Briefing Report
PROBLEMS RELATING TO FINE SUSPENDED PARTICIPATES
U. S. Environmental Protection Agency
National Environmental Research Center
Research Triangle Park, North Carolina 27711
1973
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Preface
This document was prepared by a Task Force convened under the
direction of Dr. John F. Finklea, Director, National Environmental
Research Center, Research Triangle Park (NERC/RTP). The objective
was to identify the major problem areas associated with fine par-
ti culates in the atmosphere, and their effects on human health and
welfare, with a view toward the need for control under the provisions
of the Clean Air Act, as amended.
The following members served on the NERC/RTP Task Force:
James R. Smith Andrew O'Keeffe
John Nader Robert Chapman
Jean French Paul Altshuller
J.H.B. Garner Robert E. Lee
James Dorsey James H. Abbott
Elbert Tabor Glen Fairchild
Gary Foley William E. Wilson
A. B. Craig Justice Manning - OAQPS
Jack Wagman John Sigsby
Douglas Fox James 0. Baugh
Kenneth T. Knapp Ronald L. Bradow
Robert M. Burton
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NOTICE
This document is a preliminary draft. It
has not- been formally released by EPA
and shoijM^Qt at this stape he r'ormtri'ed
to represent Agency policy. It is being
circulated for comment on it?, technical
accuracy and policy implications.
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TABLE OF CONTENTS DO NOT QUOTE OR C1
PREFACE
QIIMMADV. 1
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CONCLUSIONS ............ - .............. - --------------- ....... 5
RECOMMENDATIONS ............ -- ..... ---- ...... _ 7
I. INTRODUCTION ..... - ............ - ----- -- -------- -------- --35
II. CHARACTERIZATION METHODOLOGY ....... ------- _ _ -------- 36
A. Definitions ---- -----, ---- - ...... , ------ ,---- ---- _..---, ------- - 35
B. Particle Sizing Methods ---ซ ---- ---_-, ---- __ ------ _ 35
1 . Microscopic Methods .............. - ..... --__-_-__-, ----- ------37
2. Aerodynamic Fractionating Devices- ..... -- - ----- --____37
3. Optical Sizing Devices ---- < ---- < -------- - ---- -- ------ ---- ---- ----33
4. Particle Size Sampling -------- < - ----- ----- ------ ---- ----- --39
a. Ambient Aii ------ ................. ----- - ...... - -- - -----39
b. Stationary Sources----- ----- - -------- - ----. ,-_-___-. __ 39
c. Mobile Sources. ------ - ............... ---- - ......... - ---- - ------- 40
C. Chemical Composition ---- - <--- ---- - ---------- < ------- ---------- 40
D. Problem Areas ---- ----- ------- . ------ ....... - ---- _________. ___-A]
III. ATMOSPHERIC INPUT ...... - ........ ,..,44
A. Stationary Source Emissions and Control ,--,---. , ------ >-- ----- 44
1 . Emissions----- ...... - ----- - --------- ----------- -- ___ -------44
a. Present Status ...... -- ...... --- ---------- ---. -,-_-- 44
b. Planned R & D ---- - ----- ...... ........ _ -___, ---- 45
2. Control---- ..... ------- ........ - ..... _ ---- 45
a. Primary Fine Particulates ------- ----- ---- --__-----__. -.45
b. Secondary Fine Particulates ----- ------ ,_..-,__, ------ --,43
3. Problem Areas ---- ----_---,-,---,,, ---- >, r,^_^_r,_m^^r,,ป^,_mป^49
B. Mobile Source Emissions and Control--------- .__, ^--_^_^,_--5]
1 . General Discussion--"-"------. ----- - ------ ^-r.~-~-,--~--~ ----- _____51
2, Problem Areas--- .......... - ...... ----- ------- ---,-. ---- 53
C, Natural Sources--' ---- -- ----- - ------- -- ----- ........ _...,_->,,55
1 . General Discussion--------- ---- __-_,.---_, ---- ^.ป.7.,ปซ^^r,^r..r,^.55
2. Problem Areas- ---- ,._,.-, ------ ,,-,,-,-., ---- ^- -------- --- ---- ---56
IV. ATMOSPHERIC LOADING ....... - -- ---- ----- , ---- .,,._., 58
A. Introduction _.---, ...... ..... ~^ ----- lr.ป^---.-,^r.ป--':>Q
B, Transport and Prediction Modeling ---- -.-.,-,.,-...-,..-_.-__.,., 53
C. Transformations ---- ---- ---- ------ ...... ------- --. ----- --- ---- 60
1. Sul fates ......... - ........... ----- - ---- --- ----- . -, ..... ----60
2, Nitrates ...... -- ........ - ........ __.,_..,,_.,.-,. ----- , ---- _ป5Q
3. Organic Parti culates ---- - <-< ------ ---< ----- ----- ---- ----- ------ 59
4. Ammonia-. ----- ------- ----_--_-, ---- , ----- - ..... ^r~~~r.~~-.^-,~-~~-(:>Q
5Dav>-H/-la ^n-yo _______ซ.______--,___--__-._-.__--.__-,____ _ SI
. tar I. 1 1- I c o I /.c---"----1-- ------------- ----- - -_______,_(-) |
6. Properties ------ ---- ...... ---------, ---- ----- ------ ,-f._.,,,,,_,-___,.6i
7. Problem Areas ------ ------. ---- , ------ ------ ----------- .,., ---- ,---61
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DRAFT
TABLE OF CONTENT^ J.QJ Q^^ QR C|TE
Page
IV. CONTINUED
D. Natural Removal Processes - 62
1. General < ' '--62
2. Problem Areas--- 63
E. Physical and Chemical Characterization of Ambient Air
Particulate------- < >-- - - -. 63
1. Size Distribution-- 63
2. Composition and Concentration : 66
3. Problem Areas< , . . 66
V. EFFECTS 71
A. Health , -71
1. Experimental Studies (Man and Animals)-------"- ,--71
a. Introduction--*-< > ., 71
b. Dose-Response RElationships < >--< --- 72
c. Physical Factors --- -73
d. Host-Related Factors-------- - 75
e. Retention Factors 78
f. Biological Respirable Particles--- --< 79
2. Epidemiology----- ,.....,_, rP,r,^^r,^r,r,^,.F,r,r,r.^^^r,T,^^_r,mr,80
a. Asthma Study------------------------------------------T- --80
b. CHESS Studies - __..,,,.,.r..,,,_,,.,,._.,,.r,r...,.r,...,,,_8l
3. Relative Toxicity-----' --..,- ^--,.----83
4. Problem Areas < . ----..,.--84
a. Aerometry -- --.. :- .^---84
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B. Effects on Visibility, Weather and Climate. --86
If V I O I L) I I | U V ^1*^p^r"w^^^"^^^wซซ*"""r'^M^^wf"r*r^^'w^^^^^^,^i^i^^^^"i?^.^i^^^^^^^^r"^^QQ
2. Weather and Climate --. .--.. - ^^86
C. Ecology-- - , , ----89
VI. CONTROL STRATEGIES - --90
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SUMMARY, CONCLUSIONS AND RECOMMENDATIONS *ฐ/
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A. SUMMARY
Wfr
There is no universally acceptable definition of fine particulate. c
For the purpose of this report we have chosen an upper size in the range of
2-5 urn diameter. Based upon the limited data available, a significant
portion of the particulate found in the atmosphere would be classified
as fine. The total atmospheric loading consists of primary and
secondary particulates, as defined in Section II.
The term fine particulate implies that the characteristic of
physical size is the dominant factor relative to air pollution problems.
This is not necessarily true with respect to health effects. Chemical
composition, and related physical factors, may prove to be equally or
more significant.
For the purpose of this report, we have classified the major source
categories of fine particulates as: (1) stationary, (2) mobile,
and (3) natural. Natural sources include forest fires, wind-blown dust,
volcanic activity, and sea salts. Natural gaseous emissions of H2S,
NO , NH3, and hydrocarbons are transformed in the atmosphere to sulfate,
nitrate, ammonium compounds, and hydrocarbon aerosols. We do not have
reliable quantitative estimates of the contribution of each of these
source categories to the total atmospheric loading. There appears
to be significant regional differences in source contributions. Emissions
from mobile sources are primarily in the fine particulate category.
In Los Angeles the major portion of the mart-made fine particulates has been
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attributed to mobile sourcesprincipally the passenger car. On a national
basis, and in particular, the eastern industrial regions, the stationary
sources probably contribute the larger portion. Neither global nor local
concentrations'Of fine particulates'in the atmosphere have been adequately
characterized. Where particulate data have been characterized, by particle
size and chemical composition, it appears that each chemical constituent
may have a discrete size distribution.
The formation of secondary fine particulates in the atmosphere
represented major problem in assessing man-made and natural contributions
to the total atmospheric loading. Neither the chemical mechanisms
nor the reaction rates involved in these transformations are well known.
Very little effort has been devoted to understanding the removal
mechanisms for fine particulates in the atmosphere. The principle
mechanisms are thought to be precipitation, dry deposition, and biological;
however, none of these are well understood.
The toxicological properties of inhaled particles are related to
specific physical and chemical properties of the particles and host con-
ditions which affect response to exposure. The principal path through which an
airborne particle exerts an effect on health is presumed to be through
inhalation and consequent effects on the respiratory system. This
presumption is acceptable for a determination of short-term effects of
irritant aerosols; however, it may be less tenable in the consideration
of long-term exposure effects where such responses as carcinogenesis,
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deposition, the body insult may actually be initiated by an overburden
of particles of a specific chemical species whose effects are aggravated by
particle size.
Fine particulate control technology is now at a early state of
development, except under certain limited conditions where collection
systems have reached high mass efficiencies resulting in the capture
of fine particles along with large particle size material.
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B. Conclusions
In essence, the following conclusions reflect the problem areas
related to fine particulates in the atmosphere,
(1) The present data base, and current state of knowledge related
to the pollutant classification fine particulate, is inadequate
to serve as a basis for rational decisions regarding control strategies
under the provisions of the Clean Air Act.
(2) Available information suggests that certain chemical
elements and compounds included in the classification of fine particulate
may account for the major portion of the air pollution stress on human
health and the environment.
(3) The total atmospheric loading of fine particulate results from the
emissions of primary fine particulate and from the secondary fine particulate
formed by the complex transformation and transport processes occurring
in the atmopshere between other particulates and/or gases. Data are
inadequate to define the relative contribution of primary and secondary
fine particulate to atmospheric loading on a national basis.
(4) Atmospheric visibility, certain weather processes, and certain
climatic conditions can be related directly to fine particulate in the
atmosphere. Particle size range of greatest importance for effect
on visibility is 0.1 to 1.0 >mi,
(5) The total atmospheric loading of fine particulates is
related to source inputs, transformation, transport and removal processes.
These processes and conditions are not understood well.
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(6) At the present time, the man-made contribution to the total
atmospheric loading of fine particulate cannot be quantitatively
separated from the natural contribution.
(7) The control of the man-made contribution to the total
atmospheric loading of fine particulates will require the control
of primary fine particulates and gaseous precursor emissions.
(8) The total atmospheric loading of fine particulate and its
effect upon human health and welfare are dependent upon a complex
matrix of directly and indirectly related processes. Any compre-
hensive study of this problem cannot ignore these relationships.
(9) Solutions to the problems related to the control of man-made
contributions to the atmospheric loading of fine particulate will
require an extensive data base which must be developed over an extended
period of time. Implementation of partial control actions should
proceed in consonance with the accumulation of this data base.
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C. Recommendations
Suspended fine particulate in the atmosphere represents not
only one of the most complex scientific and technical aspects of
air pollution, but also one of the most important. In fact, it
encompasses a large segment of the total atmospheric pollution
problem. The solutions will require a closely integrated research
and development effort involving responsible federal agencies,
universities, and industry. The program must be oriented toward
specific goals, and will require extensive resources over an extended
period of time. This requires a program planning effort which
exceeds the scope of this document and the efforts of this task
force. However, an attempt has been made to identify the major
problem areas, and hence provide the basis for a more extensive planning
exercise.
The problem of suspended fine particulates is so complex that
it is difficult to place in perspective without the aid of systematic
paths of inquiry. An effort has been made to depict these paths in
Figures S-l - S-ll. These represent the essential elements
of a research and development program to achieve the following goal:
"Determine and understand the contribution
of man-made sources to the total atmospheric
loading of fine particulate; assess its effect
upon human health and welfare; develop needed
control technology; and define and implement
control strategies when and where the result
of this research effort dictates that such
are necessary."
The proposed research and development program would include five major
elements, as indicated in Figure 1. These are: (1) the atmospheric
input from man-made and natural sources, both controlled and
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uncontrolled; (2) characterization of the fine participate in
the atmopshere; including physical and chemical properties, and
transformation, transport, and removal processes; (3) quantify the
atmospheric loading in space and time, (4) determine the health
and welfare effects, and (5) develop specific control technology-
The atmospheric input element must address the contribution
from man-made stationary and mobile sources, and natural sources.
Emissions from each of these sources must be characterized in terms
of physical and chemical properties, both in the process stream
and at the source output. The output must be quantified in terms
of mass, number, and chemical composition as a function of size. This element
must consider both primary fine particulate and gaseous: secondary presursor
emissions.
Fine particulate in the atmosphere is subject to complex
physical and chemical transformation, transport, and removal processes.
These must be at least semi-quantitatively assessed and understood
if the atmospheric loading is to be efficiently controlled.
The atmospheric loading in space and time reflects the degree
to which receptors are exposed, and consequently the stresses upon
man and the environment. It represents the realistic input essential
for the assessment of effects. Adequate simulation and prediction
models must be developed to quantitatively estimate the atmospheric
loading. This will require inputs,both in terms of understanding and
quantitative values, from the program element involving transport,
transformation, and removal processes, as well as quantitative
measurements from a routine data collection network.
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In the final analysis, the assessment of health and welfare
effects must be based upon the concentrations, as well as physical properties
and chemical composition, of fine particulate observed in the atmosphere.
The program element concerned with atmospheric loading must provide
in the proper format the necessary quantitative and qualitative
input. The effects program element must be concerned with acute
effects resulting from short-term exposure to maximum concentrations,
or highly toxic substances; and chronic effects from long-term exposure.
These studies will require information on size distribution (possibly both mass
and number density), chemical composition, physical characteristics, and con-
ditions of exposure. Chronic studies will require long periods of record.
The assessment of human health effects will require extensive laboratory
and epidemiological studies. The problem of extrapolation from
laboratory experiments with animals to human response should be given
a high priority. In designing and conducting the laboratory studies
consideration should be given to interrelating them with the needs
of epidemiological studies. Close coordination and feed-back between
the effects effort and the control technology effort of the atmospheric
input element will-be essential.
The environmental effects studies will require specific inputs
from the atmospheric loading program elements-. Visibility studies will re-
quire quantitative data on size distribution, chemical composition, physical
properties, and concentrations. Ecological studies will depend heavily
upon information concerning removal processes.
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The ultimate goal of research on the heWlh) effefcWHbr-fWte ^arti-
culates is, as for other pollutants, the development of complete and
accurate dose-response relationships for humans. Fine particulate research
is beset by problems common to all pollution research. Among these are
incomplete aerometric technology and the frequent necessity to make
inferences about human response from animal studies.
Fine particulates research is especially complex, due to the
twin factors of particle size distribution and particle chemistry.
With gases, size distribution is not a problem. With :particles, it is
crucial. Without knowledge of particle size distribution, we cannot know
the principal site or sites of deposition, and thus cannot fully understand
the particulate pollutant's mechanism of physiologic action. Thus,
a prime goal of particle research must be to develop size-specific
dose-response relationships for particulates of concern. Amdur has begun
this work with sulfates, and has demonstrated the importance of particle
size.
The importance of knowing specific particle chemistries in addition
to size distributions must be stressed. For example, the finding that
different metallic sulfate compounds have different effects on airway
resistance supports the contention that the sulfate's companion
cation or cations are important to the sulfate's toxicity. Whether
the cation of the sulfate is primary responsible for the observed
effect must be determined.
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Perhaps the ultimate characterization of local atmospheres, and
thus of individual pollutant doses, will come through the use of personal
enviornmental monitors. At present, it is very difficult to conceive of
a personal monitor that is both inconspicuous and capable of making size-
specific measurements of potentially toxic pollutants. However, if the
list of pollutants can be narrowed to a few of greatest concern (and
that may not be possible), such monitors may be plausible. They would
certainly be helpful in the development of dose-response relationships.
Health research on fine particulates must be expanded in two major
ways. First, new health indicators must be examined in experimental
studies. The experimental work to date has dealt primarily with one
physiologic indicator, airway resistance. This indicator is a functional
one, which has been used to reflect acute exposures. Structural changes,
which underlie functional changes, must also be studied. Perhaps more
important, the impact of chronic particulate exposure on chronic and acute
disease must be assessed.
Second, studies of fine particulates must be extended to humans.
Of course, ethical constraints will not permit the exposure conditions to
which animals are subjected. However, carefully controlled clinical
studies involving chamber exposures will have an important place in fine
particle research. Such studies will be most helpful in the systematic
description of particle toxicity. Conceivably, clinical studies will
narrow the long list of fine particulate substances to a few of major concern
Clinical studies should also help in assessing the effects of different par-
ticle size distributions.
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Epidemic!ogic studies will be necessary to assess the chronic and
acute effects of fine particulates in ambient atmospheres. Such studies
may be particularly useful in elucidating the effects of long-term exposures.
Also, it has proven extremely difficult to find field settings in which ,a single
pollutant or pollutant class 1s present in the absence of other pollutants.
Thus, field studies may prove at least as useful in assessing pollutant
interactions as in assessing the effects of individual particulates.
The effects of particulates alone, or even of individual particulate substances
could be assessed in epidemiologic studies if a series of biological indicators,
specific for particulate exposures, were developed. It is quite conceivable, for
instance, that certain cytologic changes in the resptratory tract might
reflect exposures to particulates and to no other pollutants. Certain
changes in enzymes, other proteins, and cells away from the respiratory
tract might also reflect such exposures. The use of epidemiologic indi-
cators specific for particulates (and for other pollutants) would clarify
and complement toxicologic and clinical studies in the field of fine
particulate research. Complete epidemiologic and clinical data will
relieve us from the risky task of developing air quality standards
largely from animal data.
Given adequate information regarding health and welfare effects,
the problem of specifying control technology, and the definition and
implementation of control strategies, would depend upon the status
of technology, and cost-benefit relationships. Control technology must
be developed, to control both primary fine particulate and gaseous secondary
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particulate precursors. The problem of physical and chemical
characterizitoon of emission sources is particularly important.
Improved techniques must be developed to determine the contribution
of man-made sources to the total atmospheric loading. The problem of
relative importance of secondary pollutants resulting from precursor
emissions from stationary and mobile sources must be resolved. Solution
of these problems will require improved measurement and analysis
techniques.
A summary of current research activities related to fine particulate
is given in Table S-l. These efforts are contributing materially to our
information base, however, much remains to be done. Specific recommended
new research projects are listed in Table S-2. These projects reflect
the needs of the proposed research program; however, they do not
represent the entire scope. In essence, they represent the capabilities
of the NERC/RTP,
Finally, in our emphasis of "fine particulates", we must not
forget the importance of larger particles as objects of study. Such
particles may promote disorders in the nose, nasopharynx, sinuses,
or gastro-intestinal tract.
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FINE PARTICIPATE
AREA AIR POLLUTION CYCLE
Figure 5-1
CUE
STATIONARY.
EMISSIONS
&
CONTROL
J5to
MOBILE
EMISSIONS
&
CONTROL
\ \
\
\
\
CONTROL
STRATEGIES
NATURAL
SOURCES
ATMOSPHERIC
INPUT-
PHYSICAL AND
CHEMICAL
CHARACTERIZATION
TRANS-
FORWION
-*H
TRANSPORT!
\ fc NON-ATMOSPHERIC,
V [ POLLUTION
][ EFFECTS
NATURAL
REMOVAL
PROCESSES
r
; ATMOSPHERIC
; LOADING -
PHYSICALS
| CHEMICAL
jCHARACTER-
IZATION
HEALTH
&
WELFARE;
EFFECTS!
I
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STATIONARY EMISSIONS AND CONTROL
FINE PARTICULATE
Figure 5-2
DRAFT
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PHYSICAL &
PROPERTIES OF
STREAM
CONTROL
DEVICES
5*
PROCESS
CATION
RAW
MATERIALS
CLEANUP
\
PARTICLES
GASEOUS
PRECURSORS!
SIZE
DISTRI-
BUTION
CONCENTRATION
COMPO-
SITION
COMPO-
SITION
CONTROL
STRATEGIES!
MASS
NUMBER
DENSITY
ATMOSPHERIC
INPUT-
PHYSICAL &
CHEMICAL
CHARACTERIZATION
-------
cr>
i
FUELS
FUEL
ADDITIVES
T
MOBILE EMISSIONS AND CONTROL
FINE PARTICULATES
Figure 5=3
PHYSICALS ,
CHEMICAL I
CHARACTERI-
ZATION
WITHIN I
SYSTEM !
OPERATING
CONDITIONS-
CYCLIC
CONTROL
DEVICES
NEW
POWER i
SYSTEMS
PARTICU-
LATE
SIZE
*H DISTRI-
BUTION
CONCEN-
TRATION!
EMISSIONS!
COMPO-
SITION
GASEOUS
PRECURSORS
CONCEN-
TRATION i
CONTROL
STRATEGIES
ATMOSPHERIC
INPUT
-------
NATURAL SOURCES
FINE PARTICULATE
Figure 5-4
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PRIMARY
GASEOUS
SECONDARY
PARTICULATE
PRECURSORS
*ป
SOILDUST
VOLCANOS
FOREST
WILDFIRE
H POLLEN
aas^^u'migiimtCTBsm
FLORAi
I DECAYING
ORGANIC MATTER
OCEANS, LAKES
AND RIVERS
DISTRIBUTION!
MASS
CONCENTRATION |-
,__..^_ ^- f!
COMPOSITION
&
PROPERTIES
CONCENTRATIONS
COMPOSITION
NO.
DENSITY
TRANS-
FORMATION
i
ATMOSPHERIC
INPUT
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ATMOSPHERIC INPUT
INVENTORY & CHARACTERIZATION
FINEPAR.TJCULATE
Figure 5-5
MAN-
MADE
00
I
NATURAL
PRIMARY
GASEOUS
SECONDARY
PARTICULATE
PRECURSORS
TRANS- i
FORMATION!
URBAN
NON-
URBAN!
SIZE DIS-
TRIBUTION
CONCEN-
TRATION
COMPO-
SITION
TRANSFORMATION
TRANSPORT
8,
REMOVAL
-------
TRANSPORT
FINE PARTICIPATE
Figure 5-6
n
DO NOT QUOTE OR CITE
IPPJMAPV
rmmMK T
r^prnMnARvl
L^^^22^j
1
J-3^
>
SIZE i
niCTDIDIITIfiMI
Ulo 1 KlbU 1 IUNI
rmyrpMTDflTinM
COMPOSITION
PROPERTIES
i ' '
METEOROLOGICAL
VARIABLES i
BปW
t
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1 1
. J t .
^^N^^^^^
LESW
ATMOSPHERIC
MODEL
ATMnCDUCDIP
A I IVIUorHtnlU
LOADING <
-------
00
TRANSFORMATION
FINE PARTICULATE
Figure 5-7
CITE
ro
o
PRIMARY
COMPOSITION i
SIZE DISTRIBUTION1
CONCENTRATION ',
GASEOUS
PRECURSORS
COMPOSITION
CONCENTRATION
f**
AEROSOL i
DYNAMICS!
GAS-AEROSOL
CONVERSION !
COAGULATION
WATER VAPOR;
EFFECTS i
CHEMICAL
MECHANISM
REACTION'
IN/ON
DROPLETS
REACTION
IN/ON
PARTICLES
j^B*|CHARACTERIZATiON
ATMOSPHERIC
LOADING
-------
REMOVAL PROCESSES
FINE PARTICIPATE
Figure 5-8
DRAFT
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PO
t
ATMOSPHERIC
INPUT
WAjHJHJTj-iJ
DRY
DEPOSITION
BIOLOGICAL!
[CHEMICAL
PRECIPITATION]
AIR
-s^^WAJ^^^-
SOIL
EFFECTS
ATMOSPHERIC
LOADING
ENVIRONMENTAL
MODEL
-------
ro
ro
i
SAMPLING
&
ANALYSIS
ATMOSPHERIC LOADING
FINE PARTICULATE
Figure 5-9
TECHNIQUE DEVELOP-;
MENT, TEST & EVAL- i
UATION 1
COLLECTION!
ON A |
SURFACE !
IN-SITU
MEASURE-
MENTS
RESEARCH
FOR AEROSOL
CHARACTER-
IZATION
ROUTINE f
MONITOR-
COMPOSITION!
SIZE DIS-
TRIBUTION!
CONCEN-
TRATION
GASEOUS
PRECURSORS
ATMOS-
PHERIC
FACTORS
DO NOT QUOTE OR CITE
CONCEN-
TRATION
COMPO-
SITION
ATMOS-
PHERIC
LOADING
MODEL
EFFECTS
-------
EFFECTS
FINE PARTICIPATE
Figure 5-10
ฐ0
IX)
CO
INPUT
ATMOSPHERIC;
LOADING j
AND
REMOVAL
PROCESSES
HUMAN
HEALTH'
MATERIALS
ECOLOGICAL
ANIMAL
PRECIPITATION (ACID RAIN)
VISIBILITY REDUCTION
RADIATION BALANCE
EFFECTS
CRITERIA
CONTROL
STRATEGIES
-------
ro
i
SHORT-
TERM
EXPOSURE
o
LU 7
ฃ|
oo
LONG-
TERM
EXPOSURE
HEALTH EFFECTS ASSESSMENT
EPIDEMIOLOGIC & LAB STUDIES
Figure 5-11
SINGLE
ELEMENT
OR
COMPOUND
MULTIPLE
OR i
COMPOUNDS!
METEOR-
OLICAL
REACTIONS
POPULATION
VARIABLES
ACUTE
EFFECTS
CHRONIC i
EFFECTS
iฃ*
ฎฃ
CITE
RELATIVE
TOXJCITY
RESPONSE
DISEASE
MODELS &i
EXTRAPO-;
LATION
SYSTEMS
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Table S-l
SUMMARY OF CURRENT RESEARCH RELATED TO FINE PARTICULATES
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Table S-l
SUMMARY OF CURRENT RESEARCH RELATED TO FINE PARTICULATES
Est*
Estimated Date Costs
of Completion (Yrs) ($1000)
Task Description
1. ROAP 21AYB - Produce mono- 4
graphs describing human health
effects of long- and short-term
exposure of population subgroups
to respirable particulates.
Health effects will be identi-
fied in CHESS neighborhoods and
in selected high risk subgroups.
Human exposure chambers will be
used to provide dose response
information on the clinical and
physiologic effects of controlled
human exposures to sulfates and
nitrates.
2. ROAP 21AYF (Partially related 5
to fine particulate)- Isolated
test systems will be developed
and employed in conjunction with
relevant whole animal studies
to assess toxic effects of
environmental pollutants at the
cellular and subcellular level
pollutants include airborne
particulate and fly ash. Con-
tinuing studies to evaluate the
interaction of inhaled carcinogens
with nose mechanisms and pul-
monary defense systems. Determine
the relative biological effects
of specific sulfates. Studies to
determine the role of selected
fine particulates found in the
atmosphere as co-factors in pul-
monary carcinogenesis when com-
bined with known atmospheric
polycyclic hydrocarbons.
*Represents that portion of ROAP cost prorated for fine
particulates.
1,200
NERC/RTP
Lab
HSL
EBL
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Table S-l (Continued)
SUMMARY OF CURRENT RESEARCH RELATED TO FINE PARTICULATES
Est*
Estimated Date Costs NERC/RTP
Task Description of Completion (Yrs) ($1000) Lab
3. ROAP A26AAE - (Partially 3 ] >'951 EBL
related to fine particulate)
Estimate no-effect level using
mouse pulmonary infectivity model
(a) of appropriate Pt. group
metal compounds administered
singly (b) of base metal compounds
administered in appropriate com-
binations. Compare relative
toxicities against Pb compounds
using vn_ vitro macrophage system
(a) of Pt - group compounds (b)
of base metal compounds. Compare
pulmonary carcinogenicity of Pt
group metal compounds and of Pb
compounds in association with
polynuclear aromatics using
ir\_ vivo hometer system.
4. ROAP 21AZM - The effects of 6 1,249 CPL
aerosol composition on visibility.
Measure the optical properties of
primary and secondary aerosols.
Develop quantitative relationships
between visibility loss and aerosol
characteristics such as concen-
tration, size, shape, and chemical
composition. Determine effect of
changes in relative humidity on
particle size and optical properties.
Study conversion of NO , SO , and
organic vapors to particulars.
5. ROAP 21AKB - Determination of the 6 5,321 CPL
character and origin of aerosols.
Determine the physical and chemical
character and properties of source,
ambient, and natural aerosols.
Determine the contribution of the
various sources to the ambient
atmospheric aerosol loading.
Determine generation rates and
removal rates for important sources
and sinks. Measure effects of various
aerosols on atmospheric chemical
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Table S-l (Continued) on L
SUMMARY OF CURRENT RESEARCH RELATED TO FINE PARTICULATES
Est*
Estimated Date Costs NERC/RTP
Task Description .of Completion (Yrs) ($1000) Lab
reactions. Determine rates and
mechanisms for conversions of gases
to aerosols, growth and coagu-
lation of aerosols, and aerosol
removal mechanisms.
6. RQAP 56AAJ (Partially related 5 1,425 CPL
to fine particulates) - Regional
air pollution study air quality
characterization. Characterization
of aerosol pollution in St. Louis
to develop data base for develop-
ment and validation of models of
visibility loss and aerosol forma-
tion, growth, and removal. Determine
sources of visibility reduction;
determine aerosol chemical composition,
size distribution, and sources;
determine gas-aerosol interactions.
7. ROAP 26AAM - Development of 5 1,200 CPL
instrumental and analytical method
for the measurement of particulates
from stationary sources. Much
of the effort relates to particle
size measurements. This includes
both the development of stationary source
sampling systems that maintain sample
integrity for size measurement and size
measuring system. Several instruments
for size measurement have been developed
including an automated device that
combines with an seperator with beta
absorption measurements.
8- ROAP 26AAN - Methods development 5 300 CPL
for the determination of chemical
composition of particulate by size
fractions from stationary sources.
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Table S-l (Continued) "u NOT
SUMMARY OF CURRENT RESEARCH RELATED TO FINE PARTICULATES
Est*
Estimated Date Costs NERC/RTP
Task Description of Completion (Yrs) ($1000) Lab
9. ROAP 21ADL - Development through 6 11,042 CSL
pilot scale of at least three broadly
applicable methods or devices for
control of fine particle (less than
3.0u) emissions. Pilot ?cale demon-
stration of systems on several typical
priority hazardous particle sources.
Documentation of the relative technical
and economic feasibilities of various
systems. Development of at least one
practical, manual particle-sizing method
and one continuous method for fractional
efficiency determination and control
device performance evaluation.
10. ROAP 21ADJ - Demonstration and 3 983 CSL
comprehensive characterization of the
particulate control capability and limi-
tations of the best available full-scale,
utility applications of Fabric Filters,
electrostatic precipitators (ESP's),
and scrubbers by means of thoroughly-planned
and executed demonstration test programs
to examine major variables for at least
three major control devices. Evaluation
of the particulate control capabilities
of a representative range of commercially
available variations and types of the
three major classes of conventional par-
ti cul ate equipment: fabric filters, ESP's,
and scrubbers on several major sources.
11. RQAP 21 ADM - Evaluation and docu- 6 2,941 CSL
mentation of the relative capabilities and
limitations of fine particulate control
devices. This information will permit
selection by equipment users of collection
systems that are technically and economically
optimum for specific applications.
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Table S-l (Continued)
SUMMARY OF CURRENT RESEARCH RELATED TO FINE PARTICULATES
1st*
Estimated Date Costs NERC/RTP
Task Description of Completion (Yrs) ($1000) Lab
12. ROAP 21ADK - Current, compre- 6 1433 CSL
hensive, and accurate engineering
analysis of all particulate emission
control techniques will result. These
analyses will be in the form of indi-
vidual evaluations of particulate pro-
cesses and comparative analyses of all
processes of a similar type. The evalu-
ations will be made using common method-
ologies to facilitate comparisons. The
comparative analyses will permit rational
and timely management decisions based on
solid, technical groups; this will permit
optimum allocation of resources within
the air pollution control technology area.
13. RQAP 26ACV - Development of technology 6 4000 CPL
to measure the emissions from mobile sources.
Determination and characterization of emissions
both gaseous (precursors) and particulate.
Development of sampling and analytical tech-
niques to provide regulating capability and
to provide the basis for effects research.
14. ROAP 26AAE - Characterization and 6 3000 CPL
protocol development related to emissions
from mobile sources from fuel and fuel
additives. Definition of chemical species
and mechanisms which result from the use of
additives. Particulates are determined as
appropriate in support of Section 211 of
the Clean Air Act.
15. ROAP 21 ADO - JjodeJlnfl. 3 120 ML
Methodologies developed for calculation
for diffusion of reactive pollutant are
applicable to modeling secondary pollutant
generation and certain mechanisms have already
been applied to aerosol generation. Scavenging
and general removal processes of fine particulates
are studied in the laboratory and in the ambient
atmosphere.
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Table S-l (Continued)
SUMMARY OF CURRENT RESEARCH RELATED TO FINE PARTICULATES
Est*
Estimated Date Costs NERC/RTP
Task Description of Completion (Yrs) ($1000) Lab
16. ROAP 26AAS - Geophysical
Background classification and monitoring 5 35 ML
of atmospheric turbidity. Lidar
development and studies. Evfects of
aerosols on the radiation balance.
17. The following ROAPs contain one or 5 1,250, CSL
more tasks which are related to fine
particulate control R&D: 21AFF, 21ADC,
21AUY, 21AFA, 21AQR, 21AFE, 21AVA, 21AFH,
21ARO, and 21BAO.
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Table S-2
SUMMARY OF RECOMMENDED NEW RESEARCH
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Table S-2 QQ MOT QUOTE OR CiTE
SUMMARY OF RECOMMENDED NEW RESEARCH
Estimated time Est Costs/yr
Task Description for Completion (Yrs) ($1,000)
1. Conduct biological experiments using dynamic 5 500
atmospheres with fine particulate and gases similar
to urban atmospheres for exposure of various
species of animals. Acute, subacute, and chronic
exposures will be used to determine the significance
of factors such as particle sizes chemical
composition, concentration, and associated physical
properties or canditrans on particle deposition
retention, translocation, pulmonary clearance
rates, and other parameters related to pulmonary
defense,
2. Identify human biochemical and metabolic 5 200
changes associated with atmospheric levels of
fine particulates.
3. Conduct community health and environmental 10 1,500
surveillance studies designed specifically to
investigate the health effects resulting from
short and long-term exposure, to fine
particulates in the atmosphere. The studies
will consider particle size, chemical
composition, and concentration; as well as
meteorological and population variables,
4. Characterize and determine the relative 5 500
toxicity as single elements or compounds and
in combination, of primary and secondary
fine particulates from stationary, mobile
and natural sources.
5. Develop, test, and evaluate sampling, 3 600
measurement and analytical techniques for
monitoring and physical and chemical
characterization of atmospheric fine
particulates.
6. Development and testing of improved 5 300
fine particulate models.
7. Determine the fate of fine particles 5 500
in the atmosphere.
8. Characterization of visibility as an 2 225
indicator of particulate loading, study of
visibility trends, and determination of large-
scale particulate loading distribution and
trends from atmospheric turbidity
measurements. -32-
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Estimated time Est Costs/yr
Task Description for Completion (Yrs) ($1000)
9. Measurement of fine particles using 5 250
satelliteborne instruments.
10. Update MRI fine particulate source 2 300
inventory report using recently developed
particle sizing techniques.
11. Characterization of fine particulates 5 200
from selected industrial sources.
12. Field testing of selected industrial 5 300
combustion sources for potentially hazardous
pollutants.
13. Improved ESP collection of fine particulates 5 400
by (1) developing specdal ESP charging section to
take advantage of diffusion charging of fine
particulate; and (2) modification of high
resistivity dusts using chemical additives.
14. Construction and operation of a versatile 5 150
fabric filter system test stand for fine particulate
R&D studies.
15. Construction & operation of a multipurpose fine 5 150
particulate scrubber test stand for fine particulate
R&D studies.
16. Construction & Operation of versatile mobile 5 300
pilot scale ESP.
17. Improved fabrics & fabric finishes for fine 4 150
particulate control.
18. Develop and evaluate devices, and establish 5 500
measurement protocol, for determining mass,
fractional efficiency, aerodynamic size, and
chemical composition of fine particulate from
stationary sources.
19. Relationship of sulfate formation to fuel 1 150
sulfur in controlled non-catalyst cars, modeling.
20. Sulfate formation in other mobile source com- 4 125
bustion systems, modeling included.
21. Study of nitrate formation in mobile source 4 190
combustion and post combustion systems.
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Estimated time Est Cost/yr
Task Description for Completion (Yrs) _J$1000)
22. Expand program on emissions from 6 125
novel automotive engines.
23. Develop, test, and evaluate sampling, 5 500
measurement, and analytical techniques
for monitoring and characterization of
fine particulates from mobile sources.
24. Study relating health effects and 4 125
mobile source emissions.
25. Define effects of "smoke suppressants" 5 180
on mobile source emissions.
26. Impact of reduction catalysts on emissions. 3 70
27- Aerosol-gas Interactions Studies 3 500
a. develop quantitative theory
b. laboratory studies with collected aerosols
c. chamber studies with dispersed aerosols
d. quantify role of aerosols in transporting
nixious material to pulmonary system
e. determine effect of high humidity in
pulmonary system on deposition of hygroscopic
and deliquescent aerosols.
28. Characterization of Atmospheric Fine Particulate 3 1,000
a. nationwide research network to determine
mass and composition as a function of size.
b. relate atmospheric aerosol loading to
emission sources.
29. Determination of long-term trends in aerosol 5 25000
loading and aerosol sources including $5,000,000
installation cost, $1,000,000/yr operating costs
30. Visibility Studies 3 250
a. Develop light scattering theory for non-
ideal particles.
b. determine relationships between visibility,
light-scattering, and sub-micron aerosol
mass.
c. determine light absorption of atmospheric
fine particulates.
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Task Description
31. Transformations Studies
a. Studies in plumes
b. Sulfate mechanisms
c. Nitrate mechanisms
d. Organic mechanisms
32. Natural Source Studies
a. Sulfur cycle
b. Nitrogen cycle
c. Carbon cycle
33. Development of technology for secondary
fine particulate reduction by improved
control of gaseous precursors (SOX, NQX,
ammonia, hydrocarbons, etc.)
34. Improved control of fine particulate
emissions from stationary sources by cleaning of
raw materials and/or fuels.
35. Improved control of fine particulate emissions
from stationary sources by process modifications.
Estimated time Est Costs/yr
for Completion (Yrs) ($1000)
3 1 ,000
325
2,000
1 ,000
1 ,000
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I. INTRODUCTION -D jUO]
The objective of this Task Force is to identify problem "areas'
major concern to EPA relative to primary and secondary fine particulates
in the atmosphere. There is an increasing body of evidence which
suggest that those particulates found in the atmosphere in the size
range less than 5 ym contribute significantly to the adverse effects of
air pollution on human health and welfare.
The category of fine particulates encompasses the most complex
scientific, technical, and economic problems associated with air pollution
Not only are there fundamental questions which have not yet been
answered, but in certain areas our knowledge is so limited that questions
cannot be properly formulated. No attempts have been made here to
present an in-depth scientific treatment of fine particles as specific
chemical elements or compounds. Rather scientific discussion is limited
to that extent considered necessary to identify the major problem areas
which may impact on the need for Agency decisions. In the final
analysis, a pollutant category of fine particulates, as opposed to a
classification by chemical species, may prove to be too arbitrary and
hence impractical from the standpoint of effects criteria. Currently
available data indicate that consideration of particle size alone
in health effects research would be inadequate. Chemical composition
and other associated physical properties appear to be equally important.
From the standpoint of control technologyand to a certain extent
the effects upon visibility, weather, and climate--the size
classification of fine particulate appears to have distinct
advantages. This problem of pollutant classification is considered in
the report but not resolved. Further research will be required.
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II. CHARACTERIZATION METHODOLOGY
A. Definitions
The following definitions have been used arbitrarly through-
out this report:
1, Fine particulate matter is defined as "material that exists as
a solid or liquid below the size of 2 to 5 urn in diameter," as
measured by aerodynamic and/or optical techniques. For design
purposes, a cut-off of 3.5 ym diameter is considered acceptable.
2. Primary fine particulate is defined as all "fine particulate which
has not been modified by atmospheric transformation
processes." (Change of physical state is not considered a trans-
formation process.)
3, Secondary fine particulate is defined as "fine particulate that
is formed or modified
by atmospheric transformation processes."
4. Physical particle size is the shape and the dimensions of the
particle.
5. Aerodynamic particle size is defined as the size of a sphere of
unit density which has identical aerodynamic behavior as the
particle in question. Particles having the same aerodynamic
particle size may have differing shapes and dimensions.
B. Particle Sizing Methods
Techniques for determining the size distribution of aerosols can
be classified broadly as those based on the physical particle size and
those depending on the aerodynamic particle size. Microscopic and other
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optical methods determine the physical particle size while the inertial
devices such as impactors, cyclone separators, diffusion batteries, and
centrifugal devices determine the aerodynamic particle size. Electrical
devices,while more complex in the principle of separation, respond to a
combination of aerodynamic and physical size,
1. Microscopic Methods
The particulate matter is collected on glass slides or membrane
filters. The individual particles are viewed with a microscope
and subsequently sized with a reticule and counted. The lower limit
of resolution is about 0.5 ym in diamter, unless an electron microscope
is used.
2. Aerodynamic Fractionating Devices
These devices fractionate particles by virtue of their aerodynamic
dimension, electrical charge, or mass, and with some devices retain the
aerosol material for physical, chemical or microscopic analysis. The cyclone-
type sampler is an aerodynamic fractionating device in which vortex of air
increases the centrifugal force or, the entrained particles which throws them out
of the gas stream, at which point they either stick to the walls or drop
into a container. This type of sampler is somewhat limited in that as the airflow
is increased to impart a greater centrifugal force to the entrained
particle, the increased airflow also .-causes turbulence, which interferes
with the centrifugal force of the particle.
Rotating centrifugal devices have been developed to collect particles
smaller than those collected by cyclones and separate them according to
size. Particle collection in rotating devices is limited by geometry and
airflow. To get around these limitations, devices have.been designed
that increase centrifugal force of the entrained particles while permitting
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airflow within the.instrument to remain low enough for laminar flow.
Cascade impactors are used for determining weight, number, and chemical
composition distributions. Several stages are used in series, each with a
different air inlet geometry, resulting in progressively increasing air
velocities with descending stages. Particles with a large aerodynamic
mass are impacted and retained on the upper stages where the particle
velocities are low, while those with small aerodynamic mass are impacted
on the lower stages where the particle velocities are higher.
Electrostatic fractionators separate by means of passing charged
particles through a strong electric field. The collection efficiency
increases with smaller particle sizes because of their greater mobility.
This makes the fractionator quite valuable for the collection of submicro-
meter-size particles in the range of 0.005 to 0.5 ym. The flow rates are
insufficient to collect an adequate amount of material for chemical or
gravimetric analyses.
Diffusion batteries,coupled with an appropriate particle
counter>are used to measure particle size distribution in the
0.005 to 0.1 ym range. In a diffusion tube, smaller particles
migrate to the wall through Brownian motion and larger particles
traverse through the tube. By changing tube diameter, tube
length, and gas flow rate, the minimum size of particle penetrating
the tube can be varied and the number penetrating counted. The
data can then be converted to a number size distribution.
3. In-situ Optical Sizing Devices
Several types of devices for physical particle sizing have been developed
based on light scattering, However, the only ones that can be classed as
particle size instruments for airborne aerosols are "single particle
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counters." With these devices, the particles pass through a light
beam one at a time and the size of the particle is determined
by the amount of light scattered. Other approaches are proposed
or have been used on a research basis such as multiwave length light
scattering, angular scattering device, laser backscattering, and
polarization light scattering techniques, but instruments based on these
principles are not generally available.
Devices such as the integrating nephelometer that measures only
the total scattering o
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conditions are not too severe. Comparison of results measured before
and after a particulate control device makes possible the estimation of
the fractionating efficiency of tne control device.
c. Mobile Source. A dilution tunnel is used to simulate the
atmospheric dilution, that naturally occurs, and to lower exhaust temp-
eratures and dew points at high engine speeds. This allows formation of
particulate by condensation before sampling. Dilutions are normally
10-20 to 1 (to maintain as high concentrations as possible for the sake of
analytical measurements) rather than the roughly 1000 to 1 in the ambient
atmosphere. The sample to be sized is taken from the dilution tunnel.
This technique is particularly important on emissions from vehicles
operating on fuel that does not contain metallic additives. It has been
widely applied to automotive exhaust emissions and is currently being
extended to other mobile sources.
Cyclic operations are necessary to duplicate normal emission patterns
since the rate of emission is extremely dependent on operating mode.
Fixed cycles are required in order to allow duplication of results
and facilitate inter-laboratory comparison.
C. Chemical Composition
Compositional analysis is performed by a wide variety of techniques.
X-ray fluorescence, atomic absorption spectroscopy, optical emission
spectroscopy, and wet chemical methods have been used for elemental
analyses. Liquid chromatography, infrared and ultraviolet spectrometry,
gas chromatography, mass spectrometry, fluorescence, and wet chemical
techniques have all been used for detection and measurement of organic
components. In most cases, two or more techniques are used in concert
because of the large number of compounds present.
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The following are problem areas and/or needs requiring further
studies in the measurement area:
! Calibration of size classifying devices has always been difficult.
Ideally, such devices should be calibrated by atmospheric particulate
matter of heterogeneous composition and known size; such material is not
yet available, and is an important research need. Consequently.
laboratory aerosols consisting of polystyrene latex spheres, methylene
blue solutions or other liquid aerosols, or other homogeneous materials
have been used. These synthetic aerosols are very much unlike atmospheric
particulate matter and probably do not exhibit the same aerodynamic,
optical, or other properties of atmospheric particulate matter.
2. Cross-comparison of different in-stack cascade impactors has
been made by one contractor at a given site. Under carefully controlled
conditions, reproducibility between types of impactors was reasonably
good. However, few runs have been made and analyzed to compare:
a. different operators using the same impactor on the same source;
b- duplicate impactors on the same source used by the same
operator;
c. the same impactor used in different locations in a given stack
or duct.
3. Cross-comparison of optical, aerodynamic, and electrical sizing
devices has not been adequately done. Controlled experimental facilities are nc
available.
4. Cascade impactors are subject to error because of particle bounce-
off, re-entrainment, wall losses, and particle size changes either due to
chemical reaction or moisture content changes.
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5. All extractive techniques used for source sampling have the oroblern of
getting a truly representative sampling through the sampling interface
to the collection device. Wall losses, aaalomeration, particle fractionation
and preferential loss of one size of another are some of the problems
encountered with the sampling interface.
6. Conventional impactors isolate extremely small samples making
anything other than selected elemental and/or microscopic analyses
difficult. Four newly developed, larger size cascade impactors are
available for ambient air sampling which collect sufficient material
for gravimetric and chemical analyses. These impactors have not been
adapted for in-stack use.
7. Impactors operate over a fairly narrow range of flow rates and are
difficult to use in gas streams with heavy loading because of rapid
overloading of one or more stages or with very light loading because
of the long testing times nesessary to take an adequate sample for
weighing.
8. Optical and some electrical sizing devices take large dilution
with pure air to reduce particle loading to a measurable level.
9. No particle size distribution tests have been standardized with
any of the sizing devices available. Each group with a need tends to
go its own way.
10. Manual devices are time consuming to operate and are not able
to measure short-term changes in control systems operation. There is
an urgent need for devices that can provide size distribution data on a near
real-time basis.
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11. Filtration techniques must be accurately defined and evaluated.
Absorption, condensation, and evaporation of volatile materials cause
serious errors. Surface reactions may also be very important.
12. What is a "particulate" must be defined in each instance. No
definition is all inclusive. Specific analysis often ignores the
distinctions between particulates and gases. Conversely, adverse health
effects are more dependent upon composition than physical state.
13. Convenient measurement techniques are required for all mobile
sources. Current techniques are cumbersome and expensive, both in time
and equipment.
14. Mass measurement techniques, at least as applied to mobile
sources, need to be improved to provide increased sensitivity and
convenience.
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T
III. ATMOSPHERIC INPUT
A. STATIONARY SOURCE EMISSIONS AND CONTROL
DPA-
1. Emissions r._ '--" s 5,;J{: I
: ~ t t;'J NOT QUOTE OR CITE
a. Present Status^-
Data on the emissions from stationary sources are needed for two
purposes to determine the atmospheric input from these sources and
to permit the proper application d'f control technology to reduce the
emissions. Both particulate emissions and gaseous emissions, (SOX,
NO , hydrocarbons, etc.) from which secondary particulate form, are
A
important.
Estimated or measured emissions of SO and NO from each point source
X A
in the nation, which emit more than 25 tons/year of either of these pollutant
categories, are available from the National Emissions Data System (NEDS).
Mass emissions of hydrocarbons and particulates are also given in this data
base, but no attempt is made to identify the chemical composition of the
pollutants nor the size distribution of the particulates.
In 1971, Midwest Research Institute (MRI) completed for EPA a three
volume "Particulate Pollutant Systems Study." Volume II, "Fine Particle
Emissions", gives an estimate of 1970 emissions from stationary sources
as about four million tons of material with particle sizes of less than
3 urn diameter of which about one million tons consisted of material
with particle size smaller than 1 pm diameter. These estimates
were based on major extrapolations, because of the lack of actual data
in the fine particulate range. During the past year, techniques have been
utilized which are capable of measuring particle size distributions down
to 0.2 ym using inertia! impactors, and to about 0.01 urn with diffusion
batteries. In recent months, nearly fifty sets of particle size
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measurements have been made down to 0,2 ym and several to 0.01 ym. MRI is
currently upgrading the particle size distribution data. An automatic
stationary source particle sizing device that couples the beta gauge and an
inertial impactor has been developed and is in the final phase of testing.
b. Planned R&D
It is imperative that a better data base for fine particulate emissions
from stationary sources be developed. This will be done by utilizing particle
size distribution data, developed in recent months (fine particulate range),
that which will be obtained from currently planned and funded programs, and
that which must be obtained to fill in the gaps and will take additional
funding. A complete update of the MRI Fine Particulate Emissions report will
take about 2 years to complete. However, accuracy of our data base will
continue to improve throughout the 2 years.
2. Control
To insure that those atmospheric fine particles which may be
determined to have serious health or welfare effects can be controlled an
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active control technology development program must be pursued which
aims at primary fine participate and the gaseous precursors of secondary
fine particulate.
a. Primary Fine Particulates
(1) Present Capability
Fine particulate control technoloav
is now at a very early stage of development. Exceptions exist where
collection systems have reached very high mass efficiencies resulting in
capture of fine particulates along with large particle size material. Recent
tests have shown that under certain limited conditions, an ESP or a baghouse
can control fine particulate flyash. One high efficiency ESP (99%+ overall
efficiency) was found to be more than 90% efficient in the mass removal of
all particulate fractions down to about 0.01 urn. Unfortunately, much
of the coal burned in this country produces flyashes having electrical
properties which fall outside the range where ESP capture is most effective.
Either modification of the ESP or the flyash (or both) will be necessary
to capture the fine particulate. In addition, fine dusts from many sources
not associated with fossil fuel burning are difficult to collect electro-
statically.
A baghouse has recently been installed on a coal-fired utility boiler
and has been shown to effectively control fine particulate, at least down
to 0.2ym. However, the development of special operating techniques and
improved filter fabrics will probably be necessary to significantly broaden
the applicability of baghouses for fine particulate control.
High energy scrubbers also are capable of fine particulate control on
certain sources, but suffer from the disadvantage which their name implies
(high energy consumption).
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(2) Current R&D Activitfe? '-JOT
Particulate control technology consists of add-on
collection devices, fuel or raw material cleaning and process modifications.
Basic technology for collection devices can be developed independent of the
sources. The latter two technologies and the specific aoolication of collection
devices must be developed for the applicable industry. Therefore, two programs
for particulate control technology are possible - R&D on collection devices and
R&D aimed at reduction of oarticulate emissions from ป*ch source ^P6-
Currently both programs have been established. The particulate control
device program has the following objectives:
4. To establish a data and technology base to assist manage-
ment in decision making on fine particulate R&D.
b. To assess the collection capability of conventional
control devices using standard sources of fine particulate
emissions.
c> jo assess the collectability of dusts from the
major sources of fine particulate using standardized
collection devices.
d. To identify, evaluate and develop new concepts and novel
devices which show promise for control of fine particulate.
e. To demonstrate the use of high efficiency collection
devices on major sources.
The source oriented program has the goal of selecting and demonstrating
the most promising control technology for combustion sources, the metallurgical
industry, the chemical and petroleum, industries, open sources, etc. Emphasis
in these programs is to control all emissions from the source including
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particulate emissions with emphasis on potentially hazardous pollutants.
b. Secondary Fine Particulates
(1) S0.x
Sulfates found in secondary fine particulate, appear to
come primarily from/atmospheric oxidation of S02 to S03. Reduction of
sulfates to an acceptable level will probably require reduction of SOX
emissions by 90-99%.
The current EPA program is targeted at moderate (30-70%) reductions of
ambient concentrations of S02 in urban areas. This will be accomplished
by using stack gas cleaning on large point sources (75-90% abatement) and
cleaner fuels on most other sources (20-60% abatement). To achieve 95%
reductions of ambient concentrations of SO,, in urban areas, large point
sources will require high efficiency stack gas cleaning (90-99%) and other
sources will require increased use of clean fuels.
(2) NO^
Nitrates in the atmosphere are generally formed from NO
X
emissions. Adequate control of atmospheric nitrates may require reducing
NO emissions by 90% or better.
X
NO control by combustion modification (present program) can achieve
A
reductions of 50% to about 80%. Reduction of NO by better than 80% will
X
require major combustion process modifications. Fluid bed combustion and
catalytic combustion may have high potential here.
(3) Hydrocarbons
Although significant reduction in the emissions of reactive
hydrocarbons from many stationary sources 1s possible vfi.th. application ฐf existing
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technology, there are numerous industrial sources where adequate control
has not been demonstrated.
(4) Other
Other gaseous pollutants,such as ammonia, can increase
the reaction rate for formation of secondary fine particulates. These
pollutants must be identified, the sources and levels established, and
control techniques developed and applied.
3. Problem Areas
a. In order for the agency to make decisions with respect to the
control of fine particulate matter, it is necessary to establish
immediately a better data base on the physical and chemical
characterization of fine particulate emissions from stationary
sources.
b. To establish what important gaps in the technology base must
be filled, a rapid characterization of the collection efficiency
of conventional particulate control devices is necessary.
c. In order to identify difficult control problems, the character-
ization of the collectability of various industrial dusts
must be accomplished.
d. New concepts and devices for collecting fine particulate
matter must be identified, characterized and developed.
e. The best applicable technology for control of fine particulates
must be demonstrated at the earliest possible date on an
industry~by-industry basis.
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f. Strategy arrd methods for the control of gaseous precursors of
secondary fine particulate matter emitted by stationary sources
(SOX, NOX, hydrocarbons, NH3, etc.) must be developed. Before
the magnitude of the necessary effort,here can be determined,
we must know the level of control required.
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B. Mobile Source Emissions and Control
1- fiftnerftibneCsourcSs contribute only about 3% of the total particulate
emissions in the U. S. However, this is all in the fine particulate range
and may constitute a significant fraction of total primary fine particulate
emissions. Moreover, atmospheric transformation of the gaseous emissions
from mobile sources accounts for a major fraction of secondary fine
particulate matter in some urban areas.
The major contributor to particulate emissions from mobile sources
is the passenger car (45.8%) due mainly to the large number (87 million)
in daily operation and not to a higher emission rate (0.3g/mi) than other
forms of mobile sources. Trucks and buses account for another 15% and the
rest is split up among the wide variety of other sources: aircraft,
locomotives, lawn mowers, earth movers, etc. Emissions from all mobile
sources amounts to 600,000 tons/year.
In a study for EPA by the Dow Chemical Company, it was found that
particulate matter in automotive exhaust had a MMED of <0.1ym and
the size range observed in a series of tests was 3.2y to <0.1ym. Nearly
all studies to date on the particle size distribution of automotive
exhaust indicate that 90% or more of the mass emitted consists of particles
with diameters below 1 micron and thus the total particulate emissions may
be considered as fine.
A significant fraction of atmospheric aerosol results from atmospheric
oxidation of S02 and NOX to sulfate and nitrate and from oxidation and
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polymerization of gaseous organic compounds to carbonaceous residues.
In areas where automobiles are important sources of these gases, part of the
secondary pollutants will also belargely mobile-source derived. Nitrates and
sulfates account for about half the fine particulate material present in
the L. A. atmosphere and may be derived largely from automotive sources.
Estimated emissions rates for gasoline-powered vehicles burning fuel
containing usual quantities of tetraethyl lead (2.5 gm. Pb./gal.) are in
the order of 0.08 to 0.25 grams/mile in a typical consumer driving pattern.
Lead-free gasoline will be required in cars equipped with hydrocarbon-
control catalysts since lead emissions quickly deactivate catalyst. With these
lead-free fuels and catalysts, particulate emissions will be in the 0.02 to
0.05 gram/mile range and may be dominated by nitrates and sulfates.
Diesel smoke has been controlled by many modifications to combustion
systems, reduction in fuel injector volumes and addition of turbocharging.
However, attempts at NOX control have introduced a design trade-off with
smoke control and turbocharged power output.
Emissions from aircraft turbines are significant in some areas.
Estimates of Los Angeles turbine particulate emissions are 1/3 to 1/5 of
automobile-generated particles. In areas near approach and take-off corridors,
aircraft particulates dominate the atmospheric aerosol. Particulate
emissions range from 0.1 to 2% of the fuel burned, depending on engine type
and operating mode.
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2. Problem Areas ' " NฐT CM ft OR CUE
There 1s a need for more effort and data on the particulate emissions
from mobile sources. Some of the specific types of .data needed are more
and better size distribution data, as well as chemical composition of
particulates, and better mass emission data for the lesser known sources.
Fine particulates from mobile sources have not been specifically
regulated except as visible smoke from heavy duty engines.
Some specific problem areas include:
1. Reliability of particulate data is in question because of
difficulty in collecting volatile components which behave as particulate
matter.
2. There is not at the present time an absolute filter for automotive
exhaust particulate and thus nothing for use in determining true emission
rates. Reported results can be low but not high.
3. Adequate instrumental methods are lacking for determination of
particle sizes below 0.1 ym, which accounts for a significant portion of
automotive particulate emissions.
4. A better definition of the composition of particulate matter from
engines will be necessary in order to take into consideration the variable
volatility of many high-molecular weight organics present in the exhaust.
5. Better instruments are needed with more availability
for conducting wider surveys of the automobile population for better
monitoring of emission trends.
6. Better methods are needed to reproduce driving conditions to remove
that variable from the analysis mobile source emissions data.
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7. Smoke is currently regulated as a nuisance. Since it may be
largely carbonaceous participate matter, which could include polynuclear
aromatics, its composition must be ascertained.
8. Better emission factors are needed for all classes of mobile
sources. The emphasis should be on composition as well as mass and size.
Most sizes are very small and undoubtedly are sites for further nucleation,
agglomeration, etc.
9. Inorganic precursors to secondary aerosol formation must be
determined. Their composition as emitted will play a significant role.
Differentiation between sulfate and sulfur dioxide, nitric oxide and
nitrate, elemental metallic and soluble salts, are all examples of the
problem.
10. Gaseous emissions must be elucidated and their emission factors
determined since many of these are precursors to secondary aerosol.
II. The effect of control devices for regulated emissions must be
determined. Thus catalysts for control of total hydrocarbon and carbon
monoxide are likely to increase the conversion of S02 to sulfate.
12. The environmental impact of all control strategies must be
determined.
13. Studies are needed to determine the effects of fuel additives
on particulate emissions. (For example, the use of a manganese-containing
smoke suppressant increased the mass of particulate emissions while
reducing other visible smoke. )
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14. Novel engine designs, such as Wankel rotary, stratified charge,
and gas turbine must be evaluated for changes in composition and mass
of emissions. (For example, the rotary engine uses oil more intimately
mixed with the combustion process, which can potentially produce different
type emissions including carcinogenic organic compounds. )
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C. NATURAL SOURCES 00 ,V"ปT rM^v -
KUI QoufUR CITE
] . General Discussion
Much of the fine parti cul ate matter in the atmosphere results from
emissions by natural processes. These processes yield both primary
partlculates, such as those from volcanism or forest "fires, and
secondary particles, such as those from conversion of gaseous sul fur-
or nitrogen compounds. The most important natural sources for direct
emissions of fine particles include forest fires, wind-blown dusts
volcanic activity, and sea salt.
Natural gaseous emissions of H2S, NOX, NH3 and hydrocarbons are
transformed within the atmosphere to sulfate, nitrate, ammonium
and hydrocarbon aerosols. Specific sources of these gases include
plant exudations, biological activity and volcanic activity.
Data on the emissions and rate of formation of natural aerosols
are rather meager, and there is not complete agreement among
different information sources, Although some data are available for
particular volcanic events or dust storms, little detailed information
exists on the time and space variability of the secondary formations.
On the global scale, some crude estimates of natural emissions have been
made. These estimates show that the worldwide contribution from natural sources
to atmospheric paniculate in the size range less than 20 pm in diameter
is about 1-2 x 10^ metric tons per year.
2. Probl em Areas
Additional quantitative and qualitative data are needed in the following
areas:
a. Origin.^of natural aerosols.
b. Inventory of primary and secondary fine parti cul ate from
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natural sources. This should include size distribution,
concentrations, and chemical composition.
c. The temporal and spatial variability of fine particulate
from natural sources.
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IV. ATMOSPHERIC LOADING
A. INTRODUCTION
The atmospheric loading of fine particulates is determined by
the rate of atmospheric input of primary particulate pollutants
and gases, the rate of transformation of pollutant gases into
particles, the transport of primary and secondary pollutants through
the atmosphere, and the removal processes which are a function of
particle size and composition.
B. TRANSPORT AND PREDICTION MODELING
The transport and resulting concentration of pollutants can be
predicted by meteorological or diffusion models. The modeling of
fine particulate concentrations can be separated into two categories
based upon the sources of the particulates. To the extent that
the fine particulates may be considered inert, all the existing
modeling techniques for hourly, daily and longer term average con-
centrations are applicable. The largest difficulties in modeling
inert particulates are in determining the emission locations and
strengths. It is more difficult to model pollutants from mobile
sources than stationary sources. The mobile source is so close to
the ground that in most cases it does not emit into a representative
wind field.
Research is needed to determine mechanisms for dealing with mobile
source emissions in a general manner. One expects, for example, that
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the distribution of fine participates issuing from mobile sources
would be expected to have a very large degree of spatial variability
on a very fine scale across a city.
Much more difficult however is the modeling of fine particulates
which are secondary pollutants. In order to accomplish this, it is
necessary to fully understand the mechanisms of secondary particulate genera-
tion. Once these mechanisms are delineated it is possible to model
their-, generation and transport. The state of understanding regarding
particulate formation however is not advanced to the point of being
included in any transport and transformation models now available.
An additional consideration regarding fine particulates is their
interaction with the humidity field of the atmosphere. Through this
interaction it is possible to affect the radiation budget as well
as the local precipitation. Due to the significant interaction of
the fine particulates with water vapor it will be necessary to model
the water vapor field over a city- There is currently no work in
this important area, although consideration is being given to including
moisture processes in some dynamical models. Again however the ques-
tion of how to treat these matters in a routine fashion with a general
approach will require some significant research.
Finally the removal of fine particulates will be a problem of
relevance to the modeling. The questions of how particulates get
removed and whether these removal rates are dependent on land use,
surface foliage, and other factors must be investigated.
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A significant component of the sub-micrometer particulate is secondary
particulate formed in the atmosphere by chemical reactions which convert
gases into solid or liquid particulates.
1. Sulfates
Sulfate, in the form of sulfuric acid (H SO.), ammonium bisulfate
(NH4HS04), or ammonium sulfate KNH^JgSO^J, is formed from both natural
and man-made emissions of sulfur compounds. There are a number of
postulated mechanisms for the conversion of"S02 to sulfate. The only
one which has received extensive study, the direct photochemical oxidation,
has been shown to be of little significance in urban situations.
2. Nitrates
The ultimate fate of gaseous NOx is presumed to be gaseous or
particulate nitrate. Both organic and inorganic nitrates are found.
Nitric acid (HN03) is thought to be an end product. However, the
reaction forming HN03 occurs on or in particulates. The total nitrogen
oxides, gaseous and particulates, present after significant photo-
chemical reactions, accounts for only a fraction, 20-40%, of the
nitrogen oxides emitted or present at the start of the reaction.
3. Organic Particulates
Unsaturated organic vapors, olefins and aromatics, react in photo-
chemical smog to giye an enormous variety of oxygenated organic matter.
Some primary organic particulates also is emitted by stationary and mobile sources
4. Ammonia
Ammonia plays an important role in the formation of sulfate and
nitrate particulate by neutralizing the acid species formed.
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5. Particle Size
Smog chamber and atmospheric studies indicate that secondary
participates exist almost exclusively in the sub-micron size range.
This size range penetrates into the lung, and is also responsible
for visibility reduction.
6. Properties
Secondary particulates are generally hygroscopic or deliquescent.
At low relative humidities, they may have a coating of adsorbed
water. At higher relative humidities, they may grow in size and
become solution droplets. Solution droplets or particulate with a
liquid surface may play a key role in determining the rates and
mechanisms of gas-phase pollutant transformations. For example,
the conversion of NOX to HNC>3 is probably controlled by surface
reactions. It is also possible that the primary lung dosage of
gaseous pollutants, especially $62, may be due to transport to the
lungs on or in particulates.
7. Problem Areas
a. Mechanisms and Rate Constants
Quantitative relationships between sulfate, nitrate, ammonium,
and organic particulates formed by gas to particle conversions and their
gaseous precursors are critical to development of models and a
meaningful control strategy for this group of fine particulate.
Mechanisms and rate constants must be determined through smog chamber
and atmospheric studies.
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b. Water Vapor Effects
The effect of relative humidity and absolute water vapor content
is known to be important for sulfates. However, there are no similar
results for nitrate, lead, or organic .particulates to use in drawing
conclusions on the relative importance of water vapor on particle
properties. The state of such particles is of importance not only
for visibility but also lung penetration and biological effects.
c. Lung Deposition
Present lung deposition curves are based on inert particles.
Secondary particles, however, tend to be hydroscopic or deliquescent.
They will grow in the high relative humidity of the lung. The
fraction deposited will be higher and the point of deposition may
be different than would be predicted by present lung deposition curves.
d. Gas -Part'leul aฃfe T^ctlpns_
Secondary par'tTeuTates, especially those with, wet surfaces or liquid
droplets, will promote gas-particulate reactions and dissolve various n*s
phase pollutants. These gas-particulate reactions are thought to plav an
important role in atmospheric transformation processes; but because
of the difficulties involved in studying such reactions, little quan-
titative data has been obtained.
D. NATURAL REMOVAL PROCESSES
1. General
Particles are removed from the atmosphere by fall-out, rain-out,
wash-out, and impaction on or diffusion to surfaces. Of these, only
rain-out appears to be effective with fine particles.
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The theoretical base for understanding the joint processes of coagulation
and condensation as particles grow into the fine mode is just being
developed. At the present time, removal rates for fine particles
cannot be predicted.
2. Problem Areas
a. Agglomeration
Changes in particle size under real atmospheric conditions in
urban atmospheres is unclear. Coagulation, condensation, and gas-
particle reaction all play a role in determining the size-composition
distribution.
b. Removal Rates
The rates of removal of particles on a regional scale is not at
~2
all well quantitated. Analysis of non-urban versus urban S02 to SO 4
ratios indicates a slow rate of removal in the Northeast region of
the U. S. Long range transport into Canada and the North Atlantic
2
for some particulate species such as SO ฃ is indicated. We
know essentially nothing about removal of organic particulates on any
scale of distance.
E Physical and Chemical Characterization of Ambient Air Particulates
1. Size-Distribution
Early studies of ambient particulate used'five-stage impactors and
found that the size distribution could be adequately accounted for
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by a log-normal distribution. However, in recent years counting
techniques and eight-stage impactor studies have demonstrated a
bimodal size distribution in some locations.
Most particulate scientists agree that the atmospheric particulate is
multi-modal with a variety of particulates from different sources and
with different properties. However, it is a convenient hypothesis
to consider the atmospheric particulate as composed of two distinct size
classes of particulates. In addition to being a useful concept for
organizing data and theories, it has both an experimental and a
theoretical basis.
There are two basic mechanisms for creating new particles in the atmosphere
nucleation and gas-particle conversion produce very small particles
which grow by coagulation and condensation. As these small particles
become larger, the growth processes slow down and virtually cease
as the diameter approaches one micron. Comminution or mechanical
processes such as breaking condensed matter into smaller particles by
grinding, rubbing, etc., produce particles with a mass
mean diameter much greater than one micron. The resulting atmos-
pheric distribution in terms of number, surface, and volume is shown
schematically in FigureIV-1.The lower mode may be called the optical
mode since it covers the size range most effective in scattering light,
or the accumulation mode since smaller particles grow into this size
range. Particles in the lower mode are also within the respirable
size range.
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SMOG 8IKE DISTRIBUTION
.OOl
.01
100
Figure IV-1. Number, surface grea, and volume distributions of a
hypothetical smog. The linear ordinate normalized by total number,
area, or volume is used so that the apparent area under the curves
is proportional to the quantity in that size range.
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n'tniT f<.'- rsiP
I,) JUSt Ut'i t'l ( H
2- Compos 1t1Ton and Concentration
Although the concentration distribution between fine and coarse particles
in the ambient air has not been adequately measured, considerable information
about the composition of the fine particulate mode can be obtained.
by observing composition as a function of impactor stage. The major
body of data comes from the National Air Surveillance Cascade
Impactor Network. Other data have been obtained by research groups.
These data indicate that among the metals, Pb and V
are found primarily in the fine particulate mode; Fe, Mg, Mri, Ba, Cd,
and Cr are found primarily in the coarse particle mode. SO^, N0=, Carbon,
Cl, NHj, and organic particulate are found in the fine particle mode and
P0| in the large particle mode. Zn, Cu, Ni, and Sn do not fall firmly
in either mode. However, the data are sparse, and limited to'a few
locations.
Studies in which complete analyses of atmospheric particles have
been made (in a limited number of locations) indicate that fine particles
comprise 25-60% of the total suspended particulate matter and that from 60
to 80% of the fine particles are secondary.
3. Problem Areas
a. Sampling
We do not know how to collect a representative atmospheric sample.
Solid particles are a minor problem. However, liquid droplets may
pass through a filter, they may evaporate as the concentration in the
vapor changes, or the process of interacting with a surface may cause
them to evaporate.
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The extent of conversion of S02 to sulfate on filter media has
been reported for some individual situations but not systematically inves-
tigated. Conversion on filters used routinely versus those on optimum
filter substrates need to be determined. Similar problems may exist
for nitrates but no investigations have been conducted. Organic
particulates can be lost ^eadily from filters. This problem has been
under investigation for particulates produced from combustion of non-
leaded gasolines in motor vehicles. The metastable characteristics
of atmospheric organic particulates were reported many years ago but never
subsequently investigated from the standpoint of quantitating mass
or compositional changes. When this problem is combined with the
inefficiency of the routine benzene extracts for polar organic
particulates, it appears that organic particulate concentrations
in the atmosphere may be grossly underestimated.
Atmospheric particulate samples must be collected in the presence
of gases which tend to be absorbed on most filter papers. New filter
media and collection methods need to be developed. These must be
appropriate for use with current and anticipated analytical methods.
These sampling techniques must be properly calibrated and verified.
b. Measurement Techniques:
Current programs for the development of X-ray fluorescence and improved
collection devices should make it possible to rapidly and inexpensively obtain the
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elemental analysis of large numbers of samples by particle size for
short time intervals. However, for the lighter elements, C, 0, N, and
S problems still exist. Also, the elements associated with soil
background, Si, Al, K, Ca, etc., have not been routinely analyzed so
results for many of these elements are available from only a small
number of particulate samples. Elemental analysis, however, is in
good condition compared to compound analysis. We need to know
whether the sulfur is present as H2S04, NH4HS04, (NH4)2S04, Na2S04,
or other compounds. Similar considerations exist for nitrate an(j for metallic
elements present. Organic compounds present an even more formidable problem.
c. Particles are not Homogeneous
Analysis of particle sized fractions provides no information on
the composition or structure of individual type of particles. The
surface layers of particles, their solubility in mucous, etc., may
be of particular significance. However, there is very little pub-
lished literature on such particle properties, and detailed investi-
gation of these properties requires specialized equipment such as
scanning electron microscopes, electron probes, ESCA, and ion micro-
probes .
d. Time Resolution
Size-number distributions (and the calculated size-volume
distributions) can be determined with a time resolution of two minutes.
Size-mass distributions require 24 hours. Size-composition distributions,
for certain elements, can be obtained with a resolution of a few hours.
Short time resolution is needed to study particulate dynamics-formation
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growth, removal. However, mass and composition measurements are
required to determine sources and health effects. There is at present
no way to correlate the three types of measurements.
e. Data Base
Obviously, more and better data are needed, for compounds as well
as for elements, in more locations under a greater variety of conditions.
Measurements of number density, mass, chemical composition, and concentration
need to be performed on the same air mass.
f. Differentiating Primary and Secondary Sources &_ Natural, Mobile
and Stationary Sources
It is critical to find techniques for differentiating primary and
secondary particulates, and for determining the percent contribution
when several sources contribute to one type of particulate.
Sulfate and nitrate are largely secondary; but the SCL and NO may
c. X
come from power plants, home heating units, auto exhaust, or natural
processes in non-urban areas. Organic particulate has several primary
and secondary sources. The contribution of stationary sources to
primary fine particulate matter in the ambient atmosphere need to be
determined in a larger variety of urban areas. Stationary sources and
mobile make a major contribution to secondary fine particulate matter
through atmospheric conversion of S0~ to sulfates, N0x to nitrates,
and organic vapors to particulate organic material. This secondary particulate
will all be in the fine particulate size range. We must differentiate
between sulfate and nitrate from auto exhaust, stationary sources, and
natural sources. We must differentiate between primary and secondary
organic material from auto exhaust and stationary sources, and secondary
organic material from terpenes, solvents, and other organic vapors,
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The relative contributions of the various sources to the various classes
of particulate matter must be determined from atmospheric measurements
as well as from emission factors, and attempt should be made to correlate
the two.
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V. EFFECTS " ""
A. HEALTH
1. Experimental Studies (Man and Animal)
a. Introduction
At this point in time, the theoretical definition of suspended fine
particles as they relate to health must necessarily be broad and somewhat
arbitrary. The deposition of particles anywhere in the respiratory
tract, from the nose to the alveoli, may engender significant harmful
effects on health. There is some reason to believe,,however, that
particles deposited below the trachea may be more dangerous than
those deposited in the nasal cavity. Whether particles must reach
the alveoli to exert harmful effects is a more controversial issue.
It is plausible that particles deposited in the bronchi or bronchioles
are more important in producing bronchitis than those deposited in
the alveoli. At present, there seems to be little utility in confining
the category of suspended fine particles only to those particles which
reach the alveoli.
The Task Group on Lung Dynamics has calculated that up to 10 percent
of inhaled particles of diameter 2-5 ym are deposited in the tracheobronchial
compartment, and that up to 30 percent are deposited in the alveolar
compartment, The vast majority of particles of diameter above 5 ym
are deposited in the nasal cavity. Thus, a size range of fine particulate up
tป 2-5 ym diameter, measured aerodynamically, is of principal interest
from the standpoint of health effects.
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no f/-^
"'" fi^-'i OL/OTT on p,TP
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The toxicological properties of inhaled particles are related to
a complex of factors which include the specific physical-chemical
properties of the particles themselves and host conditions which affect
his response to exposure to these particles. With regard to the
toxicity of certain specific particulates which may exist in the
atmosphere,--moderate amounts of information are known. But such
information is not usually available in a form suitable for accurate
assessment of the minimum time-concentration for exposure which will
lead to adverse health effects.
Even less'information is known about how physical environmental
variables (weather conditions) may interact with suspended particulate
matter and alter its chemical composition, and thus affect its toxicity.
Weather conditions, per se, may affect man in such a way as to alter
his exposure to inhaled particulates. The information which is
available, however, provides a basis for estimating the relative
toxicity of certain substances and provides insights into problem
areas where our information is inadequate. '
b. Pose-Response Relati onships
The principal means through which air particulates exerts an
effect on health is presumed to be through inhalation and consequent
effects on the respiratory system. This presumption is acceptable in the
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case of a determination of short-term effects of irritant aerosols.
Such an assumption may be less tenable in the consideration of long-term
exposure effects where such responses as carcinogenesis, mutagenesis,
and subtle metabolic effects resulting from whole body burdens may
occur. In these cases other routes of entry, as well as inhalation,
may be important in establishing dose response relationships. However,
inhalation may be a significant route of entry for non-respiratory
toxicants as an initial organ where substances are deposited but
translocated to the gastro-intestinal system by muco-ciliary transport
and swallowing, where they may exert a primary toxic effect or
be absorbed and translocated to other tissues where an adverse health
effect might be elicited.
c. Physical Factors
Two physical factors common to all suspended particulate matter:
(1) particle size, and (2) particle density are of utmost importance in
ascertaining where inhaled particles may be expected to be deposited
in the respiratory tract. Most of the calculated and experimental data
on respiratory deposition of particles utilizes the term aerodynamic
diameter.
Mass median diameter is a frequently used term utilized in
studies of the respiratory deposition and retention of metallic ("hard")
particles. This term takes into consideration particle density and,
indirectly, diameter, but it must be remembered that particle size
expressed by this term relates to mass, In order to relate the number
of particles to the mass size distribution, it is necessary to a
numbernumber size distribution. Particle number can be
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very important in air pollution toxicology, since the large surface
area provided by small particles may provide both a reactive surface
for gas-particle interaction and may result in greater particle deposi-
tion in the deeper regions of the respiratory system and a more
rapid dissolution.
A moderate amount of information is available concerning respiratory
oarticle deposition in man and lower animals. These data are based
upon mathmatical calculations, and to a limited extent, experimental
data obtained from man. The calculated data agree, in general, with
experimental observations in man. A figure depicting the respiratory
deposition of particles as a function of particle diameter is shown
in Figure V-l .These data indicates that most particles larger than
five ym are deposited tn the nasal cavity or nasopharynx. As the
particle size becomes smaller, an increasing number of particles are
deposited in the lung. This point is thought to explain the experimental
results of Amdur who has reported that sulfate aerosols of 1 ym
diameter are greater respiratory irritants for guinea pigs than 2-3
i urn sized aerosols.
Only a few comparisons have been made concerning regional
respiratory particle deposition in laboratory animals which can be
compared to man (Figure V-2). Although some differences in
particle deposition in rodents have been observed, especially in
the efficiency of nasal deposition, the patterns are sufficiently
similar to justify the use of laboratory animal experimentation in
inhalation toxicology.
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VtT p.'! i '"--f','
A major question exists, however, in whether respiratory
deposition data from normal individualsare applicable in predicting
how exposure to suspended particulate matter may affect particle
deposition rates and regional deposition. To the extent that suspended
particulate may act as a respiratory irritant, consequent effects on
mechanics of breathing may affect both the rate and site of particle
deposition. Under these circumstances, the total inhaled dose
may be increased. However, this hypothesis lacks experimental verification
Also, many of the diseases and symptoms associated with elevated
levels of particulate matter are airway related. In these diseases,
the contribution of inhaled particulate matter to their pathogenesis
may not require penetration into the alveolar region to induce a toxic
effect. This point cannot be fully evaluated, however, since the
pathogenesis of chronic obstructive lung disease is not adequately
understood.
d. Host-related Factors
The state of health, especially of the cardiorespiratory system,
and the amount of activity of an individual, affect the total amount
and site of deposition of particulates that an individual may inhale
at any given time. The pattern of breathing affects the depth of
particle deposition, ie. deep breathing increases alveolar deposition
of particles. During exercise men commonly shift from nose ton'mouth
breathing and probably thereby increasing particle penetration into
lungs.
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Figure V-l Effect of Particle Size on Regional
Respiratory Particle Deposition in Man.
EACH OF THE SHADED AREAS (ENVELOPES) INDICATES THE VARIABILITY
OF DEPOSITION FOR A GIVEN MASS MEDIAN (AERODYNAMIC) DIAMETER IN
EACH COMPARTMENT WHEN THE DISTRIBUTION PARAMETERrfgVARIES
FROM 1.2 TO 4.5 AND THE TIDAL VOLUME IS 1450 ml.
0.05 0.1 0.5 1.0 5 10
MASS MEDIAN DIAMETER, microns
50 100
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FIGURE V-2
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U I
- - Mon
D- Monkey
o- Guinea Pig
Irarl'aml in ill!'
Palm ct o/.'1
SIZE OF UNIT DENSITY SPHERES, MICRONS
vursu.- particle plr
f llic f{ninc;i pij; and monkey compared villi num. (.Adiiplud
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At the same time exercise increases respiratory volume which
consequently increases the inhaled dose of any toxicant. This effect
of exercise has been demonstrated in men exposed experimentally to
ozone, and would presumably occur with inhalation of particulates
as well.
Pre-existing>'disease of the airways or alveoli are thought to
predispose affected individuals to more severe response when subsequently
exposed to atmospheres which contain high suspended particulate matter.
Exacerbation of symptoms of disease which occur in such individuals
usually occur in conjunction with weather conditions, ie. cold and high
relative humidity, which in themselves may have adverse health
effects. Just how this interaction between physical,.weather
factors, particulate matter, and gaseous pollutants interact to affect
health is inadequately understood.
e. "Retention "Factors
The deposition rate and retention time of inhaled particles are
separate phenomena but have overlapping biologic effects. Particle
retention time is dependent upon (1) the site of initial deposition
in the respiratory tract, and (2) the chemical composition and properties
of the particles.
If the particles are deposited in the ciliated epithelium of the
airways, particle clearance is reasonably rapid. In this event the
toxicity is dependent upon the solubility of the particle in mucus while
in transit up the muco-ciliary escalator. If the particle is
highly soluble, toxic inflammation in the airway epithelium may occur.
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Particles deposited in the alveoli of the lung may be only
very slowly cleared from this location. - The extent to which
it is cleared reflects it solubility and subsequent translocation
via lymphatic drainage or macrophage phagocytosis and clearance
via the muco-ciliary transport mechanisms.
The preponderance of evidence clearly indicates, however, that
non-soluble particles remain in the deep lung for"long periods of
time (weeks, months and even years). As a result of this slow clearance,
the carcinogenic hazard of long-lived radioactive metals, ie., plutonium
and uranium, and airborne chemicals, especially hydrocarbons, is of
special concern.
Because certain metals may be soluble in respiratory secretions,
the toxic properties of these substances may be manifested in the lung
parenchyma or airway epithelium, or may be translocated and induce
lesions in other sensitive tissues. Vanadium is one example of such a
metal whose effects may be exhibited through this mechanism. However,
the minimum time-concentration of vanadium exposure, and other metals,
which produces toxicity is not adequately understood. Also the toxi-
cological assessment .of metals which accumulate in the lung or other
tissues present a different problemUhan many other respiratory irritants,
since the relationship of tissue burdens to carcinogenesis, metabolic
defects and mutagenesis or tetrogeaesis is more difficult and time
consuming to assess.
f. Biological Resplrabfte Particles
There are species of pollens, fungi, bacteria and viruses within
the respirable range in particle size. These biological particles
are included among the particles which are collected for measurement
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DfMF
f\?OT P?r :
as respirable particles. However, it is difficult to characterize the
concentration of these particles because of the complexities involved
in precise species identification and, in the case of viruses and
bacteria, the concentrations may be very low thus causing problems in
measurement. Respirable biological particles have received low priority
within EPA due to lack of an appropriate technology for their control
which may be applied to the general population.
2. Epidemiology
Though numerous epidemiologic studies have assessed the effects
of total suspended particles on human health, very few have differentiated
one particle size from another. In fact, in the epidemiologic portion
of the Air Quality Criteria for Particulate Matter, no attempt is made
to relate specific particle sizes to specific health effects. The
few studies which have considered particle sizes have yielded plausible
working hypotheses. However, their findings cannot yet be interpreted
as established fact. The same caveat holds true for studies which
have specifically considered particle chemistry.
a. Asthma Study
Kenline correlated daily variations in participate levels to
daily variations in clinic visits for asthma in New Orleans in October
1963. In general, the correlation coefficient between the number
of daily asthma visits and the concentration of particulate increased
as the maximum particle size measured decreased. For particles whose
largest diameter was 22y,ffl,f was 0.61; for particles whose largest
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diameter was 8ym,r was 0.81. The author noted that on days of
particularly frequent asthma visits, particles in the following size
ranges increased in number: 0.5-1 .OynM-8ym;and 3-16ym. Particles
in the range of 1-4 did not increase in number.
Though the internal consistency of the New Orleans asthma study
is impressive, its-results must be replicated before they can be
accepted with complete confidence.
b. Chess Studies--
In 1970 and 1971, the CHESS program of EPA gathered a considerable
amount of epidemiologic data to implicate suspended particulate
sulfate as a pollutant of major importance in producing average
effects on healtn. In general, the effects of sulfates were
most clearly demonstrated in health parameters which reflected acute
exposures rather than chronic ones. In Utah, for instance, the
incidence of asthma attacks was found to increase on days of elevated
sulfate exposure. When 'Other pollutants' concentrations increased,
the frequency of asthma attacks did not increase consistently.
Similar findings were made in the New York City area. In both areas,
threshold levels of sulfates necessary to influence attack rates
were elevated at low temperatures.
In New York, panels of patients with pulmonary, cardiac, or combined
carciopulmonary disease suffered exascerbation of symptoms when daily
sulfate levels were elevated. The effect was most marked in cardio-
pulmonary patients, for whom it was estimated that a sulfate level of
8-10 yg/m might produce increased symptom rates.
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These studies also uncovered some evidence that chronic sulfate
exposures might impair health or physiologic function. In Cincinnati
neighborhoods, where annual average S02 levels wece under the moderate
level of 57 yg/m3, and sulfate levels averaged 9.5 yg/m3, white second
graders were shown to have slightly but significantly decreased three-
quarter second forced expiratory volumes.
Retrospective studies of acute lower respiratory disease in
Utah and Idaho-Montana children suggested that sulfates were more
important than SCL in producing elevated illness rates. It was
the investigators' best judgment that exposure to an annual average
o
of 15 yg/m of S02 could produce excess lower respiratory disease.
At present, the evidence from CHESS indicts acute exposures to
sulfates more strongly than chronic exposures. Before any evidence
can confidently be accepted as fact, the data from replicate studies
must be analyzed and compared to the 1970-1971 data. In these
studies , the sulfate effect could not be completely
separated from the effects of S02 and other suspended particulates
in the air, particularly suspended nitrates. Furthermore, no attempt
was made to measure particle sizes in detail. Thus, the importance
of specific particle chemistry and particle physics could not be
assessed.
At present,data are being analyzed from
Southeastern cities of Charlotte and Birmingham. These areas were
selected to contain a minimum of pollutants other than particulates.
Thus the observed effects of particulates, sulfates among them,
should not be greatly confounded by the effects of other
pollutants.
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3. Relative Toxicity
The class of fine participates which has been most studied is
sulfates. Nearly all work has been done with animals, and cannot be
directly extrapolated toniman. Amdur has examined the effects of
zinc sulfate, ammounium sulfate, zinc ammonium sulfate, and sulfuric
acid aerosols on airway flowrresistance in guinda pigs. She found
that sulfuric acid aerosol produced a greater increase in airway
resistance than zinc ammonium sulfate particulate of similar particle
size and at similar concentration. However, zinc ammonium sulfate
was more potent per molar concentration of sulfur contained.
At a particle mass median diameter of 0.29ym zinc ammonium sulfate
was found to be about twice as potent as zinc sulfate, and about four
times as potent as ammonium sulfate. For all these^compounds, toxicity
increased as mass median diameter decreased.
A great deal of work in ranking the toxicity of particulate remains
to be done. For example, there is essentially no knowledge of the
toxicity of suspended nitrates and nitric acid aerosol , relative to
other particulates or relative to each other.
Amdur has shown quite conclusively that particulate sulfates are
more irritating than sulfur dioxide gas at similar concentrations. She
has also shown that the interaction of^sulfur dioxide with the particulates
+2 +2 +5
of certain metal cations, such as Fe , Mn , and V , potentiates its
effects on guinea pig airway resistance. The latter finding is crucial,
for sulfur dioxide is certainly never found alone in urban atmospheres.
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Amdur's work has also demonstrated the wide variation in toxicTty
of different species of participates. This variability makes it quite
fruitless to compare the toxicity of fine particulates as a class
to other species or classes of pollutants.
4. Problems Areas
a. Aerometry--
(1) At present, it is prohibitively expensive and difficult to
measure all substances trapped by a particulate filter from the ambient
air. Thus, in certain individual areas, particulate substances which
may be unique to those areas, and important in causing health effects,
may not be identified.
(2) In many instances, the compounds on a particulate filter may
not be the same compounds as are present in the ambient air. For exapple,
sulfites in the air may be transformed to sulfates after the filter
has trapped them.
(3) The sizes of certain particles on the filter may be different
from their sizes in the ambient air. It is quite conceivable that certain
large particles are broken into smaller ones on impact with the filter.
It is also conceivable that certain small particles coalesce on the
filter to form larger ones. Thus, the sizes of particles in the air
may be inaccurately measured.
b. Health
1. The only rational approach to the fine particulate problem will be
to treat particle physics and particle chemistry with equal importance.
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To the present time, too many investigators have considered only one
disciplines or the other.
2. There has been very little investigation of effects of particulate
substances in locations other than their sites of deposition. Such
effects could be indirect, mediated through neurologic or immune
mechanisms. The effects could also be direct, caused by the substance
after it has been relocated in the body.
3. As yet, there are few epidemiologic indicators that specifically
reflect exposure to a single substance.
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B. EFFECTS ON VISIBILITY, WEATHER, AND CLIMATED
1. Visibility
Because of their much greater surface area per unit mass, and because
their diameter is the same order of magnitude as the wavelengths of
visible light, fine particles account for most of the light scattering.
They also have higher light absorption coefficients than larger particles
(higher imaginary index of refraction). The two mechanisms, light
scattering and light absorption by fine particles, are responsible for
visibility reduction. The absorption of water vapor by hygroscopic
and deliquescent fine particles can lead to large decreases in visibility
as relative humidity increases,
2. Weather and Climate
There are two ways in which suspended fine particulate matter
could affect weather and climate on either a local or large scale.
First, the energy budget at the earth's surface can be modified
by changes in the distribution and amount of incident solar energy.
Second, particulates are often effective condensation and ice nuclei
and, as such, can affect the physical processes of condensation and
1
precipitation. < " > - _
Atmospheric particulates attenuate^&lar radiation by re-directing,
or scattering, and by adsobring the energy incident upon them. A
fraction of this scattered energy is directed backward (in essence
reflected) away from the earth. By this process alone, the albedo
(reflectivity) of the earth is increased with a resulting decrease
in the amount of energy incident at the earth's surface. When
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particles absorb solar radiation, the energy is not lost to the
earth-atmosphere system, but is simply transferred from the surface to
the atmosphere.
Many studies of urban climates have shown that the added particles
in the atmosphere can significantly reduce the solar radiation incident
at ground level. The reduction increases with particle concentration
and with the solar path length through the atmosphere. Moreover,
the effect of the particles is most evident at the short, or ultraviolet,
wavelengths.
If particle concentrations over large areas of the
earth significantly increase, large scale weather and climate patterns
may occur. If the particles act solely as scatterers of radiation
their net effect will be to cool the earth. However, if they also
absorb energy, which many do, their net effect, i.e., whether a net
cooling or warming will occur, depends critically on the particles
absorption to backscatter ratio as well as the albedo of the underlying
earth's surface. Current research is directed toward incorporating
atmospheric particles into both local-scale and global-scale numerical
models of the atmosphere. In this manner the specific effects that
will likely result from given particle concentrations can be determined.
Another meteorological parameter that can be altered by fine
particulates is precipitation. When many particles which are active
cloud condensation nuclei are present in a supersaturated atmosphere
they compete for the available liquid water. Many small water droplets
form and a stable cloud results. Thus, this effect of fine particles
is to inhibit rainfall. Conversely, particles which are active freezing
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nuclei encourage the freezing of supercooled water drops. The associated
release of latent heat aids the cloud instability and thus the particle
effect is to enhance rainfall. Therefore, because of these competing
processes and variable effectiveness of particles with different com-
positions one cannot generally relate increased pollution levels to
a specific change in precipitation.
Recent studies of the precipitation climatology of several mid-
western and eastern U. S. cities have shown that immediately downwind
of these cities precipitation is augmented by about 5 to 10%. In addition
to the added nuclei in the urban atmosphere the recorded increases could
result from heat emissions or increased turbulence generated over
the city. Research in the St. Louis area is now focusing on eluci-
dation of the specific mechanism or mechanisms responsible for
peculiarities in urban precipitation patterns.
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C. ECOLOGY
Relatively little is known about the ecological effects of fine
participates in the atmosphere. The problems here involve complex
relationships, either direct or indirect, between atmospheric loading
and removal mechanisms. Deposition of fine participates on soil
or water surfaces may alter the characteristics of the medium, and
hence have some effect upon the flora and fauna of the area.
For example, acid rainfall may alter the pH of soil or water.
In addition the deposition of fine particulates on plant surfaces
could influence not only the plants themselves but the microflora of the
plant surfaces. Lead, chlorine and bromine containing particles have
been detected on the bark of trees. These effects are not necessarily
detrimental. Toxic elements or compounds found in fine particulates
may be taken up by plants through the root systems and concentrated
within the food chain. On the other hand, the biological processes
within the soil or water may alter the chemical nature of the
particulate material in such a manner as to inhibit the buildup of
potentiallynharmful pollutants. This appears to be the case with
carbon monoxide and a wide variety of hydrocarbons.
Much additional work needs to be done in this area. Specific
problems which should be addressed include:
(1) The identification and characterization of fine particulates
from man-made sources which may have an adverse ecological effect,
(2) The ecological effects of fine particulates from natural sources,
(3) The nature and behavior of ecological removal mechanisms for
fine particulates.
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VI. CONTROL STRATEGIES
Control strategy options must be considered in the formualation
and conduct of research and development efforts related to fine
particulates in the atmosphere. As needed Information is obtained
regarding the health and welfare effects resulting from the atmosphere
loading of fine particulates, control options under the provisions
of the Clean Air Act must be reviewed. These considerations then
become important imputs to ensure a viable program in. stationary
and mobile emissions and control. Our data base is not adequate at
this time to make final decisions regarding control strategies.
The use of a pollutant category of fine particulates, as opposed
to individual pollutant species, may not prove to be a practical .
approach.
The issue can be resolved by obtaining answers to
the fundamental scientific and technical questions regarding fine
particulates in the atmosphere and their effect upon human health
and welfare.
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