landahl 1951
. Landahl 1952
AlHhuler 1957
Muir 19*7
Giocomellt-
Malioni 1972
12
2
2
3
3
15
3
Davin 1972
Heyder 1973a 4
-H«ydw N73b I
Mar Km 1973 I
Lever 1974
I. It.3 14
0.5 15
15 IS
05 IS
05 IS
10 12
06 W>
05 15
Total
I
I i
0.1 0.2 0.3 0.5 0.7 1.0 235
Aerodynamic Diam«t»r - pm
10
20
FIGURE 7-2. Total respiratory tract deposition during itouthpiece inhala-
tions as a function of D (aerodynamic diameter in um) except
below 0-5 ym, where deposition is plotted vs linear diameter.
Data of Lippmann1*71 and Lippitiann and Altshuler4 ?tf are plotted
as individual tests, with eye-fit average line. Other data on
multiple subjects are shown with average and range of individual
tests. Monodisperse test aerosols used were ferric oxide,1*71
triphenyl phosphate, 17/^35,436
wax
269
polystyrene
, ,
latex, 5T>7 and di(2-ethylhexyl)sebacate. 187' 327,181,562
170
-------
The deposition data in Figure 7-2 were based on the difference between
471
inhaled and exhaled particle concentrations, except for Liopmann's data,
which are based on external in vivo measurements of y-tagged particle retention.
Most of his tests were performed with particles larger than 2.5 ym dia, while
smaller particles were used in most of the other studies. Despite the minimal
overlap in size range, the two sets of data appear to be consistent. The large
amount of scatter among the individual data points for the larger particles is
due to a quite variable deposition in the head and tracheobronchial tree (Fig-
ures 7-3, 7-4, and 7-5). Figure 7-3 shows data for nonsmokers only. Cigarette
smokers have a similar median behavior for head deposition, but even more
scatter. Figure 7-5 shows that the median and upper limits of tracheobronchial
deposition are higher for cigarette smokers than for nonsmokers, but the lower
limit is about the same.
Head Deposition
Some inhaled particles are deposited within the air passages between the
point of entry at the lips or nares and the larynx. The fraction deposited is
highly variable; it depends on the route of entry, particle size, and flow rate.
The nasal flow path is usually a more efficient particle filter than the oral,
especially at low and moderate flow rates. Thus, those oeople who normally
breathe through the mouth either oart or all of the time may be expected to
have more particles deposited in their lungs than those who always breathe
through the nose. During exertion, the flow resistance of the nasal passages
causes a shift to mouth breathing in almost all oeoole.
There are very few data on head deposition during mouth breathing. The
available data on nonsmoking healthy subjects (Figure 7-3) are based on external
171
-------
WOp 1 1—i—I 1 1 1—r
•0
.£
I
40
AIIODVNAMIC DIAMITII «t » »Hn/mm MSPMATOfr HOW - l»"
| i 1 4 J » 7 t f 10 II W
1 , 1 1 | | | I •—r-
i
/ °
0
0
a
1
o d
100
900 1,000 1.000
D'F
FIGURE 7-3. Deposition of monodisperse ferric oxide aerosol in the heads of
(normal) nonsmoking human males during mouthpiece inhalations
as a function of D2F, where F is the average inspiratory flow in
liters/min. An eye-fit line describes the median behavior for
deposition between 10% and 80%. Total respiratory tract depo-
sitions in these tests are shown in Figure 7-2.
172
-------
1.0
Aerodynamic Diameter at 30 litwrs/min.-ym
1 2 3 41*71*10
I I
I ' ' ' ' I
Q Mewnam 1M9
O lippmonn 1970
jt GiocenwMi-Mohoni 1972
D Mart*n» 1973
• ludelf 1974
ui
2
UI
0
.3
.2
.1
10
10O
D2F
1,000
FIGURE 7-4. Deposition of monodisperse aerosols in the head during inhalation
via the nose vs D2F. The heavy solid line is the International
Ccnmission on Radiological Protection Task Group deposition model,749
which is based on the data of Pattle. 5" For the Hounam et al.,
Giacomelli-Maltoni et al. ,269 and Rudolf and Heyder data,"^3 the
symbol shows the median value, and the bars show the range of the
individual observations. The number at the end of the bar indicates
the inspiratory flow rate in liters/min. The mnnodisperse aerosols
used were methylene blue,599 polystyrene latex,365 50^ferric oxide,1+69
carnuba wax, and di(2-ethylhexyl)sebacate. 653
173
-------
I 1 1 1 1 1 1 1 1 1 1 1 I
CU
43 o o 1
>>4J i-l Sf C
43 4J 4J
« 4-1 4J CO
00 rH (3 i-l
tfl CU
CU
C to
a) co
•H OJ CO 0) 4J rC C
J3 CU 4J HO
W O M-l l-l
oo ex Q) !-i -H
H 43 tO CO
3 4J G. O
O 00.
<4-i O CU
a) o o -a
H en < PQ
cu i
3 H
« r-)l/>
CO t80l T3
M >(T> CU
CU • (A
CU S
U CO
CU C
•H O
a. c
x
4-1 M
3 O
O 4-1
6 rt
00 4-1
C to
•H -a
w
3 CO
•a >
o
C 43
O CO
CU
M •-!
CU
x-s C
pq to
I PU
H
H cfl O P
cfl CU <4-l
#
§
co va
CU
nt
nn
n)
CU
0 tj
a C
a) 4-1 p* -H
4J m -H
4J 1-1 tJ CO
CO T3 >
^ T3 (8
tfl vj c x
bC O cfl
•i-i m to
O CO !-i
Pn Q) (U
H
4J
>.
i-l
O
4-1
tfl
Vi
•H
a
en
, 0) >w o
C .a -u
-a i-f
43 cfl -H
4-1 43
CU $
C 43
•H 4J «
-H C O60-U p<
Cfl 3 ^1 -H (1)
CO CU P~i
•a C
co to
cfl vi 0
0!
C 4J 4J
O CU tO
i-l e 43
4J Cfl 4J
•H 14
CO tfl CO
o a. cu
&
cu
a <4-r
O O
•H
4J 4J
i-l C
CD CO
O O
a. u
C «
O VJ
•H 4J
PQ CO CO
" C C
II
C i-l CU
'l
H
co cc)
cu
^.
e to
O
M
<4-( CM
i
tfl Q)
M
tfl 3
4-1 M
cfl -i
cu >-, co
oo to i-t
C i 0)
tO C C
co C
Q O
174
-------
scintillation detector measurements of y-tagged particles deposited in the
471
head immediately after inhalation via a mouthoiece.
Figure 7-4 shows head deposition data for monodisperse aerosols during
inhalations via nose masks as a function of D2F. The solid line is the Inter-
749
national Commission on Radiological Protection (ICRP) Task Group model,
599
based on Pattle's data on one subject. These data and the Hounam et al.
366
data on three subjects were based on the reduction of airborne narticle con-
centration as constant flows were drawn in through the nose and out of the
469
mouth while the subject held his breath. The data of Lippmann on 2 subjects,
269 .. 507
Giacomelli-Maltoni on 15 subjects, Martens and Jacobi on 1 subject, and
653
Rudolf and Heyder on 4 subjects were obtained during normal nasal inhala-
tions, with exhalations via the mouth. Liopmann measured the amount of y-tagged
aerosol actually deposited within the head, while Giacomelli-Maltoni, Martens
and Jacobi, and Rudolf and Heyder estimated nasal passage deposition on the
basis of the total deposition difference between oaired studies on the same
subject; i.e., mouth-in/mouth-out vs nose-in/mouth-out. Deposition in the oral
passage is assumed to be negligible in this technique. Since oral oassage
deposition values are not negligible for particles >~2 m dia, these nasal deoo-
sition values may be too high.
Pattle used methylene blue particles between 1 and 9 ym aerodynamic diameter
and constant flow rates of 10, 20, and 30 liters/min. Hounam used 1.8 to 8.0 urn
dia particles and constant flows from 5 to 37 liters/min. Lippmann used 1.3 to
3.9 ym dia ferric oxide particles and inspiratory flows averaging ~30 liters/
min. Giacomelli-Maltoni used 0.25 to 1.8 ym dia wax particles and average flows
of about 24 liters/min. Martens and Jacobi used 0.3 to 1.9 ym dia latex par-
ticles and an average flow rate of -30 liters/min. Rudolf and Heyder used 0.5
175
-------
to 3.0 vm dia di-2(ethylhexyl)sebacate particles and constant inspiratory flows
from 7.5 to 30.0 liters/min. Pattle found that the data from the three dif-
ferent flow rates could be normalized by plotting D2F against retention.
Hounam found that the best straight line fit to his data was obtained by
plotting retention against D2F1>6. In Figure 7-4, his D2F data at 37 and 30
liters/min lie close to the line, while those at 20, 10, and 5 fall increasingly
below the line. The Rudolf and Heyder data show a similar, but lesser trend,
with their 60 and 30 liter/min data tending to lie above the line while the 15.0
and 7.5 liter/min data straddle the line. A better straight line fit can be
obtained through the Rudolf and Heyder data by plotting D2F1-3 vs retention.
In the Hounam et al., Giacomelli-Maltoni, and Rudolf and Heyder data, most
366
of the scatter is due to intersubject variability. Hounam et al. also
measured the pressure drop across the nose and mouth during each deposition
study and plotted the data in terms of percent deposition vs D2R, where R is
the resistance across the nose and mouth in mm of water. Ihe same data on this
plot exhibited less scatter than the D2F plot, with the greatest improvement
at large values of percent deposition. The fact that oar tide deposition cor-
relates better with D2R than D2F indicates that the air Path dimensions are
variable. Since the air paths are distensible, their dimensions can be ex-
pected to vary with flow rate in a given subject. Perhaps this accounts for
the observation that a flow factor exponent higher than 1 helps to normalize
the data.
653
Rudolf and Heyder determined head deposition efficiency for aerosols
exhaled through the nose to be essentially the same as that measured during
inhalation for a flow rate of 7.5 liters/min. At 15 and 30 liters/min, the
efficiency for 1 to 3 mi dia particles during exhalation was approximately 25%
higher than during inhalation. However, at 60 liters/min, the exhalation
176
-------
efficiency was about 7% lower. Deposition efficiencies are similar during
inhalation and exhalation; however, the amount deposited durinq exhalation
is usually much lower because the aerosol concentration is depleted while
passing through the nasal oassages, then into and out of the lungs.
Deposition in the Tracheobronchial (T-B) Zone
The only measurements of tracheobronchial deposition in the literature are
471,472,473
those of Lippmann and his colleagues (Figure 7-5). T-B deposition
for a given particle size varies greatly among individual nonsmokers, cigarette
smokers, and patients with lung disease. The average T-B deposition is
slightly elevated in smokers, and greatly elevated in the patients with lung
disease. Healthy nonsmokers and nonbronchitic smokers exhibit individual
particle size vs deposition relationships. T-B deposition includes deposition
both by impaction in the larger airways and by sedimentation in the smaller
airways. Impaction deposition predominates for large particles ( > 3 pm dia)
and high flow rates ( >~20 liters/min). T-B deposition of smaller particles is
slight. The small amount that occurs may be attributable to either sedimenta-
tion or impaction.
Deposition in the Alveolar Zone
435,436
Landahl et al. conducted mouth-breathing experiments with monodis-
perse aerosols of triphenyl phosphate (0.11 to 6.3 m dia). The exhaled air
was separated into four sequential components. The residual airborne particle
burdens in each were presumed to have come from different lung regions. The
results obtained were compared to predicted values for the same breathing pat-
433
terns obtained from Landahl's previous theoretical calculations. The agree-
ment was sufficiently good for the authors to conclude that the predictions
were verified.
177
-------
91
Brown et al. studied reqional deposition during nose breathinq usinq
classified china clay aerosols with count medium diameters between 0.9 and 6.5
urn (a = 1.25). They collected the exhaled air in seven sequential components,
g
and used the carbon dioxide content of each fraction as a tracer to identify
the region from which the exhaled air originated. The validity of these data
depends on the accuracy of the association between the various exhaled air
17
fractions and their presumed sources. The Brown data have been criticized on
the basis that their simple two-filter model was inadequate and that the rapid
diffusion of carbon dioxide caused the measured carbon dioxide values to differ
significantly from the corresponding concentration in the alveolar soaces. The
resulting error in the volume partitioning caused an underestimation of the
alveolar deposition.
17
Altshuler et al. estimated reqional deposition from mouth-breathing
experiments on three subjects. They measured continuously, during individual
18
breaths, both the concentration of a monodisperse triphenyl phosphate aerosol
and the respiratory flow. Using a tubular continuous filter bed model as a
theoretical analog for the resoiratorv tract, regional deposition in the upper
and lower tract components was calculated for various values of anatomic dead
space. The upper tract penetration during inspiration, pause, and expiration
was derived from the expired aerosol concentration corrected for aerosol mixing,
The alveolar deposition estimates varied from subject to subject, and for each
subject varied with the volume of anatomic dead space. The particle size for
maximum alveolar deposition was estimated to be > 2 ym dia. The exact value
could not be estimated, however, since only one particle of this size was used
in the experiments.
The alveolar deposition values of Mtshuler et al., based on their best
estimates of dead space, are plotted on Figure 7-6. This figure also shows
178
-------
1.0
.9
.7
.6
J
± .5
0
.2
1 1 1 1
Alveolar
via -
mouth
0.1
0.2 0.3 0.5 0.7 1.0
10
Linear diameter, ym
Aerodynamic diameter , ym
FIGURE 7-6. Deposition in the nonciliated alveolar region, by percent of aerosol
entering the mouthpiece, as a function of diameter. Individual data
points and eye-fit solid line are for the same ferric oxide aerosol
tests plotted in Figures 7-2, 7-3, and the left panel of Figure 7-5.
The dashed line is an eye-fit through the median best estimates of
Altshuler et al.,17 based on their 1957 studies of three subjects
vtose average deposition range is indicated by the vertical lines.
The lower curve is an estimate of alveolar deposition during nose
breathing. It is based on the difference in head deposition shewn
in Figures 7-3 and 7-4.
179
-------
alveolar deposition values obtained by Lippmann durinq his mouth-breathing in-
halation tests on nonsmoking, healthy subjects. These data are based on ex-
ternal measurements of the retention of y-tagged particles after the completion
of bronchial clearance. The Lippmann and Altshuler data, in the region of
particle size overlap, are in qood agreement.
Figure 7-6 also shows an estimate of the alveolar deposition when the
aerosol is inhaled via the nose. It is based on the difference in head reten-
tion during nose breathing and mouth breathing from the straight line relations
plotted on Figures 7-3 and 7-4. For mouth breathing the particle size for
maximum alveolar deposition is ~3 urn dia. Approximately half of the inhaled
aerosol of this size deposits in this region. For nose breathing, there is a
much less pronounced maximum of ~25% at 2.5 ym dia, with a nearly constant
alveolar deposition averaging 20% for all sizes between 0.1 and 4.0 Vm dia.
PREDICTIVE DEPOSITION MODELS
Mathematical models for predicting the regional deposition of aerosols
230 433 434
have been developed by Findeisen in 1935, Landahl in 1950 and 1963, and
60
by Beeckmans in 1965. Findeisen's simplified anatomy, with nine sequential
regions from the trachea to the alveoli, and his impaction and sedimentation
749
deposition equations were used in the ICRP Task Group's 1966 model. For
289
diffusional deposition, the Task Group used the Gormley-Kennedy eouations;
for head deposition, they assumed entry through the nose with a deposition ef-
599
ficiency given by Pattle's empirical equation. A comparison between the
various predictions and the experimental data indicates that for both total and
alveolar deposition, Landahl's model comes closest, but it overestimates alve-
olar deposition for particles with aerodynamic diameters larger than 3.5 pm.
180
-------
. 749
The ICRP Task Group's 1966 model was adopted by ICRP Committee II in
1973, with numerical changes in some clearance constants. The 1966 Task Group
report has been widely quoted and -used within the health physics field. A sig-
nificant conclusion of this report was that the regional deposition within the
respiratory tract can be estimated using a single aerosol parameter, the mass
median aerodynamic diameter (MMAD) (Figure 7-7A). For a tidal volume of 1,450
cm3, there are relatively small differences in estimated deposition over a
very wide range of geometric standard deviations (1.2 < a <4.5). The Task
g
Group report calculated the mean deposition curves for 750 and 2,150 cm3 tidal
volumes (Figure 7-7B).
None of the previously proposed models provide reliable estimates of aero-
sol deposition in healthy normal adults, since their predictions for total and
alveolar deposition efficiencies differ from the best experimental data (Figures
7-2 and 7-6). Furthermore, they do not take into account the very large vari-
ability in deposition efficiencies among healthy subjects. The effect of inter-
subject variability on total respiratory tract deposition is illustrated in
595
Figure 7-8. Here, Palmes and Lippmann have used the experimental data of
269
Giacomelli-Maltoni et al. to construct curves showing deposition by percentiles
of the overall population. Within this particle size range, deposition for the
top 2% of the population is from 34% to 54% higher than for the median subject.
Other variations in deposition are produced by cigarette smoke (Figure 7-5) and
14,474
lung disease. There have been significant advances in the measurement of
deposition in recent years; however, considerable effort is underway to improve
theoretical understanding and predictive models.
181
-------
001 005 01 0.5 1.0 5 10 50100
Mass median aerodynamic
diameter, um
0-01 0-10 1-0 10 100
Mass median aerodynamic
diameter, ym
FIGURE 7-7. Regional deposition predictions based on model proposed by
the International Ccrmission on Radiological Protection Com-
mittee II Task Group on Lung Dynamics74" indicating effect of
variations in ag and flow rate. (A) Each of the shaded areas
(envelopes) indicates the variable deposition for a given mass
median (aerodynamic) diameter in each compartment when the dis-
tribution parameter ag varies from 1.2 to 4.5 and the tidal
volume is 1,450 ml. \B) Two ventilatory states, 750 and 2,150
ml tidal volume (-11 and -32 liter/min volumes, respectively),
are used to indicate the order and direction of change in com-
partmental deposition which are induced by such factors.
Reprinted with permission of Pergamon Press, Ltd., and Task
Group Chairman. From Health Physics 12:173-207, 1966.?l+9
182
-------
100
80
a* 60
8.40
o>
Q
20
0
Calculated from data of
Giacomelli-Maltoni
et al. 1972
0.1
0.2
0.5
1.0
2.0
Particle size,
FIGURE 7-8. Range of expected total respiratory tract deposition values
based on experimental data of Giaconelli-Maltoni et al.269
Each curve represents the indicated percentile of the overall
population. From Palmes and Lippmann.595 With permission
from Pergamon Press.
183
-------
DEPOSITION OF AMBIENT ATMOSPHERIC AEROSOL
^s discussed in Chapter 5, the mass or volume distribution of the ambient
aerosol as a function of oarticle size generally has two distinct modes. One
mode results from the formation of small particles in the atmosohere and their
growth by coagulation. These particles vary from ~ 0.01 to 1.5 urn dia. The
second node is created by oarticles injected into the atmosphere by mechanical
forces. Most of the mass of these particles is contributed by particles larger
than - 3 wn dia. The upper size limit is quite variable, increasing as atmos-
pheric turbulence increases.
Since total and regional deposition depend on oarticle size, changes in
size due to droplet growth can significantly change deposition pattern and
efficiency. However, for the atnvospheric accumulation aerosol, it is not clear
that major shifts will occur. When the humidity is low, the accumulation mode
is generally 0.3 ym MMAD or less. Thus, even if the particle size were to in-
crease by a factor of 3 to 5, the total deposition efficiency would remain close
to 20% (Figure 7-6), and most of the deposition would still occur within the
alveolar region. On the other hand, if a hygroscopic aerosol having a dry size
of 1 urn dia or larger is released into the atmosphere, its growth in the
143,163,588,825,826 539,615
atmosphere or in the respiratory tract could greatlv
affect its regional deposition. The amount deposited in the head and T-B zones
increases rapidly with increasing droplet size (see Figures 7-4 and 7-5).
Wherever possible, consideration should be given to the particle size
distributions for specific toxic constituents of the ambient aerosol, such as
airborne lead and particulate oolycyclic organic matter, which were the subjects
of two reports by the Committee on Medical and Biologic Effects of Environmental
571,572 575
Pollutants of the National Research Council. Natusch et al.
184
-------
measured the trace element concentrations in fly ash samples of different par-
ticle size ranges, with diameters from an upper limit of 74 ym to less than
1 ym. They reported that the percentage of arsenic, nickel, cadmium, and sul-
fur in the particles increased as particle size decreased. They attributed
this to a volatilization-condensation process within the furnace and stack.
The MMAD's of anbient airborne lead and aerosols of other metallic elements
457
were measured in six U.S. cities by Lee et al. Annual MMAD's ranged from a
low of 0.4 to 0.7 ym for lead and vanadium to a high of 2.4 to 3.5 ym for iron.
The other metals measured had median diameters of intermediate sizes. Similar
measurements of vanadium and iron aerosol MMAD's have been reported by Gladney
276
et al. for Boston, which was not one of the six cities studied by Lee and
his colleagues. This later studv did not include lead, but did include many
trace metals not measured by Lee et al. The small size of the particles con-
318 70
taining lead has also been noted by Harrison et al. and Bernstein et al.
The size distributions of several polynuclear aromatic hydrocarbons were
610
measured in and around Toronto, Canada by Pierce and Katz. MMAD's ranged
from ~ 0.5 ym near a rural freeway to ~ 3.0 ym at suburban York University.
Measurements also indicated seasonal variations. For example, at the York
University site, the average summer concentration of benzo(a)pyrene was 12.6
± 0.7 yg/g particulate, the MMAD was 2.4 ym, and the a was 2.2. The corre-
g
spending winter values were 17.1 ± 0.9 yg/g particulate, 1.5 ym, and 2.9. The
only other report on the particle siza of a polycyclic aromatic hydrocarbon is
413
that of Kertesz-Saringer et al_., who found an MMAD of 0.3 ym for benzo(a)-
pyrene in Budapest, Hungary.
185
-------
PARTICLE RETENTION
Particle retention is a time-dependent variable that is equal to the dif-
ference between the amount of aerosol deposited and the amount cleared. Rates
of clearance vary greatly among the regions of the respiratory tract. This
variation was a major basis for the characterization of the functional zones
described above. In two of these zones, the ciliated nasal passages and the
tracheobronchial tree, clearance in healthy individuals is completed in less
than one day. In the alveolar zone, clearance proceeds by slower processes,
most of which vary considerably with the composition of the particles. (See
section on ALVEOLAR CLEARANCE, Dage 205.)
MUCOCILIARY CLEARANCE
The mucociliary system of the conducting airways collects, transports, and
eventually eliminates inhaled oarticles. The ciliated epithelial lining of the
nasal passages and tracheobronchial tree is covered by a layer of mucus, which
is a mixture of material from several sources. The coordinated beating of the
cilia, which extend to the respiratory bronchioles, results in the movement of
this fluid from distal areas towards the pharynx, where it is swallowed.
Sources of Respiratory Tract Mucus
The respiratory tract mucus is derived from mucous glands, goblet cells,
151,210
Clara cells, bronchial transudate, and fluids drawn from the respiratory
*bronchioles. The total volume secreted by the mucous glands is ^ 40 times that
secreted by the goblet cells in the epithelium of the tracheobronchial tree of
637
a healthy adult human. Thus, these glands are thought to be the primary
source of the viscous mucus.
186
-------
The goblet cells are part of the respiratory tract epithelium; they are
773
more numerous in the larger proximal airways than in the more distal branches.
Mucous glands are located predominantly in the submucosa of the 'cartilage-
containing airways, and often lie between and external to the cartilage
638
plates. The glands contain both serous cells and mucous cells, whose secre-
536
tions are discharged onto the ciliated epithelium through a common duct.
Sensory and secretomotor nerve endings have been observed among the mucous
65,568,710
and serous cells of human tracheobronchial glands. Studies with
246
laboratory animals have provided physiological evidence that these glands
are innervated and secrete under nervous control. Not only the quantity, but
also the character of the secretions may be under such control; a change in the
consistency of bronchial secretions from tenacious to thin was observed in
87
humans following bronchopulmonary denervation. Secretion seems to be strnu-
246
lated cholinergically through a system mediated by the vagus nerve. Atrooine
53,742,743
reduces the secretory response of the gland cells, , while parasym-
pathomimetic stimulation causes both mucous and serous cells of the glands to
130,742,743,834 '
secrete.
Goblet cells do not appear to discharge by autonomic nerve stimulation.
53
Their secretion is not affected by atropine. No difference in the character
or number of goblet cells in denervated and normal tracheobronchial trees has
280
been observed. These cells seem to have a baseline of activity that may be
246,521
altered by local stimulation, such as irritation.
In the bronchiolar airways there are a few goblet cells but no mucous
174
glands. The Clara cells found in these airwavs are secretory. Ebert and
210
Terracio have recently summarized the work on Clara cells. In the airways,
these cells probably produce a protein secretion that forms the sol layer in
187
-------
415
which the cilia beat. Inflamnation and various immunologic stimuli may
result in the addition to these secretions of mast cells, olasma cells, aod
712
other cell types normally found under the tracheobronchial epithelium.
The lining of the tracheobronchial tree of rats contains a small number
643
of brush cells. Similar cells have been found more rarely in human tracheo-
642
bronchial epithelium. The exact role of these cells is unknown. Some
710
investigators have suggested that they are discharged goblet cells or that
642
they have a role in fluid reabsorption.
Volume, Composition, and Rheology of Respiratory Tract Mucus
Estimates of daily volume production of tracheobronchial secretions in
613
humans range from 100 cm , based on inferences from animal studies, to
758
10 cm3, based on actual work with tracheotomized adult humans.
Pure secretions from the normal human bronchial tree are difficult to col-
lect. Most studies to determine the biochemical composition of the secretions
have been conducted using expectorated sputum, often from chronic bronchitis
patients who produce more sputum than normal subjects. However, Matthews
515
et aj.. have determined the chemical composition of tracheobronchial secre-
tions from "normal" laryngectomized patients. The composition, per 100 g wet
weight, was found to be as follows: water, 94.79; protein, 1.000; carbohy-
drate, 0.951; ash, 1.13; DNA, 0.028; and lipid, 0.840. Most likely, the DMA
and lipids are derived from disrupted cells, such as degenerated bronchial
epithelial cells.
The major macromolecular components of tracheobronchial secretions are
glycoproteins. These long chain molecules consist of small polysaccharide
272
units glycosidically linked to a protein core. The polysaccharides consti-
tute about 40% of the molecular weight of the glycoprotein. The basic
188
-------
oolvsaccharide unit in human bronchial qlycooroteins is comoosed of qalactose,
N-acetylqlucosamine, and N-acetylqalactosamine. This unit is attached to the
polyoeptide chain. Superimposed upon this basic structure are fucose and
46
either N-acetylneuraminic acid, sulfate qroups, or both. The relative
amounts of these three moieties serve as a basis for the classification of
tracheobronchial qlycoproteins into three specific groups: fucomucins,
sulfomucins, and sialomucins. The fucomucins are neutral or very weakly
acidic glycoproteins characterized by a richness in fuco.se. Both the sulfo-
mucins and sialomucins are acidic glycooroteins, the former beinq rich in
sulfate and the latter characterized by a high amount of N-acetylneuraminic
acid. Histochemical analysis of mucous glands has resulted in the further
639
separation of the sulfomucins and sialomucins into two qrouos each; these
four types of acidic glycoproteins display a specific pattern of distribution
430
within mucus-secreting cells.
Other macromolecular constituents of tracheobronchial secretions are
408,511
immunoglobulins, primarily IgA oroduced locally in the mucosa, lacto-
652
ferrin, lysozyme, and kallikrein.
Normally, tracheobronchial secretions (350 milliosniol) are moderately
hyperosmotic to serum (290 milliosmol). An average electrolyte composition
(mq/1,000 g of water-soluble material) is sodium, 211; chloride, 157; potassium,
617
16.6; and calcium, 2.45.
Tracheobronchial secretions exhibit anomalous flow characteristics and
do not behave like simple fluids, such as water. Rather, mucus exhibits the
rheological phenomenon of viscoelasticity, which implies both fluidlike and
solidlike behavior. This viscoelastic behavior is probably caused by the con-
476 409
stituent glycoprotein molecules. Reiser-Nielsen demonstrated that mucous
189
-------
glycoproteins exhibit elastic properties under rapid stretch conditions and
viscous properties under slow stretch. These phenomena are characteristic of
viscoelastic materials. Tracheobronchial secretions are very shear sensitive.
That is, a reduction of viscosity occurs with increasing shear rates. This
type of behavior is known as shear rate thinning or thixotropy. It may be due
to an alignment of the glycoprotein molecules under the shear force with the
result that the viscous resistance between adjacent layers of molecules
594
decreases.
Respiratory Cilia
The beating cycle of each respiratory cilium consists of a fast, rigid ef-
fective stroke in one direction and a slower, limp recovery stroke in the oppo-
site direction. The effective stroke in the marnmalian resoiratory tract takes
47,339,541
from one-third to one-fifth of the time required for a complete cycle.
The beat frequency of mammalian respiratory tract cilia has been estimated to
34,339,541
be1 between 700 to 1,200 beats/min.
Rows of cilia do not beat synchronously. Rather, each cilium beats shortly
after the cilium in front of it, and before the cilium behind it. Because of
this metachronous rhythm, the overall ciliary activity creates an impression of
a wave travelling over the epithelial surface in a direction opposite to that
of the effective stroke of the cilia.
The exact mechanism controlling ciliary rhythm and coordination in mammals
103
is not known. Postulated mechanisms include local chemical control, similar
290
to the action of serotonin as a ciliary pacemaker in mollusks. Some inves-
705
tigators have suggested coordination by mechanical coupling, in which
rhythmical contact between adjacent cilia maintains a constant beat frequency.
704,705
A neuroid control mechanism has also been proposed. In this mechanism,
190
-------
a buildup of excitation in a pacemaker cilium determines the frequency of
beat. The other cilia beat at constant intervals thereafter as a result of
conducted impulses. However, this innervation of cilia in vertebrates has
290
been demonstrated only in the frog palate.
The energy for ciliary beating is supplied by the dephosphorylation of
adenosine triphosohate (ATP). The bending of the cilia is caused by the sliding
664
of filaments against one another.
Mucociliary Interaction
In their studies of ciliary activity and nasal clearance in maninals, Lucas
492
and Douglas noticed that under some conditions, while the cilia were vigor-
ously beating, the overlying secretory blanket did not move. Thev also ob-
served that a particle in the fluid surrounding the cilia could be propelled
beneath a stationary top fluid layer. They suggested that the total secretory
blanket was actually composed of two parts: a layer of low density, serous-tyoe
fluid (sol), which surrounded the beating cilia, and an overlying highly viscous
mucus layer (gel), which floated on top of the watery fluid and rested on the
tips of the cilia. In this model, flow results from the application of shear-
ing forces on the top fluid layer. More recent studies involving a mechanical
49,540-542
analogue of the mucociliary system indicated that optimum fluid
flow occurs only when a viscoelastic (gel) fluid layer lies above the tips of
the beating cilia.
The source of the fluid in the sol layer is unknown. Suggestions include
492 492
serous cells, intercellular fluid that oozes onto the epithelial surface,
414 526 273 210,415 576
alveoli, brush cells, bronchioles, and Clara cells. Negus
believes that both the sol and gel layers may have the same sources and that
191
-------
the two distinct layers are formed when the pressure exerted by ciliary action
on the gel mucus causes liquefaction of the layer in which the cilia beat.
Specific interplay between the cilia and the mucus blanket seems to be in-
volved in effective mucus clearance and particulate transport since ciliary
beating alone may not be enough. For example, although beating continues for
long periods after the death of laboratory animals under various adverse con-
180
ditions, particulate transport by the mucociliary system becomes irregular
338
and may even stop.
The production of effective fluid movement requires the "coupling" of cilia
to the overlying mucus layer. This may occur through the elastic properties of
475
the gel layer. It is effectively coupled with the sol layer whose flow is
650
induced by the beating cilia. Computations from a mathematical model of
73,651
the mammalian mucociliary system indicate that, although changes in
the serous (sol) fluid viscosity would significantly affect transport rate,
moderate changes in mucus (gel) viscosity would not.
658
Sade et al. have suggested that there is a minimum amount of mucus
necessary for transport. Under conditions of mucus depletion, particulate
clearance did not occur but the cilia continued to beat. This lack of partic-
late clearance was attributed to the failure of the mucous secretions to get
above the tips of the cilia. The renewed particulate clearance, which occurred
upon the addition of more mucus to the system, indicated the need for this
'- s
"coupling" mucus to be present above the ciliary tips. Sade and his colleagues
tried various solutions as substitutes for mucus on the mucus-depleted, ciliated
palates of frogs and toads, but no particulate transport occurred. However, in
further investigations, they identified some synthetic materials that restore
274,416
effective particle transport. The requirement for mucociliary transport
192
-------
is probably theological, rather than chemical. The substances that were
chemically dissimilar to mucus and also capable of sustaining transport were
all lightly cross-linked macromolecular systems like the mucus glycoproteins.
A possible further explanation for the specificity of mucus has been oro-
657
posed by Sade and Eliezer. The presence of very high molecular weight
substances in the small interciliary spaces might impede the ciliary rhythm
because of viscous forces. No viscous mucus in the interciliarv spaces of the
657
mucociliary system of the ear was observed. Microscopic examination re-
vealed that mucus passed from the goblet cells directly to the overlying mucous
657
blanket in narrow streams. This has also been observed at the mouths of
299
mucous glands.
Mucociliary Clearance Rates
The rate of mucus transport is dependent on both the motility of the respi-
ratory cilia and the physical and chemical properties of the mucus. Various
in vitro and in vivo techniques have been used to determine mucus transport
rates in many species. The reported transport rates differ greatly. Much of
this variability can be attributed to experimental artifacts. In jin vitro
preparations, it is unlikely that the thickness or composition of the mucous
layer can be maintained at normal physiologic levels. Most _ijn vivo animal
preparations and some human studies are also suspect, since they involved the
use of anesthetics and/or other drugs that could affect mucociliary transport.
In vitro preparations of the lining of the buccopharyngeal mucosa of frogs
SO
have shown mean transit rates ranging from ~ 21 to 40 mm/min. Mean rates
331
for other species are listed in Table 7-1. Iravani and Van As found the
mean mucus transport rates in _in vitro preparations of rat airways to increase
from ~0.4 mm/min in oreterminal bronchioles to 11.5 mm/min in the upper part of
193
-------
TABLE 7-1
Mean Transport Rates of In Vitro Tracheal Preparations
Animal
Cat
Cattle
Chicken
Dog
Monkey
Rabbit
Rat
Rate, ram/min
36.1
10.0
15.0
33.1
36.1
21.0
24.6
3.1
20.9
Reference
«tl2
18
10
112
112
112
112
66
112
NOTE: The discrepancies in the rates for cats and rats are real
and have not been adequately explained. Such differences
are not necessarily surprising, based on the discussion
in the text.
194
-------
41
the lobar bronchi. Using excised dog lunqs, Asmundsson and Kilburn found
mucus flow rates to average 17.6 mm/min in the trachea, 8.3 in the lobar
34
bronchi, 4.0 in the segmental bronchi, and 1.6 in distal airways. Andersen
reports that the mean tracheal transoort rate in the rabbit is 2.5 mm/min, on
the basis of both in vitro and in vivo measurements; however, his ir± vivo mea-
surements were complicated by the fact that the tracheal segment measured was
separated from the more distal airways.
ID. vivo mucus transoort rates in the lungs of various species have also
been studied. Transoort rates averaged 22 mm/min on the major longitudinal
414 48
ridge of the bullfrog lung. Barclay and Franklin found the average trans-
port rate to be 2.5 mm/min in the small bronchioles of rats and 10 mm/min in
the trachea. Table 7-2 compares in vivo transport rates for several species.
557
Morrow et al. estimated that mean transoort rates in humans were 14
mm/min in the trachea, 1 mm/min in the upper bronchial tree, and 0.4 to 0.6 mm/
min in the lower tree. At these rates, bronchial clearance would be completed
within approximately 3 hr. Mucus transport in the trachea of 42 unanesthetized,
837
healthy nonsmoking adults was studied by Yeates et al. Boluses of radio-
active microsoheres were transported in the trachea at discrete but constant
rates. The coefficient of rate variation in an individual over the period of a
few hours was 25%. There was a large interindividual variation: the 95% limits
of the geometric mean velocities were 0.8 and 10.8 mm/min (coefficient variation
75%). The geometric mean tracheal transport rate for the population studied was
3.6 mm/min. Repeat studies on 22 subjects showed that the variation within
663
individuals was less than between individuals. Santa Cruz et al. reported
a mean tracheal transport rate in humans of 21.5 mm/min, but this value may
195
-------
TABLE 7-2
Mean In Vivo Transport Rates in the Trachea
Animal Rate, mm/min Reference
Cat 15 127
Dog Ik 505
Donkey, unanesthetized 12-15 12
Rat 10 *8
22
13.5
196
-------
be influenced by the orior application o£ xylocaine and/or the presence of
a bronchoscope for visualization of the surface flow.
Although the in vivo transport rate in humans cannot be measured in smaller
ciliated airways, the total duration of bronchial clearance can be measured.
14
Albert et al. reoorted that a 90% completion of bronchial clearance among non-
smoking healthy subjects occurred anywhere from 2.5 to 20.0 hr, with an intra-
subject variability of 30%. Because particles of 2 urn dia are oresumably deoos-
ited in more distal ciliated airways than 6 urn particles, they require consid-
erably more clearance time. Therefore, the transport rates aooear to decrease
557
distally. Calculations by Morrow et al. suggest the rates in terminal
835
ciliated airways to be 100 ym/min, while calculations by Yeates suggest
1 wn/min.
Physiologic Alterations in Mucociliary Transport Rates
Mucociliary transport is controlled by cellular mechanisms in the epi-
thelium, the sympathetic and oarasymoathetic nervous systems, as well as by
environmental and other factors. Evidence indicates that goblet cells in cats
246
are not under neural control but are stimulated by local irritation. Symna-
thomimetic drugs have had varied effects on cilia beating rate and mucociliary
42 122
transport in the animal models used. However, in humans, terbutaline,
251 251
isoproterenol, epinephrine, and Thll65a (a svmnathomimetic broncho-
837
dilator) increase transoort. ParasymDathomimetic drugs also speed muco-
121
ciliary clearance in man. Parasymoatholytic drugs decrease mucus trans-
42 "251,601,837
oort in animals and, for several hours, in humans. They orobably
42
also decrease ciliary beating. Reversibility of atrooine effects was demon-
251
strated when isoproterenol aerosol was given subsequent to systemic atrooine.
197
-------
In studies where adrenerqic drugs were administered as aerosols, a small but
significant part of the clearance acceleration was attributable to the water
251
in the droplets.
Effects of Pollutants on Mucociliary Transport
Cigarette Smoke. Reported effects of smoking on mucociliary transport are
42
confusing due to the wide variation of effects of tobacco smoke on animals.
In humans, the immediate response to the smoking of several cigarettes has been
14,15,119,837
either an increase in tracheobronchial clearance or no effect.
In the donkey, short-term exposures to fresh, whole smoke from two cigarettes
12
accelerated clearance, but exposures to the whole smoke from 10 or more cig-
12
arettes, or the filtered smoke from 20 or more cigarettes impaired clearance.
15
When an increase in transport occurs, it is greatest in the small airways
probably because of the adrenergic stimulation caused by tobacco smoke.
Chronic smoking appears to have a more variable effect on mucociliary
transport. This is due to the variations in dosage and to the different degrees
of individual susceptibility to tobacco smoke. Studies of these effects have
been quite diverse, and the number of subjects studied has been small. Yeates
837
et al. have shown that tracheal transport rates were within normal limits
in nine smokers studied. Although rapid clearance occurs in some long-term
13,77,118,
smokers, impairment of large airway clearance has also been observed.
485 600 754
Pavia et al. and Thomson and Pavia were unable to demonstrate any
effect caused by long-term smoking. Cigarette smoking causes disease in the
13
small airways. Albert et al. showed that some heavy cigarette smokers had
long overall bronchial clearance times that could be interpreted as slow
clearance in small airways. Clearance observed in smokers 3 months after
198
-------
120
cessation of smoking was faster than during the smoking period. Chronic
high-level exposure to cigarette smoke has severely impaired bronchial clearance
10
in the donkey but recovery after cessation of exposure was almost contDlete
within a few weeks.
Sulfur Oxides. In vivo exposures to sulfur oxides at ambient concentra-
tions are not likely to affect mucociliary clearance. At higher concentrations,
more typical of some occupational exposures, effects have been observed. Vfolff
828
et al. exposed nine nonsmokers to 5 ppm (13 mq/m3) of sulfur dioxide for
3 hr after an aerosol exposure to albumin tagged with 99nvTc, a gamma-emitting
radionuclide. The tracheobronchial mucociliary clearance of the tagged aerosol
was essentially the same as in control tests except for a transient speedup at
1 hr after the start of the sulfur dioxide exposure. Further tests by Wolff
827
et al. show that exercise accelerates bronchial clearance, and 13 mg/m3
(5 ppm) of sulfur dioxide during exercise significantly speeds clearance beyond
that produced by the exercise alone.
Higher concentrations of sulfur dioxide can slow bronchial clearance.
Donkeys exposed for 30 min to sulfur dioxide via nasal catheters exhibited de-
layed bronchial clearance, severe coughing, and mucus discharge from the nose
718
at concentrations exceeding 785 mg/m3 (300 ppm). Mean residence times
following exposures to 139 to 785 mg/m3 (53 to 300 ppm) were not significantly
different from those at control test concentrations. The one test performed
at a lower concentration produced an acceleration in bronchial clearance, which
827,828
would be consistent with the clearance accelerations seen by Wolff et al.
with 13 mg/m3 (5 ppm) exposures. These results (acceleration at low concentra-
tions and slowing at higher concentrations) are similar to those produced by
cigarette smoke.
199
-------
223
Fairchild et al. showed that hiqh concentrations of sulfuric acid
mist, e.g., 15 mg/m3 with a median diameter of 3.2 ym administered for 4 hr
after tagged streptococcal aerosol exposures, reduced the rate of ciliary
clearance from the lungs and noses of mice. At mist concentrations of 1.5
mg/m3 with a median diameter of 0.6 vim, there were no significant effects.
Inert Particles
114
Camner et al. have conducted the only study of the effect on human
mucociliary clearance of an acute exposure to high concentrations of oarticu-
lates. They studied eight subjects exrx>sed to 20 breaths of 11 vim dia carbon
particles at a concentration of 50 g/liter. These exposures produced either
no effect or only a slight increase in mucociliary transport, presumably in
large airways.
Mucociliary Transport and Lung Disease
The tracheobronchial tree can be subdivided into four subregions: the
larynx, the trachea, the large airways, and the small airways. Each subregion
is susceptible to viral and bacterial infections as well as other disease
processes that could either cause or be caused by oerturbations in mucociliary
clearance. Cancer of the larynx and large bronchi could be due either to the
greater surface deposition of particles, to long residence times in these
regions, or to a combination of both. Small airways are orobably more sus-
ceptible to chronic obstructive lung disease involving mucus gland hypertroohy,
goblet cell hyperplasia, bronchoconstriction, edema, and airway closure. The
relationships between mucociliary transport rates in the trachea and in the
large and small airways, as well as the relationshio of these rates to disease
processes, remain unknown.
200
-------
Numerous i.n vitro and _in vivo studies indicate that the mucociliary sys-
tem can transport Particles of a wide ranqe of sizes (from < 1 wn to > 500 mi
dia) and types (charcoal, soot, lycopodium spores, cells, 680 ym dia teflon
discs, ion exchange resins, and iron oxide, protein, polystyrene, and teflon
spheres). Whether all these types of particles are removed as effectively
in each of the various ciliated reqions of the human respiratory tract has
not been established.
The carinas of the larger airways apoear to be particularly vulnerable to
337
the accumulation of inhaled particles. Hilding suggested that this is due
673,674
to ciliastasis in these carinal areas. Schlesinger et al. and Bell
61
and Friedlander have shown that carinas are also sites of enhanced particle
deposition. However, the relative roles of deposition pattern and mucociliary
clearance rate in the ability of toxic substances to cause cellular damage or
transformation has not been delineated.
Defects in passive mucociliary particle transport may be important in the
pathogenesis of lung disease. In addition, particles with biologic activity,
such as bacteria, can be inactivated by the immunologic and enzymatic activity
of the fluid lining the lung, by alveolar macroohages, and by other free cells
on the lung surface. Investigators studying tracheobronchial clearance in pa-
13,117,486,493,516,744,754,779,338
tients with chronic lung diseases have reported
transport to be faster, similar, and slower than transport in healthy subjects.
The rapid disappearance of deposited aerosol in some patients was probably
aided by more proximal deposition patterns 'and/or to coughing by which mucus
117,835,838
is eliminated from the diseased lungs. Faster transport can also
result from an increase in mucus secretion. Studies of subjects for whom con-
trol data are available indicate that poor mucociliary transport could result
201
-------
115,116,659
from infections that cause damage to human ciliated epithelium in
361
culture. (In these acute studies major hypertrophy of mucous glands could
not be expected.) This resultant defective transport may be one of the reasons
why patients with lung disease are more susceptible to insults from inhaled
pollutants.
The significance of the wide range of tracheobronchial clearance rates
found in apparently healthy subjects is not known. It has often been supposed
that slow clearance in a healthy subject is detrimental. It may be beneficial
if they have a greater reserve capacity for coping with increased secretions.
The mucociliary system can probably cope with a considerable increase in
secretions above the normal baseline level, but the relationship between mucus
volume transported and the surface transport rates is not known. Refluxing of
835,837,838
mucus could occur when mucus becomes too thick for the cilia to
propel or when there is an excessive loss of cilia, which has been observed
380
in bronchitic rats. Refluxing mucus in the trachea can be cleared by
835,838
coughing in contrast to healthy nonsmoking adults in whom cough appears
837
to have little effect. Coughing is not expected to have as much effect in
small airways although this has not been demonstrated.
The nature of the protective barrier of mucus that the airways present to
inhaled toxicants is altered in disease. This has been shown in bronchitic
, 180 380
rats by Dalhamn and Iravani. Comparisons of mucoid mucus from patients
with hypersecretory conditions such as chronic bronchitis, bronchiectasis, and
431
cystic fibrosis have produced few differences, either histochemically or
145,224,745
Theologically. However, purulent mucus from diseased subjects
515,616 194
had altered biochemical and rheological properties.
202
-------
299,539,640
The study of mucous glands and their hypertrophy has been of
major importance in understanding the pathogenesis of chronic bronchitis and
639
chronic obstructive pulmonary disease. However, Reid only measured gland
to wall ratios and not the physiologically important parameters of gland
volume/airway circumference and gland volume/lumen size. Some work using this
59
latter parameter has been reported by Bedrossian et al.
The proposed sequence of events leading to chronic obstructive oulmonary
14
disease is similar to that suggested by Albert et al. Acute exposures to dust
increase mucus production and mucociliary transport. Continuation of these
exposures leads to bronchial mucous gland hypertrophy and goblet cell hyper-
plasia. Mucus transport in small airways could remain normal or increase
during this stage. As gland hypertrophy continues, the mucociliary transport
system becomes inadequate in removing the excess secretions. This leads to
chronic cough, accumulation of secretions, and increased susceptibility to
inhaled particulates, noxious gases, and pathogenic organisms.
In summary, oarticulate atmospheric pollutants may be involved in chronic
lung disease pathogenesis as causal factors in chronic bronchitis, as predis-
posing factors to acute bacterial and viral bronchitis, especially in children
and cigarette smokers, and as aggravating factors for acute bronchial asthma and
the terminal stages of oxygen deficiency (hyooxia) associated with chronic
bronchitis and/or emphysema and its characteristic form of heart failure (cor
pulmonale).
Indirect Indicators of Mucociliary Transport Abnormalities
In addition to the direct measurement of the effects of particles on muco-
ciliary transport, there are other indices from which changes in mucociliary
203
-------
transport may be inferred; namely, sputum production, alterations in pulmonary
function, and pathologic abnormalities.
Epidemiologic studies of a qroup of men showed l±iat phlegm production de-
creased concomitantly with the reduction of airborne particulates despite little
7.14
change in sulfur dioxide concentrations. Another study indicated that con-
centrations of particulates, not sulfur dioxide, were related to decreased
226 490,491,785
pulmonary function. Lowe and his colleagues found little such
correlation. The detrimental effects of particulate sulfates on lung function
are discussed in Chapter 8.
A number of studies indicate that inhalations of very high concentrations
of inert dusts can result in increased airway resistance caused by bronchocon-
161,203,675 810
striction. Carbon dust stimulates both couqh and irritant
689
receptors thereby increasing vagal afferent activity in cats. This activity
385
is probably mediated by the nerves in the epithelium (Jeffery and Reid ) and
and may be responsible for the increased mucociliary transport mentioned above.
A few investigators have studied the gross pathology of the bronchial
mucosa after inhalation of dusts. Negative findings do not necessarily mean
that the mucosa is functioning normally. But these studies do indicate the
kind of damage that dusts can cause to the mucociliary transport system.
A six-week exposure of piglets to cornstarch or corn dust produced no
510
"significant" lesions within the respiratory tract nor were bronchial
501 670
lesions reported in monkeys exposed to fly ash for 18 months. Schiller
exposed dogs and rats to coal dust. After three years hypertrophy of the
epithelium and goblet cells had developed but no pneumonoconiotic lesions,
connective tissue reactions, or cellular infiltrations were evident. Animals
exposed for six years incurred atrophic epithelium partially denuded of cilia
204
-------
and formation of diqitate appendices probably consisting of apocrine secretion.
Intratracheal injections of silica dust in rats caused obliteration of the
298
respiratory bronchioles.
305
Hadfield studied the nasal epithelium of workers in the furniture
industry who had been exposed to wood dust. She reported adenocarcinoma
at the ethmoid sinuses, squamous metaolasia of the mucous membrane covering
the anterior ends of the middle turbinates, vasomotor rhinitis, and allerqic
nasal palpi.
ALVEOLAR CLEARANCE
Mechanisms
Once a material is deposited on the respiratory eoithelium of the alveoli,
both "absorptive" and "nonabsorptive" clearance processes ensue. Neither term
explicitly describes the pulmonary transport that occurs. *tost likely, both
processes occur together or with temporal variations.
Respiratory absorption from a mechanistic point of view is poorly under-
554
stood, but evidence exists for both passive and active transport mechanisms.
Collectively, these processes bring about an apparently unique and selective
147
permeability for the respiratory epithelium, vis-a-vis other epithelia. Per-
meation of the alveolar epithelium precedes both lymphatic transport and uptake
into the blood. Thus, both pathways also require the Penetration of an
endothelial barrier, which is generally more variable and permeable than the
553
epithelial surface.
In the "nonabsorptive" category, materials may become "fixed" within the
parenchymal tissue. Such depots may contain chemically or physically altered
material or material that has been concentrated by cytologic and/or Physio-
logic processes. These depots often appear to undergo very little clearance
205
-------
by nonabsorptive processes, but it is conceivable that both the normal turnover
of cells and endocytosis affect their persistence.
The most widely accepted "nonabsorptive" clearance mechanism is the trans-
port from the lungs of alveolcir macrophages that have phagocytosed particles.
Many investigators have studied the role of alveolar macrophages in dust
84,225,242
clearance as well as such other functions as their maintenance of
291
alveolar sterility and their etiologic significance in oulmonary disease.
Methods used to evaluate the macrophage response quantitatively include "free-
84,428
cell harvests" by endobronchial lavage and histologic examinations of
242
alveolar tissue. Despite the common acceptance of phagocytosis and subsequent
cell removal as the dominant nonabsorptive clearance mechanism, it has, so far,
defied quantification.
The clearance pathways for phagocytosed particles remain controversial.
It is generally agreed that macrophages ingest particles and transport them
proximally on the bronchial tree to the pharynx where they are swallowed.
There is considerable disagreement concerning which pathway is predominant
between the alveoli and the bronchial tree. There are proponents for an inter-
stitial route, while others favor a continuous, proximally moving surface film
that draws the cells onto the ciliated surface at the terminal bronchioles.
93
The interstitial route was proposed by Brundelet on the basis of micro-
scopic sections of rat lungs containing dye particles. He suggested that
particle-laden alveolar macrophages migrated onto ciliated airways through
292
lymphoid collections at the bifurcations of bronchi and bronchioles. Green
reported similar observations for macrophages containing coal dust. He oro-
posed that alveolar fluid, cells, and particles flow within "liquid veins"
between alveoli. This fluid flow is driven by the variation in tension created
206
-------
by respiratory movements in the alveolar walls. This moves the fluid from the
midzone of the lobule toward areas of least pressure adjacent to subpleural,
761
paraseptal, and peribronchial lymphatics. Tucker et al. reported that bare
particles (those not ingested by macrophages) follow this clearance route in
the first few hours following dye particle inhalations.
503
The surface route was proposed by Macklin, favored by Hatch and
319 225
Gross, and supported by Ferin's studies. Ferin exposed rats to titanium
dioxide at low concentrations (15 and 100 yg/m3) that were representative of
air pollution. He studied lung sections of rats killed at 1, 8, and 25 days.
Particle-laden macrophages were concentrated in alveolar ducts and at junctions
of respiratory and terminal bronchioles. A very small fraction was found in
93 292 761
lymphatics. The studies of Brundelet, Green, and Tucker et al. involved
much more massive exposures, which may have induced a change in the normal
pathway.
Forms of endocytosis such as pinocytosis cannot be easily differentiated
from true absorption, inasmuch as they both may result in transmembrane trans-
port of material. Thus, any description of an "absorptive" process that cannot
be precisely localized and made on a mechanistic basis must be considered
tentative and uncertain both as to the number and types of transport mechanisms
operating. Consequently, "absorptive" clearance of inhaled materials from the
alveolar surface is largely based on, or inferred from, the ultimate disposition
of the material, especially its appearance in the blood, other body organs, and
the urine.
Bona fide absorptive mechanisms and oathways have been established for
specific materials in the alveolar membrane. Specific information on alveolar
147
absorption mechanisms comes mainly from the studies of Chinard, Taylor
207
-------
750 464 64
et al., Liebow and Bensch and Dominquez. Other relevant data, generally
556,737
lacking mechanistic information, are available on specific materials.
Many of these lung absorption studies and the investigations of alveolar clear-
554
ance were the subjects of a recent review. An important component of
"absorptive" clearance is solubilization that either precedes or is a part of
true absorption. In other words, absorption presumably depends on materials
being either monomeric or, to a lesser extent, polymeric forms of small
554
dimension. The significance of solubilization as a principal clearance
mechanism in the alveolar region has been brought into focus by the success of
533,556
several simple, solubility models. Solubility must presently be con-
sidered the most important "absorptive" process.
Kinetics
The clearance of particles from the alveolar region proceeds in several
phases. These phases can, usually be described by a series of exponentials,
each of which presumably corresponds to a different clearance mechanism.
128
Casarett proposed that the earliest alveolar phase, with a half-time
measured in weeks, is generally associated with phagocytic clearance, while a
slower phase, with a half-time in months or years, is generally associated with
749
solubility. The ICRP Task Group model does not include the initial alveolar
phase. Casarett attributes this omission to overreliance on data from studies
in which the "fast" alveolar phase was absent because of the cytotoxicity of
384
the dusts used. Jammet et al. showed that for hematite dust, a clearance
phase with a half-time of from 10 to 12 days, is normally present in the cat,
rat, and hamster preceding a slower phase with a half-time exceeding 100 days.
The 10- to 12-day phase disappeared when the animals were exposed to toxic
208
-------
578 452
amounts of plutonium, silica dust, or carbon dust, while the half-time
for the slower phase remained relatively unaffected.
Numerous inhalation studies have been performed <>n beagles with insoluble
radioactive aerosols, with long-term follow-up of the lung retention bv ex-
45,173,241,559
ternal HI vivo gamma counting. In most, but not all, of these
studies, a fast phase with a half-time of 10 to 14 days was evident. The half-
life for the slower phase of alveolar clearance, which appears to be related
559
to _in vivo solubility, is quite variable. Morrow et al. used test aerosols
of ferric (59Fe) oxide, mercury (203Hg) oxide, barium (131Ba) sulfate, manga-
nese (5l|Mn) dioxide, and uranium dioxide. The biologic half-time for the slow
alveolar clearance phases were 58, 33, 8, 34, and -200 days, respectively.
45
Bair and Oilley found the slow phase of alveolar clearance of ferric ( Fe)
oxide to be greater than several hundred days, suggesting that the surface-
volume ratios or other surface prooerties of the particles can have a major
effect on dissolution in the lung.
Because alveolar retention of relatively insoluble particles is recognized
to be important to the pathogenesis of chronic lung disease, it is surprising
that the literature yields virtually no useful data on the rates or routes of
alveolar particle clearance in man. This paucity of data is attributable to
the laboratory sophistication required and the relatively high cost incurred
in human studies. The only feasible way to perform such studies is to have
the subjects inhale tagged test aerosols. The subsequent lung retention can
then be monitored with external detectors. In addition, the types and varieties
of particles that can be used in human studies are limited. For examole, only
demonstrably nontoxic particles can be intentionally inhaled.
The only laboratory studies of human alveolar clearance were conducted by
11 557,558
Albert and Arnett and Morrow et al.
209
-------
LI
In the Albert and Arnett study, eight healthy human males inhaled
neutron-activated metallic iron particles. Three subjects had sufficient
residual activity after completion of bronchial clearance for continued mea-
surement of retention. In a 32-year-old male nonsmoxer and a 27-year-old male
moderate smoker, the postbronchial clearance occurred in two phases—a "fast"
phase lasting about one month and a much slower terminal phase. The faster
phase was missing in a 38-year-old male two-pack-a-day cigarette smoker with
chronic cough. Although firm conclusions cannot be drawn from these limited
data, they do suggest that the "fast" alveolar phase can be detected in man,
and that dust retention may be increased by cigarette smoking (beyond the
retention of the smoke particulates themselves).
The only other studies of human alveolar clearance under controlled con-
ditions are those of Morrow et al. In an initial study, four healthy human
subjects inhaled a manganese (5LfMn) dioxide aerosol with a median diameter of
0.9 pm, a geometric standard deviation of 1.75, and a mass concentration of
558
4 mg/m3. The aerosol was inhaled for 20 to 30 min. The breathing pattern
consisted of four normal inhalations alternated with one maximal inhalation.
Measurements made more than 48 hr after the inhalation indicated a single
clearance phase in all four individuals, with biologic half-times varying
from 62 to 68 days.
557
In their other human studies, Morrow et al. used several different
aerosols and again reported alveolar clearance rates in terms of a single
exponential. The half-times varied with the composition of the particles used.
Half-times of 65, 62, and 35 days were found for manganese ( Mn) dioxide,
ferric oxide labeled with chromium-Si, and chromium-51 labeled polystyrene,
respectively. The measurements indicating the shorter half-time for the
210
-------
polystyrene particles were based on <14 days. Consequently, they may have been
influenced by a rapid initial rate of alveolar clearance in contrast to the
iron and manganese oxides, which were followed for 45 to 120 days.
Scattered data on human lung retention of inhaled oarticles exist in re-
ports of in vivo measurements in atomic energy industry workers who had been
241,301,654
accidentally exposed to airborne nuclides. While these data are
interesting and useful for some evaluations, they must be interpreted with
their significant limitations in mind. Among these limitations are:
• the time the exposure took place is either not known, or it extended
over an indeterminate period before it was discovered;
• the chemical form and particle size distribution of the inhaled aero-
sol are usually not known, and the exposure may be to more than one
aerosol and/or nuclide; and
• because the exposure may be detected from routine bioassay or in vivo
counting long after the exposure, it may be impossible to establish
the initial amount deposited.
For Atmospheric Aerosols
The foregoing suggests that a wide range of alveolar clearance rates in-
volving both absorptive and nonabsorptive processes acply to atmospheric
particulate matter. The special character of atmospheric aerosols, especially
their enormous surface area and large surface-free energy, might result in
higher reaction and dissolution rates for a given chemical species than would
be estimated from conventional laboratory aerosols or industrial dusts.
Occupational and laboratory studies of aerosols are limited in their abil-
ity to predict the biologic behavior of atmospheric aerosols. The generally
211
-------
small particle size and other characteristics of atmospheric aerosols are
difficult to simulate in the laboratory. For example, the biologic effects of
atmospheric dust may depend in large measure on synergistic actions with other
428
airborne pollutants. The generally accepted view of synergism extends
beyond potentiation to include the role of toxic vector. Such gases as sulfur
dioxide are probably either adsorbed to the particulate surface or absorbed
into the particles, and thereby transported into the alveolar regions where
they exist in high, localized concentrations. These localized high concentra-
tions could not be produced without particles. Accordingly, sulfur dioxide
sorption to particulate matter might effectively allow sulfur dioxide penetra-
tion into the alveolar regions at even nominal environmental concentrations
of the gaseous pollutant. This possibility has been widely cited by those who
believe atmospheric concentrations of sulfur dioxide and particulate matter
are associated with adverse health effects.
212
-------
CHAPTER 8
EFFECTS OF SULFUR DIOXIDE AND AEROSOLS, ALONE
AND COMBINED, ON LUN3 FUNCTION
Inhalation toxicology plays two important roles: to describe the struc-
tural, biochemical, and functional effects of air pollutants and to reveal the
mechanisms underlying these effects. A diversity of experimental models are
used, ranging from subcellular and cellular elements to intact animals or
human subjects. There is a natural inclination to extrapolate the results
from experiments on in vitro preparations or animals to predictions of ill
effects in large populations. Such extrapolations have a strong element of
uncertainty that should be recognized. The attempt at extrapolation becomes
more convincing if the experimental results can be demonstrated in more than
one mammalian species, especially in primates, and if the biologic systems
under study have close analogues in humans.
The types of exposure used in inhalation toxicology may mimic either
intense and brief or low-grade and prolonged episodes of pollution; both are
typical of urban centers. Often, experimental pollutant concentrations must
exceed ambient concentrations to be effective. At least two factors may be
responsible. One is that these models of air pollution are relatively simple
approximations of the complex, highly variable, and incompletely defined pol-
lution that is found outside the laboratory. Ill effects in communities may be
due to the cumulative action of many pollutants or to the interaction between
pollutants and other forms of environmental stress. Therefore, no single com-
ponent need be excessively high. Secondly, the most certifiable effects of
pollution are seen in Persons already ill with cardiopulmonary disease. It
213
-------
is difficult to simulate such disease in animals, and there are ethical and
legal restrictions to the use of patients with these diseases in laboratory
experiments. When human volunteers are studied, the exposures must of necessity
be relatively short and the effects must be baniqn and completely reversible.
Such considerations do not limit research on animals, but higher than ambient
concentrations must be administered to oroduce effects of sufficient severity
for a successful investigation.
This chapter concerns the effects of inhaled aerosols on lunq function.
Particular emphasis is given to sulfur oxide aerosols that are found in general
or community pollution and to studies involving realistic concentrations of
them. Pollens and aerosolized drugs, such as histamine and methacholine
chloride, which are potent bronchoconstrictors, and the great variety of aero-
sols found in occupational settings will not be discussed. Two of the largest
groups of aibient aerosols are the sulfates and nitrates. Each may be emitted
directly in a variety of combustive processes or may arise by chemical reactions
in the ambient atmosphere. Of the two groups of compounds, the sulfates have
prompted greater experimental interest and activity. (See the recent, comore-
573
hensive review on nitrogen oxides. ) Sulfur dioxide, the gas chiefly re-
sponsible for the genesis of sulfate aerosols, will also tie discussed.
?vfter a brief discussion of the effects of sulfur dioxide on the respira-
tory system, this chapter proceeds to the effects of aerosols alone and with
sulfur dioxide. The princioal focus will be on mechanical and ventilatory
functions.
Following are some of the functional measurements that are commonly used;
additional methods are requited to assess ventilation-oerfusion relations and
gas exchange:
214
-------
Flow resistance (R ) and compliance (C ) are two mechanical attributes of
L L
the lung. R is determined chiefly by the caliber of the airways, while C
L L
is an index of the size and distensibility of the lung. In animals, R can be
L
subdivided into central and peripheral components by implantation of catheters.
Less direct methods can be used to assess the peripheral airways in human sub-
jects and intact animals. Flow resistance and compliance can be measured over
a range of breathing frequencies as a means of determining the evenness of
distribution of inhaled air.
Forced Vital Capacity (FVC) is the maximal volume of air that can be
rapidly expelled followinq full inspiration. FV3 is that portion of the
i.o
FVC that is expelled during the first second of the procedure. The Maximal
Expiratory Flow Volume curve (MEFV) is a continuous recording of the maximal
expiratory flow rate plotted against changing lung volume. These ventilatory
tests are influenced by the caliber of the airways, size, distensibility, and
recoiling force of the lung and chest wall, muscular strength, and even motiva-
tion. Measurements of ventilatory function have been used from day-to-day to
447,443
assess the effects of environmental changes, including air pollution.
Clearance from the respiratory system is discussed in Chapter 7.
SULFUR DIOXIDE
Because of its ready solubility in tissue fluids, sulfur dioxide is re-
moved almost entirely by the upper airways (the nose, mouth, and Pharynx) during
34,715
quiet breathing. Greater penetration of the gas occurs when inspiratory
255
flow rate increases and gas enters the airways through the mouth. Conse-
quently, exposure of the lower airways (beginning at the larynx) and alveoli
to sulfur dioxide as well as other gases of equivalent solubility is exagger-
ated in exercise when both the ventilatory rate and the degree of penetration
215
-------
54,56
increase. Bates and his colleagues have shown that exercise potentiates
the functional effects of o;;one in human volunteers; to date there have been
no published reports of the effects of exercise on the response to sulfur di-
oxide or to irritant aerosols, although several groups of investigators have
202,236,453,
begun such studies. The vulnerability of children to air pollution
577,696,697
may reflect in oart their great activity while out-of-doors.
The site(s) of uptake of the inspired sulfur dioxide beyond the upper
airways is not known. Of the amount of gas inspired, less than 1% is likely to
reach the alveoli. A preliminary attempt at predicting the sites of uptake of
sulfur dioxide within the lower respiratory tract, and of the consequent dosage
to these sites, is shown in Figures 8-1 and 8-2. Note that sulfur dioxide might
be expected to act principallv on the central and intermediate airways.
Sulfur dioxide alters the mechanical function of the uoper and lower air-
ways in humans and in laboratory animals. Nasal flow resistance may increase
in human subjects exposed to 2.6 mq/m3 (1 ppm at 25°C, 1 atm) of sulfur dioxide
35 715
for 1 to 3 hr; the response is accelerated by higher concentrations. Nasal
mucus flow rate is slowed Dy several hours of exposure to 13.0 mg/m3 (5 pom)
35
of sulfur dioxide, an effect that could imply a reduction in resistance to in-
fection locally. However, the principal effect in acute experiments is to in-
crease pulmonary flow resistance or impair forced expiratory flow rate. The
concentrations of gas required to elicit these responses in subjects at rest
are several times higher than the primary ambient air standard of 0.36
(0.14 ppm) (24-hr average). Although 2.6 mg/m3 (1 opm) may increase R within
L
q
10 min in an occasional sensitive individual, an exposure of about 13.0 mg/m
(5.0 ppm) is reauired to affect a significant oercentage of Jrealthy volun-
253
teers. The forced exoiratory flow rate is slowed after 1 to 3 hr of exposure
216
-------
Kf
S02
VT = 500ml
t = 2 sec
trochea
tobar
bronchi
T~
5
10 15 20
Model segments
—T—
25
FIGURE 8-1. Weibel's generations of airways and respiratory structures791
have been modified to accarroodate the computer model for
estimating uptake. The chemical and physical properties of
water are used to represent the liquid layer lining the
respiratory system. Note that the mass uptake of sulfur
dioxide is virtually complete by the level of the inter-
mediate airways.
217
-------
10
-1_
r2_
to
io~3-
i
§ io'6H
o
10"
0
Dose after first breath
S02
lobar
bronchi
trachea
VT = 500 ml
t = 2sec
I
Q. 2
V) ^.
—I , f—
10 15 20
Model segments
25
FIGURE 8-2.
Sulfur dioxide uptake model for the respiratory system.
From MaJilton et al., 1972.527
218
-------
35
to 2.6 mgAi3 (1 ppm) of sulfur dioxide. When intermittent light exercise is
superimposed on the exposure, maximal expiratory flow rate may be affected by
2.0 mg/n3 (0.75 ppm) of the qas.
The variability in response to sulfur dioxide among different species of
29 26
animals, and within a single species, can be considerable. Amdur has re-
ported that guinea pigs show a statistically significant increase in R (12.8%
Q
£ <0.001) during response to a mean concentration of 0.68 mg/m (0.26 ppm)
(range: 0.08 to 1.7 mg/fa3 [0.03 to 0.65 ppm]). However, earlier data from the
same laboratory reflect a scatter of responses to different gas concentrations
29
that far exceeded this small average change. Another group of investi-
526
gators found no consistent change in R in lightly anesthetized guinea pigs
L
exposed to 2.6 mg/fo3 (1 ppm) of sulfur dioxide for 2 hr; a significant increase
in R^ resulted in response to an identical concentration of sulfur dioxide com-
bined with sodium chloride aerosol.
For reasons that are not understood, the effect of sulfur dioxide on func-
tion may vary considerably in an individual from one exposure to the next. In
several mammalian species the effect of sulfur dioxide on R is limited in
L
time. The effect may begin to recede in humans after about 10 min (10.4 to
252 254
44.2 mg/n3) and even sooner in anesthetized dogs (156 to 559 mg/m3) and
164
cats (65 to 101 mg/m3). By contrast, the change in R- in guinea pigs may be
more or less steady or continue to rise for several hours over a wide range of
23,24
concentrations (5.2 to 879.0 mq/m3). Sulfur dioxide appears to have a more
35 252
sustained effect on nasal mucus flow rate than on R .
L
A notable feature of the experiments involving short-term exposures to
sulfur dioxide is the exaggerated response among a few individuals for which
27
there is no obvious cause. Anriur has reviewed the evidence for a nonallergic
219
-------
"hypersensitive" response to sulfur dioxide in human subjects and test animals.
The studies that she considered relied on measurements to flow resistance.
She defined sensitive quinea piqs as those showing an increase in R more than
L
three times greater than the average change for the group, and sensitive human
subjects as those who resoonded with an increase in flow resistance to a con-
centration of sulfur dioxide that did not evolve anv change in the qroup or
who showed a major increase at a concentration that caused only minor changes
in the rest of the group. Roughly 10% of the humans and animals tested, all
of whom were ostensibly healthy, satisfied these criteria. The mechanism for
the hyoersensitivity is unknown.
Whether such individuals are more prone than the general population to
illness arising from chronic or repeated exposure to sulfur dioxide, or perhaps
to other airborne pollutants as well, is a challenging question.
'he change in R in man and in cats is reflex in origin and can be abol-
L 61,566
isheci by atropine or section of the vagal nerves. The more persistent
change in R in the guinea Dig suggests a different mechanism of effect. For
Hi
example, slow-reacting substance (SRS), histamine, serotonin, or prostaglandin
might be released from damaged tissues and act directly on the smooth muscle
of the airways causing constriction. Other possible mechanisms for narrowing
the airways include swelling of the bronchial wall and excessive or retained
secretions.
Ar intriguing question is whether sulfur dioxide and other inhaled irri-
tants c^n alter mechanical behavior of the lung indirectly. Two such pathways
have been postulated. One is a nasobronchial reflex in which stimulation of
the nasal mucosa chemically, mechanically, or immunologically is said to induce
bronchoconstriction. The action of oollen in asthmatic patients was cited as
220
-------
an example of this pathway by S. Ingelstedt at the Symposium on the Nose and
257
Adjoining Cavities at the Armed Forces Institute of Pathology in 1969. The
afferent pathway for this reflex would be the fifth cranial nerve. It is
arguable whether there is a nasobronchial reflex in healthy individuals leading
35
to bronchoconstriction. Andersen et al. have suggested that the nasobronchial
reflex may account for some of the functional changes observed in healthy
volunteers exposed to sulfur dioxide. Bronchodilation rather than bronchocon-
567,757 16
striction has been observed in cats and rabbits following irritation
of the nasal mucosa. The second, indirect pathway, for which there is less
persuasive evidence, involves the excretion of sulfur dioxide as a gas into the
256
lung, presumably from the pulmonary circulation. Sulfur dioxide originally
enters the blood following absorption in the upper airways.
Additional functional parameters, some directly related to the mechanical
properties of the lung, have been used to assess the irritancy of sulfur dioxide.
In 1953, healthy volunteers who were briefly exposed to 2.6 to 21.0 mq/fa3 (1 to
8 ppm) were reported to respond with rapid, shallow breathing and elevated
30'
oulse rates; similar findings had been reported earlier from the same labora-
31
tory following exposure to sulfuric acid mist. These effects of sulfur di-
253,444
oxide have not been confirmed by other investigators. It is worth
30,31,253,444
noting that all of these studies were performed with the subjects
breathing through fixed mouthpieces. The mouthpiece itself is likely to make
breathing a self-conscious act so that the ventilatory oattern during the mea-
surement often differs from that present with natural breathing. Any potential
effect of an irritant gas or aerosol on the ventilatory pattern is also sub-
ject to interference or modification. Techniques that measure respiratory
freouencv or tidal volume without recourse to a mouthpiece are more suitable
221
-------
for this type of study, particularly when the subject is at rest. In guinea
pigs, the increase in R- caused by sulfur dioxide may be accompanied by slower,
deeper breathing, an adjustment that acts to moderate the increase in work
29
of breathing.
Exposure to 2.6 mg/m3 (1 ppm) of sulfur dioxide may impose slight reduc-
709
tions in forced expiratory flow rates after only 15 min. Other investigators
35
have noted reductions only after several hours of exposure. The effects are
magnified by higher concentrations and longer exposures and may persist for a
35
day. The patency of the peripheral airways, as reflected by the measurement
35
of "closing volume," aopeared to be unaffected.
56
In 1973, Bates and Hazucha studied pulmonary function effects in human
volunteers. Sulfur dioxide (0.98 mq/m3 [0.37 ppm]) administered with ozone
(0.73 mq/m- [0.37 pom]) oroduced exaggerated effects compared with the effects
of the individual gases. Sulfur dioxide alone produced no resoonse; ozone alone
caused only slight functional changes. This important observation has spurred
a continuing series of experimental studies in animals as well as humans. The
mechanism of the exaggerated response is uncertain, but is likely to have in-
volved the oxidation of sulfur dioxide by ozone to an ultrafine aerosol of
62,112,170
sulfuric acid.
Chronic studies: Sulfur dioxide has been administered at 0.34 to 15.0
8
mg/m3 (0.13 to 5.72 ppm) to guinea nigs for one year, and at 0.37 to 3.35
mg/m3 (0.14 to 1.28 ppm) to cynomolqus macaques for 78 weeks without apparent
7
functional or structural imoairments. One group of monkeys exhibited little
functional impairment during 30 weeks of continuous exposure to 12.4 mg/m3
(4.69 ppm) of sulfur dioxide. Ait that ooint, the monkeys were accidently ex-
posed for one hour to a concentration of sulfur dioxide estimated to range
222
-------
between 524 mg/m3 (200 ppm) and 1,310 mg/m3 (1,000 ppm). For the remainder of
the 78 weeks they were maintained on clean air but continued to show persistent
functional impairment. This qroup alone had histologic evidence of tissue
damage. The injury was extensive involving the tracheobronchial tree, periph-
eral airways, and parenchyma.
It would appear that chronic exposure to low concentrations of sulfur di-
oxide alone ( < 13 mg/m3) is not associated with cumulative functional or struc-
tural impairment of the lung, particularly if the animal remains at rest.
Intermittent spiking concentrations, which may occur in occupational settings,
may represent a greater risk. Perhaps a more revealing long-term study would
involve the combination of sulfur dioxide with other pollutants with which the
gas may interact, and the testing of other aspects of function, including muco-
ciliary clearance and small airway caliber.
AEROSOLS
Chemically inert as well as chemically active aerosols may cause changes in
the mechanical behavior of the lung. Some aerosols are used therapeutically to
produce bronchodilation and improve function. Aerosols tend to deposit at or
near bifurcations of the airways, probably because of the changes in flow oat-
61
terns at these sites. Significantly, epithelial nerve endings also tend to
565
concentrate near bifurcations, a factor that increases the functional impact
of the particles. The nerve endings of the more central airways are especially
receotive to mechanical stimuli that lead to reflex coughing and bronchocon-
striction. Evidence suggests that the peripheral nerve endings are more re-
sponsive to chemical stimuli, which may result in increased breathing rates
565
and reduced pulmonary compliance.
223
-------
Many proven or oostulated factors influence the type and magnitude of the
response to aerosols. Some are inherent in the organism, others in the aerosol
itself. The bioloqic factor:; that may modify responses, while widely recog-
nized, have been assessed only superficially. These include the species, age,
nutrition, level of activity, state of health, and level of consciousness. In
animals exposed to aerosols while anesthetized, response may be influenced by
the type and depth of anesthesia. In Chanter 7 there is a discussion of venti-
latory (tidal volume, respiratory frequency, flow velocity) and morohometric
factors that influence deposition. Among the relevant aerosol properties are
mass concentration, aerodynamic size, molecular composition, oH, and solubility.
Whether the soluble aerosol is in a dry or aqueous state prior to inhalation
is important if it is administered with a soluble gas (see GAS-AEROSOL INTER-
ACTIONS). In general, as the site of deposition of a relatively insoluble par-
ticle becomes more distal, the time required for its clearance increases. Some
particles penetrate the alveolar wall and lodge in the interstitium or are dis-
seminated through the lymphatic and circulatory systems.
Evidence suggests that many potentially toxic chemicals reside chiefly in
the accumulation mode (see Chanter 2) of ambient aerosols. They include lead,
cadmium, antimony, arsenic, nickel, zinc, benzo[aloyrene (a carcinogen) as well
456, S75
as sulfate and nitrate ions. The trace elements contained in soluble
aerosols may ultimately affect extraoulmonary tissues irrespective of deoosition
site, A number of the aerosols that are found in general air pollution have
been administered to laboratory animals. These include sulfates with a wide
range of pH (e.g., ammonium sulfate and sulfuric acid); no reports on the ef-
555
fects of nitrate aerosols nave aopeared yet. Much of this work has been
24,26,28,32
done by Amdur and her associates. Their studies, conducted
-------
exclusively on guinea pigs, focused on changes in the mechanical behavior of
the lungs, both R and C . The principal effect of the different aerosols
L L
was to increase R . The extent to which the response was due to reflex con-
L
striction of the trachea and bronchi, or to edema, excessive secretions, and
the action of (humeral) smooth muscle constrictors released from local tissue,
was not determined. C , reflecting distensibility of the lungs, was reduced.
L
Often, these changes in C and R were intimately related in time; they
L L
appeared, increased in severity, and remitted almost simultaneously. Such par-
allel timing suggests the following train of events: the increase in R resulted
L
in an abnormal or uneven distribution of inspired air so that portions of the
lung became poorly ventilated. As a consequence, the "effective" size of lung,
reflected in the measurement of C , was reduced. C alone may be reduced if
L L
the principal site of effect is in the small airways or alveolar region. These
mechanical defects, besides increasing the work of breathing, may be severe
enough to impair the normal transfer of oxygen across the alveolar-capillary
581
membrane. With the exception of one study on human volunteers, there has
been no rigorous testing of gas exchange or blood gas concentrations in
experiments using aerosols.
Particles up to a few micrometers in diameter generally evoke greater
functional and structural changes in the lung than do larger particles, probably
because they are more likely to be deposited in the lower airways and alveoli
(see Chapter 7). Probably the most noteworthy study of the effect of size on
28
the magnitude of response was conducted with zinc ammonium sulfate. For par-
ticles ranging from 0.3 to 1.4 ym dia, there was an inverse relation between
the size of the particle and the change in R (see Figure 8-3). The mass con-
Li
centration was approximately 1 mg/m3. At least two factors may have contri-
buted to the result:
225
-------
LU
O
1-
t/5
GO
LU
tr
2
LU
OJ
cc
O
z
140
120
100
80
60
40
20
0
-
-
12
9*
PARTICLE SIZE,
O 0.3
D 0.54
A 0.7
• 1 4
0.4 08 12 1.6 2.0 2.4
ZINC AMMONIUM SULFATE, mg/m
2.8 3.2
3
3.6
FIGURE 8-3. Dose-response curve of zinc ammonium sulfate aerosol for dif-
ferent particle sizes. Numerals beside each poijnt indicate
number of animals. From Amdur and Corn, 1963,28
226
-------
• The site or magnitude of deposition differed with size in a manner
favoring the greatest change in R for the smallest oar tide. Para-
L
doxically, the largest aerosol (1.4 ym dia prior to inhalation) would
be expected to undergo the greatest total deoosition. (See Chapter
7.) The solubility of zinc ammonium sulfate probably caused it to
grow severalfold after inhalation. Such growth would orobably
574
influence the magnitude and site of deposition.
• The surface area/volume ratio of the particle, which is inversely
related to its diameter, may somehow influence the response. Cer-
tainly, the rate at which moderately to slightly soluble particles
enter solution (having deposited in the respiratory system) should
increase as the diameter is reduced.
Zinc ammonium sulfate was identified as a component of the severe oollu-
tion that struck Donora, Pennsylvania in 1948. Ammonium sulfate, a more conroon
component of regional and urban pollution, and zinc sulfate are less irritating
28
to the lung than zinc ammonium sulfate.
25,26,31 108,109 6
Acute, subacute, and chronic studies indicated that sul-
furic acid causes a greater increase in R in guinea oigs than zinc ammonium
L 25
sulfate at approximately equivalent particle sizes and concentrations.
Whether the greater toxicitv of sulfuric acid is related to its acidity is
unknown. No rigorous study of the role that oH olays in determining the irri-
tant potency of sulfate aerosols has vet been made. In a series of studies,
26
Amdur compared the relative effects of a variety of sulfate aerosols (sulfuric
acid, zinc ammonium sulfate, ferric sulfate, zinc sulfate, ammonium sulfate,
cuoric sulfate, ferrous sulfate, and manganous sulfate). The estimated oH of
these compounds does not correlate well with their reported effects.
227
-------
The size of the sulfuric acid aerosol does influence the response: par-
ticles 0.3 ym dia cause a greater increase in R than particles 2.6 wn dia.
L
Indeed, within limits, size appears more critical than concentration in deter-
mining the response. Figure 8-4 shows that about 0.1 mg/m3 concentration of
the smaller aerosol caused as much narrowing of the airways as did over 10
times the concentration of the larger aerosol. Ambient air may in the future
contain sulfuric acid aerosols with two distinct mass median diameters, one
between 0.4 to 0.7 urn and the other about one-tenth as large, i.e., 0.04 utm.
144
Studies near St. Louis indicate that the larger aerosol probably results from
the oxidation of sulfur dioxide and the aging of the aerosol in the atmosphere.
The smaller aerosol is generated by catalytic converters on cars and persists
in this ultrafine state a relatively short time before coalescence occurs.
Whatever hazard may be oosed by these ultrafine particles is probably confined
to areas close to traffic.
The reaction chamber must be carefully controlled if such experiments are
to provide useful information. Sulfuric acid is hygroscopic; its aerosol size
is determined by the ambient relative humidity (RH). Growth in the respiratory
system occurs within milliseconds. This growth rate is influenced by the ori-
ginal particle size; i.e., the larger the particle, the longer the time required
to reach equilibrium at the RH of the respiratory tract (Figure 3-5). To reach
equilibrium at 98% RH, a crystal of sodium chloride with a diameter of 0.3 ym
would require about 0.1 sec; a 1 ym crystal would require about 1.0 sec.
If a droplet of sulfuric acid were to impinge on the respiratory surface
before hydration were complete, its pH would be correspondingly lower than at
full hydration, a factor that might influence the biologic response. The pH of
the particles is affected by hvdration. It is lowest prior to inhalation and
228
-------
o o o
o m o
ui m o
O CM O
O rH O
OJ VO *»•
o o o
888
r-t d (N
o o o
o m o
m in o
•H i-H
O (N O
• • •
O i-H O
o o
vo
o
rH PI (N
o o o
• • •
o o o
•r—
C 14-1
3
U-4
§ §
-------
0)
CO
£
o
t-
o
O "O
pdoip/AP
a
u
°&£
88S!1"
o H
U Qj uj
3 (0 • C Q H
ro en o -P ro
rH OJ-H 4£
0)
..-HO)
^0)5^
^
g C rH 0) -H
Bs.y^ld
230
-------
rises toward neutrality as the particles take on water. If a particle impinges
on a mucosal surface before growth is complete, the pH at the instant of impact
will be relatively low. Hence, in terms of the type and magnitude of biologic
response which might be elicited by sulfuric acid, or by other hygroscopic
aerosols, there is a complex interrelation between the size, RH, pH, and depo-
sition site. (See Chapter 7.)
Changes in breathing pattern and mechanical status of the respiratory sys-
tem will add to this complexity. As a result of the transition from slow to rapid
and from nasal to oral breathing that occurs with exercise, a particle entering
the airways with a specific aerodynamic size may impinge at a different site
having undergone a different degree of hydration and a different change in pH.
440
A recent hypothesis suggests that the ammonia excreted from the lung may con-
vert sulfuric acid aerosol to ammonium sulfate while it is still airborne within
the respiratory system, thereby increasing the pH of the aerosol considerably.
Such an interaction would protect the lung. Limited knowledge precludes assess-
ment of the contributions of these factors to the functional changes.
Because the guinea pig has been used so extensively in these studies, a
brief comment about a few distinctive structural features of its lung is in
order. The walls of the bronchi and especially of the terminal airways are
thicker than in other laboratory animals or humans, and there is an abundance
529,545
of smooth muscle in the pleura. In larger laboratory animals and in
healthy young human adults, the peripheral airways are responsible for only
a small fraction of the total R ; in guinea pigs, this fraction may be much
larger. Recent evidence indicates that narrowing of the peripheral airways is
579,700" 700
chiefly responsible for the increase in both aging and emphysema.
The prominence of the bronchiolar wall in infancy suggests that peripheral
231
-------
flow resistance may also be relatively hiqh at this stage of life. Infants
appear to be more prone to "obstructive bronchiolitis" than adults. It is con-
ceivable that the guinea pig's lung may be an appropriate analog of the infant's
lung, with respect to the bronchiolar segment.
For this reason narrowing of the distal airways may go undetected (these
532
airways have been termed a "silent" zone ) unless other tests sensitive to the
distribution of ventilation are employed. Such tests have been used to demon-
strate functional impairment of the peripheral airways in circumstances as
522 439 56
diverse as cigarette smoking, coal mining, and exposure to ozone. In
guinea Digs the smooth muscle layer of the peripheral airways, especially of
529
the bronchioles, is thick. It is therefore possible that the bronchiolar or
peripheral flow resistance in these lungs is correspondingly large. The extent
to which the peripheral airways of the guinea pigs were implicated in the changes
in R produced by aerosols or irritant gases is not known. This question is
L
important because evidence suggests that damage to these airways can be a fore-
runner of chronic pulmonary disease. By the same token, there is a compelling
reason for studying species of animals, including primates, having a distribu-
tion of central and peripheral flow resistance more typical of the adult human
lung.
Research on human subjects has focused on chemically inert dusts and pow-
ders, as well as sulfuric acid. Both healthy persons and patients with chronic
203,489
ailments of the lung have been tested. In two of these studies the
particles, which were <1 yn, caused an increase in airway flow resistance after
brief administration. Abnormal intrapulmonary mixing and gas-trapping also
489
occurred. In a study using a polydispersed aerosol of calcium carbonate
with particles from 0.2 to 5.0 vm dia, a variety of functional defects were
232
-------
581
elicited in both healthy subjects and patients with lunq disease. Principal
among the defects were an uneven distribution of ventilation and impaired
gas exchange, measured by an increase in the difference between alveolar and
arterial oxygen tensions. The healthy subjects generally required longer
489
exposure to elicit a response, while recovery may have been delayed among
asthmatic patients. None of these studies reported the concentration of the
581
aerosols.
In one study, sulfuric acid aerosol was oerceived as a tickling or scratch-
ing sensation in the throat at a mean concentration of 0.72 mg/fa3 (range: 0.6
107
to 0.85 mg/m3). In an earlier study, the threshold of detection by odor,
taste, or irritation was 1 mg/m3; however, concentrations as low as 0.35 to
0.5 mg/m3 caused an increase in rate of breathing and reductions in tidal volume
and peak inspiratory and expiratory flow rates. (See previous discussion under
SULFUR DIOXIDE.) Those changes occurred within minutes of the onset of expo-
sure; the mean diameter of the particles was 1.0 ym. Higher concentrations of
sulfuric acid ranging from 3 to 39 mg/m3 (1 ym MMD at 62% RH) have been shown
701
to increase flow resistance, the effect being exaggerated at an RH of 91%.
It is worth noting that the concentration of sulfuric acid found in community
. 143
air is in the order of 10 yg/m .
Chronic exposure: Fly ash and sulfuric acid mist have been administered
to animals for periods in excess of one year. Monkeys exposed to 0.16 and 0.46
mg/m3 of fly ash for 18 months incurred no functional impairment. Slight fi-
501
brosis of the lung was noted only at the higher concentration. Sulfuric
acid mist has been administered to both monkeys and guinea Digs in a range of
6
concentrations and sizes. The guinea pigs were unaffected. In monkeys, gen-
erally in response to higher concentrations of sulfuric acid, the distribution
233
-------
of the inspired air within the lung became uneven or abnormal, and the rate of
breathing was increased. Respiratory mechanical behavior did not change. His-
tologic changes were frequent, consisting principally of epithelial hyoerplasia
and thickening of the bronchiolar walls. These structural changes probably
contributed to the uneven alveolar ventilation. Since the mass concentrations
were not constant in these experiments, it is difficult to draw conclusions
about the relative effects of particles of different sizes.
In another study, four beagles were exposed daily for 620 days to 0.9 mg/m3
463
of sulfuric acid, about 90% of the particles being less than 0.5 ym dia.
The dogs were reported to have developed a variety of functional defects by
the end of the period, including reductions in the single-breath carbon mon-
oxide diffusing capacity, C , residual volume and total lung capacity, and an
L
increase in R . Another set of animals exposed to 48.9 nn/m3 (26 com) of ni-
Jj
trogen dioxide for 191 days prior to receiving the sulfuric acid was reported
to have been less responsive to the sulfuric acid. Unfortunately, these con-
clusions are difficult to weigh because the information provided about the
functional techniques and the presentation of the results were inadequate.
Guinea pigs have been exposed to sulfuric acid aerosols for periods of 5
108,109 752
days, and from 18 to 40 days, and the effects were assessed by histo-
logic examination. The 5-day exposures to concentrations of 1 and 2 mg/m3, par-
ticle size not specified, produced lesions of the airways and parenchyma,
108,109
including edema, that persisted several weeks. During the exposures of
752
from 18 to 40 days, three particle sizes, 0.6, 0.9, and 4.0 ym dia, were
administered in concentrations ranging from 1 to 4 mg/m3. The inflammatorv
response was confined to the larynx and lower airways. The greatest damage
was elicited by the 0.9 ym dia aerosol.
234
-------
Research on the toxicity of aerosols has not infrequently led to an over-
interpretation of technically weak or insufficient data. In some studies, whose
objective was to determine the importance of particle size in producing an ef-
fect, the aerosols being compared were oolydispersed while differing in average
size by only a few tenths of a micrometer, or they were administered in unequal
concentrations. Criteria documents of the Department of Health, Education, and
Welfare, although commendable in their goals, often cite such work uncritically.
GAS-AEROSOL INTERACTIONS
When an irritant gas is combined with an aerosol, the resulting toxicity
may exceed that attributable to the two agents administered separately. The
aerosol administered alone may have no physiologic effects or could be an irri-
tant. The heightened, exaggerated response is referred to as "synergism."
Principal among the pollutant gases that have shown the potential for synergism
28
are sulfur dioxide and formaldehyde. Two exolanations of the chenomenon have
been proposed. One is physical; that is, the gas is adsorbed by the aerosol
to be transported to a more sensitive or vulnerable site. This mechanism is
thought to apply to highly soluble gases like ammonia and sulfur dioxide.
Administered alone, each gas would be removed from the airstream almost entirely
in the upper airways. The aerosol intervenes as a carrier thereby increasing
429
the penetration of the gas to the lower airways. LaBelle et al., through
281
empirical observations on mice, and Goetz, in a theoretical pacer, gave
credence to this hypothesis. The second explanation is chemical, that is, the
two or more elements react to form a new molecular compound that is more toxic
32
than the parent gas or particle. As an illustration, Amdur and Underhill
25
and Amdur propose that the synergism resulting from the administration of
sulfur dioxide and a submicrometer aerosol of sodium chloride to guinea Digs
235
-------
is attributable to the formation of sulfuric acid which exaggerates the change
in R produced by sulfur dioxide.
L
Experiments concerning synergism have elicited great interest because the
phenomenon provides a basis whereby low concentrations of common ambient pol-
lutants may be rendered more damaging to the lung. Having observed the effects
32
of mixing sulfur dioxide with a number of aerosols, Amdur and Underhill con-
cluded that synergism occurred only if the oarticles were soluble in water.
The degree of synergism appeared related to the solubility of sulfur dioxide in
the solutions of salts used to generate the aerosols. Accordingly, the relative
effects from mixtures of sulfur dioxide and aerosols, measured in terms of
changes in R , were greatest with ammonium thiocyanate, intermediate with
potassium chloride, and least with sodium chloride. Synergism occurred sooner
when sulfur dioxide was combined with soluble catalytic salts of manganese,
vanadium, and iron (ferrous). This observation was cited as evidence that
sulfur dioxide had been oxidized to sulfuric acid. By contrast, synergism was
not produced when the gas was mixed with insoluble aerosols including carbon,
32
activated charcoal, fly ash, ferric oxide, and manganese dioxide.
Amdur and Underhill hypothesized that the interaction between gas and aero-
sol occurred within the resoiratory tract, after the aerosol became a droplet.
In all probability, most of the aerosols used in these experiments were "dry"
prior to inhalation so that any absorption of, or interaction with, the gas in
the reaction chamber would have been negligible. The requirement that the
reaction occur within the airways harbors two conceptual difficulties. One is
that while the formation of aerosol droplets in the upper airways may be quite
588
rapid, perhaps requiring only milliseconds at bodv temperature and high RH,
sulfur dioxide is simultaneously absorbed at a rapid rate by the surrounding
236
-------
35,255,715
mucosal surfaces. The surface area provided by an aerosol having a
mass concentration of 1 mg/m3 is negligible compared with that of the competing
surrounding nasal passages. Comparative Surface Areas: Nasal mucosa = about
160 on2; Aerosol, 1 mg/m3 = 3 x 10~5 cm2. Therefore, exorbitant concentrations
of the aerosol and gas may be required to counteract the imbalance in competing
absorptive surfaces, if a significant amount is to be incorporated in the drop-
let and carried to the lower airways. This may account for the observation
that synergism between sulfur dioxide at 5.3 to 700.0 mg/m3 (2 to 265 pom) and
the sodium chloride aerosol was greater when the dry aerosol was administered
24
at a concentration of 10 mg/m3 than at 4 mg/m3, and that other investigators
found no synergism when the dry concentration of the gas was only 2.6 mg/m3
526
(1 ppm) and that of the aerosol only 1 mg/m3. The second conceptual dif-
ficulty is that the catalytic oxidation of sulfur dioxide to sulfuric acid by
the droplet aerosols of manganese, vanadium, or iron proceeds too slowly to
have occurred to a significant degree within the respiratory system.
Another hypothesis or plausible mechanism for synergism places the chemical
transformation of the gas, and the production of the "irritant" aerosol, in the
ambient atmosphere prior to inhalation (see Chanter 4). This hypothesis has
been tested by administering sulfur dioxide 2.6 mg/m3 (1 opm) and sodium
526
chloride aerosol (1 mg/m3) to guinea pigs at both low and high RH. Sodium
chloride aerosol is deliquescent; it is a dry crystal below 58% RH and raoidly
becomes a droplet at higher RH (Figure 8-6). Below 40% RH, this combination
caused no change in R ; above 90% RH, there was a significant increase in R
L L
consistent with bronchoconstriction (Figure 8-7). The droplet absorbed sulfur
dioxide as evidenced by the reduced concentration of gaseous sulfur dioxide in
the reaction chamber leading to the animal. The pH of the droolet fell below
237
-------
cr
a:
, 3
UJ
I
O
LU
>
UJ
a:
o
NaCl
B
D
20 40 60
RELATIVE HUMIDITY, RT t %
80
100
FIGURE 8-6. kscat = extinction coefficient due to light scattering by
both particles and gas molecules. R_ = relative humidity.
Deliquescence occurs at a relative humidity of about 70%.
From Covert, 1971.166
238
-------
80-
60
40
f>
o>
c
o
JC
o
20
Aerosol
SO-
Aerosol
2.6 mg/m3 Aerosol: 1 mg/m3
RH:
low
high
FIGURE 8-7. Values of RL from 12 exposures were averaged (cm-H20 ml"1 sec"1;
means ± S.E.) for each of the six exposure modes (sulfur dioxide;
in combination with sodium chloride aerosol, 1 mg/m3). The re-
sults of the first and second exposures were not significantly
different and were therefore combined. RL was measured at approx-
imately 4-min intervals. The increase in RL for mode 6 exceeds
the other changes by the following: compared to mode 2, P < 0.05;
compared to modes 1, 3, 4, and 5, P < 0.01. From McJilton et al.r
1973f26Copyright 1973 by the American Association for the Advance-
ment of Science. Reprinted with permission.
239
-------
4, and sulfurous acid, but not sulfuric acid, was found. It was not determined
whether the irritant effect was caused by the physically dissolved sulfur di-
oxide, increased hydrogen concentration, the bisulf:.te ion, the sulfite ion, or
by some chemical species produced in the tissue liquids following deposition of
9
the aerosol. Alarie et al. reported that sodium metabisulfite was irritating
to the upper respiratory tract of mice, while sodium sulfite had no effect. In
his experiment the release of sulfur dioxide from the metabisulfite could have
been responsible for the sensory irritation. At a lower ambient temperature,
the amount of sulfur dioxide dissolving in the droplet should increase. It
would be interesting to test this additional "environmental" factor for exag-
geration of synergism. There is anple epidemiologic evidence to indicate that
the effects of air pollution on health are exaggerated in cold, damp weather.
(See Chapter 9.) |
A mixture of approximately 3.8 mg/m3 (2 ppm) nitrogen dioxide and 330 ± i
110 vg/m3 sodium chloride aerosol has been administered at <75% RH to rats and »
monkeys for 14 months without causing structural changes in the lungs greater
265
than those caused by the same concentration of the gas alone. At this RH
the likelihood of a significant interaction between nitrogen dioxide and the
aerosol would be small. The sodium chloride aerosol administered alone was
innocuous.
Attempts to demonstrate synergism in humans have yielded conflicting re-
569,759,760
suits. Japanese investigators reported synergistic responses with
mixtures of sulfur dioxide (2.6 to 159.0 mg/m3 [1 to 60 ppm]) and either sodium
chloride (5 and 6 mg/m3) or hydrogen peroxide aerosols (0.01 to 0.1 mg/m3 and
0.8 to 1.4 mg/m3). Synergism was reported between sulfur dioxide and sodium
569
chloride for particles 0.95 Vm, but not for 0.22 un in count median diameter.
240
-------
Mixtures of nitrogen dioxide (11.3 to 75.3 rog/fa3 [6 to 40 opm]) and the aerosol
569
were also synergistic.
569,759,760
These studies relied on a method of rapid, repetitive inter-
155
ruption of gas flow at the mouth to measure flow resistance. In at least
759
one study, this interrupter method may have been used improperly, judging
from an illustration provided by the author. The brief period of interruption
should produce a relatively stable or "static" airway pressure, but Figure 2
of the referenced article shows that airway pressure changed raoidly during
that period. It is not possible to judge whether the same methodologic problem
569,760
was present in the other two studies.
Several groups of investigators in the United States have failed to elicit
106,252,709
synergism between sulfur dioxide and sodium chloride aerosol. The
aerosol in one study had the same average size and concentration as that used
252
sucessfully in guinea pigs. None of these reports provided information about
ambient RH. An experiment on anesthetized cats also gave no evidence of syner-
164
gism with mixtures of sulfur dioxide and sodium chloride aerosol.
CONCLUSIONS
These findings support the growing conviction that sulfur dioxide alone,
in realistic ambient concentrations, is not especially hazardous to health.
Instead, what aopears to be of concern are resoirable aerosols, many of which
may result from oxidative reactions involving sulfur dioxide. These reactions
and the generation of the aerosols occur to a large degree in the ambient
atmosphere. (See Chapter 3.) For this reason it would aooear necessary to
control the emission of sulfur dioxide if the aerosols are to be held to
acceptable levels.
241
-------
Among the factors shown to influence the toxic potential of sulfate aero-
sols, and presumably other aerosols as well, are their mass concentration
(little attention has been paid to molar concentration), molecular composition,
and perhaps acidity. Whether sulfite and bisulfite ions contribute to toxicity
is uncertain.
While there is an abundance of information on the toxicity of nitroqen di-
172
oxide in animals and some epidemiologic evidence suggesting that nitrogen
694
oxides may affect health, there appear to have been no toxicologic studies
involving nitrate aerosols.
242
-------
CHAPTER 9
EPIEEMIOUDGIC STUDIES CM THE EFFECTS
OF AIRBORNE PARTICLES ON HUMAN HEALTH*
Mast epidemiologic studies of air pollution have been concerned primarily
with such particles as mineral ash, carbonaceous material, sulfur oxides, and
hydrocarbons which arise from the burning of fossil fuel. (See Chapter 2.)
In Europe, the British samplers most often used collect particles in the respi-
rable size range ( < 5 pm). In the United States most data have been based on
high-volume samplers, which collect a fair nvmber of larger particle outside
the respirable range. It is therefore difficult to compare measurements made
in Europe with those made in the United States. Further, because the British
method, which uses reflected light, is calibrated against a standard British
smoke,** it cannot be used in the United States where the smoke is different
nor in areas where there may be considerable white or colored particles as,
for example, around a kraft mill.
Unless particle size is adequately considered, trends in pollution mea-
sured by a high-volvitve sampler may be quite misleading. For example, by re-
moving the larger, nonrespirable particles, the mass concentration may be
reduced without changing the respirable fraction. This may have little or no
* Portions of this chapter have been adapted from a paper presented by Dr. Ian T.T.
Higgins, Chairman of the Committee on Airborne Particles, to the Society of Auto-
motive Engineers (SAE) as part of its continuing education program. Subsequently,
that paper was published with others in Medical Aspects of Air Pollution. A Con-
tinuing Engineering Education Course,334 which was developed by the SAE Engineering
Education Activity. Permission to use this material has been obtained from the
Society of Automotive Engineers.
**In Britain smoke samples are collected on filter paper and the darkness of the re-
sulting stains is assessed photoelectrically. Readings are interpreted as if they
had been derived from stains made by a standard urban smoke, using a formula giving
the weight of equivalent standard smoke per unit volune of air.
243
-------
effect on health. In most studies, sulfur dioxide is the only sulfur compound
that has been measured. The reactions that gas undergoes in the atmosphere,
particularly its oxidation to sulfur ic acid, conversion to sulfates, and inter-
action with other gases, such as ozone and particulates, are described in
Chapter 5. The sulfur dioxide, suspended particulate, or smoke concentrations
often referred to in epidemiologic studies should be considered as indices of
pollution and not as specific pollutants causing certain effects. Pollution
that arises from the presence of specific particles, such as lead, beryllium,
or asbestos, or from viable particles, such as pollens, will not be considered
in this chapter. In addition to the ambient air pollution, pollution may also
arise from occupational exposures and from tobacco smoking, especially cigarette
smoking. It is often difficult to assess the relative contribution to ill
health of these three forms of pollution.
ACUTE EPISODES
The acute episodes of high pollution, such as those that occurred in the
238 " 678 483 296,
Meuse Valley, Belgium; Donora, Pennsylvania; London; New York City;
297 790
Osaka, Japan; and elsewhere, provide the most convincing and dramatic
evidence for an effect of air pollution on health. It has been documented
for over a century that smog can kill. The report of the British Ministry
546
of Health on the London fog of 1952 records lethal fogs in London going
back as far as 1873 and subsequently similar fogs in London and other British
83,683-685,811,812 278,
cities during the 1950's and 1960's. In New York City,
294,295,519
episodes of high pollution have also led to increased mortality
but these do not appear to have resulted in as many excess deaths as in London,
possibly because the pollutant concentrations were lower or less continuously
sustained in New York City than in London. In Britain, deaths arising from
244
-------
fogs were most often attributed-to bronchitis but also to coronary disease,
myocardial degeneration, pneumonia, and other respiratory diseases. In
New York City, deaths were attributed to to influenza, pneumonia, vascular
278
lesions of the nervous system, and cardiac diseases. In both cities,
morbidity as well as mortality increased during periods of sustained pollution,
though again, the increase in morbidity in New York City has sometimes been
less clearly associated with air pollution than has been usually the case
in London.
In New York City increasing pollution has sometimes been clearly linked
to increasing symptoms. In a study conducted during the Thanksgiving holiday
58
fog in 1966, Becker and his colleagues showed that as pollution increased
complaints of cough and phlegm, wheezing, breathlessness, and eye irritation
also increased. Those with preexisting heart or lung disease and those aged
45 and over appear to have been predominantly affected, i^ortality has been
related to concentrations of routinely measured pollutants. In London, excess
286
deaths resulted when smoke concentration exceeded 2.0 mg/n3 and sulfur di-
102
oxide rose above 1.04 mg/m3 (0.4 ppm). In New York City excess deaths
occurred when sulfur dioxide rose above 1.3 mg/m3 (0.5 ppm) and oarticlas were
278
recorded at 6 or more coefficient of haze units (COHS).
In Britain, fogs usually occurred in cold weather. Farr reported an in-
fluence of cold on mortality in 1841, and this has been confirmed many times
632 686
since. Scott and his colleagues concluded that pollution caused deaths
within three days but that cold alone acted more slowly causing deaths after
^56
about nine days. They concurred with Russell that it was not possible to
distinguish the respective shares of fog and low temperature on the genesis of
mortality. The relative contribution of low temperature, humidity, sulfur
245
-------
dioxide, and smoke to mortality in London and a rural area in Britain was
81
studied by Boyd, who found that death rates from bronchitis and pneumonia
were more closely related to cold and humidity than to fog frequency.
There has never been much doubt that these exceptional episodes of high
pollution could cause death and illness. But there was much more uncertainty
20 years ago about the effects of lower, more sustained concentrations of
pollution and their lonq-term effects. Research during the past 20 years
has related these lower concentrations to various health indices and has oro-
vided some working dose/response relationships.
FOLLOW-UP OF DONORA
That persons with chronic illness are unduly susceptible to pollution
was supported by a 10-year review of a sample of inhabitants of Donora,
Pennsylvania. Immediately after the 1948 disaster, a representative sample of
the town was studied by the U.S. Public Health Service. Ten years later Ciocco
150
and Thompson followed up this sample. They found that those affected by the
fog had a higher mortality and morbidity than those who were not. But most of
the excess occurred in persons who had chronic illness before the fog. This
suggests that the fog's main effect was exacerbation of existing disease in
sensitive people rather than initiation of illness. However, the 1948 mortality
rates were slightly but consistently higher in persons who had been affected
by the fog but had no prior chronic illness. The authors also compared the
prevalence of heart disease, asthma, arthritis, and rheumatism in survivors of
the 1948 episode with that in two neighboring Pennsylvania communities that had
not been affected by the fog. Because they found little difference between the
communities, the authors concluded that the fog had had little effect on the
prevalence of these diseases.
246
-------
VARIATION IN MORTALITY, MORBIDITY, AND LUNG FUNCTION OVER TIME
Daily Deaths and Illnesses
The relationships of daily measurements of black suspended matter (e.q.,
soot) and sulfur dioxide to daily deaths in London were first reported by
509
Martin and Bradley in 1960. They attempted to assess the effect on mortality
of relatively minor fog incidents and to establish a dose/response curve.
During the early years of their study there was a significant positive cor-
relation between black suspended matter and total deaths, a slightly lower but
still significant association between sulfur dioxide and deaths, and a negative
association between visibility and deaths. Bronchitis deaths showed lower cor-
relations than total deaths with these indices of pollution; pneumonia deaths
showed no significant association. Subsequently, the study was extended to
include morbidity based on certificates of incapacity issued by ohysicians.
These data indicated similar correlations. Since about 1963, however, this
study has produced little evidence of any effect of pollution on mortality or
morbidity. This has been attributed to the marked decline in pollution in
London since 1958. From 1958 to 1963 average annual concentrations of black
suspended matter fell from 0.30 to 0.06 mg/m3 and sulfur dioxide from 0.25 to
0.175 mg/m3 ( -0.10 to -0.07 ppm). The decline in both oollutants has continued,
508
but unfortunately no further analyses from this study have been published
after 1964. In London, the more effective reduction of oarticulate matter than
of sulfur dioxide has sometimes resulted in high 24-hr sulfur dioxide concen-
trations without correspondingly high particulate concentrations. Such oeaks
of sulfur dioxide have not aoparently been associated with excess mortality or
morbidity.
247
-------
519
• In New York City, McCarroll and Bradley first showed that excess
mortality occurred during relatively minor episodes cf pollution. Four groups
of workers explored the effects of day-to-day variation in pollution in a more
277
systematic manner. Glasser and Greenburg related daily deaths to concentra-
tions of sulfur dioxide and particulates measured by the smoke shade method*
as well as temperature and certain other weather variables from 1960 to 1964.
They noted a pronounced increase in mortality when daily sulfur dioxide concen-
trations exceeded 0.52 mg/m3 (0.2 ppm). These authors estimated that the dif-
ference in the average number of deaths between days when sulfur dioxide was
<_0.52 mg/m3 (0.2 ppm) and days when it was ^.1.04 mg/m3 (0.4 ppm) was 10 to
352
20 deaths per day. Hodgson's studies, from 1962 to 1965, indicated that
daily deaths from respiratory and cardiac diseases were highly correlated with
indices of pollution, such as oar tide concentration. Presumably, their smoke
shade measurements indicated a higher correlation than measurements of sulfur
dioxide concentrations. Mortality from other diseases was not significantly
related to levels of air pollution. Hodgson estimated that 73% of the day-to-
day variation in cardiac or respiratory deaths could be explained by variations
in air pollution or temperature. This seems remarkably high. There is a oues-
tion whether adequate allowance was made for such other factors as influenza
epidemics or seasonal influences.
100
In their five-year study from 1962 to 1966, Buechley and his colleagues
gave particular attention to temperature, season, day of the week, influenza
*In this method, the darkness of the filter stain, as measured by a reflectom-
eter, is used to calculate concentrations of smoke or other dark suspended
matter usually produced by combustion. It is rarely used in the United
States at this time.
248
-------
epidemics, and holidays. Heat waves, season, and influenza epidemics were the
main determinants of mortality; other factors, such as day of the week, were
also significant. After allowing for these, mortality still correlated with
pollution and COHS correlated as highly with daily deaths as did sulfur dioxide
concentrations. Deaths were 1.5% less than expected on the 232 days when sulfur
dioxide concentrations were < 0.0003 mg/m3 (0.0001 opm) and 2% greater than
expected on the 260 days when sulfur dioxide concentrations exceeded 0.5 mg/m3
\
(0.19 ppm). These authors present a dose/response curve that perhaps can best
be interpreted as showing no threshold of sulfur dioxide concentration for
mortality.
Finally, the initial study of Schimmel and his colleagues, which covered
671,672
the six-year period from 1963 to 1968, was extended four years to 1972.
Unlike Buechley and his coworkers, who studied the entire New York Metropolitan
area, Schimmel et al. limited their study to deaths in New York City. They
included temperature and season in their analysis but less thoroughly than
Buechley et al. The highest estimate of deaths attributable to pollution was
obtained using crude (uncorrected) pollution levels. Lower estimates were
obtained when these were corrected. The authors calculated that the average
daily excess deaths ranged from 18.2 to 36.7 (median 28.6) depending on the
degree to which the effect of air pollution is standardized for temperature
and other variables. The intermediate figure represents 12% of the more than
0.5 million deaths that occurred in the area between 1963 and 1968. From 1968
to 1972 mortality rates remained similar to those from 1963 to 1968 despite a
large reduction in sulfur dioxide concentrations in the city. This finding sug-
gests that sulfur dioxide itself cannot be the sole cause of excess mortality.
Possibly mortality is more closely related to other pollutants, for example
249
-------
sulfates, that unlike sulfur dioxide may not have declined. Alternatively,
demographic changes in the population may have offset any reduction in mortal-
ity that might have been expected from the reduction in sulfur dioxide.
Suechley, Schimmel, and thsir colleagues, based their studies on similar
material, but used very different analytic methods. Their estimates of the
effects of pollution on mortality were similar. They concluded that sulfur
dioxide pollution might be responsible for about 3% of the deaths. Further
study of these data is needed. Schimmel and Greenburg suggested that these
studies should include analysis by age and sex, additional environmental
monitoring stations, and analyses of more oollutants, notably sulfates.
Longitudinal Observations on Morbidity
Studies of day-to-day variation in mortality based, as they must be, on
analysis of death certificates provide little information on the relevant
characteristics of persons afflicted by pollution. To obtain these data, a
group of people should be closely observed. From 1961 to 1966 Fletcher and
39,243
Angel, with their respective colleagues, regularly observed over 1,000
men aged 30 to 59 living in North London. During the winter of 1962 to 1963,
they monitored a subsample of 87 men more intensively. The investigators
discovered that the incidence and prevalence of respiratory illnesses in this
subsample were related to both smoke and sulfur dioxide concentrations in the
district in which the men lived. Incidence of illnesses was related equally to
smoke and sulfur dioxide concentrations; prevalence was, however, more closely
related to smoke concentration. This group showed no significant correlation
of respiratory illnesses with low temperature. The weekly smoke concentrations
in London at that time were approximately 0.3 mg/m3 (0.16 ppm) with peaks from
250
-------
O.S to 1.0 mg/m3 (0.31 to 0.38 pom); sulfur dioxide concentrations ranged from
0.4 mg/m3 (0.15 ppm) to peaks of >_1.2 mg/m3(0.46 oom).
During the six-year study, there was a consistent decline in the volume
of morning sputum produced by all the subjects. This could have been due to
the concurrent reduction in air pollution in London but it might also be
attributable to the simultaneous reduction in the tar content of cigarettes.
451
During this same period (1960 to 1965) Lawther and his colleagues demon-
strated a progressive increase in peak expiratory flow rates by testing four
520
trained subjects regularly. For two years, McCarroll and his coworkers
studied 1,860 persons living close to a monitoring station on Manhattan Island.
These subjects reported on 25 symptoms daily and provided much more information
weekly through interviews. The complaints of 1,090 persons indicated that cough
and eye irritation were positively correlated with changes in the concentrations
of sulfur dioxide and particulates. Bye irritation was immediate whereas the
maximum effect on cough occurred one or two days after the exposure.
The possibility that respiratory disease might enhance susceptibility to
445,450,451,781,782
air pollution prompted Waller, Lawther, and their colleagues
*
to study chest clinic patients with chronic bronchitis and emphysema. Bach
patient recorded daily whether his chest felt better, the same, or worse than
on the previous day. The investigators calculated a mean score for all oatients
each day. Daily symptoms and pollution indices correlated highly when pollutant
concentrations were exceptionally high.
During the winter of 1959-1960 Waller and Lawther observed approximately
1,000 patients. Correlations between symptoms and concentrations of smoke
and sulfur dioxide were again high and positive. Five years later (1964-1965),
when the observations were rapeat«d following a considerable decline in the
251
-------
450
smoke concentration in London, the correlations were lower; two years after
this (1967-1968) the most susceptible patients in 1964-1965 showed even lower
correlations. Patients appeared most sensitive to changes in pollution during
early winter suggesting some degree of acclimatization. The minimum daily con-
centrations that appeared to lead to a significant deterioration in chest con-
dition were -0.5 mg/m3 (0.19 ppm) of sulfur dioxide and 0.25 mg/m3 of smoke.
Waller and Lawther made no attempt to study lunq function changes in their
patients although they observed daily a few healthy and bronchitic subjects
449
(Lawther et al., 1974). Ventilatory lung function was studied, however, by
216
Emerson in 1969 and 1970. He observed 18 patients with chronic obstructive
lung disease for 12 to 82 weeks. His weekly measurements of forced expiratory
volume in 1 second (FEV ) and the midexpiratory flow rate (MEFR) were cor-
i.o
related with the average concentrations of smoke and sulfur dioxide on the day
of testing and the previous four days. In no case did he observe a significant ,
correlation of lung function with smoke concentration. A significant negative
correlation of FEV1 0 with sulfur dioxide occurred in one patient and of MEFR
with sulfur dioxide in two patients. On the other hand, FEVj 0 correlated neq-
atively with temperature in six of the 18 patients and positively with relative
humidity (RH) in four of them. At that time the average annual smoke concentra-
tion in London was 0.044 mg/m3 with a maximum of 0.241 mq/m3 and the average
annual sulfur dioxide concentration was 0.193 mg/m3 (0.074 ppm) with a maximum
of 0.722 mg/m3 (0.278 ppm).
Emerson concluded that these pollutant concentrations were too low to
affect the lung function of patients with chronic obstructive lung disease.
Unfortunately, the concurrent sulfate concentrations were not measured, they
presumably varied with sulfur dioxide concentrations. This assumption suggests
252
-------
that sulfates did not affect ventilatory function. In London, Lawther has
recorded sulfate concentrations of 0.015 mg/m3 for 24 hr with an hourly maximum
of 0.678 mg/m3.
Two studies in Chicago have related symptoms in bronchitic patients to
105
environmental factors. During 1963 and 1964 Burrows and his coworkers asked
a group of 115 patients to record their synrotoms in a diary. Daily symptom
severity correlated closely with low temperature and high sulfur dioxide con-
centrations. There were also significant correlations with nitrogen oxides,
snowfall, and several other meteorologic and air pollution measurements. Most
of these associations, however, were due to the similar seasonal pattern of
respiratory symptoms and environmental conditions. When temperature and season
were constant, only hydrocarbon concentration showed an independent positive
correlation with symptoms.
125
Carnow and his colleagues used a similar approach in their study of oa-
tients in Chicago. Observations of 561 patients enrolled in a bronchopulmonary
disease registry indicated an increase in the frequency of acute chest illnesses
with increasing sulfur dioxide concentration in men aged 55 and older with
Q
advanced bronchitis. When sulfur dioxide concentrations were 0.78 mg/m (0.3
ppm) or higher, the percent of days of chest illness was twice as high as when
the concentrations were 0 to 0.104 mg/m3 (0 to 0.04 ppm). In contrast to the
younger men, those men aged 55 and over, with less severe bronchitis, and women
showed no relation between frequency of chest illnesses and sulfur dioxide con-
centrations. Some of the apparent difference between these two studies may
have been due to an inadequate allowance by Carnow et al. for meteorologic
factors, notably temperature. In neither studv were particulate concentrations
measured. They were presumably high since the average annual concentration
253
-------
in Chicago at that time, according to the National Air Sampling Network (NftSN),
was about 0.150 mg/m3 (0.058 ppm). Although the implication of an increase in
chest illness with sulfur dioxide concentration >_ 0.73 mg/m3 (0.3 pan) is com-
patible with other findings, the suggestion that sulfjr dioxide may influence
respiratory symptoms at lower concentrations should be treated with reserve.
Changes in lung function attributable to environmental factors were re-
691,692 717
ported by Shephard et al. and Spicer et al. Shephard and his colleagues
studied 10 patients with advanced respiratory impairment for three months.
They noted negative correlations between several aspects of lung function and
measurements of absolute humidity and suspended oarticulate concentrations.
The changes were attributed to bronchosoasm that might occur when oarticu-
late pollution reached 8 COHS or more. Spicer and his colleagues reported
day-to-day changes in lung function in small numbers of healthy subjects and
patients with chronic respiratory disease. They also monitored these changes
in function over a longer period in a larger group of healthy subjects. This
indicated a single cycle of function changes from October to May with lowest
levels in February and March. While changes in airway resistance were cor-
related with low temperature, they were not obviouslv related to concentrations
of either total suspended particulate or sulfur dioxide. Nevertheless, these
authors concluded that variations appeared to occur in the group concurrently
suggesting the influence of some common environmental factor or factors. Bates
55,57
and his coworkers repeatedly examined Canadian veterans with chronic
bronchitis in Winnepeg, Montreal, Halifax, and Toronto. They tested many
aspects of lung function. The cities varv in oollution; Winneoeg was bv far
the cleanest with respect to industrial dust fall and sulfur dioxide. Bates
found that veterans in Winnepeg were less severely affected than those in the
254
-------
other three cities; their lunq function was better and, over a four-year period,
showed no significant decline. Whether these effects were due to differences
in pollution or to other causes, such as selection of patients, is uncertain.
Sick Leave in Relation to Pollution
Absence from work due to illness is often a useful index of air pollution
197 196
effects. Dohan and Taylor and Dohan reported a high correlation (r = 0.964)
between the mean concentrations of suspended particulate sulfates in the air
of five cities and the incidence of respiratory illnesses lasting seven days
or more among women RCA employees from 1957 to 1960. No correlation was
observed with other pollutants, and only respiratory diseases were correlated
with particulate sulfate concentrations. The effect of sulfates aopeared to
be greatest in years of epidemic influenza. Much of this correlation may have
resulted because the effects of season and climate were ignored. Since both of
these factors have been correlated with pollution, they should be carefully
considered in analysis.
379
Ipsen et al. studied weekly morbidity rates at the RCA Camden plant for
three years from 1960 to 1963, the Curtis Publishing Company in Philadelphia
for the two years from 1960 to 1962, and the Bell Telephone Company in Phila-
delphia for two years from 1961 to 1963. Morbidity rates were higher during
the colder, windy months. Air pollutants in the ranges measured during the
study did not contribute to respiratory morbidity. Extensive analyses cor-
relating respiratory diseases with meteorologic and pollution variables were
conducted. Mean monthly values of 24-hr samples of sulfate concentrations
varied from 0.013 to 0.018 mg/m3. Ipsen noted a different pattern in the
relationship of respiratory disease to climate compared with the relationship
of pollution to climate. He believed, therefore, that it should have been
255
-------
possible to show an effect of air pollution on respiratory disease, if such an
effect existed, but he was not aible to do so. Concentrations of suspended oar-
ticulate matter, sulfur dioxide, sulfates, COHS, and nitrogen dioxide were
positively correlated with both the incidence and prevalence of respiratory
disease, though with considerable scatter. But this appeared to be explained
by the common influence of season on pollution and respiratory disease. Since
concentrations of all five pollutants changed simultaneously, separation of
individual effects was impossible.
724,725
Sterling and his colleagues studied hospital admissions in relation
to pollution using records from the Blue Cross and Blue Shield of Southern
California. Admissions were categorized as relevant, highly relevant, or not
relevant to air pollution. After allowing for the confounding effect of day
of the week on hospital admission, relevant admissions and deviation of stay
were significantly correlated with concentrations of sulfur dioxide, nitrogen
dioxide, oxidants, ozone, and particulate matter, but not with temperature or
humidity. The correlation coefficients were, however, very low even if statis-
tically significant. Taken in conjunction with the extremely low concentra-
tions of particulates and sulfur dioxide that were reported in this study, it
is difficult to accept that they represent cause and effect.
Geographic Comparisons
An obvious way of measuring the effects of air pollution is to compare
people living in areas with different pollutant concentrations. Unfortunately,
such comparisons may not be successful. Peoole who live in areas with different
air pollution usually differ in many other respects that could -also influence
their disease frequency. The degree to which such confounding factors have
256
-------
been taken into account varies greatly among studies. These factors should
always be carefully considered when drawing conclusions about the effects of
pollution.
International Differences
The large differences in bronchitis mortality among countries documented
by the World Health Organization (WHO) and others during the 1950's were
often partially attributed to differences in pollution. Much of the inter-
national variation is best explained by differences in diagnostic practice and
certification of cause of death; however, a number of careful morbidity compar-
isons have supported the existence of real differences in the frequency of
chronic respiratory disease among countries, some of which may be due to dif-
148,228,353,359,552,585,634 552
ferences in air pollution. Mork found a higher
frequency of respiratory symptoms and lower average peak flow rates in male
transport workers, aged 40 to 59, in Bergen, Norway, than in similar subjects
in London, England. He showed that these differences could not be explained
by smoking habits or socioeconomic factors, but suggested they resulted from
the exposures to air pollution of the two groups. Subsequently, Holland
358,359
et al. compared post office van drivers and telephone workers in
London and in three English country towns with outside telephone workers in
three areas of the United States. All grouos were aged 40 to 59. A higher
prevalence of respiratory symptoms, a larger volume of morning soutum, and
a lower average ventilatory lung function were found in the English workers
than in their American counterparts. Because the differences could not be
explained by differences in sitting height or smoking habits, the authors
attributed them to the variations in suspended particulate and sulfur dioxide
concentrations.
257
-------
Some difficulties encountered in international comparisons are indicated
228
by Ferris and Anderson. They compared the prevalence of respiratory symptoms
and ventilatory lung function in representative samples of the inhabitants of
two towns that differed in degree of air pollution: a one in 10 sample of
227
adults living in Berlin, New Hampshire in 1961, and a one in seven sample
37
of Chilliwack, British Columbia two years later. Comparable measurement
methods were used in each survey by the same observers, thereby eliminating
a major source of variation, At the time of these studies, total suspended
particulate concentrations were approximately 0.180 mg/rn3 and sulfation rates
were 0.731 mg of sulfites (S03)/100 cm2/day in Berlin, while Chilliwack was
free of pollution. The prevalence of respiratory disease in nonsmoking men
was essentially the same in both areas; but a slightly lower prevalence in
nonsmoking women was recorded in Chilliwack. Lung function values were con-
sistently slightly higher than expected in both men and women in Chilliwack.
The differences were not explained by anthropometric, social, or economic
factors. Although they were attributed to a small effect of air pollution,
ethnic differences could not be excluded.
636
The findings in Berlin, New Hampshire were compared with those from a
157
study by the British College of General Practitioners of a representative
sample of persons in Britain. A similar questionnaire had been used in both
studies. The concentrations of particulates and sulfur dioxide were lower in
Berlin than in most British cities. The prevalence of persistent sputum pro-
duction was similar in both countries, but the incidence of repeated chest
illnesses and breathlessness was higher in Britain. After allowing for
cigarette smoking, the prevalence of these symptoms appeared to be similar in
Berlin and in rural areas of Britain.
258
-------
DIFFERENCES WITHIN COUNTRIES
Urban/Rural
For many years British mortality statistics have Shown that death rates
from bronchitis are approximately twice as hiqh in urban compared with rural
dwellers. The gradient is much the same for both men and women. Oifferences
in socioeconomic status, occupational exposures, or smoking habits cannot ex-
plain this. In the United States the gulf between respiratory disease mortal-
ity rates in urban and rural areas is smaller for men/ and is nonexistent for
504 98,181,
women. These observations have stimulated a great deal of research.
182,504,606,733
Early studies of air pollution in Britain related mortality from bronchitis,
other respiratory diseases, and certain forms of cancer to sulfation rates,
sulfate (as dissolved impurity in deposit guages), smoke concentrations, or
102,104,181,182,325,606,733,734
dust fall. From 1950 to 1952 Pemberton and
606
Goldberg correlated bronchitis death rates in men and women aged 45 and
over with sulfation rates in 35 county boroughs in England and Wales. They
found statistically significant positive correlations in men but not in women.
There also appeared to be a much weaker association of bronchitis mortality
181,182
with particulate concentrations. Daly supported these findings. He
also developed an index of pollution based on domestic and industrial fuel
consumption per acre which he showed to be highly correlated with bronchitis
death rates and to a lesser extent with a number of other respiratory diseases.
733,734
Stocks reported high correlations of mortality from bronchitis and
certain types of cancer with dust fall and smoke concentrations in a large
number of different areas of England and Wales after allowing for population
density.
259
-------
None of these studies included smoking habits, which were not then widely
recognized as overwhelmingly important to the oathoqenesis of respiratory
98
disease. However, Buck and Brovn, in a somewhat comparable analysis, incor-
porated a crude adjustment for regional differences in cigarette smoking. Al-
lowance for socioeconomic factors and smoking differences did not abolish the
close correlation between air pollution and mortality from bronchitis. The
relative contributions of smoking and urbanization to bronchitis mortality were
192
clearly shown in Northern Ireland by Dean. However, the extent to which the
much higher death rates in central Belfast can be attributed to air pollution
is uncertain.
287,288
Gorham paid particular attention to sulfates when he correlated mor-
tality rates from bronchitis and pneumonia with various pollution indices in
53 country and metropolitan boroughs in England, Wales, and Scotland from 1950
to 1954. He studied monthly tar deposit, ash, sulfate per unit area in urban
areas, and pH of precipitation. Bronchitis mortality correlated positively
with sulfate concentrations and negatively with pH of precipitation. Partial
correlations revealed that the pH was significant but not the sulfate concen-
trations. Conversely, pneumonia mortality was related to sulfate concentrations
but not to pH. Gorham interpreted his findings to indicate that the acid drop-
lets deposited in the major bronchi produced bronchitis, whereas the sulfate
material, which was carried deeper into the lung, resulted in pneumonia.
442,443
Lave and Seskin reanalyzed mortality data from Britain using multiple
regression. Bronchitis death rates were fairly well correlated with pollution
indices (deposit index, concentration of suspended particles, sulfation rate,
and population density). Much lower correlations were reported with socio-
economic variables. These authors also studied 114 U.S. Standard Metropolitan
260
-------
Statistical Areas relating 1960 rates of mortality from all causes and infant
mortality to air pollution and other factors. Total death rates varied with
total suspended particulates and with sulfate. The correlations of infant
mortality were slightly lower.
The limitations of mortality studies makes one appreciate the need for
morbidity studies. There have been many such studies, based either on sick
leave records or on the results of specially designed surveys. A pronounced
urban/rural gradient of morbidity, such as that already shown for mortality,
resulted from a survey of a representative sample of men and women patients of
157
nearly 100 general practitioners. In 1961-1962, this was confirmed by the
547
British Ministry of Pensions and National Insurance in its investigation
of the incidence of incapacity from bronchitis and other illnesses in repre-
sentative samples throughout Britain. Bronchitis incidence in relation to
particulates and sulfur dioxide were analyzed regionally. Incapacity due to
bronchitis significantly correlated with winter concentrations of smoke and
sulfur dioxide in each of four 10-year age groups (Figure 9-1). The inter-
'i ' •
pretation of these data is somewhat uncertain, since similar correlations
between these pollutant concentrations and illnesses were attributed to
arthritis and rheumatism. Socioeconomic differences may also have contributed
to the associations.
Many surveys of respiratory disease have been conducted in different
v < • <
countries. Some were designed primarily to measure an effect of polluted
air on the respiratory tract. Others, though primarily concerned with
assessing the impact of such factors as occupational exposures or smoking
habits, also permit some conclusions about the effects of air pollution.
261
-------
190
O
5
a.
o
I
35-44
too m 300 400
I
MM
100 500 MO 4M
X denotes South Wales main towns
I
100 100 300 470 100 200 300 400
SMOKE,
I
r
65-J«
100 200 300 <00
100 200 430 400
SULFUR DIOXIDE, pg/m3
100 200 300 404
100 SOO 309 400
FIGURE 9-1.
Bronchitis inception rates for groups of towns, classified
according to size and location in relation to winter smoke
and sulfur dioxide, for four age groups.^ From Ministry of
Pensions and National Insurance, 1965.
5^7
262
-------
222,633
Fairbairn and Reid studied postal workers who, as a uniform group,
received much the sane Day wherever they worked, and, once established, tended
to remain in the same area. An effect of pollution, after allowing for the
confounding effect of socioeconomic factors, should therefore be possible.
Sick leave, premature retirement, and death due to bronchitis or oneumonia were
closely related to thick and presumably polluted foq but not to domestic over-
crowding or population density. Their pollution index, based on visibility,
812
had been developed by Wilkins. The pattern of disability among the costal
workers was similar to that of mortality in the whole British population.
165
Cornwall and Raffle, in a comparable study of London transport workers,
also showed that absence rates due to bronchitis were closely correlated with
thick, polluted fog in London and that the rates for men working in the tore
rural, peripheral areas were lower than those working in central London. In
neither study were smoking habits considered. But in a further study of a
432
sample of men and women aged 35 and over, Lambert and Reid showed that urban/
rural differences in respiratory symptom prevalence could not be explained by
smoking differences. Nearly 10,000 completed questionnaires, believed to repre-
sent 74% of a defined population aged 35 to 64, were analyzed. The prevalence
of respiratory symptoms increased with increasing air pollution. This increase
was confined mainly to smokers. Pollution appeared to have very little effect
in nonsmokers. The prevalence of symptoms increased progressively from the
lowest pollutant concentrations ( <0.1 mg/m3/year for either smoke or sulfur
dioxide) to the highest (10.2 mg/m3 for each pollutant).
More detailed studies on postal workers were conducted by Holland and
353
Reid. They compared 293 men aged 40 to 59 working in London with nearly
500 men of the same age working in three country towns in Southern England.
263
-------
-264-
Standard methods (respiratory symptom questionnaire, morning sputum volume, and
simple ventilatory lung function) were used. A higher prevalence of respiratory
symptoms and lower average vertilatory lung function were found in the London
men. There were differences in each smoking category but little real difference
between non- or exsmokers. Tbe authors concluded that excessive effects in
the London subjects were probably due to the greater degree of pollution there
as well as possible interaction with smoking.
In the United States, similar methods were used in a series of studies of
193,359
Bell telephone workers who formed a comparable occupation group of similar
age. The effect of smoking on respiratory symptom prevalence and ventilatory
lung function as observed in England was also demonstrable in the U.S. study.
The smoking-adjusted prevalence of severe symptoms was higher and the mean
FEV1>Q was lower in the United Kingdom than in the United States. After con-
sidering differences in ambient temperature and respiratory infection rates,
the authors concluded that the most likely cause of the differences were the
concentrations and types of air pollution.
In a study of male telephone workers in San Francisco and Los Angeles, the
prevalence of respiratory symptoms was found to be higher in the Los Angeles
subjects. This was attributed primarily to differences in smoking habits
between the two groups since the prevalence of persistent cough and phlegm ap-
peared to be caused by cigarette smoking, while shortness o£ breath, illnesses,
and level of lung function depended more on age.
160
Comstock et al. reexamined the East Coast telephone workers originally
studied by Holland and his colleagues after five to six years. At the same
time (1967) similar examinations were given to the same type of employees
160
in Tokyo, Japan. In all three surveys respiratory symptoms increased with
264
-------
age and with the number of cigarettes smoked per day. ^fter allowance for age
and smoking, there was no significant association of the findings with resi-
dence, from birth to time of study, nor with current place of employment. This
study then is one of few that found no association between air pollution and
respiratory disease. The reason for the discrepancy between this and most
other studies is not clear. Selective migration of persons with respiratory
411
symptoms from high to low pollution areas seemed unlikely since there was
no positive correlation of such symptoms with past residence or birthplace.
A comparison of respiratory disease and lung function in two Pennsylvania
towns with contrasting levels of air pollution was made by the U.S. Public
620
Health Service. In Seward, the more polluted town, average dust fall was
3.2 times and sulfur dioxide 6.2 times that of New Florence. The only dif-
ference in lung function was a higher average airways resistance in Seward.
Since there were other differences between the inhabitants of the two towns
in addition to their exposure to air pollution, the higher airways resistance
in Seward cannot be attributed solely to higher air pollution.
One of the most extensive studies of air pollution was conducted by the
841-843
U.S. Public Health Service in Nashville, Tennessee. Pollution was
monitored through a network of 123 stations throughout the city. Dust fall,
soiling index (COHS), sulfation rates, and sulfur dioxide were all measured.
Mortality from respiratory diseases varied inversely with socioeconomic class.
The large middle income class incurred increased resoiratory disease mortality
as sulfation rates and COHS increased. Most of these deaths must have been due
to influenza and pneumonia since mortality from bronchitis and emohysema
actually declined as pollution increased. Morbidity from all causes in all
age groups and from cardiovascular diseases in men and women over 54 increased
265
-------
with most indices of pollution. An association of increased asthma attack
rates with pollution was also demonstrated in Nashville.
Pollution levels have alsD been related to mortality and morbidity in
823,824
Buffalo, New York where particulates and sulfation rates were extensively
monitored from 1961 to 1963. From 1959 to 1961 mortality from all causes in
men and women over 49 and mortality from chronic respiratory diseases in men
aged 50 to 69 were both positively correlated with suspended particulate con-
centrations (Table 9-1). No significant relationship was found between mor-
tality from all causes and sulfation rates. There was, however, a positive
association between sulfation and the death rates from chronic respiratory
disease in each of the two lowest socioeconomic groups of men aged 30 to 69.
In these mortality studies, smoking habits and occupation were not considered.
822
In a further study of resoiratory symptoms in relation to pollution,
conducted on a random sample of white women in Buffalo, smoking habits were
included. Among nonsmokers aged 45 and over cough and phlegm were oositively
correlated with suspended particulate concentrations. Among smokers, however,
the findings were confounded by an interaction between resoiratory symptoms
and residential mobility. Among smokers who did not change residence, cough
and sputum were positively correlated with oarticulate concentrations measured
near their home; but among women who had moved within the oast 5 years, there
was a negative association. Socioeconomic factors could not explain these dif-
ferences. There was no association between sulfur dioxide concentrations and
prevalence of respiratory symptoms.
One of the most interesting studies of the effects of oollution in dif-
609
ferent parts of one city was conducted in Genoa, Italy, by Petrilli et al.
Genoa is a rapidly growing industrial city situated between the Aopennines
266
-------
TABLE 9-1
Mean Annual Deaths Attributed to Asthma, Bronchitis,
or Emphysema in White Males, Aged 50-69 Years, per
100,000 Population, Buffalo, New York, 1959-1961a
Median family Mean annual Particulate concentration, yg/m3
income for each
census tract, $
3,005- 5,007
5,175- 6,004
6,013- 6,614
6,618- 7,347
7,431-11,792
<80
—
136
—
70
79
80-
126
154
74
80
109
100-
271
172
110
177
h
0°
135+
392
199
128
—
—
From Winkelstein et al., 1967.823
b
Rate based on less than five deaths.
267
-------
and the Mediterranean. Its topography causes the phenomena of strikingly
different climates in various {arts of the city. Fron 1954 to 1964, oollution
was assessed at 19 sites. The investigators monitored sulfation, sulfur di-
oxide, carbon monoxide, lead, dust fall, suspended master, estimated gravimet-
rically and by particle size, and 3:4 benzpyrene. Mean values for available
data from 1962 to 1964 showed an increase of -20% from 1954 to 1961. Petrilli
et al. studied respiratory symptoms in nonsmoking women over 64 who had not
worked in industry but who had resided for a long period in the same area.
They also analyzed the results by floor level of residence. There were strong
associations between the frequency of respiratory disease and the concentration
of sulfur dioxide.
In seven districts where air oollution was measured continuously, 1961
and 1962 morbidity rates for bronchitis and other respiratory diseases varied
with average annual sulfur dioxide concentrations. Unfortunately, inadequate
analysis of this material prevents one from judging the effectiveness with
which the authors standardized for socioeconomic factors or utilization of
health facilities.
Studies of Children. Many studies of air oollution have been conducted
on children because there are no occupational exposures to be considered and
because cigarette smokers under 12 years old are rare. Children may also be
483
unduly susceptible to pollution, as was suggested in the London fog of 1952.
635
Furthermore, as Reid has suggested, bronchitis may begin in infancy or child-
hood and lung development during these early years may be adversely affected
by environmental assaults. Reid has also indicated that international patterns
in mortality from bronchitis are apparent even at young ages. He has drawn
attention to a reversal of the urban/rural gradient of bronchitis mortality
268
-------
in the S- to 14-year-old qrouo. He attributes this to the fact that the country
•hill first encounters infection when startinq school. Thi^ 'x^rurs at- i lat°r
1 l>? than Lhdt of. the urban child's first exoosure to infection.
&n early comparison of schoolchildren livinq in hiqhly ool luted Sheffield,
779
Enqland, with children livinq in the unpolluted Vale of Glamor lan, showed
that the orevalence of ear disease, sinus ooacitv, reoeated attacks of chest
disease, and impaired ventilatory lunq function was hiqher in the city than
in the country.
These Cindinqs were subsequently confirmed by Lunn and his colleaques who
provided some evidence of the pollutant concentrations that produced effects.
497
In their first study, there was a oroqressive increase in respiratory mor-
bidity from the lowest to the hiqhest pollutant concentrations. The lowest
averaqe winter mean concentrations of smoke were 0.097 mq/m3 and of sulfur di-
oxide, 0.123 mq/m3 (0.005 oom) . Mean ventilatory lunq function was siqnificantly
lower in children livinq in the hiqhest pollution areas with daily concentra-
tions of smoke at 0.301 mq/m3 and sulfur dioxide at 0.275 mq/m3 (0.106 PPTI).
493
Four years later, durinq a follow-up study, the lowest concentrations of
smoke and sulfur dioxide were 0.04R >m/Ti3 (0.018 oom) and 0.094 -
ppm) . Other areas ranqed from 0.041 to 0.169 mq/m3 of smoke and 0.1*>ii to 0.2M
mq/m3 (0.064 to 0.097 PCTTI) of sulfur dioxide. Hurinq this study, no siinificant
differences in disease morbidity or lunq function were found.
Additional quantitative estimates of the effects of air oollutants were
202
provided by Douqlas and Waller in their study of health and development.
They observed a qroup of children born within a one-week oeriod in March 194o
from birth until 1961. Their illness experience was related to the irea of
their re^iJence and, therefore, probably to exposures to air pollution. The
269
-------
results showed that lower respiratory infections were consistently related to
pollution but that upper respiratory infections were not (Table 9-2). Both
the frequency and severity of such infections increased with the amount of
pollution. The lowest concentrations of smoke and sulfur dioxide were 0.67
and 0.90 wq/m3 (0.346 pprn), respectively. Higher illness rates were noted in
all higher pollution classes.
The importance of childhood residence as a factor in respiratory illness
649
was further supported by Rosenbaum. He showed that the incidence of respi-
ratory disease in servicemen correlated positively with previous residence in
an industrial area.
A number of large-scale studies in Britain have evaluated the effects of
pollution, past respiratory disease, and various social factors on respiratory
357
symptoms and lung function in children. Holland and his colleagues studied
over 10,000 schoolchildren in four areas of Kent, two predominantly urban and
two rural. They found peak expiratory flow rates to be related to area of
residence, socioeconomic status, family size, and history of pneumonia, bron-
chitis, or asthma. These factors appeared to act independently; their effects
were additive.
158
Colley and Holland attempted to assess the varying influences of smoking,
places of residence and work, overcrowding, family size, and genetic factors in
the etiology of chronic respiratory disease by measuring respiratory symotoms
and lung function in all family members. ^ preliminary analysis of 2,342
families living in two areas of North London indicated that the frequency of
such symptoms as winter cough in mothers and children differed between the
two areas. In the fathers, however, differences due to socioeconomic factors,
occupation, or smoking seemed to mask any geographic differences.
270
-------
TABLE 9-2
Frequency of Lower Respiratory Tract Infections of
Children in Britain by Pollution Levels, %a
Lower respiratory
tract infections
First attack in first 9 months
At least one attack in first
two years
More than one attack in first
two years:
Boys
Girls
Middle class
Manual working class
Admission to hospital in first
five years:
Lower respiratory infection
Bronchitis
Pneumonia
Smoke:
S02:
Mean annual Pollution levels, yg/m3
Very LowLowModerateHigh
67 132 190 205
90 133 190 251
7.2
19.4
4.3
1.1
0.0
1.1
11.4 16.5
24.2, 30.0
7.9 11.2
2.3
0.9
1.4
2.6
1.0
1.6
17.1
34.1
12.9
5.7
2.9
3.0
5.1
8.1
7.7
4.0
10.8
10.9
12.1
7.7
13.9
16.2
9.7
9.3
15.4
3.1
1.4
1.8
From Douglas and Waller, 1966.z02
271
-------
159
Colley and Reid studied respiratory disease frequency in urban and rural
areas of England and Wales. T.iey observed a pronounced socioeconomic gradient
of chronic cough, bronchitis history, and ear and nosa disease. The frequency
of chest conditions in children of semi- and unskilled workers grew with in-
creasing air pollution.
202
The cohort of children originally studied by Douglas and Waller were
159
reviewed at the age of 20 by Colley and Reid. They obtained information on
respiratory symptoms and illnesses by a self-administered mailed questionnaire.
Cigarette smoking was the main determinant of symptoms, but a history of chest
illness under two years of age was also significant. Neither social factors
nor air pollution appeared to influence respiratory disease. However, since
202
Douglas and Waller had originally related air pollution to lower respiratory
illnesses during the first two years of life, an indirect effect of pollution
must clearly have been present.
Many studies of the effects of air pollution on children have been con-
ducted by the Environmental Protection Agency (EPA) as part of their Community
235-237,577,696,697
Health and Environmental Surveillance System (CHESS).
This ambitious program was designed to assess the health effects of air pollu-
tants in a large number of communities in many parts of the United States.
Acute and chronic diseases (mainly respiratory), variation in lung function,
and concentrations of different pollutants in the body are related to estimated
pollutant concentrations in the areas of the subjects' residence. Studies have
577
been conducted in communities in the Salt Lake Basin, Utah; the Rocky Moun-
236 235 696
tain area, Idaho/Montana; Chicago/Indiana; New York metropolitan areas;
697
Cincinnati; and other areas. Although elementary schoolchildren less than
12 years old have received most interest, some studies included high school
272
-------
children, and one study concentrated on nursery children aged two to five years.
Other family members have been included in most of the studies.
Information has been obtained by questionnaires usually completed by
mothers or guardians, by teleohone surveillance of illnesses, and, in some
studies, by ventilatory lunq function testing. Various indices of respiratory
disease have been related to present and past measurements of pollution or to
estimates of probable pollution based on emissions. The adequacy of the al-
lowances usually made for social circumstances and parents' smoking habits is
sometimes debatable.
Attack rates of lower respiratory illnesses, particularly croup, were
higher in the most polluted communities of the Salt Lake Basin and Rocky Moun-
tain areas. Asthmatic children were particularly susceptible. The validity
of these conclusions is, however, open to doubt. The attack rates in the Salt
Lake Basin were strikingly higher only in the area of highest pollution. The
excess bronchitis was 100% for children aged 9 to 12, but less than 50% for
the younger and older children. Sulfate concentrations varied almost threefold
(0.005 to 0.014 mg/m3); sulfur dioxide concentrations differed even more widely;
while suspended particulates were either higher in the low pollution areas or
similar. Furthermore, unadjusted three-year attack rates in the Rocky Mountain
areas showed marked variation within the low pollution areas. Rates in the
lowest pollution area were often higher than in more polluted areas. Rates
differed little in the two high pollution areas despite a doubling of the pol-
lutant concentrations. Adjustment for socioeconomic factors would probably not
affect these attack rates very much. Pooling of the high and low pollution
areas permitted statistically significant associations to be shown. But the
legitimacy of such pooling is open to question.
273
-------
In Chicago and New York, illnesses were monitored by twice-weekly telephone
interviews of mothers. Significantly increased incidence of acute respiratory
illnesses, restricted activity, and otitis media were reported in subjects
living in high pollution areas of Chicago. In New York, both the incidence
and severity of acute lower respiratory illnesses were higher in the more pol-
luted areas. Again, these data show some inconsistencies that lead to questions
concerning some of the conclusions.
Ventilatory lunq function has been related to pollution in several of the
695
EPA studies. Shy and his colleagues studied second grade schoolchildren in
Cincinnati and Chattanooga and kindergarten through sixth-grade children in New
York City. The forced expiratory volume (FEVQ 75) and forced vital capacity
(FVC) were measured weekly for a 2- to 3-month period in Cincinnati and Chat-
tanooga and four times during the 1970-1971 school year in New York City. In
Cincinnati, the FEV was lower among white children living in the more polluted
areas, but among black children no differences attributable to pollution could
be demonstrated. The FEV tended to be lower in the winter months when pollution
was high. But the measurements did not appear to be closely related to the
levels of pollution during the lung function testing. Children aged 9 to 13
living in relatively unpolluted New York City suburbs had a significantly higher
FEV than children of a similar age living in two, more polluted central com-
munities. In contrast, children aged five to eight showed no differences which
could be related to variations in Pollution. Shy et al. suggested that reduced
pollution in New York City could have caused these findings.
The authors did not, however, control for the possible effects of ciga-
rette smoking by the older children. Moreover, in a later report they indicated
that their measurements of lung function were in doubt because of instrumental
malfunctioning.
274
-------
453
Lebowitz and his colleagues have recently described studies of children,
adolescents, and adults in two Arizona communities. Ventilatory lunq function
tests were administered after exercise in Tucson and in a smelter mining town
in southern Arizona. A reduction in FEVj Q and midmaximum expiratory flow
rates (MMEF) after exercise was observed on days of high pollution and high
temperature. The extent to which the effects were due to pollution or heat is
not clear. The authors indicated that longitudinal studies and possibly exoeri-
ments are needed to confirm and quantify these results.
In the CHESS studies, the EPA studied pollution effects in adults as well
134,233,234,258,282,283,320,341,367,487
as in children. Although most adults
were the parents of the CHESS children, military inductees and panels of oa-
tients with cardiorespiratory disease were also studied. Although effects of
pollutant concentrations in adults reflected those found in children with regard
to prevalence of respiratory symptoms, there are sufficient discrepancies in
the attacks of respiratory illnesses or worsening of bronchopulmonary and
cardiac conditions to indicate a need for further study. It is particularly
difficult to be confident about the levels of individual Pollutants that are
likely to produce these effects, particularly to exacerbations of asthma with
which several of these studies have been concerned. An important finding in
several CHESS studies is that particulate sulfates have a more important effect
on health than either total suspended particulates or sulfur dioxide. Future
studies should include sulfate measurements, including, if possible, different
sulfate compounds, to clarify the dose/response relationships involved.
156
Cohen and his colleagues studied the effects of pollution on 43 asth-
matics who lived near a power plant. These subjects had all experienced three
or more attacks of respiratory distress with wheezing during the preceding
275
-------
year. Twenty-nine of them wers observed for seven months or more. The inves-
tigators correlated reported attacks with daily temoerature and with concen-
trations of such pollutants as total suspended particulates, sulfur dioxide,
soiling index, suspended sulfates, and suspended nitrates. Attack rates were
highest at low temperatures and high pollution. The effect of pollution on
attacks was greater at moderate than at low temperatures. The authors concluded
that increased asthma attack rates might occur at pollutant concentrations com-
monly encountered in polluted cities. The results show an upward trend in the
average attack rates as pollution increased. Attack rates rose from 35% in the
absence of pollution to 50% or 60%, depending on pollutant and concentration.
On the other hand, there is wide variation around this mean regression.
Pollution probably played a relatively minor role in asthma attacks. The
findings preclude identification of pollutant concentrations that would be
innocuous to such attacks.
EFFECT OF REDUCING POLLUTION
Reductions in pollution appear to affect respiratory disease and lung
229
function. In 1967 Ferris and his colleagues reviewed the Berlin, N.H. sub-
jects who were first studied in 1961. In the intervening six years, pollution
as measured by sulfation rates or total suspended particulate concentrations
had declined from 30% to 40%. The prevalence of chronic respiratory disease
was less in 1967 than in 1961 after allowances were made for aging and changes
in cigarette smoking. Lung function measurements were also slightly better
than predicted. Concentratioas measured during these studies were:
Sulfation: 0.731 + 0.241 mg S03/cm2/day in 1961 and
0.469 + 0.111 mg S0-/cm2/day in 1967.
•™ 0
276
-------
Particulates: 0.180 + 0.710 mg/rc3 in 1961 and
0.132 + 0.830 mg/m3 in 1967.
Changes in smoking habits or the use of filter-tioped cigarettes could not
explain these differences. These findings apparently supported the conclusion
drawn in the Berlin/Chilliwack comparison, i.e., that the 1961 pollutant con-
centrations in Berlin were associated with decreased ventilatory lung function.
Dose/Response Relationships
Table 9-3 provides estimated concentrations of oarticulates and sulfur di-
oxide that may affect health. To reiterate, these two pollutants may not be
the most important. They serve only as indices of other, perhaps more impor-
tant, pollutants. In London, mortality has clearly resulted when 24-hr smoke
concentrations have exceeded 1.0 mg/m and sulfur dioxide concentrations have
reached 0.750 mg/fa3 (0.288 pan). These peaks used to occur in London during
average annual background concentrations of 0.3 to 0.4 mg/m3 of smoke and 0.25
to 0.30 mg/m3 (0.1-0.12 ppm) sulfur dioxide. Such concentrations are now fortu-
nately only of historical interest. They should certainly not be tolerated.
In London, 24-hr concentrations of -0.5 mg/fa3 of smoke and 0.4 mg/m3 (0.15
ppm) of sulfur dioxide exacerbated bronchitis. With the present lower concen-
trations, such exacerbations are infrequent. Some correlation still existed
when the average annual concentration of smoke was 0.06 mg/m3 and of sulfur
dioxide was 1.70 mg/ftt3 (0.654 ppm). Since then, pollution has declined further
in London but it is not clear if exacerbations still occur with increases in
pollution.
In Britain, sick leave attributed to bronchitis appeared to correlate
linearly with winter smoke and sulfur dioxide concentrations over 0.1 mg/m3
277
-------
CO
01
m
o
•H
Q
H
3
CO
en
0)
-p
ro
t-1
3
O
•H
P
ti
(0
(X
t.
o
x:
w
o
•H
•P
Q)
a:
a,
w
c
o
a,
w
CU
•a
fO
w
p
o
0)
IP
4-1
w
m
- e
CM^
co 6
n
W
cu
•H
O
•r-t C*)
P 6
ti -~-
tO bo
0, g
0)
O
rfl
H
P_i
0*
' C
.- z co
4-> -H .p
P C
bO 3 CU
c r-i e
•<-{ <-: 0)
bO O SH
ft) & 3
ti W
0) ti ft)
> o i
< IP B
CM IO O
o j- in
•-> J- J-
W
•H
P
•H
x:
o
c
0
p
X)
4-1
o
c
0
•H
^^ ^-t "P
•p -p ft)
• ,-) »rH XI
H H tl
IT) n3 ^
•P -P O
t* tl ft)
0 0 X
£ £ U
J H 0
o r- m
H 0 0
O U1 O
O C*^ LO
• • •
CM O O
c
o
T3
c
o
v-3
£_i
o
x:
CM
t-. ID
CTi O>
CM CM
£**! K**l
p 4->
•H -H
H -0
rd -H
•P X)
ti ti
O O
£ £
O O
in r~-
o o
«
CO CO
a: tr;
0 0
O 0
<£> CO
>,
4_J
•rH
O
,X
tl
0
^H
5
0)
Z
in
CM
i— i
w
•rH
P
•H
x:
o
c
0
ti
X)
UH
0
CO
c
o
•H
•p
fO
j^J
&
o
m
x
w
0
t^
0
"T3
QJ
•M
ft)
p
CO
p
o
2;
o
bO
fd
0
•H
x:
o
U3
CO
CO
>>
ti
0
P
fd
P
•H
a.
w
0)
ti
4-(
O
(1)
a
C
0)
r-H
rO
>
0)
ti
a
w
"xiJ E
0) O
(fl 4->
fO CU
Q) c
ti ^
O W
c
M
tD
CO
CM
O
,— ^
0-
•f
v,^
LO
J-
H
•
O
>i
4~i
•H
O
,x
ti
O
^-4
5:
0)
3
(£ t^~
CO C^
CO CM
^
CH
0
•P
fO
t.
•H
a,
w
CO
ti
4M
o
!U
CJ
c
OJ
H
rt!
0)
t<
CX
W
T) e >i
0) O -P
M P -H
H3 fit r— (
, -P
O W tl
C 0
M £
UD
CM CN
O in
0 O
CM
CM LO
* HH
0 O
1 O
00
H IT)
• •
O CM
>,
•P
•H
g 0
rC A;
bO k
-5 ^
e
ti S
-rH Cl)
« S
cn
ro
4n
O
0) >,
^ i^
CX O
4-<
*r^ n3
CJ EH
to «H
(0 CU
0) W
p QJ
O t<
M
O
d"
O
0
CM
•
O
C
O
£
o
v 1
c
rO
CD
S
j>>
v
(U
0)
t~v
J-
LO
^
P
O
2
6
O
P
4H
0)
O
P
0)
tf>
ft
rO
M
(/)
0)
C
a
•H
CO
CO
•r-(
•p
•H
x:
o
c
o
PQ
O
CM
O
0
CM
•
o
c
•H
tfl
P
•H
PQ
CO
x:
p
£
o
s
^
0)
•p
•H
UD
CM
o
CM
C
0)
•§
-H
•H
x:
o
c
•H
c
0
•H
-P
O
0)
4H
C
•M
>i
O
-P
(0
ti
•H
a
w
0)
ti
0)
s
o
CD
O
O
[ —
O
•
o
c
m
p
•H
ti
m
ro
R
c
CO
Ti
J-
N t^-
•O CT>
d- J-
1
O
C
3
4H
bO
C
3
H
T)
C
(0
CU
O CO
c e
Q) O C
H -P 0)
(0 d. P
> E T)
, r-(
P CO -H
cx x:
>, o
W ti
•HOC
4-1 -P -H
*M ft)
x: ti c
O -H O
C CL.-H
o to -p
ti
£ a
*Q ?3
LT) CO
^ ^
O O
CO CO
0 H
• •
o o
o
H C
ft) -H
4n ti
3 0)
C-Q CQ
•
^"»
fO
•a
(M
E
O
0
o
H
m
O
a
CO
£***
fO
"0
o
ro
\_
CM
B
O
V,
ro
O
CO
bO
e
rCi
.
to
•p
•H
C
IH5
0)
N
(0
4-1
0
I)
C
CU
o
4-1
CU
o
O
278
-------
(0.038 pom). It would be very interesting to know if similar correlations can
still be demonstrated at the oresent lower pollutant concentrations.
In New York City, 24-hr coefficient of haze units (COHS) of 5 or more and
sulfur dioxide of 2.0 mg/m3 (0.769 opm) have resulted in deaths; 3 COHS and
0.7 mg/ft3 (0.269 ocm) sulfur dioxide have caused illness. Studies of daily
mortality in relation to pollution suggest that excess deaths may occur when
sulfur dioxide is as low as 0.35 mg/m3 (0.013 pan). In Chicago, exacerbations
of bronchitis were associated with daily sulfur dioxide concentrations of
~0.75 mg/n3 (0.288 pan), probably in the presence of high concentrations of
particulates.
In Buffalo, mortality from respiratory illness appeared to increase pro-
gressively from the lowest to the highest pollutant concentrations. The lowest
level of smoke was <0.08 mg/m3 and of sulfation, 0.045 mg/onVday. A number of
other British studies suggest that average annual concentrations of particulates
and sulfur dioxide should both be held to under 0.100 mg/m3.
Conclusions from the CHESS studies are shown in Tables 9-4 and 9-5. Un-
fortunately, as the best case/worst case estimates indicate, the results are
questionable. As suggested earlier, the findings should be confirmed before
expensive decisions are based on them.
PARTICULATES IN RELATION TO RESPIRATORY CANCER
The evidence that cigarette smoking is the main cause of lung cancer is
200,201,312-314
now generally well recognized. Certain occupational exposures,
notably to radioactivity, chromates, nickel, asbestos, arsenic, and the
199
distillation products of coal are also well established. Some syner-
gism, such as that between occupation and smoking among uranium miners and
279
-------
3-
1
01
U^
a
s
m
• S
•o ^
Q P b<
T3 to a
CO H. O
C H c\
H
1
0 CM O
cr>
IB
m
t) -^
tx dl CO *
rH t) dl TJ
CB C V P
E 0- CO 01
«P -rt 0, IP.
to
01
t
1
C
t
<4-l
0.
o
V
V
it
4J
1
•H
4->
CO
O
01
UH
UH
M
_c
rH
IE
X
o
CO
Tl
o
14-1
CO
4-1
•rH
P
to
W
•O
rH
5
M
0)
1-
H
f.
GO
a
X
u
£
£
a
i
r-
C
£
en
cu
y*j
H
""
01
IB
rH
3
0
•H
4J
CO
CU
01
01
to
3
cn
10
0
c
to
CO
01
10
UH
3
5
B
3
O
rH
•1
ro
(X,
t. tO rH O
- 0. 3 3 C
c tn m *^
CO IB CO
IB IB IB
•0 -O -0
0 O 0
z z z
•H C
STJ
CO) • e
C -0 -v.
>,«H -P bl
P IB CO 3.
01 4->
IP. C c\j in
to O O uo
C/3 O yi CO
01
1
o t^ o
ro
C
0
•rl
ro
£4
3
C
^ t< (H
a- rf a-
CM CM CM
W
f-
1 O
O O O O
vn o in ro
CM in CM
m
e
"^ 01
&0 4->
3. CO
• g a>
rH O P
01 -rl tO
01 p. rH
r-l S 3
IX tO
I)
CO 10 IB
CO CO 10
•O TD -O
0 O O
Z Z Z
CO
°d s
U to
1 O
O O O 0
co o o a-
in
-------
T3
It
ft
X
C
C[
B
>
b
s
Si fc
«lS ,-* a
(B § .5 c
3 0 ??•*
X oj m -n
0*1 S 5
•* M c
Q 1 1 X *H
, E 4-> C8
w J H I 01 4->
3| 01 1 14-1 C
<*-> H 10 0
3 bj W °
•
T3
+J
n
OM
CO
E-.
T)
E
*^v
M
3.
O CO CO
I" CO CO CO
r~ rH ,H
T3
01 U
•o o>
C V
o n
r\ ll!j
tli *4^
0 M
3 3
W M v
.
13
p
B
o
c
-< o o o
• f1
E>
w
CM
O C
co a
= CO
JO -H
3. 1
O CN fsg
' m H rH
2 CM CM
co el
O) „
5 H c
- .3
«;b 2
11 2 „
IF °&
•Ofco I
§ Eg
1 II
C c C
J 3 3 o
•H|0)l
•^ I*1* 1
•»-> (dl
j_j Ljj j
<|3
•P
4J 4->
"> UlM o>
1 0>|r3| ^
c*> CM Jo. 1 ^
u u-o 5
j jiil ^
< ° o
sfc ^
t.fS u
&,
CO
t-
in tn in
CO t^ t-.
rH rH rH
TI
01 W
T> 01
— 4^
1) ro
iUn
3 3
CO B
fvl
O
CO
IB 1C CO
4-1 4^ 4-1
CO CO CO
T) T3 T>
O O O
2 X Z
1 CO
o en o o
CM rH IO in
rH CM CM
om
14-1
CO B*
" "I 0)
ite -s «
2 h 0> -H
5H ^"
a> a
01 0) |
B w bO
ro <8 -O
o 03
•r~i 4->
4-1 4-1 C
W B p Ql
£^ 0} B E
0 0) 0)
a j m
T3|+->[
•"*! fJ
°HI
to I y
a'M!
CH N-> _,-. ,-
41 !!
0) t,
« Q.
01 Q,
>,
I
o
• ro
01
ei j=
CO
[< C
s g
ss
Excess
mortality
CO
CO
0 0 CO
d- co
rH
o o o
CM
^
1
O in en
O rH
3-
co CM in
rH
1 O
o o o o
CO M CO O
-H rH
01 O3-
CM rH
1 O
o CT> ^ in
in o OT
d-
0 Q) 1 ^
w w bo
ITJ fO t3
0 (JP
•n 4->
*-* *^ c
W » •*-> 0)
fj (OWE
5 SS
1
o
•H
1
•o
»r-l
O.
U
Increase in
prevalence
of chronic
bronchitis
O r-. co
to co
rH
O O O
3-03-
rH in H
rH CO CO
CO O O
r> o o
CM rH
CTl CO O
CM
rH O rH
CTl O Ol
01 01 1
B B bO
CO CO T3
O O 3
4-* P c
CO B 4-* 01
it a a E
O 01 111
•^ T -fl q-j
>,
OS
o
o
•H
§
T.1
*r-i
Cu
u
1 1
01 IH .ri |
t O D.rH
Crt fw B rH 4)
0 >> 0) -rt B
1^:^11;
g = S>^OB&rH.'
J)li> 3+J«)j-;(Bi
!j3010COIl)tS
OCT-tflrO^COili
M
CO rH rH
(0 O O
iH rH
0 O 0
CO CM CO
CO *H CO
CM
C
%
O
c
A:
rH C CO
CD rH rH
CM in m
rH rH rH
* CD -^
rH H rH
SO CO
in O
rH CM H
01 0) i
B U &0
CO CO -O
O O 3
•n 4-»
4-» 4-> C
B B 4-> fll
(4 CO CO E
O ft> 01
Sfe O CO
&
o
rH
o
.iH
•a
•H
a.
u
1 M
-o .5 3 1 8 S
5 ai^g'g
•• W r-H 3 O
H Iff -H Cfl M -O
: V E a <4H ..H
K t co 01 c a,
•< O IP C -iH 01
281
-------
«
rt
k
it>
•s
IB
n
>i
i
*t
•> a
c
•H C
bO-H
i,
i a
>>T"
V IB
D p
M* C
38
• m
•o e
•p --
CO 00
3.
Pw
££
t3 '^
U} CO •
T3 HI -O
C P P
fl) IB W
CL >P.
WHO
3 3 C
CO CO v
• <*1
•0 S
•p ~v
ui bo
3.
CS
o o
to co
cn
Sk
01
a
X
U
U CO
I-O 41
C , o
i> a
0 ^
jj c c •
IB -H -H
co *H 4-1 en
n) a o c
cj co nj o
T3 cti
a)
On
IB
en
282
-------
asbestos workers, is definite. But occupational exposures are unlikely to
cause more than a small fraction of the total number of lunq cancer cases.
Urban/rural differences in respiratory cancer mortality have long been a
feature of the vital statistics of many countries. They have been supported
by incidence data from certain cancer registries and by special surveys. Dif-
ferences in smoking habits or occupational exposures between urban and rural
areas cannot account for all the excess urban cancer rates, nor can better
reporting of lung cancer in towns or the movement of people to towns for diag-
nosis. The presence in urban air of polycyclic hydrocarbons and other parti-
culates known to cause lung cancer suggests that pollution might explain the
urban/rural differences. But despite considerable research, this is still
uncertain.
Early studies in Britain suggested that pollution exerted a small or
negligible effect on lung cancer after allowances had been made for social
732,736
factors and population density. Among British researchers, only
Stocks considered the possibility that pollution contributed substantially to
lung cancer mortality. He compared death rates from lung cancer to pollution
and smoking in Liverpool and its surrounding areas. In his first paper on the
734
subject, he claimed that approximately half of the lung cancer deaths in
Liverpool were attributed to smoking habits and three quarters of the remainder
were due to a factor that was only slightly present in the rural areas. He
suggested that benzpyrene "might be one of the factors involved."
Stocks also related age-standardized mortality ratios for lung cancer to
3:4 benzpyrene, 1:12 benzperylene, pyrene, fluoranthene, sulfur dioxide, and
smoke obtained from 17 locations in Liverpool and North Wales. Lung cancer
standardized mortality ratios (SMR's) correlated both highly and positively
283
-------
with all these pollution measurements. Cancer of the intestine and rectum, on
the other hand, correlated neither with smoke nor with population density.
36
Anderson reanalyzed Stocks data by stepwise regression. He concluded
that although polycyclic hydrocarbons contributed significantly to the multiple
correlation coefficient, the contribution was infinitesimal compared with popu-
735
lation density. In a further study Stocks collected data at 26 localities.
He also used a socioeconomic scale, or "social index", based on the proportion
of males aged 15 and over in the lowest income group. Smoke and 3:4 benzpyrene
correlated positively with lung cancer mortality. Here, too, Anderson reana-
lyzed the data and found that lung cancer did not correlate significantly with
benzpyrene if smoke and social index remained unchanged. In further studies,
Stocks positively correlated lung cancer mortality rates with smoke, 3:4 benz-
pyrene, 1:12 benzperylene, arsenic, beryllium, and molybdenum in eight dif-
ferent localities and between lung cancer and both cigarette and solid fuel
cons_nption in 20 countries.
126
Carnow and Meier extended Stocks' analyses to include age-specific lung
cancer death rates and cigarette consumption for 19 countries. They also
analyzed lung cancer death rates in relation to smoking (based on cigarette
sales per person over 14 years old in 1963) and benzpyrene (based on a
weighting of urban and rural values from unpublished data of R. I. Earsen
and J. B. Clements) in the 48 contiguous states of the United States. They
concluded that a 5% increase in lung cancer mortality will be produced by an
increase of 0.001 mg/1,000 m3 of benzpvrene. The benz(a)oyrene figures for the
different states are questionable because of the procedures used to estimate
them. Even if they are accepted as valid, their correlation with lunq cancer
death ratas is not impressive and appears to be due mainly to some low values
in a few rural states.
284
-------
The most systematic studies of urban/rural ratios of lunq cancer death
rates in the United States have been those conducted by Haenszel and his col-
307,308
leagues. In 1958 they studied the smokinq habits and residential
histories of a representative sample of the population and of a 10% sample of
victims of lung cancer deaths in the United States. They found the expected
gradients of increased lung cancer mortality with increased cigarette smoking.
Differences in death rates (SMR's) for different categories of smokers living
in urban and rural areas are shown in Figure 9-2. Differences in death rates
of nonsmokers by residence were trivial; but the joint effects of smoking and
residence were far greater than would have been expected, assuming that smoking
and residence exerted additive effects. Finally, there were higher risks among
the more mobile groups as compared with lifelong residents. U.S. farm-born
and foreign-born residents of large metropolitan centers were particularly
high lung cancer risks.
When allowance is made for mobility and only lifelong residents are com-
pared, the SMR of nonsmokers living in urban areas is appreciably higher than
that of nonsmokers living in rural areas. The number of deaths among lifelong
residents is, however, small, reflecting the very high mobility of the U.S.
population. Ability, then, should be considered in addition to smoking habits
when assessing the effects of pollution on disease.
343
In 1965-and 1966, Hitosuqi studied lung cancer in relation to smoking
and air pollution in two Japanese cities near Osaka. The air pollution in
these cities was broken down into three categories based on extensive measure-
ments of dust fall, sulfur dioxide, suspended particulates, trace elements,
and aromatic hydrocarbons. Hitosugi obtained information on the smoking
habits of lung cancer patients as well as a representative sample of healthy
285
-------
600
500
400
DC
s 300
LO
200
i nn
0
16 14
.•
I
49
ijiW:
Urban
Rural
29
^n
137
:-x:x':x*
11
104
565
£:•:?:•
*•*•"•"•*•"
&S
fxW
ss?
• x-::x
: •:•:•:•:•
• Xv'"r"
" X'X*"
'; XvX
•X'Xv
•X-X-I-
::-':¥:-V
x:S:x'
•l-l'i-x
384
Never
Occasional or
Exsmoker
Regular
1 pack/day Over 1
or less pack/day
FIGURE 9-2.
Standardized mortality ratios (SMR's) for lung cancer in U.S.
vMte males in 1958 according to smoking and residence.
Data from Haenszel et al., 1962.307 Figure from Higgins,
1976.336
286
-------
persons living in each of the three pollution areas. Death rates for lung
cancer rose with increased smoking in each pollution category. The death rates
among smokers also increased slightly with increased pollution, but not among
nonsmokers. The author suggested that this might indicate synergism between
smoking and air pollution and lung cancer.
Studies of immigrants support the hypothesis that air pollution is a
209
factor in the causation of lung cancer. British immigrants to New Zealand,
190 191 306 171
South Africa, Australia, the United States, or Canada have lower
death rates than the British population, but higher rates than natives of
their adopted countries. Immigrants who left Britain aged 30 and over have
higher rates than younger immigrants. The differences cannot be explained on
the basis of differences in smoking habits. Maybe they reflect environmental
exposures before migration. However, it is well established that immigrants
are not a representative sample of the country from which they emigrate. Nor
has any consideration been given to the types of jobs adopted by immigrants.
One way in which the impact of pollution on lung cancer can be assessed
is to see what happens when pollution is reduced. To test the hypothesis
that particulate pollution contributes to the development of respiratory
cancer, trends in mortality from the disease from 1950 to 1970 in London,
where particulate pollution declined greatly, were compared with trends in
the rest of England and Wales, where the decline was less. The results are
somewhat equivocal. A somewhat greater decline in the age-soecific death
335
rates in men under 55 years occurred during this period in London. This
did not appear to be entirely attributable to different trends in smoking
habits.
287
-------
SUMMARY
Q
There is good evidence that exceptional episodes of pollution (>1.0 mg/m
[0.385 pom] sulfur dioxide and particulates) caused illness and death. There
is also a good deal of evidence that sustained lower levels of pollution
>0.1 mg/m3 (0.039 ppm) of sulfur dioxide and particulates for a number of years
affect health adversely. Pollution predominantly affects those who are already
suffering from disease, particularly of the heart or lungs; however, evidence,
especially from studies of children, suggests that pollution can initiate
disease as well as exacerbate it. Particulate pollution, especially from sul-
fur compounds, probably plays a considerable role in the development and pro-
gression of bronchitis and emphysema. There have also been suggestions that it
plays a role in lung cancer; however, this is much more debatable.
There is insufficient knowledge concerning safe pollutant concentrations.
The orimary air quality standards for particulates were probably reasonable
when they were adopted, bearing in mind the inadequate information then avail-
able on the character of the oarticles. There is now a clear need for much
more precise specification of particles and their characteristics, particularly
their size distribution. The trend in emohasis on the health effects of sulfates
is an indication; however, information on dose/response relationships for sul-
fates is insufficient to suggest acceptable standards for these compounds.
Much more information is also needed on the effects of interactions be-
tween pollutants, or between pollutants and meteorologic, climatic, or personal
factor^. The possibility of pollutant interaction raises questions about the
validity of any national standard for a particular pollutant. The pattern of
pollution should be considered when a standard for any particular pollutant is
set. Any sulfate standard should take into consideration the type of sulfate.
288
-------
CHAPTER 10
EFFECTS OF PARTICULATE AIR POLLUTANTS ON VEGETATION*
Many gaseous air pollutants are readily recoqnized as the cause of injury
to various types of vegetation. In contrast, relatively little is known and
limited studies have been conducted on the effects of particulate air pollutants
on vegetation. Published results of experiments are confined principally to
settleable dusts emitted from the kilns of cement plants. There are a few re-
ports on effects of fluoride dusts, soot, sulfuric acid mist, lead particles,
and particulate matter from various types of metal processing. Most of the re-
search is related to the direct effects of dusts on leaves, twigs, and flowers,
as opposed to the indirect effects from dust accumulation in the soil.
Gaseous air pollutants have direct access to interior leaf tissues
through the stomata, those openings in the eoidermis of leaves through which
normal gas exchange required for growth takes olace. Most crop plants are
broad-leaved and the majority of functional stomata are located on the lower
leaf surface. Thus, settleable dusts would be deposited in most cases on
the upper leaf surface. The mere physical presence of chemically inert par-
ticles might alter the quality and intensity of light reaching chlorophyll-
bearing cells, to the detriment of photosynthesis. Such dusts could also
interfere with biologic control of insects. Those dusts with some chemical
activity could induce injury by radical changes in pH or by dissolving or
rupturing the cuticle, thus altering water balance or allowing epidermal
*Adapted from Chapter 7, "Particulates," by S.L. Lerman and E.F. Oarley from
Responses of Plants to Air Pollution, edited by J. Brian Mudd and Theodore T.
Kozlowski.Academic Press 1975.ALL rights reserved. Reprinted with per-
mission.
289
-------
penetration of toxic chemical constituents. Of course there is the possibility
that some dust may deposit on the lower leaf surface. In so doing it may
even cover or clog stomata and interfere with normal gas exchange. But it
is unlikely that particles would ever have direct access to inner leaf tissues
as do gases.
Because of the dearth of results from experiments, many reports are directed
to the question of whether particles have deleterious effects on plants rather
than to discussions of the extent of plant injury. Because particulate matter
is a conglomerate of chemically heterogeneous substances, it is reasonable to
anticipate some disagreement concerning its impact on vegetation. The various
types of particles and their effects on vegetation are discussed below.
EFFECTS OF SPECIFIC PARTICUIATE MATTER ON VEGETATION
Cement-Kiln Dust
This dust is not derived directly from processing of cement. It is con-
tained in waste gases from kilns. Some reports indicate, however, that the
composition of wastes from different kilns .operating at different efficiencies
varies considerably. At times the effluents may contain cementitious materials
that belong in the finished product. Reports describing effects of dust depo-
sited on various plants in the field relate to kiln-stack materials, whereas
dusts applied in laboratory or field studies are taken from various collectors
in the waste-gas system between the kiln and the stack. Differences in results
caused by this factor have not been reconciled.
Fallout levels, as well as the physical and chemical properties of kiln
dusts, ar determined by such factors as the nature of raw material, cement
manufacturing processes, and the type of equipment employed for the control of
460
particulate matter emissions. Lerman recorded dust deposits of 1.5 g/fa2/day
290
-------
in the vicinity of a cement plant in California. The rotary kilns in the plant
were equipped with a multiple cyclone emission control device. According to re-
ports from Germany, the maximum amount of dust that might be deposited near
592 76
cement factories varies from 1.5 g/m2/day to 3.8 g/m2/day. The diversity
in chemical composition and pH reactions of cement-kiln dust samples from
various sources are presented in Table 10-1.
Direct Effects; Field Observations and the Nature of Dust Deposition.
Most reports concerning harmful effects of cement-kiln dust on plants stress
605
that crusts form on leaves, twigs, and flowers. In California, Peirce and
597
Parish noted that settled dust in combination with mist or light rain formed
a relatively thick crust on upper leaf surfaces of affected olants. The crust
would not wash off and could be removed only with force. The central theme
175-178
about which Czaja builds his case for harmful effects is the crust
formation in the presence of free moisture. He states that crust is formed be-
cause some portion of the settling dust consists of the calcium silicates that
are typical of the clinker (burned limestone) from which cement is made. When
this dust is hydrated on the leaf surface, a gelatinous calcium silicate hydrate
is formed. This later crystallizes and solidifies to a hard crust. When the
crust is removed, a reolica of the leaf surface is often found, indicating
intimate contact of dust with the leaf. The relatively thick crust formed from
continuous deposition is confined to the upper leaf surface of deciduous species
but completely encloses needles of conifers. During orolonged dry periods when
dust is deposited, the lack of hydration prevents crusts from forming. Dust
deposits that are not crusted are readily removed by wind or hard rain.
Photographs taken in Germany by Darley and Lerman (Figures 10-1 and 10-2)
show incrustations of cement-kiln dust on branches of fir trees. Atmospheric
291
-------
TABLE 10-1
Chemical Oonposition of Sore Cement-Kiln Dusts,
Sample
California
(Cal-1)
Arizona
(Ariz-3)
Germany
(G-l)
Germany
(G-2)
Na Ca
K
pH of water-
Mg Al Fe dust suspension
0.40 31.20 2.16 0.40 0.40 1.15 12.3
0.13 23.00 8.00 1.00 0.32 0.55 10.8
2.80 17.56 13.00 1.08 0.94 1.10 10.4
7.60 8.00 32.50 0.56 0.48 0.60 7.3
292
-------
FIGURE 10-1. Cement-kiln dust on fir branches. Incrustation has built up
on the older twigs of a fir tree exposed to cement-kiln dust
particles in the vicinity of a cement plant. Needles have
fallen prematurely.
293
-------
FIGURE 10-2.
Cement-kiln dust on fir branches. Very heavy incrustation on
a branch of a dead fir tree exposed to cement-kiln dust par-
ticles in the vicinity of a cement plant.
294
-------
r\
concentrations of dust in this area were probably in excess of 1.0 g/fa /day.
Incrustations built up on the older twigs (Figure 10-1) and caused needles to
fall prematurely. Some of the twigs were dead and incrustations were forming
on the newest needles. The net effect was a shortening of each succeeding year's
flush of growth. A dead tree had heavy incrustations on the branches (Figure
10-2).
76
Bonne reported a marked reduction in growth of ooplar trees located
about 2.2 km from a cement plant in which production had more than doubled.
The change in growth rate was determined by the width of annual rings in the
184
wood. Darley observed a reduction of spring growth elongation on conifers
in Germany, where the oldest needles were incrusted.
38
Anderson observed in New York that cherry fruit set was reduced on the
side of the tree nearest a cement plant. He demonstrated that the dust on the
stigma prevented pollen germination.
592
Pajenkamp reviewed the unpublished work of several German investigators,
some of whom had applied dust artificially to test plants, and stated that he
was opposed to the view that dusts are harmful to plants. He concluded that
depositions from 0.75 to 1.5 q/m2/clav (the higher amount representing the maxi-
mum that might be found near a cement factory) had no harmful effect on plants.
631
Raymond and Nussbaum concurred that cement dusts have little effect
300 793
on wild plants. On the other hand, Guderian and Wentzel disagreed with
Pajenkamp. Ihey stated that the limited evidence at best oresented a contra-
175-178
dictory picture and that Pajenkamp had not cited Czaja's earlier work.
They also pointed out that a deposit of 1.5 g/m2/day was not maximum, since
2 76
other investigators had found up to 2.5 g/m /day. Bohne has since reported
weekly averages of up to 3.8 g/m2/day.
295
-------
605
Physical Effects. Peirce demonstrated that incrustations of cement-
kiln dust on citrus leaves not only interfered with the liqht required for
photosynthesis, but also reduced starch formation. This was later confirmed
177 76 .. 722
by Czaja and Bohne in a variety of plants. More recently, Steinhubel
compared starch reserve changes in undusted common holly leaves and those dusted
with foundry dust. He concluded that the critical factor preventing starch for-
mation was the light absorption by the dust layer, and that the influence on
transpiration or overheating of leaf tissue was of minor significance. Lecrenier
454
and Piquer attributed the reduced yields from dusted tomato and bean plants
184
to interference with light imposed by the dust layer. Darley demonstrated
that dust deposited on bean leaves in the presence of free moisture interfered
with the rate of carbon dioxide exchange, but he did not measure starch formation.
178
Czaja has presented good histoloqic evidence that stomata of conifers
may be plugged by dust, thereby preventing normal gas exchange by the leaf
tissue. Uninhibited exchange of carbon dioxide and oxygen by leaf tissue is
necessary for normal growth and development.
460
Lerman demonstrated limited clogging of stomata on bean leaves that
were heavily dusted with dry dust. Scanning electron micrographs of upper and
lower surfaces of dusted bean leaf are shown in Figures 10-3 and 10-4. Only a
few dust particles can be observed on the lower surface of the leaf (Figure
10-3), where most of the stomata are located. Many stomata on the upper surface
of the leaf (Figure 10-4) are clear of dust particles in spite of the fact
that the leaf was dusted with 6.64 g/m2, a dust load that would normally cause
severe damage to bean plants in the presence of free moisture.
184
Chemical Effects. Darley applied kiln dusts of particles <10 Pm dia at
rates of 0.5 to 3.8 g/m2/day to leaves for two to three days in the laboratory.
296
-------
FIGURE 10-3.
Scanning electron micrograph of the lower surface of a cement-
kiln dusted bean leaf. Only a few dust particles can be observed
on the lower surface C5f a leaf that was dusted with a total of
6.64 g/m2. (X 300.)
297
-------
FIGURE 10-4.
Scanning electron micrograph of the upper surface of a cement-
kilrrdusted bean leaf. Many stxmata of the upper leaf surface
are clear of dust particles despite the fact that the leaf was
dusted with 6.64 g/m2. (X 300.)
298
-------
Water mist was applied several times each day. Even though the dust adhered to
the leaf in a uniform layer, it was not crustlike, probably because the experi-
ments were of short duration. Reduction in carbon dioxide uptake was reported.
Leaves of bean plants dusted for two days with cement-kiln dust from 8 to
20 \m dia at the rate of 4.7 g/m2/day, and then exposed to naturally occurring
dew, were moderately damaged. Itie edges (Figure 10-5) of the leaves curled and
some interveinal tissues died. Leaves that were dusted but kept dry were not
injured.
184
In two- to three-day experiments Darley dusted the primary leaves of
bean plants with fractionated precipitator dust obtained from Germany. The dust
contained relatively high amounts of potassium chloride. When a fine mist
was applied to dusted leaves, up to 29% of the leaf tissue was killed. This
action was attributed to the potassium chloride. In later experiments other
fractions of the same dust containing verv little potassium chloride caused an
almost equivalent amount of injury, indicating that ootassium chloride was ap-
parently not the only factor involved.
Detail on the injury to be expected from certain cement-kiln precipitator
178
dusts was given by Czaja. His work is based on comparisons of chemical com-
position of dusts and resultant injury to leaf cells of a sensitive moss plant,
Mnium punctatum. A cut leaf was mounted in water on a microscope slide. EXist
was placed in contact with the water at the edge of the cover slip. Any effect
of the resultant solution on leaf cells could be observed directly. Eighteen
of the dusts tested in this way fell into the following categories:
• no permanent injury to living cells, but some olasmolysis attributed
to the solution;
299
-------
*i
CO JH^ Q)
0) 'ti r-t
o -P
's
C
CO (0
-P H
I §£
o£
co nj •
-P -^ m
S m
r3 0)
rH . iH
(13 "TJ
^"s S
-*-1 • J
(/} ^p rQ •
rS ' W
O co "co
•H -S U
-U
a)
O
CM
B'H
coB
o
H
300
-------
• slight injury to the cells most accessible to the solution, disrup-
tion of the cytoplasm, and displacement of chloroplasts; and
• severe injury to all cells.
Dusts were described as follows:
• group 1, pH 9.5 to 11.5, relatively high rate of carbonation, an
intermediate amount (19% to 29%) of clinker phase (calcium silicates),
and a high (36% to 79%) amount of secondary salts;
• group 2, oH approximately 11, a high rate of carbonation, a lower (13%
to 16%) clinker phase and a significantly high (81% to 35%) proportion
of raw feed;
• group 3, pH 11 to 12, a very slow carbonation rate and a significantly
high (17% to 49%) clinker phase.
The greatest injury was related to the largest amounts of clinker phase, which
in turn resulted in higher and prolonged alkalinity. But Czaja also oointed out
that the composition of dusts within the three grouos was not consistent and
that, although not vet demonstrated, the constituents of a given dust undoubtedly
influence one another.
177
Czaja stated that the hydration process of crust formation released
calcium hydroxide. The hydrated crusts gave solutions of pH 10 to 12. Severe
injury of naturally dusted leaves, including killing of oalisade and narenchyma
cells, was revealed by microscopic examination. The alkaline solutions oene-
trated stomata on the upper leaf surface, particularly the rows of exposed
177
stomata on needles of conifers, and injured the cells beneath. Czaja
stated that on broad-leaved species with stomata only on the lower leaf surface,
the alkaline solutions first saponified the protective cuticle on the upper
surface, permitting migration of the solution through the epidermis to the
301
-------
palisade and parenchyma tissues. Typical alkaline precioitation reaction
with tannins, especially in leaves of rose and strawberry, was evidence that
76
calciun hydroxide penetrated the leaf tissue. Bohne described similar
"corrosion" of tissues under the crust formed on oak leaves.
460
Observations made by Lerman with a scanninq electron microscope re-
vealed disorqanization of the cuticle on the surface of dust-dew treated bean
plants (Fiqure 10-6). The breakdown of the layer appeared first in the form
of cracks. This later develoned into a mass of dust particles surrounded by
peeled-off cuticular strips. Fiqure 10-7 shows the smooth upper surface of a
control leaf. Chemical analysis of extracts from the leachate of the treated
leaves revealed relatively larqe quantities of free hexadecanoic acid, and
small amounts of free tetradecanoic, dodecanoic, and nonanoic acid. These fatty
acids are among the cuticular wax constituents. Extracts from the leachate
of control plants did not have any detectable amounts of these fatty acids.
461
S .udies by Lerman and Darlev revealed that bean plants respond in
various ways to dust-dew treatment usinq dusts from different sources. Oust
from California (Cal-1) caused moderate damaqe: the oH of the dust-water
susoension reached 12.3 (Table 10-1). Arizona (^riz-3) dust caused severe
damaqe but the pH of the suspension was only 10.8. Dust from one cement olant
in Germany (G-l) had a relatively low content of calcium with a oH reaction
of 10.4; this dust had no harmful effects on plants. The level of potassium
was very high in the dust samole from a second nlant (G-2) and the oH reaction
was near neutral; yet, bean plants dusted with G-2 dust showed damaqe symptoms
and reduced carbon dioxide fixation. This hiqh potassium chloride dust could
act on the olant as airborne salinity. Most of the calcium in the dust samoles
was in the form of calcium oxide, calcium hydroxide, and calcium carbonate.
302
-------
FIGURE 10-6. Scanning electron micrograph of the damaged upper surface of
cement-kiln dust-dew treated leaf. Dust deposit 5.0 g/ra2, an
advanced stage in the breakdown of the cuticle, marked by the
mass of dust particles surrounded by peeled-off cuticle strips.
(X 300.)
303
-------
FIGURE 10-7.
Scanning electron micrograph of the upper surface of primary
bean leaf. Control undusted leaf. (X 300.)
304
-------
The high pH reactions of the dust-water suspensions were positively correlated
with a high content of calcium hydroxide, as was demonstrated by X-ray powder
diffractometry. These results indicate that the response of plants to dust-dew
treatment is directly related to the chemical composition of the dust. In ad-
dition, they indicate that the physical effects of the dust alone are negligible
since dust treatment without dew had no detectable harmful effects on plants.
592
Indirect Effects. Pajenkamp reported on unpublished work by Scheffer
in Germany during two growing seasons. He indicated that even considerable
quantities of precipitator dust applied to the soil surface brought about
neither harmful effects nor other lasting effects on growth or crop yield of
oats, rye grass, red clover, and turnips. The dust content was 29.3% limestone
(analyzed as lime, CaO) and 3.1% potassium oxide. The maximum rate of deposit
was 1.5 g/m2/day. Discontinuous dustings, made at 2.5 g/m2/day, averaged 0.75
g/m2/day. In one year the yield of red clover and the weight of turnips were
higher in the dusted plots, although the yield of turnip leaves decreased.
Acid manuring of the soil appeared to increase yield but the interaction of
dusting and manuring was not understood.
669
While Scheffer et al. found no direct injury to plants, they indicated
that there might be indirect effects through changes in soil reaction, which
in time might impair yield.
The indirect effects of cement dust on soil fertility and crop growth near
596
a cement factory were reported by Panda et al.
In 1956, Stratmann and van Haut studied the effects of cement dust on
vegetation in Germany (personal communication). They dusted plants with
quantities of dust ranging from 1.0 to 48.0 g/n ^day; dust falling on the soil
305
-------
caused an increase in alkalinity, which was unfavorable to oats but favorable
to pasture grass.
677
Schonbeck treated a field olanting of sugar beets biweekly with 2.5
g/m2 of dust and observed that infection by leaf-spotting fungus, Cercospora
beticola, was significantly greater than in undusted olots. He postulated that
the physiologic balance was altered by dust, increasing susceptibility to
infection.
184
Darley noted that plants were stunted and had few leaves in the heavily
dusted portions of an alfalfa field downwind from a cement plant in California.
Plants appeared normal in another part of the field where there was no visible
dust deposit. The dusted plants were also heavily infested with aphids.
Entomologists suggested that the primary effect of the dust was to eliminate
the aphid predators, thereby encouraging high aphid populations whose feeding
caused poor plant growth. While this effect of cement-kiln dust was not
52
proved Bartlett had shown that deposits of several kinds of mineral dusts
on leaves greatly reduced or eliminated hymenopterous insects that were par-
asitic to citrus pests. His review of the literature indicates that dusts
have a similar effect on a wide range of insect predators.
Vftiile assessing the long-term effects of limestone dust on vegetation under
85
natural environmental conditions, Brandt and Rhoades comoared dusted and non-
dusted forest communities in the vicinity of limestone quarries and processing
plants. At a heavily dusted site, the seedling-shrubs, saplings, and tree
strata Incurred significant changes in structure and composition. In a compar-
86
ative study the same investigators demonstrated a reduction of at least 18%
in the lateral growth of Acer rubrum L. (red maple), Quercus prinus L. (chestnut
oak), and Q. rubra L. (red oak). However, lateral growth of Liriodendron
306
-------
tulipifera (yellow poplar) increased by 76%. Chanqes in soil reaction and
nutrient availability were considered as possible factors in both the increase
in lateral growth of L. tulipifera and in reductions of qrowth of dominant trees
in the dusty site.
Fluorides
Particles containing fluoride appear to be much less injurious to veget-
589
ation than gaseous fluorides. Pack et al. reported that 15% of the gladi-
olus leaf area was killed when Plants were exposed four weeks to 0.79 yg/m3 of
fluoride as hydrofluoric acid, but no necrosis developed when plants were
exposed to fluoride aerosol averaging 1.9 ug/m3 fluoride. Inasmuch as the aero-
sol was collected from a gas stream that was treated with limestone and hydrated
lime, its composition was probably calcium fluoride. Moreover, when the accu-
mulated concentrations of fluoride in leaf tissues were about the same, whether
from gas or particulate, injury from the particulates was much less.
524
McCune et al. reported an increase of only 4 mm tipburn on the leaves
of gladiolus exposed to cryolite (sodium-aluminum fluoride dust). The washed
leaf tissue from this treatment showed an accumulation in the leaf tissue of
29 ppm fluoride on a dry weight basis. A 70 mm increase in tipburn would have
been expected if a similar accumulation had occurred from exposure to hvdro-
fluoric acid. Except for this slight tipburn, McCune and his colleagues found
that cryolite produced no visible effects on a variety of plants nor did it
reduce growth or yield.
524
It is evident from the work of McCune et al. that fluoride accumulates
in plant tissue as a result of exposure to cryolite, but that the rate of accu-
mulation is much slower than would be expected from a comparable treatment with
307
-------
hydrofluoric acid. For example, when comoarinq washed leaf samples, exposure of
gladiolus to hydrofluoric acid for three days at 1.01 uq/m3 fluoride resulted in
an accumulation of 26.4 ppm fluoride, whereas only 34 oom was accumulated from
an exposure to cryolite for 40 days at 1.7 yq/m3 fluoride. Further, when
approximately equivalent amounts of fluoride had been absorbed from dust ao-
plications of sodium fluoride, calcium fluoride, and cryolite onto the leaves
of tomato, leaf injury occurred only on those leaves treated with sodium fluo-
ride. The authors suqqest that the effect of a particulate fluoride is de-
525
pendent upon its solubility. Very recent experiments by McCune et al. show
this to be the case. Increasinq the dosaqe of cryolite on mandarin orange
leaves from about 120 pg/m3/hr to 900 gq/m3/hr in an atmosphere at 75% RH did
not increase leaf absorption over that of controls. At a dosaqe of 7,800
yg/m3/hr at 85% RH, foliar fluoride was three times that of the controls. The
presence of a water mist on the leaves, however, increased foliar concentra-
tion • / a factor of 5 over the equivalent dose at 85% RH. Similar results
were obtained with spinach leaves, but at lower doses of cryolite.
Both the investigations cited above indicate that much of the particulate
matter remains on the surface of the leaf and can be washed off, although that
which remains after washing is not necessarily internal fluoride. Reduced
phytotoxicity of particulate fluoride is ascribed in cart to the inability of
524,525
the material to penetrate the leaf tissue. In addition, McCune et al.
suggest that inactivity of particles may be due to their inability to penetrate
the lea, in a physiologically active form.
Lead Pa.-ides
123,417,458,561,590,680,789
Published results of several studies show that
lead accumulation by veqetation near highways varies with motor vehicle traffic
308
-------
densities and generally declines with distance from heavily traveled roads.
591
Page et al. demonstrated that lead accumulations in and on plants next to
highways in southern California were caused principally by aerial deposition
and to a lesser extent by absorption from lead-contaminated soils. Although
lead concentrations near highways have been high, there are no known reports of
injury to vegetation.
Soot
389
Jennings suggested that soot may clog stomata and orevent normal gas
exchange but noted that most investigations discount this effect. Microscopic
examination failed to show significant clogging of stomata on leaves of broad-
leaved species of shade trees. He further stated that interference with light
can be more serious but he offers no data from critical exoeriments to sub-
stantiate this theory.
67
A well-illustrated report by Berge showed plugged stomata on conifers
growing near Cologne, West Germany. His report also stated that growth was
adversely affected.
Necrotic spotting was observed on leaves of several plants where soot from
544
a nearby smokestack had entered a greenhouse. The necrosis was attributed to
acidity of the soot particles. Plants outside the greenhouse were not damaged,
possibly because the particles had been removed by rain before severe injury
644
could occur. Ricks and Williams observed oak leaves in the vicinity of a
phurnacibe smokeless fuel plant in which briquettes composed of a mixture of
finely divided coal and pitch are carbonized in ovens at 750°C to 850°C. During
the manufacturing process, large quantities of dust and smoke containing gaseous
sulfur compounds are emitted. Scanning electron micrographs of the oak leaves
309
-------
revealed aggregation of particles on both leaf surfaces, At high magnification,
individual stomata were shown to contain several particles in the pore opening.
These leaves had a lower maximal diffusion resistance than that measured in un-
polluted leaves.
Magnesium Oxide
The possible indirect effect on vegetation of magnesium oxide falling
699
on agricultural soils was reported by Sievers. He noted poor growth in the
vicinity of a magnesite-processing plant in Washington. To prove the role of
magnesium as a cause of poor growth, Sievers planted oats in pots containing
1,000 g of soil collected at distances of 0.201, 0.804, and 3.22 km from the
calcining plant. Five grams of magnesium carbonate were added to half of the
pots in each series; the remaining pots were left untreated, After 10 weeks,
plants in the untreated soil collected at 0.201 km exhibited the stunting and
discolc- ing characteristic of affected plants in the field. The addition of
the rr^nesium carbonate caused no further injury. Plants in untreated soil col-
lected at 0.801 km grew somewhat better; however, adding the magnesium carbonate
reduced growth comparable to the untreated sample at 0.201 km. Plants in the
untreated soil at 3.22 km grew normally but the added magnesium carbonate still
caused some typical discoloring. After the processing plant ceased operation,
injury to crops in the area lessened, indicating that the injurious effect was
not permanent.
Iron Oxid~
" 68
Berof , in Germany, dusted experimental plots with iron oxide at the rate
of 0.15 mg/cm2/day over 1- to 10-day intervals through the growing season for
six years. The plots were planted with cereal grains or turnips. Effects of
treatment on the primary product, on straw, and on leaves were noted. No
310
-------
harmful effect of the dust was detected on either crop. There was a tendency
for improvement of yields of grain and turnip roots, but this was not statis-
tically significant.
Foundry Dusts
Changes in starch reserves were compared in common holly leaves that were
722
either untreated or treated with dusts emitted from foundry operations.
The critical factor was the amount of light absorbed by the dust layer and not
the effects of dust particles on transpiration or temperature of the leaf.
These observations agree with some of those reported above concerning the
range of effects of cement-kiln dust on vegetation.
Acid Aerosols and Acid Rain
3y burning fossil fuels and by various industrial processes man releases
large quantities of sulfur and nitrogen oxides to the atmosphere. These com-
pounds, in addition to naturally occurring gaseous forms of sulfur and nitrogen,
are oxidized and hydrolized in the atmosphere to sulfuric and nitric acids at
varying rates depending upon environmental conditions. If these acids are not
neutralized by alkaline substances also present in the atmosphere, they will
ultimately settle to the ground as mist or precipitation. The impact of acid
aerosols and acid rain on vegetation includes direct effects, in the form of
injury to above-ground plant parts, or indirect effects, by creating unfavorable
conditions for plant growth. This may involve acidification of irrigation water
(lakes and rivers), increases in the leaching rates of soil nutrients, and
shifts in the balance of microorganism populations in the soil.
537
Direct Effects. Middleton et al. observed necrotic spots on the upper
leaf surface of vegetation in the Los Angeles area following periods of heavy
311
-------
753
air pollution accompanied by foq. Thomas et al. exposed olants to sulfaric
acid mists in concentrations ranqinq from 108 to 2,160 mq/m3. Necrotic spots
were developed only on the upper surface of wet leaves.
285
Gordon exposed several species of western nine to an atomized solution
of sulfuric acid havinq a oH below 4.0. He observed a 50% reduction in needle
qrowth compared to controls. In 1974, qrowth abnormalities of Christmas trees
340
were attributed by Hindawi and Ratsch to sulfur dioxide and particulate
829
acid aerosol. That same year, Wood and Bormann reported irreqular develoo-
ment of leaf tissue and spot necrosis on yellow birch seedlinqs that were
exposed bo artificial sulfuric acid mist at pH 3.0. In 1975, they also ob-
830
served an increase in leachinq of nutrients from birch foliaqe by acidifi-
cation of an artificial mist to pH 4.0. Injury symptoms developed on seedlinqs
of kidney and soybeans that were subjected to simulated rain acidified with
693
sulfuric acid to pH 3.2.
Severe reductions in yield and quality occurred on field-qrown tomatoes in
427
the Kona district on the Island of Hawaii. Tomato olants qrown under plastic
rain shelters produced normal crops. A definite atmospheric haze that appeared
at this time coincided with volcanic eruption. Althouqh the rain water of low
pH (4.0) decreased pollen qermination and oollen tube qrowth, the authors did
not rule out the possibility that other factors were involved since appreciable
quantities of chlorides and sulfates olus 27 detectable orqanic compounds in the
ppb ranqe were found in the rain water.
179
Indirect Effects. In 1971, Norweqian investiqators Dahl and Skre showed
a clear connection between decreases in productivity of forests and the amount
of calcium in the topsoil of forest land. However, liminq of the soil did not
312
-------
78
result in the expected growth increase. Bolin et al. tried to explain this
contradiction by stating that the relation between calcium and oroductivity is
probably indirect and that the effects of additions or losses only show up after
394
quite a long time. A study in Sweden correlated soil acidification with
78
significant reduction in forest growth between 1945 and 1965. Bolin et al.
estimated reduction in growth to be 0.3% per year in Sweden. In 1974, Whittaker
809
and his associates, in a study of a New Hampshire hardwood forest, tenta-
tively attributed a striking 18% decrease in volume growth and productivity that
took place in 1960 to the effects of acid rain and/or drought.
The effects of acid rain on host-parasite interactions were demonstrated
693 466
by Shriner. Likens and Bormann suggested numerous indirect effects that
could lead to reduction in plant vigor. Direct nutrient leaching and erosion
of the cuticle, providing ready access to pathogens, can combine with other
460
impinging stresses to cause an adverse effect. Lerman demonstrated that
erosion of the cuticle on the upper leaf surface can also lead to negative
water balance in the plant.
313
-------
CHAPTER 11
EFFECTS ON BUILDING MATERIALS
Deposition on building materials of such airborne particles as dust
and soot cannot only significantly reduce the aesthetic appeal of structures,
but also, either alone or in concert with other environmental factors, re-
sult in direct chemical attack. It is not entirely understood which specific
class of particulate, or chemical constituent thereof, under what ambient
conditions, actually results in significant damage or soiling of specific
building materials. Therefore, knowledge of the effects of air oollutants
on building materials should be reviewed oeriodically to determine whether
additional understanding of these matters has been achieved.
This chapter updates the information on materials contained in the
1969 National Air Pollution Control Administration publication, Air Quality
768
Criteria for Particulate Matter. It describes and assesses knowledge con-
cerning the effects of particulate pollutants on building materials. Based
on an extensive literature search and discussions with a broad range of
building industry professionals and trade association representatives, this
chapter focuses on the effects of particulate pollutants on metals, masonry
and concrete, paints and finishes, polymeric materials, textiles, porcelain
enamels, and asohalts. Available data on the estimated cost of material
soiling and degradation due to oollutants are also oresented. Conclusions
are based on these findings.
The quantity of the literature on building materials does not neces-
sarily correlate with the degree of importance or use of materials in the
315
-------
building industry. For example, although masonry and concrete are used
extensively in building construction, there is little information regarding
the effects of pollutants on these materials. In comoarison, although elas-
tics are used very little, except in building interiors, there is consider-
able information concerning the effect of air pollutants on these materials.
Available data are based on exposure of materials to outdoor pollutant
concentrations; therefore, the relationship between outdoor and indoor con-
centrations must be considered if the effects on material used for building
33
interiors are to be accurately assessed. Anderson showed that over a 7.5-
month period the average indoor concentrations of oarticulates and sulfur
dioxide were, respectively, 69% and 51% of simultaneous outdoor values.
Worldwide studies of the variance of indoor/outdoor oollutant concentrations
also indicate that both particulate and sulfur dioxide concentrations are
markedly reduced in indoor atmospheres. The indoor/outdoor ratios vary
considerably, presumably because of differences in room sizes, building
materials, ventilation rates, external pollutant concentrations, etc.
Particulate matter may react with, influence, or be influenced by
other constituents of the atmospheric environment, both natural and manmade.
Without consideration of these other pollutants, accurate assessment of the
effects of particulate matter on building materials is not possible.
The behavior of particulate matter in relation to other pollutants is
particularly important in two respects:
Particulates can act as nuclei for absorbed and adsorbed gases
such as sulfur dioxide, hydrogen sulfide, and nitrogen dioxide.
This can occur while the particulate is still airborne or after
it has settled. Thus, the actual effect of the oarticulate as a
316
-------
polluting agent can be completely different from that expected
of the particulate as emitted. To assess its damage potential, it
is necessary to understand both the chemical effects of the par-
ticulate and its synergism with pollutants such as adsorbed and
absorbed gases whose presence or accumulation on a material surface
is due to or increased by the particulate. Since there are very
few data on the effects of particulates known to contain adsorbed
or absorbed gases, information on the effect of gases alone is in-
cluded below to provide at least some indication of potential
synergism.
Gaseous pollutants can convert immediately to liquid acids or salts,
which are classified as particulates, on contact with moisture in
the air or on the surface of a material. Fbr examole, sulfur di-
oxide (approximately 80% of which results from the oxidation of
hydrogen sulfide) reacts with moisture to form liquid sulfur tri-
oxide, sulfuric acids, and sulfate salts. Further, sulfur dioxide
in the presence of nitrogen dioxide and hydrocarbons photooxidizes
to produce aerosols containing sulfuric acid, which are also clas-
sified as particulates. Similarly, nitrogen dioxide combines with
moisture to form liquid nitric acid, which in turn can react to
form nitrate salts such as ammonium nitrate, both of which are
also classified as particulates. There is little information on
the effects of liquid particulates. The effect of gases alone are
discussed below since most test results probably reflect effects
of both gaseous and liquid oollutants.
317
-------
Gaseous pollutants include sulfur oxides, nitrogen oxides, hydrogen
sulfide, ammonia, and ozone. Ozone, althouqh a naturally occurring element
of the atmosphere, is considered to be a oollutant because it can be formed
by the action of sunlight on oxygen in the presence of nollutants, both par-
ticulate and gaseous (e.g., hydrocarbons and nitrogen oxides). In certain
areas on days during bad smog, the ozone concentration may reach 0.5 pom
304
or more for short periods.
Finally, natural environmental factors such as moisture, temperature,
sunlight, and wind can significantly influence the effect of air pollutants
on building materials. They are discussed below, where applicable.
METALS
Current application of metals in buildings extends far beyond its
traditional uses as roofing sheet for large warehouse-tyoe facilities and
as cladding and piping. Some major metals and their most common uses, de-
pending on processing procedure and specific composition, are:
steel: structural columns and beams, roofing sheet, curtain walls,
stacks and storage tanks, cladding, pipe balustrades, stairways,
balconies, safety rails, structural elements of bridges, boiler
tubes, wire, and bolts, rivets, and other fasteners.
iron: rods, lath, gas and water oipes, and decorative railing.
aluminum: curtain walls, siding, roofing sheet, air ducts, window
frames, doors, screening, trim, flashing, protective and decorative
railings, rainwater leaders, and gutters.
zinc: flashing and protective coating for iron and steel.
copper: cladding, flashing, wiring, pining, and decorative cornices
and soandrels.
318
-------
• brass and bronze: decorative doors, window frames and sashes,
balustrades, screws and other hardware items, and ornamentation.
• lead: piping and coating for iron and steel.
Moisture and temperature play critical roles in the corrosion of metals,
687,703
whether or not air pollutants are present. Without moisture in the
atmosphere there would be little, if any, electrochemical atmospheric cor-
rosion, even in the most severely polluted environments. Direct chemical
attack, of course, could occur in such conditions.
Evidence demonstrates that corrosion of metals can be accelerated by
atmospheric pollutants, not only as a result of direct chemical attack by
smoke particles, acid aerosols, or mist but also because acids, salts, and
other particulates could be contained in or trapped by moisture condensed
on a metal surface. Moisture (or electrolyte) thus contaminated is very
likely to have greater electrical conductivity and to accelerate corrosion.
In addition, moisture can react with sulfur dioxide to form liquid sulfuric
acid which is extremely corrosive to certain metals.
The following paragraphs present evidence, by type of metal, where
possible, on the effects of particulates alone, of combined pollutants, and
of some gaseous pollutants alone.
284
Goodwin et al. provided the only information on erosion of metals by
particulates. Tests of quartz particles on steel and nylon indicated that
particles s 5 pm cause relatively little damage. Larger particles cause
progressively more damage until saturation is reached. Erosion varied with
a simple power of velocity—2.0 for small particles and 2.3 for particles
£ 100 yg. Both degree of fragmentation of the imoacting particle and prop-
erties of the target material influenced erosion behavior. T4hile agreeing
319
-------
to a relationship between imoact anqle and erosion, the authors stated that
observed particle size and velocity effects seem to occur regardless of angle.
324 528
Hermance and McKinney ;ind Hermance showed that airborne particulates
high in nitrate concentration caused stress-corrosion cracking and ultimate
failure of nickel-brass wire spring relays and other electrical equipment in
the Los Angeles area. Examinations indicated that particulate matter had
collected on insulating surfaces around stress nickel-brass wire in an envi-
ronment of unregulated humidity. Bulk dust samples from the air of Los
Angeles, New York, Philadelphia, Baltimore, and Chicago were analyzed. The
highest nitrate concentrations were in the Los Angeles sample, apparently
because of the nitrogen dioxide in the air that reacted with moisture to
yield nitric acid, much of which eventually associated with fine particulate
matter such as ammonium and alkali nitrates. The combination of these fine
materials in the Los Angeles sample, the absence of soot, and the high pro-
portion of oxidized, polar compounds in the organic fraction orobably made
the dust deposits from Los Angeles more reactive to moisture than the samples
from the eastern areas.
528
Subsequently, McKinney and Hermance, in their laboratory tests, sim-
ulated conditions of electrolysis of hygroscopic salts in the dust deposits.
They used ammonium salts of sulfate, nitrate, and chloride. Results showed
that of the major ions in dust deposits, only the nitrate ion was highly
active in producing stress corrosion in nickel-brass alloys, depending on
relative humidity. Below a critical humidity, which appeared to be between
40% and 50%, stress-corrosion cracking dropped to a negligible rate. They
also investigated the influence of applied positive Potential and temper-
ature. They found that the rate of stress-corrosion cracking was directlv
320
-------
dependent on these factors as well as on nitrate concentrations and humidity.
They extrapolated from these results to conclude that noticeable stress-
corrosion cracking of the nickel-brass wire could occur in the Los Angeles
environment within two years. New wire-sprinq relays made with 80% copper-
20% nickel springs are being used since nitrate corrosion does not appear
in the absence of zinc. Cracking in existing nickel-brass relays is con-
trolled by high efficency filters and cooling systems which have been re-
designed to maintain the relative humidity below 50%.
1
In Japan, Abe et al. tested copper specimens exoosed for two years in
marine, industrial, urban, and rural atmospheres. Their analysis of metal-
lic deposits on the surface of exposed soecimens revealed basic sulfates,
sulfides, and chlorides of copper. This indicated attack bv particulate
pollution.
When exposed to the atmosphere, copper and its alloys gradually develop
839
a dark color which finally changes to a Dale green. Yocom and McCaldin
identified this as the familiar green protective patina that can be either
basic copper sulfate or, in a marine atmosphere, basic copoer chloride—both
of which are extremely resistant to further atmospheric attack.
703
Simpson and Horrobin indicated that the ^normal time for patina forma-
tion is 5 to 10 years, depending on the concentration of sulfur or chlorine
pollutants, the amount of moisture in the air, and the temperature. Fink
232
et al. reported typical corrosion rates of copper in industrial atmo-
spheres to be approximately 0.05 mils oer year (mpy) compared with 0.02 moy
in rural atmospheres.
Even though pollutants accelerate corrosion of copper, the higher rate
was not considered sufficient to cause significant damage. The higher rate
321
-------
caused more rapid formation of the patina that retards the attack. Typi-
cally, a copper roof or other component will outlast the building or structure
of which it is a part whether the air is polluted or not. According to
839
Yocom and McCaldin 20-year exposure tests with copper specimens conducted
by the American Society for Testing and Materials (ASTM) verify this: the
specimens showed a loss in thickness of < 0.025 moy and 0.1 mpy in rural
and industrial atmospheres, respectively.
In the ASTM studies, corrosion rates of copper in industrial atmospheres
were greater than those in marine atmospheres. A number of formulations were
tested. With the exception of a high tensile brass, all appeared to be
suitable for use in industrial atmospheres. Like the high tensile brass,
bronze also may be more susceptible to attack by atmospheric pollutants.
Although aluminum forms an invisible protective film of oxide, it be-
comes covered with dirt and soot particles in a polluted atmosphere. This
tends to mottle and pit the surface. In time the surface appears roughened,
703
but no general thinning occurs. Simpson and Horrobin reported that pro-
longed exposure of aluminum to industrial atmospheres results in the forma-
tion of spots of white crystalline corrosion products on the surface of the
aluminum. Depending on the amount of soot in the atmosphere, the metal will
acquire a greyish or darkish appearance. These authors found that corrosion
of aluminum is greater in severe industrial atmospheres than in marine or
rural atmospheres.
232
Fink et al., summarizing the work of others, reported that after ex-
posure of many aluminum alloys for seven years in an atmosphere with sulfur
dioxide concentration >0.14 ppm, which implies industrial and therefore high
particulate concentration, oits as deep as 13.8 mils formed. (See Table 11-1.)
322
-------
0)
I
a
w
o
H
fl
•H
co
C
M
O
i
O
I
w
-P
H
W
Q)
c
o
•H
W
O
£4
su
o
a
0)
>,
g
A
0)
•P
2
C
o
•H
CO
0
Cj
P
0
o
co
cu
C
•H
:*
0
bO
it)
O
•H
o
o
J
o
•H
(A
CO
^-
o
•
o
CO
CM
O
O
^
0
•
0
rQ
0)
bO
CO Q)
P H
rO H
•P O
CO O
1
i
o
r-l
<
rH
O
O
tn
o
o
o
4-
m
O
in
in
o
ID
O
•H
in
O
O
«— 4
o
0
•
0
1
1
CT>
CJ)
r— j
1 — I
1
1
in
CM
0
o
•
o
^
H
E
1
in
CO
r-l
H
(T)
H
O
•
O
00
CN
O
O
•
o
_^
1— 1
a:
i
CO
0
o
CO
o
CM
O
•
O
1
1
(D
CO
X
1
J-
o
o
CO
1
1
CD
CN
O
O
•
O
^
CO
1
J-
o
o
CO
[-~
, — I
o
• 1
0 I
m
CN
O
O
1
1 O
CO CO
E X
1 1
J- in
in o
•H 0
in in
m
H
0
o
CN
O
O
•
O
U3
H
1
,—f
to
O
03
O
H
O
»
O
1
1
CD
H
1
CO
(D
O
to
CM
•
H
CD
H
* 1
P|
d)|
V
C
•H
P ,
e
o
J-4
IX,
<3
V
in
CO
j"
PH
CO
2:
H
«^
^^
0)
f-t
0)
^£
a,
CO
0
4_)
(Tj
,—|
n)
j^
2
PH
rQ
^
bO
n)
CM
O
00
e
5.
a
H
o
•
o
>"'
r-i
ftj
•H
Cj
P
0]
•3
fj
•H
T)
•H
S
O
00
§
W)
>
d)
A
OJ
O
W
g
a
a
j-
H
•
O
\^s
H
(T)
•H
f^
P
W
3
G
M
^
•
T5
C
§
W
«t
CO
0)
C
•H
S
«l
It)
•H
j_i
P
co
•d
C
•H
0)
0)
0)
co
323
-------
In rural clean air, pitting was neqliqihle and loss of thickness was
0.028 mpy compared to rates as hiqh as 0.15 mpy in industrial atmospheres.
Most of the pittinq occurred durinq the first two years. Afterward, oene-
tration increased only sliqhtly so that the depth after 20 years was similar
to that measured after three years. Based on these findinqs, the investi-
gators concluded that corrosion of aluminum and its alloys by air oollution
does not significantly affect the life of externally exoosed structural
elements and components.
Particulate matter is an imoortant factor in the corrosion of metals,
especially in the presence of acidic, qaseous pollutants. This was sub-
stantiated by field work at the Chemical Research Laboratory in Teddinqton,
839
England. Investigators there exoosed one samole of iron to a moist atmo-
sphere containing traces of sulfur dioxide and particulates, and another
sample to the same atmosphere but protected from the oarticulate matter with
a muslin filter. Rusting of the orotected samole was neqligible comoared
with the unorotected sanrole; however, the amount of moisture and sulfur di-
oxide absorbed by the muslin was not determined.
The influence of particulates on corrosion of metals has also been es-
tablished from laboratory tests in which various coated and uncoated metallic
surfaces were innoculated with fine oowders or nuclei of sodium chloride,
839
ammonium sulfate, ammonium chloride, sodium nitrate, and flue dust. The
samples were then exposed to atmosoheres at various humidities. Corrosion
of all surfaces occurred and, except for coated surfaces innoculated with
ammonium chloride, corrosion rate increased with increased humidity. The
addition of sulfur dioxide traces to the test atmosphere greatly increased
corrosion at high humidities. Further, these authors reported that a much
324
-------
more rapid corrosion rate occurs when the air contains both charcoal particles
and sulfur dioxide than when it contains only sulfur dioxide. From these
observations, they reasoned that the action of the charcoal particles was
primarily physical, i.e., they increased the concentration of sulfur dioxide
on the surface of the metal by absorbing it, thus creating hot spots at the
748
point of contact between the metal surface and charcoal particle. Tajiri
232
reported this to be the general case for dust particles. Fink et al. also
stated that when hygroscopic particles settle on a metal surface they usually
accelerate the corrosion rate, particularly in the presence of sulfur dioxide,
and may cause corrosion at <70% KH. Dust can disrupt the protective oxide
films formed on metal surfaces such as stainless steel and can result in
corrosion. Such general statements attest to the fact that particulates in-
fluence corrosion rates, and that airborne particulate matter is a corrosive
factor in both industrial and urban regions.
131
Chandler and Kilcullen investigated the nature of the relationship
between the corrosion of two mild steels with different copper contents
and atmospheric pollution at 11 sites near Sheffield, England. Their re-
sults confirmed that there was an important relationship between the cor-
rosion of steel and the level of atmospheric smoke and sulfur dioxide.
However, only about 50% of the variations in corrosion rate at the different
sites could be attributed to sulfur dioxide. The influence of smoke inten-
sity on the corrosion rate of steels was similar to that of sulfur dioxide.
Because the correlation between sulfur dioxide and smoke was high, their
effects on the corrosion rate could not be considered independently. The
combined effect of smoke and sulfur dioxide was only slightly greater than
their individual effects. The corrosion rate could not be accurately pre-
dicted from the quantity of the two pollutants.
325
-------
322
Haynie and Upham exposed >plain carbon, copper-bearing, and weatherinq
steel samples to both urban and rural atmospheres (see Table 11-2). Twenty-
five samples of each steel were mounted at 30° anglos facinq south.* Reoli-
cate samples were examined at 4, 8, 16, 32, and 64 nronths. Urban exposure
sites were selected in or near eight cities in which the pollutant concentra-
tions were being monitored (Table 11-3). Rural areas near the cities were
selected as control sites because of their low pollution but similar meteor-
ologic conditions. Pollutant concentrations at these rural sites were not
measured during exposures. Results of these exposures, which may or may not
have been influenced by oarticulate concentration, are tabulated in Table
11-4.
These authors reported that the rate of steel corrosion is diffusion-
controlled by the type and thickness of the rust film that forms. Some struc-
tural carbon steels form a loosely adherent rust that provides very little
protection from further corrosion; both copper-bearinq and weathering steels
form more adherent protective films. Because the residual copper in the
carbon steel tested was relatively high, its corrosion behavior was similar
to that of copper-bearing steel. In each case a protective film was formed.
322
Haynie and Upham concluded that nnore than 90% of the variability in
corrosion behavior of steels could be attributed to the variability of the
concentrations of both sulfur dioxide, which increases corrosion rate, and
oxidants, which decrease it. Because these pollutants are counteractive,
*Position in space is an important variable in the testing of materials for
atmospheric corrosion. Test samples are usually mounted at or near 45° from
the horizontal because this more nearly simulates actual use conditions.
The undersurfaces often are corroded more rapidly than the upper surfaces
because corrosive agents are not washed off as well by rain.
326
-------
CM
I
CO
E-
•a
3
CO
c
0)
to
0)
-------
TABLE 11-3
,b
Averagea Pollutant Concentrations at Urban Sites (yg/m3)
NO
164
145
130
53
49
46
44
44
119
106
96
92
80
65
119
93
97
100
23
25
20
20
82
57
58
67
63
119
111
102
102
102
62
58
50
46
47
Averages for total periods of exposure, calculated from monthly averages
weighted by the actual number of days of exposure in each month.
b
From Haynie and Upham, 1971.322
328
City
Chicago
Cincinnati
Detroit
Los Angeles
New Orleans
Philadelphia
San Francisco
Washington
Nominal expo-
sure , months
4
8
16
4
8
16
32
64
4
8
16
32
64
4
8
16
32
64
4
8
16
32
4
8
16
32
64
4
8
16
32
64
4
8
16
32
64
SO 2
419
479
400
76
97
68
86
79
139
139
132
121
118
45
47
42
39
39
34
29
26
24
191
194
197
194
218
10
13
29
34
34
222
207
141
136
126
03
39
43
47
65
53
61
58
59
16
19
22
23
24
106
92
84
76
75
39
34
37
35
45
45
53
56
57
39
38
37
37
37
33
41
47
49
50
-------
d-
1
H
H
W
, "j
£P
<
a
H
a>
4->
C/D
HH
O
C
O
•H
W
O
fi
M
o
a
c
o
rr-J
0
bO
rt>
8
W
<
?
-f
CO
CN
00
CO
>-l
00
3-
<
-j
P
•H
O
oo
cr>
t^
^^^^^^ "
CN
00
CO
*XJ tS tJ ^J 'XJ "XJ CN
O CO O H 3- O 00
OO J- H H CD CO H
CN in cn H o o co
in j- co 3- 3- co CN
co CN oo co o d- j-
J- J- CO O"> H 00 CT>
o o co oo cn H co
CO CO CN CN CN CN H
CN cn CD o to in d~
CN in 00 CO O CN CO
CD 00 CO it cJ" CN zf
rH ! — 1 rH rH > — f > — 1 rH
< « cj < m o <
C rH C
rd ftJ nj
i-Q JH (JQ
s 3 a
•H
P
(0
0 C
bO C
(Tj >r^
0 a
•H ff
o o
CO
r-
00
0
H
oo
CN
H
in
CN
CN
CO
>H
00
H
in
o
^
H
CO
3- cn j- r-
j- r~- co o
m CD CN cn
CN r^ co co
O cn in zf
in H o H
cn H co CD
rH in in CN
oo in j- d-
3- m o cn
CO (O r- CN
H oo co CN
co uo m co
in j- r— cn
00 H O 3-
H CN CN H
CO CO O- rH
OO 00 CO O
H J- CO rH
rH H rH rH
O < pq CJ
H
(0
3
OO f- J- OO CD H
rH O rH in O 00
j- j- cn o CN cn
r-- r- ^- co co co
in in t^ m j- CN
CD r~( CO CD CO Z)-
en o in o o CD
j- m co zf zf CN
CD zf 00 O H O
rH CD C*- 00 3- t-~
zf CO CD CO CO H
CO CO CN CN CN CN
CN cn co rH to H
H CO rH cO r-i cn
in rt cn oo oo oo
CN CN rH rH rH rH
zf CN rH J- O CD
CN rH CO O O rH
CN co co o cn co
rH rH rH rH
< « CJ < CO CJ
C rH
(T3 n3
^ SH
C j ^J
^J
•H
o
-p
0)
ft
rH CO rH
CO CO CN
m j- co
CN CN CN
t^- H H
in r~ co
cn oo r^
H rH rH
r» CN m
cn oo o
in J- zf
H rH rH
00 CM H
co zj- a>
rH 0 0
rH rH rH
CN 00 CN
t»~ cn co
cn oc cn
< m o
c
i-Q
^
W
H 0 CO
CN CN H
oo o J-
CD CO CO
J- OO CN
rH rH rH
in co oo
CO cn co
o oo cn
rH
< « CJ
H
a)
rH
p?
tj ts ts
co m H
CO 00 CO
m j- in
CO CO CN
CN CO CO
in 3- o
J- co cn
CN CN rH
rH CN in
uo co o
CD Zf- CO
rH rH rH
CN CO CO
rH UO CD
o oo co
rH
< W CJ
C
(0
1
M
C
f$
o)
H
£(
O
^J
0)
£H
co oo 3-
Cn rH rH
CO UO rH
in in zf
cO H *
cn 4- o
CN H cO
CO CO CN
_^4- , J ify
CO CO ^J-
cn oo co
rH rH rH
o oo r~-
cn j j-
cn co oo
CO CO 3-
O CO C-i
J- co 4-
<; m o
rH
rO
p
3
329
-------
o m co rH r— c—
in cn co r- to rH
•H o co cn o co
in in co r- co 3-
co cn o
d- cn r-H co rH r~
o in co co in c^
co CM co co in m
4- J- CM to to oo
ID
cu
3
q
•H
p
o
o
i
H
H
W
«
H
W
x:
p
c
o
E
ri
CD
3
W
o
ft
X
CD
i
e
,-j.
r>
c
o
w
o
8
M-i
O
x:
p
ft
T)
CD
bO
fd
>
CM
CO
CO
, — |
03
-3"
r-^
CO
H
CD
O
CN
CO
IO
H
-j.
CM
O
in
CD
iH
rH
4-
o
d-
-J-
in
H
CO
CO
rH
CO
CN
cn
o
CO
H
o
IN
IN
CM
o
CN
CO
CN
00
00
t^.
rH
ro
t^
in
rH
01
rH CD CO
cn in r—
o o to
CO c£> CO
;± O CO
CO LD rt
co co cn
zf- J- CN
co cn co
oo CM cn
co r-- o
CM CN CN
rH O CN
o oo in
CN O IN
CM CM rH
J- CO CM J-
4- rH CM cn
rH rH [-• T>
3- J- CM *XJ ""O tj co
r-| in H J- O rH I>-
10 cp oo in co co co
co c^ 01 rH o t~^ m
CN CM H CM CM rH CM
^
t-^ co n- o oo cn m
IN ID CO CM O O O
H H H H rH iH CM
o r- CM o co o co
oo m r~ CN H co in
o co oo o cn cn 4-
H H H
in
CO
CO
CO
CO
H
m
CM
d-
co
cn
rH
J-
H
CO
rH
l>
rH
rH
CN
in
d-
co
H
cn
CO
CN
H
CM
r~
o
rH
, — t
CO
f^
d-
cn
•*
CO
CO
0)
CN
CM
0
CN
05
CT>
CO
00
H
CO
cn
CO
d-
o
f-
CM
CO
t
cn
cn
00
rH
C
CN
O
CN
H
00
IN
IN
CN
-j.
in
H
CN
*-.
in
=1-
J-
H
K
in
H
o
rH
CU
•p
•M
00
o < cn cj
o <;
c_>
o
0)
w
c*
o
rQ
rO
o
G
•H
rd
H
ft
II
"*•
• •
W
>>>
o
H
H
rd
h
0
0)
TJ
O
CJ
O
of wind damage or vandalism.
0)
w
3
rd
O
CU
rM
<^
05
W
CD
6
•H
O
CD
ft
cn
0)
CD
?-t
X<
•P
e
0
r.j
LM
t3
a>
C
• (-)
e
£•*
0)
•p
d)
"0
Q)
bO
<^
'r-^
330
-------
steel corrosion behavior can vary considerably amonq cities as the clean-
liness of the environment is improved. A national reduction in pollution
should result in less steel corrosion; however, in cities where sulfur di-
oxide concentrations are low and oxidant concentrations are high, lowering
the total pollution level will increase steel corrosion.
Average relative humidity, rainfall, and temperature usually correlate
well with steel corrosion. While atmospheric factors were not significant
322
in the results obtained by Haynie and Upham, the authors did not rule out
their influence. The range of average relative humidities among cities was
within 15%. It is quite likely that the differences in time-of-wetness of
the samples was also slight. Another possible explanation was that the rust
film at the relative humidities encountered remained moist most of the time.
587
Oma et al. investigated the influences of meteorologic factors and
pollutant concentrations on the outdoor corrosion rate of steel near Tokyo.
Their statistical analysis showed that, within a 95% confidence limit, a
combined relation does exist. Based on this, these investigators developed
an equation to calculate and predict corrosion rates in industrial areas.
The equation considers: level of humidity; concentration of sulfur dioxide,
chlorides, soluble and insoluble substances, sulfates, and tar substances;
amount of precipitation; temperature; and wind velocity.1
Some investigators have stated that industrial air pollution is the
greatest factor in zinc corrosion because acids, gases, and vapors destroy
839
the basic carbonate protective coating that normally forms on zinc.
748 703
Tajiri and Simpson and Horrobin pointed to sulfurous pollution as the
cause of the greatest increase in the corrosion rate of zinc, especially when
the material surface is wet. Sulfurous and sulfuric acids reportedly react
331
-------
with the basic zinc carbonate film and convert it to zinc sulfate, which
is soluble and washes off wi:h rainfall. The zinc carbonate layer then rapidly
renews and remains protective until subjected to further attack. More spe-
531
cifically, McLeod and Rogers reported an average corrosion rate of 24.7
mpy during the first seven days that zinc is exposed to a movinq mixture of
sulfurous acid and air. The rate decreased until it became constant at
5 mpy after 500 days. Corrosion products were sulfur, zinc sulfite, and
zinc sulfate. The corrosion rate of zinc completely immersed in an unaerated
solution of sulfurous acid at 21.11°C to 23.89°C was much higher and increased
as the acid concentration was increased. In a solution containing 8 g/liter
of sulfur dioxide, the average corrosion rate was 279 mpy; in a solution
containing 16 g/liter, the average rate was 496 moy. As the sulfurous acid
content of the unaerated solutions decreased due to corrosion, hyposulfite,
302
sulfide, thiosulfate, and elemental sulfur were produced. Guttman's math-
ematical expressions for predicting corrosion rates of zinc consider time-
of-wetness and sulfur dioxide content of the atmosphere. Acknowledging a
relationship between time-of-wetness and relative humidity, he provided a
means of estimating time-of-wetness from relative humidity data.
A striking example of the relationship between zinc corrosion and pol-
lution level is the almost fourfold reduction in the corrosion rate of zinc
in Pittsburgh associated with a twofold reduction in dustfall and a threefold
769
reduction in sulfur dioxide (from 0.15 opm to 0.05 ppm) from 1926 to 1960.
839
Yocom and McCaldin conducted tests on exposed mild steel plates at
35 sites in metropolitan St. Louis, Missouri. Plates were removed and
examined after exposures of 2, 4, 8, and 16 months. Corrosion rates were
30% to 80% greater in urban and industrial locations than in suburban and
332
-------
rural areas. No relationship between dustfall and corrosion was detected.
The relationship between corrosion and sulfation rates was strongest during
the early stages of exposure. In similar studies made at 20 stations in
the Chicago, Illinois area, downtown corrosion rates were ~70% greater than
in the suburbs after a 12-month exposure. The measurements of sulfur dioxide
concentrations at seven of the Chicago sites indicated a direct relationship
593
with corrosion rates (Figure 11-1). In similar experiments, Palmer found
that iron specimens exposed as long as 12 weeks in Tulsa, Oklahoma averaged
corrosion rates three times greater than residential areas near Tulsa.
703
Simpson and Horrobin reoorted that high chromium and chromium-nickel
stainless steels are very resistant to atmospheric corrosion. They attri-
buted this to a thin oxide film, which is always present on the surface and
which is self-repairing when damaged. Superficial deterioration, staining,
or soiling in highly polluted, aggressive atmospheres could be prevented
by regular washing.
703
Simpson and Horrobin retorted that lead is very resistant to atmo-
spheric corrosion whether pollutants are present or not. In clean atmosoheres,
the protective layer of lead carbonates and sulfates that forms on the metal
surface gives the metal a whitish-grey aooearance which might darken in
industrial areas. Weight loss measured over 20 years at seven U.S. cities
indicates decreasing corrosion rates in all but coastal atmospheres. Both
basic and antimonial lead were extremely durable; their corrosion rates were
-0.02 mpy. At this rate, a 3/32 inch ( -2.34 mm) thick lead sheet
would corrode to half its thickness in 2,500 years.
Several investigators exposed various metals to atmospheric pollutants.
270
Gibbons studied the corrosion behavior of major architectural and structural
333
-------
0
100
200
300
400
500
Sulfur Dioxide, ug/m3
FIGURE 11-1. Relationship between corrosion of mild steel and corresponding
mean sulfur dioxide concentration at seven Chicago sites.
From Yocom and McCaldin, 1968. 839
334
-------
metals exposed to various outdoor Canadian atmospheres for 10 years.
He tested three aluminum alloys, two magnesium alloys, three steel alloys,
three stainless steels, and rolled zinc. He oositioned all specimens
at 30° angles to the horizontal and facing south. Ihe eight sites used were
classified as rural, semirural, industrial, marine, or marine-industrial.
While most results were reported in terms of sulfur dioxide effects, because
they are based on exposure to actual outdoor atmospheres, particulates may
or may not have contributed.
The three stainless steels had the best corrosion resistance. Their
corrosion was negligible at all but the marine-industrial sites. The
aluminum alloys were next in resistance with little difference in perfor-
mance among the three alloys exposed. Rolled zinc rated third. The three
steel alloys and magnesium alloys had the highest corrosion rates. The
marine-industrial atmosphere was the most corrosive. One semirural and all
rural-marine and industrial atmospheres had similar corrosion rates. They
were next in order of corrosivity. Following was an urban site; then a
marine, rural, and a second semirural site. The rate of atmospheric cor-
rosion was markedly influenced by the sulfur dioxide content of the atmo-
sphere; the high sulfur dioxide concentration at the marine-industrial site
made it the most aggressive atmosphere. The corrosion rate usually de-
creased after the first year of exposure. With the exception of the rolled
zinc and the magnesium alloys, the earthward sides of the soecimens were
more severely attacked than the skyward sides.
The corrosion rates of all three stainless steels decreased after a
one-year exposure, and the stainless appearance of two tvpes, although some-
what dulled, was retained after 10 years. The sample that was exposed to
335
-------
the marine-industrial atmosphere remained very black even after cleaning;
but specimens of the same type exposed at all other sites not only retained
their brightness and lust-et: aftei' cleanmq, but, except for staining, were
quite bright even before cleaning.
After the initial years of exposure, corrosion rates of the steel
specimens decreased significantly at all but the rural sites where the cor-
rosion rates were lowest from the start. The residua] copper content of the
low carbon steel was sufficient to decrease its corrosion rate. The copper-
nickel steel alloy formed an adherent ototective oxide film that maintained
the low corrosion rate after five years, particularly at the rural and
industrial sites. The corrosion rate of zinc was fairly constant at all
sites. Corrosivity was related to sulfur dioxide concentration; therefore,
zinc corrosion rates correlated with atmospheric co itent of sulfur dioxide
at the various sites. The combined effect of atmospheric chlorides and/or
time-of-wetness on zinc opecimens was evident at some sites. The corrosive
attack was essentially uniform, although some pitting occurred at the more
aggressive sites.
27]
In a second series of experiments. Gibbons tested two lead alloys,
a nickel-copper alloy, copper sheet, and a copper-zinc alloy for 10 years.
He exposed specimens in the same manner to the same Canadian atmospheric
sices used in the previously described experiments, ihe corrosion rates
of all the metals tested were very low at all sites.. The atmosphere at the
mar ine-industr .,.ai site again proved the most aggressive. But even at that
site, only the copper-zinc aliov corroded more than 0.^ moy at the end of
the 10-year •.-xijosure. 'Hie rut ^1 site orovviec the Least corrosive exposure
conditions; 5e»erai nateraa.s were :>pj.y .-j ..ihtly du: .ed on completion of the
-------
test period. Lead was an exception. It exhibited brown-red corrosion pro-
ducts identified as lead peroxide. At the marine-industrial site,
unidentified black soot deposits formed on lead. Apart from some minor pit-
ting in areas adjacent to the insulators supporting the samples, no pitting
of any consequence was observed at either site. In general, the corrosion
rates decreased with years of exposure for all metals with the possible
exception of the copper-zinc alloy, for which the corrosion rate was fairly
constant throughout the 10-year study. There was little doubt that atmo-
spheric sulfur dioxide played a predominant role in the corrosion behavior
of different metals. Additional factors including time-of-wetness, temper-
ature, weather conditions at the time of exposure, and atmospheric chlorides
as well as location and orientation of the metal on the building could con-
tribute to corrosion. Gibbons cautioned that all factors should be con-
sidered when selecting a metal for service.
303
In another series of similar experiments, Guttman and Gibbons exposed
nine different metal-coated panels to the same Canadian atmospheres and in-
vestigated their corrosion behavior over 14 years. Coatings tested were:
cadmium electroplated steel, 0.2 to 0.5 mils thick; hot-dipped galvanized
steel, 2.2 to 2.4 mils thick; zinc electroolated steel, 1.0 mil thick; con-
tinuous galvanized steel, 1.0 mil thick; corrosion-resistant hot-dipped alu-
minized steel, average thickness 2.0 mils; unsealed zinc metallized mild steel,
5.0 to 7.0 mils thick; zinc metallized mild steel sealed with vinyl copolymer
with 10% nonleafing aluminum flake, 5.0 to 7.0 mils thick; unsealed aluminum
metallized mild steel, 5.0 to 6.0 mils thick; and aluminum metallized mild
steel sealed with one coat of polyvinyl butyral wash primer and one coat of
vinyl copolymer with 10% nonleafing aluminum flake, 5.0 to 6.0 mils thick.
337
-------
The sealed aluminum and zinc metallized coatinqs afforded heavy-duty
protection under very aggressive atmospheric conditions. The wash-primer
vinyl sealant was virtually unaffected at all test locations after 11 years
of exposure. These results suggest that thinner metallized coatings plus
the sealant are capable of offering long, acceptable service at most Canadian
locations. The aluminum zinc metallized coatings, in the thicknesses tested,
provided protection in excess of 12 years at the severe marine-industrial
site. The authors suggested that sealed coatings should be selected when
conditions are similar to those at the marine-industrial sites.
The hot-dipped aluminized coating performed well at all sites. Staining
aopeared at cut edges early in the testing but did not progress to any
serious extent. There were no signs of significant base-metal corrosion
at any site, including the marine-industrial site where roughness with an
underlying white corrosion product developed. The failure of the electro-
plated and hot-dipped applied zinc coatings at the aggressive sites was
predictable because of the thinness of the coating and site corrosivity.
Guttman and Gibbons recommended that the zinc coatings be painted if they
are to be used in industrial atmospheres. Elsewhere, even the relatively
thin coating can provide a long, useful service life. The thin cadmium
coatings had relatively short service lives at all but the nonaggressive
rural locations. Similar coatings are aoolied in practice to fasteners,
small stampings, and miscellaneous small articles.
370
Hukui and Yamamoto described tests of 29 metals, including iron,
steel, stainless steel, aluminum, and zinc plating, which were exoosed to
falling dust, sulfur dioxide, and salt particles at 13 randomly selected
locations in Japan. Severity of corrosion was dependent on the level of
338
-------
air pollution. It was related specifically to concentrations of sulfur di-
oxide in the ambient air and of sulfates and chloride ions in the fallinq
dust. Iron experienced the greatest degree of corrosion, followed by steel,
SUS 22 stainless, aluminum, and SUS 27 stainless. Zinc plating exhibited
little tendency (about 0.01 that of iron) to corrode. Results of corrosion
experiments conducted in the laboratory using sulfur dioxide and periodic
exposure to clean water, ultraviolet radiation (arc lamp), and heat did not
correlate well with those obtained from the outdoor exposure tests. As a
result, Hukui and Yamamoto concluded that oarticulate matter should be in-
cluded when conducting laboratory corrosion tests.
The corrosion rate of metals in acids such as sulfurous acid, nitric
acid, sulfuric acid, and hydrochloric acid with a normality between 1 and
530
10,000 is expressed mathematically by McLeod and Rogers in terms
of type of metal and acid concentration. By determining values of constants
in the developed equation, corrosion rates of various metals in sulfurous
acid can be compared with those of the same metals in nitric, sulfuric, and
hydrochloric acids. The corrosion rate of the metals in sulfurous acid of
various normalities can then be determined. Results thus obtained showed
that nonstainless steel, with or without nickel, is highly susceptible to
sulfurous acid corrosion; however, when a substantial proportion of chromium
is present in an alloy that contains nickel, steel is not attacked by either
sulfurous or nitric acid. Copper and chromium are not appreciably suscep-
tible to sulfurous acid corrosion in solutions lower than N/1.3. Tin cor-
rodes more rapidly than other nonferrous metals between N/100 and N/1,000
but less than cadmium and zinc at N/10. Cadmium, lead, and zinc corrode
more rapidly in sulfurous acid then in nitric acid. Lead corrodes less
339
-------
rapidly in sulfucous than in nitric acid. Aluminum is iraoidly corroded by
hydrochloric acid hut less su ny nitric or sulfurous acid. Hukui and
Yamamoto concluded that suJfm >us acid solutions causing the greatest damage
in urban and industrial areas have normalities between N/l and N/10,000.
4
Ailor conducted seven-year exoosure tests of seven aluminum alloys,
mild steel, and pure zinc, at Richmond, Virginia; Chicago, Illinois; Phoenix,
Arizona; Manila, The Philippines; and Widnes, England. Examination of the
test panels at the end of the first, second, and seventh years indicated
that corrosion of aluminum in industrial atmospheres generally takes the
form of pitting. Pitting and corrosion of a clad material was usually con-
fined to the cladding alloy. No loss of mechanical properties was noted
for the dad-alloy 3003-H14 after seven years. There were property losses
for bare aluminum alloys in severe environments of Chicago and Widnes, but
the bare aluminum panels were much superior in corrosion resistance to the
mild steel in industrial locations. The bare aluminum alloys showed rela-
tively high initial corrosion rates which decreased rapidly over the seven
years. Depth of pitting increased at a much reduced rate after two years.
The Widnes site was the most severe, followed by Chicago. The Manila and
Richmond locations were comparable in corrosivity, and the Phoenix atmo-
sphere was the least corrosive to all metals exposed.
Several investigations of the effect of only sulfur dioxide on metals
have been conducted. In one, the influence of the dew-quantity and dew-
cycle interval on the corrosion rate was examined. Mild steel panels were
exposed to air containing 20 opm sulfur dioxide at 95% to 100% RH. Results
indicated that corrosion was greatest when dewing was heaviest and time-of-
833
wetness to time-of-drying intervals w^re shortest. Other studies indicated
340
-------
rather direct relationships between metal corrosion rate and sulfur oxide
pollution in several ambient atmospheres whose annual average lead peroxide
769
sulfation rates ranged from - 0 to 12 mg S03/100 cm2/day. The increase in
corrosion per unit increase in sulfation was greater at lower sulfation
rates. For example, approximately half of the corrosion on iron at 12 mq
S03/100 cm2/day occurred at a sulfation rate of 2 mg S03/100 cm2/day; in the
case of zinc, one-fifth had occurred at 2 mg S03/100 cm2/day. A lead per-
oxide sulfation rate of 2 mg SQ3/100 cm2/day is equivalent to an average
concentration of 0.056 DOT of sulfur dioxide. The investigators reasoned
that average annual sulfur dioxide concentrations of < 0.05 ppm can result
in considerable corrosion, particularly on iron.
339
Yocom and McCaldin have summarized the results of various researchers.
They reported that there appears to be a critical atmospheric humidity that,
when exceeded in the presence of sulfur dioxide, oroduces a sharo rise in
the corrosion rate. Critical humidities reported include 80% for aluminum,
60% and 75% for mild steel, 70% for nickel, 63% for copper, 70% for zinc,
and 90% for magnesium.
839
Yocom and McCaldin also reported that aluminum and its alloys are
resistant to sulfur dioxide concentrations normally found in polluted atmo-
spheres. Under laboratory conditions in air containing 280 ppm sulfur di-
oxide at 52% RH, a highly refined grade of aluminum and an aluminum alloy
(AA 3003) exhibited the same weight increase and reached a limited value
essentially the same as aluminum in air with sulfur dioxide. These authors
concluded that, at relatively low humidities, sulfur dioxide does not in-
fluence atmospheric corrosion of aluminum nor does it cause any visually
discernible changes to the metal surfaces, At higher humidities (72% and
341
-------
85%), both kinds of aluminum corrooted much faster, but the highly refined
grade lost only approximately half the weight of the AA 3003 alloy. The
white powdery deoosit formed on the surface of samples under these conditions
was aluminum sulfate, an indication that sulfur dioxide played an essential
role in the corrosion.
321
Haynie and Upham exposed zinc panels, positioned at 30° to the
horizontal, to the atmospheres of eight cities for five years during which
continuous air monitoring facilities correlated corrosion rates of metals
with atmospheric sulfur dioxide concentrations. Rural sites near each city,
assumed to have the same meteorologic conditions but less pollution, were
used as control sites, but sulfur dioxide was not measured. Corrosion rates
were generally higher at urban sites than at rural sites. At San Francisco,
Cincinnati, and New Orleans the corrosion rates were initially higher at the
rural sites but eventually converged with the urban rates. In Philadelohia,
the corrosion rates at the rural site were exceptionally high, but not as
high as at the urban site. Estimates of sulfur dioxide at the rural sites
were revised to conform with the amount of corrosion observed. Haynie and
Upham concluded that atmospheric sulfur dioxide concentration can be esti-
mated from average zinc corrosion rates and average relative humidities.
There has been little research to determine the influence of other gas-
eous pollutants, such as nitrogen oxides and hydrogen sulfide, on corrosion.
232
However, Fink e_t a!L. reported that nitric acid may react with traces of
ammonia. It may then be absorbed by hygroscopic Particles that may ultimately
213
settle on surfaces, thereby enhancing corrosion rates. Elliott and Franks
described the effects of hydrogen sulfide in concentrations of 100 to 120
ppm on various metallic finishes of a variety of base metals (Table 11-5).
342
-------
s
0)
•O
3
c/1
&
g
"P
U
10
&
o
CO
c
IB
O
CM
O
U
UH
•1
c
•H
W
a:
to
1
o
CD
01
p
UH
X
CO
It
o
CM
fj
V
V
U-l
<
bo
C
•H
B
0)
CJ
H
XI
0>
•P
01
a.
§
a
c
0
•H
p
O
UH
01
•O
•H
UH
•H
CO
>
X
•H
CO
O
(H
O
O
A:
CJ
re
•°
^
re
0)
rr|
C3
O
•H
P
10
o
UH
•O
•fH
UH
^
CO
£»
10
0)
X
BO
C
-3
p
•H
a
r-l
IB
CJ
O
-i
£
60
•H
-H
*o
01
4-^
O
U-i
Cp,
s
j
to
o
o
CJ
•o
a
c
o
•H
^j
re
b
O
O
O
CO
•H
C
•H
p
P
O.
p
j:
M
•H
CO
ft
T5
4J
O
0)
U-4
UH
S
63
C
M
C
H
cn
M
C
C
h
10
W
01
C
01
CJ
•o
o>
4J
CJ
UH
O
3
T)
4J
10
a.
•a ,
01
p
o
I O
us
r-j
CN
. o
0,0
o
z
x;
p
m
01 o
v O
o •
•H O
Z ^
•o c
0) -H
(0 CN
?l
•-H O
O
O
O
T) C
01 *H
P
4S
0.0
C •
•rt O
10
E
01
W
re
n
ex
o,
0
CJ
01
i,
s
0.
CH
01
a
a.
O
o
Li
o.
o
CJ
o.
o
o
01
CL
3
cj
3
CJ
CO
to
2
ffi
£
a.
CO
Ji
Cb
0
H
XI
I
to
o
343
-------
h
(u
C
•H
cyj
rg
s
o
CM
1
0
o
rH.
O
4->
CO
g
^
w
8,
X
£
MH
O
to
4J
H
3
CO
PS
to
JS
"O
0
to
t,
0)
4-1
4H
C
o
to
o
o
o
•u
c
re
c
o
•H
ro
0
o
o
CO
Q
bo
CO
•S"
o
CM
r.
O
>*H
•H
4J
•H
a
H
s
o
H
•o
c
re
M
C
•H
X
CO
•H
C
i,
a
E-
bO
c
•H
4-1
•H
a
H
re
o
o
H
4J
.C
M
•H
C/5
•o
01
4--
MH
MH
c
o
o
o
MH
S
•a .c
0) 4->
H O
-------
MASONRY AND CONCRETE
Masonry and concrete materials used in the building industry include
brick, stone, clay tile, mortar, small precast masonry units of concrete,
and large poured-in-place or precast concrete units. Brick, both calcareous
and noncalcareous (basically aluminum silcate), is applied extensively as a
veneer facing for buildings and as walls and chimneys or stacks. Clay tile,
basically of the same materials as brick, is employed as roofing, interior
partitions, exterior walls, furring, and flooring. Stones, including lime-
stone, marble, slate, and sandstone, are excellent materials for load-bearing
walls, facing, roofing, trim, and ornamentation. Small precast concrete
masonry units are used as backing for veneer brick walls, partitions, facing,
furring, lintels, trim, and cornices. Concrete, either poured-in-place or
precast to form larger building components, consists essentially of a cal-
careous-based cementitious material, predominantly Portland cement, and aggre-
gates of various sizes that have been mixed with water. Concrete components
serve as structural elements of buildings (e.g., columns and beams, curtain
walls, foundations, and floors), structural elements of bridges, and simple
slabs for patios.
Atmospheric pollutants that affect masonry and concrete materials in-
clude particulates (such as soot), sulfuric and sulfurous acids (formed when
atmospheric sulfur dioxide reacts with water), and several of the acidic
gases. Deleterious effects include simple discoloration or staining, erosion
and corrosion, and leaching.
Natural environmental factors such as relative humidity, rain, and wind
can also influence the effect of pollutants. For example, intense pain fol-
lowed by bright warm sunshine that quickly evaporates moisture from the
345
-------
816
masonry or concrete surface can provide a cleansing action. However, Wilson
reported that high humidity slows the natural evaporative process, especially
in sheltered are4s. The moisture that is then prevented from leaving the
material, if polluted with atmospheric acids, can dissolve the calcareous
elements in masonry or concrete. Wind velocity largely determines the force
with which both rain and particulate matter strike a building and, thus, the
abrasiveness. These factors plus the porosity and texture of the surface
determine the amount of particulates that remain on that surface. Yocom and
839
McCaldin reported that under high wind conditions large particulates en-
trained in the windstream actually result in a slow erosion of surfaces similar
to sandblasting.
Effects on building stones depend on their chemical composition.
668
Schaffer reported that soot fills the surface pores of many sandstones
causing them to become uniformly darkened; however, erosion of exposed sur-
facr3 of limestones precludes the retention of soot so that only the sheltered
sides become blackened. He further stated that soot also contributes to
chemical decay of stone because it carries with it acids and soluble salts.
Softer building stones, such as marble, limestone, and dolomite, are readily
769
attacked by acids formed when atmospheric smoke and moisture interact.
All are calcareous minerals containing carbonates which convert to relatively
soluble sulfates by sulfuric acid and can then be leached away by rainwater.
The calcium sulfate formed on the surface of such stones is twice as bulky
as the carbonate in the stone from which it was formed.
Stones such as granite and some sandstone in which the grains are ce-
mented together with materials containing no carbonate, well-baked bricks, and
769,839
glazed tires are relatively unaffected by atmospheric sulfur dioxide.
346
-------
619
Pressley reported, however, that refractory brick can be influenced by
participate acids and salts at high temperatures. Thermal cycling of
magnesite-containing bricks in sulfur trioxide at temperatures between 760 C
and 1,040°C considerably increased the strength of the bricks. This was
attributed to the formation of magnesium sulfate which filled the pores in
the brick. Under similar test conditions, sodium metavanadate considerably
reduced the strength of magnesite brick, It also reduced the strength of
magnesite-chrome brick, but less severely.
The effect of atmospheric acids on sandstone, concrete, brick, and mortar
is not confined to the surface. Water can transport the aggressive agents to
92
the interior of the materials. Brown wrote that substances taken into so-
lution usually come out of solution and form secondary encrustations elsewhere.
With sulfuric acid, the reaction product would be calcium sulfate or gypsum.
518
McBurney indicated that sulfuric acid displaces chlorides and carbonates
from alkali (sodium and potassium) and alkaline (calcium and magnesium) com-
ponents of masonry. He cited the reaction of sulfuric acid with sodium sulfate
or sodium bisulfate to form gas which, in the presence of water, forms hydro-
chloric acid. When water carrying the reaction products in solution moves
to the surface, both the water and hydrochloric acid evaporate leaving behind
efflorescent sodium sulfate to discolor the surface.
477
Litvin studied the effects of outdoor exoosure on concrete samoles
containing white portland cement, white silica sand, and grey-white coarse
marble aggregate. The samples were exoosed 30° from the horizontal at a
site in Buffington, Indiana, which is adjacent to two highly industrialized
areas. The aggregate became slightly affected, but the white matrix areas
had weathered to a light brown color and showed evidence of etchingf probably
347
-------
due to acid attack. Litvin compared these results with results obtained
using similar samples protected with 14 different commerical polymeric
coatings. (These tests are discussed under POLYMERIC MATERIALS, p. 364.)
Results indicated that concrete may fare better uncoated than with a coating
of unproven service, particularly in nonindustrial areas. Sealing of the
surface of porous materials such as concrete unfortunately often leads to
spalling which is usually more deleterious than surface deterioration or
discoloration.
816
Wilson, reporting on variables affecting concrete exposed to the
atmosphere, stated that performance is a function of both the uniform
quality of the material and the nature of the surface. Aggregates of
angular shape and crystalline surface texture, such as crushed rocks of all
types, hold dirt more readily than aggregates of a rounded shape and glass
texture, such as river or seashore gravels. Although patterned or profiled
slal s or curtain walls are subject to general darkening, they collect more
particulates on certain facets of the pattern than on others. This often
3
results in a highly interesting and pleasing appearance. Similarly, Adams
reported that on smooth facings, stains show UP more clearly but are easier
to wash off. Surfaces such as those with exposed variegated stone aggregates
seem to dispense dirt readily and their roughness mitigates unsightliness.
816
Wilson concedes that it would be more reasonable to use dark colored sur-
faces in highly industrial areas, and that dense concrete would reduce the
chance for water-carrying atmospheric acids to enter the material.
The effect of sulfur dioxide on oolitic limestone was reported by
713
Spedding. Table 11-6 shows that the uotake of sulfur dioxide is very de-
pendent on humidity and that saturation appears to be reached rapidly—in
348
-------
TABLE 11-6
Uptake of Sulfur Dioxide (SC^) by Oolitic Limestonea
Relative
humidity, %
11
13
79
81
S02 concentration,
Ug/m3
360
280
100
370
Time of expo- yg S02/cm2
sure, min of ^irface
20 0.069
40 0.061
48 0.24
10 0.28
a
From Spedding, 1969.7l3
349
-------
at least 10 min durinq the high humidity experiments. From these findings,
Spedding reported that a freshly exposed matrix would be rapidly saturated
with sulfur dioxide at normal atmospheric humidities and that the erosion
process associated with calcium sulfate formation would be virtually
continuous.
Little quantitative data are available on the actual chemical effect
of pollutants on masonry and concrete structures; however, their potential
deleterious effect to works of art or historical monuments has been reported.
769
One investigation indicated that sulfate, resulting from the attack on the
stone by atmospheric acids, was found in cracks and fissures as deep as
50 cm beneath the surface of the British Houses of Parliament. An increase
from 1.0 to 4.2 in the volume of crystallization of calcium and magnesium
salts along the cleavage planes of the stones in these buildings had thrown
off great pieces.
Cle
-------
pallazzi, churches, and other historical buildings and also provides Venetian
homeowners with financial aid to convert oil heating systems to less polluting
methane gas systems. Interesting, however, is a recent investigation by
92
Brown that showed no evidence of attack by sulfuirous oarticulates on the
Lincoln Memorial in Washington, D.C., but that there were dust and soot par-
ticles in open joints.
PAINTS AND FINISHES
Paints (opaque film coatings) and finishes (varnishes and lacquers) are
used extensively in the building industry to beautify and protect all tyoes
of substrates from metals serving as a critical structural element in bridge
construction to wood used simply as a decorative fence. The paint or finish
acts as a protective shield between the construction materials and the
environmental factors that can attack and deteriorate them.
Paints basically consist of two components: the film-forming comoonent,
which is generally referred to as the vehicle and which may have a legion of
components, and pigments, which make the film opaque and provide the desired
decorative feature. Generally speaking, the degradation of these two compo-
nents by environmental factors results in the undesirable appearance of painted
surfaces. The principal substances employed as vehicles, either alone or in
combination with other additives, include oils (e.g., linseed) and natural,
modified natural, and synthetic resins. Of the resin-type Paints, the
synthetics are most commonly used now, particularly the vinyls and acrylics.
Pigments are divided into two major classes, colored and white. Commonly
used white pigments include silicates, barium sulfates, white lead, titanium
oxides, zinc oxide, basic lead silicate, and zirconium oxide. Organic,
mineral, and metal compounds are used as colored pigments.
351
-------
Natural environmental factors such as sunlight, particularly ultra-
violet, temperature variations, moisture, and fungi significantly influence
the appearance, performance, and service life of paints and finishes.
Natural chemical environments, such as those laden with salt water, also
can greatly affect the appearance and performance of paints.
In addition to these natural factors, evidence indicates that degra-
dation of paint properties can be caused by many air pollutants, particularly
particulates, hydrogen sulfide, sulfur oxides, ammonia, and ozone. The
effects of air pollutants on paints are loss of gloss, scratch resistance,
adhesion, and strength; discoloration; increased drying time; and unattrac-
tive, dirty appearance. Significant arid prolonged attack without preventive
maintenance also can result in exposure and subsequent attack of the sub-
strate being protected. Obviously, exterior paints encounter more destruc-
tive influences than those used on interior surfaces.
Part culate matter (dust, soot, hydrocarbons, and other solid matter)
affects primarily the aesthetic quality of paints since its accumulation on
surfaces (due to thermal, electrostatic, and mechanical forces) gives the
716
paint a dirty appearance. Spence and Haynie reported that painted fences
at various U.S. locations became blackened from soot deposits. Efforts to
remove it or clean the tarry matter embedded in the paint destroyed the
film. Further, the two coats of paint used to cover the soiled paint had
a shortened lifespan, and its appearance was marred.
168
According to Cowling and Roberts, particulates also promote the chem-
ical deterioration of wet or tacky paints in a moist environment by acting as
wicks which transfer corrosive agents to the underlvina surface or serve as
nucleation sites at which other oollutants can concentrate. These authors
352
-------
state that moderately chalky paint removes the participate matter. Hence,
for exterior surfaces in industrial communities, these authors suqgest using
paints with the maximum pigmont concentration that is consistent with
durability requirements.
Severe staining of paint films also can be affected by 0.5 ppm cooper
and 0.1 pan iron salts, two metals identified as airborne oarticulate mat-
355
ter but also found in rainwater in the United States, according to Holbrow
716
and Spence and Haynie. A specific example of particulates reacting with
839
painted surfaces was cited bv Yocum and McCaldin. They described the
grinding by iron particles on surfaces of cars. Brown stains surrounded
each particle. Many cars had to be repainted. The deposit resulted from
the formation of ferrous hydroxide in the presence of moisture. In colloidal
form this substance reportedly diffused in the paint film. Upon drying and
oxidizing, it left the brown stain, ferric oxide. Spence and Haynie reported
damage to automobile paints by alkali mortar dust from the demolition of
brick buildings. These vehicles also had to be repainted.
Spence and Haynie, summarizing investigations of others, also reported
the effect of particulate matter on paints based on frequency of painting and
maintenance practices of homeowners. One investigation involved three suburbs
of Washington, O.C.—Suitland and Rockville, Maryland, and Fairfax, Virginia—
and two cities in the uooer Ohio valley—Steubenville and Uniontown. (See
Table 11-7.) The number of years between reoaintings decreased as the partic-
ulate concentrations increased. Repaintinq in Steubenville, which has partic-
ulate concentrations as high as 234 uq/m3, was necessary almost every year.
In Fairfax, where particulate concentrations were ~ 60 w/m3, repainting
occurred every four years. This maintenance frequency increased as local par-
ticulate concentration increased. (See Figure 11-2.)
353
-------
TABLE 11-7
Interval for Exterior Repainting as a Function_
of Particulate Concentration in Five US Cities^
Steubenville Uniontown Suitland Rockville Fairfax
Particulate con- 235.00 115.00 85.00 75.00 60.00
centration,
yg/m3
Maintenance 0.88 1.89 2.93 3.62 3.90
interval, yr
Maintenance 1.14 0.53 0.34 0.28 0.26
frequency,
number per
From Spence and Haynie, 1972.7l6
Reciprocal of maintenance interval in years.
354
-------
s
S
£S
•H S.
1.25
1.00
0.75
0.50
0.25
0
Fairfax
50
Steubenville
Uhiontown
Suitland
'Rockville
100
150
200
250
Particulate Concentration, pg/m3
FIGURE 11-2. Relationship of maintenance frequency for exterior repainting
to particulate concentration. From Spence and Haynie, 1972.*1
355
-------
Spence and Haynie suggested that there is a significant relationship
between the frequency of repainting and particulate concentration. However,
extrapolation of the line in Figure 11-2 indicates that repainting does not
occur at zero particulate concentration and that repainting frequency con-
tinues to increase as particulate concentration increases. A leveling out
of the line to form a plateau at the low and high extremes of particulate
concentration should be expected. These authors indicated that additional
data are needed, particularly for cities with mean annual particulate con-
centrations > 150 Mg/m3.
In their study of particulate concentrations in the Philadelphia area
(see Table 11-8), Spence and Haynie considered socioeconomic and other factors.
They suggested that the inclusion of these factors partially explains why no
statistically significant difference in painting frequency as a function of
particulate concentration was detected.
168
Covling and Roberts stated that sulfur dioxide is readily absorbed
in wet paints and reacts with the vehicle to form soluble compounds. Unspe-
cified concentrations of sulfur dioxide with high humidity during application
may cause paints to be tacky. This facilitates additional contamination by
particulates whose electrical charge can affect the adhesiveness of the paint.
355
Holbrow also reported that sulfur dioxide concentrations from 1 to 2 ppm
increase the drying time of linseed, tung, and bodied dehydrated castor oil
paint films from 50% to 100%. At 7 to 10 ppm, drying was delayed by up to
two or three days. Only unbodied castor oil paint was not affected greatly.
The drying times of paints containing basic pigments such as white lead or
zinc oxide *ere not greatly affected, but oleoresinous and alkyd paints pigmented
with titanium dioxide had both their touch- and hard-dry times increased
356
-------
TABLE 11-8
Mean Annual Frequency for Exterior Wall Painting in Philadelphia
Area as a Function of Particulate Concentration"
Exterior veil painting
Particulate concentration
ranges, pg/m3
< 75
75-100
100-125
>125
Mean annual
frequency
0.28
0.35
0.35
0.29
Standard error
of mean
0.016
0.053
0.041
0.055
From Spence and Haynie, 1972.716
357
-------
substantially. Analysis of the dried films showed that sulfur dioxide had
reacted with the drying oil, orobably modifying the oxidation-oolymerization
process. Holbrow concluded tnat sulfur dioxide concentrations in fogs near
industrial sites can increase the drying and hardening times of certain paints.
839
YOCOTTI and McCaldin could find no studies of the effects of sulfur di-
oxide on drying time of latex-base (synthetic resin) paints. They surmised
that when the paint is applied, the sulfur dioxide may interfere with the
evaporation of water and, therefore, the coalescence of polymeric-pigment
particles. Upon reaction with water in the paint, sulfur dioxide forms sul-
furous acid which could cause instability of the protective colloid around
latex particles and, consequently, flocculation. Poor film formation would
be possible with resulting loss of aesthetic as well as protective value.
Some investigators reported that the effect of sulfur dioxide (presumably
between 1 to 2 ran) is negligible when the paint films are hard and dry, in
contrast to the effect on wet oaint.
355
In studies of gloss, Holbrow exposed paint films to a 1.2% sulfur
dioxide solution for 15 min after the films were first dried for 24 hr under
normal laboratory conditions, then cooled in a refrigerator to effect mois-
ture condensation on the surface. Sulfur dioxide and moisture caused only
a small decrease in gloss; however, after further exposure to moisture and
warmth in an accelerated weathering chamber, a significant change occurred
in the gloss of some paints. \ pentaerythritol alkyd was scarcely affected;
a linseed stand oil paint experienced the greatest change; the extent of gloss
loss wa proportional to the water sensitivity of the films. Very high con-
centrat •_-«ns of sulfur dioxide rendered the films water sensitive; during
the accelerated weathering, the moisture absorbed by the oaint resulted
358
-------
in excessive swelling. Holbrow reported the same effect when films
were exposed to hydrogen chloride vapor. Another closely related effect
was the blueing of green paint during the early life of the film when it
still had a high gloss. Sulfur dioxide and moisture together need not
cause a color change, but when followed by exposure to warmth and humidity
(accelerated weathering), the change can occur. The blueing was attributed
to a bleaching of the lead chromate pigment when the film was exposed to
sulfur dioxide shortly after application. The paint loses its sensitivity
to this effect after a few hours of exposure to concentrations- 0.2 ppm sul-
fur dioxide, but remains sensitive to higher concentrations from one to three
days. The paints containing large quantities of oil were most prone to the
effect and remained sensitive longer. The introduction of basic pigments and
additives reduced the effect, but large amounts were necessary (e.g., 10% zinc
oxide). The presence of copper, cerium, and vanadium was especially effec-
tive in preventing blueing. The addition of cppper compounds, such as copper
phthalate, prevented blueing under laboratory test conditions. Similar quan-
tities of oil-soluble soaps—1% copper, 0.5% cerium, or 0.5% vanadium—as
naphthenates in the oil component also were effective.
While no quantitative data could be found on the effects of sulfuric
716 168
acid on painted surfaces, Spence and Haynie and Cowling and Roberts
reoorted that the acid may cause damage by reacting with such paint ingre-
dients as pigments, fungicides, and the vehicle itself. The effects of
sulfuric acid are implied in the data on the effects of sulfur dioxide,
which converts readily to this acid in the presence of moisture.
Sulfur dioxide and moisture in the oresence of ammonia causes crystal-
355
line bloom. Holbrow ascribes this to the formation of small crystals (0.5
359
-------
to 1.0 urn dia) of ammonium sulfate on the surface of varnish and oaint films.
Formation of the bloom is influenced significantly by moisture and paint
composition. Quantitative measurements indicated that a deposit of 3 to 4
yg/on2 of ammonium sulfate can cause a moderate bloom in either a penta-
o
erythritol or glycerol alkyd paint film, while a deposit of 10 yg/cm can re-
sult in a severe bloom. Holbrow calculated that sulfur dioxide concentrations
of ~0.1 ppm in 2 m3 of air would be sufficient to cause a moderate bloom
(4 yg/cm2) over 100 cm2. Since only five times this volume of air would
probably be required to supply the ammonia and since the volume of air that
passes over a paint film dailv is considerable, blooming can easily occur.
69
Berger et al. reported results of tests conducted on both oil-base
(alkyd and linseed) and synthetic resin-base (polyvinyl acetate latex ancl
acrylic latex) paints on aluminum, wood, masonite, and transite after sepa-
rate exposures to sulfur dioxide and ozone. Specimens were exposed for 750
hr in an accelerated weathering chamber in air under the conditions of
37,"?8°C, 65% RH, 2 ppm sulfur dioxide, and 2.2 mWhr/hr ultraviolet radiation.
Conditions were similar for the ozone tests except that the exposure lasted
1,000 hr and the ozone concentration was 0.5 orm. Exposed specimens were
examined for, among other changes, loss of gloss, scratch resistance, and
adhesion. They were then compared with control soecimens and specimens ex-
posed to two natural outdoor environments, a heavily Dolluted urban indus-
trial area high in sulfur dioxide content and a rural area free of sulfur
dioxide but high in ozone content. The paint gloss on all substrates de-
creased with duration of exoosure to either pollutant. Ozone seemed to
cause i_r.c least change and sulfur dioxide the most. The alkyd paint incurred
greatest gloss loss on control soecimens regardless of substrate. Outdoor
360
-------
exposures to sulfur dioxide caused greater gloss loss than outdoor exposures
to ozone. Scratches that resulted from exposures to sulfur dioxide or to
outdoor exposures with high sulfur dioxide content were consistently wider
than those caused by exposures to ozone or outdoor exposures with high ozone
content. Most scratch widths ranged from 0.1 tire to 0.5 mm. Some scratches
on paints covering aluminum substrates were much wider, indicating major
adhesion loss. No comparisons were made with control specimens. Although
some researchers reported that ozone seemed to effect adhesion the least
and sulfur dioxide the most, they questioned the scrape-adhesion test method
used to evaluate pollutant effects.
716
Spence and Haynie reported that tests conducted by the Illinois
Institute of Technology Research indicated a definite reduction in creep com-
pliance of oil-base paints exposed to ozone; extent of reduction for second-
quality paints was about three times greater than that for the first-quality
paints tested. The films of the first-quality paints retained more flexi-
bility than the second-quality paints. These paints were exposed to 6%
ozone at 35° C and 65°C for up to 505 hr.
716
Hydrogen sulfide attacks painted surfaces. Spence and Haynie noted
that in the southern portion of the San Francisco Bay area it darkened house
paints to various tones of grey and even jet black. The discoloration
occurred around doors and windows and under eaves. These locations tend to
remain moist, indicating that the attack was enhanced by moisture. The most
severe discoloration occurred during winter, although the maximun 2-hr
average air concentration of hydrogen sulfide was twice as great in the
summer. This supported the contention that high humidity increases damage.
The actual concentration of hydrogen sulfide at which paint begins to darken
361
-------
is not known; however, Spence and Haynie quote investigators who indicate
that—under certain conditions—paint darkening can occur at hydrogen sul-
fide concentrations between 70 to 140 pg/m3. Further, they reported that
some laboratory studies have indicated that darkening of paint does not
occur unless the films are actually wet with water. Although no studies
produced dose-response data on the effects of relative humidity and hydrogen
sulfide on paint films, the darkening effect has been attributed to the for-
mation of dark-colored metal sulfide by the chemical reaction of hydrogen
sulfide on lead additives and on organometallic driers and preservatives
in the paint.
839
Yocom and McCaldin similarly reported that house paints containing
lead compound pigments are rapidly darkened by hydrogen sulfide which causes
the formation of black lead sulfide. They reported that the severity of dis-
coloration is apparently related to the lead content of the paint, amount of
hydrogen sulfide in the air, duration of exposure (several hours of exposure
to as little as 0.05 pom was reported to effect a change), and moisture during
exposure. They further reported that little damage occurs if both paint sur-
355
face and air are dry. Holbrow confirms a reaction between hydrogen sulfide
and the metal component of the drier or pigment, Particularly lead.
POLYMERIC MATERIALS
Plastics and elastomers (including rubber) are considered jointly in
this section. Chemically, both are high molecular weight polymeric materials
and most such materials are now largely synthetic. The types of polymers
and possible variations of each are innumerable. In the course of their
manufacture or processing, they can be compounded with varying amounts of a
variety of ingredients including fillers, plasticizers, pigments, dyes,
362
-------
vulcanizers, stabilizers, antioxidants, and a host of: other substances, each
of which is intended to enhance some special property or properties or to
minimize others. Generally, polymeric materials are classified as thermo-
plastics (e.g., polyvinylchloride [PVC] or polyethylene) or as thermosets
(e.g., epoxy or silicone); however, depending on formulation and processing,
certain thermoplastics can be made thermosetting and vice versa. Molecularly,
thermoplastics are linear or chain-like polymers capable of experiencing
repeated softening by heat and hardening by cooling. Thermosets are highly
interconnected and extensively cross-braced, molecularly. As a result,
465
deterioration of such materials is usually a surface phenomenon.
Vinyls constitute approximately 50% of all polymeric materials used in
the building industry. They are used extensively as floor tile, wall
covering and paneling, siding, piping, vaoor barriers, protective coatings,
cladding, window frames, and electrical insulation. PVC, which is the most
extensively used vinyl, has recently been applied as a membrane material for
air structures. Other polymers are polyethylenes; polyesters; polystyrenes;
acrylics; polyurethanes; ohenolics; polycarbonate; and silicone.
Few investigations have been made to determine the effect of atmospheric
pollutants on these materials. In general, particulate matter such as dust,
soot, and smoke dirty the surfaces and liquid and gaseous acids appear to
195
cause fading, gloss loss, or disintegration.
721
Stedman examined the possible effects of atmospheric pollutants on
rigid PVC under exposure to ultraviolet radiation. In these tests, 0.75
inch ( - 18.75 mm) strips of white, rigid PVC were inserted in sealed Vycor
test tubes each of which was filled with one of the following: ammonia,
carbon monoxide, hydrogen sulfide, methane, nitrous oxide, nitric oxide,
-------
nitrogen dioxide, sulfur dioxide, or atmospheric air. In addition, a PVC
strip of a similar compound and one of a different compound, but known to
yellow extensively under ultraviolet radiation (fluorescent sunlamp/black
lamp), were placed in test tubes opened at both ends. All tubes were exposed
outdoors on a 45° angle test deck. Although cloudy weather prevailed for
several days at the start of the exposure, after 22 hr the sample in sulfur
dioxide had begun to darken. After 144 hr, the strip was almost black and
the inside wall of the tube was hazy; the reverse side of the strip facing
the deck was uniform, but slightly yellowed.
In a similar test using sulfur dioxide, strips of white, rigid PVC of
a different compound, which were exposed to fluorescent sunlamp/black lamp
radiation, produced similar results. The only difference was the type of
discoloration of the PVC. The primary reactions appeared to be the reduc-
tion of the sulfur dioxide to elemental sulfur, recombination of the
stabilizers' heavy metal to form colored sulfides, such as tin, barium, and
cadmium, and some oxidation of the PVC.
The sample enclosed in the nitrogen dioxide exhibited a different
phenomenon. Initial discoloration of the PVC could not be detected visually
because of the color of the gas, but after 29 days the strip was yellowish-
tan and the gas colorless. When the tube was opened, the brown color of
nitrogen dioxide reappeared immediately, indicating a redox reaction whereby
the PVC reacted with the oxygen provided by the reduction of nitrogen di-
oxide co nitric oxide. The yellowness of the strip had increased from
1.1 tc jfK>ut 17.3; 26 days later, during which time the strip was stored
in the dark, it had increased to 79.1. After exposing different rigid PVC
compounds in nitrogen dioxide to fluorescent sunlamp/black lamo radiation,
364
-------
differences in discoloration again appeared, the degree depending on
particular compound in the strip.
The yellowness index of PVC strips having the same composition as those
exposed to the atmospheric pollutants increased only about 4.8 points after
exposure to fluorescent sunlamp/black lamo radiation and 27 days in the dark.
This could indicate differences between artificial and natural radiation.
The yellowness index of the sample enclosed in ammonia increased from 1.1 to
7.7 in 33 days, while its green tristimulus value changed only from about
75.0 to 73.6. In comparison, after 63 days of exposure to hydrogen sulfide,
the yellowness index of the sample increased only about 0.1 points, but its
green tristimulus value decreased from about 75.2 to 63.8, indicating general
darkening or greying. Nitrous oxide showed the least change in yellowness
index, an increase of about 5.5 points, even after 123 days.
During a 63-day period, the control strip in the closed-end test tube
showed a slight decrease in yellowness index whereas the sample of the same
composition in the open-end tube showed an increase. After an additional
25-day exposure, the yellowness index of the open-end control specimen in-
creased about 6.2 points are3 that of the closed-end specimen about 1.9 points.
The open-end specimen with the different comoound increased about 2.0 points
in yellowness index. After a total of 123 days, the specimen having the
different compound had changed very little, but the control strips continued
to increase in yellowness, the one in the ooen-end tube at a higher rate
presumably because of the continual supply of oxygen.
721
Stedman also reported polymeric changes in the samples as a result of
the various exposures. For example, cracking of PVC samples as produced in
some cases by fluorescent sunlamp/black lamp radiation was duplicated outdoors
365
-------
following exposure to nitroqen dioxide in the Vycor tubes for 29 days and
storage in the dark for over 26 additional days. Ihe sample cracked approxi-
mately 90% through its thickness when folded 180° c»n itself, indicating in-
depth polymeric degradation resulting from oxidation.
386
Jellinek studied chain scission of various polymers in the form of
thin films exposed to 1 atm of air, near ultraviolet radiation (wavelength
o
greater than 2,800 A) in the presence and absence of sulfur dioxide and
nitrogen dioxide in various concentrations. He concluded that most vinyl
polymers are scarcely affected by long exposures to either gas at concentra-
tions of 1 to 5 ppm at or near room temperature. Polyethylene and poly-
propylene suffered some cross linking. Chain scission by nitrogen dioxide
occurred with nylon. Isotactic polystyrene exposed to the same concentra-
tions of sulfur dioxide in the presence of air and ultraviolet radiation
suffered only negligible chain scission after a 1-hr exposure. In other
investigations, no chain scission occurred without the small sulfur dioxide
387,388
pressure (0.85 mm Hg).
386
Jellinek reported studies in which sulfur dioxide concentrations of
2 ppr in air had no appreciable effect on the tensile strength and elongation
of vinyl plastics. The investigators concluded that from two to six months
exposure to 100 ppm sulfur dioxide is required to cause significant changes
in the tensile strength of PVC polymers. Still other investigations indicated
that 18 pom sulfur dioxide and ultraviolet radiation only slightly affected
vinyl polymers; small amounts of carbon dioxide and water evolved at 7.22°C
and so- ^ discoloration took place. No change was noted in the flexibility
of polyethylene, polyethylene-terephthalate, polyester (cross-linked), and
PVC after 500 hr exposure to 18 ppm sulfur dioxide; only polystyrene became
366
-------
brittle after this time. Very little effect on the infrared spectra of the
polymers was observed. There were some changes in FVC, polyvinylfluoride,
and polystyrene, probably due to the incorporation of sulfur dioxide groups
along the polymer backbones and loss of some chlorine and fluorine. Jellinek
stated that nitrogen dioxide might also be incorporated along the polymer
backbone and that polystyrene becomes quite polar if sufficient nitrogen
dioxide groups are thus incoroorated, indicating that chain scission is not
the only possible kind of deterioration.
69
Berger et al. provided results of tensile tests on plastic films
(polycarbonate, polypropylene, polyvinylfluoride, and PVC acetate) and gloss
and adhesion tests on coatings of PVC and oolyvinylfluoride on aluminum
siding after exposure to sulfur dioxide and ozone. Specimens were exposed
for 750 hr in an accelerated weathering chamber in air under conditions of
37.78°C, 65% RH, 2 ppm sulfur dioxide, and 2.2 mWhr/hr ultraviolet radiation.
Conditions were similar for the ozone tests, except that exposure lasted
1,000 hr and ozone concentration was 0.5 opm. In addition, results were
compared with control specimens and specimens exoosed to two natural outdoor
environments, one a heavily polluted urban industrial area high in sulfur
dioxide content, and the second free of sulfur dioxide but high in ozone
content.
Partial results of these tests indicated that polyvinylfluoride and PVC
films were unaffected by any of the exoosure conditions. The oolycarbonate
film incurred reduced tensile strength from exposures to xenon arc alone
and with ozone. The most severe effect was a reduction of approximately
17% in tensile strength after a 250-hr exposure to the xenon arc plus sulfur
dioxide. Outdoor natural weathering of the PVC and polyoroDvlene samples
367
-------
was discontinued after four and two months, respectively, because the samples
had become so brittle, they could no longer undergo tensile testing. The
polycarbonate sample lost little tensile strength after a five-month exposure;
however, the sample in the urban outdoor area with high ozone content incurred
an approximately 45% loss in the seventh and ninth months of exposure. This
reduction was attributed to biodegradation of undetermined source.
After all exposures to air pollutants, PVC siding maintained its gloss
better than polyvinylfluoride, on which sulfur dioxide caused the greatest
change. The control PVC samples exhibited the maximum change. Ozone caused
the least change in gloss of either coating. Gloss appeared to be affected
less at the two outdoor sites than under artificial weathering conditions;
the rural exposure did not affect the samples as severely as the heavily
polluted industrial site. Ozone affected adhesion of PVC samples more than
sulfur dioxide. Sulfur dioxide had essentially no effect on adhesion of the
polyv nylfluoride; however, adhesion decreased with exposure to ozone.
TEXTILES
Textiles are used by the building industry almost exclusively in acces-
sory i^-ems such as draperies, carpeting, and furniture. The textiles may be
made from both natural fibers (cotton, wool, hemp, jute, linen, silk) and
modified natural or synthetic fibers (regenerated animal and vegetable
fibers; viscous and acetate rayons; polyamides, acrylonitriles, polyesters,
polyvinyls, nylons). Generally, textiles consist of the fiber component
and such additives as dyes, water repellants, and finishes.
As on the case of paints and finishes, natural environmental factors,
such as sunlight, oxygen, and water vaoor, and air pollutants, such as par-
ticulate matter, sulfur oxides, hydrogen sulfide, nitrogen oxides, and
368
-------
795,839
ozone, can significantly affect the performance and service life of
textiles. The degree and rate of effect depend on many variables, notably
concentrations and number of different environmental factors to which the
fabric is exposed, type of fabric, and types and number of additives.
Although apportionment of textile degradation between natural environmental
factors and pollutants is difficult, the relative effect of the various
pollutants can be gleaned from the existing literature.
839
In a discussion of textile fibers, Yocom and McCaldin reported that
cellulose fibers such as linen, hemp, cotton, and rayon are especially sus-
ceptible to damage by acid aerosols, which attack and weaken the cellulose
780
chain in the glucosidic linkage. According to Waller, sulfuric acid re-
acts with the cellulose fibers to produce a water-soluble product with
little tensile strength. Animal fibers such as wool, fur, and hair are more
resistant to sulfur dioxide and nitrogen dioxide than the synthetic fibers
839
since they already contain compounds of both nitrogen and sulfur.
Although particulate matter obviously soils fabrics, Yocom and
839
McCaldin noted that it is only damaging when the particles are highly
abrasive and the fabric is flexed frequently. Deterioration results mainly
from repeated attempts to clean the fabric. Other investigators have con-
cluded that the more tightly woven the cloth, the more resistant it is to
soiling. Soiling resulting from thermal precipitation is directly related
to the number of degrees below the ambient air temperature to which the sur-
face temperature of the fabric is cooled. Thicker samples of cloth would
collect less dust since their surface temperatures would be higher.
Soiling by particulate matter also results from electrostatic attrac-
tion. Certain fabrics, such as acetate rayon, become electrostatically
369
-------
839 583
charged by friction during their manufacture. Nuessle described labora-
tory tests in which equal positive and negative charges were applied sepa-
rately to a cotton fabric. Although soiling increased with the magnitude
of both charges, it was greater with the positive charge, perhaps because
of the predominance of negatively charged particles in the atmosphere.
Nuessle referred to reports that indicate that two-thirds of all airborne
particulate matter may be negatively charged and to experiments in which
1,000 volts applied to a cotton fabric tripled the attraction of airborne
particles. In these experiments, loose fibers protruding from the surface
of the fabric were soiled the most.
Curtains soil greatly in polluted areas. Hanging at open windows, they
serve as filters, not only for particulate matter but also for acid droplets.
Weakened as a result of such exposure, curtains often split in oarallel
lines along the folds, on which impinged acidic materials reach the inner
839
fiber-.
844
Zeronian et al. investigated the weathering of oolymeric fabrics
(modacrylic, acrylic, nylon, and polyester) by exposing them to sunlight
and polluted air containing 0.2 ppm nitrogen dioxide, 0.2 ppm sulfur di-
oxide, or ozone. Compared with control specimens exposed to sunlight and
unpolluted air, nylon incurred the greatest degree of degradation on
exposure to sulfur dioxide. Breaking load, rupture energy, and breaking
extension were greatly reduced, the relative viscosity and number of amine
groups decreased, and the number of carboxyl end groups increased. In con-
trast to nylon degraded by acid hydrolysis, there was no yield point in the
load extension curve of the nylon degraded by sulfur dioxide. There was some
evidence that nitrogen dioxide affected the prooerties of the acrylic, nylon,
370
-------
and polyester fabrics, and that ozone might affect the properties of acrylic
and nylon fabrics. The modacrylic fabric was not affected by any of the pol-
lutants. The polyester was not affected by either sulfur dioxide or ozone.
Cotton broadcloth, cotton broadcloth with a wash-and-wear finish, poly-
ester, polyester and cotton blend with a permanent-press/soil-release finish,
and a polyester and cotton blend were exposed to ambient air, air containing
nitrogen dioxide, and carbon-filtered clean air (control) for 90 days.
365
Following the exposures, Hosking reported that the cotton with the wash-
and-wear finish had the poorest resistance to abrasion and the polyester and
cotton blend the best. The polyester fabric had the greatest initial abra-
sion resistance, but at the end of the 90-day test period had deteriorated
to a greater extent than either of the polyester blends. Next to the cotton
with the wash-and-wear finish, the polyester also incurred the greatest
percentage of weight loss following exposure to nitrogen dioxide. Nitrogen
dioxide was the most damaging to the fabrics.
Fading of dyed fabrics by both gaseous and oarticulate pollutants has
263
received considerable attention in the literature. Fuiii and Tsuda sub-
stantiated the effect of dye formulation on resistance to fading of fabrics
exposed to nitrogen dioxide, sulfur dioxide, nitric oxide, carbon monoxide,
and particulates. Seven kinds of fabrics with three types of dyes (dis-
persed, direct, and acidic) were tested. Overall, acidic dye was affected
most by the pollutants. The dispersed dye was affected most bv nitrogen
dioxide and particulates; the direct dye, by sulfur dioxide. The investi-
gators concluded that fading caused by sulfur dioxide and particulates was
greater than that caused by nitric oxide, nitrogen dioxide, or carbon
monoxide.
371
-------
262
Fujii and Hirata conducted tests on viscous rayon, acetate, tetron,
and wool fabrics dyed blue. They determined that particulates caused a
greater degree of fading than sulfur dioxide. Other Investigations indi-
cated the synergistic effect of sulfur dioxide, nitrogen dioxide, and carbon
839
monoxide on the fading of dyed fabrics. Exposure of fabrics to filtered
air with 50% RH and 1 ppm sulfur dioxide produced negligible dye fading.
The same result occurred when dilute auto exhaust (111 ppm carbon monoxide,
0.2 ppm nitrogen dioxide) was added. However, irradiated auto exhaust
(88 ppm carbon monoxide, 0.7 ppm nitrogen dioxide) produced substantial dye
fading, and the addition of 1 ppm sulfur dioxide to the irradiated auto
exhaust caused the greatest color change.
630
Ray et al. reported similar findings from tests conducted to deter-
mine the comparative effects of small quantities of nitrogen oxides and
sulfur dioxide on the color and strength of representative rayon fabrics.
The ox des of nitrogen caused by far the greatest color changes; sulfur
dioxide caused little or no fading. \ combination of the two pollutants
caused more fading than sulfur dioxide alone, but decidedly less than the
nitrogen oxides alone. The sulfur dioxide appeared to reduce fading when
used in combination with nitrogen oxides, undoubtedly because of an interaction
between the gases under prevailing conditions. The fadings caused by the
nitrogen oxides were most similar to those enco^jitered during actual use.
661
Salvin reported the results of laboratory tests conducted on 28
fabrics co assess the individual and combined effects of nitrogen oxides,
ozone, and acid or alkali surface conditions on lightfastness. The most
significant changes occurred with direct dyes on cottons. Direct Red 75
and Direct Blue 76 dyes were changed appreciably in shade by nitrogen oxides
372
-------
and, along with Direct Blue 78, suffered aporeciable reduction in color
when the fabric surface was acid. The laboratory ozone tesi 3 resulted in
slight fading, which was more evident in acid fabrics. In general, there
were no significant changes on the dyed nylon and wool fabrics tested.
The investigators concluded that the variations in absorbed acid gases,
nitrogen oxides, and ozone influence results of outdoor exoosure tests.
Such testing is consequently not reproducible in different locations and
seasons. Salvin also has stated that nitrogen oxides in the air cause
reddening of blue curtains and draperies and that ozone can bleach colored
189 63
acetate, cotton, and nylon. Beloin confirms that appreciable fading
of dyed fabrics results from exposure to nitrogen dioxide, sulfur dioxide,
and ozone as well as variations in temperature and humility.
PORCELAIN ENAMELS
Porcelain or vitreous enamels are protective glossy coatings that are
fired on metals. They are comoosed chiefly of quartz, fieldspar, clay,
soda, and borax. Although enameled metals are used orimarily as siding and
roofing, since World War II their use has expanded raoidly. In modern
architectural design, they are used as exterior finishes, especially on
buildings employing curtain-wall construction. Their popularity may be due
to the wide variety of colors available and to the ease of cleaning.
The increased use of porcelain enamels led to a National Bureau of
Standards (NBS) program involving 1-, 3-, 7-, and 15-year outdoor exposure
tests to determine the weatherability of post-war enamels. Exposure condi-
tions were the same for each test. Pertinent results of the 7-year test pro-
gram and some from the 3-year test are discussed below. The 15-year test is
not yet complete.
373
-------
655
Rushmer and Burdick reported that there were seven exposure sites
in the NBS program. The two at Kure Beach, North Carolina, were temperate,
rural, seacoast locations. One site was 24 m from the ocean; the second,
240 m. Washington, D.C. and Pittsburgh, Pennsylvania were temperate, com-
mercial locations; New Orleans, Louisiana, a semitropical, commercial location;
and Dallas, Texas and Los Angeles, California were commercial locations.
Except for Kure Beach, samples were exposed on rooftops at 45 to the
horizontal* and faced south. At Kure Beach samples were exposed at ground
level and faced the ocean at east-southeast. Weather data and air quality
measurements for these sites are given in Table 11-9. Air pollution measure-
ments made during the three-year tests are given in Table 11-10. These data
indicate the content of acid gases in the various atmospheres. Several enamel-
coated metals were exposed at each site.
After seven years, all specimens except those in Pittsburgh and Los
Angelas could be cleaned easily; at Los Angeles a gumlike film had been
deposited on the specimens and at Pittsburgh the panels were covered with
a dirt film that consisted mostly of soot and fly ash. Corrosion of the
base trotal was noted only on 1 specimen at New Orleans, 10 at Kure Beach
(240 m), and 29 at Kure Beach (24 m). In most cases, corrosion occurred
on enamels exhibiting pinhole defects or blisters prior to exposure.
550
*Moore and Potter reported that after the 3-year exposure tests enamels
of poor weathering resistance exposed vertically at Washington, D.C.,
exhibited significantly smaller changes in gloss and color than similar
specimens exposed at 45° to the horizontal. Enamels with good weather
resistance exhibited only minor differences in the degree of attack with
exposure angle.
374
-------
a
PP
<
E-.
13
O
•H
W
O
ft
X
W
0)
p
C
OJ
W
03
OJ
P
•rH
H
O1
3
<
c
03
o)
P
cu
x;
p
it)
0)
OJ --v.
P bO
T) o) a
OJ H
T3 3 »
C 0 h
OJ -H 0)
ft P P
CO fn p
3 n3 03
w ft e
a
H O
03 -H
3 P
C 03
C P
03 -H
ft
rH -H
03 O
P OJ'XJ
0 P C
E- ft-rH
f~H r-l
o) x:
C "
C QJ
03 C
•H
H XI
03 CO
P C
Of*
,-J
E-i 10
"0
a
H 0
03
3 '
C OJ
C ^
ID 3
1 1
OJ 03
bO k
rt) QJ
r-l ft
OJ E
> OJ
< P
rH co o en un en
CO O OD 00 Cn CD
H ,H rH
00 O ^rr CO O rH
LTJ OO O') CO J^- H
cn CD CM j- H j-
co c-- o j- H co
co in CM t- en CM
CM CM CM CM CM CO
to cn o H cn cn
in co o H oo co
• •••••
LT> CO O H CO CO
rH H H CM H H
H
03
3
C
C
03
QJ
bO
03
f-i
p>
•H
P
03
OJ
JL(
0\°
n
>,
P
•H
•X3
•H
3
x:
ft
0
CO
CO
CD
CM
CP
l>
CD
CM
CO
d-
CD
0)
p
•H
to
V
p
3
to
o
ft
X
W
<»
x;
o
03
0)
PQ
0)
^
3
M
C
o
p
bfl
C
•rH
XI
M
03
S:
X!
W)
JH
3
43
W
P
P
•rH
Oi
CO
C
0!
0)
H
^
O
S
QJ
S
W
t!
0)
Q
0)
bO
C
W
O
IT)
I/}
tD
•
CD
to
CD
« — 1
"
_ V
O
•H
T3
fn
^J
CQ
-d
C
03
£_l
OJ
j|
m
^j
OH
E
O
£•<
tM
^
03
MH
H
OJ
T)
C
03
r\
C
o
•H
P
03
O
rj
T3
W
IN
^d
p
H
03
QJ
0
P
C
Q)
E
P
03
ft
QJ
Q
QJ
i-C
p
4-1
O
^
f^
O
^
p
CD
bO
f^
•H
rH
e
(D
to
^
•H
<^
rQ
the atmosphere with 50 ml of
pproximately biweekly interva.
6 IT)
0
£-t P
(^H o3
QJ T3
P 03
•P E
(T)
6 W
p
QJ C
P QJ
o) E
H Q)
3 fc
0 3
•H CO
P 03
03 E
ft
MH
ip O
O
to
P QJ
O bO
3 m
•H QJ
rH >
03 03
Ovp Q)
00 f-j
03
C
03 CO
QJ
M 3
C H
•H fT)
X >
3
H
QJ H
fc e
>, 0
XI 00
T3 O
0) P
03 bO
ft C
OJ -H
fn P
ft 3
W -H
C T3
O
•H Tj
P C
3 fl
H
O k
CO QJ
P
in 03
0 2
U_i
4—1
TJ
QJ H
f-( < 1
3 -H
to p
03 W
Q) -H
2S 'd
o
•
to
'd
C_j
o
o
(P
05
3
rt3
QJ
^J
CQ
£j
OJ
P
0)
OJ
X!
P
E
O
W
CO
bfl
03
f-i
QJ
j>
<5^
'ts
QJ
H
(t)
H
•rH
03
OJ
QJ
CD
03
P
03
•d
o
C
XI
O
•H
XI
J5
fa
o
UH
ft
x:
o
fd
CQ
d)
JH
3
C
fl
x:
p
k
QJ
X!
P
03
t\
«
O
s
A
CO
03
QJ
P
P
03
QJ
ft
03
O
c
O
"P
03
P
03
Q
CU
375
-------
TABLE 11-10
Averages of Air Pollution Measurements Made
During 1958 by the National Air Sampling Network of the
U,
City
Los Angeles
Pittsburgh
Washington, B.C.
New Orleans
Dallas
,S. Department of Health, Education
Total
suspended -,
particulates
214
167
111
92
113
, and Welfare0
Composition of particulates
Organic
matter
30.4
13.0
12.9
11.4
10.2
SOU
16.1
15.2
12.4
9.5
7.1
NO 3
9.5
2.7
3.1
2.2
2.3
Other
158.0
136.1
82.6
68.9
93.4
6.0
6.4
6.7
7.0
7.1
a
From Moore and Potter, 1962. 55°
-3 of air. Values are averages of measurements taken at approximately
biweekly intervals.
'Measured for solutions prepared by refluxing an 8% aliquot of particulates
with 50 ml of distilled water, then diluting to 80 ml. Values are averages
of measurements made at approximately biweekly intervals.
376
-------
Figures 11-3 and 11-4 show the effect of exposure lenqth on gloss and
color retention. Neither white porcelain enamels, which normally retain
their initial color after even a severe surface attack, nor screening oaste
enamels, which incur abnormally large color changes, were considered in
computations of average color changes. The results from Pittsburgh and New
Orleans were averaged together because there was no significant difference
in the degree of attack on the enamels at these locations.
All the enamels lost gloss most rapidly during the first three years
of exposure; during the remainder of the period, the retained gloss remained
nearly constant on all enamels except those at both Kure Beach locations
where it continued to decrease. The slight increase in gloss at Los Angeles
after the second year was attributed to incomplete removal of the gumlike
film during cleaning. This resulted in a doubly reflecting surface which
increased gloss readings. Color change was greatest during the first two
years, after which it became nearly constant, although different, at all
seven sites.
Concentration of acidic air contaminants correlate well with site
severity. At the most severe sites the particulates had more acidic pH
values, while at the mild sites the oH was nearly neutral. The noncor-
relation of enamels exposed at Pittsburgh and Los Angeles might be partially
explained by the protective action of the adherent films on the specimens
exposed at these locations. A good correlation was also observed between
relative humidity and changes in gloss and color. Rushmer and Burdick
suggested that this correlation could be attributed to the moisture from
high humidity which leaches salts from the deposited oarticulate matter
producing acidic solutions that vary according to the contaminants.
377
-------
100
90
80
70
60
50
40
30
Los Angeles
"A
TO Dallas
Pittsburgh,
Orleans
AWashington
oKure Beach
(240m)
t Kure Beach
(24m)
2 3456789
Exposure Time, Yrs
FIGURE 11-3. Change in average percentage of gloss retained with exposure
time. (Points are averaged for all enamels except screening
pastes.) From Rushmer and Burdick, 1966.655
378
-------
100
98
96
94
92
90
.Dallas
Los Angeles
o Pittsburgi, New
., Orleans
A
Washington
7 Rure Beach
(240m)
re Beach
(24m)
0
34567
Exposure Time, Yrs
8 9 10
FIGURE 11-4.
Change in average color retention with exposure time.
(Points are averages for all nonwhite enamels except
screening pastes.) From Rushmer and Burdick, 1966.65S
379
-------
The glossy, acid-resistant enamels on steel had the best color retention;
the screening paste type, the poorest. Some enamels on steel retained their
color well even when exposed to the salt air at Kure Beach. The best of the
enamels on aluminum incurred little color change at Dallas, Los Angeles, and
Pittsburgh, but moderate chances in Washington and fairly significant changes
at the two Kure Beach sites and in New Orleans. The severe effects in New
Orleans were unexpected. Although the cause was not determined, the authors
did not believe that it could be attributed to salt particles carried from
either the Gulf of Mexico or Lake Pontchartrain since the site was on a four-
story building several kilometers from the nearest salt water. The attack
at Kure Beach was tentatively ascribed to chlorides. In most cases, the re-
tained gloss correlated with the color change.
Similar types of enamels exhibited a direct correlation between acid
resistance, as measured by either the acid soot test or the boiling acid
solubi-ity test, and weather resistance, as measured by changes in gloss
and color. The correlation with the citric acid soot test, however, was
evident only when averages were considered. The boiling acid solubility
test was more reliable in predicting the color retention of the regular
enamels on steel than was the citric acid soot test.
ASPHALTS
Asphalt is a dark brown to jet-black material, which can be either solid
or semisolid. The predomina :ing constituents are either natural bitumens
or bitumens made from residuals of petroleum refining. Asohalt and its
product^ sre used in road construction and as roofing, wateroroofing pacer,
electrical insulation, an adhesive, and as an additive to certain paints.
380
-------
Asphalt is affected by natural constituents of the atmosphere, par-
ticularly sunlight and humidity. In time it becomes brittle and cracks.
General property chanqes that occur include: loss of color and gloss;
deterioration in uniformity; increase in density, viscosity, hardness,
hardening point, softening point, flash point, and others; and decreases
in spreading rate, shear strength, adhesive oower, and volatility.
311
Hamada et al. have provided the only information concerning the
effects of air pollutants on asphalt. They conducted tests to determine
the resistance of asphalts to outdoor weathering and to acids.
In their teats to determine the resistance of asphalts to acids the
investigators used 19 blown, 8 straight, and 1 compound asphalt produced
from the same crude oil; 1 blown, 4 straight, and 1 compound asphalt pro-
duced from other crude oils; and 7 compounds of Nos. 18-23 asphalts with
rubber or other inorganic fillers added. Acids used in the tests were
sulfuric acid (80%, 50%, and 12%), hydrochloric acid (10%), and ammonium
sulfate (15%). Steel rods approximately 170 mm long were immersed in
asphalt. These rods were then dipped to a depth of 150 mm in the acid
solutions contained in test tubes, then left standing at room temperature.
Changes were observed at different intervals.
In tests of 28 specimens exposed to 80% sulfuric acid, there was no
311
corrosion, but cracks, bulges, and air bubbles formed. Hamada et al.
attributed this to penetration through oinholes in the asphalt by the acid
solution and subsequent reaction with the steel to form sulfate which caused
expansion and consequent cracking and exfoliation.
Compounds of No. 18 and No. 23 asphalt were also exposed to 80% sul-
311
furic acid. All specimens cracked and flaked. This was attributed to
381
-------
the effect of additives which, by decreasing the impermeability of the
asphalt, allowed the acid solution to penetrate deeply. Hamada et al. pro-
vided the test results for asphalts produced from other crude oils immersed
in the acids of all concentrations. In each case, there was some degree
of transformation. In some cases, change of color in the solution occurred.
The investigators concluded that sulfuric acid, hydrochloric acid, and
ammonium sulfate cause some transformation, exfoliation, or crumbling in
asphalts. Generally speaking, blown asphalts appear to have good acid
resistance, but the coating quality does not appear to be good. Straight
asphalts, on the other hand, have a good quality of coating, but, compared
with blown asphalt, their acid resistance is not so good. The authors sug-
gest that the application of a regular asphalt coating to blown asphalt
would provide an adequate degree of both acid resistance and coating quality.
COST
Cost data often include damage to materials other than those used in
buildings (e.g., tires and clothing) and to agricultural goods and human
health. In most cases, it is therefore impossible to isolate costs of
damage to building materials. Accordingly, such data are not included in
this report.
660
Table 11-11, comoiled by Salmon, presents the results of perhaps the
most comprehensive effort undertaken to estimate the economic losses due
to the effects of air Pollution on materials. The values of interaction
are estimates of the difference between the rate of material deterioration
in polluced atmospheres and in unpolluted atmospheres. This is expressed
in dollars lost per year. The in-place values of exposed materials, which
include an estimated labor factor, are based on the product of annual
382
-------
TABLE 11-11
Summary and Rankings of Damage Factors
a
In-place value
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
,
36
37
38
39
40
Material
Paint
Zinc
Cement and concrete materials
Nickel
Cotton (fiber)
Tin
Synthetic rubber
Aluminum
Copper
Wool (fiber)
Natural rubber
Carbon steel
Nylon (fiber)
Cellulose ester (fiber)
Building brick
Urea and melamine (plastic)
Paper
Leather
Phenolics (plastic)
Wood
Building stone
Polyvinyl chloride (plastic)
Brass and bronze
Polyesters (plastic)
Rayon (fiber)
Magnesium
Polyethylene (plastic)
Acrylics (plastic)
Alloy steel
Polystyrene (plastic)
Acrylics (fiber)
Acetate (fiber)
Polyesters (fiber)
Polypropylene (plastic)
Acrylonitrile-butadiene-
styrene (plastic)
Epoxies (plastic)
Cellulosics (plastic)
Bituminous materials
Gray iron
tylon (plastic)
Value of
interaction,
$/yr
0.50 x 10"1
0.29 x 10"1
0.10 x 10~2
0.25 x 10"1
0.40 x HT1
0.26 x 10-1
0.10 x 10°
0.21 x 10~2
0.20 x 10-2
0.40 x 10"1
0.10 x 10°
0.50 x 10~2
0.40 x 10~ l
0.40 x 10"1
0.10 x 10~2
0.10 x 10-1
0.30 x 10~?
0.40 x 10~?
O.K) x 10"1
0.10 x 10~2
0.23 x 10~2
0.10 x 10"1
0.42 x 10~3
0.10 x 10"1
0.40 x 10"1
0.20 x 10~2
0.10 x 10"1
0.10 x 10"1
0.40 x 10~2
0.10 x 10"1
0.40 x 10"1
0.40 x 10"1
0.40 x ID"1
0.10 x 10"1
0.10 x 10"1
0.10 x 10"1
0.10 x 10"1
0.10 x 10~3
0.50 x 10"3
0.10 x ID"1
of materials
exposed,
$ billion
23.90
26.83
316.21
10.40
3.80
5.53
14.00
^4.08
54.88
2.48
0.54
10.76
0.95
0.82
24.15
2.27
7.53
5.15
1.98
17.61
7.65
1.54
33.12
1.37
0.33
6.50
1.17
1.00
2.18
0.85
0.19
0.19
0.16
0.64
0.61
0.47
0.40
22.45
3.86
0.17
Loss,
$ million
1,195.0
778.0
316.0
260.0
152.0
1U4.0
140.0
114.0
110.0
99.2
54.0
53.8
38.0
32.8
24.2
22.7
22.6
20.6
19.8
17.6
17.6
15.4
13.9
13.7
13.2
13.0
11.7
10.0
8.7
8.5
7.6
7.6
6.4
6.4
6.1
4.7
4.0
2.2
1.9
1.7
383
-------
TABLE 11-11: Continued
Value of
In-place value
cf materials
Rank
41
42
43
44
45
46
47
48
49
50
51
52
53
Material
Polyolefins (fiber)
Stainless steel
Clay pipe
Acetate (plastic)
Malleable iron
Chromium
Silver
Gold
Flat glass
Lead
Molybdenum
Refractory ceramics
Carbon and graphite
interaction,
$/yr
0.40 x 10'1
0.85 x I0~k
0.10 x 10-2
0.10 x 10"1
0.16 x 10~2
0.75 x ID'3
0.12 x 10~2
0.10 x 10"3
0.10 x 10"^
0.11 x 10~3
0.25 x 10~3
0.10 x 10~4
0.10 x 10~5
exposed,
$ billion
0.04
18.90
1.44
0.12
0.58
1.08
0.57
5.80
28.59
2.18
0.51
1.93
0.30
Loss,
$ million
1.6
1.5
1.4
1.2
0.9
0.8
0.7
0.6
0.3
0.2
0.1
0.02
0.00
TOTAL
3,800.00
From Salmon, 197O.660
384
-------
production volume in dollars, times a weighted average economic material life
based on usage, times a weiqhted average factor for the percentage of the
material that is exposed to air pollution. Economic losses or damage factors
reported in the table represent the product of the interaction values and
in-place values. When assessing these economic losses, it is important to
remember that the values were derived simoly to rank materials in order of
their relative importance in air-pollution-induced damage. These values
should not be interpreted as actual economic loss, although Barrett and
50
Waddell suggest that they appear reasonable. The reported losses represent
only actual damaged materials or impaired serviceability, but not losses
associated with surface soiling.
In 1968, 3arrett and Waddell estimated the total cost to the nation
of air pollution damage to be $16.132 billion. They arrived at this figure
after reviewing both published and unpublished estimates. They attributed
$9.952 billion to damage on residential prooerties and materials and the
balance, $6.180 billion, to damage to health and vegetation. The investi-
gators considered various pollutants both individually and synergistically.
Their estimates were allocated in direct prooortion to emission levels.
(See Table 11-12.)
The liability for the costs in Table 11-12 are assigned in Table 11-13
to sources of the total particulates and sulfur oxides emitted nationally.
For example, 24%, or $1.248 billion, of the $5.2 billion in residential
property losses is assigned to industrial orocesses because such sources
account for 24% of the nation's sulfur oxide and oarticulate emissions.
Table 11-14 presents estimates by the Office of Air Programs, Environmental
Protection Agency, of 1968 national emissions of principal pollutants by
major source.
385
-------
TABLE 11-12
National Ccstr. of Pollution Damage, ty Pollutants,
1968, $ billion"
Loss category
Residential property Materials Totals
SOX 2.808 2.202 5.010
Particulates 2.392 0.631 3.083
Oxidants —• 1.127 1.127
NOX ~- 0.732 0.732
Totals 5.200 4.752 9.952
Fr:m Barrett and Waddell, 1973.50
386
-------
TABLE 11-13
Costs of Pollution Damage in United States
in 1968, By Source and Effect, $ billion^
Effects
Stationary source
fuel combustion
Transportation
Industrial
processes
Soild waste
Miscellaneous
Totals
Residential property Materials
2.802 1.853
0.156 1.093
1.248 0.808
0.104 0.143
0.884 0.855
5.200 4.752
Totals
4.655
1.249
2.056
0.247
1.739
9.952
From Barrett and Waddell, 1973.
50
387
-------
TABLE 11-14
Estimates of Nationwide Emissions in 1968,
Source category
Transportation
Fuel combustion in stationary
sources
Industrial processes
Solid waste disposal
Miscellaneous
Total
109 }
CO
63.8
1.9
9.7
7.8
16.9
100.1
cg/yra
Particulates
1.2
8.9
7.5
1.1
9.6
28.3
SOX
0.8
24.4
7.3
0.1
0.6
33.2
HC
16.5
0.7
4.6
1.6
8.5
32.0
NOX
8.1
10.0
0.2
0.6
1.7
20.6
a
From Barrett and Waddell, 1973.50
388
-------
The Battelle Memorial Institute estimated that the extra service cost
resulting from air pollution corrosion of metals, particularly steel and
232
zinc, totalled approximately $1.45 billion in 1970. This value is based
on the nine major classifications of external metal istructures for which
annual losses have been estimated. (See Table 11-15.)
232
Fink et al. projected total national cost of corrosion by air pol-
lution from 1970 to 1980. This cost will be influenced significantly by
variations in the total metal surface exposed to attack and by changes in
the corrosivity of the atmosphere which, in turn, will be influenced by
such factors as increased population and energy production. Table 11-16
lists these estimated changes along with the estimated changes in levels
of sulfur oxide pollution in four projected regulatory situations.
Although the authors recognize that humidity changes affect corrosivity,
the literature does not indicate that atmospheric corrosivity has been
altered significantly in any recent 10-year oeriod by changes in moisture
and related meteorologic factors. Significant changes in corrosion rates
have usually been accompanied by changes in pollution levels often in
association with a higher rate of consumption of sulfur-bearing fuels.
Based on the estimate that 80% of the 1970 steel systems would still
be in use in 1980, the authors projected an increase in maintenance costs
even with improved technology in corrosion control and increased use of
labor-saving techniques. However, these costs would probably be offset by
the lower maintenance costs of newer structures which have been designed
•^t
to reduce maintenance expense. Allowing for some increase in both steelwork
and population and assuming no change in pollution, they estimated that the
per capita annual corrosion cost would be essentially the same in 1980 as
389
-------
TABLE 11-15
Summation of Annual Extra Losses from Corrosion
Damage by Air Pollution to External Metal
Structures in 1970*2
Steel system or structure
Steel storage tanks
Highway and rail bridges
Power transformers
Street lighting fixtures
Outdoor metal work
Pole-line hardware
Chain link fencing
Galvanized wire and rope
Transmission towers
Extra costs
Maintenance
Maintenance
Maintenance
Maintenance
Maintenance
Replacement
Maintenance and
replacement
Replacement
Maintenance
Annual loss, $ thousands
$ 46,310
30,400
7,450
11,910
914,015
161,000
165,800
111,800
1,480
$1,450,165
From Fink et al., 1971.232
390
-------
TABLE 11-16
Economic and Pollution Factors used to Assess Probable
a
Cost of Corrosion Damage by Air Pollution, 1970 to 1980
Change from
1970-1980, %
Population Increase
For nation 11
For metropolitan districts 12
Energy Production
Increase in power plant capacity
Space heating plant capacity 15
Sulfur Oxide Pollution
No regulation 55
With regulation and improved technology <10
With strictly enforced regulation and major -40
technological breakthroughs
Complete enforcement of current legislation -60
External Structures
Old steel structures (decrease) -20
Replacement steel 20
New steel 10
New other materials 20
Total change 30
Total increase in steel 10
From Fink et al., 1972.232
391
-------
it was in 1970. The per caoita extra annual maintenance costs were established,
then converted to a national basis.
The Stanford study also disclosed that more money is soent combatinq
the effects of sulfur dioxide and hydrogen sulfide on low-voltaqe electrical
contacts than is spent combatinq all other air pollution effects on all
electrical devices. Organic gases form "frictional" polymers on sliding
contacts. Particulate pollutants present special oroblems because they are
excellent absorbers of water and corrosive aqents. The effects of organic
gases and particulates are less imoortant, however, than the effects of
sulfur dioxide and hydrogen sulfide.
Salvin conservatively estimates the total annual cost of damage to tex-
189
tiles by air pollution to be $2 billion per year. He considered dis-
integration of natural and manmade fibers before the end of a normal wsar
cycle—specifically $300 to $400 million for cotton and nylon; extra
laundering and dry cleaning due to soiling by oily dust particles—$800
million; fading of colors of nylon caroet, acetate fabrics, cottons, and
permanent press fabrics—$350 million; and discoloration of white fabrics
due to the effect of hydrogen sulfide and various acids on the fibers and
50
finishes—aoproximatelv $540 to $550 million. Barrett and Waddell reported
that Salvin is planning a comprehensive investigation to determine more
accurately the annual estimated cost of air Pollution damage to dyed textiles.
The estimate will include not only the cost resulting from damage but also
the cost of the steps taken to mitigate the damage such as substitution of
more costly materials, additional Protection, modified production techniques,
implementation of better quality control techniques, research and development,
and environmental testing.
39?.
-------
CONCLUSION
The literature dealing with the effects of Dollutants on building
materials is easily misleading and should be interpreted with caution.
Although the literature generally implies a detrimental effect, however
small, it contains no guidelines by which one can assess impact on intended
function and normal service life of the affected materials. This applies
even to documentation of catastrophic damage, particularly in the case of
historical buildings and irreplaceable art sculptures.
Particular care must be taken when assessing estimates of costs result-
ing from damage or soiling of materials by pollutants. In many instances
all costs associated with services or materials are attributed to air pol-
lutants although there is inadequate justification for including even por-
tions of such costs. These estimates are often used by others as a base
for additional, supposedly more inclusive estimates, thereby compounding
the problem. Further, except for tests involving extended, natural outdoor
exposures, principally of metals, most investigators use pollutant concen-
trations significantly in excess of those found in even the most polluted
atmospheres. Results from accelerated weathering tests such as these are
difficult, if not impossible, to correlate with actual natural weathering
conditions.
To place effects of air pollutants on building materials in true per-
spective, several additional factors must be considered. Notably, sulfur
oxides and the liquid acids formed from them are the most detrimental pol-
lutants because of their chemical attack on a material. Although partic-
ulate matter such as soot and fly ash can also result in chemical attack of
materials, particularly in concert with the sulfur oxides and their acids,
393
-------
its primary effect on materials is surface dirtyinq. In many cases this
can be mitiqated by proper cleaninq procedures. However, atmospheric con-
centrations of both sulfur oxides and particulates are presently being
reduced with introduction and use of low-sulfur fuels and emission control
equipment. Based on the realistic assumption that newer fuels and control
technoloqies will emerqe, nollutant concentrations should continue to de-
crease. In addition, new paints and materials more resistant to specific
pollutants or whose surfaces are more readily cleanable are beinq developed.
Another factor to be considered is the synerqistic effect pollutants
have on materials. Considerably more testinq with particulates of known
composition actinq in concert with all other Pollutants is essential if the
true cause of the detrimental effect is to he understood adequately. In
olanninq such studies, it should be recoqnized that results from accelerated
tests involvinq hiqher than normal concentrations of only one pollutant and
normal concentrations of others are not likely to correlate well with results
from actual outdoor exposures.
The structure itself and the constraints Placed upon its desiqner also
must be taken into account. The initial desiqn parameters (e.q., function,
intended service life, initial cost, and aesthetic value) ~iqnificantly
influence choice of materials used in construction and, thus, the struc-
ture's performance under either polluted or nonpolluted conditions. For
example, in buildinq warehouses, initial cost is of paramount concern.
Decisions may be made durinq the planning staqe to use materials more sus-
ceptible to pollutants than others—if the intended service life can be
still assured—simply because aesthetic qualities are of little concern.
394
-------
The fact that today's buildings generally are not considered to be as
durable as those built in the past, and that future buildings will probably
not be more durable, reflects the constraints placed on designers who try
to meet society's demand for low cost and fast construction. Consumers
simply can no longer afford buildings designed and constructed with expensive
safety factors and excessive materials. To remain competitive during the
past 20 years or longer, designers have employed newly developed materials
simply because they were less expensive or because they facilitated the con-
struction process regardless of their susceptibility to air pollutants.
Designers have only recently begun to select materials for different building
elements because of their resistance to particular air oollutants. Similarly,
only recently have design criteria for mitigating the effects of air pol-
lutants begun to emerge.
Proper selection of materials, use of emerging design criteria, and
application of proper maintenance procedures should significantly reduce
the effect of air oollutants on building materials. Consequently, the
effect of pollutants on construction materials used today cannot be assessed
simply in terms of the past oerformance.
395
-------
CHAPTER 12
SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS
SUMMARY AND CONCLUSIONS
During the past five years there has been a revolution in our knowledge
and our understanding of atmospheric aerosols as a result of both routine
monitoring and special aerosol characterization studies. These studies have
emphasized the importance of both size distribution and chemical composition
in understanding the sources, effects, and sinks of atmospheric aerosol.
Aerosols; Characteristics, Behavior, and Measurement
Recent studies have elucidated several important features of the aerosol
size distribution. This distribution consists of three separate modes. The
first mode, named the nuclei or Aitken mode, includes oarticles that range in
diameter from approximately 0.01 to 0.1 ym. This mode is formed by a dynamic
equilibrium between new nuclei formed in the atmosphere plus nuclei from com-
bustion and coagulation into the next larger mode, the accumulation mode.
The first mode numerically accounts for most of the oar tides in the atmo-
sphere except for very well-aged background aerosols most of which are found
in the accumulation mode. Most of the submicrometer mass tends to accumulate
in this second mode because of the twin mechanisms of coagulation and hetero-
geneous nucleation (condensation of one material on another). The particles
in this accumulation mode range in diameter from about 0.1 to 2.0 ym and com-
er ise most of the total surface area of the atmospheric aerosol. The nuclei
and accumulation modes are collectively referred to as "fine Particles".
397
-------
Little mass is transferred from the accumulation mode into the coarse
particle mode. This third mode consists of particles >2 vm dia and mass that,
on a long-term average, is about equal to that in the accumulation mode. The
almost complete independence of the origin, behavior, and removal processes
of fine and coarse particles result in different effects on health, visibility,
and meteorology. There are variations over several orders of magnitude in the
amounts of fine and coarse particles in clean and polluted atmospheres. These
factors suggest that fine and coarse particles should be controlled separately.
Both differential and integral measurements of atmospheric aerosol should
respect not only these size dependent differences. It is also imoortant to
recognize the pitfalls that are generally associated with sample collection
and subsequent laboratory analysis vs i.n situ sampling. The trend in aerosol
monitoring is towards the reolacement of collection methods for both physical
and chemical analyses with in situ, automatic methods.
v
Aerosol Cycles
When studying the life histories of aerosol particles, one must distinguish
coarse ( 21.2.0 ym dia) from fine ( f.2.0 ym dia) oarticles. Coarse oarticles
arise primarily from mechanical processes, both naturally (windblown dust, sea
spray) and anthrooogenically (fly ash, comminutive orocesses). Fine oarticles
are formed in the nuclei mode by condensation of hot, low vapor pressure ma-
terials, such as metallic vaoor, and of cold, low vaoor pressure materials, such
as partially oxygenated aromatics.
Aerosol transformation orocesses are also distinctly different for coarse
and fine particles. Coarse oarticles are not significantly transformed in the
atmosphere, whereas fine oarticles are. These fine oarticle transformation
processes include both gas-particle and particle-particle interactions.
398
-------
Gas-particle interactions usually involve gas-liquid reactions because fine
particles have sufficient water associated with them under most atmospheric
conditions to present a liquid surface to the gas phase. Particle-particle
interactions (e.g., coagulation) are governed by Brownian diffusion. Since
aerosol size distributions are rarely monodisperse, coagulation usually occurs
between unlike size particles. Coagulation of particles from the nuclei mode
to the accumulation mode is imoortant in the atmosohere, whereas coagulation
from the accumulation mode into the coarse mode is not.
Most coarse particles are emitted close to the earth's surface where they
are removed by gravitational settling and washout before being transported very
far. Fine particles, esoecially in the accumulation mode, are not strongly af-
fected by these processes and are transported much longer distances ( ~ 103 km).
Urban aerosol is usually dominated by human activity. The size distri-
bution and composition of the average qlobal aerosol is less certain but there
are indications that the well-aged aerosol throuqhout the bulk of the atmo-
sphere is dominated by a single mode, the accumulation mode.
Measurement of the Size Distribution and Concentration
1 There is an inevitable trade-off between intensity and duration of measure-
ment programs. Results are either continuous aerosol measurements that provide
only limited information on size distribution and chemical comoosition or de-
t
tailed aerosol data that were collected over only a short time.
Background measurements over the oceans indicate that the aerosol is
dominated by coarse particle sea salts mechanicallv produced at the sea surface
and by aged coarse and fine particles above the mixing layer that have been
transported from land. Background aerosol over land varies with location.
Over remote snow and ice surfaces, aerosol concentrations are as low as or
399
-------
lower than over the oceans. Background aerosol over dry, desert regions is
dominated by coarse particles, usually windblown dust. In areas of average
precipitation and vegetative cover, the coarse particle concentrations are
on the average much lower than over dry areas, and there is a small but oer-
sistent background concentration of accumulation mode aerosol.
In urban areas coarse particle concentrations are highly variable. Al-
though urban accumulation mode aerosol concentratioas sometimes exceed several
hundred micrograms per cubic meter, concentrations average between 10 and 30
yg/m3. Significant concentrations by mass of nuclei mode aerosols are found
only near highways. Accumulation mode aerosols oroduced in urban areas can
be transported several hundred kilometers. Increasing evidence indicates that
accumulation mode aerosols, a large fraction of which is sulfate, may be trans-
ported several thousand kilometers.
Chemical and Trend Data
The chemical comoosition and molecular character of atmospheric aerosol
as a function of oarticle size should be extensively examined, ^t moderate or
low relative humidities, toxicitv, water solubility, hygroscooicity, deli-
quescence, refractive index, oarticle shape, and ohvsical state deoend on
molecular nature rather than on the oresence of a single atomic or ionic
species, such as sulfate. However, in the case of a highly hydrated droplet
aerosol, composed of a large number of anions and cations, the ionic comoo-
sition clearly dominates the svstem behavior. The definitive molecular comoo-
sition measurements as a function of oarticle size, time, and location have
yet to be made.
Recent data suggest that a chemically well-mixed aerosol, one that has a
similar comDOsition at all sizes and in all three modes, is orobably rare.
400
-------
Rather, certain classes of substances appear to dominate the coarse particle
node while other classes dominate the fine mode. The fine particles consist
mainly of sulfates from sulfur dioxide oxidation, nitrates from NO reactions,
X
ammonium ions from ammonia reactions, condensed organic matter (partially
oxygenated), and primary emitted substances such as lead, arsenic, antimony,
and carbon. The coarse particles consist largely of mechanically produced
substances such as soil or rock dust (e.g., silicon, calcium, iron, and aluminum),
road and tire dust, fly ash, and sea salt. The frequent particle-particle
interactions within the fine mode suggest a homogeneously mixed submicrometer
aerosol. However, the less frequent interactions of the coarse mode suggest
discrete coarse particles consisting of relatively pure substances.
Depending on their chemistry, fine particles can grow at high humidity to
1.5 to 2.0 times their initial dry diameter in a fraction of a second. This
growth can influence aerosol effects such as deposition in the respiratory
tract, visibility in the atmosphere, and condensation processes in clouds.
With the exception of sea salt, coarse particles usually do not exhibit this
growth. Fine particles, however, almost always do, resulting in a dramatic
increase in the amount of material (usually water) in the fine particle mode.
Although total suspended particulate matter mass concentrations in se-
lected urban areas throughout the United States have decreased from 1960 to
1971, nonurban values remained the same. The lack of size resolution and chem-
ical composition precludes a detailed understanding of these trends.
Effects on Atmospheric Processes
Aerosols can influence atmospheric processes bv interacting with both in-
coming solar radiation and cloud processes. The extinction of solar radiation
by atmospheric aerosol can be generally classified into scattering and absorption
401
-------
components. The scattering component is theoretically a comolex function of
the fine particle mass concentration, the total mass concentration, the aero-
sol size distribution, the relative humidity, the wavelength of liqht, and
the particle's refractive index and shape. However, a stronq correlation has
been found in the atmosphere between fine particle mass concentration and scat-
tering coefficient. Increases in relative humidity are usually accompanied by
increases in particle light scattering because aerosol growth resulting from
water vapor condensation mainly occurs in the fine particle mode, which dom-
inates light scattering.
Besides degradation of visibility, aerosol extinction also decreases the
intensity of direct sunlight reaching the ground. Mthough most scattered
light reaches the surface along with the direct beam, some is absorbed and some
is scattered back into space by the aerosol. The turbid air mass centered over
the eastern United States has twice the extinction coefficient of the air over
the rural western United States. However, disagreement exists on whether there
will be a decrease or an increase in temperature as a result of changes in aero-
sol concentration, both regionally or globally. More measurements are needed
on the absorptive component as a function of particle size, the hemi-
spheric backscatter coefficient, and their soatial dependencies. The role of
relative humidity on these oarameters should also be examined. The relatively
few measurements of absorption indicate that the fraction of extinction due ho
absorption can be as high as 30%. Oirect measurements of this absorption com-
ponent are preferable because size dependence of the aerosol chemical compo-
sition, and thus the refractive index, must be considered when estimating the
absorption component from chemical data.
402
-------
Aerosol interaction with clouds occurs because the transformation of water
vapor, at approximately 1% suoersaturation, into water droolets and ice crystals
is a nucleation phenomenon requirinq the presence of specific size nuclei.
These "weather active" nuclei, which comprise 1% of the total aerosol number
concentration, influence cloud droplet and ice crystal concentrations. These,
in turn, influence cloud dynamics and the probability and amount of rainfall.
The precipitation probability is a complex function of the concentration,
size distribution, and molecular form of these active nuclei. In urban areas,
the effect is generally an increase in precipitation downwind because of the
emission of these active nuclei.
Fogs are also requlated by atmospheric aerosol. Due to condensation and
coalescence, fog stability is increased by the formation of small (1 to 3 ym
dia), unactivated droos, and decreased by large (15 ym dia), activated ones.
The factors that determine activation in both foqs and clouds deserve further
study.
Aerosol can also affect the chemistry of precipitation through both below-
cloud and in-cloud scavenging. Fine particles are scavenged mainly by in-
cloud process, whereas coarse particles are scavenged by both in-cloud and
below-cloud processes. This chemical modification of the rainwater is compli-
cated by the fact that such gases as sulfur dioxide can also contribute to the
same species in raindrop solutions as the aerosol, e.g., sulfate. The relative
-,
importance of rainout and washout mechanisms should be studied further.
Effects of Inhaled Particles on Man and Animals
Particle deposition efficiencies and patterns within the respiratory
tract are highly variable. They are determined by dimensions and configura-
tions of the air oath in the exposed individual, the pattern and depth of
403
-------
the respirations, and the characteristics of the airborne particles. The
size of bronchial airways varies considerably amonq normal nonsmoking adults
and more so among smokers withojt clinical disease symotoms. However, the
greatest variations occur amonq individuals with clinical evidence of
bronchitis.
The distribution of particle deposition sites depends qreatly on the
aerodynamic diameters of the particles. In normal, healthy humans, inhaled
nonhygroscopic particles that impact in the head and ciliated airways of the
lungs are concentrated onto a small fraction of the surface. Cigarette
smoking and bronchitis Produce a proximal shift in the deposition pattern.
For nonhygroscopic aerosols with aerodynamic diameters ^3 ym, an increasing
fraction remains airborne as particle size decreases and is exhaled. Total
respiratory tract deposition in normal subjects reaches a minimum of ^ 10% to
20% for particles between ^0.2 and 1.0 ym, and increases for particles ^ 0.2
ym. Th- major factor determining the probability of deposition of the smaller
particles is their transfer from tidal to reserve air. They may remain airborne
within the reserve and residual air for a number of breaths before they are
actually deposited.
The dominant deposition mechanisms are impaction (for particles ^1.5 ym),
sedimentation (^ 0.5 to 1.5 ym), and diffusion (£ 0.5 ym). Both sedimentation
and diffusion produce relatively uniform surface deposits in small bronchioles,
alevolar ducts, and alveolar sacs. Hygroscopic particles grow rapidly within
the warm, moist airways, becoming dilute aqueous droplets ^ 3 times larger
than the inhaled particles.
For particles that are soluble in respiratory tract fluid, systemic uptake
may be relatively complete for all deposition patterns, and local toxic and/or
404
-------
irritant effects may result. On the other hand, slowly soluble particles
depositing in the head beyond the anterior nares, or on ciliated tracheobron-
chial airways, are transported by the surface flow of respiratory tract fluid
to the glottis, then swallowed within 24 hr.
Mucociliary transoort rates are highly variable, both along the ciliated
airways in a given individual and between individuals, depending on the thick-
ness and character of the secretions and the number and beat rate of the cilia.
Effective fluid movement depends upon the couoling of the ciliary motion with-
in the sol layer with the overlyinq mucus layer. A moderate increase in secre-
tions, such as those produced by a few cigarettes, or therapeutic dossiers of
some adrenergic drugs, can accelerate mucus transport. Larger dosages or long-
term exposures, which can cause an incrnase in the number and/or size of the
secretory cells and glands, can oroduce mucous layers which are too thick to be
effectively propelled by the cilia, and clearance stasis and oeriodic retro-
grade flow can result.
Mucocilary transport rates decrease distally within the bronchial tree.
Measurements of normal mean tracheal transport rates in man and animals have
mostly fallen within the range of 2.5 to 25.0 mm/min. The total duration of
bronchial clearance in healthy humans varies from ^ 2.5 to 20.0 hr. The changes
in clearance rates produced by drugs, cigarette smoke, and various environmental
pollutants can greatly increase or decrease these rates. However, the imoor-
tance of alterations of mucociliary transport in the oathogenesis of chronic
lung disease is not yet clear.
The relatively small particles deoosited in nonciliated airways have large
surface-to-volume ratios. Therefore, significant clearance by dissolution can
occur for materials generally considered insoluble. They can also be cleared
405
-------
as free particles either by oassive transport alonq surface liquids or, after
phaqocytosis, by transport within alveolar macrophaqes. If the particles
penetrate the epithelium, either bare or within macrophaqes, they can be
sequestered within cells or enter the lymphatic circulation in which they are
transported to pleural, hilar, and more distant lymph nodes. In most cases
the quantitative aspects of these clearance pathways vary with the composition
of the particles and are poorly described. Nontoxic insoluble particles are
cleared from the alveolar reqion in a series of temporal Phases. The earliest,
lasting several weeks, appears to involve the clearance of ohaqocytized par-
ticles via the bronchial tree. The terminal phases appear to be related to
solubility at interstitial sites. The effects of infectious diseases, ciqa-
rette smokinq, and various environmental factors on kinetics of alveolar
clearance are not known.
The mechanisms and dynamics of particle deposition and clearance have been
reasonably well determined, but many quantitative aspects and relative contri-
butions of competing and/or interactinq processes have not been established.
There is very little information on the relationships amonq normal physiologic
clearance rates, reserve capacity to cope with environmental exposures, and
secretion or transport rates that compensate for environmental exposures in the
development and progression of temporary or oermanent dysfunction. Bronchitis
produces marked chanqes in regional particle deposition and sputum production.
However, there are very few data on the Quantitative aspects of regional deoo-
sition in well characterized bronchitics, or on sputum composition, transport,
or volume in healthy subjects. For alveolar deposition, the clearance pathways
and rateo dapend on the physical and chemical characteristics of the particles.
There are few well established rate constants adequate for estimatinq toxic
dose levels.
406
-------
The major uncertainties about the effective toxic doses resulting from
inhalation exposures can and should be resolved throuqh further in vivo inves-
tigations on humans and laboratory animals. Studies of humans would also helo
to identify susceptible segments of the peculation that would benefit from per-
sonal protective measures during exoosures to high concentrations. Most inves-
tigations can be performed with available techniques. Consequently, an in-
tensified research effort could oroduce useful data within a few years after
its initiation.
Effects of Sulfur Dioxide and Aerosols, Alone and Combined, on Lung Function
The structural, biochemical, functional, and genetic effects of air pol-
lutants may be assessed by experiments on in vitro oreoarations, animals, and,
in some instances, human volunteers. Apart from the inherent biologic dif-
ferences among species, there are well recognized difficulties in extrapolating
results from animals to human copulations. Only simple approximations of
ambient pollution are possible in the laboratory, and the simulation of human
cardiorespiratory disease in animals for the ourpose of determining the re-
sponse of vulnerable members of the peculation is difficult to achieve. Eth-
ical and legal restrictioas oreclude many studies on human subjects, esoeciallv
those involving carcinogens and chronic exposure. In Chapter 8 the effects
of inhaling sulfur dioxide or aerosols alone are considered before Proceeding
to the consequences of gas-aerosol interactions on the mechanical and venti-
latory functions of the lung.
During quiet breathing, sulfur dioxide is removed almost entirely in the
upper airways. The mouth is less efficient than the nose as a scrubber of
soluble gases, especially at the high flow rates occurrinq during exercise.
In healthy subjects inhalation of 2.6 mq/m3 of sulfur dioxide for 1 to 3 hr at
407
-------
rest increases nasal and pulmonary flow resistance and impairs forced expiratory
flow rate. Inhalation of 13.0 mq/m3 of sulfur dioxide for several hours causes
greater effects on these functions and also reduces nasal mucus flow rate.
These concentrations of sulfur dioxide are significantly in excess of ambient
concentrations.
There is considerable variability in resoonse within and among animal
species, and among individuals. It is not known why the effect of sulfur di-
oxide may vary in an individual from one exposure to the next. Adaptation,
measured as a remission of bronchoconstriction, begins in man after an approxi-
mately 10-min exposure to sulfur dioxide, and sooner in cats and dogs. In
guinea pigs flow resistance may remain elevated or may increase for several
hours. The response in man and cats is reflex in origin via the vaqal nerve.
It can be abolished by atrooine. The possibility that more remote mechanisms
may operate either through nasobronchial reflexes or the excretion of sulfur
dioxide into the lung from the bloodstream has been suggested. Sulfur dioxide
has !-*?en administered to guinea pigs in concentrations up to 13.0 mq/m3 and in
concentrations UP to 3.4 mg/m3 to monkeys for 1 to 1.5 vrs without apparent
structural or functional consequences.
Chemically inert and chemically active aerosols can change lung mechanics.
Aerosols tend to deposit .at or near bifurcations, where epithelial nerve endings
are concentrated. Nerve endings in central airways are considered especially
responsive to mechanical stimuli; peripheral receotors appear to be more re-
sponsive to chemical stimuli. The functional response varies with species, age,
level of consciousness, type of anesthesia, activity, nutrition, and state of
health; -cha mass concentration, aerodynamic size, molecular composition, oH,
and solubility of the aerosol are additional important factors.
408
-------
Evidence suggests that many potentially toxic chemicals that are oresent
in airborne particles, such as lead, cadmium, antimony, arsenic, nickel, zinc,
and benzola]pyrene, as well as sulfate and nitrate ions reside chiefly in
the accumulation mode. Studies in guinea pigs have shown that sulfuric acid
and other molecular forms of sulfate may increase air flow resistance; but
the extent to which this response is due to reflex bronchoconstriction, release
of smooth muscle constrictors, excessive secretion of mucus, or submucosal
edema is not known. Pulmonary compliance may also be reduced. Such mechanical
defects increase the work of breathing and, insofar as they may be unevenlv
distributed throughout the lung, affect the distribution of inspired air.
Functional and structural defects are reportedly greater with <1 ym dia par-
ticles than with larger oar tides, Presumably reflecting differences in the
sites of deposition based on size and, oossibly, differences in the surface
area to volume ratio of the particles.
Sulfuric acid is more effective than zinc sulfate in causing an increase
in flow resistance at equivalent particle sizes and concentration. Over limited
ranges, the size of the droplet appears to be more critical than mass concen-
tration in determining the response. Following inhalation, hygroscooic aerosols
may undergo changes in aerodynamic and chemical properties that have implications
for the biologic response. In one study of healthy subjects functional changes
resulting from 0.5 to 0.7 mg/m3 of sulfuric scid have been reoorted; most
studies have resorted to higher concentrations to elicit responses.
Animals exposed 18 months to fly ash and sulfuric acid have shown little
structural or functional changes to concentrations of 0.16 and 0.46 mg/m3.
In monkeys, higher concentrations of sulfuric acid have caused maldistribution
of ventilation, increased breathing rates, and histologic changes, such as
409
-------
epithelial hyperolasia and thickening of bronchial walls. The carbon monoxide
Q
diffusing capacity has been ieduced by administration of 0.9 mg/tn of sulfuric
acid (90% > 0.5 ym) for 620 clays.
Synergism between gas-aorosol mixtures has been demonstrated in guinea
pigs. Several mechanisms are oossible: adsorption of the gas onto the surface
of the particle (dry), absorption of the gas into the particle (droolet), or
chemical reaction of the gas within the particle with the formation of a more
toxic compound. It is more likely that the interaction between the gas and
particle occurs in ambient air before inhalation rather than following inhala-
tion. An important exception is the possible reaction between inhaled ammonia
and inhaled acid sulfate aerosols, which may mitigate the effects of the
inhaled acid sulfate aerosols by themselves. Relative humidity may be an
important determinant of the reaction. Synergism is reported to occur more
.rapidly in the presence of certain catalytic salts. Reports in Japan of
syne^gism between sulfur dioxide or nitrogen dioxide and sodium chloride
aerosols in man have not been confirmed in this country.
There is a growing conviction that sulfur dioxide alone is not especially
hazardous to health. Aerosols resulting from the oxidation of sulfur dioxide
in the atmosphere may be more hazardous. If this supposition is borne out
experimentally, it may become necessary to control the emission of sulfur di-
oxide to keeo these oxidative products at acceptable levels. There is virtually
no information about the experimental effects of nitrate aerosols.
Epidemiology
Severe episodes of pollution first drew attention to the serious effects
of pollution on health. Tha lethal effect of smog was Particularly evident in
Europe where fogs occurred mainly in cold weather. Deaths due to pollution
410
-------
were therefore fewer in New York City than in London. Differentiation of the
effect of cold from that of pollution proved difficult. Persons with chronic
respiratory and cardiovascular diseases appeared to be predominantly affected
though the very young and the aged may also have been vulnerable. Support for
an increased susceptibility to fog among those with chronic disease came from
a 10-year follow-up of the population of Donora, Pennsylvania.
The interest stimulated by these exceptional episodes of pollution
initiated a great deal of research on the effects of air pollution on health.
During the 1950's and early 1960's a variety of studies were designed mainly
to determine if the more usual pollutant concentrations in most industrial
cities adversely affected human health. Temporal and spatial variations in
mortality, morbidity, respiratory disease symptom prevalence, lung function
levels, and sickness were related to various measures of air pollution in dif-
ferent populations and in different segments of the population. Studies were
conducted in more or less representative communities, occupational groups,
infants, young children, and patients with respiratory and other diseases.
During the late 1960's, stimulated by the determination to formulate air
quality standards and preoare preliminary air quality criteria documents,
interest focused on quantifying pollution in relation to its effects on health.
Exposure/effects relationships or dose/response curves relating various indi-
cators of pollution to different indicators of health impairment were urgently
sought. Much of the evidence on which the Federal Air Quality Standards were
based came from studies that had beeen conducted in Europe, mainly Britain,
whose relevance to the American scene was debatable. At this time, information
on exposure/effects relationships in the United States were urgently needed.
A major thrust to provide this evidence came from the Environmental Protection
Agency's Community Health and Environmental Surveillance System (CHESS) studies.
411
-------
Perhaps inevitably, in an attemot to provide a great deal of information in a
short time, these studies, though well designed, had a number of deficiencies
in their execution that have made their interoretation uncertain. Reolication
is essential if the margin of uncertainty is to be reduced. Durinq the oast
5 to 10 years there has also been an increasing awareness that more aooropriate
measurements of environmental oollutants must be made if firmer conclusions on
permissible concentrations of oollutants are to be reached.
Tentatively, however, the exposure concentrations likely to cause mortality
or morbidity or reduce lung function are summarized in Table 9-3, while con-
clusions that have been reached from the CHESS studies, expressed in terms of
best case, worst case, and best judgment estimates, are indicated in Tables 9-4
and 9-5.
Effects on Vegetation
There has been little research on the effects of settleable particulate
matter on vegetation. Most exoeriments have dealt with given dusts near
soecific stationary sources rather than the conglomerate mixture normally
encountered in the atmosphere.
The significance of dusts as nhytotoxicants is not yet entirely clear,
but there is considerable evidence that certain fractions of cement-kiln dusts
adversely affect olants when such dusts are naturally deoosited on moist leaf
surfaces. Dry cement-kiln dusts appear to have little deleterious effect, but
when deposited on olants in the field over a long oeriod in the presence of
dew, the dust solidifies into a hard adherent crust that can damage leaf tissue
and inhibit growth. Oust deoosited in excess of 1.0 g/m2/day solidifies into
a hard crust which results in damage to leaf tissue and inhibits growth. The
calcium hydroxide in alkaline solutions accomoanying crust formation was found
412
-------
within parenchyma tissues of affected leaves. At levels in excess of 1.0
g/m2/day, incrustations, premature needle droo, and shorteninq of each suc-
ceeding year's flush of growth have been observed on branches of fir trees.
A marked reduction in the growth of poolar trees 2.2 km from a cement plant
was observed after cement production was more than doubled.
Although crusts were not formed, moderate damage has been observed on the
leaves of bean olants dusted in the laboratory at the rate of about 4.7 g/m2/
day for two days, then followed by exposure to naturally occurring dew. In
similar treatments the calcium oxide and calcium hydroxide in the dust-dew
solution caused breakdown of the cuticle and release of the fatty acids that
are among the cuticular constituents. Thus, while the mechanism by which injury
occurs is not entirely understood, screening of light, oartial clogging of
stomata, and direct injury to the plant tissue by the chemical reaction of the
dust on the leaf surface have been demonstrated.
The harmful effect of cement-kiln dusts on vegetation is not fully sub-
stantiated and has been questioned by some investigators. This is not
surprising in view of the limited research to date and because not all studies
have been conducted under identical conditions or with dusts of the same com-
position. The problem is further complicated by the effects of cement-kiln
dust deposits on the soil. .Some investigators report no harmful effect at
deposit rates from 1.5 to 7.5 q/m2/day; others report that deposits from 1.0
to 48.0 g/m2/day cause shifts in the soil alkalinity that may favor one croo
but harm another.
The great disparity between results of experiments and the conclusions
drawn by many investigators exists because the pollutant called "cement-kiln
dust" is actually a heterogeneous substance whose constituents and amounts vary
413
-------
with time and location. No general conclusions can be drawn about the effects
of cement-kiln dust until each dust source is classified and studied separately.
Fluorides in particulate form are less damaging to vegetation than gaseous
fluorides. Although fluoride may be absorbed from deoositions of soluble fluo-
ride on leaf surfaces, the amount absorbed is small compared to that entering
the plant in gaseous form. The fluoride from particulates apparently has great
difficulty penetrating the leaf tissue.
The research evidence suggests that there are few, if any, effects on
vegetation attributable to fluoride oarticulate concentrations below 2 yg/m3.
Concentrations of this magnitude can be found near sources of fluoride oarti-
culates, but rarely in urban atmospheres. Fluorides absorbed by or deposited
on plants may be detrimental to animal health. Fluorosis in animals has re-
sulted from ingestion of vegetation covered with oarticulates containing fluo-
rides.
; Although lead concentrations and accumulations bv plants in the vicinity
of highways have been high, there are no known reports of injury to vegetation.
Soot may clog leaf stomata and may also oroduce necrotic spotting if it
carries with it a soluble toxicant, such as one with excess acidity. Particles
from a phurnacite factory aggregating around leaf stomata resulted in a lower
maximal diffusion resistance than that measured on clean leaves. Oeoosits of
magnesium oxide on soils reduce olant growth, while deposits of iron oxide
(Fe-Pg) have no harmful effects and may be beneficial.
Emissions of sulfur and nitrogen oxides into the atmosphere may be oxidized
and hydrolized to form sulfuric and nitric acid at varying rates, deoending
on atmospheric conditions. Such acids may ultimately settle to the ground
as mist or precipitation. The impact of acid aerosols and acid rain on
414
-------
veqetation include direct offsets in the form of loaf necrosis, irreqular devel-
opment of leaf tissue, and Inching of nutrients from leaves and the indirect
effects of excessive soil acidification creatinq an unfavorable environment for
plant growth.
Effects on Materials
Studies of effects of oarticulate matter on materials has been broadened
to include other pollutants because under natural conditions exposures consist
of a combination of constituents. Airborne oarticles can act as a nuclei of
absorbed or adsorbed qases such as sulfur dioxide, hydroqen sulfide, and ni-
troqen dioxide. Additionally, these qases can form aerosols in the atmosphere.
The normal corrosion of metals can be accelerated by atmospheric pollut-
ants. A notable example is the stress corrosion crackinq and ultimate failure
of nickel-brass wire sorinq relays and other electrical equipment in the Los
Angeles area caused by nitrate accumulation from the atmosphere. Chapter 11
summarizes the corrosion rates for various metals under different exposure
conditions.
Masonry and concrete are affected by oarticulates, sulfuric acid, sulfu-
rous acid, and several other acidic gases. Deleterious effects include simple
discoloration or staininq, erosion or corrosion, and leachinq. Environ-
mental factors that influence the effects of pollutants (positively or nega-
tively) include relative humidity, rain, and wind.
Paints and finishes can be deqraded by particulates, hvdroqen sulfide,
sulfur oxides, ammonia, and ozone. The effects are generally manifested as:
loss of qloss, scratch resistance, adhesion and strength; discoloration; in-
creased drying time; and unattractive, dirty appearance. Significant and
415
-------
prolonged attack can result in exoosure and deterioration of the substrate
being protected.
Plastics and elastomers may be affected by pollution. Among the types of
deterioration found are discoloration, cracking, and loss of tensile strength.
Textile fibers can be damaged by atmospheric pollutants. Cellulose fibers
such as linen, hemp, cotton, and rayon are especially susceptible to damaae by
acid aerosols. Particulate matter soils fabrics but does not damage them unless
the particles are highly abrasive and the fabric is flexed frequently. Deteri-
oration is caused mainly by reoeated attempts to clean the fabric.
Studies of the exposure of porcelain enamels on test panels designed for
exterior use at several locations from 1 to 7 years indicated that the loss of
gloss correlated well with acidity of the oarticulate matter. In general the
color retention was good.
Test results indicated that the oresence of sulfuric acid, hydrochloric
acid, and ammonium sulfate caused asphalts to exhibit some transformation,
exfoliation, or crumbling. The application of a regular asohalt coating to
blown asphalt would provide an adequate degree of acid resistance and coatinq
quality.
Attempts to place a monetary value on the damage to buildings and materials
by air pollution have produced estimates that range as high as $9.9 billion/vr.
One study attributes $3 billion of this damage to oarticulate matter.
RECOMMENDATIONS
Measurement of Aerosols
It is important to understand the composition of airborne particles as
they exist in their suspended state and as a function of size to understand
their effects and their sources. This comoosition is difficult to measure.
416
-------
Current and past methods all have inherent limitations and ambiquities which
must be considered in interoretinq data.
The chemical composition of particles as a function of size should be
measured. Ttie fine oarticle -nodes are of oarticular interest due to their
relation to respirable particles, their role in determininq the optical
oroperties of the atmosohere, their composition, which includes toxic substances,
and the fact that they accumulate the products of all secondary aerosol forma-
tion in the atmosphere.
When possible, the molecular nature of the oarticulate matter should he
determined, in view of its role in deterrnininq effects.
Difficulties will certainly be incurred in future attempts to implement
such broad recommendations. The necessary technology is only partly developed,
and the cost of monitorinq molecular comoosition as a function of oarticl? size
in many locations could be excessive, until the techniques are better estab-
lished, it will be difficult to make comorehensive recommendations. As a
minimum, it is recommended that the fine oarticle and coarse particle fractions
be samoled and analyzed for composition separately. However, it is nossible
to suqgest a strateqv that has proved effective as a basis for understanding
the basic physical/chemical nature of oarticles in such studies as the Aerosol
Characterization Experiment (ACHEX) and the Reqional Air Pollution Study
(RAPS). Soecificallv, in these studies, routine monitorinq efforts were suo-
olemented bv intensive, short-term studies by teams of scientists. The data
acquired from such combined efforts have been of much more use than monitorinq
alone.
417
-------
Health Effects
Characterization of the health imoact of ambient aerosols should be based
on sampling techniques that permit the aerodynamic classification of the oar-
tides .
Aerodynamic particle classifications should either Demit characteriza-
tion of the overall size-mass distribution of the total aerosol and/or its PO-
tentially toxic constituents, or the separation into two size fractions based
on the sampler acceptance criteria of the American Conference of Governmental
Industrial Hygienists (ACGIH).
Future in vivo inhalation studies should determine:
• The effects of age, sex, respiratory disease, cigarette smoking, and
exposure to other airborne contaminants on regional particle depo-
sition, bronchial clearance, and alveolar clearance.
• The effects of oarticle shape and hygroscopicity on regional particle
deposition.
• Quantitation of the Pathways and rates of alveolar clearance of
inert insoluble particles, toxic insoluble particles such as quartz,
asbestos, transuranic oxides, etc., and lipid and water-soluble
particles.
• The effects of cigarette smoke, sulfur oxides, nitrogen oxides, oxi-
dants, and other common pollutants on the mucociliary clearance of
inert particles on mucus production and on morphologic changes in
all types.
Agencies sponsoring research on the biologic effects of gases and aerosols
should insist that the investigators are competent in both the physical and
biologic disciplines needed to produce useful as well as fundamental data.
418
-------
More emphasis should be qiven to studies of realistic sizes and concentra-
tions of aerosols shown by atmospheric chemists to be: present in urban atmo-
spheres. It is important to assess the effect of chronic as well as acute
exposure to these aerosols.
Investigators should be encouraged to combine oollutants with other forms
of stress to which our peculation is exoosed, including variations in temper-
ature, relative humidity, nutritional state, exercise, and coexistent pul-
monary and circulatory disease.
Epidemiology
More precision in measurement of airborne particles and in the assessment
of dosage is needed in epidemiologic studies. The time is long past when esti-
mates of particulate pollution can be based on total suspended matter as mea-
sured by a high-volume sampler. Particles should be characterized physically
and chemically•into at least the fine and coarse fractions. Particular atten-
tion should be given to their surface absorptive characteristics, hygroscopicitv,
and size distribution. Not only should oar tides in the respiratory size range
be differentiated from the total suspended particulate matter, but if the sig-
nificance to health of submicrometer particles is to be adeouately assessed,
separation of the aerosol at 1 pm radius is desirable. While the emphasis
should probably be on Particles within the respiratory size range, larger par-
ticles should not be ignored. Pertinent chemical characteristics include PH,
oxidation state, and reactive attributes.
Although particular interest is now focused on sulfuric acid and acid
sulfates, improved methods for measuring these substances are badly needed.
Experiments with animals suggest that there are considerable differences in the
irritancy of different acid sulfates. \t present, such differentiation in
419
-------
epidemiologic studies is nonexistent. Tn addition to the sulfates some atten-
tion should also be oaid to oarticulate nitrates.
The problems involved in assessing dosage, even over short periods, from
current knowledge of pollution concentrations at different Places are consid-
erable. Accurate assessments over a number of years, or life, are especially
difficult. Various assumptions can be adopted in deriving estimates of daily
exposure based on pollution concentrations both at home and in the work olace
and the proportion of the 24 hr spent in each. These estimates should be
validated by concurrent measures using personal monitors. Biologic estimation
of exposure, such as measurement of chemicals in hair samples, while useful for
certain particles appear to offer little for the particles discussed in this
document.
'•tore information is needed on the health effects of exposure to low con-
centrations of pollution and on the changes in these effects that may follow
changes in exposure. There has been a surprising lack of interest in any
guantification of the benefits of reduction in pollution as shown by reduced
mortality or morbidity. Studies of this kind are, of course, liable to be con-
founded by other changes that may have occurred over the same period. But
changes in Pollution have varied from place to place and reduction in parti-
culate pollution has sometimes affected some urban areas earlier than others.
Consequently, it should be possible to make appropriate allowance for these
other changes. In no city has reduction in oarticulate Pollution been more
dramatic than in London. The reduction there preceeded similar reductions in
most British cities. Yet, comparative analyses of mortality or morbidity have
seldom been made. Since national morbidity records are available in Britain,
the effect of pollution reduction on illness as well as on death could be
420
-------
studied there. The differential effects of pollution from oarticulates rather
than sulfur dioxide can be evaluated in Britain more accurately than elsewhere.
Day-to-day correlations yf collation concentrations with mortality should
continue, provided better estimates of pollution over the whole metropolitan
area under study can be ensured. More attention also needs to be given to aqe,
sex, and cause of excess deaths in the peculations uader study. Studies of the
kind being conducted in New York City would be useful in ^'-.her U.S. cities and
elsewhere, especially in London, Tokyo, and Osaka. In London, where day-to-day
correlations were first shown to be useful, updating of the earlier studies
would be particularly interesting.
Mortality, although an extremely valuable index of the effect of pollution
on health, should not be overemphasized, it is after all a terminal event in a
long disease process much of which has usually been determined by other factors.
Pollution needs to be related to the initiation and exacerbation of illness and
to any functional changes, which can be readily measured. "Morbidity records,
as has been indicated, are sometimes available and suitable for this purpose.
But more often the degree of precision now needed will only be possible by
special surveys. These surveys should include not onlv the general community
but also groups that are especially vulnerable to the effects of oollution, such
as the elderly and patients with chronic respiratory disease. In the cer.eral
community representative samples should be selected on tne GG.£_S ^: z^:.^-".~:,~
tions and types of pollutant exposures and on the expectation of change. Lor.qi-
tudinal observations should be made on respiratory symptoms, concentrations,
and changes in lung function and mortality in relation to concentrations of and
changes in pollution. Of Particular value are studies of children. In con-
trast to adults the effects of pollution in children can be more readily separ-
ated from the effects of occupational exposures and smoking.
421
-------
Surveillance of oatients with cardioresoiratorv disease is the most
practicable way of relatinq short-ter'm concentrations of oollution Iro d^tari-
oration of health. The measurement of lunq function is a most valuable, objec-
tive addition to such surveillance. It is possible to obtain repeated daily
lunq function tests in small qrouos of oatients and occuoational qrouos. Hailv
measurements of this kind, combined with homa measurements of oollution and,
oossibly, oersonal monitorinq, miqht provide much qreater orecision at the lower
end of the dose/resoonse curves. In these special surveys obtaininq informa-
tion on the interaction of oar tides with other pollutants, as well as with
meteoroloqic, climatic, or bioloqic factors, should be considered. Conversely,
situations should be souqht in which there may be dissociation between oollu-
tants. In these cases it miqht be possible to assess the effects of relativelv
cure pollutants.
Effects on Vegetation
The direct effects of oarticulates on veqetation affect a much small3r
seqment of the total population than io =>ff^cts on climat? and visihilitv, on
man and animals, and on naterial^. TVie demand for research into effects on
veqetation has not been qreat and may not increase siqnificantlv ?x.-ent in v^iv
localized situations with soecific settleable dusts. With the or*"'. ?nt cf^^o;-
tition for research dollars, olant bioloqists mav find it difficult to mount
any larqe-scale Projects just for the sake of basic research. Research miqht
well be predicated upon local industry/aqriculture-related problems that demand
an answer. Of course, there may be exceptions. Two that come to mind are:
(1) situations in which Particles or some of their chemical constituents are
known to be harmful to man or animal" an! ^oul^l v^t into food chains via olant-
foodstuff or foraae; and (2) the relativelv recent and expanding intere3t
422
-------
in the possible effects of acid rain in those reqions where sulfur compounds
are important air pollutants.
It. is difficult to make recommendations for research in this area that
have as broad an application as those concerninq the effects of narticulates
on man. With these reservations in mind, recommendations are made as
follows:
Now that scanning electron microscopv is qenerallv available, surveys
of a number of plant soecies could be made in areas where settleable particles
are a problem to determine the prevalence of the cloqqinq of functional stomata.
These data should be related to particle deposit rates.
Similarly, the effect of the oarticles on the cuticle of uooer leaf surfaces
could be examined by the same scanninq electron microqraph (SEM) technioues.
Leaf examination should be timed to encompass pertinent weather factors such
as alternate wettinq and dryinq of leaf surfaces. Whether particulate deposits
tend to form crusts should also be noted.
If particles are to be applied to leaves in laboratory experiments, a
special effort should be made to collect particle samoles from the atmosohere
near the source in an attempt to preserve particle-size inteqrity and chemical
composition. Special equipment woull be needed to collect sufficiently larqe
samples in a relatively short time. This approach would be particularly im-
portant with chemically complex material such as cement-kiln dusts but less
so with more inert materials such as iron oxides.
In lonq-term studies, experiments could be conducted to elucidate further
the real importance of particles in preventinq essential liqht enerqv from
reachinq leaf surfaces. Such experiments may best be conducted in the laboratorv
where deoosit rates can be monitored and adequate control Plants maintained.
423
-------
Field experiments miqht be developed if appropriate oarticle-free leaves could
be maintained without interferinq with normal liqht.
While particles containinq fluorine and lead aooear to have little direct
effect on plants, we should remain alert to the oossibility of some comoounds
of these elements qettinq into tha food chain via veqetation.
3ecause of the new and exoandinq interest in acid rains, and because of
the reqional nature of their effects, continue:) research on the effects on
vegetation should be encouraqed. /Jhere preoared acid mists are bainq applied
directly to olant leaves, qreat care should be taken to ensure that the mist
is chemically comoarable, and oerhaos even identical, to the acil rain that
is being studied.
Most concern for the effects of participates on olants is related to the
direct effect of the oarticle settling on olant leaves. Such oacticles also
fall on soils in which the olants are qrowinq. This oossible indirect effect,
whethet harmful or beneficial, should not be ignored. The exoeriments require
careful olanninq and might require several years to orodnce results of statis-
tical significance.
424
-------
REFERENCES
426
-------
REFERENCES
1. Abe, H., Y. Ishii, end H. Kato. Evaluation of atmospheric factors by
analyses of corrosion products and surface deposits on copper
plates. Rail. Tech. Res. Inst. 12(3):170-174, 1971.
2. Acheson, E. D., R. H. Cowdell, and E. Rang. Adenocarcinoma of
the nasal cavity and sinuses in England and Wales. Biit. J.
Ind. Med. 29:21-30, 1972.
3. Adams, A. A Study of Exposed Reinforced Concrete Facings. Division of
Building Research Technical Translation 993. (Translated by D. A.
Sinclair from Ann. de 1'Inst. Techniq. du Batiment et des Travaux
Publics (159-160):377-388, 1961) Ottawa: National Research
Council of Canada, 1961.
4. Ailor, W. H., Jr. Aluminum corrosion at urban and industrial locations,
J. Structural Div. Proc. Amer. Soc. Civil Eng. 95:2141-2160, 1969.
5. Aitken, J. Collected Scientific Papers of John Aitken, L.L.D. ,
F.R.S. Edited by C. G. Knott. London: Cambridge University
Press, 1923. 591 pp.
6. Alarie, Y., W. M. Busey, A. A. Krumm, and C. E. Ulrich.
Long-term continuous exposure to sulfuric acid mist in
cynomolgus monkeys and guinea pigs. Arch. Environ. Health
27:16-24, 1973.
427
-------
7. Alarie, Y., C. E. Ulrich, W. M. Busey, A. \. Krumm, and
H. N. MacFarland. Long-term continn its exposure to sulfur
dioxide in cynomolgus monkeys. Arch. Environ. Health 24:
115-128, 1972.
8. Alarie, Y., C. E. Ulrich, W. M. Busey, H. E. Swann, Jr., and
H. N. MacFarland. Long-term continuous exposure of guinea
pigs to sulfur dioxide. Arch. Environ. Health 21:769-777, 1970.
9. Alarie, Y., I. Wakisaka, and S. Oka. Sensory irritation by sulfite
aerosols. Environ. Physiol. Biochem. 3:182-184, 1973.
10. Albert, R. E., D. Alessandro, M. Lippmann, and J. Berger. Long-term
smoking in the donkey: Effect on tracheobronchial particle
clearance. Arch. Environ. Health 22:12-19, 1971.
11. Albert, R. E., and L. C. Arnett. Clearance of radioactive dust from
the lung. Arch. Ind. Health 12:99-106, 1955.
12. Albert, R. E., J. Berger, K. Sanborn, and M. Lippmann. Effects of
cigarette smoke components on bronchial clearance in the donkey.
Arch. Environ. Health 29:96-101, 1974.
13. Albert, R. E., M. Lippmann, and W. Briscoe. The characteristics
of bronchial clearance in humans and the effects of cigarette
smoking. Arch. Environ. Health 18:738-755, 1969.
14. Albert, R. E., M. Lippmann, H. T. Peterson, Jr., J. Berger,
K. Sanborn, and D. Bohning. Bronchial deposition and
clearance of aerosols. Arch. Intern. Med. 131:115-127, 1973.
428
-------
15. Albert, R. E., H. T. Peterson, Jr., D. E. Bohninp, nnd M. Lippmann.
Short-term effects of cigarette smoking on bronchial clearance
in humans. Arch. Environ. Health 30:361-367, 1975.
16. Allison, D. J., T. P. Clay, J. M. B. Hughes, H. A. Jones, and
A. Shevis. Effects of nasal stimulation on total respiratory
resistance in the rabbit. J. Physxol. 239:23P-24P, 1974, (Abstr.)
17. Altshuler, B., E. D. Palmes, and N. Nelson. Regional aerosol
deposition in the human respiratory tract, pp. 323-335.
In C. N. Davies, Ed. Inhaled Particles and Vapours II.
Proceedings of an International Symposium organized by the
British Occupational Hygiene Society, Cambridge, 28 September-
1 October 1965. Oxford: Pergamon Press, 1967.
18. Altshuler, B., L. Yarmus, E. D. Palmes, and N. Nelson. Aerosol
deposition in the human respiratory tract. I. Experimental
procedures and total deposition. A.M.A. Arch. Ind. Health
15:293-303, 1957.
19. Altshuller, A. P. Atmospheric sulfur dioxide and sulfate.
Distribution of concentration at urban and nonurban sites in
United States. Environ. Sci. Technol. 7:709-712, 1973.
20. Altshuller, A. P, Characteristics of the chemical composition
of the fine particulate fraction in the atmosphere. May
1976. (Unpublished paper)
21. Altshuller, A. P., and J. J. Bufalini. Photochemical aspects
of air pollution: A review. Environ. Sci. Technol. 5:39-64, 1971,
429
-------
22. Altshuller, A. P., D. K. Klosterman. P. W. Leach, I. T Hindawi,
and J. E. Sigsby, Jr. Product:- and biological "ff"cts froir
irradiation of nitrogen oxides with hydrocarbon^. ot aldehydes
under dynamic conditions. Air Water Pollut. Int. J. 10:81-98,
1966.
23. Amdur, M. 0. The physiological response of guinea pif,: to
atmospheric pollutants. Int. J. Air Pollut. 1:170-183,
1959.
24. Amdur, M. 0. The effect of aerosols on the response to irritant
/
gases, pp. 281-292. In C. N. Davles, Ed. Inhaled Particles
and Vapours. Proceedings of an International Symposium
organized by the British Occupational Hygiene Society, Oxford,
29 March-1 April 1960. Oxford: Pergamon Press, 1961.
25. Amdur, M. 0. Toxicologic appraisal of particulate matter, oxides
of sulfur, and sulfuric acid. J. Air Pollut. Control Assoc.
19:638-644, 1969.
26. Amdur, M. 0. Animal studies, pp. 175-205. In Assembly of Life
Sciences-National Academy of Sciences-National Research
Council. Proceedings of the Conference on Health Effects of
Air Pollutants, Washington, D.C., October 3-5, 1973.
Washington, D.C.: U.S. Government Printing Office, 1973.
27. Amdur, M. 0. The long road from Donora. 1974 Cunnings Memorial
Lecture. Amer. Ind. Hyg. Assoc. J. 35:589-597, 1974.
430
-------
28. Amdur, M. 0., and M. Corn. The irritant potency of zinc ammonium
sulfate of different particle sizes. Amer. Ind. Hyg. Assoc. J,
24:326-333, 1963.
29. Amdur, M. 0., and J. Mead. A method for studying the mechanical
properties of the lungs of unanesthetized animals:
Application to the study of respiratory irritants, pp. 1.50-
159. In Proceedings of the Third National Air Pollution
Symposium, Pasadena, California, April 18-20, 1955.
30. Amdur, M. 0. , W. W. Melvin, and P. Drinker. Effects of
inhalation of sulphur dioxide by man. Lancet 2:758-759, 1953.
31. Amdur, M. 0., L. Silverman, and P. Drinker. Inhalation of sulfuric
acid mist by human subjects. A.M.A. Arch. Ind. Hyg. Occup.
Med. 6:305-313, 1952.
32. Amdur, M. 0., and D. Underhill. The effect of various aerosols on
the responses of guinea pigs to sulfur dioxide. Arch. Environ.
Health 16:460-468, 1968.
33. Andersen, I. Relationships between outdoor and indoor air pollution.
Atmos. Environ. 6:275-278, 1972. (Technical note)
34. Andersen, Ib. Mucociliary Function in Trachea Exposed to
Ionized and Non-ionized Mr. Arhus, Denmark: Akaderaisk
Boghandel, 1971. 178 pp.
431
-------
35. Andersen, Ib., G. R. Lun^.j vis t, P. L. Jensen, and D. F. Proctor.
Human response to controlled levels of sulfur dioxide.
Arch. Environ. Health 28:31-39, 1974.
36. Anderson, D. 0. The effects of air contamination on health:
A review. Part II. Canad. Med. Assoc. J. 97:585-593, 1967.
37. Anderson, D. 0., B. G. Ferris, Jr., and R. Zickmantel. The
Chilliwack respiratory survey, 1963: Part III. The prevalence
of respiratory disease in a rural Canadian town. Can. Med.
Assoc. J. 92:1007-1016, 1965.
38. Anderson, P. J. The effect of dust from cement mills on the
setting of fruit. Plant World 17:57-68, 1914.
39. Angel, J. H., C. M. Fletcher, I. D. Hill, and C. M. Tinker.
Respiratory illness in factory and office workers. A study
of minor respiratory illnesses in relation to changes in
ventilatory capacity, sputum characteristics, and atmospheric
pollution. Brit. J. Dis. Chest 59:66-80, 1965.
40. Antweiler, H. ftber die Funktion des Flimmerepithels der Luftwege,
insbesondere unter Staubbelastung, pp. 509-535. In K. Thomas,
Ed. Grundfragen aus der Silikoseforschung, II. Berlcht liber
die von der Bergbau-Berufsgenossenschaft am 30. November und
1. Dezember 1956 in Gtittingen veranstaltete Tagung der Arbeits-
gemeinschaft fur Silikose-Grundfragenforschung. Bochura:
Hauptverwaltung der Bergbau-Berufsgenossenschaft, 1956.
432
-------
41. Asmundsson, T., and K. H. Kilburn. Mucociliary clearance rates at
various levels in dog lungs. Amer Rev. Resp. LUS. 102:388-
397, 1970
42. Asmundsson, T., and K. H. Kilburn. Mecnanisms of respiratory
tract clearance, pp. 107-180. In M. J. Dulfano, Ed.
Sputum. Fundamentals and Clinical Pathology. Springfield:
Charles C Thomas, Publisher, 1973.
43. Atwater, M. A. Planetary albedo changes due to aerosols.
Science 170:64-66, 1970.
44. Azarniouch, M. K., A. J. Bobkowicz, N. E. Cooke, and E. J. Farkas.
Growth of a sulfuric acid droplet exposed to water vapor.
Can. J. Chem. Eng. 51:590-595, 1973.
59
45. Bair, W. J., and J. V. Dilley. Pulmonary clearance of F6?^ and
Cr.O, in rats and dogs exposed to cigarette smoke, pp. 251-
268. In C. N. Davies, Ed. Inhaled Particles and Vapours II.
Proceedings of an International Symposium organized by the
British Occupational Hygiene Society, Cambridge, 28 September-
1 October 1965. Oxford: Pergamon Press, 1967.
433
-------
46 Baker, A. P., and J. R. Munro. Multiplv^osyltransferase system
of canine respiratory tissue. J. Biol. Chem. 246:4358-
4362, 1971.
47. Ballenger, J. J. A study of ciliary activity in the respiratory
tract of animals. Ann. Otol. Rhine1. Laryngol. 58:351-369,
1949.
48. Barclay, A. E., and K. J. Franklin. The rate of excretion of
Indian ink injected into the lungs. J. Physiol. 90:482-484,
1937.
49. Barnett, B., and C. E. Miller. Flow induced by biological
mucociliary systems. Ann. N. Y. Acad. Sci. 130:891-901, 1966.
50. Barrett, L. B., and T. E. Waddell. Cost of Air Pollution Damage:
A Status Report. Publ. AP-85. Research Triangle Park, N.C.:
National Environmental Research Center, Environmental Protection
Agency, 1973. 73 pp.
51. Barrie, L. A., and H. W. Georgii. An experimental investigation of
the absorption of sulphur dioxide by water drops containing
heavy metal ions. Atmos. Environ. 10:743-749, 1976.
52. Bartlett, B. R. The action of certain "inert" dust materials on
parasitic Hymenoptera. J. Econ. Entomol. 44:891-896, 1951.
434
-------
53 Basch, F. P., P- Holinger, and H. G. Poncher. Physical and
chemical properties of sputum. II. Influence of drugs,
steam, carbon dioxide and oxygen. Ajner. J. Dis. Child.
62:1149-117.'., 1941.
54. Bates, D. V., G. M. Bell, C. D. Burnham, M. Hazucha, J. Mantha,
L. D. Pengelly, and F. Silverman. Short-term effects of
ozone on the lung. J. Appl. Phyaiol. 32:176-181, 1972.
55. Bates, D. V., C. A. Gordon, G. I. Paul, R. E. G. Place, D. P. Snidal,
C. R. Woolf, M. Katz, R. G. Fraser, and B. B. Hale. Chronic
bronchitis: Report on the third and fourth stages of the
co-ordinated study of chronic bronchitis in the Department of
Veterans Affairs, Canada. Med. Serv. J. Can. 22:5-61, 1966.
56. Bates, D. V., and M. Hazucha. The short-term effects of ozone on the
human lung, pp. 507-540. In Assembly of Life Sciences-National
Academy of Sciences-National Research Council. Proceedings of
the Conference on Health Effects of Air Pollutants, Washington, D.C.,
October 3-5, 1973. Washington, D.C.: U.S. Government Printing
Office, 1973.
57. Bates, D. V., C. R. Woolf, and G. I. Paul. Chronic bronchitis.
A report on the first two stages of the co-ordinated study
of chronic bronchitis in the Department of Veterans Affairs,
Canada. Med. Serv. J. Can. 18:211-305, 1962.
435
-------
58 Becker, W. H., F. J. Schilling, and M. P. Verma. The effect on
health of the 19otj eastern seaboard air pollution episode
Arch. E:v.iron. Health 16:414-419, 196E.
59. Bedrossian, C. W. M., S. D. Greenberg, and B. S. Duran.
Bronchial gland measurements: A continuing search for a
"yardstick." Exper. Molec. Pathol. 18:219-224, 1973.
60. Beeckmans, J. M. The deposition of aerosols in the respiratory
tract. 1. Mathematical analysis and comparison with
experimental data. Can. J. Physiol. Pharmacol. 43:157-172,
196..
61. Bell, K. A., and S. K. Friedlander. Aerosol deposition in models of
a human lung bifurcation. Staub-Reinhalt. Luft 33(4);178-182,
1973.
62. Bell, K. A., W. S. Linn, M. Hazucha, J. D. Hackney, and
I). V. Bates. Respiratory effects of exposure to ozone
plus sulfur dioxide in Southern Californians and
Eastern Canadians. (Unpublished)
61. Seloin, N. J. A chamber study. Fadlnp of dyed fabrics exposed to
air pollutants. Text. Chem. Color. 5:128/29-133/34, 1973.
436
-------
64. Bensch, K. G. , and E. A. M. Domlnfu.'; Studies on the
pulmonary air-tissue barrier. i..rt IV. CytocheraicaJ
tracing of macromolecules during absorption. Yale J.
Biol. Med. 43:236-241, 197± .
65. Bensch, K. G. , G. B. Gordon, and L. R. Miller. Studies on the
bronchial counterpart of the Kultschitzky (argentaffin) cell
and innervation of bronchial glands, J. Ultrastruct. Res.
12:668-686, 1965.
66. Berfenstam, R., T. Edlund, and L. Zettergren. Hyaline membrane
disease. The influence of high oxygen concentration on
ciliary activity in the respiratory tract. An experimental
study on rabbits. Acta Paediatr. 47:527-533, 1958.
it
67. Berge, H. Luftverunreinigungen im Raume Koln. Allgem. Forstz.
20(51/52) =834-838, 1965.
68. Berge, H. Emissionsbedingte Eisenstaube und ihre Auswirkungen auf
Wachstum und Ertrag 1 andwi rtsrhaf 11 irher Kulttiren.
Luftverunreinigung 2:1-7, 1966.
69. Berger, H. W., M. Tryon, E. J. Clark, and L. F. Skoda. Final
Project Report on the Effects of Atmospheric Contaminants on
the Durability of Building Materials. NBS Report 10 504.
For the National Air Pollution Control Administration.
Washington, D.C.: National Bureau of Standards, 1970. 36 pp.
437
-------
70. Bernstein, D., M. T. Kleinman, T. J. Kneip, T. L. Chan, and
M. Lippmann.1 A high-volume sampler for the determination
of particle size distributions in ambient air. J. Air
Pollut. Control Assoc. 26:1069-1072, 1976.
71. Bielke, S., and H. W. Georgii. Investigation on the incorporation
of sulfur-dioxide into fog- and rain-droplets. Tellus 20:
435-442, 1968.
72. Bigg, E. K., S. C. Mossop, R. T. Meade, and N. S. C. Thorndike.
The measurement of ice nucleus concentrations by means of
Millipore filters. J. Appl. Meteorol. 2:266-269, 1963.
73. Blake, J. On the movement of mucus in the lung. J. Biomechanics
8:179-190, 1975.
74. Bodhaine, B. A., and B. G. Mendonca. Preliminary four wavelength
nephelometer measurements at Mauna Loa Observatory. Geophys.
Res. Letters 1:119-122, 1974.
ii
75. Bohlau, V., Ed. Aerosole in Physik, Medizin und Technik. Proceedings
of a conference held in Bad Soden, October 17-18, 1973. Bad Soden,
West Germany: Gesellschaft fur Aerosolforschung, 1973. 165 pp.
76. Bohne, H. Schadlichkeit von Staub aus Zementwerken fur WaldbestMnde.
Allgem. Forstz. 18(7) :108-111, 1963.
438
-------
77. Bohning, D. E., R. E. Albert, M. Lippmann, and W. M. Fostei.
Tracheobronchial particle deposition and clearance. A study of
the effect.1; of cigarette smoking in monozygotic twins.
Arch. Environ. Health 30:457-462, 1<)75.
78. Bolin, B. , L. Granat, L. Ingelstam, M. Johannesson, E. Mattsson,
S. Oden, H. Rodhe, and C. 0. Tamm. Air Pollution Across
National Boundaries. The Impact on the Environment of Sulfur
in Air and Precipitation. Royal Ministry for Foreign Affairs.
Royal Ministry of Agriculture. Stockholm: P. A. Norstedt &
So'ner, 1971. 96 pp.
79. Bolin, B., G. Witt, and R. J. Charlson. Stockholm tropospherii.
aerosol seminar: Measurement of regional to global scale
pollution by airborne particles. Bull. Amer. Meteorol. Soc.
55:228-231, 1974.
80. Boyd, E. M., J. W. Clark, and W. F. Perry. Estrogens and their
effect on ciliated mucosa. Arch. Otolaryng. 33:909-915, 1941.
81. Boyd, J. T. Climate, air pollution and mortality. Brit. J.
Prev. Soc. Med. 14:123-135, 1960.
82. Bracewell, J. M., and D. Gall. The catalytic oxidation of sulphur
dioxide in solution at concentrations occurring in fog droplets,
pp. 17-26. In Air Pollution. Proceedings of the Symposium on
the Physico-chemical Transformation of Sulphur Compounds in
the Atmosphere and the Formation of Acid Smogs, 8-9 June, 1967,
Mainz, Germany. Paris: Organisation for Economic Co-operation
and Development, 1967.
439
-------
83. B'.iu v, W. H., W. P. D. Logan, and A. F.. Martin. The London
,og of December 2nd-5th, 1957. Monthly Bull. Min. Health
L7:156-166, 1958.
84. Brain, J. D. Free cells in the lungs. Some aspects of their
role, quantisation, and regulation. Arch. Intern. Med.
126:477-487, 1970.
85. Brandt, C. J., and R. W. Rhoades. Effects of limestone dust
accumulation on composition of a forest community.
Environ. Pollut. 3:217-225, 1972.
86. Brandt, C. J., and R. W. Rhoades. Effects of limestone dust
accumulation on lateral growth of forest trees. Environ.
Pollut. 4:207-213, 1973.
87. Brantigan, 0. C., E. Mueller, and M. B. Kress. A surgical
approach to pulmonary emphysema. Amer. Rev. Resp. Dis. 80:
194-206, 1959.
88. Bricard, J., G. J. Madelaine, and D. Vigla. The formation and
evolution of aerosols generated through the action of
ultraviolet and solar radiation, pp. 173-176. In Proceedings
of the 7th International Conference on Condensation and
Ice Nuclei, September 18-24, 1969, Prague and Vienna.
Prague: Academia, 1969.
89. Brock, J. R. Condensational growth of atmospheric aerosols.
J. Coll. I. Sci. 39:32-36, 1972.
90. Brosset, C., K. Andreasson, and M. Perm. The nature and possible
origin of acid particles observed at the Swedish west coast.
Atmos. Environ. 9:631-642, 1975.
440
-------
91 Brown, J. H., K. M. Cook, F. C,. Ney, and T. Hatch. I fltiencc-
of partlcJe size upon the retention oi particular mattf-
in tne human lung. Amer. J. Public .-iealth 40:4^0-458, 480, 195(1
92. Brown, L. S. Evaluation of the Condition of the Lin oln Memorial
Stonework. Alexandria, Va. : Value Engineerinj Laboratory,
1971. 5 pp. (Study conducted for the U.S. Department of
the Interior, National Park Service)
93, Brundelet, P. J. Experimental study of the dust-clenrance
mechanism of the lung. I. Histological study in rats of
the intra-pulmonary bronchial route of elimination. Acta
Pathol. Microbiol. Scand. Suppl. 175:1-141, 196"..
94. Bryson, R. Climatic modification by air pollution, pp. 134-174.
In N. Polunin, Ed. Proceedings of the first International
Conference on Environmental Future, held in Finland from
27 June to 3 July 1971. London: The Macmillan Press, 1972.
95. Bryson, R. A. "All other factors being constant..." A reconcilia-
tion of several theories of climatic change. Weatherwise 21:
56-61, 1968.
96. Bryson, R. A. A perspective on climatic change. Climate responds
rapidly and significantly to small changes of the independent
variables. Science 184:753-760, 1974.
97. Bryson, R. A., and D. A. haerreis. Possibilities of major climatic
modification and their- implications: Northwest India, a case
for study. Bull. Amor. Meteor. Soc. 48:136-142, 1967,
441
-------
9h< Buck, S. F., and r>. A. Brown. Mortalltv from Lunp Cancer and
Bronchitis in Relation to Smoke and Sulphur Dioxide Concentration,
Population Density and Social Index. Tobacco Research Council
Research Paper No. 7. London: Waterlow and Sons, Ltd., 1964.
27 PP.
99. Budyko, M. I. The effect of solar radiation variations on the
climate of the earth. Tellus 21:611-619, 1969.
100. Huechley, R. W. , W. B. Riggan. V. Hasselblad, and J. B. VanBruggcn. SOj
levels and pertrubations in mortality. A study in the New York-
New Jersey Metropolis. Arch. Environ. Health 27:134-137, 1973.
101. Bufalini, M. Oxidartion of sulfur dioxide in polluted
atmospheres—A review. Environ. Sci. Technol. 5:685-700, 1971.
102. Burgess, S. G., and C. W. Shaddick. Bronchitis and air pollution.
Roy. Soc. Health J. 79:10-2/4, 1959.
103. Burn, J. H. Functions of Autonomic Transmitters. Baltimore:
The Williams and Wilkins Company, 1956. 227 pp.
104. Burn, J. L., and J. Pemberton. Air pollution bronchitis and lung
cancer in Salford. Int. J. Air Water Pollut. 7:5-16, 1963.
105. Burrows, B., A. L. Kellogg, and .1. Buskey. Relationship of
symptoms of chronic bronchitis and emphysema to weather and
air pollution. Arch. Lnviron. Health 16:406-413, 1968.
442
-------
106. Burton, G. G., M. Corn, J. B. L. Gee, C. Vasallo, and A. P. Thomas.
Response of healthy men to inhaled low concentrations of
gas-aerosol mixtures. Arch. Environ. Health 18:681-692, 1969.
107. Bushtueva, K. A. The determination of the limit of allowable
concentration of sulfuric acid in atmospheric air, pp. 20-36.
In V. A. Ryazanov, Ed. Limits of Allowable Concentrations
of Atmospheric Pollutants - Book 3. Translated by B. S. Levine,
U.S. Department of Commerce, Office of Technical Services,
Washington, D.C. , 1957.
108. Bushtueva, K. A. The toxicity of I^SO^ aerosol. U.S.S.R.
Literature Air Pollut. Related Occup. Dis. l:63-66b, 1960.
109. Bushtueva, K. A. Experimental studies on the effect of low
oxides of sulfur concentrations on the animal organism,
pp. 92-102. In V. A. Ryazanov, Ed. Limits of Allowable
Concentrations of Atmospheric Pollutants - Book 5.
Translated by B. S. Levine. U.S. Department of Commerce,
Office of Technical Services, Washington, D.C., 1962.
«
110. Cadle, R. D. Particles in the Atmosphere and Space.
New York: Reinhold Publishing Corporation, 1966. 226 pp
111. Cadle, R. D. The Measurement of Airborne Particles. New York:
John Wilev and Sons, Inc., 1975. 342 pp.
443
-------
112. Cadlc, •- . D. , and P. L. Magi 11. Chemist rv of contaminated
atmospheres, pp. 3-1 - 3-27. In P. L. Magill, F. R.
Holden, and C. Ackley, Eds. Air Pollution Handbook.
New Y-'-k: McGraw-Hill BOOR Company, Inc., 1956.
113. Calvert, J. G. Interactions of air pollutants, pp. 19-101.
In Assembly of Life Sciences-National Academy of Sciences
National Research Council. Proceedings of the Conference
on Health Effects of Mr Pollutants, Washington, D.C.,
October 3-5, 1973. Washington, D.C.: U.S. Government
Printing Office, 1973.
. Catnner, P., P. Helstrom, and K. Philipson. Carbon dust and
mucociliary transport. Arch. Environ. Health 26:294-296, 1973.
115. Camner, P., C. Jarstrand, and K. Philipson. Tracheobronchial
clearance in patients infected with microplasma pneumoniae ,
pp. 236-238. In J. F. Ph. Hers and K. C. Winkler, Eds.
Airborne Transmission and Airborne Infection: Concepts and
Methods. Presented at the Vlth International Symposium on
Aerobiology. Held at the Technical University at Enschede ,
The Netherlands, 1972. New York: John Wiley and Sons, 1973.
116. Camner, P., C. Jarstrand, and K. Philipson. Tracheobronchial
clearance in patients with influenza. Amer. Rev. Resp. Dis .
108:131-135, 1973.
117. Camner, P., B. Mossberg, and K. Philipson. Tracheobronchial
clearance and chronic obstructive lung disease. Scand. J.
Resp. Dis. 54:272-281, 1973.
444
-------
J18. Canmer, P., and K. Philipson. Tracheobronoliial clearance i-
smoking-discordant twins. Arch. Environ. Health 25:bO-j3, 1972.
119. Camner, P., K. Philipson, and T. Arvidsson. Cigarette smoking in man.
Short-term effect on mucociliary transport. Arch. Environ.
Health 23:421-426, 1971.
120. Camner, P., K. Philipson, and T. Arvidsson. Withdrawal of
cigarette smoking. A study on tracheobronchial clearance.
Arch. Environ. Health 26:90-92, 1973.
121. Camner, P., K. Strandberg, and K. Philipson. Increased muco :iliary
transport by cholinergic stimulation. Arch. Environ. Health
29:220-224, 1974.
122. Camner, P., K. Strandberg, and K. Philipson. Increased mucociliary
transport by adrenergic stimulation. Arch. Environ. Health 31:
79-82, 1976.
123. Cannon, H. L., and J. M. Bowles. Contamination of vegetation by
tetra-ethyl lead. Science 137:765-766, 1962.
124. Carlson, T. N., and B. M. Prospero. The large-scale movement of
Saharan air eutbreaks over the northern equatorial Atlantic.
J. Appl. Meteor. 11:283-297, 1972.
125. Carnow, B. W., M. H. Lepper, R. B. Shekelle, and J. Stamler. Chicago air
pollution study. SC>2 levels and acute illness in patients with
chronic bronchopulmonary disease. Arch. Environ. Health 18:768-776,
1969.
445
-------
Camow, !•. \s . , and P. Meier. Air pollution nnd pulmonar\' rancor.
Arcn. ..nviron. Health 27:207-218, 197 j.
127. Carson, S., R. Goldhamer, and R. Carpenter. Mucus transport in
the respiratory tract. Amer. Rev. Resp. Dis. 93 (Suppl) :86-
92, 1966.
128 Casarett, L. J. The vital sacs: Alveolar clearance mechanisms
in inhalation toxicology, pp. 2-36. In W. J. Hayes, Jr., Ed.
Essays in Toxicology, Volume 3. New York: Academic Press, 1972
129. Cassatt, W. A., and R. S. Haddock, Eds. Aerosol Measurements.
The Proceedings of a Seminar on Aerosol Measurements,
May 7, 1974 sponsored by The National Bureau of Standards
and The Food and Drug Administration. National Bureau of
Standards Special Publication 412. Washington, DC: U.S.
Government Printing Office, 1974. 182 pp.
130. Chakrin, L. W. , A. P. Baker, S. S. Spicer, J. R. Wardell, Jr.,
N. DeSanctis, and C. Dries. Synthesis and secretion of
macromolecules by canine trachea. Amer. Rev. Resp. Dis.
105:368-381, 1972.
131. Chandler, K. A., and M. B. Kilcullen. Survey of corrosion and
atmospheric pollution in and around Sheffield. Brit. Corros. J.
3:80-84, 1968.
132. Changnon, S. A., Jr. The La Porte weather anomaly — fact or
fiction? Bull. Amer. Meteorol. Soc . 49:4-11, 1968.
446
-------
]33. Chanfnon, h. 4., Jr., F. A. r./ff, anH R. C. Semonin.
Necroraex: An inve.sti^aL. .11 of inadvertent weather modification.
Bull. Amsr. Meteorol. DO,. 52:958-967, 1971.
134. Chapman, R. S., C. M. Shy, J. F. Finklea, D. E. House, H. E. Goldberg,
and C. G. Hayes. Chronic respiratory disease. In military inductees
and parents of schoolchildren. Arch. Environ, Health 27:138-142,
1973.
135. Charlson, R. J. Atmospheric visibility related to aerosol mass
concentration. A review. Environ. Sci. Technol. 3:913-918, 1969.
136. Charlson, R. J., N. C. Ahlquist, and H. Horvath. On the
generality of correlation of atmospheric aerosol mass
concentration and light scatter. Atmos. Environ. 2:455-464, 1968.
137. Charlson, R. J., N. C. Ahlquist, H. Selvidge, and P. B. MacCready, Jr.
Monitoring of atmospheric aerosol parameters with the integrat-
ing nephelometer. J. Air Pollut. Control Assoc. 19:937-942, 1969.
138. Charlson, R. J., D. S. Covert, Y. Tokiwa, and P. K. Mueller.
Muitiwavelength nephelometer measurements in Los Angeles smog
aerosol. 111. Comparison to light extinction by N02, pp. 333-338.
In G. M. Hidy, Ed. Aerosols and Atmospheric Chemistry.
Proceedings of the American Chemical Society. Los Angeles,
California, March 28-April 2, 1971. New York: Academic Press,
1972.
139. Charlson, R. J., H. Harrison, and G. Witt. Aerosol concentrations:
Effect on planetary temperatures. Science 175:95-96, 1972.
447
-------
140. Charlson, R. J., and M. J. PiiaL. Climate: The influence of
aerosols. J. Appl. MeLeorol. 8:1001-1002, 1969.
141. Charlson, R. J., and M. J. Pilat. Reply [to S. H. Schneider on
climateT] . J. Appl. Meteorol. 10:841-842, 1971.
142. Charlson, R. J., W. M. Porch, A. P. Waggoner, and N. C. Ahlquist.
Background aerosol light scattering characteristics:
Nephelometric observations at Mauna Loa Observatory compared
with results at other remote locations. Tellus 26:345-160, 1974.
143. Charlson, R. J., A. H. Vanderpol, D. S. Covert, A. P. Waggoner,
and N. C. Ahlquist. H?SO^/(NH^)oSO^ background aerosol:
Optical detection in St. Louis region. Atmos. Environ.
8:1257-1267, 1974.
144. Charlson, R. J., A. H. Vanderpol, D. S. Covert, A. P. Waggoner,
and N. C. Ahlquist. Sulfuric acid-ammonium sulfate aerosol:
Optical detection in the St. Louis region. Science 184:156-
158, 1974.
145. Chairman, J., and L. Reid. Sputum viscosity in chronic bronchitis,
hronchiectasis, asthma nnd cvstir fibrosis. Biorheologv
9:185-199, 1972,
146. Cheng, R. T., M. Corn, and J. 0. Frohliger. Contribution to the
reaction kinetics of water soluble aerosols and SO,, in air
at ppm concentrations. Atmos. Environ. 5:987-1008, 1971.
448
-------
147. Chinard, F. P. The permeability characteristics of the puli;. ar>
blood-gab barrier, pp. 106-147. In C. G. Caro, Ed.
Advances in Respiratory Physiology. London: Edward Arnold Ltd,,
1966.
148. Christensen, 0. W., and C. H. Wood. Bronchitis mortality rates
in England and Wales and Denmark. Brit. Med. J. 1:620-622, 1958.
149. Chylek, P., and J. A. Coakley, Jr. Aerosols and climate.
Science 183:75-77, 1974.
150. Ciocco, A., and D. J. Thompson. A follow-up of Donora ten years
after: Methodology and findings. Amer. J. Public Health 51:
155-164, 1961.
151. Clara, M. Zur Histobiologie des Bronchalepithels. Z. Mikrosk.
Anat. Forsch. 41:321-347, 1937.
152. Clark, W. E. Measurements of Aerosols Produced by the Photochemical
Oxidation of Sulfur-Dioxide in Air. Ph.D. Thesis, University
of Minnesota, Minneapolis, Minn., 1972. 152 pp.
153. Clark, W. E., and K. T. Whitbv. Concentration and size distribution
measurements of atmospheric aerosols and a test of the theory
of self-preserving size distributions. J. Atmos. Sci. 24:
677-687, 1967.
449
-------
154. Clark, W. E., and K T. WMtbv. Measurements of aerosols producer
by the photocliemical oxidation of SO- in air. J. Coll. 1. Sci.
51:477-490, 1975.
155. Clements, J. A., J. T. Sharp, R. P. Johnson, and J. 0. Elam.
Estimation of pulmonary resistance by repetitive interruption
of airflow. J. Clin. Invest. 38:1262-1270, 1959.
156. Cohen, A. A., S. Bromberg, R. W. Buechley, M. A. Heiderscheit,
and C. M. Shy. Asthma and air pollution from a coal-fueled
power plant. Amer. J. Public Health 62:1181-1188, 1972.
157. College of General Prartitioners. Chronic bronchitis in
Great Britain. A national survey carried out by the
respiratory diseat.es study group of the College of
(teneral Practitioner.,. Brit. Med. J. 2:973-979, 1961.
158. Colley, J. R. T., and W. W. Holland. Social and environmental
factors in respiratory disease. Arch. Environ, Health 14:
157-161, 1967.
159. Colley, J. R. T. , and D. 1). Reid. Urban and social origins of
childhood bronchitis in England and Wales. Brit. Med. J.
2:213-217, 1970.
160. Comstock, G. W., R. W. Stone, Y. Sakai, T. Matsuva, and J. A. Tonascia.
Respiratory findings and urban living. Arch. Environ. Health 27:
143-150, 1973.
450
-------
161. Constantine, H., L. Dautrebandf, N. Kaltreider, F. W. Lovejoy, Jr.,
P. Morrow, and P. Perkins. Influence of carbachol and of
fine dust aerosols upon tb" breathing mechanics and thi-
lung volumes of normal subjects and of patients with chronic
respiratory disease before and after administering sympathomimetie
aerosols. Arch. Int. Pharnacodyn. Ther. 123:239-252, 1959.
162. Cooke, D. D., and M. Kerker. Response calculations for light-scattering
aerosol particle counters. Appl. Opt. 14:734-739, 1975.
163. Cooper, D. W., R. L. Byers, and J. W. Davis. Measurements of
laser light backscattering vs. humidity for salt aerolols.
Environ. Sci. Technol. 7:142-146, 1973.
164. Com, M. , N. Kotski, D. Stanton, W. Bell, and A. P. Thomas.
Response of cats to inhaled mixtures of SC>2 and S02-NaCl
aerosol in air. Arch. Environ. Health 24:248-256, 1972.
165. Cornwall, C. J., and P. A. B. Raffle. Bronchitis—sickness absence
in London transport. Brit. J. Ind. Med. 18:24-32, 1961.
166. Covert, D. S. The Relationship hetween Chemical Composition,
Relative Humidity and Light Scattering by Aerosols.
M.S. thesis, University of Washington, 1971. (On file
at University of Washington Library)
451
-------
£24. Winkelstein, W., Jr., S. Kantor, E. W. Davis, C. S. Maneri, and
W. E. Mosher. The relationship of air pollution and economic
status to total mortality and selected respiratory system
mortality in men. II. Oxides of sulfur. Arch. Environ. Health
16:401-405, 1968.
825. Winkler, P. The growth of atmospheric aerosol particles as a
function of the relative humidity. II. An improved concept
of mixed nuclei. J. Aerosol Sci. 4:373-387, 1973.
826. Winkler, P., and C. Junge. The growth of atmospheric aerosol
particles as a function of the relative humidity.
Part I. Method and measurement at different locations.
J. Recherch. Atmos. 6:617-638, 1972.
827. Wolff, R. K., M. Dolovich, G. Obminski, and M. T. Newhouse.
Effects of sulfur dioxide on tracheobronchial clearance
at rest and during exercise. In W. H. Walton, Ed.
Inhaled Particles IV. London: Pergamon Press Ltd, 1977.
828. Wolff, R. K., M. Dolovich, C. Rossman, and M. T. Newhouse. Sulfur
dioxide and tracheobronchial clearance in man. Arch. Environ.
Health 30:521-527, 1975.
829. Wood, T., and F. H. Bormann. The effects of an artificial acid
mist upon the growth of Betula alleghaniensis Britt. Environ.
Pollut. 7:259-268, 1974.
830. Wood, T., and F. H. Bormann. Increases in foliar leaching caused by
acidification of an artificial mist. Ambio 4:169-171, 1975.
552
-------
173. Cuddihy, R. G., and B. B. Boecker. Controlled administration of
respiratory tract burdens of inhaled radioactive aerosols
in h«'-"'le uogs. Toxicol. Appl. Pharmaccl. 25:597-605 (Aug.),
1973.
174. Cutz, E., and P. E. Conen. Ultrastructure and cytochemistry of
Clara cells. Amer. J. Path. 62:127-142, 1971.
175. Czaja, A. T. Die Wirkung von verstaubtem Kalk und Zement auf
Pflanzen. Qual. Plant Mater. Vegetabiles 7:184-212, 1960.
176. Czaja, A. ': . Zementstaubwirkungen auf Pflanzen: die Entstehung
der Zementkrusten. Qual. Plant Mater. Veg. 8:201-238, 1961.
M
177. Czaja, A. T. Uber das Problem der Zementstaubwirkungen auf
Pflanzen. Staub 22:228-232, 1962.
178. Cjfaja, A. T. Uber die Einwirkung von Stauben, speziell von
Zementofenstaub auf Pflanzen. Angew. Botan. 40:106-120, 1966.
179. Dahl, E., and 0. Skre. An investigation of the effects of acid
precipitation on land productivity, pp. 27-40. In
Konferens om avsvavling, Stockholm, 11 November 1969.
Helsinki: Nordforsk Miljovardssekretariatet, 1971. (in Norwegian)
453
-------
180. Dalhamn, T. Mucous flow and ciliary activity in the trachea of
healthy cats and rats exposed to respiratory irritant gases
(SC>2, H-jN, HCHO) : A functional and morphologic (light
microscopic and electron microscopic) study, with special
reference to technique. Acta Physiol. Scand. 36: Suppl. 123,
9-161, 1956.
181. Daly, C. Air pollution and bronchitis. Brit. Med. J. 2:687-688, 1954,
182. Daly, C. Air pollution and causes of death. Brit. J. Prev. Soc.
Med. 13:14-27, 1959.
183. Dana, M., J. M. Hales, C. E. Hane, and J. M. Thorp. Some
references pertinent to the field of precipitation chemistry,
pp. 121-136. In Appendix B of Precipitation Scavenging
of Inorganic Pollutants from Metropolitan Sources. Report /'
EPA-650/3-74-005. Richland, WA: Battelle-Pacific Northwest
Laboratories, 1974. (Prepared for U.S. Environmental Protection
Agency. Distributed by National Technical Information Service,
Springfield, VA)
184. Darley, E. F. Studies on the effect of cement-kiln dust on
vegetation. J. Air Pollut. Control Assoc. 16:145-150, 1966.
185. Davies, C. N. Deposition and retention of dust in the human
respiratory tract. Ann. Occup. Hyg. 7:169-183, 1964.'
454
-------
186. Davies, C. N. The deposition 2-8r>7
191. Dean, G. Lung cancer in South Africans and British immigrants.
Proc. Royal Soc. Med. 57 (2) :984-987, 1964.
192. Dean, G. Lung cancer and bronchitis in northern Ireland, 1960-2.
Brit. Med. J. 1:1506-1514, 1966.
455
-------
193. Deane M. , J. k. Goldsmith, and D. lurnn. Respiratory condition:,
in outside worker:,. Report on out.sidt- plan;, telephone
workers in San Francisco and Los Angeles. Arch. Environ.
Health 10:323-331, 1965.
194. Denton, R. Bronchial obstruction in cystic fibrosis : theological
factors. Pediatrics 25:611-620, 1960.
195. Dietz, A. G. H. Plastics for Architects and Builders. Cambridge:
The MIT Press, 1969. 129 pp.
196. Dohan, F. C. Air pollutants and incidence of respiratory
disease. Arch. Environ. Health 3:387-395, 1961.
197. Dohan, F. C., and E. W. Taylor. Air pollution and respiratory disease,
A preliminary report. Amer. J. Med. Sci. 240:337-339, 1960.
198. Dolan, D. F., D. B. Kittelson, and K. T. Whltby. Measurement of
Diesel Exhaust Particle Size Distributions. ASME Preprint
//75-WA/APC-5. Present LM! at tin- Winter Anniu 1 Meeting of the
American Society of Mechanical Engineers, November 30-
December 3, 1975, Houston, Texas.
199. Doll, R., Ed. Methods of Geographical Pathology. Report of
the Study Group Convened by the Council for International
Organizations of Medical Sciences Established Under the
Joint Auspices of UNESCO and WHO. Oxford: Blackwell Scientific
Publications, Ltd., 1959. 72 pp.
456
-------
200. Doll, R., and A. K. Hill. Mortality in relation to smoking:
Ten years' observations of British doctors. Brit. Med. J.
1:1399-1410,
201. Dorn, H. F. Tobacco consumption and mortality from cancer and
other diseases. Public Health Rep. 74:581-593, 1959.
202- Douglas, J. W. B., and R. E. Waller. Air pollution and
respiratory infection in children. Brit. J. Prev. Soc.
Med. 20:1-8, 1966.
203. DuBois, A. B., and L. Dautrebande. Acute effects of breathing
inert dust particles and of carbachol aerosol on the mechanical
characteristics of the lungs in man. Changes in response after
inhaling sympathomimetic aerosols. J. Clin. Invest. 37:1746-
1755, 1958.
204. Durham, J. L. , W. E. Wilson, T. G. Ellestad, K. Willeke, and
K. T. Whitby. Comparison of volume and mass distributions for
Denver aerosols. Atmos. Environ. 9:717-722, 1975.
205. Dzubay, T. G. , and R. K. Stevens. Ambient air analysis with
dichotomous sampler and x-ray fluorescence spectrometer.
Environ. Sci. Technol. 9:663-668, 1975.
457
-------
206. Dzubay, T. G., and R. K. Stevens. The Characterization of
Atmospheric Aerosol by Physical and Chemical Methods.
Presented at the American Chemical Society at its 171st
National Meeting in New York on April 4-9, 1976. Preprint
in Volume 16, No. 1. Available through the ACS Environmental
Chemists Division.
207. Dzubay, T. G., R. K. Stevens, and C. M. Peterson. Application of
the dichotomous sampler to the characterization of ambient
aerosols, pp. 95-106. In T. G. Dzubay, Ed. X-Ray Fluorescence
Analysis of Environmental Samples. Ann Arbor: Ann Arbor Science
Publishers, Inc., 1977.
208. Eagan, R. C., P. V. Hobbs, and L. F. Radke. Particle emissions
from a large Kraft paper mill and their effects on the
microstructure of warm clouds. J. Appl. Meteorol. 13:
535-552, 1974.
209. Eastcott, D. F. The epidemiology of lung cancer in New Zealand.
Lancet 1:37-39, 1956.
210. Ebert, R. V., and M. J. Terracio. Observation of the secretion on the
surface of the bronchioles with the scanning electron microscope.
Amer. Rev. Resp. Dis. 112:491-496, 1975.
458
-------
ill. Egpert, J. i .vsical Chemistry. ('1 r.ins L-ited by S. J. GreRf,) New York:
D. Van Nostrand Co., Inc., 19JJ. 632 pp.
''12. Eisenbud, M. , ind T. J. Kneip. Trace Metals in Urban Aerosols.
Research Project 117. Final Report. Prepared by New York
Universi*-" for Electric Power Research Institute (EPRI).
1975.
213. Elliott, J. F. E. , and A. C. Franks. Design of telephone exchanges
for corrosive atmospheres. Systems Tech. No. 6:39-48, 1969.
214. Ellis, H. T., and R. F. Pueschel. Solar radiation: Absence of
air pollution trends at Mauna Loa. Science 172:845-846, 1971.
215. Elterman, L., R. B. Toolin, and J. D. Essex. Stratospheric aerosol
measurements with implications for global climate. AppJ . Opt.
12:330-337, 1973.
216. Emerson, P. A. Air pollution, atmospheric conditions and chronic airways
obstruction. J. Occup. Mcd. 15:635-638,
217. Engelmann, R. J. , and W. G. N. Slinn. Precipitation Scavenging.
Proceedings of a symposium held at Richland, Washington,
June 2-4, 1970. Oak Ridge, Tenn . : USAEC Division of
Technical Information Extension, 1970. 499 pp.
459
-------
Knsoi , I'. S., K. .1. Char 1 son, N. C. Ahlquist, K. T. Wliitln,
K. B. llusai , and I',. Y. II. Liu. Mu I t i wave I eiift h iH'phi- I on... I ei
iiKMt."re men ts in Los Angeles smo)', aerosol. I. Compnr i son of
calculated and measured light scattering,, pp. 315-324.
In (!. M. liidy, Kd . Aerosols and Atmospheric Chemistry.
Proceed in)',:- of the American Chemical Society, l.os An^clc:,,
C.-i 1 i torni.i, Hit-ill :'H-April 2, 1971. New York: Academit Cress,
1971'.
219. Ensor, ». S. , and M. J. Pilat. Calculation of smoke plume
opacity from participate air pollutant properties.
J. Air I'ollut. Control Assoc. 21:496-501, 1971.
220. Ensor, 1). S., W. M. Porch, M. J. Pilat, and R. J. Charlson.
Influence of the atmospheric aerosol on albedo. .1. Appl.
MeLeoroJ . 10:1 30 )-) j()(;, 1971 .
221. Kvans, C. R. , and A. I". Roddy. The condensation nuclei formed
in polluted air by ultraviolet radiation whose wavelengths
are longer than 2900 A, pp. 369-373. In Proceedings of
the 7th International Conference on Condensation and
Ice Nuclei, September 13-24, 1969, Prague and Vienna.
Prague: Academla, 1969.
222. Fairbairn, A. S., and 1). D. Reid. Air pollution and other
local factors in respiratory disease. Brit. .1. Prev. Sot.
Med. 12:94-103, 1958.
460
-------
223. Fairchild, C. A., P. Kane, B. Adams, and D. Coffin. Sulfuric arid anil
streptococci clearance from respiratory tracts of mice. Arch.
Environ. Health 30:538-545, 1975.
224. Feather, E. A., and G. Russell. Sputum viscosity in cystic fibrosis
of the pancreas and other pulmonary diseases. Brit. J. Dis.
Chest 64:192-200, 1970.
225. Kcrin, J. Lung clearance of particles, pp. 64-78. In E. F. Aharonson,
A. Ben-David, and M. A. Klingberg, Eds. Air Pollution and the
Lung. Proceedings of the Twentieth Annual "OHOLO" Biological
Conierence, Mu'alot, Israel, Marcli 16-19, 1975. New York:
John Wiley & Sons, Inc., 1976.
226. Ferris, B. G. Effects of air pollution on school absences and
differences in lung function in first and second grades in
Berlin, New Hampshire, January 1966 to June 1967. Amer.
Rev. Resp. Dis. 102:591-606, 1970.
227. Ferris, B. G., Jr., and D. 0. Anderson. The prevalence of
chronic respiratory disease in a New Hampshire town.
Amer. Rev. Resp. Dis. 86:165-177, 1962.
228. Ferris, B. G., Jr., and D. 0. Anderson. Epidemiolopical studies
related to air pollution: A comparison of Berlin, New Hampshire,
and Chilliwack, British Columbia. Proc . Roy. Sor. Mr.I. 57:
979-987, 1964.
461
-------
•>29. Ferris, B. (,., Jr., I. 1. 1 . Hif'in.s, M. W. Higgins, and .). M. Peter...
Chronic nonspecific respnaLory disease in Berlin,' New Hampshire,
1961 to 1967. A follow-up study. Amer . Rev. Kesp. Dis. 107:
110-122, 1973.
n
230. Findeisen, W. Uber das Absetzen kleiner, in der Luft suspendierter
Teilchen in der menschlichen Lunge bei der Atraung. Arch. Ges.
Physiol. 236:367-379, 1935.
231. Findeisen, W. Zur Frage der Repontropfenbildung in reinen
Wasserwolken. Meteorol. Z. 56:365-368, 1939.
232. Fink, F. W., F. H. Buttner, and W. K. Boyd. Technical-
Economic Evaluation of Air-Pollution Corrosion Costs
on Metals in the United States. Final Report.
Prepared for the Air Pollution Control Office,
Environmental Protection Agency. APTD-0654.
Columbus, Ohio: Battelle Memorial Institute, 1971.
[160 pp.]
233. Finklea, J. F., D. C. Calafiore, C. J. Nelson, W. B. Riggan, and
C. G. Hayes. Aggravation of asthma by air pollutants:
1971 Salt Lake Basin studies, pp. 2-75 to 2-91. In U.S.
Environmental Protection Agency, Office of Research and
Development. Health Consequences of Sulfur Oxides: A IVport
from CHESS, 1970-1971. EPA-650/1-74-004. Washington, DC:
U.S. UwcrnniL'iit Printing Oliiri1, l')7A.
462
-------
234. Finklea, J. F. , J. H. Farmer, G. J. Love, D. C. Calafiore, me!
G. W. Sovocool. Aggravation of asthma by air pollutants:
1970-1971 New 'fork studies, pp. 5-71 to 5-84. In U.S.
Environmental 'Protection Agency, Office of Research and
Development. Health Consequences of Sulfur Oxides: A Report
from CHESS, 1970-1971. EPA-650/1-74-004. Washington, DC:
U.S. Government Printing Office, 1974.
235. Finklea, J. F., J. G. French, G. R. Lowrimore, J. Goldberg,
C. M. Shy, and W. C. Nelson. Prospective surveys of arute
respiratory disease in volunteer families: Chicago nursery
school study, 1969-1970, pp. 4-37 to 4-55. In U.S. Environ-
mental Protection Agency, Office of Research and Development.
Health Consequences of Sulfur Oxides: A Report from CHESS,
1970-1971. EPA-650/1-74-004. Washington, DC: U.S. Government
Printing Office, 1974.
236. Finklea, J. F., D. I. Hammer, D. E. House, C. R. Sharp, W. C. Nelson,
and G. R. Lowrimore. Frequency of acute lower respiratory
disease in children: Retrospective survey of five Rocky
Mountain communities, 1967-1970, pp. 3-35 to 3-56. In
U.S. Environmental Protection Agency, Office of Research
and Development. Health Consequences of Sulfur Oxides:
A Report from CHESS, 1970-1971. EPA-650/1-74-004.
Washington, D.C.: U.S. Government Printing Office, 1974.
463
-------
2!7. 1 inklea, .! . 1'., C. M. Shy, G. .1. Love, C. G. Haves, W. C. Nelson,
K. S. Chapman, and I). L. House. Health consequenc es ol sulfur
oxides: Summary and conclusions based upon C11KSS studies ol
1970-19/1, p|'. 7-1 to /-24. In U.S. hnvi ronmen t a 1 Protection
Agency , 01 lice ol Research and Deve 1 opuient . Health Consequence'
of Sulfur Oxides: A Report irom CHESS, 1970-1971.
KPA-650/1-74-004. Washington, DC: U.S. Government Printing
Office, 1974.
/
.Mh. F.iket, .1. Sur les causes des aitidents survenus dans la vallee
de la Mouse, lors des brouillardt, de decembre 1930. Hull. Acad.
Koy. Med. lielg. 11:68}-Ml, 1931.
239. Fischer, K. hestimmung der Absorption von sichtbarer Strahlunj',
durch Ac'rosolpart ikeln . lie i t i . Phys. Atmo:,. 45:M4-?54, 1970.
ti
240. Fischer, K. Massenabsorptionskoeffizient naturlichei
Aerosol tcilchen im We 11 enlangenbereich zwischen 0.4 mid ^.4 inn,
Beitr. Phys. Atmos. 46:89-100, 1973.
241. Fish, B. R. Inhalation of uranium aerosols by mouse, rat, doj;
and man, pp. 151-165. In C. N. Davies, Ed. Inhaled Particles
and Vapours. Proceedings of an International Symposium
organized bv the British Occupational Hygiene Society, Oxford,
29 Marcb-1 April 1960. Oxford: Perpamon Press, 1961.
'42. Fisher, M. V., P. E. Morrow, and C. L. Yuile. Effect of Freund's
complete adjuvant upon clearance of iron-59 oxide from rat
lungs. J. Reticuloendothel. Soc. 13:536-556, 1973.
464
-------
24J. Fletcher, C. M., C . M. Tinker, 1. U. Hill, and F. E. Speizer.
A five-year prospective field study of earJv obstructive-
airway disease, pp. 249-23J. In U. S. ix.'p_ Lment of Health,
Education, and Welfare, Public Health Service. Current
Research in Chronic Respiratory Disease, Pi jceedings of the
Eleventh Aspen Conference. Washington, D.C.: U.S. Government
Printing Office, 1968.
244. Fletcher, N. H. The Physics of Rainclouds. Cambridge, Eng.:
University Press, 1962. 386 pp.
245. Flocchini, R. (,'. , T. A. Cahil], D. J. Shadoan, S. J. Lange,
H. A. Eldred, P. J. Fecney, G. W. Wolfe, D. C. Simmeroth,
and J. K. Suder. Monitoring California's aerosols by size
and elemental composition. Environ. Sci. Technol. 10:76-82, 1976.
246. Florey, H., H. M. Carleton, and A. Q. Wells. Murus secretion in
the trachea. Brit. J. Exp. Path. 13:269-284, 1932.
247. Flowers, E. C., R. A. McCormick, and K. R. Kurfis. Atmospheric
turbidity over the United States. J. Appl. Meteorol. 8:955-
962, 1969.
248. Flueck, J. A. Statistical Analysis of the Ground Level Pre-
cipitation Data. Part V of I he- Final Report on Project
Whitetop, A C'onvective Cloud Randomized Seeding Project.
Chica"T "nivpr^i'fv of Chii.i^u, 1971, 294 pp.
465
-------
249. Flyper, H., K. liansen , W. J. Mepau-, ami L. C. Cox. The background
level of the summer Lropospheric aerosol over Greenland ami
the North Atlantic Ocean. J. Appl. Meteor. 12:161-174, 1973.
250. Flyger, H., N. Z. Hcldarn, K. Hansen, W. J. Megaw, E. C. Walther, and
A. W. Hogan. The background level of the summer tropospheric
aerosol, sulfur dioxide and ozone over Greenland and the North
Atlantic Ocean. J. Aerosol Sci. 7:103-140, 1976.
251. Foster, W. M., E. H. Bergofsky, D. E. Bohning, M. Lippmann, and
R. E. Albert. Effect of adrenergic agents and their mode of
action on mucociliary clearance in man. .1. Appl. Physiul.
41:146-152, 197<>.
252. Frank, N. R., M. 0. Amdur, and J. L. Whittenberger. A comparison
of the acute effects of S0n administered alone or in com-
bination with NaCl particles on the respiratory mechanics
of healthy adults. Int. J. Air Wat. Pollut. 8:125-133, 1964.
253. Frank, N. R. , M. 0. Amdur, .1. Worcester, and .1. L. Wliittenberger.
Effects of acute controlled exposure to SO on respiratory
mechanics in healthy male adults. J. Appl. Physiol. 17:
252-258, 1962.
254. Frank, N. R. , and F. E. Speizer. S02 effects on the respiratory
system in dogs: Changes in mechanical behavior at different
levels of the respiratory system during acute exposure to
the gas. Arch. Environ. Health 11:624-634, 1965.
466
-------
255 Frank, N. R., R. E. Yoder, J. D. Brain, and E. Yokoyama.
o f-
SO ( S JUbt:led) absorption by the nose and mouth under
conditions oi varying i. ~mcentration and flow. Arch.
Environ. Health 18:315-J22, 1969.
256. Frank, N. R., R. E. Yoder, t. Yokoyama, and F. E. Speizer. The
diffusion of SO from tissue fluids into the lungs following
exposure of dogs to So . Health Phys. 13:31-36, 1967.
257. Frank, R. The effects of inhaled pollutants on .nasal and pulmonary
flow-resistance. Ann. Otol. Rhinol. Laryngol. 79:540-546, 1970.
258. French, J. G. , G. Lowrimore, W. C. Nelson, J. F. Finklea, T. English, and
M. Hertz. The effect of sulfur dioxide and suspended sulfates on
acute respiratory disease. Arch. Environ. Health 27:129-133, 1973.
259. Friedlander, S. K. Theoretical considerations for the particle size
spectrum of the stratospheric aerosol. Amer. Meteor. Soc. J.
Meteor. 18:753-759, 1961.
260. Friend, J. P. The global sulfur cyc]e, pp. 177-201, In
S. I. Rasool, Ed. Chemistry of the Lower Atmosphere.
New York: Plenum Press, 1973.
L'61. Fuchs, N. A. The Mechanics of Aerosols. New York: Pergamon Press,
1964. 408 pp.
467
-------
262. Fujii, T., and A. Hirata. Studies of the effects of air pollution on
the fading of dyed fabrics. Taiki Osen Kenkyu (J. Jjp. Soc. Air
Pollut.) 5:164, 1970. (in Japanese)
263. Fujii, T., and C. Tsuda. Studies on the effects of air pollution
on the fading of dyed fabrics. J. Jap. Soc. Air Pollut.
6(1)162, 1971. (in Japanese)
264. Fuller, E. C., and R. H. Christ. The rate of oxidation of sulfite
ions by oxygen. J. Araer. Chem. Soc. 63:1644-1650, 1941.
265. Furiosi, N. J., S. C. Crane, and G. Freeman. Mixed sodium chloride
aerosol and nitrogen dioxide in air. Biological effects on
monkeys and rats. Arch. Environ. Health 27:405-408, 1973.
266. Garland, J. A., J. R. Branson, and L. C. Cox. A study of
the contribution of pollution to visibility in a radiation
fog. Atraos. Environ. 7:1079-1092, 1973.
267. Gartrell, G., Jr., and S. K. Friedlander.' Relating particulate
pollution to sources: The 1972 California aerosol charac-
terization study. Atmos. Environ. 9:279-299, 1975.
268. Gerhard, E. , and H. F. Johnstone. Photochemical oxidation of
sulfur dioxide in air. Ind. Eng. Chem. 47:972-976, 1955.
468
-------
26l>. Giacomelli-Mal toni, G., C. Melandri, V. Prodi, and C. Tarroi.i .
Deposition efficiency of monodisperse particles in human
respiratory tract. Amer. Ind, Hyg. Asaoc. J. 33:603-6)0, l'J72,
27C Gibbons, E. V. The Corrosion Behavior of Some ArcliitecturaJ
Metals in Canadian Atmospheres. Summary of Ten-Year Results
of Group 1. Division of Building Research Technical Paper No.
328. Ottawa: National Research Council of Canada, 1972.
81 PP.
271. Gibbons, E. V, The Corrosion Behavior of Some Architectural
Metals in Canadian Atmospheres: Summary of Ten-Year Results
of Group II. Division of Building Research Technical Paper
No. 373. Ottawa: National Research Council of Canada, 1972.
272. Gibbons, R. A. The biochemical and physical properties of
epithelial mucus. Amer. Rev. Resp. Dis. 83:568-569, 196J.
273. Gil, J., and E. R. Weibel. Extracellular lining of bronchioJes
after perfusion-fix.it ion of rat lungs for electron
microscopy. Anat. Rec. 169:185-200, 1971.
274. Gilboa, A., and A. Silberborp. Characterization of epithelial mucus
and its function in clearance bv ciliarv propulsion, pp. 49-63.
In L. F, Aharonsnn, A. Ben-David, am) M. A. Klingberg, Kds .
Air Pollution and tlio Lung. Proceedings of the Twentieth
Annual "OHOLO" Biological Conference, Ma'alot, Israel,
March 16-19, 1975. New York: John Wiley & Sons. Inc., 1976.
469
-------
275. Gillette, D. A., 1. H. Blifford, Jr., and C. 1'. henster. Measure-
ments o£ aerosol size distributions and vertical fluxes oi
aerosols on land subject to wind erosion. J, Appl. Meteor. 11:
977-987, 1972.
276. Gladney, E. S., W. H. Zoller, A. G. Jones, and G. E. Gordon.
Composition and size distributions of atmospheric particulate
matter in Boston area. Environ. Sci. Tech. 8:551-557, 1974.
277. Glasser, M., and L. Greenburg. Air pollution, mortality, and
weather. New York City, 1960-1964. Arch. Environ. Health
22:334-343, 1971.
278. Glasser, M., 1. Greenburg, and F. Field. Mortality and morbidity during
a period of high levels of air pollution. New York, Nov 23 to 25,
1966. Arch. Environ. Health 15:684-694, 1967.
279. Glasstone, S. Textbook of Phvsical Chemistry. (2nd ed.)
New York: D. Van Nostrand Co., Inc., 1946. 1320 pp.
280. Goco, R. V., M. B. Kress, and 0. C. Brantigan. Comparison of
mucus glands in the tracheobronchial tree of man and
animals. Ann. N. Y. Ac-ad. Sci. 106:555-571, 1963.
281. Goetz, A. On the nature of the synergistic action of aerosols.
Int. J. Air Water Pollut. 4:168-184, 196].
470
-------
282. Goldberg, H. E., A. A. Cohen, J. F. Finklea, J. H. Fanner,
F. B. Benson, and G. J. Love. Frequency and severity of
cardiopulmon.iry symptoms in adult panels: 1970-1971
New York studies, pp. 5-85 to 5-108. In U.S. Environmental
Protection Agency, Office of Research and Development.
Health Consequences of Sulfur Oxides: A Report from CHESS,
1970-1971. EPA-650/1-74-004. Washington, DC: U.S. Government
Printing Office, 1974.
283. Goldberg, H. E., J. F. Finklea, C. J. Nelson, W. B. Steen,
R. S. Chapman, D. H. Swanson, and A. A. Cohen. Prevalence
of chronic respiratory disease symptoms in adults: 1970
survey of New York communities, pp. 5-33 to 5-47. In
U.S. Environmental Protection Agency, Office of Research and
Development. Health Consequences of Sulfur Oxides: A Report
from CHESS, 1970-1971. EPA-650/1-74-004. Washington, DC:
U.S. Government Printing Office, 1974.
284. Goodwin, J. E., W. Sage, and G. P. Tilly. Study of erosion by solid
particles. Inst. Mech. Eng. Proc. 184(15) :279-292, 1969-1970.
285. Gordon, C. C. Mount Storm Study. Report to Environmental Protection
Agency under Contract 68-02-0229, November 17, 1972.
286. Gore, A. T., and C. W. Shaddick. Atmospheric pollution and
mortality in the County of London. Brit. J. Prev. Soc. Med,
12:104-113, 1958.
471
-------
287. Gorham, E. Bronchitis and the acidity of urban precipitation.
Lancet 2:691, 1958.
288. Gorham, E. Pneumonia and atmospheric sulphate deposit. Lancet 2:
287-288, 1959.
289. Gormley, P. G., and M. Kennedy. Diffusion from a stream
flowing through a cylindrical tube. Proc. Roy. Irish
Acad. A52:163-169, 1949.
290. Gosselin, R. E. Physiological regulators of ciliary motion.
Amer. Rev. Resp. Dis. 93 (Suppl. - Symposium on Structure,
Function and Measurement of Respiratory Cilia. Duke University
Medical Center, Durham, North Carolina, February 18-19, 1965):
41-59, 1966.
291. Green, G. M. Integrated defense mechanisms in models of chronic
pulmonary disease. Arch. Intern. Med. 126:500-503, 1970.
292. Green, G. M. Alveolobronchiolar transport mechanisms. Arch.
Intern. Med. 131:109-114, 1973.
293. Green, H. L. , and W. R. Lane. Particulate Clouds: Dusts, Smokes and
Mists; Their Physics and Physical Chemistry and Industrial and
Environmental Aspects. New York: D. Van Nostrand Co., 1957.
452 pp.
294. Greenburg, L., C. Erhardt, F. Field, J. I. Reed, and N. S. Seriff.
Intermittent air pollution episode in New York City, 1962.
Public Health Rep, 78:1061-1064, 1963.
472
-------
,295. Greenburg, L., F. Field, C. L. Erhardt, M. Glasser, and J. I. Reed.
Air pollution, influenza, and mortality in New York City,
January-February 1963. Arch. Environ. Health 15:430-438, 1967.
296. Greenburg, L., F. Field, J. I, Reed, and C. L. Erhardt. Air
pollution and morbidity in New York City. J.A.M.A. 182:
161-164, 1962.
297. Greenburg, L., M. B. Jacobs, B. M. Drolette, F. Field, and
M. M. Braverman. Report of an air pollution incident in
New York City, November 1953. Public Health Rep. 77:7-16, 1962.
298. Gross, P., and H. Brieger. Silicotic bronchiolitis obliterans—
a focal clearance failure, pp. 105-110. In C. N. Davies, Ed.
Inhaled Particles and Vapours II. Proceedings of an Inter-
national Symposium organized by the British Occupational
Hygiene Society, Cambridge, 28 September-1 October 1965.
Oxford: Pergamon Press, 1967.
299. Gudbjerg, C. E., and G. Thomsen. Inflammatory changes in the
bronchial glands in chronic bronchitis. Acta Radiol. 42:
269-275, 1954.
300. Guderian, R. Kurzberichte: H. Pajenkamp. Einwirkung des
Zementofenstaubes auf Pflanzen und Tiere. Staub 21:518-519,
1961.
301. Gupton, E. D., and P. E. Brown. Chest clearance of inhaled cobalt-60
oxide. Health Phys. 23:767-769, 1972.
473
-------
302. Guttman, H. Effects of atmospheric factors on the corrosion of
rolled zinc, pp. 223-239. In Metal Corrosion in the Atmosphere.
A Symposium presented at the Seventieth Annual Meeting,
American Society for Testing and Materials, Boston, Mass.,
25-30 June, 1967. ASTM Special Technical Publication No. 435.
Philadelphia: American Society for Testing and Materials, 1968.
303. Guttman, H., and E. V. Gibbons. Corrosion Behavior of Metal-Coated
Panels at Eight Canadian Locations: Summary of a Fourteen-Year
Program. Division of Building Research Technical Paper 354.
Ottawa: National Research Council of Canada, 1971.
304. Haagen-Smit, A. J., M. F. Brunelle, and J. W. Haagen-Smit. Ozone
cracking in the Los Angeles area. Rubber Chem. Technol.
32:1134-1142, 1959.
305. Hadfield, E. H. Damage to human nasal mucosa by wood dust,
pp. 855-861. In W. H. Walton, Ed. Inhaled Particles III,
Vol.- II. Proceedings of an International Symposium
organized by the British Occupational Hygiene Society in
London, 14-23 September, 1970. Old Woking, Surrey, England:
Unwin Brothers Limited, 1971.
306. Haenszel, W. Cancer mortality among the foreign-born in the
United States. J. Nat. Cancer Inst. 26:37-132, 1961.
474
-------
307. Haenszel, W., D. B. Loveland, and M. G. Sirken. Lung-cancer
mortality as related to residence and smoking histories.
I. White mal"s. J. Nat. Cancer Inst. 28:947-1001, 1962
>308. Haenszel, W., and K. E. Taeuber, Lung-cancer mortality as
related to residence and smoking histories. II. White
females. J. Nat. Cancer Inst. 32:803-838, 1964.
309. Hagen, L. J., and N. P. Woodruff. Air pollution from duststonns in
the Great Plains. Atmos. Environ. 7:323-332, 1973.
310. Hall, T. C., Jr. Photochemical Studies of Nitrogen-dioxide and
Sulfur-dioxide. (Ph.D. thesis; University of California/
Los Angeles, 1954)
311. Hamada, M., R. Fujikawa, C. Itakura, K. Kishitani, M. Koike,
E. Tajima, and others. Durability of Asphaltic Materials.
Parts 1-5. Division of Building Research Technical Trans-
lation 1146. (Translated by H. J. Kondo from Proc. Architect.
Inst. Jap. 69: 53-72, 1961) Ottawa: National Research
Council of Canada, 1964. 57 pp.
312. Hammond, E. C. Smoking in relation to death rates of one million
men and women. Nat. Cancer Inst. Monogr. 19:127-204, 1966.
313. Hammond, E. C., and D. Horn. The relationship between human
smoking habits and death rates: A follow-up study of
187,766 men. J.A.M.A. 155U316-1328, 1954.
475
-------
314. Hammond, E. C., and D. Horn. Smoking and death rates—report on
forty-four months of follow-up of 187,783 men. II. Death rates
by cause. J.A.M.A. 166:1294-1308, 1958.
315. Hanel, G. New results concerning the dependence of visibility on
relative humidity and their significance in a model for
visibility forecast. Beitr. Phys. Atmos. 44:137-167, 1971.
ii
316. Hanel, G. Computation of the extinction of visible radiation by
atmospheric aerosol particles as a function of the relative
humidity, based upon measured properties. Aerosol Sci. 3:
377-386, 1972.
ii
317. Hanel, G. The ratio of the extinction coefficient to the mass of
atmospheric aerosol particles as a function of the relative
humidity. Aerosol Sci. 3:455-460, 1972.
318. Harrison, P. R. , W. R. Matson, and J. W. Winchester. Time
variations of lead, copper and cadmium concentrations in
aerosols in Ann Arbor, Michigan. Atmos. Environ. 5:613-619,
1971.
319. Hatch, T. F., and P. Gross. Pulmonary Deposition and Retention of
Inhaled Aerosols. New York: Academic Press, 1964. 192 pp.
476
-------
,320. Hayes, C. G., D. I. Hammer, C. M. Shy, V. Hasselblad, C. R. Sharp,
) J. P. Creason, and K. E. McClain. Prevalence of chronic
respiratory disease symptoms i; adults: 1970 survey of five
Rocky Mountain communities, pp. 3-19 to 3-33. In U.S.
Environmental Protection Agenc^ , Office of Research and
Development. Health Consequences of Sulfur Oxides: A Report
from CHESS, 1970-1971. EPA-650/1-74-004. Washington, DC:
U.S. Government Printing Office, 1974.
321. Haynie, F. H., and J. B. Upham. Effects of atmospheric sulfur dioxide
on the corrosion of zinc. Mater. Prot. Perform. 9(8):35-40, 1970.
322. Haynie, F. H., and J. B. Upham. Effects of atmospheric pollutants on
corrosion behavior of steels. Mater. Prot. Perform. 10:18-21, 1971.
323. Heinsohn, R. J., C. Birnie, Jr., and T. A. Cuscino. Fugitive Dust
from Vehicles using Unpaved Roads. Center for Air Environment
Studies (CAES) Publication No. 419-75. University Park, PA:
The Pennsylvania State University, 1975. 29 pp.
324. Hermance, H. W. Combatting the effects of smog on wire-spring
relays. Bell Lab. Rec. 44:48-52, 1966.
325. Hewitt, D. Mortality in the London boroughs, 1950-52, with special
reference to respiratory disease. Brit. J. Prev. Soc. Med. 10:
45-57, 1956.
477
-------
326. Heyder, J., L. Annbruster, J. Gebhart, and W. Stahlhofen.
Depositon of aerosol particles in the human respiratory tract,
pp. 122-125. In V. Bohlau, Ed. Aerosole in Physik, Medizin
it
und Technik. Bad Soden, West Germany: Gesellschaft fur
Aerosolforschung, 1973.
327. Heyder, J., J. Gebhart, G. Heigwer, C. Roth, and W. Stahlhofen.
Experimental studies of the total deposition of aerosol
particles in the human respiratory tract. Aerosol Sci. 4:
191-208, 1973.
328. Hidy, G. M., Ed. Aerosols and Atmospheric Chemistry. Proceedings
of the American Chemical Society. Los Angeles, California,
March 28-April 2, 1971. New York: Academic Press, 1972. 348 pp.
329. Hidy, G. M. Some aspects of airborne particles and radiation
in the atmosphere, pp. 1286-1298. In 0. F. Nygaard,
H. I, Adler, and W. K. Sinclair, Eds. Radiation Research.
Biomedical, Chemical, and Physical Perspectives. Pro-
ceedings of the Fifth International Congress of Radiation
Research, Seattle, Washington, July 14-20, 1974. New
York: Academic Press, 1975.
478
-------
330. Hidy, G. M. , B. Appel, R. J. Charlson, W. E. Clark, D. Covert
D. DockweiLer, S. K. Friedlander, P, Friedman, R. Giauque,
S. Green, 3. Heisler, W. W. Ho, J. J. Huntzicker, R. B.
Husar, K.. Rubier, G. Lauer, P. K. M.jeller, T. Novakov,
R. Ragaini, L. W. Richards, T. B. Smith, E. R. Stephens,
G. Sverdrup, S. Twiss, A. Waggoner, S. Wall, H. H. Wang,
J. J. WesoJowski, K. T. Whitby, and W. White. Character-
ization of Aerosols in California (ACHEX). Final Report,
Vol. I - IV. Submitted to the Air Resources Board, State
of California, Sept. 30, 1974.
331. Hidy, G. M., B. R. Appel, R. J. Charlson, W. E. Clark,
S. K. Friedlander, D. H. Hutchison, T. B. Smith, J. Suder,
J. J. WesoJowski, and K. T. Whitby. Summary of the California
aerosol characterization experiment. J. Air Pollut. Control
Assoc. 25:1106-1114, 1975.
332. Hidy, G. M., and J. R. Brock. The Dynamics of Aerocolloidal
Systems. New York: Pergamon Press, 1970. 379 pp.
333. Hidy, G. M., and J. R. Brock. An assessment of the global sources
of tropospheric aerosols, pp. 1088-1097. In H. M. Englund and
W. T. Beery, Eds. Proceedings of the Second International
Clean Air Congress. Held at Washington, D.C., December 6-11,
1970. New York: Academic Press, 1971.
334. Higgins, I. T. T. Sulfur oxides and particulates, pp. 20-33.
In Medical Aspects of Air Pollution. A Continuing
Engineering Education Course developed by SAE Engineering
Education Activity. Detroit, Michigan, January 14, 1971.
New York: Society of Automotive Engineers, Inc., 1971.
479
-------
335. Higgins, I. T. T. Trends in respiratory cancer mortality in the
United States and in England and Wales. Arch. Environ. Health
28:121-129, 1974.
336. Higgins, I. T. T. Epidemiologies! evidence on the carcinogenic risk
of air pollution, pp. 41-52. In C. Rosenfeld and W. Davis, Eds.
Environmental Pollution and Carcinogenic Risks. INSERM Symposium
Series Vol. 52. IARC Scientific Publications 13. Paris: INSERM
(Institut National de la Sante et de la Recherche Medicale), 1976.
337. Hilding, A. C. On cigarette smoking, bronchial carcinoma and
ciliary action. II. Experimental study on the filtering
action of cow's lungs, the deposition of tar in the bronchial
tree and removal by ciliary action. New Eng. J. Med. 254 :
1155-1160, 1956.
338. Hilding, A. C. Ciliary streaming in the lower respiratory tract.
Amer. J. Physiol. 191:404-410, 1957.
339. Hilding, A. C. Experimental studies on some little understood
aspects of the physiology of the respiratory tract and
their clinical importance. Trans. Amer. Acad. Ophthal.
Otolaryng. 65:475-495, 1961.
340. Hindawi, I. J., and H. C. Ratsch. Growth Abnormalities of Christmas
Trees Attributed to Sulfur Dioxide and Particulate Acid Aerosol.
ACPA Paper No. 74-252, presented at the Mr Pollution Control
Association meeting at Denver, Colorado, June 9-13, 1974.
480
-------
341. Hinton, D. 0., T. D. English, B. F. Parr, V. Hasselblad,
R. C. Dickerson, and J. G. French. Human exposure to air
pollutants in the Chicago-Northwest Indiana metropolitan
region, 1950-1971, pp. 4-3 to 4-21. In U.S. Environmental
Protection Agency, Office of Research and Development.
Health Consequences of Sulfur Oxides: A Report from CHESS,
1970-1971. EPA-650/1-74-004. Washington, DC: U.S. Govern-
ment Printing Office, 1974.
342. Hirayama, T. Smoking in Relation to the Death Rates of •
, 265,118 Men and Women in Japan. A Report of Five Years of
Follow-up. Presented at the American Cancer Society's
Fourteenth Science Writers' Seminafr, March 24-29, Clearwater
Beach, FL, 1972. 15 pp.
343. Hitosugi, M. Epidemiological study of lung cancer with special
reference to the effect of air pollution and smoking habits.
Inst. Pub. Health Bull. 17:237-256, 1968.
344. Ho, W., G. M. Hidy, and R. M. Govan. Microwave measurements of
the liquid water content of atmospheric aerosols.
J. Appl. Meteorol. 13:871-879, 1974.
345. Hobbs, P. V. Comparison of ice nucleus concentrations measured with
an acoustical counter and Millipore filters. J. Appl. Meteorol.
9:828-829, 1970.
346. Hobbs, P. V., and J. P. Locatell. Ice nuclei from a natural
forest fire. J. Appl. Meteorol. 8:833-834, 1969.
481
-------
347. Hobbs, P. V., and L. F. Radke. Cloud condensation nuclei from
a simulated forest fire. Science 163:279-280, 1967.
348. Hobbs, P. V., L. F. Radke, and S. E. Shumway. Cloud condensation
nuclei from inuustrial sources and their apparent influence on
precipitation in Washington State. J. Atmos. Sci. 27:81-89, 1970.
349. Hocking, L. M., and P. R. Jonas. The collision efficiency of
small drops. Q. J. Roy. Meteorol. Soc. 96:722-729, 1970.
350. Hodge, P. W. Large decrease in the clean air transmission of
the air 1.7 km above Los Angeles. Nature 229:549, 1971.
351. Hodge, P. W., N. Laulainen, and R. J. Charlson. Astronomy and
air pollution. Science 178:1123-1124, 1972. .
352. Hodgson, T. A., Jr. Short-term effects of air pollution on
mortality in New York City. Environ. Sci. Technol. 4:589-
597, 1970.
353. Hoffman, A. J. , T. C. Curran, T. B. McMullen, W. M. Cox, and
W. F. Hunt, Jr. EPA's role in ambient air quality monitoring.
Science 190:243-248, 1975.
354. Hogan, A. W. Antarctic aerosols. J. Appl. Meteorol. 14:550-559, 1975.
355. Holbrow, G. L. Atmospheric pollution: Its measurement and some
effects on paint. J. Oil Colour Chem. Assoo. 45:701-718, 1962,
482
-------
356. Holland, A. C., and G. Gagne. The scattering of polarized light b\
polydisperse systems of irregular particles. Appl. Opt. 9:111
1121, 1970.
357. Holland, W. W., T. Halil, A. E. Bennett, and A. Elliott. Factors
influencing the onset of chronic respiratory disease.
Brit. Med. J. 2:205-208, 1969.
358. Holland, W. W., and D. D. Reid. The urban factor in chronic
bronchitis. Lancet 1:445-448, 1965.
359. Holland, W. W., D. D. Reid, R. Seltser, and R. W. Stone.
Respiratory disease in England and the United States. Studies
of comparative prevalence. Arch. Environ. Health 10:338-343, 1965,
360. Holzworth, G. C. Some effects of air pollution on visibility
in and near cities, pp. 69-88. In Public Health Service,
Robert A. Taft Sanitary Engineering Center. Symposium.
Air Over Cities. Held November 6-7, 1961, Cincinnati,
Ohio. SEC Technical Report A62-5. Washington, D.C.:
U.S. Government Printing Office, 1962.
/
361. Hoorn, B., and D. A, J. Tyrrel. A new virus cultivated in organ
cultures of hunan ciliated epithelium. Arch. Ges. Virusforsch.
18:210-225, 1966.
362. Horsfield, K., G. Dart, D. E. Olson, F. F. Filley, and G. Gumming.
Models of the human bronchial tree. J. Appl. Physiol.
31:207-217, 1971.
483
-------
363. Horvath, H. On the brown color of atmospheric haze.
Atmos. Environ. 5:333-344, 1971.
364. Horvath, H., and K. E. Noll. The relationship between atmospheric
light scattering coefficient and visibility. Atmos. Environ.
3:543-550, 1969.
365. Hosking, E. S, Effects of Air Pollution on the Abrasion Resistance
of Selected Fabrics. M. S. Thesis. Los Angeles: Loma Linda
University, 1970. 61 pp.
366. Hounam, R. F., A. Black, and M. Walsh. Deposition of aerosol
particles in the nasopharyngeal region of the human respiratory
tract. Nature 221:1254-1255, 1969.
367. House, D. E., J. F. Finklea, C. M. Shy, D. C. Calafiore, W. B. Rlggan,
J. W. Southwick, and L. J. Olsen. Prevalence of chronic
respiratory disease symptoms in adults: 1970 survey of Salt
Lake Basin communities, pp. 2-41 to 2-54. In U.S. Environmental
Protection Agency, Office of Research and Development. Health
Consequences of Sulfur Oxides: A Report from CHESS, 1970-1971.
EPA-650/1-74-004. Washington, DC: U.S. Government Printing
Office, 1974.
368. Howell, W. E. The growth of cloud drops in uniformly cooled air.
J. Meteorol. 6:134-149, 1949.
369. Huff, F. A., and S. A. Changnon. Precipitation modification by
major urban areas. Bull. Amer. Meteorolog. Soc. 54:1220-1232,
1973.
484
-------
370. Hukui, S., and A. Yamamoto. Studies OK the corrosion of metallic
materials by polluted air. Netsu ivanri (Heat Management,
Energy and Pollution Control) 21(6):28-44, 1969. (in Japanese)
371. Husar, R. B. Coagulation of Rnudsen Aerosols. (Ph.D. thesis;
University of Minnesota, 1971. 212 pp.)
372. Husar, R. B., N. V. Gillani, J. D. Husar, and D. E. Patterson.
A Study of Long Range Transport from Visibility Observations,
Trajectory Analysis and Local Air Pollution Monitoring Data.
Presented at the 7th International Technical Meeting on
Air Pollution Modeling and its Application, NATO Committee on
the Challenges of Modern Society. Held September 7-10, 1976
in Airlie, Virginia.
373. Husar, R. B., K. T. Whitby, and B. Y. H. Liu. Physical mechanisms
governing the dynamics of Los Angeles smog aerosol. J. Colloid
Interface Sci. 39:211-224, 1972.
374. Husar, R. B., and W. H. White. On the color of the Los Angeles smog.
Atmos. Environ. 10:199-204, 1976.
375. Huschke, R. E., Ed. Glossary of Meteorology. Boston: American
Meteorology Society, 1959. 638 pp.
376. IIT Research Institute. Particle Technology 1973. Proceedings
of the First International Conference in Particle Technology.
August 21-24, 1973, Chicago. Chicago: IIT Research
Institute, 1973. 328 pp.
485
-------
377. Inadvertent Climate Modification. Report of the Study of Man's
Impact on Climate (SM1C). Cambridge: The MIT Press, 1971.
308 pp.
378. International Conference on Environmental Sensing and Assessment.
Las Vegas, Nevada, September 14-19, 1975. New York: Institute
of Electrical and Electronics Engineers, 1976.
379. Ipsen, J., M. Deane, and F. E. Ingenito. Relationships of acute
respiratory disease to atmospheric pollution and meteorological
conditions. Arch. Environ. Health 18:462-472, 1969.
380. Iravani, J. Clearance function of the respiratory ciliated
epithelium in normal and bronchitic rats, pp. 143-146.
In W. H. Walton, Ed. Inhaled Particles III, Vol. I.
Proceedings of an International Symposium organized by
the British Occupational Hygiene Society in London,
14-23 September, 1970. Old Woking, Surrey, England:
Unwin Brothers Limited, 1971.
381. Iravani, J., and A. Van As. Mucus transport in the tracheobronchial
tree of normal and bronchitic rats. J. Path. 106:81-93, 1972.
382. Jaenicke, R., and C. Junge. Studien zur oberen Grenzgrosse des
naturlichen Aerosoles. Beitr. Phys. Atmos. 40:129-143, 1967.
486
-------
383. Jaenie.e, R. , C. Junge, and H. J. Kanter. Messungen der
«erosolgr8s.senverteilung liber dem Atlantik. "Meteor"
Forschungse-gebnisse , Reihe B. 7:1-54, 1971.
Jammet, H. , J. Lafuma, J. C. Nenot, M. Chameaud, M. Perreau,
M. LeBouffant, M. Lefevre, and M. Martin. Lung clearance:
Silicosis and anthracosis, pp. 435-437. In H. A. Shapiro, Ed.
Pneumoconiosis . Proceedings of the International Conference,
Johannesburg, 1969. Capetown: Oxford University Press, 1970.
385. Jeffery, P., and L. Reid. Intra-epithelial nerves in normal rat
airways: A quantitative electron microscopic study.
J. Anat. 114:35-45, 1973.
386. Jellinek, H. H. G. Chain scission of polymers by small concentrations
(1 to 5 ppm) of sulfur dioxide and nitrogen dioxide, respectively,
in presence of air and near ultraviolet radiation. J. Air Pollut.
Control Assoc. 20:672-674, 1970.
387. Jellinek, H. H. G., and J. F. Kryman. Photolytic oxidation of
isotactic polystyrene in presence of sulfur dioxide.
Part I. Chain scission as function of temperature at constant
oxygen and sulfur dioxide pressures and constant light intensity,
pp. 85-90. In R. F. Reinisch, Ed. Photochemistry of Macromolecules
Proceedings of a Symposium held at the Pacific Conference on
Chemistry and Spectroscopy, Anaheim, California, October 8-9, 1969.
New York: Plenum Press, 1970.
487
-------
388. Jellinek, H. H. G., and J. Pavlinec. Photolytic oxidation of
isotactic polystyrene in presence of sulfur dioxide.
Part II. Photolysis reaction as function of light _utensity,
sulfur dioxide and oxygen pressures, pp. 91-104.
In R. F. Reinisch, Ed. Photochemistry of Macromol-cules.
Proceedings of a Symposium held at the Pacific Conference on
Chemistry and Spectroscopy, Anaheim, California, October 8-9,
1969. New York: Plenum Press, 1970.
389. Jennings, 0. E. Smoke injury to shade trees, pp. 44-48. In
R. P. White, Ed. Tenth Annual Shade Tree Conference.
Proceedings of Annual Meeting, Pittsburgh, August 30-31, 1934.
390. Jiusto, J. E. Aerosril and cloud microphysics measurements in Hawaii.
Tellus 19:359-368, 1973.
391. John, W. Contact electrification applied to particulate matter-
monitoring, pp. 649-667. In B. Y. H. Liu, Ed. Fine Particles.
Aerosol Generation, Measurement, Sampling, and Analysis.
Proceedings of a Symposium by the U.S. Environmental Protection
Agency held in Minneapolis, Minnesota, May 28-30, 1975.
New York: Academic Press, Inc., 1976.
392. Johnstone, H. F., and D. R. Coughanowr. Absorption of sulfur
dioxide from air: Oxidation in drops containing dissolved
catalysts. Ind. Eng. Chem. 50:1169-1172, 1958.
393. Johnstone, H. F., and A. J. Moll. Formation of sulfuric acid in
fogs. Ind. Eng. Chem. 52:861-863, 1960.
488
-------
394. Jonsson, B., and R. Sundberg. Has the Acidification by Atmospheric
Pollution Causad a Growth Reduction in Swedish Forests? A
Comparison of 3rowth between Regions with Different Soil
Properties. Research Note 20. Stockholm: Royal College
of Forestry, Department of Forest Yield Research, 1972.
(in Swedish with summary in English)
395. Joseph, J. H., and A. Manes. Secular and seasonal variations of
atmospheric turbidity at Jerusalem. J. Appl. Meteorol. 10:
453-462, 1971.
396. Judge, J. Venice fights for life. Nat. Geographic 142:591-631, 1972.
397. Junge, C. Die Konstitution der atmospharischen Aerosole.
Ann. Meteorol. 5 (Beiheft) :l-55, 1952.
398. Junge, C. Die Rolle der Aerosole und der gasfHrmigen Beimengungen
it
der Luft im Spurenstoffhaushalt der Troposphare. Tellus 5:1-26,
1953.
399. Junge, C. The size distribution and aging of natural aerosols as
determined from electric and optical data on the atmosphere.
Amer. Meteor. Soc. J. Meteor. 12:lJ3-25, 1955.
/
400. Junge, C. E. The chemical composition of atmospheric aerosols,
I: Measurements at Round Hill Field Station, June-July
1953. J. Meteorol. 11:323-333, 1954.
489
-------
401. Junge, C. E. Vertical profiles of condensation nuclei in the
stratosphere. Amer. Meteor. Soc. J. Meteor. 18:501-509, 1961.
402. Junge, C. E. Air Chemistry and Radioactivity. New York:
Academic Press, 196 j. 382 pp.
403. Junge, C. E. Our knowledge of the physico-chemistry of aerosols In
the undisturbed marine environment. J. Geophys. Res. 77:5183-
5200, 1972.
404. Junge, C. E., and T. G. Ryan. Study of the S02 oxidation in solution
and its role in atmospheric chemistry. Q. J. Roy. Meteorol. Soc.
84:46-56, 1958.
405. Karuhn, R. F. The development of a new acoustic particle counter
for particle size analysis, pp. 202-207. In IIT Research
Institute. Particle Technology 1973. Proceedings of the
First Internaitonal Conference in Particle Technology.
August 21-24, 1973, Chicago. Chicago: IIT Research Institute,
1973.
406. Katz, M. Photoelectric determination of atmospheric sulfur
dioxide, employing dilute starch-iodine solutions.
Anal. Chem. 22:1040-1047, 1950.
490
-------
,407. Katz, M., and S. B. Gale. Mechanism of photooxidation of sulfur
dioxide in atmosphere, pp. 336-343. in H. M. Englund and
W. T. Beery, Eds. Proceedings of the Second International
Clean Air Congress, Held at Washington, D.C., December 6-11,
1970. Sponsored by The International Union of Air Pollution
Prevention Associations. New York: Academic Press, 1971.
408. Keimowitz, R. I. Immunoglobulins in normal human tracheobronchial
washings. A qualitative and quantitative study. J. Lab.
Clin. Med. 63:54-59, 1964.
409. Reiser-Nielsen, H. Mucin. Copenhagen: Dansk Videnskabs Forlag,
1953. 307 pp. (in Danish)
410. Keith, C. H., and A. B. Arons. The growth of sea-salt particles
by condensation of atmospheric water vapor. J. Meteorol.
11:173-184, 1954.
411. Kelsey, J. L., E. W. Mood, and R. M. Acheson. Population mobility and
epidemiology of chronic bronchitis in Connecticut. Arch. Environ.
Health 16:853-861, 1968.
412. Kensler, C. J., and S. P. Battista. Chemical and physical
factors affecting mammalian ciliary activity. Amer. Rev.
Resp. Dis. 93: (Suppl. - Symposium on Structure, Function
and Measurement of Respiratory Cilia. Duke University Medical
Center, Durham, North Carolina, February 18-19, 1965):93-102,
1966.
491
-------
413. Kertesz-Sa'ringer, M. , E. Mcszaros, and T. Varkonyi. On the
size distribution of bar,ao(a)pyrene containing particles in
urban air. Atmos. Environ. 5:429-431, 1971.
>
414. Kilburn, K. H. Mucociliary clearance from bullfrog (Rana
cantesbiana) lung. J. Appl. Physiol. 23:804-810, 1967.
415. Kilburn, K. H. A hypothesis for pulmonary clearance and its
implications. Amer. Rev. Resp. Dis. 98:449-463, 1968
416. King, M., A. Gilboa, F. A. Meyer, and A. Silberberg. On the
transport of mucus and its rheologic simulants in ciliated
systems. Amer. Rev. Resp. Dis. 110:740-745, 1974.
417. Kloke, A., and K. Riebartsch. Verunreinigung von Kulturpflanzen
mit Blei aus Kraftfahrzeugabgasen. Naturwissenschaften 51:
367-368, 1964.
418. Kocmond, W. C., W. D. Garrett, and E. J. Mack. Modification of
laboratory fog with organic surface films. J. Geophys. Res.
77:3221-3231, 1972
419. Kocmond, W. C., D. B. Kittelson, J. Y. Yang, and K. L. Demerjian.
Determination of the Formation Mechanisms and Composition of
Photochemical Aerosols. Annual Summary Report (Final).
Prepared for the Environmental Protection Agency under
Contract EPA-68-02-0557, 1973.
420. Kocmond, W. C., and E. J. Mack. The vertical distribution of
cloud and Aitken nuclei downwind of urban pollution sources.
J. Appl. Meteorol. 11:141-148, 1972.
492
-------
421. Koenig, L. R. Some observations suggesting ice multiplication
in the atmosphere. J. Atmos. Sci. 25:460-463, 1968.
422. Kondratyev, K. Ya. The Complete Atmospheric Energetics Experiments.
Global Atmospheric Research Programme (GARP) Publication Series
No. 12. Geneva: World Meteorological Organization, 1973.
43 pp.
423. Koschmieder, H. Theorie der horizontalen Sichtweite.
Beitr. Phys. Freien Atmos. 12:33-55, 1925.
424. Koschmieder. H. Theorie der horizontalen Sichtweite II: Kontrast
und Sichtweite. Beitr. Phys. Freien Atmos. 12:171-181, 1925.
i i
425. Kotrappa, P., and M. E. Light. Design and performance of the
Lovelace aerosol particle separator. Rev. Sci. Instrum. 43:1106-
1112, 1972.
426. Krahl, V. E., and M. H. Bulmash. Studies on living ciliated
epithelium. Amer. Rev. Resp. Dis. 99:711-718, 1969.
427. Kratky, B. A., E. T. Fukunaga, J. W. Hylin, and R. T. Nakano.
Volcanic air pollution: Deleterious effects on tomatoes.
J. Environ. Quality 3:138-140, 1974.
428. LaBelle, C. W., and H. Brieger. Synergistic effects of aerosols.
II. Effects on rate of clearance from lung. A.M.A. Arch. Ind.
Health 20:100-105, 1959.
493
-------
429. LaBelle, C. W., J. E. Long, and E. L, CrLstofano. Synergistic
effects of aerosols. Particaiates as carriers of toxic
vapors. Arch. Ind. Healtn ll:297-:k;4, 1955,
430. Lamb, D., and L. Reid. Histochemical types of acidic glycoprotein
produced by mucous cells of the tracheobronchial glands in man.
J. Path. 98:213-229, 1969.
431. Lamb, D., and L. Reid. The tracheobronchial submucosal glands in
cystic fibrosis: A qualitative and quantitative histochemical
study. Brit. J. Dis. Chest 66:239-247, 1972.
432. Lambert, P. M., and D. D. Reid. Smoking, air pollution, and
bronchitis in Britain. Lancet 1:853-857, 1970.
433. Landahl, H. D. On the removal of air-borne droplets by the
human respiratory tract: I. The lung. Bull. Math.
Biophys. 12:43-56, 1950.
434. Landahl, H. D. Particle removal by the respiratory system. Note
on the removal of airborne particulates by the human respiratory
tract with particular reference to the role of diffusion.
Bull. Math. Biophys. 25:29-39, 1963.
435. Landahl, H. D., T. N. Tracewell, and W. H. Lassen. On the retention
of air-borne particulates in the human lung: II. A.M.A. Arch.
Ind. Hyg. Occup. Med. 3:359-366, 1951.
436. Landahl, H. D., T. N. Tracqwell, and W. H. Lassen. Retention of
air-borne particulates in the human lung: III. A.M.A. Arch.
Ind. Hyg. Occup. Med. 6:508-511, 1952.
494
-------
437. Landsberg, H. E. The climate of towns, pp. 584-606. In
W. L. Thomas, Jr., Ed. Man's Role in Changing the Face of
the Earth. Chicago: University of Chi:ago Press, 1956.
43g Lapp, N. L., J. L. Hankinson, H. Amandus, and E. D. Palmes.
Variability in the size of airspaces in normal human lungs as
estimated by aerosols. Thorax 30:293-299, 1975.
439. Lapp, N. L., and A. Seaton. Lung mechanics in coal workers'
pneumoconiosis. Ann. N. Y. Acad. Sci. 200:433-454, 1972.
440. Larson, T. V., D. S. Covert, R. Frank, and R. J. Charlson.
Ammonia in the human airways: Neutralization of inspired
acid sulfate aerosols. Science 197:161-163, 1977.
441. Laurenzi, G. A., S. Yin, and J. J. Guarneri. Adverse effect of
oxygen on tracheal mucus flow. New Eng. J. Med. 279:333-
339, 1968.
442. Lave, L. B., and E. P. Seskin. Air pollution and human health.
The quantitative effect, with an estimate of the dollar
benefit of pollution abatement, is considered. Science
169:723-733, U70.
443. Lave, L. B., and F. P. Seskin. Air pollution, climate, and home
heating: Their effects on U.S. mortality rates. Amer. J.
Public Health 62:909-916, 1972.
444. Lawther, P. J. Effects of inhalation of sulphur dioxide on
respiration and pulse-rate in normal subjects. Lancet 2:
745-748, 1955.
495
-------
445. Lawther, P. J. Climate, air pollution and chronic bronchitis.
Proc. Roy. Soc. Med. 51:262-266, 1958.
446. Lawther, P. J. Compliance with the Clean Air Act: Medical
. aspects. J. Inst. F el 36:341-344, 1963.
447. Lawther, P. J., A. G. F. Brooks, P. W. Lord, and R. E. Waller.
Day-to-day changes in ventilatory function in relation to the
environment. Part I. Spirometric values. Environ. Res. 7:
27-40, 1974.
448. Lawther, P. J., A. G. F. Brooks, P. W. Lord, and R. E. Waller.
Day-to-day changes in ventilatory function in relation to
the environment. Part II. Peak expiratory flow values.
Environ. Res. 7:41-53, 1974.
449. Lawther, P. J., A. G. F. Brooks, P. W. Lord, and R. E. Waller.
Day-to-day changes in ventilatory function in relation to the
environment. Part III. Frequent measurements of peak flow.
Environ. Res. 8:119-130, 1974.
450. Lawther, P. J., R. E. Waller, and M. Henderson. Air pollution
and exacerbations of bronchitis. Thorax 25:525-539, 1970.
451. Lawther, P. J., R. E. Waller, and A. E. Martin. Clean air and
health in London, pp. 71-78. In National Society for Clean
Air. Clean Air Conference, Eastbourne, 21-24 October 1969.
Part 1, Pre-prints of Papers. London: Spottiswoode, Ballantyne
and Co. Ltd., 1969.
496
-------
452. Le Bouffant, L. Influence de la nature des poussieres et de la
charge pulmonaire sur 1'epuration, pp. 227-237. In
W. H. Walton, Ed. Inhaled Particles III, Vol. I. Proceedings
of an International Symposium organized by the British
Occupational Hygiene Society in London, 14-23 September, 1970.
Old Woking, Surrey: Unwin Brothers, Ltd., 1971.
453. Lebowitz, M. D. , P. Bendheim, G. Cristea, D. Markovitz,
J. Misiaszek, M. Staniec, and D. Van Wyck. The effect of
air pollution and weather on lung function in exercising
children and adolescents. Amer. Rev. Resp. Dis . 109:262-
273, 1974.
454. Lecrenier, A., and G. Piquer. Essais sur 1'action des poussieres
de cimenterie sur la vegetation. Bull. Hort. 74:56-58, 1956.
455. Lee, R. E. , Jr. The size of suspended particulate matter in air.
Science 178:567-575, 1972.
456. l&e, R. E., Jr., S. S. Goranson, R. E. Enrione, and G. B. Morgan.
National Air Surveillance cascade impactor network. II. Size
distribution measurements of trace metal components. Environ.
Sci. Technol. 6:1025-1030, 1972.
457. Lee, R. E. , Jr., R. K. Patterson, and J. Wagman. Particle-size
distribution of metal components in urban air. Environ. Sci.
Technol. 2:288-290, 1968.
458. Leh, H. 0. Verunreinigungen von Kulturpf lanzen mit Blei aus
Kraftfahrzeugabgasen. Ges. Pflanzen 18:21-24, 1966.
497
-------
459. Leonov, L. F., P. S. Prokhorov, T. A. Efanova, and I. A. Zolotarev.
Passivation of condensation nuclei by cetyl alcohol vapor,
pp. 12-20. In V. A. Fedoseev, Ed. Advances in Aerosol Physics.
No. 2. New York: Halsted Press, 1972.
460. Lennan, S. Cement-Kiln Dust and the Bean Plant (Phaseolus
vulgaris L. Black Valentine var.); In-depth Investigations
into Plant Morphology, Physiology and Pathology.
Ph.D. thesis, University of California, Riverside, 1972.
461. Lerman, S. L., and Darley, E. F. Participates, pp. 141-158.
In J. B. Mudd and T. T. Kozlowski, Eds. Responses of
Plants to Air Pollution. New York: Academic Press, 1975.
462. Levy, H., II. Normal atmosphere: Large radical and formaldehyde
concentrations predicted. Science 173:141-143, 1971.
463. Lewis, T. R. , W. J. Moorman, W. F. Ludmann, and K. I. Campbell.
Toxicity of long-term exposure to oxides of sulfur. Arch.
Environ. Health 26:16-21, 1973.
464. Liebow, A. A. Aspects of transcapillary fluid and protein
exchange in the lung, pp. 99-112. In A. P. Fishman and
H. H. Hecht, Eds. The Pulmonary Circulation and Interstitial
Space. Chicago: The University of Chicago Press, 1969.
465. Lightbody, A., M. E. Roberts, and C. J. Wessel. Plastics and rubber,
pp. 537-595. In G. A. Greathouse and C. J. Wessel, Eds.
Deterioration of Materials. Causes and Preventive Techniques.
New York: Reinhold Publishing Corporation, 1954.
498
-------
466. Likens, G. E., and F. H. borraann. Acid raan. A serious regional
environmental problem. Science 184 : 1J/ ij-1179 , 1974.
467. Lin, C., M. Baker, and R. J. Charlson. Absorption coefficient of
atmospheric aerosol: A method for measurement. Appl. Opt. 12:
1356-1363, 1973.
468. Lindberg, J. D., and L. S. Laude. Measurerne.it of the absorption
coefficient of atmospheric dust. Appl. Opt. 13:1923-1927, 1974,
469. Lippmann, M. Deposition and clearance of inhaled particles in
the human nose. Ann. Otol. Rhinol. Larvngol. 79:519-528, 1970,
470. Lippmann, M. "Respirable" dust sampling, Amer, Ind. Hyg. Assoc. J.
31:138-159, 1970.
471. Lippmann, M. Regional deposition of particles in the human
respiratory tract, pp. 213-232. In D. H. K. Lee, H. L. Falk,
and S. D. Murphy, Eds. Handbook of Physiology, Section 9:
Reactions to Environmental Agents. Bethesda, MD: The
American Physiological Society, 1977.
472. Lippmann, M., and R. E. Albert. The effect of particle size on
the regional deposition of inhaled aero:,ol:> in the human
respiratory tract. Amer. Ind. Hyg. Assoc. J. 30:257-275, 1969.
473. Lippmann, M., R. E. Albert, and H. T. Peterson, Jr. The regional
deposition of inhaled aerosols in man, pp. 105-120. In
W. H. Walton, Ed. Inhaled Particles III, Vol. I. Proceedings
of an International Symposium organized by the British
Occupational Hygiene Society in London, 14-23 September, 1970.
Old Wokin;1,, Surrey: Unwin Brothers, Ltd., 1971.
499
-------
474. Lippmann, M., and B. Altshuler. Regional deposition of aerosols,
pp. 25-48. In E. F. Aharonson, A. Ben-David, and M. A. Klingberg,
Eds. Mr Pollution and the Lung. Proceedings of the Twentieth
Annual "OHOLO" Biological Conference, Ma'alot, Israel, March 16-19,
1975. New York: John Wiley & Sons, Inc., 1976.
475. Litt, M. Flow behavior of mucus. Ann. Otol. Rhinol. Laryngol.
80:330-335, 1971.
476. Litt, M. Rheological aspects of mucociliary flow. Ann. N.Y.
Acad. Sci. 221:212-213, 1974.
477. Litvin, A. Clear coatings for exposed architectural concrete.
J. Portland Cem. Assoc. 10:49-57, 1968.
478. Liu, B. Y. H. , Ed. Fine Particles. Aerosol Generation, Measurement,
Sampling, and Analysis. Proceedings of a Symposium by the
U.S. Environmental Protection Agency held in Minneapolis,
Minnesota, May 28-30, 1975. New York: Academic Press, Inc.,
1976. 837 pp.
479. Liu, B. Y. H., and K. W. Lee. An aerosol generator of high stability.
Amer. Ind. Hyg. Assoc. J. 36:861-865, 1975.
480. Liu, B. Y. H., and D. Y. H. Pui. On the performance of the
electrical aerosol analyzer. J. Aerosol Sci. 6:249-264, 1975.
481. Liu, B. Y. H., and D. Y. H. Tui. Electrical Behavior of Aerosols.
Presented at the 82nd National Meeting of American Institute of
Chemical Engineers, Atlantic City, August, 1976.
500
-------
482. Lodge, J. P., Jr., and E. R. Frank. Chemical identification of
some atmospheric components in the Aitken nucleus size range.
J. Rech. A<-mospheriques 2:139-140, 1966.
483. Logan, W. P. D. Mortality in the London fog incident.
Lancet 1:336-338, 1953.
484. Loo, B. W., J. M. Jaklevic, and F. S. Goulding. Dichotomous virtual
impactors for large scale monitoring of airborne particulate
matter, pp. 311-350. In B. Y. H. Liu, Ed. Fine Particles.
Aerosol Generation, Measurement, Sampling, and Analysis.
Proceedings of a Symposium by the U.S. Environmental Protection
Agency held in Minneapolis, Minnesota, May 28-30, 1975.
New York: Academic Press, Inc., 1976.
485. Lourenco, R. V., M. F. Klimek, and C. J. Borowski. Deposition and
clearance of 2 ,1 particles in the tracheobronchial tree of
normal subjects—smokers and nonsmokers. J. Clin. Invest.
50:1411-1419, 1971.
486. Lourenco, R. V., R. Loddenkemper, and R. W. Carton. Patterns of
distribution and clearance of aerosols in patients with
bronchiectasis. Amer. Rev. Resp. Dis. 106:857-866, 1972.
487. Love, G. J., A. A. Cohen, J. F. Finklea, J. G. French, G. R. Lowrimore,
W. C. Nelson, and P. B. Ramsey. Prospective surveys of acute
respiiatorv disc.ibc in volunteer families: 1970-1971 New York
studies, pp. 5-49' to 5-69. In U.S. Environmental Protection
Agency, Office of Research and Development. Health Consequences
of Sulfur Oxides: A Report from CHESS, 1970-1971. EPA-650/1-74-004.
Washington, DC: U.S. Government Printing Office, 1974.
501
-------
488. Love, R. G., and D. C. F. Muir. Aerosol deposition and airvjy
obstruction. Amer. Rev. Resp. Dis. 114:891-897, 197b.
489. Lovejoy, F. W., Jr., H. Constantine, J. Flatley, N. Kaltreider,
and L. Dautrebande. Measurement of gas trapped in the lungs
during acute changes in airway resistance in normal subjects
and in patients with chronic pulmonary disease. Amer. J.
Med. 30:884-892, 1961.
490. Lowe, C. R., H. Campbell, and T. Khosla. Bronchitis in two
integrated steel works. III. Respiratory symptoms and
ventilatory capacity related to atmospheric pollution.
Brit. J. Ind. Med. 27:121-129, 1970.
491. Lowe, C. R., P. L. Pelmear, H. Campbell, R. A. N. Kitchens,
T. Khosla, and T. C. King. Bronchitis in two integrated
steel works. 1. Ventilatory capacity, age, and physique
of non-bronchitic men. Brit. J. Prev. Soc. Med. 22:1-11, 1968.
492. Lucas, A. M., and L. C. Douglas. Principles underlying ciliary
activity in the respiratory tract. II. A comparison of nasal
clearance in man, monkey and other mammals. Arch. Otolaryng.
20:518-541, 1934.
493. Luchsinger, P. C., B. LaGarde, and J. E. Kilfeather. Particle
clearance from the human tracheobronchial tree. Amer.
Rev. Resp. Dis. 97:1046-1050, 1968.
494. Ludwig, J. H., G. B. Morgan, and T. B. McMullen. Trends in
urban air quality, pp. 321-338. In W. H. Matthews, W. W. Kellogg,
and G. 0. Robinson, Eds. Man's Impact on the Climate.
Cambridge: The MIT Press, 1971.
502
-------
495. Lundgren, D. A. Mass Distribution of Large Atmospheric Particler..
Ph.D. Tnesis, University of Minnesota, Minneapolis, Minn., 1973.
161 pp.
496. Lundgren, D. A., L. D. Carter, and P. S. Daley. Aerosol mass
measurement using piezoelectric crystal sensors, pp. 485-510.
In B. Y. H. Liu, Ed. Fine Particles. Aerosol Generation,
Measurement, Sampling, and Analysis. Proceedings of a
Symposium by the U.S. Environmental Protection Agency held
in Minneapolis, Minnesota, May 28-30, 1975. New York:
Academic Press, Inc., 1976.
497. Lunn, J. E., J. Knowelden, and A. J. Handyside. Patterns of
respiratory illness in Sheffield infant school children.
Brit. J. Prev. Soc. Med. 21:7-16, 1967.
498. Lunn, J. E., J. Knowelden, and J. W. Roe. Patterns of respiratory
illness in Sheffield junior school children. A follow-up study.
Brit. J. Prev. Soc. Med. 24:223-228, 1970.
499. Lyons, W. A., and R. B. Husar. SMS/GOES visible images detect
a synoptic-scale air pollution episode. Mon. Weather Rev.
104:1623-1626, 1976.
500. Lyons, W. A., and S. R. Pease. Detection of particulate air
pollution plumes from major point sources using ERTS-1
imagery. Bull. Amer. Meteor. Soc. 54:1163-1170, 1973.
503
-------
501. MacFarland, H. N., C. E. Ulrich, A. Martin, A. Krumm, W. M. Busey,
and Y. Alarie. Chronic exposure of cynamolgus monkeys to fly
ash, pp. 313-327. In W. H. Walton, Ed. Inhaled Particles III,
Vol. 1. Proceedings of an International Symposium organized
by the British Occupational Hygiene Society in London, 14-23
September 1970. Old Woking, Surrey, England: Unwin Brothers
Limited, 1971.
502. Macias, E. S., and R. B. Husar. A review of atmospheric particulate
mass measurement via the beta attenuation technique, pp. 535-564.
In B. Y. H. Liu, Ed. Fine Particles. Aerosol Generation,
Measurement, Sampling, and Analysis. Proceedings of a
Symposium by the U.S. Environmental Protection Agency held
in Minneapolis, Minnesota, May 28-30, 1975. New York: '
Academic Press, Inc., 1976.
503. Macklin, C. C. Pulmonary sumps, dust accumulations, alveolar fluid
and lymph vessels. Acta Anat. 23:1-33, 1955.
504. Manos, N. E. Comparative Mortality among Metropolitan Areas
of the United States, 1949-1951, 102 Causes of Death.
Ratios of Observed to Expected Mortality for 163 Metropolitan
Areas, Mortality Rates and Ratios by Degree of Urbanization
for the Total United States, and other Background Information
Necessary to the Interpretation of these Rates and Ratios.
PHS Publication 562. Washington, D.C.: U.S. Government
Printing Office, 1957. 143 pp.
504
-------
505. Marin, M. G., and P. E. Morrow. Effect of changing inspired
0_ and CO. levels on tracheal mucociliary transport rate.
J. Appl. Physiol. 27:385-388, 1969.
506. Marble, V. A., and K. Willeke. Inertial impactors: Theory, design
and use, pp. 412-446. In B. Y. H. Liu, Ed. Fine Particles.
Aerosol Generation, Measurement, Sampling, and Analysis.
Proceedings of a Symposium by the U.S. Environmental Protection
Agency held in Minneapolis, Minnesota, May 28-30, 1975.
New York: Academic Press, Inc., 1976.
507. Martens, A., and W. Jacobi. Die in-vivo-Bestimmung der
Aerosolteilchendeposition im Atemtrakt bei Mund- bzw.
Nasenatmung, pp. 117-121. In V. BBhlau, Ed. Aerosole
in Physik, Medizin und Technik. Kongressbericht der
Aerosoltagung im Taunus-Sanatorium am 17. und 18.
Oktober 1973 der LVA Wttbg. Bad Soden, West Germany:
Gesellschaft fllr Aerosolforschung, 1973.
508. Martin, A. E. Mortality and morbidity statistics and air pollution.
Proc. Roy. Soc. Med. 57:969-975, 1964,
509. Martin, A. E., and W. H. Bradley. Mortality, fog, and atmospheric
pollution. An investigation during the winter of 1958-59.
Monthly Bull. Kin. Health Pub. Health Lab. Serv. 19:56-73, 1960.
510. Martin, S. W., and R. A. Willoughby. Organic dusts, sulfur dioxide,
and the respiratory tract of swine. Arch. Environ. Health 25:
158-165, 1972.
505
-------
511. Martinez-Tello, F. J., D. G. Braun, and W. A. Blanr. Immunoglobulin
production in bronchial mucosa and bronchial lymph nodes, par-
ticularly in cystic fibrosis of the pancreas. J. Immunol.
101:989-1003, 1968.
512. Massachusetts Institute of Technology. Man's Impact on the
Global Environment. Assessment and Recommendations for
Action. Report of the Study of Critical Environmental
Problems (SCEP). Cambridge, Mass.: MIT Press, 1970. 319 pp.
513. Matsuba, K., and W. M. Thurlbeck. The number and dimensions of
small airways in nonemphysematous lungs. Amer. Rev. Resp. Dis.
104:516-524, 1971.
514. Matteson, M., W. Stober, and H. Luther. Kinetics of the oxidation
of sulfur dioxide by aerosols of manganese sulfate. Ind. Eng.
Chem. Fund. 8:677-687, 1969.
515. Matthews, L. W., S. Spector, J. Lemm, and J. L. Potter.
Studies on pulmonary secretions. I. The over-all chemical
composition of pulmonary secretions from patients with
cystic fibrosis, bronchiectasis, and laryngectomy.
Amer. Rev. Resp. Dis. 88:199-204, 1963.
516. Matthys, H., M. Muller, and N. Konietzko. Quantitative and
"nu,
selective bronchial clearance studies using ™c-sulfate
particles. Scand. J. Resp. Dis. Supp]. 85:33-37, 1974.
517. May, K. R. The cascade impactor: An instrument for sampling coarse
aerosols. J. Sci. Instrum. 22:187-195, 1945.
506
-------
518. McBurney, J. W. Effect of atmosphere on masonry and related
materials, pp. 45-56. In Symposium on Some Approaches
to Durat^lity in Structures. ASTM Special Technical
Publication No. 236. Philadelphia: American Society
for Testing and Materials, 1959.
519. McCarroll, J., and W. Bradley. Excess mortality as an indicator of
health effects of air pollution. Aiaer. J. Public Health 56:
1933-1942, 1966.
520. McCarroll, J., E.'j. Cassell, D. W. Wolter, J. D. Mountain,
J. R. Diamond, and I. M. Mountain. Health and urban environment,
V. Air pollution and illness in a normal urban population.
Arch. Environ. Health 14:178-184, 1967.
521. McCarthy, C., and L. Reid. Intracellular mucopolysaccharides in
the normal human bronchial tree. Q. J. Exp. Physiol. 49:
85-94, 1964.
522. McCarthy, D. S., R. Spencer,' R. Greene, and J. Milic-Emili.
Measurement of "closing volume" as a simple and sensitive
test for early detection of small airway disease. Amer.
J. Med. 52:747-753, 1972.
523. McCormick, R. A., and J. H. Ludwig. Climate modification by
atmospheric aerosols. Science 156:1358-1360, 1967.
524. McCune, D. C. , A. E. Hitchcock, J. S. Jacobson, and L. H. Weinstein.
Fluoride accumulation and growth of plants exposed to
particulate cryolite in the atmosphere. Contrib. Boyce
Thompson Inst. 23:1-12, 1965.
507
-------
525. McCune, D. C. , D. H. Silberman, and L. H. Weinstein. Effects of
relative humidity and free water on the phytotoxicity of
hydrogen fluoride and cryolite, pp. 116-119. In Proceeuj.ngs
of the Fourth International Clean Air Congress, Tokyo,
16-20 May 1977. Tokyo: Japanese Union of'Air Pollution
Prevention Associations, 1977.
526. McJilton, C., R. Frank, and R. Charlson. Role of relative humidity
in the synergistic effect of a sulfur dioxide-aerosol mixture
on the lung. Science 182:503-504, 1973.
527. McJilton, C., J. Thielke, and R. Frank. Ozone Uptake Model for the
Respiratory System. Paper presented at American Industrial
Hygiene Association Conference, San Francisco, California,
May 14-19, 1972. (Abstract: Amer. Ind. Hyg. Assoc. J. 33:
20, 1972.)
528. McKinney, N., and H. W. Hermance. Stress corrosion cracking rates of
a nickel-brass alloy under applied potential, pp. 274-291.
In American Society for Testing and Materials. Symposium
on Stress Corrosion Testing, presented at the sixty-ninth
annual meeting, Atlantic City, 26 June-1 July 1966. ASTM
Special Technical Publication No. 425. Philadelphia: American
Society for Testing and Materials, 1967.
529. Mclaughlin, R. F., Jr., W. S. Tyler, and R. 0. Canada. Subgross
pulmonary anatomy of the rabbit, rat, and guinea pig, with
additional notes on the human lung. Amer. Rev. Resp. Dis.
94:380-387, 1966.
508
-------
530. McLeod, W., and R. R. Rogers. Corrosion of metals by aqueous solutions
of the atmospheric pollutant sulfurous acid. Electrochem.
Technol. 6:231-235, 1968.
531. McLeod, W., and R. R. Rogers. The nature of corrosion of zinc by
sulfurous acid at ordinary temperatures. Corrosion 25:74-76, 1969.
532. Mead, J. The lung's "quiet zone." New Eng. J. Med. 282:1318-
1319, 1970.
533. Mercer, T. T. On the role of particle size in the dissolution
of lung burdens. Health Phys. 13:12ll-1221,' 1967.
534. Mercer, T. T. Aerosol Technology in Hazard Evaluation. New York:
Academic Press, 1973. 394 pp.
it
535. Mercer, T. T., P. E. Morrow, and W. Stober, Eds. Assessment of
Airborne Particles. Fundamentals, Applications, and Implications
to Inhalation Toxicity. Springfield, 111.: Charles C Thomas,
1972. 540 pp.
536. Meyrick, B., J. M. Sturgess, and L, Reid. A reconstruction of
the duct system and secretory tubules of the human bronchial
submucosal gland. Thorax 24:729-736, 1969.
537. Middleton, J. T., E. F. Darley, and R. F. Brewer. Damage to
vegetation from polluted atmospheres. J. Air Pollut.
Control Assoc. 8:9-15, 1958.
509
-------
538. Middleton, W. E. K. Vision Through the Atmosphere. Toronto:
University of Toronto Press, 1952. 250 pp.
539. Milburn, R. H., W. L. Crider, and S. D. Morton. The retention
of hygroscopic dusts in _he human lungs. A.M.A. Arch.
Ind. Health 15:59-62, 1957.
540. Miller, C. E. Flow induced by mechanical analogues of mucociliary
systems. Ann. N. Y. Acad. Sci. 130:880-890, 1966.
541. Miller, C. E. The kinematics and dynamics of ciliary fluid systems.
J. Exp. Biol. 49:617-629, 1968.
542. Miller, C. E. Streamlines, streak lines, and particle path lines
associated with a mechanically-induced flow homorphic with
the mammalian mucociliary system. Biorheology 6:127-135, 1969.
543. Miller, M. S., S. K. Friedlander, and G. M. Hidy. A chemical
element balance for the Pasadena aerosol, pp. 301-312.
In G. M. Hidy, Ed. Aerosols and Atmospheric Chemistry.
Proceedings of the American Chemical Society. Los Angeles,
California, March 28-April 2, 1971. New York: Academic Press,
1972.
544. Miller, P. M., and S. Rich. Soot damage to greenhouse plants.
Plant Dis. Rep. 51:712, 1967.
545. Miller, W. S. Muscle in the pleura, pp. 155-156. In The Lung.
(2nd ed.) Springfield, 111.: Charles C Thomas, 1947.
510
-------
546. Ministry of Health (Great Britain). Mortality and Morbidity
During the London Fog of December 1952. Report by a
Committee of Departmental Officers and Expert Advisers
appointed by the Minister of Health. Report No. 95.
London: Her Majesty's Stationery Office, 1954. 61 pp.
547. Ministry of Pensions and National Insurance. Report on an
Enquiry into the Incidence of Incapacity for Work.
Part II. Incidence of Incapacity for Work in Different
Areas and Occupations. London: Her Majesty's Stationery
Office, 1965. 163 pp.
548. Mitchell, J. M., Jr. Summary of the problem of air pollution
effects on climate, pp. 167-175. In W. H. Matthews,
W. W. Kellogg, and G. 0. Robinson, Eds. Man's Impact on
the Climate. Cambridge: The MIT Press, 1971.
549. Mitchell, J. M. , Jr. The effect of atmospheric particles on
radiation and temperature, pp. 295-301. In W. H. Matthews,
W. W. Kellogg, and G. 0. Robinson, Eds. Man's Impact on the
Climate. Cambridge: The MIT Press, 1971.
1
550. Moore, D. G., and A. Potter. Effect of Exposure Site on Weather
Resistance of Porcelain Enamels Exposed for Three Years.
National Bureau of Standards Monograph 44. Washington, D.C.:
U.S. Government Printing Office, 1962. 13 pp.
511
-------
551. Morgan, A., A Black, J. C. Evans, E. H. Hadfield, R. G. Macbeth,
and M. Walsh. Impairment of nasal mucociliary clearance
in woodworkers in the furniture industry, pp. 335-338.
In Proceedings, First International Congress on Aerosols in
Medicine, 19-21 September 1973, Baden/Wien, Austria.
Baden/Wien: Internationale Gesellschaft fur Aerosole
in der Medizin, 1973.
552. Mork, T. A comparative study of respiratory disease in England
and Wales and Norway. Acta Med. Scand. 172 (Suppl. 384):1-100, 1962,
553. Morrow, P. E. Lymphatic drainage of the lung in dust clearance.
Ann. N.Y. Acad. Sci. 200:46-65, 1972.
554. Morrow, P. E. Alveolar clearance of aerosols. Arch. Int. Med.
131:101-108, 1973.
555. Morrow, P. E. An evaluation of recent NO toxicity data and an
attempt to derive an ambient air standard for NO by established
toxicological procedures. Environ. Res. 10:92-112, 1975.
556. Morrow, P. E., F. R. Gibb, H. Davies, and M. Fisher. Dust
removal froni ,R' i ung parenchyma: An investigation oi
clearance simulant'-. Toxicol. Appl. PharmacoJ. ]2:372-39b, 1968,
557. Morrow, P. E., F. R. Gibb, and K. M. Gazioglu. A study of
patLiculate clearance from the human lungs. Amer. Rev.
Reap. Dis. 96:1209-1221, 1967.
512
-------
558. Morrow, P. E., F. R. Gibb, and K. Gazioglu. The clearance of dust
from the lower respiratory tract of man. >vn experimental stu__, ,
pp. 351-358. In C. N. Davies, Ed. Inhaled Particles and Vapours II.
Proceedings of an International Symposium organized by the British
Occupational Hygiene Society, Cambridge, 28 September-1 October 1965.
Oxford: Pergamon Press, 1967.
559. Morrow, P. E., F. R. Gibb, and L. Johnson. Clearance of insoluble
dust from the lower respiratory tract. Health Phys. 10:543-555, 1964.
560- Mossop, S. C. Comparisons between concentration of ice crystals
in cloud and the concentration of ice nuclei. J. Rech.
Atmospheriques 3:119-124, 1968.
•*"" ~
561. Motto, H. L., R. H. Daines, D. M. Chilko, and C. K. Motto.
Lead in soils and plants; Its relationship to traffic
volume and proximity to highways. Environ. Sci. Technol. 4:
231-237, 1970.
562. toir, D. C. F., and C. N. Davies. The deposition of 0.5 u diameter
aerosols in the lungs of man. Ann. Occup. Hyg. 10:161-174, 1967.
563. Mulcahy, M. F. R., J. R. Steven, and J. C. Ward. The kinetics
of reaction between oxygen atoms and sulfur dioxides:
An investigation by electron spin resonance spectrometry.
J. Phys. Chem. 71:2124-2131, 1967.
564. Munn, R. E., and B. Bolin. Global air pollution—meteorological
aspects. A survey. Atmos. Environ. 5:363-402, 1971.
513
-------
565. Nadel, J. A. Aerosol effects on smooth muscle and airway visualization
technique. Arch. Intern. Med. 131:83-87, 1973.
566. Nadel, J. A., H. Salem, B. Tamplin, and Y. Tokiwa. Mechanism of
bronchoconstriction during inhalation of sulfur dioxide.
J. Appl. Physiol. 20:164-167, 1965.
567. Nadel, J. A., and J. G. Widdicombe. Reflex effects of upper
airway irritation on total lung resistance and blood pressure.
J. Appl. Physiol. 17:861-865, 1962.
568. Nagaishi, C. Functional Anatomy and Histology of the Lung.
Baltimore: University Park Press, 1972. 295 pp.
569. Nakamura, K. Response of pulmonary airway resistance by interaction
of aerosols and gases in different physical and chemical nature.
Jap. J. Hyg. 19:322-333, 1964. (in Japanese). (Translated by
EPA; available from the Air Pollution Technical Center, Research
Triangle Park, N.C. as APTIC No. 11425.)
570. National Academy of Sciences, Committee on Geological Sciences.
Enter pollutants, pp. 29-30. In The Earth and Human Affairs.
San Francisco: Canfield Press, 1972.
571. National Research Council, Committee on Biologic Effects of
Atmospheric Pollutants. Lead: Airborne Lead in Perspective.
Washington, D.C.: National Academy of Sciences, 1972. 330 pp.
514
-------
572. National Research Council, ConnnittL on Biologic Effects of
Atmospheric Pollutants. Part-.ulate Polycyclic Organic Matter.
Washington, D.C.: National Academy of Sciences, 1972. 361 pp.
573. National Research Council, Subcomnu ctee on Nitrogen Oxides,
Committee on Medical and Biologic Effects of Environmental
Pollutants. Nitrogen Oxides. Washington, D.C.: National
Academy of Sciences, 1977. 330 pp.
574. Natusch, D. F. S., and J. R. Wallace. Urban aerosol toxicity:
The influence of particle size. Science 186:695-699, 1974.
575. Natusch, D. F. S., J. R. Wallace, and C. A. Evans, Jr. Toxic
trace elements: Preferential concentration in respirable
particles. Science 183:202-204, 1974.
576. Negus, V. E. The function of mucus. Acta Otolaryng. 56:204-213,
1963.
577. Nelson, W. C., J. F. Finklea, D. E. House, D. C. Calafiore,
M. B. Hertz, and D. H. Swanson. Frequency of acute lower
respiratory disease in children: Retrospective survey of
Salt Lake Basin communities, 1967-1970, pp. 2-55 to 2-73.
In U.S. Environmental Protection Agency, Office of Research
and Development. Health Consequences of Sulfur Oxides:
A Report from CHESS, 1970-1971. EPA-650/1-74-004.
Washington, D.C.: U.S. Government Printing Office, 1974.
515
-------
578. Nenot, J. C. Etude de 1'influence de 1'irradiation sur 1'epuration
pulmonaire, pp. 239-246. In W. H. Walton, Ed. Inhaled Particles
III, Vol. I. Proceedings of an International Symposium organized
by the British Occupational Hygiene Society in London, 14-23
September, 1970. Old Woking, Surrey: Unwin Brothers, Ltd., 1971.
579. Niewoehner, D. E., and J. Kleinerman. Morphologic basis of
pulmonary -resistance in the human lung and effects of aging.
J. Appl. Physiol. 36:412-418, 1974.
580. Noll, K. E., P. K. Mueller, and M. Imada. Visibility and aerosol
concentration in urban air. Atmos. Environ. 2:465-475, 1968.
581. Norris, R. M., and J. M. Bishop. The effect of calcium carbonate
dust on ventilation and respiratory gas exchange in normal
subjects and in patients with asthma and chronic bronchitis.
Clin. Sci. 30:103-115, 1966.
582. Novakov, T., S. G. Chang, and A. B. Harker. Sulfates as
pollution participates: Catalytic formation on carbon
(soot) particles. Science 186:259-261, 1974.
583. Nuessle, A. C. Soil and stain resistance, pp. 465-505. In
H. F. Mark, N. S. Wooding, and S. M. Atlas, Eds. Chemical
Aftertreatment of Textiles. New York: Wiley-Interscience, 1971.
584. Ogden, T. L. The effect of rainfall on a large steelworks.
J. Appl. Meteorol. 8:585-591, 1969.
516
-------
585. Olsen, H. C., and J. C. Gilson. Respiratory symptoms, bronchitis,
and ventilatory capacity in man. An Anglo-Danish comparison,
with special reference to differences in smoking habits.
Brit. Med. J. 1:450-456, 1960.
586. Olson, D. E., M. F. Sudlow, K. Horsfield, and G. F. Filley.
Convective patterns of flow during inspiration. Arch. Intern.
Med. 131:51-57, 1973.
587. Offla, K. , T. Sugaro, T, Ueki, and Y. Hirai. Studies on atmospheric
corrosion of steels related to meteorological factors in Japan.
II. Multiple correlation of meteorological and atmospheric
pollution substances on corrosion of steel. Division of Build-
ing Research Technical Translation 1281. (Translated from Boshoku
Gijutsu (Corros, Eng.) 14:16-19, 1965) Ottawa: National
Research Council of Canada, 1965.
588. Orr, C. , Jr., F. K. Kurd, and W. J. Corbett. Aerosol size and
relative humidity. J. Colloid Sci. 13:472-482, 1958.
589. Pack, M. R., A. C. Hill, M. D. Thomas, and L. G. Transtrum.
Determination of gaseous and participate inorganic fluorides
in the atmosphere, pp. 27-44. In American Society for Testing
Materials Special Technical Publication No. 281. Symposium
on Air Pollution Control, San Francisco, California, October 16,
1959. Philadelphia: American Society for Testing Materials,
1960.
517
-------
590. Pa8e» A. L., and T. J. Ganje. Accumulations of lead in soils
for regions of high and low motor vehicle traffic density.
Environ. Sci. Technol. 4:140-142, 1970.
591. Page, A. L., T. J. Ganje, and M. S. Joshi. Lead quantities in
plants, soil, and air near some major highways in
southern California. Hilgardia 41:1-31, 1971.
592. Pajenkamp, H. Einwirkung des Zementofenstaubes auf Pflanzen und
Tiere. Zement-Kalk-Gips 14:88-95, 1961.
593. Palmer, J. D. Corrosion control involves pollution too. Can. Chem.
Process. 53(10):78-81, 1969.
594. Palmer, K. N. V., D. Ballantyne, M. L. Diament, and
W. F. D. Hamilton. The rheology of bronchitic sputum.
Brit. J. Dis. Chest 64:185-191, 1970.
595. Palmes, E. D., and M. Lippmann. Influence of respiratory air
space dimensions on aerosol deposition, pp. 127-136. In
W. H. Walton, Ed. Inhaled Particles IV. London: Pergamon
Press Ltd, 1977.
596. Panda, S. C., R. C. Nayak, and I. C. Mahapatra. A note on effect
of cement dust on the soil fertility and crop growth around
the factory area of Rajgangpur (Orissa). Indian J. Agron.
18:389-391, 1973.
597. Parish, S. B. The effect of cement dust on citrus trees.
Plant World 13:288-291, 1910.
518
-------
598. Patterson, R. K., an^ J. Wagman. Mass and composition of an
urban aerosol as a function of size for several visi-
bility levels. J. Aerosol Sci. 8:191-201, 1977.
599. Pattle, R. E. The retention of gases and particles in the human
nose, pp. 302-309. In C. N. Davies, Ed. Inhaled Particles
and Vapours. Oxford: Pergamon Press, 1961.
600. Pavia, D., M. D. Short, and M. L. Thomson. No demonstrable long
term effects of cigarette smoking on the mucociliary mechanism
of the human lung. Nature 226:1228-1231, 1970.
601. Pavia, D., and M. L. Thomson. Inhibition of mucociliary clearance
from the human lung by hyoscine. Lancet 1:449-450, 1971.
602. Payne, W., L. J. Stief, and D. D. Davis. A kinetics study of
the reaction of HO with SO and NO. J. Amer. Chem. Soc.
95:7614-7619, 1973.
603. Pedace, E. A., and E. B. Sansone. The relationship between "soiling
index" and suspended particulate matter concentrations.
J. Air I'ollut. Control Assoc. 22:348-351, 1972.
604. Pedley, T. J., R. C. Schroter, and M. F. Sudlow. Flow and pressure
drop in systems of repeatedly branching tubes. J. Fluid Mech.
46:365-383, 1971
605. Peirce, G. J. An effect of rement dust on orange trees.
Plant World 13:283-288, 1910.
519
-------
606. Pemberton, J., and C. Goldberg. Air pollution and bronchitis.
Brit. Med. J. 2:567-570, 195A.
607. Penkett, S. A. Oxidation of SCL and other atmospheric gases by
ozone in aqueous solution. Nature (Phys. Sci.) 240:105-106,
1972.
608. Penkett, S. A., and J. A. Garland. Oxidation of sulphur dioxide
in artificial fogs by ozone. Tellus 26(1-2):284-290, 1974.
609. Petrilli, F. L., G. Agnese, and S. Kanitz. Epidemiologic studies
of air pollution effects in Genoa, Italy. Arch. Environ.
Health 12:733-740, 1966.
610. Pierce, R. C., and M. Katz. Dependency of polynuclear aromatic
hydrocarbon content on size distribution of atmospheric
aerosols. Environ. Sci. Tech. 9:347-353, 1975.
611. Pilat, M. J. Application of gas-aerosol adsorption data to the
selection of air quality standards. J. Mr Pollut. Control
Assoc. 18:751-753, 1968.
612. Podzimek, J., W. A. Sedlacek, and J. B. Haberl. Aircraft measurements
of Aitken nuclei in the lower stratosphere. Technical report to
the Office of Naval Research, Contract N00014-75-C-0413 and to
the U.S. Department of Transportation, CIAP, from the Graduate
Center for Cloud Physics Research. Rolla Rolla, MO: University
of Missouri, 1975.
520
-------
613. Policard, A., and P. Galy. Les Bronches. Structures et
Mechanisms a L'etat Normal et Pathologique. Paris: Masson
et Cie, 1945. 191 pp.
614. Porch, W. M. , D. S. Ensor, R. J. Charlson, and J. Heintzenberg.
Blue moon: Is this a property of background aerosol?
Appl. Opt. 12:34-36, 1973.
M
615. Porstendorfer, J. Untersuchungen zur Frage des Wachstums von
inhalierten Aerosolteilchen im Atemtrakt. Aerosol Sci . 2:
73-79, 1971.
616. Potter, J. L. , L. W. Matthews, J. Lemm, and S. Spector. Human
pulmonary secretions in health and disease. VI. Studies on
mucus in relation to human disease. Ann. N. Y. Acad. Sci.
(Art. 2) 106:692-697, 1963.
617. Potter, J. L., L. W. Matthews, S. Spector, and J. Letnm.
Studies on pulmonary secretions. II. Osmolality and the
ionic environment of pulmonary secretions from patients
with cystic fibrosis, bronchiectasis, and laryngectomy.
Aiaer. Rev. Resp. Ms. 96:83-87, 1967.
618. Prager, M. J., E. R. Stephens, and W. E. Scott. Aerosol formation
from gaseous air pollutants. I/EC Ind. Eng. Chem. 52:521-524,
1960.
619. Pressley, H. Some effects of attack on refractories by the
oxides of sodium, sulphur, and vanadium. Trans. Brit.
Ceram. Soc. 69:205-210, 1970.
521
-------
620. Prindle, R. A., G. W. Wright, R. 0. McCaldin, S. C. Marcus,
T. C. Lloyd, and W. E. Bye. Comparison of pulmonary function
and ot^er parameters in two communities with widely different
air pollution levels. Amer. J. Public Health 53:200-217, 1963.
621. Proctor, D. F., Ib. Andersen, and G. Lundqvist. Clearance of inhaled
particles from the human nose. Arch. Intern. Med. 131:132-139, 1973.
622. Prospero, J. M., and E. Bonatti. Continental dust in the atmosphere
of the eastern equatorial Pacific. J. Geophys. Res. 74:3362-3371,
1969.
623. Prospero, J. M., and T. N. Carlson. Vertical and areal distribution
of Saharan dust over the western equatorial North Atlantic.
J. Geophys. Res. 77:5255-5265, 1972.
624. Pueschel, R. F., R. J. Charlson, and N. C. Ahlquist. On the
anomalous deliquescence of sea-spray aerosols. J. Appl. Meteorol.
8:995-998, 1969.
525. Pueschel, R. F., and G. Langer. Sugar cane fires as a source of
ice nuclei in Hawaii. J. Appl. M.2t"niol. 12 : 5 '>')• 551 , 1973.
Radke, L. F., and F. M. Turner. An improved automatic cloud
condensation nucleus counter. J. Appl. Meteorol. 11:407-409, 1972,
522
-------
627. Rao, A. K. An Experimental Study of Inertial Impactors.
Ph.D. Thesis, University of Minnesota, Minn., 1975. 212 pp.
628. Rasmussen, R. A., and F. W. Went. Volatile organic material of
plant origin in the atmosphere. Proc. Nat. Acad. Sci. U.S.A.
53:215-220, 1965.
629. Rasool, S. I., and S. H. Schneider. Atmospheric carbon dioxide
and aerosols: Effects of large increases in global climate.
Science 173:138-141, 1971.
630. Ray, F. K., P. B. Mack, F. Bonnet, and A. H. Wachter. A comparison
of the effect on rayon fabrics of various gases under controlled
conditions. Amer. Dyest. Rep. 37:391-396, 1948.
Rayleigh, Lord. See Strutt, J. W.
631. Raymond, V. , and R. Nussbaum. A propos des poussie.res de cimenteries
et de leurs effets sur I'homme, les plants et les animaux.
Pollut. Atmos. 8:284-294, 1966.
632. Registrar-General, Great Britain. Appendix, pp. 71-362. In
Third Annual Report of the Registrar-General of Births,
Deaths and Marriages in England. London: Her Majesty's
Stationery Office, 1841.
633. Reid, D. D. Environmental factors in respiratory disease.
Lancet 1:1289-1294, 1958.
523
-------
634. Reid, D. D. Air pollution as a cause of chronic bronchitis.
Proc. Roy. Soc. Med. 57:965-968, 1964.
635. Reid, D. D. The beginnings of bronchitis. Proc. Roy. Soc.
Med. 6°: 311-316, 1969.
636. Reid, D. D., D. 0. Anderson, B. G. Ferris, and C. M. Fletcher. An
Anglo-American comparison of the prevalence of bronchitis.
Brit. Med. J. 2:1487-1491, 1964.
637. Reid, L. Measurement of the bronchial mucous gland layer:
A diagnostic yardstick in chronic bronchitis. Thorax 15:
132-141, 1960.
638. Reid, L. Bronchial mucus production in health and disease,
pp. 87-108. In A. A. Liebow, and D. E. Smith, Eds. The Lung.
Baltimore: The Williams and Wilkins Company, 1968.
639. Reid, L. Evaluation of model systems for study of airway
epithelium, cilia, and mucus. Arch. Intern. Med. 126:428-
434, 1970.
640. Reid, L. The bronchitic component in airways obstruction.
Bull. Physio-pathol. Resp. 9:913-923, 1973.
641. Renzetti, N. A., and C. J. Doyle. Photochemical aerosol formation
in sulfur dioxide-hydrocarbon systems. Int. J. Air Pollut.
2:327-345, I960.
524
-------
642. Rhodin, J. G. infrastructure and function of the human tracheal
mucosa. Amc.r. Rev. Resp. Dis. 93 (Suppl. - Symposium on
Structure, j'unction and Measurement c>f Respiratory Cilia.
Duke Univer: ity Medical Center, Durham, North Carolina,
February 18-19, 1965):41-59, 1966.
643. Rhodin, J. G., and T. Dalhamn. Electron microscopy of the
tracheal ciliated mucosa in rat. Z. Zellforsch. Mikrosk.
Anat. 44:345-412, 1956.
644. Ricks, G. R. , and R. J. H. Williams. Effects of atmospheric
pollution on deciduous woodland. Part 2: Effects of
particulate matter upon stomatal diffusion resistance in
leaves of Quercus petraea (mattuschka) Leibl. Environ.
Pollut. 6:87-109, 1974.
645. Robinson, E. Effect on the physical properties of the atmosphere,
pp. 349-400. In A. C. Stern, Ed. Air Pollution. Vol, I.
Mr Pollution and Its Effects. New York: Academic Press, 1968.
646. Robinson, E., and R. C. Robbins. Sources, Abundance, and Fate
of Gaseous Atmospheric Pollutants. Prepared for the
American Petroleum Institute by the Stanford Research
Institute. SRI Project PR-6755. Menlo Park, California:
Stanford Research Institute, 1968. 123 pp.
647. Rodhe, H., and J. Grandell. On the removal time of aerosol
particles from the atmosphere by precipitation scavenging.
Tellus 24:442-454, 1972.
525
-------
648. Roosen, R. G., R. J. Angione, and C. H. Klemcke. Worldwide
variations in atmospheric transmission: 1. Baseline results
from Smithsonian observations. Bull. Amer. Meteorol. Soc.
54:307-316, 1973.
649. Rosenbautn, S. Home localities of national servicemen with
respiratory disease. Brit. J. Prev. Soc. Med. 15:61-67, 1961.
650. Ross, S. M. A Wavy Wall Analytical Model of Mucociliary
Pumping. Ph.D. thesis, The Johns Hopkins University,
1971. 305 pp.
651. Ross, S. M., and S. Corrsin. Results of an analytical model of
mucociliary pumping. J. Appl. Physiol. 37:333-340, 1974.
652. Roussel, P., P. Degand, A. Randoux, and R. Havez. Activites
fonctionnelles des mucines bronchiques, pp. 15-28. In
Progress in Respiration Research, Vol. 6. Chronic Inflammation
of the Bronchi. Basel: S. Karger, 1971.
653. Rudolf, G., and J. Heyder. Deposition of aerosol particles in the
n
human nose. In V. Bohlau, Ed. Aerosole in Naturwissenschaft,
Medizin irid Technik. Proceedings of a conference held in Bad Soden,
October 16-19, 1974. Bad Soden, West Germany: Gesellschaft fur
Aerosol ::orschung, 1974.
654. Rundo, J. • ^ase of accidental inhalation of irradiated uranium.
Brit. !. Radiol. 38:39-50, 1965.
526
-------
661. Salvin, V. S. Effect of atmospheric contaminants on j.ightfastness
testing. Amer. Dyest. Rep. 47:P450-P451, 1958.
662. Samuels, H. J., S. Twiss, and E. W. Wong. Visibilit> , Light
Scattering and Mass Concentration of Particulate Matter.
Report of the California Tri-City Aerosol Sampling Project.
Sacramento: State of California Air Resources Board, 1973.
60 pp.
663. Santa Cruz, R., J. Landa, J. Hirsch, and M. A. Sackner. Tracheal
mucous velocity in normal man and patients with obstructive
lung disease; effects of terbutaline. Amer. Rev. Resp. Dis.
109:458-463, 1974.
664. Satir, P. How cilia move'. Sci. Amer. 231(4) :44-52, 1974.
665. Saxena, V. K., D. J. Alofs, and A. C. Tebelak. A comparative study
of Altken nuclei counters. J. Rech. Atmos. 6:495-505, 1972.
666. Schaefer, V. J. The Air Quality Patterns of Aerosols on the
Global Scale. Part 1 and Part 2. Final Report. Pre-
pared for the National Science Foundation. ASRC-SUNY
Publ. No. 406. Albany, N.Y.: Atmospheric Sciences
Research Center, State University of New York, 1976.
110 pp and 262 pp.
528
-------
667. Schaefer, V. J. The inadvertent modification of the atmosphere
by air pollution. Bull. Amer. Meteorol. Soc. 50:199-206, 1969.
668. Schaffer, R. J. The Westhering of Natural Building Stones.
London: His Majesty's Stationery Office, 1932. 149 pp.
669. Scheffer, F. , E. Przemeck, and W. Wilms. Untersuchungen liber
den Einfluss von Zementofen-Flugstaub au,f Boden und Pflanze.
Staub 21:251-254, 1961.
670. Schiller, E. Inhalation, retention and elimination of dusts from
dogs' and rats' lungs with special reference to the alveolar
phagocytes and bronchial epithelium, pp. 342-347. In
C. N, Davies, Ed. Inhaled Particies and Vapours. Proceedings
of an International Symposium organized by the British Occupa-
tional Hygiene Society, Oxford, 29 March-1 April 1960.
Oxford: Pergamon Press, 1961.
671. Schimmel, H., and L. Greenburg. A study of the relation of pollution
to mortality. New York City, 1963-1968. J. Air Pollut. Control
Assoc. 22:607-616, 1972.
672. Schimmel, H., and T. J. Murawski. S0_—Harmful pollutant or air
quality indicator? Air Pollut. Control Assoc. 25:739-740, 1975.
673. Schlesinger, R. B. , V. R. Cohen, and M'. Lippmann. Studies of
int_rabronchial particle deposition using hollow bronchial casts,
pp. 116-127. In E. Karbe and J. F. Park, Eds. Experimental
Lung Cancer. Carcinogenesis and Bioassays. New York: Springer-
Verlag, 1974.
529
-------
674. Schlesinger, R. B., and M. Lippmann. Particle deposition in casts
of the human upper tracheobronchial tree. Amer. Ind. Hyg.
Assoc. J. 33:237-211, 1972.
675. Schlipkoter, H. W. Dip gesundheitliche Bedeutung des
atraospharischen Staubes. Staub 25:378-384, 1965.
676. Schneider, S. H. A comment on "climate: the influence of
aerosols." J. Appl. Meteorol. 10:840-841, 1971.
677. Schonbeck, H. Beobachtungen zur Frage des Einflusses von
industriellen Immissionen auf die Krankheitsbereitschaft
der Pflanze, pp. 89-98. In (Nordrhein-Westfalen) Berichte aus
n
der Landesanstalt fur Bodennutzungsschutz, Bochum, 1960.
678. Schrenk, H. H., H. Heimann, G. D. Clayton, W. M. Gafafer, and
W. Wexler. Air Pollution in Donora, Pennsylvania. Epidemiology
of the Unusual Smog Episode of October 1948. Preliminary
Report. Public Health Bulletin No. 306. Washington, D.C.:
U.S. Government Printing Office, 1949. 173 pp.
679. Schroeter, L. C. Kinetics of air oxidation of sulfurous acid
salts. J. Pharmaceut. Sci. 52:559-563, 1963.
680. Schuck, E. A., and J. K. Locke. Relationship of automotive lead
particulates to certain consumer crops. Environ. Sci. Technol.
4:324-330, 1970.
530
-------
681. Schuetzle, D., A. L. Crittenden, and R. J. Charlson. Application
of computer controlled high resolution mass spectrometry to
the analysis of air pollutants. J. Air Pollut. Control Assoc .
23:704-709, 1973.
682. Schiitz, L., and R. Jaenicke. Particle number and mass distributions
above 10 cm radius in sand and aerosols of the Sahara desert.
J. Appl. Meteor. 13:863-870, 1974.
683. Scott, J. A. Fog and deaths in London, December 1952. Public
Health Rep. 68:474-479, 1953.
684. Scott, J. A. Fog and atmospheric pollution in London, winter
1958-59. Med. Officer 102:191-193, 1959.
685. Scott, J. A. The London fog of December, 1962. Med. Officer 109:
250-252, 1963.
686. Scott, J. A., I. Taylor, A. T. Gore, and C. W. Shaddick. Mprtality
in London in the winter of 1962-63. Med. Off. 111:327-330, 1964T
687. Seabright, L. H., and R. J. Fabian. The many faces of corrosion.
Mater. Des. Eng. 57(1):85-91, 1963.
688. Sehmel, G. A. Particle resuspension from an asphalt road caused by
car and truck traffic. Atmos. Environ. 7:291-309, 1973.
531
-------
689. Sellick, H., and J. G. Widdicombe. Stimulation of lung irritant
receptors by cigarette smoke, carbon dust and histamine aerosol.
J. Appl. Physiol. 31:15-19, 1971.
690. Setnonin, R. G. Urban-induced weather modification, pp. 40-41.
In 1974 Earth Environment and Resources Conference Digest of
Technical Papers. New York: Lewis Winner, 1974.
691. Shephard, R. J., M. L. Thomson, G. C. Carey, and J. J. Phair.
Field testing of pulmonary dynamics. J. Appl. Physiol. 13:
189-193, 1958.
692. Shephard, R. J., M. E. Turner, G. C. R. Carey, and J. J. Phair.
Correlation of pulmonary function and domestic microenvironment.
J. Appl. Physiol. 15:70-76, 1960.
693. Shriner, D. S. Effects of Simulated Rain Acidified with Sulfuric
Acid on Host-Parasite Interactions. Ph.D. Thesis. Raleigh:
North Carolina State University, 1974. 85 pp.
694. Shy, C. M. Human health consequences of nitrogen.dioxide: A
review, pp. 363-405. In Assembly of Life Sciences-
National Academy of Sciences-National Research Council.
Proceedings of the Conference on Health Effects of Air
Pollutants, Washington, D.C., October 3-5, 1973.
Washington, D.C.: U.S. Government Printing Office, 1973.
695. Shy, C. M., V. Hasselblad, R. M. Burton, C. J. Nelson, and A. A! Cohen.
Air pollution .effects on ventilatory function of U. S. schoolchildren.
Results of studies in Cincinnati, Chattanooga, and New York. Arch.
Environ. Health 27:124-128, 1973.
532
-------
696. Shy, C. M., V. Hasselblad, J. F. Finkle-, R. M. Burton, M. Pravda,
R. S. Chapman, and A. A. Cohen. Ventilatory function in
school children: 1970-1971 New York studies, pp. 5-109 to
5-119. In U.S. Environmental Protection Agency, Office of
Research and Development. Health Consequences of Sulfur
Oxides: A Report from CHESS, 1970-1971. EPA-650/1-74-004.
Washington, D.C.: U.S. Government Printing Office, 1974.
697. Shy, C. M., C. J. Nelson, F. B. Benson, W. B. Riggan, V. A. Newill,
and R. S. Chapman. Ventilatory function in school children;
1967-1968 testing in Cincinnati neighborhoods, pp. 6-3 to 6-14.
In U.S. Environmental Protection Agency, Office of Research
and Development. Health Consequences of Sulfur Oxides: A
Report from CHESS, 1970-1971. EPA-650/1-74-004. Washington,
D.C.: U.S. Government Printing Office, 19~,4.
698. Sidebottom, H. W., C. C. Badcock, G. E. Jackson, J. G. Calvert,
G, W. Reinti.rdt, and E. K. Damon. Photooxidation of sulfur
dioxide. Environ. Sci. Technol. 6:72-79, 1972.
699. Sievers, F. J. Crop injury resulting from magnesium oxide dust.
Phytopathology 14:108-113, 1924.
700. Silvers, G. W., J. C. Maisel, T. L. Petty, G. F. Filley, and
R. S. Mitchell. Flow limitation during forced expiration
in excised human lungs. J. Appl. Physiol. 36:737-744, 1974.
701. Sim, V. M., and R. E. Pattle. Effect of possible smog irritants
on human subjects. J.A.M.A. 165:1908-1913, 1957.
533
-------
702. Simmons, W. A., and W. Young. Correlation of the Integrating
Nephelometer to High Volume Air Sampler. Commonwealth of
Massachusetts Department of Public Health, Bureau of Air Use
Management, Boston, Mass., 1970. 6 pp. (Available from
Commonwealth of Massachusetts, Department of Environmental
Quality Engineering Division of Air Quality Control,
600 Washington Street, Boston, MA 02111)
703. Simpson, J. W., and P. J. Horrobin, Eds. The Weathering and Performance
of Building Materials. New York: Wiley-Interscience, 1970. 286 pp.
704. Sleigh, M. A. Further observations on co-ordination and the
determination of frequency in the peristomial cilia of
Stentor. J. Exp. Biol. 34:106-115, 1957.
705. Sleigh, M. A, Some aspects of the comparative physiology of cilia.
Amer. Rev. Resp. Dis. 93 (Suppl) :16-31, 1966.
706. Slinn, W. G. N., and J. M. Hales. A reevaluation of the role of
thermophore;,i;; as a mechanism of in- and below-cloud scavenging.
J. Atmos. Sci. 28:1465-1471, 1971.
707. Smith, F. B. Tin' turbulent spread of a falling cluster,
pp. 193-210. In H. E. Landsberg and J. Van Mieghem, Eds.
Advances in Geophysics, Vol. 6. New York: Academic Press, 1959.
708. Smith, J. P., and P. Urone. Static studies of sulfur dioxide
reactions. Effects of NO., C.H,, and H»0. Environ. Sci.
L j o L
Technol. 8:742-746, 1974.
534
-------
709. Snell, R. E., and P. C. Luchsinger. Effects of sulfur dioxide
on expiratory flow rates and total respiratory resistance in
normal human subjects. Arch. Environ. Health 18:693-698, 1969.
710. Sorokin, S. P. The respiratory system, pp. 661-711. In
R. 0. Creep and L. Weiss, Eds. Histology. (3rd ed.)
New York; McGraw-Hill Book Company, 1973.
711. Soulage, G. Contribution des fumees industrielles a 1'enrichissement
s s
de ['atmosphere en noyaux glacogenes. I. Fumees d'acieries
electr.iques. Bull. Observ. Puy Dome No. 4:121-124, 1958.
712. Spector, W. G., and D. A. Willoughby. The inflammatory response.
Bact. Rev. 27:117-154, 1963,
713. Spedding, D. J. Sulphur dioxide uptake by limestone. Atmos.
Environ. 3:683, 685-686, 1969. (short communication)
714. Speizer, F. E. An epidemiological appraisal of the effects of
ambient air on health: Particulates and oxides of sulfur.
J. Air Pollut. Control Assoc. 19:647-655, ]969.
715. Speizer, F. E. . and N. R. Frank. The uptake and release of S0_
by the human nose. Arch. Environ. Health 12:725-728, 1966.
716. Spence, J. W. , ,jnd F. H. Haynie, Paint Technology and Air Pollution:
A Survey and Economic Assessment, pp. 20-24. Environmental
Protection Agency, Office of Air Programs. Washington, D.C.;
U.S. Government Printing Office, 1972.
535
-------
717. Spicer, W. S., Jr., P. B. Storey, W. K. C. Morgan, H. D. Kerr, and
N. E. Standiford. Variation in respiratory function in
selected patients and its relation to air pollution.
Amer. Rev. Resp. Dis. 86:705-712, 1962.
718. Spiegelman, J. R., G. D. Hanson, A. Lazarus, R. J. Bennett,
M. Lippmann, and R. E. Albert. Effect of acute sulfur dioxide
exposure on bronchial clearance in the donkey. Arch. Environ.
Health 17:321-326, 1968.
719. Squires, P. The microstructure and colloidal stability of warm
clouds. Part I. The relation between structure and stability.
Tellus 10:256-261, 1958.
720. Squires, P. An estimate of the anthropogenic production of cloud
nuclei. J. Rech. Atmos. 2:297-307, 1966.
721. Stedman, H. F. Natural and artificial weathering performance of
rigid polyvinyl chloride (PVC) and other plastic materials,
pp. 751-760. In Performance Concept in Buildings. Vol. 1:
Invited Papers. Proceedings of a Symposium. National Bureau
of Standards Special Publication 361. Washington, D.C.:
U.S. Government Printing Office, 1972.
722. Steinhubel, G. Changes of starch reserves of the leaves of Ilex
aquifolium after artificial spoiling by immovable dust.
Biologia (Bratislava) 18:23-33, 1963. (in Slovak)
(Abstract in German, pp. 32-33)
723. Stell, P. M. Smoking and laryngeal cancer. Lancet 1(7751):617-618,
1972.
536
-------
724. Sterling, T. D., J. J. Phair, S. V. Po^'ack, D. A. Schumsky, and
I. DeGroot. Urban morbidity and fir pollution. A first
report. Arch. Environ. Health 13:158-170, 1966.
725. Sterling, T. D., S. V. Pollack, and J. J. Phair. Urban hospital
morbidity and air pollution. A second report. Arch. Environ.
Health 15:362-374, 1967.
726. Stevens, R. K., A. R. McFarland, and J. B. Wedding. Comparison
of the Virtual Dichotomous Sampler with the Hi-Volume Sampler.
Presented at the American Chemical Society at its 171st
National Meeting in New York on April 4-9, 1976. Preprint
in Volume 16, No. 1. Available through the ACS Environmental
Chemists Division.
727. Stevenson, C. M. An improved Millipore filter technique for
measuring the concentrations of freezing nuclei in the atmosphere.
Q. J. Roy. Meteorol. Soc. 94:35-43, 1968.
728. Stevenson, H. J. R., D. E. Sanderson, and A. P. Altshuller.
Formation of photochemical aerosols. Air Water Pollut . Int. J.
9:367-375, 1965.
729. Stober, W. Design, performance and applications of spiral duct
aeroso] centrifuges, pp. 351-397. In B. Y. H. Liu, Ed.
Fine Particles. Aerosol Generation, Measurement, Sampling,
and Analysis. Proceedings of a Symposium by the U.S. Environ-
mental Protection Agency held in Minneapolis, Minnesota,
May 28-30, 3975. New York: Academic Press, Inc., 1976.
537
-------
/30. Stober, W., and H. Flachsbart. Size-separating precipitation in
spinning spiral duct. Environ. Sci. Technol. 3:1280-1296,
a
731. Stober, W., and F. J. Monig. Measurements with a prototype mas-
distribution monitor for particulate air pollution. In
Session 5, Monitoring and Evaluation of Atmospheric Particulate
Matter. In International Conference on Environmental Sensing
and Assessment, held in Las Vegas, Nevada, September 14-17, 1975.
Now York: Institute of Electrical and Electronics Engineers, 1976
732. Stocks, P. Air pollution and cancer mortality in Liverpool He. pit i1
region and North Wales. Int. J. Air Pollut . 1:1-13, 1958.
733. Stocks, P. Cancer and bronchitis mortality in relation to
atmospheric deposit and smoke. Brit. Med. J. 1:74-79, 1959.
734. Stocks, }' . On the relations between atmospheric pullut:r.n j,i urban
and rural localities and mortality from i iru < ) , I .
pneumonia, with particular reference to 3:4 benzopy reiu- ,
beryllium, molybdenum, vanadium and arsenic. Brit. J. Cancer
14:397-418, 1960.
735. Stocks, P. Lun^, cancer and bronchitis in relation to cigarette
smoking dm fuel ronsumpt i on in I'O roun tri«-. . l>i >i i. I <• > .
Soc. Med. 11:181-185, 1967.
736. Stocks, P., and J. M. Campbell. Lung cancer death rates among
non-smokers and pipe and cigarette smokers. An evaluation
in relation to air pollution by benzpyrene and other substances.
Brit. Med. J. 2:923-939, 1955.
538
-------
737. Stokinger, H. E., L. T. Steadman, H. B. Wilson, G. E. Sylvester,
S. Dziuba, and C. W. LaBelle. Lobar deposition and retention
of inhaled insoluble particulates. A.M.A. Arch. Inu. Hyg.
Occup. Med. 4:346-353, 1951.
738. Storeb«i, P. B. Formation of radioactivity size distributions in
nuclenr bomb debris. J. Aerosol Sci. 5:557-577, 1974.
739. Storozhilova, A. I. Passivation of hygroscopic condensation nuclei
by surfactant adsorption from gas phase, pp. 47-52. In
V. A. Fedoseev, Ed. Advances in Aerosol Physics. No. 1.
New York: Halsted Press, 1972.
740. Strutt, J. W. (Lord Rayleigh). On the scattering of lif,-c by
small particles. Phil. Mag. 41:447-4)4, 1871.
741. Stuart, B. 0. Deposition of inhaled aerosols. Arch. Int.
Med. ni:fif)-7}, 1973.
742. Sturgess, J., and L. Reid. Secretory activity of the human
bronchial ™,
-------
745- Sturgess, J. M., and L. Reid. A new pattern of sputum v-
pp. 368-385. In J. Lawson, Ed. Proceedings of the iifth
International Cystic Fibrosis Conference, Churchill College,
Cambridge, England. September 22nd-26th, 1969. London:
Cystic Fibrosis Research Trust, 1969.
746. Sverdrup, G. M., and K. T. Whitby. On the variation of the aerosol
volume to light scattering coefficient. Particle Technology
Laboratory Publication No. 273. Minneapolis: Mechanical
Engineering Dept., University of Minnesota, 1976.
747. Sverdrup, G. M., K. T. Whitby, and W. E. Clark. Characterization of
California aerosols—II. Aerosol size distribution measurements
in the Mojave Desert. Atmos. Environ. 9:483-494, 1975.
748. Tajiri, Y. Effect of air pollution on metals. Kuki Seijo (Air Clean.
J. Jap. Air Clean. Assoc.) 10(5):90-99, 1972. (in Japanese)
749. Task Group on Lung Dynamics (Committee II - ICRP). Deposition and
retention models for internal dosimetry of the human respiratory
tract. Health Phys. 12:173-207, 1966.
750. Taylor, C. E., A. C. Guyton, and V. S. Bishop. Permeability
of the alveolar membrane to solutes. Circ. Res. 16:
353-362, 1965.
751. Telford, J. W. Freezing nuclei from industrial processes.
J. Meteorol. 17:676-681, 1960.
540
-------
752. Thomas, M. D., R. H. Hendricks, F. D. Gunn, and T. Critchlow.
Prolonged exposure of guinea pigs to sulfuric acid aerosol.
A.M.A. Arch. Ind. health 17:70-80, 1958.
753. Thomas, M. D., R. H. Hendricks, and G. R. Hill. Some impurities
in the air and their effects on plants, pp. 41-47. In
L. C. McCabe, Ed. Air Pollution. Proceedings of the United
States Technical Conference on Air Pollution, Washington, D.C.,
1950. New York: McGraw-Hill Book Company, Inc., 1952.
754. Thomson, M. L. , and D. Pavia. Long-term tobacco smoking and
mucociliary clearance from the human lung in health and
respiratory impairment. Arch. Environ. Health 26:86-89, 1973.
755. Timbrell, V. An aerosol spectrometer and its applications, pp. 290-330.
In T. T. Mercer, P. E. Morrow, and W. Stober, Eds. Assessment of
Airborne Particles. Fundamentals, Applications, and Implications
to Inhalation Toxicity. A Proceedings Publication of the Third
Rochester InLcrnational Conference on Environmental Toxicity.
Springfield: Charles C Thomas, 1972.
7f6. Timbrell, V. Inhalation and biological effects of asbestos, pp. 429-441,
u
In T. T. Mercer, P, E. Morrow, and W. Stober, Eds. Assessment of
Airborne Particles. Fundamentals, Applications, and Implications
to Inhalation Toxicity. A Proceedings Publication of the Third
Rochester International Conference on Environmental Toxicity.
Springfield: diaries C Thomas, 1972.
757. Tomori, Z., and J. G. Widdicombe. Muscular, bronchomotor and
cardiovascular reflexes elicited by mechanical stimulation
of the respiratory tract. J. Physiol. 200:25-49, 1969.
541
-------
758. Toremalm, N. G. The daily amount of tracheo-bronchial secretions
in man. A method for continuous tracheal aspiration in
laryngectomized and tracheotomlzed patients. Acta Otolaryng.
Suppl. 158:43-53, 1960.
759. Toyama, T. Studies on aerosols: I. Synergistic responses of
pulmonary resistance on inhaling sodium chloride and S02
in man. Jap. J. Ind. Med. 4:18-24, 1962.
760. Toyama, T., and K. Nakamura. Synergistic response of hydrogen
peroxide aerosols and sulfur dioxide to pulmonary airway
resistance. Ind. Health (Japan) 2:34-35, 1964.
761. Tucker, A. D., J. H. Wyatt, and D. Undery. Clearance of inhaled
particles from alveoli by normal interstitial drainage
pathways. J. Appl. Physiol. 35:719-732, 1973.
762. Twomey, S. The nuclei of natural cloud formation. Part II. The
supersaturation in natural clouds and the variation of cloud
droplet concentration. Geofis. Pura Appl. 43:243-249, 1959.
763. Twomey, S. The influence of droplet concentration on rain
formulation and stability in clouds. Bull. Observ. Puy
Dome No. 2:33-41, 1959 .
764. Twomey, S., and P. Squires, The influence of cloud nucleus
population on the microstructure and stability of convective
clouds. Tellus 11:408-411, 1959.
765. Twomey, S., and J. Warner. Comparison of measurements of cloud
droplets and cloud nuclei. J. Atmos. Sci. 24:702-703, 1967.
542
-------
766. Urone, P., H. Lutsep, C. M. Noyes, and J. F. Parcher. Static
studies of sulfur dioxide reactions in air. Environ. Sci.
Technoi. 2:611-618, 1968.
767. Urone, P., W. H. Schroeder, and S. R. Miller. Reactions of
sulfur dioxide in air, pp. 370-375. In H. M. England and
W. T. Beery, Eds. Proceedings of the Second International
Clean Air Congress, Held at Washington, D.C., December 6-11,
1970. Sponsored by The International Union of Air Pollution
Prevention Associations. New York: Academic Press, 1971.
768. U.S. Department of Health, Education, and Welfare. Air Quality
Criteria for Particulate Matter. National Air Pollution
Control Administration Publ. No. AP-49. Washington, D.C.:
U.S. Government Printing Office, 1969. 211 pp.
769. U.S. Department of Health, Education, and Welfare. Air Quality
Criteria for Sulfur Oxides. National Air Pollution Control
Administration Publ. No. AP-50. Washington, D.C.: U.S.
Government Printing Office, 1970. 178 pp.
770. U.S. Environmental Protection Agency, Office of Air and Waste
Management, Cifice of Air Quality Planning and Standards.
Position Paper on Regulation of Atmospheric Sulfates.
Report No. i;PA-450/2-75-007. Research Triangle Park, NC:
U.S. Environmental Protection Agency, 1975.
771. Venice preserved. Time 101:54, June 11, 1973.
543
-------
772. Vohra, K. G., K. N. Vasudevan, and P. V. N. hair. Mechanisms
of nucleus-forming reactions in the atmobphere, J. Geophys. Res.
75:2951-2960, 1970.
773. von Hayek, H. The Human Lung. (Translated by V. E. Krahl)
New York: Hafner Publishing Company, Inc., 1960. 372 pp.
774. Waggoner, A. P., and R. J. Charlson. Simulating the color of
polluted air. Appl. Opt. 10:957-958, 1971.
775. Waggoner, A. P., and R. J. Charlson. Measurements of aerosol optical
parameters, pp. 511-533. In B. Y. H. Liu, Ed. Fine Particles.
Aerosol Generation, Measurement, Sampling, and Analysis.
Proceedings of a Symposium by the U.S. Environmental Protection
Agency held in Minneapolis, Minnesota, May 28-30, 1975.
New York: Academic Press, Inc., 1976.
776. Waggoner, A. P., A. H. Vanderpol, R. J. Charlson, S. Larsen,
L. Granat, and C. TragaVdh. Sulphate-light scattering ratio as
an index of the role of sulphur in tropospheric optics. Nature
261:120-122, 1976.
777. Wagman, J., R. E. Lee, Jr., and C. J. Axt. Influence of some
atmospheric variables on the concentration and particle size
distribution of sulfate in urban air. Atmos. Environ. 1:479-
489, 1967.
778. Wagner, H. N., Jr., V. Lopez-Majano, and J. K. Langan. Clearance
of particulate matter from the tracheobronchial tree in
patients with tuberculosis. Nature 205:252-254, 1965.
544
-------
779. Wahdan, M. H. Atmospheric Pollution and Other Environmental
Factors in Respiratory Disease in Children. (Ph.D. Thesis)
London: University of London, 1963. 240 pp.
780. Waller, R. E. Acid droplets in town air. Air Water Pollut. 7:
773-778, 1963.
781. Waller, R. E., and P. J. Lawther. Some observations on London fog.
Brit. Med. J. 2:1356-1358, 1955.
782. "Waller, R. E., and P. J. Lawther. Further observations on London
fog. Brit. Med. J. 2:1473-1475, 1957.
783. Walter, H. Coagulation and size distribution of condensation
aerosols. J. Aerosol Sci. 4:1-15, 1973.
784. Wang, W-C., and G. A. Domoto. The radiative effect of aerosol
in the earth's atmosphere. J. Appl. Meteorol. 13:521-
534, 1974.
785. Warner, C. G., G. M. Davies, J. G. Jones, and C. R. Lowe.
Bronchitis in two integrated steel works. II. Sulfur
dioxide, and particulate atmospheric pollution in and
around two works. Ann. Occup. Hyg. 12:150-170, 1969.
786. Warner, J. A reduction in rainfall associated with smoke from
surgar-cane fires—an inadvertent weather modification?
J. Appl. Meteorol. 7:247-251, 1968.
787. Warner, J. The micrestructure of cumulus cloud. Part II. The
effect on droplet size distribution of the cloud nucleus
spectrum and updraft velocity. J. Atmos. Sci. 26:1272-1282, 1969.
545
-------
788. Warner, J., ana S. Twomey. The production of cloud nuclei by
cane fire;, and the effect on cloud droplet concentration.
J. Atmos. Sci. 24:704-706, 1967.
789. Warren, H. V. and R. E. Delavault. Lead In some food crops and
trees. J. Sci. Food Agricul. 13:96-98, 1962.
790. Watanbe, H. Air pollution and its health effects in Osaka, Japan.
(Preprint) Presented at the 58th Annual Meeting, Air Pollution
Control Association, Toronto, Canada, June 20-24, 1965.
791. Weibel, E. R. Morphometry of the Human Lung. New York: Academic
Press, 1963. 151 pp.
792. Weibel, E. R. Geometric and dimensional airway models of
conductive, transitory and respiratory zones of the
human lung, pp. 136-140. In Morphometry of the Human
Lung. New York: Academic Press, 1963.
793. Wentzel, K. F. Literaturberichte: H. Pajenkamp. Einwirkung des
Zementofenstaubes auf Pflan2en und Tiere. Z. Pflanzenkr.
69:478, 1962.
794. Wesolowski, J. J., A. Alcocer, and B. R. Appel. The Validation
of the Lundgren Impactor. AIHL Report No. 138-B. Berkeley:
Laboratory Services Branch, California State Department of
Health, September 1975.
546
-------
795. Wessel, C. J. Textiles and cordage, pp. 408-506. In G. A. Greathouse
and C. J. Wessel, Eds. Deterioration of Materials. Causes and
Preventive Techniques. New York: Reinhold Publishing Corporation,
1954.
796. Whitby, K. T. Second International Workshop on Cloud and
Ice Nuclei held at Fort Collins, Colorado, 5-19 Aug.
1970. Particle Technology Laboratory Report No. 173.
Environmental Division, Mechanical Engineering Depart-
ment, University of Minnesota, 1973.
797. Whitby, K. T. Modeling of multimodal aerosol distributions. In
ii
V. Bohlau, Ed. Aerosole in Naturwissenschaft, Medizin und
Technik. Proceedings of a conference held in Bad Soden,
October 16-19, 1974. Bad Soden, West Germany: Gesellschaft
11
fur Aerosolforschung, 1974.
798. Whitby, K. T. Modeling of Atmospheric Aerosol Particle Size
Distributions. A Progress Report on EPA Research Grant
No. R800971, Sampling and Analysis of Atmospheric
Aerosols. Particle Technology Laboratory Report No. 253.
Environmental Division, Mechanical Engineering Depart-
ment, University of Minnesota, 1975.
799. Whitby, K. T. Electrical measurement of aerosols, pp. 584-624. In
B. Y. H. Liu, Ed. Fine Particles. Aerosol Generation,
Measurement, Sampling, and Analysis. Proceedings of a Symposium
by the U.S. Environmental Protection Agency held in Minneapolis,
Minnesota, May 28-30, 1975. New York: Academic Press, Inc.,
1976.
547
-------
800. Whitby, K. T., A. B. Algren, and R. C. Jordan. The dust spot method
for evaluating air cleaners. Heating-Piping Air Cond. 28(11):
151-157, 1956.
801. Whitby, K. T., and B. Cantrell. Atmospheric aerosols—characteristics
and measurements. In Session 29, Fine Particles. In International
Conference on Environmental Sensing and Assessment, held in
Las Vegas, Nevada, September 14-17, 1975. New York: Institute
of Electrical and Electronics Engineers, 1976.
802. Whitby, K. T., R. E. Charlson, W. E. Wilson, and R. K. Stevens.
The size of suspended particle matter in air. Science 183:
1098-1099, 1974. (Letter response to Lee, R. E., Jr.
The size of suspended particulate matter in air. Science 178:
567-575, 1972)
803. Whitby, K. T., W. E. Clark, V. A. Marple, G. M. Sverdrup,
G. J. Sem, K. Willeke, B. Y. H. Liu, and D. Y. H. Pui.
Characterization oJ? California aerosols—I. Size distribu-
tions of freeway aerosol. Atmos. Environ. 9:463-482, 1975.
804. Whitby, K. T., W. E. Clark, V. A. Marple, G. M. Sverdrup, K. Willeke,
B. Y. H. Liu, and D. Y. H. Pui. Evolution of the Freeway Aerosol.
Presented at the American Chemical Society Annual Meeting, Chicago, 111.
August 29, 1973.
------ - - - . t .
805. Whitby, K. T., R. B. Husar, and B. Y. H. Liu. The aerosol size
distribution of Los Angeles smog. J. Colloid Interface Sci.
39:177-204, 1972.
548
-------
806. Whitby, K. T., D. B. Kittelson. B. K. Cantrell, N. J. Barsic,
D. F. Dolan, L. I). Tarvestad, D. J. Nieken, J. L. Wolf, and
J. R. Wood. Aerosol size distribution.'; and concentrations
measured during the General Motors Proving Grounds sulfate
study, pp. 29-80. In R. K. Stevens, P. J. Lamothe, W. E. Wilson,
J. L. Durham, and T. G. Dzubay, Eds. The General Motors/
Environmental Protection Agency Sulfate Dispersion Experiment.
Selected EFA Research Papers. EPA-600/3-76-035. Research
Triangle Park, N.C.: U.S. Environmental Protection Agency, 1976.
(Available from the National Technical Information Service,
Springfield, Va.)
807. Whitby, K. T., and B. Y. H. Liu. Advances in Instrumentation and
Techniques for Aerosol Generation and Measurement. Particle
Technology Laboratory, P. L. Publ. No. 216. Minneapolis:
University of Minnesota, 1973. 34 pp.
308. White, W. H., J. A. Anderson, D. L. Blumenthal, R. B. Husar, N. V. Gillani,
J. D. Husar, and W. E. Wilson, Jr. Formation and transport of
secondary air pollutants: Ozone and aerospls in the St. Louis urban
plume. Srtfnco 194:187-189, 1976.
309. Whittaker, R. H., F. H. Bormann, G. E. Likens, and T. G. Siccama.
The Hubbard Brook ecosystem study: Forest biomass and
production. Ecol. Monogr. 44:233-254, 1974.
810. Widdicombe, J. G., D. C. Kent, and J. A. Nadel. Mechanism of
bronchoconstriction during inhalation of dust. J. Appl.
Physiol. 17:613-616, 1962.
549
-------
811. Wilkins, E. T. Air pollution and the London fog of December, 1952.
J. Roy. Sanit. Inst. 74:1-21, 1954.
I 812. Wilkins, E. T. Air pollution aspects of the London fog of
December 1952. Roy. Meteorol. Soc. Q. J. 80:267-278, 1954.
813. Willeke, K., and B. Y. H. Liu. Single particle optical counter:
Principle and application, pp. 697-729. In B. Y. H. Liu, Ed.
Fine Particles. Aerosol Generation, Measurement, Sampling,
and Analysis. Proceedings of a Symposium by the U.S. Environ-
mental Protection Agency held in Minneapolis, Minnesota,
May 28-30, 1975. New York: Academic Press, Inc., 1976.
814. Willeke, K., and K. T. Whitby. Atmospheric aerosols: size distri-
bution interpretation. J. Air Pollut. Control Assoc. 25:529-
534, 1975,
815. Willeke, K., K. T. Whitby, W. E. Clark, and V. A. Marple. Size
distributions of Denver aerosols—a comparison of two sites.
Atmos. Environ. 8:609-633, 1974.
816. Wilson, J. G. Exposed Concrete Finishes, Vol. 2., pp. 115-124.
New York: John Wiley and Sons, Inc., 1965.
817. Wilson, W. E., Jr., and A. Levy. A study of sulfur dioxide in
photochemical smog. I. Effect of S02 dioxide and water
vapor concentration in the l-butene/NOx/S02 system>
J. Mr Pollut. Control Assoc. 20:385-390, 1970.
550
-------
81fc. Wilson, W. E., Jr., E. L. Merryman, and A. Levy. A Literature
Survey of Aerosol Formation and Visibility Reduction in
Photochemical Smog. A research report for the American
Petroleum Institute. Columbus: Battelle Memorial
Institute, 1969. 41 pp.
819. Wilson, W. E,, Jr., E. L. Merryman, and A. Levy. Aerosol formation
in photochemical smog. 1. Effect of stirring. J. Air Pollut.
Control Assoc. 21:128-132, 1971.
820. Winchester, J. W. Trace metal associations in urban airborne
particulates. Bull. Amer. Meteorol. Soc. 54:94-97, 1973.
821. Winchester, J. W., T. B. Johanson, and R. E. Grieken. Marine
influences on aerosol composition in the coastal zone.
J. Rech. Atmos. 8(3-4):761-776, 1974.
822. Winkelstein, W., Jr., and S. Kantor, Respiratory symptoms and
air pcJlution in an urban population of northeastern United
States. Arch. Environ. Health 18:760-767, 1969.
823. Winkelstein, W., Jr., S. Kantor, E. W. Davis, C. S. Maneri, and
W. E. Mosher. The relationship of air pollution and
economic status to total mortality and selected respiratory
system mortality in men. I. Suspended particulates. Arch.
Environ. Health 14:162-171, 1967.
551
-------
£24. Winkelstein, W., Jr., S. Kantor, E. W. Davis, C. S. Maneri, and
W. E. Mosher. The relationship of air pollution and economic
status to total mortality, and selected respiratory system
mortality in men. II. Oxides of sulfur. Arch. Environ. Health
16:401-405, 1968.
825. Winkler, P. The growth of atmospheric aerosol particles as a
function of the relative humidity. II. An improved concept
of mixed nuclei. J. Aerosol Sci. 4:373-387, 1973.
826. Winkler, P., and C. Junge. The growth of atmospheric aerosol
particles as a function of the relative humidity.
Part I. Method and measurement at different locations.
J. Recherch. Atmos. 6:617-638, 1972.
827. Wolff, R. K., M. Dolovich, G. Obminski, and M. T. Newhouse.
Effects of sulfur dioxide on tracheobronchial clearance
at rest and during exercise. In W. H. Walton, Ed.
Inhaled Particles IV. London: Pergamon Press Ltd, 1977.
828. Wolff, R. K., M. Dolovich, C. Rossman, and M. T. Newhouse. Sulfur
dioxide and tracheobronchial clearance in man. Arch. Environ.
Health 30:521-527, 1975.
829. Wood, T., and F. H. Bormann. The effects of an artificial acid
mist upon the growth of Betula alleghaniensis Britt. Environ.
Pollut. 7:259-268, 1974.
830. Wood, T., and F. H. Bormann. Increases in foliar leaching caused by
acidification of an artificial mist. Ambio 4:169-171, 1975.
552
-------
831. Woodcock, A. H., and D. C. Blanchard. Tests of the salt-nuclei
hypothesis of rain formation. Tellus 7:437-448, 1955.
832. Yamamoto, G., and M. Tanaka. Increase of global albedo due to
air pollution. J. Atmos. Sci. 29:1405-1412, 1972.
833. Yamasaki, S., and Y. Yokoi. Accelerated atmospheric corrosion tests
in polluted air. (2nd report) Influence of dewing on mild
steel in su3fur dioxide environment. Boshoku Gijutsu
(Corrosion Engineering) 20(11/12)123-29, 1971.
83.4. Yeager, H., Jr. Tracheobronchial secretions. Amer. J. Hed. 50:
493-509, 1971,
835. Yeates, D. B. The Clearance of Soluble and Particulate Aerosols
Deposited in the Human Lung. Ph.D. Thesis, University of
Toronto, Ontario, Canada, 1974.
836. Yeates, D. B., NT. Aspin, A. C. Bryan, and H. Levison. Regional
clearance 01 ions from the airways of the lung. Amer. Rev.
Resp. l>is. 107:602-608, 1973.
837. Yeates, D. B., N. Aspin, H. Levison, M. T. Jones, and A. C. Bryan.
Mucociliary tracheal transport rates in man. J. Appl. Physiol.
39:487-495, 1975.
553
-------
838. Yeates, D. B., J. M. Sturgess, S. R. Khan, H. Levison, and N. Aspin.
Mucociliary transport in trachea of patients with cystic fibrosis.
Arch. Dis. Child. 51:28-33, 1976.
839. Yocom, J. E., and R. 0. McCaldin. Effects of air pollution on
materials and the economy, pp. 617-654. In A. C. Stern, Ed.
Air Pollution (2nd ed.), Vol. 1. Air Pollution and its Effects.
New York: Academic Press, 1968.
840. Yudine, M. I. Physical considerations on heavy particle diffusion.
Adv. Geophys. 6:185-191, 1959.
841. Zeidberg, L. D., R. A. Prindle, and E. Landau. The Nashville
air pollution study. I. Sulfur dioxide and bronchial asthma.
•' ' !<-ry report. Amer. Rev. Resp. Dis. 84:489-503, 1961.
342. Zeidberg, L. D., R. A. Prindle, and E. Landau. The Nashville
air pollution study. III. Morbidity in relation to air pollution.
Amer. J. Public Health 54:85-97, 1964.
&43. Zeidberg, L. D., R. J. M. Horton, E. Landau, R. M. Hagstrom, and
H. A. Sprague. The Nashville air pollution study. V. Mortality
from diseases of the respiratory system in relation to air
pollution. Arch. Environ. Health 15:214-224, 1967.
844. Zeronian, S. H., K. W. Alger, and S. T. Omaye. Reaction of fabrics
made from synthetic fibers to air contaminated with nitrogen
dioxide, ozone, or sulfur dioxide, pp. 468-476. In
H. M. Englund and W. T. Beery, Eds. Proceedings of the
Second International Clean Air Congress, Washington, D.C.,
December 1970. New York: Academic Press, 1971.
554
-------
TECHNICAL REPORT DATA
c read Inunictions on the rcierse before i.(>inptct:ng)
i Rt '^ORT NO
EPA-600/1-77-053
3 RECIPIENT'S ACCESSION NO.
4 TITLE AND SUBTH LE
AIRBORNE PARTICLES
6. PE RFORMING ORGANIZATION CODE
5 REPORT DATE
November 1977
7. AUTHOR(S)
Subcommittee on Airborne Particles
8. PE RFORMING ORGANIZATION REPORT NO.
9, PERFORMING ORGANIZATION NAME AND ADDRESS
Committee on Medical and Biologic Effects of
Environmental Pollutants
National Academy of Sciences
Washington, D.C. 20460
10. PROGRAM ELEMENT NO.
1AA601
11. CONTRACT/GRANT NO.
68-02-1226
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
RTP,NC
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA 600/11
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This document summarizes the literature on airborne particles related to
effects on man and his environment for consideration of the Environmental Protection
Agency in updating the information in the Air Quality Criteria for Particulate Matter.
Specific particles such as lead, arsenic, or asbestos are not discussed. These
substances have been the subject of other NAS publications. Nor are living particles
considered.
The emphasis of the report is on particles that result from man's activities.
The origins, behavior, and fate of such particles, their physical and chemical
characteristics, their interactions, transport, and removal from the ambient air
are discussed in chapters 2 through 5. Routine and special monitoring trends are
reviewed in chapter 6. In chapters 7 and 8 there is a detailed discussion of the
deposition, clearance, and retention of particles, their effects on man and on other
animals. Chapter 9 is devoted to the available epidemiologic evidence from which
conclusions can be drawn about the effects of particulate pollution on man. It
indicates the gaps in our knowledge about exposure/response relationships and
suggests studies that should be conducted to remedy these deficiencies. Chapters 10
and 11 consider the effects of particulate matter on vegetation and materials.
Summaries, conclusions and recommendations are consolidated in Chapter 12.
17
a
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
particles
aerosols
air pollution
toxicity
health
ecology
chemical analysis
b.IDENTIFIERS/OPEN ENDED TERMS
particulates
COS AT i Field/Group
06 H, F, T
°, DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report}
UNCLASSIFIED
21. NO. OF PAGES
563
20 SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
PA Form 2220-1 (9-73)
555
------- |