EPA-450/5-82-001
REVIEW OF THE NATIONAL AMBIENT AIR QUALITY STANDARDS FOR PARTICULATE MATTER:
ASSESSMENT OF SCIENTIFIC AND TECHNICAL INFORMATION
OAQPS STAFF PAPER
Strategies and Air Standards Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
January, 1982
U.S. Environmental Protection Agency
Region V, Library
230 South Dearborn Street
Chicago, Illinois 60604 ...
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11
ACKNOWLEDGMENTS
This staff paper is the product of the Office of Air Quality
Planning and Standards (OAQPS). The principal authors include John
Bachmann, Larry Zaragoza, Jeff Cohen, and John Haines. The report
includes comments from OAQPS, the Office of Research and Development,
and the Office of General Counsel within EPA and was formally reviewed
by the Clean Air Scientific Advisory Committee.
Helpful comments and suggestions were also submitted by a number
of independent scientists, by officials from several state agencies
(California, New York, Arizona and Massachusetts), and by environmental
and industrial groups including the National Resources Defense Council,
the National Audubon Society, the Sierra Club, the American Iron and Steel
Institute, the American Mining Congress, the American Petroleum Institute,
the Utility Air Regulatory Group, and the Non-Ferrous Smelter Companies.
jS. Environmental Protection Asomy
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TABLE OF CONTENTS
^ List of Figures v
List of Tables vi
Executive Summary ix
^"^
^ I. Purpose 1
II. Background 1
^ III. Approach 3
£ IV. Air Quality Considerations 6
A. Historical Trends 7
B. Current U.S. Aerosols 14
V. Critical Elements in the Review of the Primary Standards ... 23
t A. Mechanisms 23
B. Effects of Concern 40
C. Sensitive Population Groups 45
D. Concentration/Response Information 48
VI. Factors to be Considered in Selecting Primary Standards for
Particles 64
A. Pollutant Indicator(s) 64
B. Averaging Time and Form of the Standards 79
* C. Level of the Standards 83
D. Summary of Staff Conclusions and Recommendations Ill
VII. Critical Elements in the Review of the Secondary Standard ... 115
A. Visibility and Climate 115
B. Materials Damage and Soiling 135
C. Vegetation Damage 141
D. Personal Comfort and Well-Being 143
^ E. Acid Deposition 145
F. Summary of Staff Conclusions and Recommendations 145
Appendix A - Factors that Influence Deposition and Clearance of
Particles A-l
^ A. Inhalation Patterns A-l
B. Subject Airway Dimensions, Disease State A-2
C. Aerosol Composition A-4
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IV
Page
B-l
Appendix B - Evaluation of Evidence for Effects of Concern ....
A. Respiratory Mechanics and Symptoms B-l
B. Aggravation of Existing Respiratory and Cardiovascular
Disease B-l 7
C. Alterations in Host Defense Mechanisms—Clearance and
Infection B-20
D. Morphological Damage B-28
E. Cancer B-35
F. Mortality B-40
Appendix C - Visibility—Effects, Mechanisms and Quantitative
Relationships C-l
A. Evaluation of Visibility C-l
B. Mechanisms and Quantitative Relationships C-8
Appendix D - Major Particle Indicators D-l
Appendix E - CASAC Closure Memorandum E-l
References
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• v
LIST OF FIGURES
gt. Number Page
4-1 Trends in TSP and Benzene Soluble Organics at a
Central London Site and TSP Trends for New York 9
»~ 4-2 Grand Average Volume Size Distribution for Seven
Q Sites in the California ACHEX Study 15
4-3 Bimodal Mass-Size Distributions - 15
4-4 Results of Microscopy/Chemical Analyses of Urban
Particles 17
5-1 Regional Deposition of Monodisperse Aerosols by
Indicated Particle Diameter for Mouth Breathing
and Nose Breathing 26
6-1 Conceptual Relationship Between Level of Standard
~ and Size Indicator 87
t
6-2 Average Deviations of Daily Mortality from 15-day
Moving Averages by Concentrations of Smoke (BS) and
SC>2 (London, November 1, 1958 to January 31, 1959) 91
6-3 Hypothetical Concentration-Response Curves Derived
* from Regressing Mortality on Smoke in London During
Winters 1958/59 to 1971/72 93
7-1 Median 1974-76 Visibilities and Visibility Isopleths
for Suburban/Nonurban Airports 117
^ 7-2 Visual Range as a Function of Fine Mass
Concentration 124
7-3 Cumulative Frequency Distributions of Visibility at
Urban/Suburban Locations 131
9 7-4 Summertime Fine Particle Levels at Non-Urban Sites 134
B-1 Concentration Response Relationship for Two Sulfate
Aerosols in Guinea Pigs B-5
B-2 Bacterial Mutagenicity of Three Organic Fractions of
I Size Specific Particulate Matter B-37
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VI
LIST OF TABLES
Number Page
1 Staff Assessment of Short-Term Epidemiological
Studies xiv
2 Staff Assessment of Long-Term Epidemiological
Studi es xvi
4-1 Comparison of Measured Components of TSP in U.S.
Cities (1960-65) and Maximum 1-hour Values in
London (1955-63) 11
4-2 Normal Size Ranges for Commonly Found Chemicals,
Based on Impactor Studi es 17
4-3 Characterization of Particulate Matter Concen-
trati ons '20
5-1 Major Regions of the Respiratory Tract 24
5-2 Possible Responses to Particle Deposition in the
Respiratory Tract 32-33
5-3 Sensitive Population Groups 46
5-4 Summary of Epidemiological Studies Providing Most
Useful Concentration/Response Information for Acute
Particle Exposures 51
5-5 Summary of Epidemiological Studies Providing Most
Useful Concentration/Response Information for
Long-Term Particle Exposures 58
6-1 Standard Level as a Function of Exceedances 82
6-2 Assessment of Short-Term Epidemiological Studies 97
6-3 Assessment of Long-Term Epidemiological Studies 105
7-1 Summary of Qualitative Evidence for Visibility
Related Values 120
7-2 Visibility Associated with Alternative Primary
Standards 125
B-l Respiratory Diseases and Related Impairments
Associated with Occupational Exposures to
Particles B-2
B-2 Effects of Sulfuric Acid and Other Sulfates on
Respiratory Mechanics and Symptoms B-6
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vn
LIST OF TABLES
Number Page
B-3 Evidence From Epidemiological Studies Showing
Qualitative Associations Between Changes in
Respiratory Mechanics and Symptoms and Exposure
to Particles B-14-15
B-4 Evidence From Epidemiological Studies Showing
Qualitative Associations Between Aggravation
of Pre-Existing Cardio-Respiratory Disease
and Exposure to Particles B-18
B-5 Effects of Sulfuric Acid, Carbon Exposure on
Mucociliary Clearance B-21
B-6 Effect of Particulate Matter on Host Defense
Systems B-23
B-7 Evidence From Epidemiological Studies Showing
Qualitative Associations Between Respiratory
Tract Infections/Altered Clearance and Exposures
to Particles B-26-27
B-8 Results of Selected Long-Term Animal Studies of
Effects of Lung Structure and Function B-29
B-9 Retrospective Pathology Studies B-32
B-10 Evidence From Epidemiological Studies Showing
Qualitative Associations Between Short-Term Changes
in Mortality and Exposure to Particles B-41
B-ll Evidence From Retrospective Regression Analyses
Relating Mortality Rates to Chronic Sulfur-
Containing Particle Exposure B-46-47
C-l Summary Results of Iterative Bidding Visibility
Studies C-4
D-l Terms Used in the Staff Paper to Indicate
Particulate Matter D-2
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7X
EXECUTIVE SUMMARY
This paper evaluates and interprets the available scientific and
technical information that the EPA staff believes is most relevant to the
review of primary (health) and secondary (welfare) National Ambient Air
Quality Standards (NAAQS) for particulate matter and presents staff recom-
mendations on alternative approaches to revising the standards. Review of
the NAAQS is a periodic process instituted to ensure the scientific
adequacy of air quality standards and is required by Section 109 of the
1977 Clean Air Act Amendments. The assessment in this staff paper is
intended to help bridge the gap between the scientific review contained
in the EPA criteria document "Air Quality Criteria for Particulate Matter
and Sulfur Oxides" and the judgments required of the Administrator in setting
ambient standards for particulate matter. The staff paper is, therefore,
an important element in the standards review process and provides an
opportunity for public comment on proposed staff recommendations before
they are presented to the Administrator.
Particulate matter represents a broad class of chemically and physically
diverse substances that exist as discrete particles (liquid droplets or
solids) ranging in size from molecular clusters of about 0.005 micrometers
(ym) to coarse dusts on the order of 100 urn. Particles originate from a
variety of stationary and mobile sources and may be emitted directly or
formed in the atmosphere by transformations of gaseous emissions such as
SOp. The major chemical and physical properties of particulate matter
vary greatly with time, region, meteorology and source category, complicating
the assessment of health and welfare effects as related to various indica-
tors of particulate pollution. Typical particle distributions reveal
differences in origin and composition for fine particles (< 2.5 ym) and
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r
coarse particles (> 2.5 urn). The reference method for the current standards
for particulate matter is the "hi volume" sampler which collects particulate
matter of particle sizes up to 25-45 urn (so called "Total Suspended
Particulate" or TSP).
At elevated concentrations, particulate matter can adversely affect
human health, visibility, climate, materials, economic values, personal
comfort and well-being, and vegetation. Components of particulate matter
(e.g., sulfuric acid) also contribute to acid deposition. Typical long-
3
term average levels of TSP range from 20-40 pg/m in rural areas to over 150
pg/m in the most polluted urban industrial areas. Maximum 24-hour TSP
concentrations exceed 500 pg/m . Long-term fine particle (< 2.5 pm) levels
3 3
range from 2 to 5 pg/m in isolated arid western areas to 20-25 pg/m in
the rural East. The highest annual fine particle levels, on the order of
50 pg/m , occur in the most polluted urban industrial areas.
Primary Standards
The staff has reviewed scientific and technical information on the
known and potential health effects of particulate matter cited in the
criteria document. The information includes studies of respiratory tract
deposition of particles, studies of mechanisms of toxicity, effects of
high exposures to various particulate substances in controlled human and
animal studies, epidemiological studies, and air quality information.
Based on this review, the staff derives the following conclusions.
1) The mechanisms by which inhaled particles may pose health risks
involve (a) penetration into and deposition of particles in the
various regions of the respiratory tract, and (b) the biological
responses to the deposited materials.
2} The risks of adverse effects associated with deposition of ambient
fine and coarse particles in the thorax (tracheobronchial and
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XT
alveolar regions of the respiratory tract) are markedly greater
than for deposition in the extrathoracic (head) region. Maximum
particle penetration to the thoracic regions occurs during oronasal
or mouth breathing.
3) The major effects categories of concern associated with high expo-
sures to particulate matter include: (a) effects on respiratory
mechanics and symptoms, (b) aggravation of existing respiratory and
cardiovascular disease, (c) effects on clearance and other host
defense mechanisms, (d) morphological alterations, (e) carcinogenesis,
and (f) mortality.
4) The major subgroups of the population that appear likely to be most
sensitive to the effects of particulate matter include: (a) indivi-
duals with chronic obstructive pulmonary or cardiovascular disease,
(b) individuals with influenza, (c) asthmatics, (d) the elderly,
(e) children, (f) smokers, and (g) mouth or oronasal breathers.
5) Although controlled animal and human studies, and qualitative
epidemiological results can provide important insights into the
health risks from particles, the most useful concentration-response
information comes from a limited set of community epidemiological
studies conducted over the last 25 years in Great Britain and the
United States.
Based on the scientific and technical reviews as well as policy con-
siderations, the staff makes the following recommendations with respect
to primary particulate matter standards.
1) Despite the variability in the composition of ambient particles
with time and space, the available data suggest that reductions in
ambient particulate matter in Great Britain and the U.S. have
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xi i
benefited public health and reduced the need for separate control
programs for many of the more innately toxic components of parti -
culate matter. Elevated particulate matter exposures in current
U.S. settings most frequently occur without concomitant high
S02 levels. Considering these observations, a separate general
particulate matter standard remains a reasonable public health
policy choice.
2) The current TSP standard directs control efforts towards particles
of lower risk to health because of its inclusion of larger particles
which can dominate the measured mass concentration, but which are
deposited only in the extrathoracic region. A new particle
indicator representing those particles capable of penetrating the
thoracic regions (thoracic particles, TP) is recommended. Protec-
tion of sensitive individuals breathing oronasally or by mouth,
sampler reliability, and the convention recently adopted by the
International Standards Organization (ISO) suggest that the
particle size range include those particles less than a nominal
10 vim (DCQ). Sampler performance criteria should be related to
respiratory tract deposition data. Prototype samplers meeting
these criteria are being field tested; reliable commercially
available models must await test results.
3) Both short-term (24-hour) and annual arithmetic mean standards
are recommended. The short-term standard should be expressed in
statistical form with the decision on the allowable number of
exceedances made in conjunction with establishing a level for
the standard.
4) Selecting a level for a particulate matter standard with an
adequate margin of safety will involve a number of uncertainties
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xi i i
in addition to those involved in making judgments on health
risks associated with specific substances such as CO or SCL.
Quantitative assessments must be based on limited epidemiological
studies conducted in times and places where pollutant composition
may have varied considerably from current U.S. atmospheres. Epidemio-
logical studies are generally subject to a number of inherent
difficulties involving confounding variables and somewhat limited
sensitivity. Most studies have used British smoke (a pseudo
mass indicator related to small particle (< 4.5 ym) darkness) or
TSP as particle indicators. None of the published studies have
used the recommended TP (< 10 ym) indicator. Thus, appropriate
assumptions must be used to express available results in common
units.
The staff assessment of short-term epidemiological data is summarized
in Table 1; levels are expressed in both the original and TP units. The
"effects likely" row denotes concentration ranges derived from the criteria
document at or above which there appears greatest certainty that effects
would occur. The data do not, however, show evidence of clear population
thresholds but suggest a continuum of response with both the risk of effects
occurring and the magnitude of any potential effect decreasing with concen-
tration. Thus, effects may be possible at levels below those listed in
the "effects likely" row, but the evidence and risks at lower levels are
much less certain.
Based on this staff assessment, the range of 24-hour TP levels of
interest are 150 to 350 yg/m . Under the conditions prevailing during the
London studies, the upper end of the range represents levels at which
effects are likely in the sensitive populations studied. Given the uncer-
tainties in translating these results to U.S. conditions and the seriousness
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XIV
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XV
of the potential health effects, the upper end of the above range contains
no identifiable margin of safety and should not be considered as an appro-
priate standard alternative. The uncertainties and the nature of the
potential effects are important margin-of-safety considerations. Neither
the studies summarized above nor more qualitative studies of effects in
other sensitive population groups (e.g., asthmatics, children), or effects
in controlled human or animal stuides provide scientific support for health
risks of consequence below 150 yg/m . These qualitative data as well as
factors such as aerosol composition and exposure characteristics should
also be considered in evaluating margins of safety associated with alterna-
3 3
tive standards in the range of 150 yg/m to something below 350 yg/m .
The staff assessment of important long-term epidemiological data is
summarized in Table 2. Long-term epidemiological studies are subject to
additional confounding variables that reduce their sensitivity and make
interpretation more difficult. The "effects likely" levels are derived
from the criteria document, but again, no clear population thresholds
exist for all effects indicators. Some risk of effects are possible at
lower levels, but these are uncertain and difficult to detect in these
studies.
Based on this staff assessment, the range of annual TP levels of
•3
interest are 55 to 110 yg/m . The upper end of this range overlaps the
somewhat uncertain "effects levels" derived from these studies. Due to
o
these uncertainties, the upper end of the range (110 yg/m ) may not include
any margin of safety, and should not be considered as an appropriate
standard alternative. The lower end (55 yg/m ) represents a level where
some risk of symptomatic effects might remain but no detectable differences
in pulmonary function or marked increases in respiratory diseases are
expected. Increases in symptomatic effects at the lower levels are uncertain
and small in comparison to baseline rates.
-------
xvn
When evaluating margins of safety for an annual standard, it is
particularly important to examine the results of qualitative data from a
number of epidemiological, animal, and air quality studies. These
suggest concern for effects not directly evaluted in the studies listed in
Table 2. Such effects include damage to lung tissues contributing to chronic
respiratory disease, cancer, and premature mortality. The available scientific
data do not suggest major risks for these effects categories at current ambient
particle levels in most U.S. areas. Nevertheless, the risk that both fine
and coarse particles may produce these responses supports the need to
limit long-term levels of TP for a variety of aerosol compositions.
Because of different form, averaging procedure and size range,-
precise comparisions between the above ranges of TP standards and the
current primary TSP standards are not possible.* The lower bounds, taken
together, result in standards roughly equivalent in stringency to the
current standards. In general, the rest of the ranges represent increasing
degrees of relaxation as compared with the current standards. At the lower
concentrations in the ranges, much of the relaxation would result because
only smaller particle sizes would be collected. Thus, a city where exceedance
of the TSP standard was largely dominated by coarse mode dust (with sub-
stantial mass of particles greater than 10 ym) would be less likely to
violate a comparable TP standard than would an area where exceedance of
the TSP standard was dominated by particles smaller than 10 urn. At higher
concentrations in the above ranges, standards would permit increased levels
for TP as well as for larger particles.
*By applying observed TP/TSP ratios and other factors, crude comparisons can
be made. The current annual TSP standard (75 yg/m , geometric mean) is
roughly equivalent to an arithmetic mean of 50 yg/m as TP. The numerical
value of the 24 hr TSP standard (260 yg/m ) is roughly equivalent to 140
yg/m TP, but this does not account for differences between the deterministic
(current standard) and recommended statistical form.
-------
xviii
Secondary Standards
The staff examined information in the criteria document relevant to
the review of the secondary standards. Categories of welfare effects
examined include visibility and climate, man-made materials, vegetation,
and personal comfort and well-being. Major staff conclusions and recommenda-
tions are summarized below.
1) a) Impairment of visibility by fine particles over urban to multi-
state regions clearly affects public welfare. Fine particles or
major constituents thereof also are implicated in climatic effects,
materials damage, soiling, and acid deposition. Neither the
current secondary TSP standard nor the recommended ranges of TP
standards will protect visibility in an effective manner. The
staff, therefore, recommends consideration of a fine particle
secondary standard, based primarily on the relatively well-defined
quantitative relationships between fine mass and visibility.
b) If a fine particle standard is selected, a seasonal (calendar
quarter) averaging time could provide a statistically stable target
and yet achieve most short or long-term visibility goals.
Consideration should be given to specifying a spatial average of
three or more monitors placed at distances on the order of 16-50 km.
c) Despite the fact that the public is concerned about visibility
and is willing to pay something for clean air, quantitative bases
for evaluating visibility goals have not been established. There-
fore, the level of any standard must be based on the judgment of
the Administrator after consideration of aesthetics and transporta-
tion, as well as non-visibility related effects. The staff recom-
mends that any national standards focus on welfare effects associated
-------
XIX
with multistate eastern regional (and western urban) haze. Such
standards would not of themselves protect sensitive scenic areas
of the West, but these areas are directly and indirectly addressed
by other provisions of the Clean Air Act.
d) Empirical ranges for standards can be derived from approximate
estimates of eastern natural background and current summertime
fine particle levels. The range thus derived is 8-25 pg/m , seasonal
and spatial average. The upper portion of the range would tend to
maintain the status quo in the East. Current summertime visual
range in much of the East is about 9-15 miles. Because the lower
portion of the range approaches natural background levels, standards
set at the lower levels would be, in all practicality, unattainable
in most of the eastern U.S. Estimated summertime visibility under
eastern natural background conditions is on the order of 3 to 5 times
greater than under current conditions.
e) Because regional fine particles in the East appear to be
influenced most strongly by sulfates, adoption of a fine particle
standard would trigger a substantial departure from current
approaches to particle control strategies. The evidence suggests
that multistate control of regional sulfur oxide emissons might
be needed to reduce fine particle levels. Thus, fine particle/
visibility-climate effects are linked to acid deposition, and
these problems would likely be ameliorated by similar control
strategies. Addressing these welfare effects with a common
standard or control strategy is likely to be more efficient
than establishing separate control approaches for each.
Appropriate scientifically based targets and control strategies
for acid deposition are not yet available.
-------
XX
2) Although potential effects on climate support the consideration of
a fine particle standard, quantitative relationships are not well
enough developed to provide the principal basis for selecting
the level of the standard.
3) Consideration should be given to soiling and nuisance effects in
determining whether a secondary standard for TP or for TSP or some
other large particle indicator is desirable to supplement the
primary health and secondary fine particle standards. The available
data base on such effects is, however, largely qualitative. There-
fore, the basis for selecting a particular level for a secondary
TP or TSP standard is a matter of judgment.
4) While chemically active fine mode and hygroscopic coarse mode
particles have been qualitatively associated with materials
damage, the available data do not clearly suggest major effects
of particles on materials for concentrations at or below the
ranges recommended for the primary health and secondary visibility
standards. Therefore, a secondary standard based solely on
materials damage is not recommended.
5) The staff concludes that a secondary particle standard is not
needed to protect vegetation.
6) The acid deposition issue will not be addressed directly in the
review of the particulate matter standards.
-------
REVIEW OF THE NATIONAL AMBIENT AIR QUALITY STANDARDS FOR PARTICULATE MATTER:
ASSESSMENT OF SCIENTIFIC AND TECHNICAL INFORMATION
OAQPS STAFF PAPER
I. PURPOSE
This paper evaluates and interprets the most relevant scientific and
technical information reviewed in the draft EPA document "Air Quality
Criteria for Particulate Matter and Sulfur Oxides" (EPA, 1981) in order to
better specify the critical elements which EPA staff believes should be
considered in the possible revision of the primary and secondary particulate
matter National Ambient Air Quality Standards (NAAQS). This assessment is
intended to help bridge the gap between the scientific review contained
in the criteria document and the judgments required of the Administrator
in setting ambient standards for particulate matter. As such, particular
emphasis is placed on identifying those conclusions and uncertainties in
the available scientific literature that the staff believes should be
considered in selecting a particulate pollutant indicator, form, and
level for the primary standards. While the paper should be of use to
all parties interested in the standards review, it is written for those
decision makers, scientists, and staff who have some familiarity with
the technical discussions contained in the criteria document.
II. BACKGROUND
Since 1970 the Clean Air Act as amended has provided authority and
guidance for the listing of certain ambient air pollutants which may endanger
public health or welfare and the setting and revising of NAAQS for those
pollutants. Primary standards must be based on health effects criteria and
provide an adequate margin of safety to ensure protection of public health.
As several recent judicial decisions have made clear, the economic and
-------
technological feasibility of attaining primary standards are not to be
considered in setting them, although such factors may be considered to a
degree in the development of state plans to implement the standards (D.C.
Cir., 1980, 1981). Further guidance provided in the legislative history
of the Act indicates that the standards should be set at "the maximum
permissible ambient air level . . . which will protect the health of any
(sensitive) group of the population." Also, margins of safety are to be
provided such that the standards will afford "a reasonable degree of
protection . . . against hazards which research has not yet identified."
(Committee on Public Works, 1974). In the final analysis, the EPA
Administrator must make a policy decision in setting the primary standard,
based on her judgment regarding the implications of all the health effects
evidence and the requirement that an adequate margin of safety be provided.
Secondary ambient air quality standards must be adequate to protect the
public welfare from any known or anticipated adverse effects associated
with the presence of a listed ambient air pollutant. Welfare effects, which
are defined in section 302(h) of the Act, include effects on vegetation,
visibility, water, crops, man-made materials, animals, economic values and
personal comfort and well-being. In specifying a level or levels for
secondary standards the Administrator must determine at which point the
effects become "adverse" and base her judgment on the welfare effects criteria.
The current primary standards for particulate matter (to protect
3
public health) are 75 micrograms per cubic meter (yg/m ) annual geometric
mean, and 260 yg/m , maximum 24 hour concentration not to be exceeded more
than once per year. The current secondary standard for particulate matter
(to protect public welfare) is 150 yg/m , maximum 24 hour concentration,
-------
not to be exceeded more than once per year. In addition, the secondary
standard specifies a 60 yg/m annual geometric mean guide for the achieve-
ment of the 24-hour standard. The reference method for measuring attainment
of both the primary and secondary standards is the "hi-volume" sampler
(40 CFR Part 50, Appendix B), which effectively collects particulate matter
in the range of up to 25-45 micrometers (ym) (so-called "total suspended
particulate," or "TSP"). Thus, TSP is the current indicator for the
particulate matter standards.
Preliminary drafts of this paper were reviewed by the Clean Air
Scientific Advisory Committee (CASAC) in July and November, 1981. This
final product incorporates the suggestions and recommendations of the CASAC
as well as other appropriate comments received on the initial drafts. The
CASAC closure memo on the staff paper (Friedlander, 1982) is reprinted
in Appendix E.
III. APPROACH
The approach used in this paper is to assess and integrate information
derived from the criteria review in the context of those critical elements
which the staff believes should be considered in the review of the
primary and secondary standards. Particular attention is drawn to those
judgments that must be based on the careful interpretation of incomplete or
uncertain evidence. In such instances, the paper states the staff's evaluation
of the evidence as it relates to a specific judgment, sets forth appropriate
alternatives that should be considered, and recommends a course of action.
Sections IV and V review and integrate important scientific and
technical information relevant to standard setting. Because of the
complex nature of particulate pollution, this review is unusually lengthy.
Therefore, much of this material is included in appendices (A and B) with
-------
only summaries in the main body of the paper. Section IV presents relevant
features of historical and current U.S. air quality to support discussions
of both primary and secondary standards. Section V addresses the essential
elements with regard to the primary standards; these include the following:
1) identification of possible mechanisms of toxicity;
2) description of effects and judgment of critical
effects of concern for standard setting;
3) identification of most sensitive population groups; and
4) discussion of community studies relating level(s) and duration(s)
of exposure to indicators of health effects.
Drawing from the discussion in Sections IV and V, Section VI identifies
and assesses the factors the staff believes should be considered in selecting
a particulate pollutant indicator, form, and level of primary standards.
Preliminary staff recommendations on alternative policy options in each
of these areas also are presented.
Section VII examines information in the criteria document the staff
believes is most relevant with respect to secondary standards and focuses
on the effects of particulate matter on visibility and climate, man-made
materials, vegetation, and personal comfort and well-being. Some of the
scientific and technical review is included in Appendix C. The elements
addressed include:
1) description of effects and judgment of the critical effects
of concern for standard setting;
2) identification of causal mechanisms;
3) studies relating level(s) and duration(s) of exposure to
indicators of effects; and
-------
4) factors to be considered in selecting a participate pollutant
indicator, form, and level of secondary standards.
Preliminary staff recommendations on policy options for secondary standards are
also presented.
-------
IV. AIR QUALITY CONSIDERATIONS
More than any other criteria pollutant, "particulate matter" represents
a broad class of chemically and physically diverse substances. Their
principal common feature is existence as discrete particles in the condensed
(liquid or solid) phase ranging in size from molecular clusters of
0.005 ym to coarse particles on the order of 100 pm.* The major chemical
and physical properties of particulate matter vary greatly with time, region,
meteorology, and source category. It is to be expected, then, that the
effects of given quantities of particles on public health and welfare also
will vary. This variable composition complicates the evaluation of the
applicability of specific particle health and welfare studies for establish-
ing National Ambient Air Quality Standards. This section of the staff
paper summarizes some key features of our understanding of historical and
current particulate matter composition to provide perspective for subsequent
interpretation of health and welfare effects studies.
The historical aerosol composition information is intended to assist
in interpreting the relevance of historical health effects studies to
current U.S. atmospheres. Many of the more important epidemiological studies
were conducted in Great Britain, particularly in London, and in New York City
in the 1950's and 60's. Important aspects of current physical and chemical
distribution of aerosols are presented to support identification of those
aerosol fractions potentially responsible for health and welfare effects and
evaluation of standard levels.
*Where not otherwise specified, particle sizes reported in this paper
reflect aerodynamic equivalent diameter (AED). A number of terms (e.g.,
fine, coarse, inhalable, thoracic, TSP) are used to describe various functions
of particulate matter. Many of these terms are defined by the instruments
used for measurement. The major particle indicators discussed in this
paper are defined in Appendix D.
-------
A. Historical Trends
1. London 1950's - 196Q's
Although implementation of the British Clean Air Act effected dramatic
air quality improvements from 1956 to 1970, particle and sulfur oxide levels
from 1955 to 1963 were remarkably high by present day standards. Typical
annual SCL and smoke (a pseudo-mass indicator related to small particle
(< 5 ym) darkness, McFarland e_t etl_., 1981) concentrations ranged between
200 to over 300 yg/m3 in Metropolitan London from 1955-1960 (WSL, 1967).
Details on short and long-term levels of interest are reported in the later
health effects discussions. The major source of these pollutants was the
inefficient combustion of fuel, particularly domestic coal. In addition,
"industrial processes, building and demolition, wear of roads, tyres (sic)
and other materials, the burning of vehicle fuels containing additives"
contributed to particulate loadings (Lawther e_t al_., 1968). One would expect
atmospheres dominated by incomplete coal combustion emissions to contain
large amounts of carbonaceous material ranging from fine soot to coarse
cinders, various inorganic elements (e.g., mercury, arsenic, zinc) found
in coal, primary sulfuric acid aerosol as well as SO,,, and particularly
in the case of British coal, chlorine containing compounds such as
gaseous hydrochloric acid.
Unfortunately, actual ambient measurements of expected components are
rare. The best bench-mark for evaluating the composition of London particles
(and comparing them to contemporary U.S. aerosols) is found in a series of
investigations conducted by Waller, Lawther, Commins and other air pollution
researchers with the Medical Research Council at the St. Bartholomew's
Hospital Medical College in London. This location in the "City," a one square
-------
8
mile area encompassing the business district of London, may not be
representative of greater London levels, but should reflect general
composition and trends. The monitors were fairly elevated, generally 22
m or more above ground level. SOp levels appear 50 to 100 yg/m higher
than levels reported elsewhere in London, but smoke readings were 50 to
100 ug/rn3 lower (Commins and Waller, 1967; WSL, 1967). The authors
suggest that their site may be strongly influenced by local point sources
of S02» making S0? levels and trends atypical (Commins and Waller, 1967).
The reason for lower smoke readings is less clear and could involve
lower amounts of nearby domestic coal use, since the site was in a smoke
control zone; the lower readings also might be due in part to the more
reliable calibration of the smoke readings with actual mass concentrations
as performed by the St. Bartholomew's group (Waller, 1964).
The investigators operated standard U.S. hi-volume air samplers
(particle size range collected usually less than about 25-45 ym) as well as
conducting special size and composition studies over the eight year period
from 1955-1963. TSP readings are plotted in Figure 4-1. Contemporary
readings from some New York City sites (Eisenbud, 1980) are shown for
comparison. The beneficial effects of pollution control programs are
apparent from the trends. Although analyses of the composition of London
TSP samples were performed, long-term composition data are regrettably
available only for the benzene soluble organics (BSO) fraction (see Figure
4-1). This fraction contains polycyclic organics (POM) as well as other
non-polar organic aerosols. On average, about 16% of collected TSP mass
consisted of this organic material, but some individual samples taken
during periods of high pollution contained more than 50% BSO (Commins and
Waller, 1967). Benzo(a)pyrene (BaP), often used as an indicator of
-------
300
CO
i
*
O
P
oc
5 200
O
o
o
z
100
• NYC (TSP)
A LONDON (TSP)
D ORGANIC (BSD)
A *
A
A
1950
1960
1970
YEAR
Figure 4-1. Trends in TSP and benzene soluble organics at a central
London site (Commins and Waller, 1967), and TSP trends for New York
City as summarized by Eisenbud (1980). TSP in both cities were
considerably higher than present day levels in most urban areas.
-------
10
carcinogenic POM, typically ranged from 2-30 ng/m3 with maximal peaks on
3
the order of 1 yg/m .
Some annual (1964-65) and episodic data for London also are available
for strong acids (reported as sulfuric acid) as measured by filtration and
subsequent titration (Waller, 1963). Because of potential interferences
in sampling, handling and analysis, these numbers should be viewed with
3
caution. The annual level was 5.4 yg/m , with winter averages twice those
of summer. Despite potential methodological problems, these values are not
inconsistent with levels expected if 1-2% of the seasonal and annual SO
/\
emissions were in the form of primary sulfuric acid. Episodic levels (1957-
64), however, present a different picture, with maximal daily sulfuric acid
values of 30-350 ug/m and maximal hourly readings of 30-680 yg/m . In
these cases, sulfuric acid values were 5-10% of measured S02 levels, suggesting
the occurrence of secondary formation. Under the episodic conditions of
high particle loadings and humidity, heterogeneous formation of sulfuric
acid is likely (Criteria Document (CD), p. 2-33).
Measurements of a number of other substances were also made, but
unfortunately, only maximum hourly values were reported. These are reproduced
in Table 4-1 to indicate the relative ranking. Maximum 24 hour values are
also provided for selected U.S. sites (1960-65). Obviously, these peak
values are not representative of typical conditions.
The St. Bartholomew's group also examined size distributions of particles
and sulfuric acid. Using a thermal precipitator and electron microscopy,
Waller e_tal_. (1963) found numerous single particles smaller than 1 ym, aggregates
up to 1 - 2 ym, and evidence of partially neutralized sulfuric acid droplets.
-------
11
TABLE 4-1. COMPARISON OF MEASURED COMPONENTS OF TSP IN U,S, CITIES (1960-65)
WITH MAXIMUM 1-HOUR VALUES IN LONDON (1955-63)
Pollutant
Suspended Particles
Fractions:
Benzene-soluble organics___
Chloride (water soluble)
Nitrates
Sul fates
Sulfuric acid
Ammonium
Antimony
Arsenic
Beryl 1 i urn
Bismuth
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Molybdenum
Nickel
Tin
Titanium
Vanadium
Zinc
Gross beta radioactivity
UNITED STATES a
Concentration ug/m
Number of Arith. Maximum
Stations average 24-Hour
291
218
96
96
56
35
133
100
35
35
f
103
35
103
104
104
103 .
35
103
85
104
99
99
323
105
6.8
2.6
10.6
1.3
0.001
0.02
<0.0005
<0.0005
0.002
0.015
O.0005
0.09
1.58
0.79
0.10
<0.005
0.034
0.02
0.04
0.050
0.67
(O.S pCi/
m3)
1254 (TSP)
39.7
101.2
75.5
0.160
0.010
0.064
0.420
0.330
0.060
10.00
22.00
8.60
9.98
0.78
0.460
0.50
1.10
2.200
58.00
(12.4 pCi/m3)
LONDON b
Maximum
1-Hour (1 site)
9700 ( Smoke f
410
5 .
666
680
<1
<1
<1
1-
82
2
<1
2
25
22
5
<1
1
2
1
2
24
aU.S. HEW, 1969.
}Commins and Waller, 1967.
GBritish Smoke (BS) data reported as
yg/m . These data are not directly
comparable with TSP.
-------
12
The aggregate, which varied with source area, apparently consisted of
carbonaceous material (carbon and organics) from incomplete combustion.
The mass median diameter (MMD) was 0.5 - 1 ym in normal weather and
somewhat higher (but indeterminate) in foggy weather.
These values may underestimate the true mass median diameter* of
the total aerosol. Due to the nature of the thermal precipitator (Hodkinson,
1960), larger particles (* 2-5 ym) may settle out or be inefficiently moved
to the collection plate. The fact that the estimated mass from the microscopy
determination generally approximated smoke readings (Waller ejt al_., 1963),
tends to support the notion that only the smaller portion of the aerosol was
actually examined. At this site, calibrated smoke readings were consistently
about 100 yg/m below TSP levels, particularly at lower concentrations
o
(< 500 yg/m ) (Commins and Waller, 1967). Moreover, samples collected at
the elevation of the St. Bartholomew's site (22 m) would not be representative
of ground level large particle concentrations. Other considerations, notably
measurements of dry deposition and the dispersed nature of coal and oil
emissions (which include large particles), support the notion that substantial
quantities of large particles (2 to over 30 ym) were emitted and were probably
present in the ambient air of British cities (Carey, 1959). Nevertheless,
during extreme episodes (BS > 500 yg/m ), with low windspeeds, large particles
would be expected to settle relatively rapidly near source areas.
Waller (1963) estimated the size distribution of sulfuric acid droplets
(pH < 2) using a cascade impactor coated with a pH indicator. At lower
humidities, the mass median diameter of these droplets was less than 0.5 ym.
During an episode with higher humidities (^ 85%), the mass median diameter
*MMD is used as an indicator of relative particle size of a lognormally
distributed aerosol. The term is used loosely here, since the distribution
may not have been lognormal.
-------
13
was 0.5 ym, but 16% of the sulfuric acid mass was greater than 4.0 ym
(estimated a of 2.1). During high humidity fogs measurable amounts of
large (20 ym) sulfuric acid droplets (pH < 2.0) were often observed.
2. U.S. Particle Trends
As indicated in Figure 4-1, annual TSP levels from 1955-65 in New
York City were in the same range as those in London. However, even
during this period, the influence of particles from inefficient fuel
combustion may have been somewhat lower than for London. Organics (BSO)
from 1961-65 were about 10% or less of total particulate mass as compared to
15-20% at the London site (DHEW, 1969). Long-term and maximum dai.ly
values of a number of compounds for a number of U.S. cities are compared
with maximum hourly London data in Table 4-1. Although hourly values
cannot be strictly compared to 24 hour data, maximum levels for sulfates,
lead, and some trace elements were probably higher in London. Maximal
levels of nitrates, manganese, and some additional elements were higher
in U.S. cities. A striking feature of available information in both
London and the U.S. is the inability to account for more than about 25%
of TSP by the available compositional analyses.
From the early 1960's through the mid-1970's, U.S. control programs
continued to result in substantial reductions in TSP and S02 levels in
most of the more polluted urban areas. In these areas, concentrations
of a number of components of interest also decreased markedly, most notably
carbonaceous material (BSO), trace elements (lead, nickel, vanadium, cadmium,
and iron), and in some areas, sulfates (Faoro and McMullen, 1977; Faoro,
1975; Altshuller, 1976). During this same time period, available information
suggests that eastern U.S. regional levels of summertime fine particles,
-------
14
particularly sulfates, increased (EPA, 1975b, 1979; Frank and Posseill,
1976; Altshuller, 1976).
B. Current U.S. Aerosols
Changes in the nature and distribution of combustion related and
other sources, and the implementation of various control programs since
the 1970's have brought about substantial changes in the distribution,
quantity and composition of airborne particles in the U.S. Moreover,
the quantity and nature of accompanying pollutant gases are also sub-
stantially different than those of the earlier London and U.S. atmospheres
discussed above. Notably, areas or times with higher particle loadings
are now more likely to be accompanied by lower SIX, levels and higher
oxidant levels than occurred in the past. Although the diversity of
particles and gases in U.S. atmospheres is, if anything, greater, important
advances in measurement and approach in aerosol science during the
1970's have afforded a far greater understanding of the general features
and origins of contemporary airborne particles. The criteria document
discusses the results of a number of these advances in chapters 2-6.
Some key features, and their implications, are outlined below.
1. The Multimodal Distribution
The atmospheric aerosol surface area, volume, and mass tend to be
distributed in two to three distinct size modes (Figure 4-2):
1) The nuclei (Aitken) mode (< 0.1 vim) accounts for most of the
particles by number, some of the surface area, and little
mass, but is short-lived and observed only near combustion
sources. Through coagulation, nuclei mode particles grow
into the next mode, the accumulation mode.
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15
R- RICHMOND
SF- SAN FRANCISCO AIRPORT
F - FRESNO
HL-HUNTER-UGGETT
HF-HARBOR FREEWAY
P -POMONA
G -GOLOSTONE
Figure 4-2. Grand average volume size distribution for seven sites in the
California ACHEX study in 1972. Particle size reflects optical rather than
aerodynamic diameter. Volume (and mass) tends to be bimodally distributed
although the relative proportion of fine (l-3 ym) modes
as well as location of maxima and minima vary considerably. The increased
volume of 0.01 - 0.1 ym particles at the Harbor Freeway site is evidence of
the transient nuclei mode near a strong source (automobiles) (Whitby, 1980).
180
80
s-
20
Scalt Chang*
Run Conctntration Ptretnt
No
I 3 10
Particle Diameter * fj.n\
30
100
300
Figure 4-3. Bimodal mass-size distributions measured with impactors. Unlike
Figure 4-2, particle size reflects aerodynamic diameter. The increase in
coarse mode particles in Run 14 shows the influence of upwind construction
activity. Note that the "minimum" in the original distribution disappears and
the coarse increase occurs in the range of 1 to 300 ym. (Reprinted from NAS,
1977).
-------
16
2) The accumulation mode (0.1 - 2.5 ym) contains much of the
surface area and about 1/3 to 1/2 of particulate volume and
mass. Under normal circumstances, little mass is transferred
into the next larger mode. Collectively, the nuclei and
accumulation modes are termed the fine mode (< 2.5 ym).
3) The coarse mode ( > 2.5 ym) contains small numbers of particles
and about 1/2 to 2/3 of particulate volume and mass. Although
much of the aerosol surface area is associated with the fine
mode, a secondary peak in surface area often appears in the
coarse mode at about 10 ym (NAS, 1977a).
Although substantial overlap can exist, the fine and coarse modes tend
to have more or less distinct origins, elemental distribution, residence times,
and removal processes. Fine particles originate in the nuclei mode by conden-
sation of materials produced during combustion (e.g., inorganic lead) or
atmospheric transformation (e.g., sulfuric acid). Due to long residence times
and atmospheric formation, fine particle levels can build up far from source
regions over large geographical areas. Coarse particles are largely derived
from mechanical processes such as grinding or wind erosion. Because they
settle out more rapidly, elevated levels of coarse particles usually occur
only near strong source emissions, for example, construction activity
(Figure 4-3).
Because fine and coarse modes are often derived from separate mechanisms,
the chemical species comprising each mode are not usually evenly distributed
between modes. Table 4-2 and Figure 4-4 show the size distribution of various
substances derived from available chemical analysis of size segregated samples
and microscopy of hi-vol filters. Although regular elemental/chemical
segregation occurs, each mode is chemically heterogeneous in the sense
that each consists of a number of different substances. The dominant
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17
TABLE 4-2. NORMAL SIZE RANGES FOR COMMONLY FOUND CHEMICALS, BASED ON IMPACTOR STUDIES
(After Miller et al... 1979)
Normally fine
Sul fates
Organic (condensed
vapors)
Soot (carbon)
Water (except fog)
Lead
Anmonlum Ion
Hydrogen 1on
Arsenic
Selenlun
Normally coarse
Iron, calcium
Titanium
Organic, biological
Magnesium
Aluminum
Silicon
Potassium
Phosphate
Normally blmodal
Chloride
Nitrate
Variable
Nickel
Tin
Lead
Vanadium
Copper
Zinc
Antimony
Manganese
AEROSOLS COLLECTED ON HI VOL FILTERS. MULTIPLE CITIES IORAFTZ. ItMl
MANGE Of ESTIMATED
CONCENTRATION PERCENT
OF TOTAL) FOUR CITIES*
(AFTER MAS. IttOI
NOT MEASURED
NOT MEASURED
ELEMENTAL CARSON 4J • •>
SULFATES 11A-SU
FIVASH —
COAL FRAGMENTS
FOLLENS * STORES 1-1««
TIRE FRAGMENTS —
PAVEMENT MATERIALS 13 •«•
SOIL MINERALS U-44
VOLATILE CARSON a-SQCITIUI
UNACCOUNTED FOR S-47
L-L
ai
PARTICLE SIZE bull
• THE FOUR AREAS NOTED INCLUDE PORTLAND. OREGON, LOS ANGELES, ST. UMMS,
AND WASHINGTON, D. C.
•• 14 CITY STUDY (RECORD «
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18
substances in the fine mode, in rough order of mass, are water, ammonium
sulfate and sulfuric acid, carbonaceous material (carbon and a variety of
condensed organics), lead, nitrates, and small amounts of trace elements.
These may take the form of mixed salt droplets, and a variety of heterogeneous
particles with adsorbed gases, organics, or trace element as surface coatings.
Sulfates and some other aerosols are hygroscopic (absorb water), growing to
several times their original size (and mass) at higher relative humidities.
This growth has important implications for deposition in the respiratory
tract and for effects on visibility and climate.
The coarse fraction is more variable and less well characterized,
containing a number of crustal and industrial minerals such as quartz, clays,
limestone, and asbestos, rubber tire particles, as well as organics, nitrates
and both road and sea salt. Salt is also hygroscopic. Among the trace
substances that may be associated with coarse particles are pesticides,
biological toxins, and soil dwelling microbes (Fraser and McDade, 1979).
2. Exceptions
The bimodal model of particulate matter is an extremely useful tool
in describing typical aerosol distributions and elucidating formation and
removal mechanisms and source contributions. This model also may be useful
in considering welfare effects of particulate matter such as visibility
or dustfall where a single mode clearly dominates. In evaluating the
health effects of particles, however, conditions under which the distinction
between modes becomes blurred may assume some importance.
Table 4-2 and Figure 4-4 list a number of important substances that,
depending on location, apparently may be readily found in both modes. These
substances include fly ash, coal fragments, minerals, nitrates, and trace
-------
19
elements such as vanadium. The relative contribution varies substantially.
Under strong source or meteorological conditions that produce very high
coarse or fine particle levels, the overlap between modes can increase
substantially, thus making the demarcation between the two more difficult
to detect. See, for example, the Pomona data of Figure 4-2 or Run 14 of
Figure 4-3. In these cases, substantial fine or coarse particle mass
may occur in the 2-5 urn range, which coincides with a maximum in deep lung
deposition efficiency (CD, Figure 11-14). These extreme conditions of
high concentration therefore may often be of more interest for primary
standard setting than the more typical distributions encountered with
lower levels.
3. Exposures
As a basis for comparison, Tables 4-3a and b provide estimates of
typical ranges of TSP, dichotomous total (labeled Inhalable Particles or
IP-ic. <15 pm), and fine particles (<2.5 ym) as measured in three size
specific particle sampling networks* for varying periods during 1977-81
(Pace, 1981). Analysis of limited temporal trends indicate that maximum
seasonal averages for all three particle indicators occur in the summertime,
particularly in the East (Pace ejt a]_., 1981). Overall ratios of IP,,-/TSP
in the most recent urban data remain fairly close to that reported by
Pace (1980) for earlier data, which was 0.65 j^0.12. Interpolation of
TSP, IP, and FP results and examination of expected particle size distribu-
tions (Watson et_ al_., 1981) suggest that the ratio of particle mass
<10 ym (PM-|Q) to TSP in most areas would lie between about 0.5 to 0.6.
Data on composition of these particles are not yet available.
*The data used from the three networks include: EPA's Inhalable Particulate
Network, 35 urban sites, April 1980-March 1981; EPA's Western Fine Particle
Data Based, 40 non-urban sites, Summer 1980-Spring 1981; Electric Power
Research Institute SURE data base, 9 rural sites, 15 months, 1977-1978
(Pace 1981).
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20
TABLE 4-3. CHARACTERIZATION OF PARTICIPATE MATTER CONCENTRATIONS FROM
SIZE SPECIFIC NETWORKS, 1977-81 (Pace,1981)
a) LONG-TERM (6-12 MONTHS) AVERAGE
EASTjRN LOCATIONS
Undisturbed
Downtown
Industrial
ARID WESTERN LOCATIONS
Undisturbed
Downtown
WEST COAST
Los Angeles Area
Pacific Northwest
TSP
30-40
60-90
60-110
15-20
75-130
90-180
45-95
IP15
25-35
40-50
45-70
10-15
40-70
50-110
20-65
FP
15-20
20-30
25-45
3-5
' 15-25
30-40
15-25
b) TYPICAL 24-HOUR MAXIMA*
EASTERN LOCATIONS
Undisturbed
Downtown
Industrial
ARID WESTERN LOCATIONS
Undisturbed
Downtown
WEST COAST
Los Angeles Area
Pacific Northwest
TSP
60-100
90-210
150-360
50-100
125-310
170-460
115-310
IP15
50-100
75-140
100-250
25-40
70-180
150-200
50-190
FP
30-80
40-90
50-180
10-15
45-70
100-110
45-90
*60 Samples/Year
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21
Given reduced outdoor particle loadings and the trend toward year-
round heating/cooling cycles, the relative contribution of indoor pollution
to total particle exposures has clearly increased in the U.S. Indoor
particle levels can be higher than outdoors because of smoking and other
activities. For homes of non-smokers homes, the mass of smaller particles
(e.g., sulfates) tends to be similar indoors and outdoors, but larger
outdoor particles (as indicated by TSP) apparently do not completely
penetrate (CD, p. 5-121 to 5-131). The size and compositional differences
between indoor and outdoor particles, as well as routine daily activities,
complicate the assessment of personal exposure and confound appraisal of
both health and welfare (e.g., soiling) effects of particulate matter.
4. Comparison with Historical Composition
Although current particle levels are clearly lower than those
reported in the historical London data, it is more difficult to assess
differences in composition and comparisons are limited to sulfuric acid
and primary carbonaceous material. Near major U.S. sulfur oxide sources,
short-term peaks of 1 ppm S02 might be accompanied by primary sulfuric
acid concentrations on the order of 50 yg/m *. Episodic levels of
3
sulfuric acid equivalents in the range of 15-20 ug/m may occur over
large scale regions during the summer, accompanied by elevated oxidant
levels (Lioy e_t al_., 1980). These levels are an order of magnitude
lower than the highest peaks reported during fall and winter British
episodes but represent a greater proportion of particulate matter mass
*Assuming 1-2% of emitted SO is primary sulfuric acid. In this context
"primary" refers to pollutants directly emitted from sources, while "secondary"
pollutants are formed in the atmosphere from precursor materials as in the
case of secondary particulate sulfates derived from oxidation of gaseous
S02 . s
-------
22
and may occur over far larger regions. The frequency of occurrence of
such peaks, particularly in urban areas or during nighttime inversions where
substantial ammonia neutralization may occur, is not well characterized. The
relative proportion or primary organic and carbon particles probably is
lower than that of London particles. This could change with increased
use of residential wood or coal and passenger diesels. Secondary organic
particle (e.g., oxygenated organics) levels probably are higher in the
U.S. Peak levels of extractable organic particles can comprise as much
as 50% or more of TSP in Southern California. Thus, the total extractable
or volatizable organic fraction of particulate loading (as percent of
TSP) in some U.S. cities can be equivalent to that of London (see Figure
4-4), but components within the organic fraction probably differ.
Although it is reasonable to expect substantially higher quantities of
fine particles during London episodes, reliable comparisons of other
particle components (e.g., coarse carbon, dust) or of relative particle
size distributions is not possible.
-------
23
V. CRITICAL ELEMENTS IN THE REVIEW OF THE PRIMARY STANDARD
A. Mechanisms
This section discusses the deposition and clearance of particles in
the respiratory tract and the possible physiological and pathological
responses to particulate substances. Implications of relevant deposition
studies are assessed in light of current U.S. particle distributions and
qualitative evidence from animal, controlled human, and epidemiological
studies is used to identify potential mechanisms of toxicity. The major
purposes of this discussion are to provide a basis for identifying the
most appropriate indicator for those fractions of particulate matter
of most concern to health and to examine plausible links between regional
deposition of particles and observed responses in humans.
1. Particle Deposition and Clearance
a) Major Regional Divisions
An evaluation of the mechanisms by which inhaled particles ultimately
may affect human health must recognize the importance of deposition and
clearance in the respiratory tract. The major regions of the respira-
tory tract differ markedly in structure, size, function, and sensitivity
or reactivity to deposited particles. They also have different mechanisms
for particle elimination or clearance (Lippmann, 1977). As described by
the criteria document (CD, Chapter 11), in discussing deposition and
clearance, three major regions can be specified: extrathoracic, tracheo-
bronchial, and pulmonary or alveolar. The nature and characteristic
deposition and'clearance mechanisms of these regions are outlined in
Table 5-1.
The criteria document presents the range of available experimental
deposition data for total and regional deposition in a series of figures •
-------
24
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25
(CD, Figs. 11-3 to 11-9). For simplicity, only alveolar and an estimate of
tracheobronchial deposition (mouth breathing) are reproduced in Figure 5-1.
A variety of subject related and environmental factors can influence
deposition and clearance of aerosols, including inhalation patterns (rate
and route), airway dimensions, disease state, particle composition, and
the presence of pollutant gases. Their impacts are briefly summarized in
Appendix A.
b) Deposition and Clearance of the Ambient Particle Distribution
The available data on respiratory tract deposition as discussed in
Appendix A can be used to provide a preliminary qualitative evaluation of
deposition of typically observed ambient particle distributions. Based on
the deposition curves for normal nasal breathing in Chapter 11 of the
criteria document, over half of the total mass of a "typical" mass distribution
(see Section IV-2) would be deposited in the extrathoracic region, most of
this being coarse particles. Clearance of most of this material to the
esophagus would occur within minutes. Up to about half of the hygroscopic
fine mass (e.g., sulfates and nitrates that grow to 2-4 pm in the respiratory
tract) also might be deposited and dissolve in this same region. Smaller
fractions (5-25%) of the hygroscopic and non-hygroscopic fine particles
(mostly <1 um) would be deposited in the tracheobronchial and alveolar
regions, respectively. A similar fraction of coarse particles (size range
2.5-8 pm) will be deposited in these thoracic regions. Clearance of
hygroscopic material by dissolution and reaction would be relatively rapid
in both regions. Clearance of insoluble coarse mode substances would
increase from less than an hour for the larger particles deposited in the
upper portion of the tracheobronchial region to as much as a day for the
more distally deposited. Insoluble fine and coarse particles deposited in
-------
26
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the alveolar region would be expected to have lifetimes on the order of
weeks to months or longer.
With mouth only breathing, the regional deposition pattern changes
markedly, with extrathoracic deposition reduced and thoracic deposition
enhanced. Extrathoracic deposition, although reduced, still would be dominated
by coarse mode aerosols and contain little fine mode contribution. Both
tracheobronchial and alveolar deposition of coarse mode and hygroscopic fine
mode aerosols would be substantially increased (Figure 5-1). The higher
endogenous ammonia in the mouth may, however, reduce the net deposition of
acid aerosols (Larson ejt al_., 1977). Remaining fine particle deposition
efficiency would be little changed over nasal breathing (<20%). .
In essence, regional deposition of ambient particles in the respiratory
tract does not occur at divisions clearly corresponding to the atmospheric
aerosol distributions. Coarse mode and hygroscopic fine mode particles are
deposited in all three regions. A fraction (5-25%) of the remaining fine
mode particles (e.g., organics and carbon not associated with hygroscopic
material) is deposited in the tracheobronchial and alveolar regions. Little
particle mass in excess of 15 ym is deposited in the thoracic region, and
little mass greater than 10 urn is deposited in the alveolar region.
The above discussion represents a qualitative assessment of regional
deposition of a "typical" ambient distribution for normal adults and breathing
rates. Because atmospheric distributions and individual deposition characteris-
tics, as well as other factors, vary widely, the above may not be represen-
tative of potentially important exposure/deposition cases. Considerations
include:
1) Regional deposition data for mouth breathing tend to overestimate
resting thoracic deposition for oronasal breathing and are strictly applicable
-------
28
to those individuals who breathe only through the mouth. Nevertheless, a number
of disease states and other conditions temporarily or permanently result in
mouth only breathing. During exercise, even oronasal breathing can permit
flow through the mouth comparable to or greater than used in mouth only
studies (CD, p. 11-11). Moreover, the results of Hounam e_t aJL (1969) and
Andersen e_t a]_. (1979) suggest conditions or subject-related variability
causing substantially lower nasal removal efficiency for coarse particles
(in the 2.5 to over 12 ym range) than the ICRP model (CD, Figure 11-5)
suggests. This would result in enhanced thoracic deposition for coarse
particles during nasal breathing.
2) The peak in alveolar deposition efficiency for mouth and nose
breathing (Figure 5-1) tends to occur at or near the normal minimum in the
bimodal distribution (2-4 ytn MMAD). The data of figures 4-2 and 4-3 suggest,
however, that near sources or in other polluted conditions, substantial
increases can occur in the coarse or fine mode contribution to this most
efficiently deposited size range. Moreover, near sources a transient nuclei
mass mode may be present (Figure 4-2). Theoretical models (Yu, 1978) and
limited experimental results (CD, Figure 11-4) suggest that nuclei mode
particles will be more efficiently deposited than accumulation mode aerosols.
3) As discussed in Appendix A, the deposition of both coarse and fine
particles in the tracheobronchial region can be increased over "normal" ranges
for: a) increased breathing rates during exercise; b) mouth breathing;
c) cigarette smokers; d) bronchitics; and e) asthmatics. Although it
reduces subsequent alveolar deposition, enhanced tracheobronchial deposition
may not be protective, particularly for disease states such as bronchitis
(Chan and Lippmann, 1980).
4) Regional mass deposition data do not provide insights into localized
"hot spots". Significantly higher mass/lung surface ratios can occur in
-------
29
the extrathoracic and tracheobronchial regions as compared to the alveolar
region. As noted in Appendix A, enhanced deposition in the carina and
other airway bifurcations should occur for both coarse and fine particles
(Bell and Friedlander, 1973). Natural or deposition related slowing in
clearance may occur in these areas (NAS, 1977a). Particles with surface
coatings of toxic elements, organics, allergens, or gases (LaBelle et al.,
1955; Natusch and Wallace, 1974) may result in greater effects than that
suggested by total mass deposited because of initial localized surface
reaction with tissue or macrophages (Camner ejt al_., 1974a).
5) Although probability of deposition of particles larger than 10 ym
in the alveolar region is low, small numbers of such particles have been
found in human lungs (Michel ejt al_., 1977). Some evidence suggests that
those large insoluble coarse substances that do penetrate may be cleared at
a much slower rate. Animal tests indicate that 15 urn particles instilled in
this region clear much more slowly than smaller particles of the same
composition (Snipes and Clem, 1981).
2. Mechanisms of Toxicity
Upon deposition, particles may produce physiological and ultimately
pathological effects by a variety of mechanisms. Although the respiratory
tract is equipped to remove inhaled foreign materials, if particle exposures
are sufficiently high or if clearance mechanisms are impaired, accumulation
of particles may reach levels that produce responses. Variations in subject
related characteristics and aerosol physical and chemical composition play
important roles in the nature of these responses. For purposes of discussion,
the major mechanisms by which particles potentially may produce effects can
be categorized as follows:
-------
30
1) Chemical or mechanical irritation of tissues or nerve receptors
at the site of deposition. This may result in immediate functional
changes or cumulative insult. Substances as diverse as fine acid
aerosols, insoluble coarse dusts, and SCL/aerosol combinations can,
in varying degrees, produce these responses in animals and humans.
2) Alteration of host defense systems, particularly clearance mechanisms.
This may result in increased susceptibility to infection and potentiate
development of chronic lung disease. Acid aerosols and, to a lesser
extent, insoluble dusts might affect clearance rates by altering
deposition patterns, increasing mucous secretion, or affecting
the physiochemical properties of the mucous. Various particles
may also damage alveolar macrophages.
3) Direct or indirect damage leading to morphological changes. This
may lead to compromised lung function, potentiating development of or
aggravating existing disease. Acid aerosols may produce direct
tissue damage; certain coarse dusts, notably silica, may act
indirectly through macrophage damage.
4) Systemic toxicity. Particularly toxic particles may be transported
to and produce effects in other areas of the body. Examples include
trace elements such as lead and arsenic or carcinogens such as
polycyclic organics.
The extent to which these mechanisms may be operative depends strongly
on the region of deposition, concentration, and relative chemical/toxicological
activity of the aerosol, and the time the material remains in contact with
respiratory surfaces. Pharmacological principles would indicate that
response should be related to the dose delivered to the target area and hence
-------
31
be related to mass. In some cases, however, the effective dose may be related
to other moments of the particle distribution, particularly surface area
(NAS, 1977a; Natusch and Wallace, 1974). Particle deposition efficiency and
surface area are inversely related in some regions of the respiratory tract,
which may explain some apparently paradoxical animal and human study results.
For example, depending on concentration, smaller particle sizes may result in
either increased or decreased flow resistances in guinea pigs as compared to
larger particle sizes (Amdur, 1958).
Table 5-2 presents a summary of potential mechanisms that might account
for some of the responses and associations observed in toxicological and
epidemiological studies of particulate matter. Potential mechanisms, con-
sequences, and responses to particle deposition are organized according to
the major regions of the respiratory tract. This summary is for qualitative
purposes only; many of the mechanistic studies cited involve exposures signi-
ficantly higher than those encountered under ambient conditions. The extent
to which any one of these mechanisms explain observed epidemiological results
or unexamined potential effects from ambient air exposure is speculative, but
does serve to suggest which regions of the respiratory system are at greatest
risk, based on current understanding. The following subsections briefly
discuss some of the listed potential mechanisms following deposition by
region. Discussion of studies relating to effects of concern is presented in
Section V.B. and Appendix B.
a) Extrathoracic Deposition
The major ambient materials deposited in the extrathoracic region
are coarse mode particles, with some contribution from hygroscopic fine
particles. This region appears to be significantly less responsive to
pollutant irritation than the tracheobronchial region (Nadel, 1973; Widdicombe
-------
32
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-------
34
et_ aj_., 1962). Exposures of normal subjects to high levels of coarse "inert"
dust* (carbon impregnated plastic) resulted in a mild increase in symptoms,
especially dryness of the nose and throat, but no effect on mucociliary
clearance (Andersen e_t al_., 1979). Studies of nasal exposure of normal subjects
o
to fine sulfuric acid aerosol for 1 hour at levels of 110-980 ug/m reported
no extrathoracic related symptoms (Leikauf et al_., 1981), but particle clearance
in this region was not measured. Oral exposure to sulfuric acid (220-940
yg/m ) produced throat irritation that affected greater numbers of subjects
with higher concentrations (Horvath e_t al_., 1981). Deposition of pollens
or other allergens may result in rhinitis, the major nasal response to
irritation. The findings of slowed nasal mucociliary clearance from
exposure to wood dust (Schlesinger and Lippmann, 1978) and S0? (Andersen
ejt al_., 1974) suggest that additional study is needed on the effects of
aerosol exposure on nasal mucociliary clearance, especially in view of
the findings of nasal cancer in wood workers. Available information
provides no indication of substantial effects on clearance at typical
ambient levels.
b) Tracheobronchial Deposition
The tracheobronchial region is exposed to a mixture of fine (particularly
hygroscopic fine) and coarse particles. Among the major effects possibly
associated with deposition of particles in this region are bronchoconstriction,
altered clearance, aggravation and promotion of chronic respiratory diseases
(e.g. asthma, bronchitis) and cancer.
Bronchoconstriction is one of the most common responses associated with
particle exposure and has been reported following short-term exposure to
*This synthetic particle as well as a number of insoluble mineral dusts are
often termed "inert" because of their general chemical and biological stability.
Because such materials can produce biological responses, however, quotation
marks are used.
-------
35
high concentrations of a variety of "inert" dusts, and acidic and alkaline
aerosols of varying particle sizes (<1 to over 10 ym). Current evidence suggests
that bronchoconstriction produced by acute exposures is probably a reflex
reaction resulting from chemical and/or mechanical stimulation of irritant
neural receptors (Widdicombe e_t ^1_., 1962). Although dose/response characteris-
tics vary among substances, both dusts and chemically active substances
appear to induce bronchoconstriction in a similar manner because broncho-
constriction can be blocked by the administration of drugs or surgical
removal of nerves (Nadel e_t a\_., 1967; Widdicombe e_t al_., 1962; Toyama, 1964).
Because deposition is elevated at, and epithelial nerve end'ings tend to
be concentrated near, airway bifurcations, deposition at bifurcations may
well have a major influence on pulmonary mechanical changes induced by either
mechanical or chemical stimulation of receptors (Nadel e_t al_., 1967).
The nerve endings of the more central airways are especially receptive to
mechanical stimulation that lead to reflex coughing and bronchoconstriction.
Alterations of lung function in this region may be, in part, related to
effects observed in epidemiological studies of particle exposure, such as the
aggravation of chronic respiratory disease, including asthma, bronchitis and
emphysema. The airways of asthmatics are hyperreactive to a variety of
irritants (Boushey e_t a]_., 1980). Individuals with chronic obstructive
lung disease may not be hyperreactive, but typically have abnormal lung
function. Further depressions in lung functions by particle exposures that
may be of no consequence to normal individuals could be incapacitating for
individuals with asthma, or even life threatening for individuals in the
later stages of chronic lung disease suffering some degree of oxygen
deficiency (hypoxia) (Morris and Bishop, 1966). Moreover, as indicated
earlier, individuals with asthma and bronchitis may have significantly
higher deposition rates in the tracheobronchial region (Albert et al.,
-------
36
1973). This enhanced particle deposition may trigger further broncho-
constriction and further increase deposition above that in the initial
exposure condition.
Another carefully studied biological endpoint in the tracheobronchial
region is mucociliary clearance. As with bronchoconstriction, pollutant
effects on mucociliary transport involves mediation, in part, through the
nervous system (Camner ^t aj_., 1974b; Camner et al_., 1976). As indicated
in Table 5-2, human studies have found that mucociliary clearance is
affected by fine sulfuric acid, high levels of coarse carbon dust, and
cigarette smoke. Substances that affect clearance do not always cause
bronchoconstriction at similar levels (Lippmann ^t al_., 1981).
Repeated exposures to substances that alter mucociliary clearance may
potentiate development of chronic obstructive pulmonary disease. Lippmann
et^ aj_. (1981) proposes the following sequence of events in producing chronic
bronchitis: Acute high level exposures to particles increase mucus production
and mucociliary transport. Continuation of these exposures leads to bronchial
mucous gland hypertrophy and goblet cell hyperplasia. Mucus transport in
small airways might be normal or increased during this stage. As gland
hypertrophy continues, the mucociliary transport system becomes inadequate in
removing mucous secretions. This leads to chronic cough, accumulation of
secretions, and further susceptibility to inhaled particles, noxious gases,
and pathogenic organisms.
Following this sequence of events, particulate exposure may be: 1) causal
factors in chronic bronchitis; 2) predisposing factors to acute bacterial and
viral bronchitis, especially among children and cigarette smokers; and
3) aggravating factors for acute bronchial asthma and the terminal stages
of oxygen deficiency associated with chronic bronchitis and/or emphysema and
-------
37
its characteristic form of heart failure (cor pulmonale) (MAS, 1977a). In-
creased prevalence of bronchitis has been observed in cigarette smokers and
people exposed to high community particle and sulfur oxide pollution (Holland
and Reid, 1965) or various occupational!,/ derived mineral dusts (Morgan,
1978).
In vitro studies suggest that some particles deposited in the tracheo-
bronchial region may become attached to the mucosal surfaces of the airways
(Mossman ejt al_., 1978). Larger particles (10-15 ym) can be lodged on trachea!
surfaces despite continued mucociliary action; these particles have been
associated with the in vitro sloughing of cells shortly thereafter. Smaller
particles (0.5-1 urn) may be transported to the submucosa where they can be
taken up by mesenchymal cells of the trachea (Mossman ejt al_., 1978). These
findings indicate that not all insoluble particles are necessarily rapidly
cleared from the tracheobronchial region by mucociliary action.
As noted above, the bifurcations of the larger airways appear to be
especially vulnerable to the accumulation of particles. Increased deposition
and potentially resulting slower clearance (Hilding, 1957) in these sites
are correlated with major locations of lung tumors (Schlesinger and Lippmann,
1978).
c) Pulmonary (Alveolar) Deposition
Particle deposition within the alveolar region of the lungs is essentially
limited to particles less than 10 ym. Several important characteristics in
the alveolar region affect response to particle inhalation. As indicated
earlier, clearance from the alveolar region of the lungs is much slower than
from the tracheobronchial region. The alveolar region is the site of oxygen
uptake and of various non-respiratory functions of the lungs that may be
affected by pollutant exposures.
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38
Many victims of the London air pollution episodes were patients suffering
from cardiopulmonary disease and were thought to have emphysema and bronchitis.
Such diseases normally reduce the ability of the lung to transfer oxygen to the
blood. It is hypothesized that the disturbance of normal ventilation and
perfusion in the lung by acute pollution exposure may shunt air from some
alveoli so that a sudden lack of available oxygen may be experienced. A
reflex constriction of blood vessels supplying part of the lungs may follow,
resulting in increased pulmonary arterial pressure. Although this added load
(associated with pollution exposure) should be tolerable in normal individuals,
the added stress and chain of events could possibly lead to fatal or irreversible
damage in individuals compromised with cardiopulmonary disease.
The alveolar region of the lung is the site of several respiratory
diseases that are associated with inhalation of particles. Long term exposures
to high levels of acid aerosols, as well as some other pollutants, have
produced conditions resembling emphysema in controlled animal exposure
studies (Hyde et^ £1_., 1978). Various animal, occupational, and community
exposures to insoluble particles, including coal dusts, silica, asbestos, and
ambient dust may result in accumulation of material in lungs, and possibly
through damage to macrophages, are associated with inflammation, fibrosis and
other conditions (Brambilla et. a]_., 1979; Sherwin et a]_., 1979; Ziskind et
al., 1976). This "dust lung disease" or pneumoconiosis may vary in severity
and pathological condition.
d) Thoracic Deposition, (Not Necessarily Specific to TB, AL Regions)
Infection may be initiated in any area and spread to other regions.
Exposure to specific particle components has been shown to affect clearance
(Leikauf j^t !]_., 1981) and the immune system (Zarkower, 1972), both of which
are considered to be important host defense mechanisms against infection.
-------
39
Observational studies show that exposure to particle/sulfur oxide pollution
is related to increased prevalence rates of infection among children (Lunn e_t
a1., 1967). Observational studies also indicate that when children experience
a history of greater respiratory illness (associated with pollutant exposure),
these illnesses may produce small decrements in pulmonary mechanics. Speizer
et_ aHL (1980) speculate that the lungs of those children affected by respiratory
diseases associated with pollutant exposure ultimately may not develop full
potential capacity as adults. Long term British studies of individuals born
in 1945 (Douglas and Waller, 1966; Colley e_t al_. 1973; Kiernan et al_., 1976)
appear to support this possible mechanism in that a history of childhood
respiratory disease is associated with persistent changes in airways as
indicated by increased prevalence of respiratory illness in later years.
Systemic toxicity may result from deposition in any region. Some con-
stituents of particulate matter produce systemic toxicity when they enter the
blood and are transported to extra-respiratory sites. Systemic toxicity has
been shown following inhalation of several metals including lead (EPA, 1977),
mercury (Hammond and Beliles, 1980), arsenic (NAS, 1977b), cadmium (Hammond
and Beliles, 1980), and some organic substances (NAS, 1972). Clearance of
inhaled carcinogenic particles to the gastrointestinal tract might account
for the observed association of elevated gastrointestinal cancer with high
particle levels (Winklestein and Kantor, 1967). The observed association is,
however, questionable (CD, p. 14-83).
-------
40
B. Effects of Concern
This section identifies and describes the principal effects of concern
associated with exposure to participate matter. Evidence for such associa-
tions drawn from animal toxicology, controlled human exposures, and community
epidemiological studies is discussed and evaluated in Appendix B. Based
on these data, the following effects areas appear to be of most interest:
1) Respiratory Mechanics and Symptoms;
2) Aggravation of Existing Respiratory and Cardiovascular Disease;
3) Clearance and other Host Defense Mechanisms:
4) Morphological Alterations;
5) Carcinogenesis; and
6) Mortality.
The major implications of the literature evaluated in Appendix B
relating to each of these effects areas are briefly summarized below.
1. Respiratory Mechanics and Symptoms
Effects on respiratory mechanics can range from mild transient
changes of little direct health consequence to incapacitating impairment
of breathing. Symptomatic effects also vary in severity, but at minimum
indicate a biological response. Key conclusions with respect to the
effects of particles include:
1) A number of long-term observational studies (Table B-3) have
found that populations living in areas with high particulate pollution
(usually with high SCL) tend to have a higher prevalence of respiratory
symptoms and lower lung function capability compared with other groups
in areas with lower pollution levels. When differences in particle
concentrations are small, effects are difficult to detect.
2) Only two community studies (Lebowitz e_t a]_., 1974; Dockery et a].,
1981) have reported lung function decrements (in children and adolescents,
some exercising) in association with short-term particle exposures.
Occupational studies, controlled human expoures, and animal studies
-------
41
discussed in Appendix B suggest that a variety of particles can, at
high levels, produce relatively rapid functional changes.
3) Most short-term (10 minutes-4 hours) animal and human investigations
of sulfuric acid and other sulfates have found no direct respiratory
mechanical changes below 1000 Mg/m , a level higher than those seen
even in peak London episodes (Table B-2). Asthmatics show some
enhanced response, but other sensitive groups and longer exposures
(> 2-4 hours) have not been tested. Responses to sulfates in
both asthmatics and normals generally decrease with lower particle
acidity. Differences in subject sensitivity and health status may
be in part responsible for some observations of respiratory
mechanical changes at lower sulfuric acid levels in guinea pigs
(100-1000 yg/m ) and humans (350 ug/m ). The importance of health
status is illustrated by the reactivity of people with influenza
to an apparently neutral nitrate salt (Utell e_t al_., 1980), at
high concentrations that produced no responses when the same
subjects were healthy.
4) Short-term exposures (minutes - 4 hours) to various insoluble
•3
particles and resuspended dustfall at high levels (2 to > 50 mg/m )
have produced variable degrees of bronchoconstriction and respiratory
symptoms in normal healthy adults and in diseased subjects. In some
of these studies, coarse dusts (2 to > 12 ym) are clearly implicated
(McDermott, 1962; McKerrow, 1964; Andersen et^ al_., 1979; Toyama, 1964).
Although some negative findings are reported, the lower concentrations
o
tested and found to produce responses in some subjects (2-10 mg/m )
are in the range of peak 1-hour smoke levels reported in London
-------
42
•3
(10 mg/m ), and within an order of magnitude of likely hourly peaks
during less severe British and U.S. episodes.
5) Particles can enhance penetration and toxicity of soluble
pollutant gases, notably, SOp (McJilton e_t al_., 1976; Amdur and
Underhill, 1968). The nature of the interaction is a matter of
some complexity and debate (NAS, 1978). The data suggest that
higher particle solubility and surface area increase interaction
potential.
2. Aggravation of Existing Respiratory and Cardiovascular Disease
Particle-induced brochoconstriction, mucous secretion, and other
effects might aggravate those with respiratory and cardiovascular disease.
A number of community observational studies (Table B-4) of episodic as
well as more moderate peak exposures to particles (usually with $02)
suggest that these exposures aggravate the conditions of cardiovascular
patients and, individuals with bronchitis, emphysema, pneumonia,
asthma, and influenza.
3. Alterations in Host Defense Mechanisms
The major mechanisms discussed include clearance of particles and
other foreign matter from the respiratory tract and other respiratory
system-related defenses against infectious agents. Important conclusions
include:
1) Studies of animals (donkeys) and humans suggest that exposure to
3
repeated short-term peaks of sulfuric acid (100 jjg/m , 1 hour/day,
6 months) may produce long-term slowing of mucociliary clearance,
and by analogy to cigarette smoke, might play a role in the etiology
of chronic bronchitis (Lippmann ejt aj_., 1981). These sulfuric acid
-------
43
levels are roughly within an order of magnitude of possible repeated
U.S. peaks, and within the range of maximal London episode peaks
(Section IV).
2) Community epidemiological studies (Holland and Reid, 1965;
Lambert and Reid, 1970) of particles and sulfur oxides and
occupational studies of industrial bronchitis in workers exposed
to high dust levels (Morgan, 1978) suggest that high long-term particle
exposure is associated with an increase in the prevalence of
bronchitis.
3) Animal exposure studies show that particles of various types
may damage alveolar macrophages and affect immunology (CD,
Section 12.3.4.2). Animal infectivity model results do not provide
convincing evidence of enhanced mortality following administration
of pathogens and exposure to particle components commonly found
in the ambient air, with the possible exceptions of high levels
of sulfuric acid and carbon or ozone exposure mixtures. The
relevance of these results to human exposures is unclear.
4) Community studies (Table B-7) suggest increased infectious
disease during pollution episodes and in children and adults living
in areas of higher particle and SCL pollution. As noted in Table 5-2,
such infections in children might have longer term consequences.
4. Morphological Damage
Long-term exposures to particles damage lung tissue, but the available
evidence is mainly qualitative. Specifically:
1) Multi-year studies of dogs exposed to sulfuric acid/SCL mixtures
(Table B-8) indicate damage to the tracheobronchial region and
-------
44
alveolar lesions that are analogous to an incipient stage of emphysema.
Damage apparently continued to increase following the termination of
exposure. Several factors outlined in Appendix B complicate application
of the results to real world human exposures.
2) 12-18 month exposures of monkeys and guinea pigs to various
mixtures of sulfuric acid, SCU, and fly ash suggest that most
morphological damage reported was due to sulfuric acid perhaps
in combination with ammonium sulfate salts (Table B-8). Although the
fly ash particles were somewhat large for deep lung penetration
in this small animal, some accumulation was noted, but without
obvious effect. Post exposure examinations similar to those
in the above dog studies were not performed.
Retrospective autopsy studies (Table B-9) of animals and humans exposed
to various crustal dusts at near to slightly above ambient levels suggest
these exposures result in silicate pneumoconiosis. Responses range from
the build up of particles in macrophages with no clear clinical significance
to possibly pathological fibrotic lesions. The studies suggest deposition
of ambient coarse particles in the alveolar region is of some concern but
do not provide a basis for quantitative health assessments.
5. Carcinogenesis
Cigarette smoking is generally considered to be the major determinant
of lung cancer (Higgins, 1976; Doll, 1978). The high particulate air pollution
of the 1940-60's contained carcinogens and may have potentiated or otherwise
contributed to elevated cancer rates in urban areas. Based on filter
chemical analyses, levels of some particulate carcinogens have declined
since that time and hence carcinogenic risk from these substances
-------
45
presumably has been reduced. The available evidence does not unequivocally
show that current particle exposures contribute to cancer. Neither does
•
it disprove any effect. Because lung cancer is the leading cause of
cancer-related deaths, the risk of a small effect could assume some
importance. The presence of mutagens in organic particulate fractions
from unidentified sources (Pitts et al_., 1977) and potential interaction
between these or inert particles and carcinogens from cigarettes or
occupational exposures suggests some need for caution and further study.
6. Mortality
A number of epidemiological studies demonstrate an association
between peak particle and S02 pollution and mortality in certain sensitive
populations (Table B-10). While some analyses suggest that the observed
pollution effects may be more attributable to particles, it is not clear
that the available data permit such a determination.
Regression analyses of long term mortality and pollution data
(Table B-ll) have been used to suggest that sulfur-containing particulate
matter at current ambient levels is associated with excess mortality.
A number of inherent difficulties confound such studies to the extent
that they do not provide reliable evidence on such effects of particles
and sulfur oxides. They are not, however, inconsistent with the possibility
of associations at levels below those observed in the more extreme episodes.
C. Sensitive Population Groups
This section identifies those groups most likely to be among the
most sensitive to the effects of particulate matter, based principally
on material presented in Sections A and B. Available estimates of the
size of each of these groups in the U.S. population are also given.
-------
46
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The presence of certain diseases appears to be an important factor
in the predisposition of certain individuals to the harmful effects of
particulate matter. The history of catastrophic pollution episodes
(Firket, 1931; Schrenk e_t al_., 1949; Ministry of Health, 1954) as well as
the lesser episodes in London (Martin, 1964) has clearly indicated that
chronically ill individuals, especially those with cardiovascular and
respiratory diseases, as well as the very young and the very old, were
more severely affected than other groups.
Data derived from lower levels of community exposures and from other
sources suggest additional segments of the population that may be at
higher than average risk. These include children, asthmatics, smokers,
obligatory mouth breathers, and individuals with pneumoconiosis or
influenza. Table 5-3 draws upon information from epidemiological, toxico-
logical, human clinical and physiological research in summarizing the
observations that have identified various subgroups and possible explana-
tions for their sensitivity. Much individual variation exists among the
sub-groups. For example, at any given level of particles, some exposed
children may note only symptomatic irritation, while others may suffer
deterioration of respiratory function. Moreover, in some respects, these
groups can sometimes be at lower risk, as in the case of influenza
patients confined to indoor environments with lower than ambient pollution
levels.
Data from the U.S. National Health Safety Survey for 1970 indicates
that chronic respiratory disease makes up ten percent of all conditions
causing disability of one week or more. In 1970, there were about 6.5
million chronic bronchitics, 6.0 million asthmatics, 1.3 million
-------
48
individuals with emphysema and about 10 million adults with heart disease
severe enough to limit activity (DHEW, 1973). These are rough estimates
since some surveys have reported higher figures depending on age, sex, and
the definition of disease that is used. Limited physiological studies
suggest that about 15% of the population are habitual mouth or oronasal
breathers (Saibene, et^al_., 1978; Niinimaa e_t al_., 1981). Anyone may temporarily
switch to mouth breathing during exercise, illness, and conversation.
Although there are about 50 million smokers, the number of people at
a higher than expected risk because of smoking may also include children
living with smokers, and ex-smokers (DHEW, 1977). In addition, some
workers who are occupationally exposed to dusts might become more .susceptible
to community particulate pollution, even if they are not classified as
having respiratory disease. The more sensitive individuals, however, often
do not remain in such work environments (Morgan, 1978).
D. Concentration/Response Information
As outlined in Section B, reactions to particulate matter can be
divided into acute and chronic effects in healthy individuals as well as
those with existing pulmonary or cardiovascular diseases. Air pollution
clearly has been associated with an increase in both mortality and
morbidity during smog episodes, as well as impaired lung function and
increased respiratory symptoms among individuals with long-term high-level
exposures. The literature summarized in Appendix B shows that the existence
of these general associations has been demonstrated in many countries and
population groups, and is at least qualitatively supported by controlled
laboratory exposures of animals and humans to various components of particulate
matter.
-------
49
Trying to assess the precise level of particulate pollution associated
with observed effects on health, however, has many problems. Suspended
particulate matter is not a uniquely defined entity. The comprehensive
physical and chemical characteristics are not only hard to measure and
relate to health effects, but vary with monitoring device, geography,
and time. This increases the uncertainty of any extrapolations from
one set of circumstances to another, and greatly limits the utility of
laboratory studies of single substances for quantitative purposes.
Epidemiological studies can provide strong evidence for the existence
of pollutant effects, but are more limited for identifying accurate effects
levels for specific pollutants or pollutant classes. Among the more
important limitations of epidemiology as discussed in Section 14.1.1 of the
criteria document are: 1) inadequate and inconsistent measurement of the
exposure burden of individuals; 2) variability in the measurement of
health endpoints (e.g., lung function, hospital admissions, frequency of
symptoms) and in the sensitivity of populations studied; 3) failure, especially
in cross-sectional studies, to control fully for confounding, or covarying
factors, such as cigarette smoking and socioeconomic status; 4) difficulty
in distinguishing particles from other pollutants; and 5) inability
to establish a causal relationship, or negate one, based only on statistical
associations.
Recognizing these limitations, epidemiological studies must still
form the principal basis for developing concentration response assessments
for particulate pollution. The following review summarizes those studies
cited by the criteria document as providing the most reliable quantitative
information as well as other studies that provide reasonable evidence of
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50
exposure response relationships without allowing derivation of specific levels.
A further assessment of these studies as applied to selecting alternative
levels for air quality standards is presented in Section VI.
1. Acute Exposures
a) Mortality
During the historical London pollution episodes, significant increases
3
in mortality occurred when daily averages of British smoke exceeded 1000 yg/m
together with daily average S02 levels in excess of 1000 yg/m (Ministry
of Health, 1954; Scott, 1963). Smaller increases in mortality also have
been observed in episodes in New York (Glasser et^ aj_., 1967). The
criteria document states that these studies "tentatively suggest that
small increases in excess mortality may have occurred at simultaneous
elevations of 1000 yg/m3 S02 and PM above 5.0-8.0 CoH, but this is much
less clearly established "(CD, p. 14-15). Most of these episode-related
effects were among particularly vulnerable sections of the population,
such as the elderly and those with cardiopulmonary disease.
Studies of pollution/mortality associations during less extreme
conditions are more relevant for current purposes. Several studies,
listed in Table 5-4, have examined minor or non-episodic variations in
pollution. Martin and Bradley (1960) related daily mortality from all
causes (and from bronchitis and pneumonia) to daily levels of smoke and
S02 in London during the winter of 1958/59 which was an unusually foggy
period. A considerable number of coincident peaks in pollution concen-
tration and daily mortality were found. British smoke and S02 correlated
highly with mortality from all causes. An influenza epidemic during the
month of February may have confounded the results. The correlation
between mortality and mean daily temperature was not significant and
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52
only marginally significant for humidity. Visibility, which is influenced
both by fog and particulate pollution, was also highly correlated with
mortality.
Martin (1964) analyzed the winter of 1959-60 in which there were fewer
incidents of high pollution and still found significant positive correlations
between mortality and pollution. Both studies relied on measurements
taken from a seven station monitoring network in central London that, according
to the criteria document, was a good index of city-wide concentrations.
The errors for individual measurements are difficult to calculate. Ware
e_t ^1_. (1981) re-examined the data from both winters after excluding the
month of the influenza epidemic and provided evidence that positive deviations
3
in mortality occurred with BS levels greater than 500 yg/m with increasingly
negative deviations below that level. The criteria document points out
that it is unclear at what level significant excess mortality occurred, but
concludes that notable increases in excess mortality occurred in the
range of 500-1000 yg/m BS and SO,, and were most likely when both pollutants
3
exceeded 750 yg/m ; small increases in mortality may also have occurred at
levels below 500 yg/m of either pollutant (CD, Table 14-7).
The Ware e_t al_. (1981) and some other analyses (CD, Appendix 14-D) omit
data for the month of February 1959 because an influenza epidemic confounds
the results. The relationship between mortality and pollutant levels continued
during this month, but the mortality deviations appear exaggerated compared to
previous months. Significantly, the peak daily mortality deviation during
the epidemic, as well as the entire winter (+ 150 deaths), occurred on the
day of peak smoke (1600 yg/m ) and SOp (0.6 ppm) levels for the month.
On this same day sulfuric acid levels at a central London site reached
3
350 yg/m (Commins and Waller, 1967). The peak daily deviation for the
rest of the winter, even with similar pollution levels was about + 60.
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53
Although the influenza epidemic was undoubtedly the major factor, the
clinical results showing pulmonary functional changes in influenza patients
with exposures to a normally innocuous neutral salt, (sodium nitrate, Utell
_et aJL , 1980) support the suggestion that the more irritant London aerosol
may have been causally involved in increasing mortality during the epidemic.
Such enhanced responses in influenza patients might also occur at lower
concentrations, and suggest that inclusion of such epidemics in daily
mortality analyses might be appropriate.
An exploration of daily mortality in London extended to 14 winters,
(1958/59 to 1971/72, Mazumdar et_ al_., 1981) provides a much larger, and
thus more reliable, data base, and may be of more relevance to current
conditions. This 14-year study period saw a major change in London's
pollution mix, with declines in SCL and BS of 50% and about 80%, respectively,
as well as a change in the nature of the particulate complex from the
black tarry matter of the 1950's and early 1960's. After adjusting for
meteorological variables, seasonal and yearly trends, and multi-collinearity
of the pollutants, a strong association between daily mortality and
daily pollution for the entire period was found. The authors concluded
that: l)this association was primarily due to smoke and not S02 and no
synergistic effects between SCL and smoke could be shown; 2) when
"episodic" days, classified as a day when BS concentrations
exceeded 500 ug/m plus the seven adjacent days on each side, and "non-
episodic" days, which made up the balance, were analyzed separately, the
association persisted throughout both classes of days, and; 3) linear
and quadratic models of exposure-response between daily smoke and daily
mortality were both compatible with the data.
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54
Based on the exposure-response curves derived from these models
(depicted in Figures 14-2 and 14-3, CD), the criteria document concludes:
1) steadily rising increases in excess mortality were associated with
3 3
increasing BS concentrations over 500 yg/m , 2) under 500 yg/m the
relationship is uncertain, but the data provide some indications of small
increases in mortality in the range of 150-500 yg/m BS (CD, p. 14-21) and,
3) it is unclear whether the Mazumdar e_t al_. analysis truly distinguished
the effects of BS from SOp or whether the associations are due to some
other unmeasured covarying factor (CD, p. 14-24). Comparison of the
Mazumdar regression analyses (both linear and quadratic models) with
the Ware and EPA reanalyses of the Martin and Bradley (1960) data ('CD,
Appendix 14-D) indicate that the four analyses were reasonably consistent
in both direction and magnitude.
Other time-series analyses of daily variations in mortality and
pollution in New York City suggest weak but positive associations between
nonepisodic mortality and daily levels of PM (daily peaks up to 5.0-6.0
CoHs, Schimmel and Murawski, 1976; Schimmel, 1978). According to site-
specific mass calibrations of particulate density readings in New York
during this period, these CoH values were approximately equivalent to
575-750 yg/m BS (Ingram and Golden, 1973). Although these results
appear to be consistent with those from the London studies, the reliance
on a single, central Manhattan monitoring station as an estimate of
pollutant exposures for the entire New York City area precludes evaluation
of quantitative effect levels.
b) Morbidity
The work of Lawther e_t a]_. (1970) is widely regarded as among the
most reliable epidemiological investigations of the effects of particles
and sulfur oxide pollution. Day-to-day changes in the health status
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55
among a group of 180 and later about 1000 chest clinic patients (mostly
bronchi tics, but some patients had asthma or emphysema) were shown to
depend on daily variations in London pollution, measured at seven sampling
sites, most close to ground level, in a ring around the city's inner
residential area. The same seven sites were referred to earlier in the
London mortality analyses. Although exposures varied, the pollution levels
derived from the measurements in central London were considered reasonable
estimates of exposure, since most subjects worked in the central district.
For two winters, 1959-60 and 1964-65, the minimum daily pollution level
leading to exacerbations among this group of bronchitics is considered
to be about 250 yg/m BS together with about 500-600 vig/m3 S02 (CD, p. 14-28).
As the criteria document (CD, Table 14-7) points out, however, a summary
of results in a subgroup of sensitive patients for the winter of 1967-68
(Table III, Lawther ejt aj_., 1970) indicates a statistically significant
correlation between smoke and symptoms in a winter with only one day of
BS >_ 250 yg/m and SOo > 500 yg/m . Because daily temperature, SO^* and
BS levels were all significantly correlated with symptoms during the
winter, the pollutant or combination of pollutants responsible for the
observed effects could not be determined. Interestingly, sulfuric acid
was strongly correlated with effects in a sample of patients during one
winter, but less so the next.
The authors concluded that the reported aggravations in health
likely reflected the effects of brief exposures to the maximum concentrations
occurring during the day. These peaks were probably several times the
24-hour averages, but, because of the wide dispersion of subjects and
the variation in the magnitude and timing of such peaks across the study
area, the impact of peak values could not be directly examined. The smoke
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56
shade data were obtained from the same network as used in the mortality
studies. A centrally sited unit not in the network was calibrated with
mass readings and according to the criteria document, this calibration
tends to conform "reasonably" well with the mass calibrations in the seven
station network from 1959-63 (CD, p. 14-18). After that time, the calibration
may have tended to overstate the true ambient mass levels (CD, Table 14-7).
Two other studies used hospital admissions/visits as indicators of
acute morbidity. Martin (1964) found that applications for hospital
admissions for cardiovascular and respiratory conditions among London
men (45-79 yrs) were highly correlated with particulate matter (BS) and
S02 during two winters of periodic fogs and minor pollution episodes.
Again, no clear threshold exists; where deviations from the adjusted
15-day moving average become positive, however, marked increments in
hospital admissions can be discerned, but only at concentrations above
those apparently associated with excess mortality. Hospital admissions
suggest a relatively serious effect and are clearly not as sensitive an
indicator of pollution related morbidity as that used by Lawther et a!.
(1970). Because of these and other limitations in the use of hospital
admissions data (Bennett, 1980), the Martin (1964) results do not provide
reliable estimates of morbidity effects levels.
Samet et aj_. (1981), related hospital emergency room visits during
March, April, October, and November of 1974-1977 to daily levels of TSP,
SOp, N02» CO and 0, in Steubenville, Ohio, a heavily industrialized town.
After adjusting for meteorological variables, weekly, seasonal and yearly
cycles, possible day-of-week effects, and multi-collinearity of the pollu-
tants in a quartile analysis, emergency room visits for all respiratory
diseases did not vary significantly with pollution. However, the largest
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57
deviations from average numbers of visits occurred at the highest pollutant
levels (>_ 202 yg/m3 TSP and >. 121 yg/m SO,,). A regression model utilized
to test for linear relationships identified a significant same-day effect
of both TSP and S02 on respiratory disease visits. This effect was quite
small, only 1% of these visits could be explained by changes in TSP and 1%
by SOp. Based on the model, the authors suggested that an increase from the
observed daily mean TSP level (156 yg/m ) of 100 yg/m might result in a
corresponding 3% increase in emergency room visits for respiratory disease.
Nevertheless, no level at which increased visits occurred can be derived
from this study.
The use of emergency room visits as a health end-point is analagous to
hospital admissions data. Neither would be expected to be as sensitive
an index of morbidity as that used by Lawther et^ al_. (1970). The Samet
et. aj_. (1981) work does indicate that effects may occur in groups other than
bronchi tics.
2. Chronic Exposures
The relationship between long-term exposure to air pollution and
health has been extensively studied, but few of the studies provide sound
data or consistent findings sufficient to make quantitative conclusions.
Geographic comparisons of morbidity (see Appendix B.5) and mortality rates
among populations suffer from many limitations (see CD, Sections 14.1.1.1 and
p. 14-35). Those studies that are useful in delineating quantitative
relationships between particulate matter and chronic morbidity effects are
summarized in Table 5-5.
a) Ch i1dren
As pointed out in Section V-C, children who suffer respiratory insults
may be predisposed to developing chronic respiratory diseases as adults.
Therefore, results on children should be considered as particularly important.
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58
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Lunn e_t al_. (1967, 1970) studied respiratory disease and lung functions
of school children in four areas of differing pollution levels in Sheffield,
England. At ages 5-6 both chronic upper respiratory infections and lower
respiratory tract illness were associated with residence in more polluted
areas. An illness gradient corresponding to increasing pollution was found
and was independent of socio-economic factors, although parental smoking,
parental respiratory diseases, and home heating systems were not taken into
account. Lung function (FEV 75, FVC) was lower among the children in the
most polluted area compared with the other areas. Based on the results
from the lung function tests, the authors concluded that, "a pattern of
respiratory disability had appeared at an early age and was sufficiently
established to persist although the factors of pollution and infection were
temporarily absent or at a low level." The criteria document notes that
the effects levels listed in Table 5-5 have been widely accepted as being
valid by several reviews (CD, p. 14-47). However, the levels must now be
considered only as very approximate "observed effects" levels due to the
uncertainties associated with estimating PM mass based on BS readings
(CD, Table 14-8).
After four years of improving air quality, differences in the incidence
of respiratory illness and in lung function among these children, now
nine years old, were no longer significant (Lunn e_t al_., 1970). The authors
attributed the disappearance of differences over this period to the reduction
in air pollution, especially in smoke levels with a small decrease in SO
levels. Given the size of the population, it is not likely that the study
had sufficient power to detect small changes among the cohorts. Also, no
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60
site-specific calibrations of the BS mass readings were made at the time of
the later study. Because of these limitations, the criteria document
concludes that smoke levels at which no differences in respiratory disease
symptoms or in lung function among the children occurred cannot be determined.
b) Adults
A series of investigations followed changes within Berlin, N.H.,
adults over a 12-year period (Ferris and Anderson, 1962; Ferris e_t al_., 1973,
1976). After an essentially negative cross-sectional survey in the winter
of 1961, the population was followed up in the summer of 1967 when pollution
levels dropped. Small reductions in respiratory disease symptom rates,
principally chest colds, together with an indication of small lung function
improvement (as measured by FVC and PEFR), were associated with a decline
3
in TSP levels from 180 to 130 ug/m and in sulfur pollution levels, which
were apparently moderate (based on unreliable measurements using "lead
candles"). Although the TSP level for 1961 was based on only two months of
monitoring, levels were clearly higher in 1961 than in 1967. Another
survey in 1973 when TSP levels dropped further to 80 ug/m and sulfur
pollution slightly increased (based on lead candle and limited S02 data)
found no further improvements in respiratory health. Because the trend in
SO- did not correspond with the changes in the respiratory health of the
population, the observations apparently reflected the effects of reduced
particulate pollution.
Although seasonal factors were not directly controlled between the first
two surveys, the investigators attempted to rule out possible confounding effects
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61
by retesting some subjects in the winter and the summer in 1961. No signi-
ficant differences were found. In addition, the survey regarding respiratory
illnesses was in reference to the previous three years, which likely minimized
seasonal effects on illness and symptom differences between the years.
The results from this study must be interpreted with caution inasmuch
as air pollution in Berlin, N.H., is dominated by the emissions of a pulp
mill, unlike more typical situations in the U.S. However, the findings are
generally consistent with those of other studies and suggest that marginal
decrements in respiratory health and mechanics occurred between 130 and 180
o o
yg/m TSP (annual average) and that the range of 80-130 yg/m TSP (annual
average) is a possible lower limit at which any effects are difficult to
detect.
A comparison of residents in two communities in Connecticut with
different ambient exposures to TSP and S02 found no differences in pre-
valence rates of chronic bronchitis symptoms among white adults (25 years
of age and older) nor in lung function among persons seven years of age and
older (Bouhuys ejt ci]_., 1978). A history of bronchial asthma was signifi-
cantly higher among residents in the cleaner town, Lebanon. However, the
prevalences of cough, phlegm, and dyspnea (when hurrying on level ground or
walking uphill) were significantly higher for adult non-smokers in Ansonia.
Prevalence of cough and phlegm in this group increased along a gradient from
lifetime rural, to partly urban, to lifetime urban residences. The prevalence
of recent wheeze was also higher in Ansonia residents, but only in comparison
to lifetime rural residents in Lebanon, while part-time urban residents in
Lebanon and Ansonia had equal prevalence rates as lifetime urban residents.
Response rates differed markedly between the two towns (56% versus
, however, follow-up analysis of the non-responders indicated that
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62
little potential for bias existed. Seasonal effects were not accounted
for, but as in the Ferris study, these may have been minimized by the
nature of the survey questions. The authors state that occupation was
controlled for, though no data are provided to support this.
Although no differences in lung function or bronchitis prevalence were
detected, the significantly increased symptom rates among the Ansonia
residents indicate some small differences in respiratory health associated
with pollution. It is not clear whether the reported effects related to
then-current or historical pollutant levels. As the criteria document
notes (p. 14-45), average annual TSP levels for the previous seven
years in the urban area were between 65 and 150 yg/m . This is perhaps
best characterized as the median value of about 110 yg/m. TSP levels in
•3
the rural area were provided for only one year (40 yg/m ) but were reported
to be consistently low. SOp was low in both areas in 1973, but might have
been higher in previous years in the urban area. The lack of a detectable
difference in lung function accompanied by some contrast in symptom rates
is consistent with other studies (Ferris e_t al_, 1976, 1979; Aubry et a!.,
1979) in which effects were either undetectable or marginal at annual
TSP levels between 60 and 130 yg/m3.
As the criteria document notes (p. 14-45), size-fractionation of a
limited number of TSP samples in Ansonia by Hosein e_t a]_. (1977) showed
that 81% of the TSP sample was 9.4 ym or less in diameter. This estimate,
however, was based on 15 samples taken only on "dry days" with a cascade
impactor of uncertain reliability. The size data were apparently
characterized as log-normal, suggesting particle bounce problems and
underestimation of the "MMD" common to much impactor data.
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63
Other studies of community health provide mainly qualitative support
for the existence of exposure/response relationships between sulfur oxide/
particle pollution and chronic morbidity (see Appendix B). Notable examples
include two well conducted British studies (Douglas and Waller, 1966;
Lambert and Reid, 1970) that indicate positive gradients of respiratory
illness with increasing coal consumption. Because of various deficiencies
in design or methodology, these studies cannot be considered useful in
yielding information on levels of pollution at which the observed effects
occurred.
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64
VI. FACTORS TO BE CONSIDERED IN SELECTING PRIMARY STANDARDS FOR PARTICLES
This section, drawing upon the previous summary of scientific
information, enumerates the key factors that should be considered by the
Administrator in deciding what particle fractions should be used as an
indicator of particulate pollution, establishing the levels of primary
standards and designating appropriate averaging times and frequency
criteria. Preliminary staff recommendations on the most appropriate
policy options in each of these interrelated areas also are presented.
A. Pollutant Indicator(s)
1. Major Approaches
Faced with obvious evidence of adverse health effects in heavily
polluted areas in the decades after World War II, public health au-
thorities in the U.S. and Great Britain pushed for reductions in general
particulate matter as indexed by available monitors, despite the fact
that the identity of causative agents and mechanisms was not well-known.
That these efforts were largely successful is evidenced by the review of
epidemiological data; it is extremely difficult to reliably detect
particle related health effects in areas where levels approach the
current U.S. primary standards. Furthermore, as Section IV indicates,
concentrations of many of the more innately toxic components of par-
ticulate matter (e.g., trace metals, BaP) have declined substantially in
previously polluted areas. This has reduced the need to consider
additional regulations (ambient or source) for control of such sub-
stances. The initial steps to control particles largely undifferen-
tiated in terms of size and chemical composition appear to have been good
public health policy, even though "particulate matter" is toxicologically
undefined.
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65
Nevertheless, the efficiency and effectiveness of total particulate
standards have been justifiably questioned in recent years. In this
standards review, then, it is necessary to use available information to
specify what measurable particulate fractions are the most suitable
indicators of those particles potentially of concern to health; in
essence, we must define the pollutant.
Although a number of approaches are available, the major policy
options with respect to particle indicators include:
1) Indicators used in community epidemiological studies (TSP, BS,
CoH);
2) Chemically specific indicators - (By class, e.g., sulfates, or
compound, e.g., sulfuric acid);
3) Size specific indicators (e.g., FP, MRP, BMRC, IP); and
4) Combined particle (as above)/S02 index.
Each of these approaches is discussed and evaluated briefly below.
a) Indicators used in Community Epidemiological Studies
Three major indices of particulate matter have been associated with
health effects in community epidemiological studies: Total Suspended
Particulate Matter (TSP), British Smoke (BS), and Coefficient of Haze
(CoH). The advantages of using these techniques as indicators include
direct relationship to the quantitative health data base and/or his-
torical continuity of particle data. None of these approaches,
however, were designed to account for respiratory tract deposition or
variable ambient composition. Each has specific design flaws making
application for U.S. health standards much less than optimal. Briefly,
major problems include:
i) TSP - Windspeed dependent particle acceptance of the hi-vol
sampler (< 25-45 vim) is unrelated to respiratory tract
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66
deposition. In current U.S. atmospheres, substantial quantities
of coarse particles too large to reach the thoracic region are
collected. Thus, large (> 10 \im) coarse particle control is
emphasized.
ii) BS, CoH - Particle acceptance of these instruments (< 4-5 ym)
includes much of the material potentially deposited in the
alveolar region of the lung, but may exclude some alveolar
deposition, and a major fraction of particles that can be
deposited in the tracheobronchial region. More importantly,
the BS reading varies more with darkness of the particles •
(carbon content) than with mass, making associations with mass
highly site and time specific. Control of primary elemental
carbon emissions is emphasized; elemental carbon is a minor
contributor to fine and total mass in current U.S. atmospheres.
iii) TSP/BS Relationships - In addition to the above problems, the
lack of any consistent relationship between TSP mass and BS
reflectance diminishes one of the major advantages of these
indicators; direct relatability to the available quantitative
health data.
b) Chemically Specific Indicators
Regulation of specific chemical substances or identified classes
could potentially improve the effectiveness of particulate control
programs. Ideally, it would be useful to identify a few specific chemical
substances of defined size range that are responsible for the vast
majority of observed effects. Despite efforts on three continents over
the last thirty years, however, no such specific "active agents" have
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been unequivocally identified. Instead, our review suggests that a
large number of different particulate substances may produce responses
in animals and humans, usually at levels higher than those found to be
associated with effects in community epidemiological studies.
Identification and control of each of the many ambient aerosol
components would be difficult to accomplish, time-consuming,
and would place excessive monitoring, compliance, and other requirements
on affected agencies and industries with no clear potential for improv-
ing public health protection over general particulate regulation.
Exceptions, such as trace constituents of high toxicity which are inade-
quately controlled by general particle standards, can be regulated by
specific ambient or emissions standards, as in the case of lead or asbestos.
A somewhat more practical intermediate approach would be to use
chemical classes (e.g., "sulfates", "organics") as indicators of particulate
pollution. The available epidemiological data base, however, does not
provide quantitative or qualitative support for chemical class standards
and both animal and human laboratory studies indicate variable toxicity
even within such categories. Given current knowledge and technical
capabilities, separate standards for chemical classes would be difficult
to support and implement, again with no obvious advantages for improving
health protection. Work to identify particularly significant classes/
sources/substances is needed to support future standard reviews.
c) Size Specific Indicators
All commonly used particulate monitoring devices are in some measure
size specific; the key issue is to determine what the most appropriate
size fractions are for ambient air quality standards. Aside from con-
tinuity with historical epidemiological instruments (see a) above), the
two major approaches to selecting such size fractions include
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68
1) size divisions according to regional human respiratory tract de-
position and 2) size divisions according to typical atmospheric size
distributions, for example, fine and coarse. These two approaches are
not necessarily completely independent.
i) Human Respiratory Tract Deposition
Particulate indicators based on regional human respiratory tract
deposition have long been adopted in occupational settings (Lippmann,
1970) and were recently recommended for ambient particles (Miller ejt
al_., 1979; ISO, 1981). Although this approach forms the most logical
basis for defining a health related particulate standard, there may be
difficulties in relating deposition derived indicators to the epide-
miological results, as well as uncertainties in translating available
human deposition data into uniform size fractions. Criteria are dis-
cussed more fully in Section 2 below.
ii) Ambient Size Distribution
Recognition that ambient particle mass and volume are typically
distributed bimodally has led to the suggestion that the health (as well as
other) effects of the two modes might ultimately be treated separately
(NAS, 1977a; Miller e_t_ al_., 1979). Because the chemistry of the two
modes tends to differ, this approach is essentially a simplified version
of the chemical class index approach discussed above.
This "natural" dividing line is at least partially relatable to
human deposition. The typical minimum dividing the fine and coarse
modes (1 - 3 urn) is near the 50% size "cut" used in occupational settings
to indicate insoluble "respirable" particles (3.5 - 5 ym).* Signif-
icant alveolar penetration, the enhanced effects with decreased
*A1though precise collection methods may vary, "respirable" particles have
been defined as those penetrating to the non-ciliated portions of the lung
(Miller et al., 1979).
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69
particle size noted in some animal studies, and the substantial surface
area in the sub-micrometer range have long been cited as indications of
the need to develop data in support of separate fine particle standards
(Natusch and Wallace, 1974; NAS, 1977a). Moreover, it has been argued
that the British epidemiological studies might be relatable to a fine
particle index, both because of the nature of the BS measurement and the
nature of the historical British aerosol (Waller, 1980).
Nevertheless, some difficulties and uncertainties exist in adopting
a fine/coarse fractionation for primary standards. Briefly, these
include:
1) The dividing line between fine and coarse particles is neither
sharp nor fixed and substantial over-lap may occur.
2) The minimum in the bimodal distribution may, in effect, disappear near
strong sources or under other peak loading conditions (see Section IV);
this minimum as well as smaller coarse particles lie near the size
range of maximum efficiency for alveolar deposition (2-4 urn).
3) Although the two modes have differing origins and chemistries,
each is chemically heterogeneous.
4) The respiratory tract in effect alters the ambient distribution,
with a mixture of fine and coarse particles being deposited in
the tracheobronchial and alveolar regions.
5) The mixing of modes in the respiratory tract and the heterogen-
eity within each mode blur the distinction between the modes in
terms of health effects. For example, with respect to health effects,
fine sulfates may have more in common with coarse nitrates than
with fine polycyclic organic compounds. Similarly, it is not
clear that 1 pm carbon particles are more likely to result in
pneumoconiosis than 4 urn silica particles.
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6) Respirable sampling used in occupational studies is ap-
parently not a good indicator of some effects associated with
occupational exposure to insoluble mineral dusts, particularly
industrial bronchitis (Morgan, 1978). The fine fraction
alone, then, also would not adequately include particles re-
lated to such effects.
7) Given that coarse "insoluble" dusts can result in responses
such as bronchoconstriction, altered clearance and alveolar
tissue damage (Section V), and the likelihood that coarse
particles were present in British air (Section IV), it would
be premature to ascribe all of the effects noted in British
studies solely to fine particles. Neither the British nor other
community epidemiological studies permit unequivocal separation
of the effects of fine and coarse particles. Indeed, until
ongoing studies make more definitive divisions possible, the
most prudent and defensible course may well be to combine both
British and U.S. epidemiological data in support of a single
size specific indicator based on human deposition data.
d) Combined PM/SCL Index
Elevated particle levels associated with health effects in historical
episodes were most often accompanied by high levels of sulfur dioxide.
As discussed in previous sections, it has been difficult to separate the
effects of particles and S02 in these cases, and both pollutants might
have been acting as indicators for some hitherto unidentified "active
agent." Mechanistically, particles may increase penetration of sorbed
SCL or otherwise enhance toxicity by chemical or physical transfor-
mations. Combined SCu/PM indices have been suggested to account for
these potential interactions.
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The relevance of such a combined index to contemporary U.S. at-
mospheres is, however, unclear. The sources of high SCL levels often
are well-controlled with respect to particulate matter while many major
sources of particles emit little or no SCL. The combination of high
levels of both S02 and particles is comparatively rare, since the S02
standards are largely met. Moreover, particles may interact with other
gases more commonly found in U.S. atmospheres than in historical epidem-
iological studies, notably photochemically generated pollutants such as
ozone, and N02.
Epidemiological evidence suggests that reduction in particulate
matter levels may improve health status even when S02 levels remain
elevated or are initially low (Lawther e_t al_., 1970; Ferris e_t al_., 1973).
As Lawther et aj_. (1970) point out, this should not be construed as an indi-
cation that SOp produces no effect, merely that control of one indicator
can reduce risks.
In light of the above considerations, linking the allowable U.S.
particle levels to S02 concentrations through a combined index would not
necessarily offer any improvement in health protection over a separate
particle standard. Even with a separate particle standard, the pos-
sibility of linking S02 standards to particle levels still can be con-
sidered later in the review of the S02 standard.
2. Staff Recommendations for a Particle Indicator
a) Recommendations for Approach
Based on the above evaluation, the EPA staff reaches the following
conclusions with respect to an approach to selecting a particle indicator:
1) The current primary standard indicator, TSP, can and should
be improved upon during this standard review. Choice of other
indicators used in historical epidemiological studies (BS, CoH)
is not advisable, both on health and technological grounds.
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2) Movement to chemically specific indicators ultimately may be
desirable but not advisable during this review. Of the particulate
chemical classes, most is known about sulfates. Nevertheless,
most reviews have concluded that insufficient data exist to
set a separate national sulfate or sulfuric acid standard
(NAS, 1977a, 1978). We concur with these judgments.
3) From the standpoint of protecting public health from the
effects of particulate matter, a combined SO?/PM index is not
necessary.
4) Choosing a size specific particle indicator based primarily
on respiratory tract deposition data is the best approach for
improving the particulate matter standard. The multimodal
nature of the ambient aerosol distribution should be consid-
ered, but should not form the principal basis for selecting a
health-related indicator at this time.
b) Recommendations for a Size Specific Indicator
The main questions to be addressed in selecting a size specific
indicator are i) what particles deposit in various regions of the respira-
tory tract; and ii) what are the potential health consequences of such
deposition for normal and sensitive population groups? Drawing on the
discussion in Section V of available regional deposition data as applied
to various ambient size distributions, potential mechanisms of toxicity
and possible health responses, a brief summary of key considerations for
each region is outlined below.
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i) Extrathoracic Region - The only particles uniquely deposited in
this region are coarse mode particles larger than 10 - 15 ym.
Because clearance is normally rapid (minutes), only systemic
toxicants (not normally present at high levels in this size
range), direct irritants, or pollens are likely to
produce effects. The major responses are symptoms
such as rhinitis and dryness in the throat. Occupational
exposures suggest wood dusts can slow clearance and may produce
cancer, but no evidence suggests that inert dusts or other
common ambient coarse particles produce these effects.
ii) Tracheobronchial Region - Particles deposited in this region
(<15 pm) are also deposited in one or both of the other
regions. Average clearance takes hours to days, but may be
slower at the airway bifurcations. Potential physiological responses
to high levels of both coarse "inert" dusts and acid aerosols
include bronchoconstriction, altered clearance, and buildup of
fine and coarse particles at the bifurcations. These responses
may result in reduced lung function, aggravation of existing
respiratory disease (particularly in bronchitics and asthmatics
with enhanced tracheobronchial deposition), increased infectious
disease and potentiation of the effects of cigarette smoking or
other exposures in development of bronchitis and the most common
forms of lung cancer. Although many of these responses have been
observed in community epidemiological studies, the relative role of
fine and coarse particles in producing them is not clear.
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74
iii) Alveolar Region - Particles less than 10 ym may be deposited
in this region. Because clearance of insoluble materials may
require months to years, any material deposited is of concern.
Possible responses include reduced lung function, damage to
lung tissues, increased susceptibility to infection, and
aggravation or potentiation of cardiopulmonary diseases.
Although more of the total deposited mass in this region is
likely fine mode, much of this is soluble and cleared rapidly
by dissolution. In current U.S. atmospheres, over half of the
insoluble material deposited in this region likely originates
in the coarse mode. Autopsies of groups exposed to fugitive
dusts suggest potential for damage from such deposition.
Based on the above considerations, it appears that the risk of
adverse health effects associated with extrathoracic deposition of
commonly found particles larger than 10 to 15 urn is sufficiently low
that they can be safely excluded from the primary particulate standard.
In rare cases where systemic toxicants are present in significant concen-
trations in this fraction, any general particle standard likely would be
insufficient and other sections of the Clean Air Act (Hid, 112) would
have to be considered. Pollens, although included in TSP samples, have
not generally been subject to particulate pollution control programs, so
their exclusion would not materially affect health protection.
Our review suggests that the risks of adverse effects associated
with deposition of coarse particles in the tracheobronchial region are
markedly greater than those for extrathoracic deposition. Support for
this position can be found in the International Standards Organization
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75
(ISO) report (1981) which states "It was the opinion of the ad hoc
working group that tracheobronchial deposition is more often of health
interest than extrathoracic deposition." Until the chemical and physical
characteristics and biological effects of coarse particles and accompanying
trace constituents are better understood, it would be premature to
exclude those deposited in this region from control. It follows that
fine particles, particularly hygroscopic particles, both acid and neutral,
depositing in this region also should be included in a particle indicator.
The risks of fine and coarse particles deposited in the alveolar
region also are of clear concern. Nevertheless, because substantial
overlap exists between particle deposition in the tracheobronchial•and
alveolar regions and because epidemiological studies frequently do not
permit distinction between these regions or between the effects of fine
and coarse particles deposited in these regions, separate indices for
alveolar and tracheobronchially-deposited particles are not advisable at
this time. Rather, an index representing particles that penetrate to the
thoracic region or "thoracic particles" (TP)* is recommended. This indicator
includes both alveolar and tracheobronchial penetration.
The approach and criteria for defining TP advocated by Miller et al.
(1979) and utilized by the International Standards Organization (ISO)
are consistent with Clean Air Act guidance for protecting sensitive popu-
lations and providing a margin of safety. Specifically, size specific
deposition estimates should reflect those portions of the population who
through illness, habit, exercise or other conditions breathe through the mouth.
*The term "thoracic particles" ('TP') will be used throughout the remainder
of this paper to mean particles penetrating to the thoracic region. The
term is intended for use only in the context of this staff paper to distinguish
it from other particle indicators associated with specific size cuts, namely
inhalable particles (<15 ym), respirable particles (3.5-5 urn), and fine
particles (<2.5
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Using available data for mouth only deposition, the ISO has essen-
tially recommended two alternative definitions for particles potentially
depositing in the thoracic region; those particles less than 15 pm and
10 pm respectively. In effect, TP monitors would need a 50% "cut" point
at one of these diameters with a specified geometric standard deviation
(GSD) or other indicator of sharpness. Both are based on extrapolation
of extrathoracic deposition data for mouth breathing which suggests that
under normal flow conditions, less than 10% of 15 pm or larger particles
reach the tracheobronchial region. The 15 pm definition of TP represents
the precautionary "envelope" approach advocated by Miller ejt al_. (1979)
in defining "Inhalable Particles". The 10 ym definition of TP represents
the more traditional approach of approximating the intake deposition profile
of the respiratory tract, in this case, the thoracic region. Although
particle deposition patterns vary with factors such as individual
characteristics and flow patterns, based on controlled experiments
involving mouthpiece inhalation (Figure 5-1), roughly 50% of inspired
particles of 10 pm size are deposited in the tracheobronchial region
with mouth breathing.
The staff believes that both definitions have merit. Some con-
siderations in this regard include:
1) These alternatives happen to lie near the peak of the
coarse mode (see Figure 4-3). The major difference will be
in the amount of coarse material collected.
2) The 15 pm limit ensures almost all tracheobronchial deposition
and additional extrathoracic deposition (< 5 pm) are included,
and, in that sense, is more conservative. The 10 pm limit may
be somewhat conservative for thoracic deposition because the
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77
data are based on mouthpiece experiments. The use of mouth
pieces should tend to increase particle penetration. The
"margin of safety" however, is a function of both the size
fraction and level of the standard. Thus, a 15 urn cut does
not inherently provide any greater "margin of safety", than
a 10 ym cut.
3) The probability of thoracic deposition, time for clearance,
and risk of health effects increases as particle size is
decreased from 15 urn to 10 ym.
4) Both definitions offer an envelope for particles penetrating
the alveolar region. This is a desirable feature, in that the
full range of alveolar penetration (up to 10 urn) is included in
the sample.
5) Based on indoor/outdoor studies (CD, pp. 5-127-131), the 10 ym
fraction may be a more reliable indicator of that portion of
ambient particles that contributes most to indoor exposures.
6) Either definition would tend to place greater weight on
controlling smaller particles than does a TSP standard.
7) The availability of 10 ym monitors and ambient data for regu-
latory analyses is not a serious constraint on this decision.
Prototype samples and inlets for retrofitting the existing IP
(15 ym) network are available and data from the current size
specific networks can be interpolated to provide reasonably
reliable estimates of mass <10 ym for interim use. Theoretical
and practical experience to date would suggest that 10 ym
samplers would be more reliable and less sensitive to windspeed
than 15 ym samplers (CD, p. 2-61).
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8) The representatives of member countries of the ISO recently
voted to adopt the 10 ym definition for measuring the thoracic
fraction of particulate matter (Ogden, 1981).
Given these considerations, the staff recommends that the 10 ym
alternative be selected for the particle standard indicator. This
alternative appears to be at least somewhat conservative with respect to
thoracic penetration and, all else being equal, offers the possibility
of more reliable monitoring. Moreover, matching the intake profile of
the thoracic region places greatest emphasis on fine particles, while
including those coarse particles most likely to be of health concern.
Based on typical urban particle size distributions, fine particles con-
stitute over 60% of the particle mass less than 10 ym. A 10 ym particle
sampler would collect 100% of the fine mass (<2.5 ym) and between 50 and
100% of the coarse mass in the 2.5 to 10 ym range. In contrast, the deposi-
tion data of Figure 5-1 show that most fine mass is not deposited in
the respiratory tract, while for mouth breathing most coarse mass in the
2.5 to 10 ym range is deposited. Given the larger surface area in the
fine mode as well as other concerns outlined previously, the greater
weight given fine vs. coarse particles by a 10 ym indicator appears to
be prudent and appropriate.
In addition to selecting a particle size, practical tolerance
limits for both the midpoint and shape of a sampler particle acceptance
curve must be specified. At 10 ym, it is possible to design sharp (low
GSD =1.1-1.3) or somewhat less steep particle inlets. The sharper
acceptance curves tend to more accurately reflect the ambient concen-
tration, while less steep curves appear to more closely conform to the
ideal of matching respiratory tract characteristics. An EPA analysis of
sampling alternatives has been conducted in support of this staff paper
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(Rodes et jjl_., 1981). The following conclusions and recommendations are
derived from that analysis:
1) The respiratory tract penetration/particle size data are not
lognormal and hence a single GSD is not realistic. The Chan
and Lippmann (1980) data provide a reasonable basis for an
"ideal" sampler that matches respiratory tract penetration.
2) Recommended sizing tolerance limits for TP samplers are D5Q =
10 _+ 1 pm for all windspeeds from 2 to 24 km/hr. No exact
constraints are given for sharpness of cut. However, the
total mass collected by the sampler should be in agreement
with that collected by the "ideal" sampler for expected ranges
of windspeed and particle distributions.
3) At least two prototype sampling systems are available that are
expected to produce mass concentration results within +_ 10%
of the ideal TP sampler and within 15% of each other under
"worst case" fugitive dust sampling conditions.
In summary, the staff recommends that the particle standard indicator
represents those particles penetrating the thoracic region. The size
range should include those particles less than a nominal 10 urn and
sampler performance criteria should be related to respiratory tract
deposition data.
B. Averaging Time and Form of the Standard
1. Averaging time(s)
The current averaging times for the particulate matter NAAQS are
annual and 24 hour and were based on available epidemiological studies.
The quantitative and qualitative studies outlined previously still
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suggest the need for both a 24 hour and annual standard. Some epidemio-
logical investigators (Lawther e_t a]_., 1970) have speculated that the
observed health effects might be largely due to short-term peaks on the
order of an hour. Controlled human exposures to specific particles also
indicate that some effects can occur after exposures of minutes (e.g., Utell
et_ al_., 1980) to hours (McDermott, 1962). Controlled human data on
specific substances, however, do not provide a satisfactory quantitative
basis for selecting general particulate standards and epidemiological
studies have as yet been unable to provide exposure/response information
for less than 24-hour periods.
Therefore, the staff recommends retention of 24 hour and annua-1
averaging times for particulate matter standards.
2. Form of the Standard
The current particulate matter annual primary National Ambient Air
Quality Standard (NAAQS) is based on the geometric mean of all valid
daily total suspended particulate (TSP) measurements in a calendar year.
The use of a geometric mean in the standard may have originated from the
fact that TSP and other pollutant levels do not follow a normal distribution.
It may also, in part, be a carry over of its use to describe long-term
air quality in the Winkelstein (1967) study, which was a major epidemiological
study featured in the 1969 criteria document for particulate matter
(DHEW, 1969).
The use of an annual average based on the arithmetic mean of the
daily averages may provide a more appropriate form of the standard for
providing health protection. Health effects are most likely a function
of dosage, a quantity more directly related to the arithmetic mean
(Mage, 1980). The arithmetic mean is more sensitive to repeated short-
term peaks than is the geometric mean. If these peaks fall below the
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level of the short-term (24 hour) standard (which is designed to protect
against acute effects from maximal 24-hour exposures), but above some
lower level at which repeated short-term exposures can adversely affect
health over the long run, the arithmetic mean can provide better health
safeguards. An arithmetic mean form of the standard will also allow
comparison and consistency with other annual NAAQS's. For these rea-
sons, the staff recommends an arithmetic mean form of the annual particu-
late matter NAAQS.
The staff recommends that the 24 hour standard be stated in a statistical
form rather than the current deterministic form (the current standard is not
to be exceeded more than once per year). This would mean either 1). that the
allowable number of exceedances would be expressed as an average or expected
number per year, or 2) that a given percent of the daily values would be
expected to be less than or equal to the standard level. The emissions
reductions to be achieved in the required control implementation program
would be based on statistical analysis of monitoring data over a multi-year
period (e.g., the preceeding 3-year period).
The statistical form can offer a more stable target for control programs
and, with reasonably complete data, is less sensitive to truly unusual meteoro-
logical conditions than the deterministic form. The general limitations of
the deterministic form are discussed more fully elswhere (Biller and Feagans,
1981). Recognition of the limitations has led EPA to promulgate or propose
statistical forms for the ozone and carbon monoxide standards.
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An additional consideration arises in the case of participate
matter. Unlike ozone or CO, participate matter is not monitored con-
tinuously but, typically, on a one in six day schedule. In a year where
there are actually two exceedances of a standard level, the probability
of detecting both is only 0.03. -Thus, the relative protection provided
varies significantly with frequency of sampling. This represents a flaw
in both the form of and monitoring requirements for the current standard.
The interaction between form of the standard and alternative monitoring
requirements should be considered in developing the standard. The issue
of allowable number of exceedances is an important one in that it inter-
acts with selection of the level of the standard. This interaction
should be specified so that it can be explicitly considered.
Conceptually, the least complex approach might be first to select
an acceptable standard level based on one exceedance and complete
sampling, and then adjust the level so as to provide roughly equivalent
protection under alternative exceedance/sampling schedules. Table 6-1
illustrates the relationship between standard level and exceedances for
one representative temporal distribution function (Frank, 1981) and a
sampling frequency of 365/yr.
TABLE 6-1. STANDARD LEVEL AS A FUNCTION OF EXCEEDANCES
1
1.00
Number
2
0.92
of Allowable
3
0.87
Exceedances*
4 5
0. 84 0. 81
6
0.79
*Entries are the relative levels of an expected exceedance (statistical
form of the standard, 3 year attainment test) that provide the same
degree of protection as provided by 365 sampling days per year
with one allowable exceedance (normalized to 1.0). Values are for
an assumed exponential distribution (xe = 2.0) but are also close to
those for lognormal (GSD =1.6) and Wei bull (K = 1.5) distributions
(Frank, 1981).
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The table shows that as the number of allowable exceedances increase,
the level of the standard to provide equivalent protection decreases. The
analysis of Frank (1981) shows that the degree of protection is not very
sensitive to sampling frequencies between 60 and 365 per year for the
statistical form of the standard. More complete sampling does, however,
provide a more stable target. For the statistical form with one expected
exceedance, as the sampling frequency is decreased from 365 to 61/yr,
the equivalent standard level decreases from 1.0 to 0.98. In contrast,
with the current deterministic form and the same distribution function,
as the sampling frequency is decreased from 365 to 61/yr, the equivalent
standard level decreases from 1.0 to 0.76 (Frank, 1981).
For the purposes of this paper, ranges for 24-hour standards pre-
sented later will assume a statistical form, with no more than one
expected exceedance per year over any consecutive three year period.
Alternative numbers of exceedances (and sampling frequencies) may be
desirable and should be considered. In so doing, the interaction
between these alternatives and the level of the standards can be speci-
fied.
C. Level of the Standard(s)
1. General Considerations
Selecting a particulate matter air quality standard with an ade-
quate margin of safety is a difficult challenge for the decision maker.
In addition to the normal uncertainties involved in making judgments on
the health risks of specific substances (such as carbon monoxide or NO*)
in real world atmospheres, the decision-maker must take into account the
fact that the chemical and physical characteristics of particles vary
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with time and location. This makes translation of epidemiological
evidence difficult and diminishes the utility of controlled human and
animal studies in making quantitative judgments. Some important general
considerations in approaching this problem are outlined below.
1) Particulate matter remains a pollutant class with variable
composition. The relative proportion of fine and coarse
particles and chemical components such as sulfuric acid,
carbon, and silica vary significantly with geographical
location, source mix, meteorology and time. The recommended
size specific indicator (TP) only partially reduces this
variability, but does limit control to those particles .with
the greatest potential for damage. Nevertheless, the risks
(margins of safety) associated with attainment of a given
national standard will vary from one location to another.
2) It follows that, although the scientific literature supports
the notion that various mixes of particles pose risks to
health, the basis for any general particulate standard is
largely a public health policy judgment. The more rigorous
approach of identifying each key toxicant and combination must
continue, but control of size-specific particles ultimately
may continue as an effective policy response to reduce the
need for more numerous specific standards.
3) As noted earlier, epidemiology, with mechanistic support from
toxicological and deposition studies, provides the major basis
for identifying and/or setting the level of the standard.
None of the published studies have used TP as a pollutant
indicator.
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4) The difficulties in conducting and interpreting epidemiological
studies are discussed in Section V-D and in the criteria
document. All epidemiological studies appeared flawed to some
degree (e.g., confounding variables, characterization of
exposures), further limiting the reliance that can be placed on
the results of any single study. Furthermore, discord is
apparent among epidemiologists over the acceptability and proper
use of some studies (e.g., Holland ot_ al_., 1979; Shy, 1980;
Ware et al_., 1981).
5) As pollutant levels decrease, it becomes extremely difficult to
discern effects in epidemiological studies, indicating that pollutant
effects, if any, are small in comparison to other causes. In
some cases (e.g., mortality), however, even small differences
in effects may be viewed as serious. In this context, it should
be noted that a prospective epidemiological study would need
a study group of about 200,000 people to detect a 2% (2/100)
difference in mortality rate (Wilson et. a1., 1981).
6) Even the best epidemiological studies can do no more than provide
site, time, and monitor specific associations between levels of a
given particulate/other air pollutant mix and observed health
responses. Moreover, such studies often provide no clear
evidence of population "thresholds." Thus, the approach of
identifying specific "lowest demonstrated effects levels" and
adding margins of safety considerations is less appropriate in
this case. Instead, attempts must be made to assess the nature
of health risks along a continuum of exposures using the full
range of available health and exposure data.
-------
86
7) Based on the above considerations, it is apparent that decison
makers will have to deal with unusually large uncertainties in
selecting national particle standards. In evaluating health
risks (margins of safety), the following aspects must be
balanced:
a) Particle size range selected as an indicator;
b) Level (concentration);
c) Range of expected aerosol composition; and
d) Potential effects not examined in the more quantitative
epidemiological studies.
The conceptual relationship between size index and levels of 'the
standard in the range of interest is illustrated in Figure 6-1. The
range of aerosol composition initially must be considered in comparing
current U.S. compositional data to the composition of particles in the
relevant epidemiological studies (if available). In most cases, it may
be reasonable or necessary to assume comparable toxicity due to a lack
of detailed data. In addition, the quantitative community epidemiological
data base does not provide exposure-response information for some of the
likely effects of major TP components (e.g., pneumoconiosis from insoluble
particles). Thus, the levels of interest for TP derived from the quantitative
studies also should be evaluated with respect to any unquantified potential
effects that may be reasonably anticipated, based on TP composition and
the qualitative effects studies summarized in Section V-B.
2. Qualitative Assessment of Risks of Thoracic Particles
The most useful epidemiological studies for establishing exposure-
response relationships are presented in the main text of Chapter 14 of the
criteria document and summarized in Section V-D and Tables 5-4 and 5-5
-------
87
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STANDARD LEVEL (NORMALIZED TO TSP = 1)
Figure 6-1. Conceptual relationship between level of standard and size
indicator. Assuming a typical ambient distribution and equal toxicity
in the 10-15 ym range, equivalent health protection may be achieved for
<10 or <15 ym size fractions by adjusting the level of the standard as
indicated. In essence, as the size of the indicator increases, a larger
portion of the coarse mode is collected, permitting the standard level to
increase with no change in health risk.
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88
of this paper. Following the approach used in the criteria document and by
other reviewers, the PM and SCL concentrations listed represent indicator
levels at or above which the pollutant mix present in the particular
study location is likely to be associated with observed health effects.
As such, they are characterized as "effects likely levels" in Table 5-4 and 5-5.
They must not be viewed as "thresholds" below which no_ effects can be
inferred. Given the variable pollutant mixes and indicators studied,
they also can not be unequivocally considered "demonstrated effects
levels" in the context of current U.S. particulate matter exposures.
Study authors and various reviewers often differ with respect to specifying
effects levels from these studies.
As noted in the criteria document, by some reviewers (Ware et al.,
1981; Wilson et al_., 1981; NAS, 1978) and in Section V-D of this paper,
a striking feature of many of these studies is the lack of strong evidence
for any threshold levels and the suggestion of a dose response relationship
along a continuum of exposures. Nevertheless, the most common approaches
to assessing risks of particulate matter and sulfur oxides have been:
1) tabular or graphical listing of "effects levels" from these studies,
sometimes normalized to single indicators; and 2) regression analyses of
national mortality statistics, making little or no use of the remaining
epidemiological data (e.g., Lave and Seskin, 1977). The first approach
gives no clear sense of the risk of effects below the stated levels, even
though the original data often suggest this possibility. The second
approach, while usually consistent with a continuum of exposure/response
even at low levels, looks only at one endpoint and often produces con-
flicting results with respect to pollutant indicator and strength of the
relationship because of confounding variables. Although some reviewers
-------
89
feel that these studies suggest particle-sulfur/mortality associations
at ambient levels (Thibodeau et al_., 1980; Wilson et aj_., 1980), it does
not appear that these studies provide reliable quantitative estimates of
risk (Ware .et _al_., 1981). Furthermore, neither of the above approaches
makes much use of the weight of evidence from relevant qualitative
epidemiology, controlled human exposures, and animal toxicology.
The following sections present a brief staff assessment of the
concentration/response relationships suggested by the most significant
epidemiological studies in the criteria document and how these studies
may be applied in developing ranges for decison-making on standards for
particulate matter, as indicated by Thoracic Particles (<10 ym). The
presentation also outlines a qualitative assessment of the key factors
that affect the margins of safety (risks) associated with the concen-
tration/response relationship derived from these studies, as translated
to contemporary U.S. exposures. This includes identification of those
important aspects of the qualitative human and animal health studies as
summarized in Section V (and Appendix B) that should be incorporated
into margin of safety considerations. Short and long-term exposures are
discussed separately.
a) Short-term Exposures
1) Derivation of Ranges of Interest from Epidemiological Studies
1. Concentration-Response Relationships
Although a number of epidemiological investigations provide
qualitative evidence for the effects of short-term exposure to particulate
matter (usually with S02 and other pollutants), the criteria document
indicates that those most useful for developing quantitative conclusions
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90
include a series of studies and reanalyses of daily mortality in London
(Martin and Bradley, 1960; Martin, 1964, Ware et al_. 1981; Mazumdar et. al_.,
1981; CD, p. 14-16 to 14-24) and studies of bronchitis patients in London
(Lawther et a].., 1970).
The London mortality studies have been characterized by the
criteria document as suggesting notable increases in excess mortality
3
occurred in the range of 500-1000 yg/m BS and S02 and are most likely when
3
both pollutants exceeded about 750 yg/m . These estimates represent judgments
of the most scientifically reliable "effects levels", for daily smoke and
mortality, at least in the context of historical London pollution exposures.
Because of the severity of the health end points and the need to consider
margins of safety in standard setting, it is important to determine whether
the data support the possibility of health risk below these "effects likely
levels." As discussed in Section 14.3.1.2 of the criteria document, the London
mortality studies and reanalyses do support the possibility of a monotonic
dose-response relationship for particles (and perhaps SO,,). Figure 6-2
(CD, Figure 14-1) illustrates the relationship between deviations from
average mortality(15 day moving mean) and smoke and S02 concentration
for the London winter of 1958-59 (Ware et _a]_., 1981). Figure 14D-3
in the criteria document presents unadjusted mortality data from the same
winter but includes confidence intervals that show the uncertainties
added by monitoring and other errors. Both seasonally adjusted and crude
mortality data suggest the possibility of a gradient in mortality across
a range of exposures from about 150 yg/m (the lowest average daily
3
values) to over 1200 yg/m of both BS and SO^. Analyses by Martin and
Bradley (1960) indicate that, during this winter, temperature was not
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91
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INDICATE NUMBER OF DAYS
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CONCENTRATIONS IN THE
RANGE SURROUNDING THE
POINT
j_
200
400
BS,
600
800
1000
1200
, 24 hr. AVERAGE
Figure 6-2. Average deviations of daily mortality from 15 day moving
average by concentrations of smoke (BS) and SUg (London, November 1,
1958 to January 31, 1959). Martin and Bradley (1960) data as summarized
by Ware ejt a]_. (1981). As daily pollutant levels decrease, the
positive mortality deviations also decline. At still lower pollution
levels, daily mortality deviations fall increasingly below the 15 day
moving mean, suggesting the possibility of a continuum of exposure-
response over the range examined. Uncertainties in mortality data and
aerometry are not depicted by these averaged points. Examination of
Figures I4D1 and 14D3 (CD) give some sense of the variability in
unadjusted mortality and in aerometry. Note that point with asrow
represents mortality deviation for all days with SCL >500 yg/m .
-------
significantly correlated with mortality, and humidity was only marginally
significant. The analysis of Figure 14D-3 suggests that at lower concentration
o
ranges (150-500 jjg/m ), errors associated with variability in air quality
estimates from the seven station London network are small to negligible.
Other possible errors in aerometry are more difficult to specify (CD,
p. 14-18 to 19). Because of the variability in the mortality data and
the nature of the confidence intervals, the criteria document notes that
the relationship becomes increasingly less certain below about 500
Although the Ware et a]_. (1981) and criteria document analyses both omit
data from a month with an influenza epidemic, the Martin and Bradley (1960)
data show that the association between mortality and pollution continued
during the epidemic. Peak mortality during the epidemic occurred on the
day with peak smoke and S02-
As indicated in the criteria document (CD, p. 14-21) and by data
summarized by Mazumdar et. al_. (1981), the winter of 1958-59 may have
been unusual in the following respects: (1) mortality rates were higher
than for 12 of 13 subsequent winters; (2) particle and S02 levels were
higher than in all subsequent winters; and (3) relative humidity and
the number of days of intense fog contributing to episodic conditions
(with concomittant high sulfuric acid) were increased. Thus, examination
of mortality-pollution relationships in subsequent years is important
in determining whether any indication of health risks below the suggested
effects levels persists in later years.
Analysis of the adjusted daily mortality for all London winters from
1959-72 (Mazumdar et al. 1981) again illustrates the possibility of
a continuum of response over a wide range of particle concentrations
(Figure 6-3a,b) (CD, Figures 14-2 and 3). Of particular interest is the fact
-------
93
a)
HYPOTHETICAL DOSE/RESPONSE CURVES
DERIVED FROM REGRESSING MORTALITY
60
s
30
2O
10
5OO 1000 1500 2000
SMOKE (jog/m3 )
2500
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8
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190
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Figure 6-3. a) Hypothetical concentration-response curves derived from
regressing mortality on smoke in London during winters 1958/59 to 1971/72
Results obtained with linear (•) and quadratic (A) models are depicted
for comparison, b) Same concentration and response models plotted on the
scattergram of adjusted mortality and smoke for same winters as in (a).
Note that the smoke scale (abscissa) is logarithmic. This plot illustrates
variability in the data (Mazumdar et al., 1981).
-------
94
o
that the investigators analyzed episodic (days of >500 pg/m and adjacent 7
o
days on either side) and non-episodic days (remainder when BS <500 ug/m )
separately and attempted to separate the effects of particles and S02- In
discussing their regression analyses, the authors point out that "in the non-
episodic period when the pollutants (SOp and BS) are considered separately,
the coefficients are positive, significant, and similar. When they are
considered together, only the coefficients for smoke remain statistically
significant" (Mazumdar ejt al_., 1981). This analysis provides clear support
for the possibility of health risks associated with BS concentration below
500 ug/m over 12 London winters, and suggest that S02 might be less impor-
tant in non-episodic mortality. Because the early winters contained no
non-episodic periods, the non-episodic analysis actually reflects only
winters from 1960-61 to 1971-72, a time span that includes a significant
change in the composition of London particulate matter as smoke controls
were implemented. That the regression still indicates significance for
the combined non-episodic days in these winters gives some confidence
that the results may be relevant to areas with different particle composi-
tion, lower humidities and fewer periods of intense fog.
A comparison of the various analyses of London mortality (CD,
Section 14.3.1.2, Appendix D) show qualitative similarities and suggest
that smoke accounts for a small but statistically significant portion of
daily mortality in London. The quantitative estimates vary with model
and, as noted in the criteria document, the estimates should be viewed
with caution and are quite uncertain, particularly at lower concentrations.
No basis exists for selecting any of the approaches as most representative,
-------
95
although the Mazumdar analysis does reflect a much larger number of observa-
tions and conditions. Mazumdar et^ a]_. (1981) indicate linear and quadratic
models are "both compatible with the data" and suggest consideration of
controlled experiments or of further analyses.
Although the data are uncertain, the London mortality analyses suggest
a risk of effects below the more certain effects levels of 500-1000 ug/m .
Based on the comparison of analyses in the criteria document (CD, Section 14.3.1.2
Table 14-7), some small risk may exist at BS levels as low as 150 ug/m ;
the risk of any effect as well as the potential magnitude of the effect
increases in the range of 150 to 500 yg/m . The criteria document (CD, p.
14-26) suggests that qualitative support for "weak but positive" associations
between mortality and non-episodic particle concentrations (5-6 CoHs) is
provided by analyses of New York City data by Schimmel and Murawski (1976),
Schimmel (1978), and others (summarized in Table B-10). Qualitative data
from regression analyses (Table B-ll) are not inconsistent with the possi-
bility of cumulative short-term mortality effects in U.S. atmospheres
although their inherent difficulties limit their utility even in a
qualitative context. Data from controlled human, animal, and other
epidemiological studies, outlined in Section V.A. and B, suggest
mechanisms by which various exposures to particles might result in
mortality in susceptible individuals, but do not provide evidence for
specific levels of concern.
Lawther1s studies of bronchitic patients began during periods
of high pollution (1954) and continued through the time when levels were
considerably lower (e.g., 1967-68; mean winter S02, 204 pg/m3, BS, 68
2
ug/m ). Lawther et a]_. (1970) found an association between peak pollution
and health status of bronchitics and that responses declined as controls
reduced pollutant levels. Because of the nature of the study, effects
-------
96
were related to peak daily concentrations, but the authors felt the
effects were more likely the result of brief exposures to short-term
peaks "several-times the 24-hour average." While this suggestion is
plausible, the available data preclude any quantitative evaluation.
Thus 24-hour, or to a lesser extent, long-term pollutant averages, must
be used to indicate the possibility of peak short-term levels of concern.
3
Lawther's suggestion that 24 hr. averages of 250 yg/m smoke and 500
3
pg/m SOg represent "the minimum pollution leading to any significant
response" appears reasonable, although the possibility that short-term
peaks of concern may occur at lower 24-hour levels cannot be discounted.
The criteria document notes that a summary of results for selected patients for
the winter 1967-68 (Table III, Lawther et_ al_., 1970) suggest a statistically
significant correlation between smoke and symptom scores for a winter
3 3
with only one day of SOp > 500 yg/rn and BS >_ 250 yg/m . The criteria
document also suggests that BS measurements after 1963 may have overstated
actual levels (CD, Table 14-7).
2. Translation to Thoracic Particle Indicator
A number of factors make use of these British studies in
assessing risks of U.S. aerosols difficult. The most reliable conclu-
sion that can be drawn is that as daily particle and S02 levels increase,
mortality and symptoms increase. However, because the majority of U.S.
studies of acute effects have been judged to be inadequate for quantita-
tive evaluation of these effects, an attempt at translation of the
British work must be made. The assessment outlined below incorporates
reasonable assumptions concerning indicator pollutants, pollution compo-
sition, relative role of particles, and the nature of U.S. vs. British
exposure regimes. In some cases assumptions are conservative (in the
-------
97
sense that they increase the margin of safety); in other cases their
relative nature cannot be identified. This staff assessment is summarized
in Table 6-2 and discussed below.
TABLE 6-2. STAFF ASSESSMENT OF SHORT-TERM EPIDEMIOLOGICAL STUDIES
Effects/
Study
Effects
Likely
Effects
Possible
Measured British Smoke Levels (as yg/m )
Daily Mortality
in London
500-1000
150*- 500
Aggravation^of
Bronchitis
250*- 500*
<250*
Combined
Range
250-500
150-250
Equivalent TB
Levels (yg/m )
3
Combined Range
350-600
150-350
1
*Indicates levels used for upper or lower bound of range.
Martin and Bradley (1960); Ware et al_. (1981); Mazumdar et al_. (1981)
"Lawther et a]_. (1970)
Boundary assumptions for estimating TP levels from BS readings detailed in text.
Both the mortality and bronchitic studies represent population
groups among the most sensitive to pollutant effects. Because mortality,
even in the sick and elderly population at greatest risk, is a more
serious consequence than symptom aggravation, the risk of an effect at
concentrations below the "effects likely levels" in the mortality studies
should be given more weight than similar concerns for the bronchitic
studies. As noted above and in Table 6-2, effects may be possible at
the lower concentrations indicated, but the evidence and risks are much
less certain. Therefore, the lowest pollutant levels of interest in
the short-term studies were 150-500 yg/m3 (BS) and 150-500 yg/m3 (SOJ
(based on the mortality studies) and 250 yg/m3 (BS) and 500 yg/m3 S02
(based on the bronchitic studies). The relative importance of S00
-------
98
cannot be unequivocally specified, but for reasons outlined in
Section VI.A a separate particle standard is warranted. Thus, the
conservative assumption (with respect to particles) is made that similar
responses might have occurred without substantial amounts of SCL present.
The Mazumdar et. aj_. (1981) and Schimrnel (1978) analyses suggest this
might not be a conservative assumption for mortality risks.
Because the smoke reading responds to darkness instead of
mass, any relationship between BS and any mass index is particularly
uncertain. Insofar as can be determined from the literature, smoke
readings made prior to 1964 in British networks were not routinely
calibrated against comparable mass readings (Holland et al_., 1979). The
most notable exception was the St. Bartholomew's site in central London
(Waller, 1964). BS levels at this site are approximately related
to particle mass less than about 5 ym. No such approximation is possible
for the 7 stations in the exposure network used for the mortality and
bronchitic studies, but the criteria document indicates that the central
London site calibration tends to confirm "reasonably well" the mass
calibrations in the 7 station network from 1959-63. After that time, BS
readings may have overestimated actual concentrations (CD, Table 14-7).
Comparisons of long-term averages of TSP vs. BS in central London from
1955 to 1963 suggest that when smoke levels in the range of 100-500
3 3
ug/m are calibrated, they are consistently (about 100 ug/m ) below TSP
readings (Commins and Waller, 1967), further confirming the presence of
particles larger than 5 ym, some of which must have been in the range
that can be deposited in the thorax. At sites where BS is not calibrated
to sampled mass (e.g. Salford in Lee et. aj_. 1972), seasonal BS readings
may actually exceed TSP readings.
-------
99
Although far from conclusive, the available data as discussed
above and in Section IV suggest the following generalizations on the
comparison between BS and TP (< 10 ym) are reasonable for the historical
London data:
o
1) When London BS readings are in the range of 100-500 yg/m ;
fine particle mass < calibrated BS value < TP mass < TSP mass.
2) Where BS values are not calibrated, the uncertainty in these
general relationships increases significantly; the extent of
this uncertainty is difficult to assess.
3) Given the uncertainties in the uncalibrated data, it may be
reasonable, but not highly conservative, to assume for historical
(1959-72) London data, during the lower BS readings of interest
(100-500 yg/m BS), the following boundaries;
a) As a lower bound, BS reading - TP mass.
b) As an upper bound, BS reading < TP mass - TSP mass.
c) As an upper bound for multiple daily readings, TP mass =* TSP
mass = BS reading + 100 yg/m3 (Holland et. aj_., 1979).
Based on these general boundary relationships, 24 hour TP levels of interest
3
derived from the British studies would range between 150 yg/m and 350
•3
yg/m (Table 6-2). By virtue of the assumptions in their derivation, these
estimates should not be considered as demonstrated "effects levels."
Although no generally applicable relationships exist for predicting
TP levels from specific BS readings, the available aerometric evidence sug-
gests that the above ranges represent true boundaries that are likely to
encompass the majority of values. In this regard, lower bounds derived
from the above relationship include an additional margin of safety over
that derived from the assessment of health data in the original units
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100
while upper bounds would tend to reduce any margin of safety incorporated
in the original assessment of health data. Thus, under British conditions,
o
the upper end of the range of interest (350 yg/m ) overlaps levels at which
effects are likely and does not include any margin of safety.
ii) Additional Factors to be Considered in Evaluating Margins of
Safety and Risks - Short-term Exposures
As applied to the British exposures and particulate composi-
tion of 1959-1965, TP standards in the above range would provide a
moderate to negligible "margin of safety" for the sensitive populations
and effects studied. When applied to U.S. pollution, the following
additional factors should be considered:
1. Aerosol Composition
1) Where high S02 levels are present with the above TP levels,
the risks of effects are increased; any margin of safety inherent
in applying the London data to U.S. areas with low S02 is reduced.
2) Where high photochemical smog levels are present, effects not
accounted for by the British data may ensue.
3) Where U.S. particle components differ substantially from British
particles, risks will vary.
As indicated in Section IV, it is difficult to compare acute toxicity
of U.S. and British particles on a unit mass basis. The variability of
TP composition among U.S. cities might be as great as that between any single
U.S. city and historical London. Many U.S. urban areas have lower primary
carbonaceous material, and higher sulfate, nitrate and secondary organics
than London. This may not be the case in areas with heavy residential wood
burning. Some areas have a relatively higher proportion of coarse mode
material in the TP range. Therefore, risks associated with daily levels
of 150-350 ug/m TP will vary among U.S. cities, but it is difficult to pre-
dict the magnitude of the variability based solely on composition.
-------
101
2. Relative Exposure
Based on measurement of indoor exposures and general ventilation
rates reported by Lawther et^ &]_. (1970), indoor pollutant exposures in
British residences more closely tracked outdoor levels than is the case
in more tightly sealed U.S. residences. Thus, for comparable outdoor
concentrations, the overall exposure to maximum 24-hour outdoor pollution
was likely to have been greater in urban areas of Great Britian than in
contemporary U.S. exposure situations. Since many of the more sensitive
individuals may be confined indoors, the extent of increased mortality or
symptoms would tend to be lower in the U.S. than observed at comparable
levels in the British studies.
3. Risks for Other Sensitive Groups, Effects Not Evaluated
Based on the evaluation of toxicological, controlled human, and
qualitative epidemiological data, Section V-B and Table 5-3 identify a
number of groups that would be expected to be sensitive to ambient particles
and a variety of effects that have been observed or anticipated to occur
as a result of such exposures. The studies used to derive ranges address
a number of these groups and effects, but omit others. Specifically, the
derived range addresses 1) premature mortality in very sensitive individuals
with chronic respiratory and cardiovascular diseases, individuals with
influenza, and the elderly, and 2) morbidity (aggravation of disease) in
bronchitic patients. Because it is reasonable to expect morbidity at or
below levels at which mortality occurs in these sensitive groups, the
London mortality studies also may be considered as an indicator of
morbidity. Due to the unequivocal nature of the end point, the unusually
large study population and substantial number of study days, the chance
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102
of detecting any marginal mortality effects is likely to be greater than for
most studies of morbidity. Thus, to the extent the London data suggest a small
risk of slight increases in mortality in the range of concern, an additional
risk of morbidity is suggested and should be considered. Because the range
is substantially below the mortality "effects" levels, the derived range
would appear to be protective against the unmeasured morbidity risk.
Other sensitive groups not expressly addressed by the short-term
British studies are children and asthmatics. Daily exposure to particles
and SOp appear to be associated with increased symptoms of respiratory
disease, particularly in sensitive children (Lebowitz et. aK, 1972). Other
qualitative studies (see Table B-3) suggest possible effects of particulate
matter on lung function in children and exercising adolescents in contemporary
U.S. cities (Lebowitz e_t a]_., 1974; Dockery e_t al_., 1981). The significance
of these preliminary findings is not clear, however, and no reason exists
to suggest important effects below the range noted above. Animal and
controlled human exposures support the notion that acute exposure to a
variety of particles can affect lung function (Section V.B.I) but usually
only at high short-term (minutes to hours) exposures.
Asthmatics have proven difficult to evaluate in community studies.
Clinical evidence suggest that they may respond to SOp alone (or in combina-
tion with particles) at levels likely seen in a number of community studies
(e.g., Sheppard ejt al_., 1981; Koenig et al_., 1981). This confounds the
results of studies where high SO levels also were present. As discussed
in the criteria document (CD, p. 14-30 to 14-33), both positive and negative
findings have been reported for asthma and few studies have adequately
controlled for temperature or other confounding variables. Thus, although
clinical studies (Utell et al., 1981) and mechanistic considerations
-------
103
(Boushey et al_., 1980) suggest asthmatics are a sensitive group, the data
do not support the existence of significant effects below the suggested
range.
The above discussion addresses, in part, three of the six major
categories of expected effects of particulate matter: 1) respiratory
mechanics and symptoms; 2) aggravation of existing disease; and 3) mortality.
The available data summarized in Appendix B suggest that two other categories
(morphological alterations and carcinogenesis) may be better related to
long-term exposure. Qualitative evidence summarized in Section V.B. suggests
acute exposure to high levels of specific particles and community air pollu-
tion can affect clearance and other host defense mechanics, possibly re-
sulting in increased infections and disease. In children, such infections
might have longer-term consequences (Table 5-2).
Studies of hospital admissions or emergency room visits, although
a crude indicator of morbidity, sometimes can provide some suggestion of
the effects of pollution on several of the above categroies. The results
of Samet £t al_. (1981), although essentially negative, provide a suggestion
of a very small, but statistically significant, association between daily
particle loadings and emergency room visits for respiratory diseases for
TSP levels in the range of 14 - 700 pg/m3 with S02 levels of 2 - 369 yg/m3.
b) Long-Term Exposures
i) Derivation of Ranges of Interest from Epidemic!ogical Studies
Cross-sectional and longitudinal studies most useful in establishing
ranges of interest for long-term (annual) exposures for particulate matter
are summarized in Section V-D. As noted in that section and in the criteria
document, cross sectional studies are subject to a number of methodological
uncertainties and confounding variables, such as differences in smoking,
-------
104
occupational exposures, and socioeconomic status among communities. Moreover,
differences may exist in particle composition among areas, magnifying or
diminishing apparent differences in effects. Nevertheless, the studies
listed in Table 5-5, as well as more qualitative studies, suggest a relation-
ship between various health responses and long-term exposures to particles.
A key feature of studies where more than two geographic areas are com-
pared is the existence of a gradient of exposure and response for a number
of health indicators. Examples suggesting a continuum of response from
several qualitative European cross-sectional studies include Douglas and
Waller (1966), Lunn et al_. (1967) (see CD, Figure 14-4) and, less reliably,
Lambert and Reid (1970). Although no obvious thresholds exist for many
responses, not all of the health responses measured in these studies show
a gradient.
When only two geographic areas or time periods are involved in a study,
the levels that happened to exist in the more polluted area or time period
usually are listed as the "effects" levels (Ware et al_., 1981; CD, p. 14-49).
Effects levels thus derived are somewhat arbitrary, but do represent con-
centrations where effects can be ascribed with some certainty. Because a
gradient of effects is often observed for multiple area studies, however,
some risk exists that effects decrease but do not necessarily disappear
at concentrations substantially below those of the more polluted area.
Therefore, "effects" levels derived from two-area (or time) studies cannot
be regarded as thresholds or "no detectable effect" levels.
Table 6-3 is a staff assessment of the levels of interest derived
from the most useful long-term epidemiological studies. In this Table,
the "effects likely" line lists concentrations in the more polluted area
-------
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(or time) as derived from the similar "effects likely levels" column of
Table 5-5. For the Limn study, effects are possible at lower concentrations,
but lower boundaries cannot be specified. Based on the evaluation of the
Lunn follow-up study (Lunn ejt aj_., 1970) in the criteria document, the "no
effects" level for smoke sometimes ascribed to these studies (140 yg/m BS;
Holland et .ah, 1979) is not reliable. The "effects possible" levels
for Ferris represent a lower bound for detectable effects in the Ferris
studies, based on the lack of measurable differences in effects between
years when TSP dropped from 130 to 80 yg/m . Based on the mixed but
suggestive results from Bouhuys et^ al_. (1978), effects are possible at
levels observed in the more polluted city. Effects, if any, are most
likely to have resulted from higher exposures in previous years (60 - 150 yg/m ),
with the median concentration (110 yg/m ) serving as a reasonable lower
bound.
Based on the above assessment, levels of interest for effects measured
in these studies are as follows: 1) Decreased lung function and increased
acute respiratory disease in children may occur at levels below 230 yg/m BS
(Lunn) 2) Decreased lung function in adults may occur at TSP levels as
low as 130-180 yg/m3 TSP (Ferris) but is less likely to be detectable at
about 110 yg/m (Bouhuys). 3) Some risk of increased respiratory disease
and/or symptoms in adults may exist at levels of 110-180 yg/m TSP (Bouhuys,
Ferris).
It must be stressed that effects are not demonstrated within these
ranges; the lower bounds represent conservative estimates where some risk
-------
107
of effect is not ruled out by the data. Moreover, the differences in effects
at lower levels (e.g., Bouhuys) were, as might be expected, small in com-
parison to baseline rates.
Conversion of the BS data to TP is quite uncertain for these long-term
studies because sites were located in different geographic areas and times
and because no mass calibrations are available for these areas. Because reliable
lower bounds cannot be estimated for the Lunn study and because the levels
in the more polluted areas are relatively high, no attempt at translation
of these results to thoracic particle equivalents will be attempted.
Approximate conversions of TSP data to that fraction more likely
to have produced the observed responses (TP) may be accomplished by using
relationships developed from reliable particle size distribution measurements
and compared with data from the inhalable particle (IP) network (Watson et
atl_., 1981). For TP <10 ym, the TP to TSP ratio expected for typical urban
U.S. sites averages between 0.5-0.6. Although these average ratios might
not have been obtained in the Ferris and Bouhuys studies, the range
is probably reasonable and conservative. Applying these factors to the U.S.
studies summarized above (Table 6-3), the range of some interest
for TP is 55 to 110 yg/m . The upper end of this range overlaps the
somewhat uncertain "effects level" derived from these studies. As such,
the upper bound contains no identifiable margin of safety. It is emphasized
that the results of the original studies, assessment of risks at lower levels,
and conversion to a common indicator all are subject to considerable uncertainties.
ii) Additional Factors to be Considered in Evaluating Margins of
Safety and Risks - Long Term Exposures
It is apparent that long-term concentrations in the range of 55-110
ug/m are in the "noise level" for the above epidemiological studies and that
effects measured to date are likely to be small for the groups studied. Preliminary
-------
108
results of cross sectional data from the ongoing "Six Cities Study" tend to
support this judgment (Ferris e_t aK, 1979, 1980). When evaluating margins of
safety (risks) in this range, the following additional factors should be
considered.
1. Aerosol Composition:
1) Because S02 levels in New Hampshire were generally low,
the Ferris study provides some support for separate standards.
Where high SO^ levels co-exist with TP, however, the lower
portion of the above range still is protective.
2) The Bouhuys and perhaps the Ferris studies are directly rele-
vant to current U.S. atmospheres with periodic elevations of
ozone.
3) Although relative aerosol toxicity among the various regions
studied cannot be compared on a unit mass basis, the results
of the above analysis of U.S. and British studies do not
suggest an order of magnitude difference. Each area, however,
probably contained city specific sources producing somewhat
different particle composition. For example, particles in the
city studied by Ferris were largely affected by pulp mill
emissions. As such, their composition may be somewhat
unusual, but no measurements are available. The risks of
lung function and symptomatic effects noted in these chronic
studies can be expected to vary with composition, but reliable
estimates of the variability are not available.
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109
2. Relative Exposures
The Bouhuys and possibly the Ferris studies may represent
contemporary U.S. indoor/outdoor exposures. It is apparent, however, that
at lower outdoor particle levels (< 130 ug/m TSP), longer term particle
exposures may be significantly affected by indoor pollution. With one
or two smokers present, indoor particle exposures will exceed outdoor
exposures. This can be viewed in two ways: a) reduction in outdoor
particle levels will not produce proportional reduction in total exposures;
or b) in terms of total body burden, the uncontrolled indoor contribution
reduces the subject's capacity for dealing with outdoor levels, thereby
increasing concern over both sources of exposure. About 50% of homes,
however, have no smokers in them and indoor particle generation is normally
much smaller (Spengler et aJL, 1980),
3. Risks for Other Sensitive Groups, Effects Not Evaluated
The groups examined in the studies used to derive ranges include
children and adults in the general population. Effects categories addressed
include 1) respiratory mechanics and symptoms and 2) effects on host defense
mechanisms, as suggested by increased respiratory diseases. Different
effects categories and other, more sensitive, subgroups were not analyzed
separately. Although children can, on the basis of mechanistic and
activity pattern arguments, be considered a sensitive group, they are
not necessarily the most sensitive.
Other sensitive groups listed in Table 5-3 not directly addressed by
the long-term studies include asthmatics, bronchitic subjects, the elderly,
and individuals with cardiopulmonary disease. Based on the summary of
-------
no
mechanisms and qualitative effects data in Section V, these groups would
appear most likely to respond to single or repeated acute exposures. They
should be largely protected against such effects by the 24 hour standard.
However, these as well as other sensitive groups in Table 5-3 may be subject
to additional potential effects of concern associated with long-term exposures
that were not adequately addressed in the studies used to derive ranges.
These potential effects include:
1) Direct or indirect effects on lung tissues contributing to develop-
ment or aggravation of emphysema, cardiopulmonary disease, and pneumoconiosis.
Controlled animal and human studies of the effects of acid aerosols on
clearance (Table B-5), community studies of high long-term exposures to
sulfur oxide-particle pollution (Table B-7), the occurrence of industrial
bronchitis with very high mineral dust exposure (Morgan, 1978), and the well
established effects of cigarette smoke suggest that long-term exposures to
repeated peaks of ambient particles, particularly acid aerosols, may play a
role in the etiology of chronic bronchitis, and ultimately aggravation of
emphysema and associated cardiopulmonary difficulties. Toxicologic studies
of high exposures to sulfuric acid/ammonium sulfate S02 aerosols (Table B-8)
and autopsies of humans and zoo animals (Table B-9) show that long-term
exposures to both acid aerosols and crustal dusts can damage or alter lung
tissues. Acid aerosols effects were related in one study to an incipient
stage of emphysema, while crustal dusts produce silicate pneumoconioses with
varying degrees of clinical significance. Although these qualitative data
generally involve exposures higher than any expected with the derived range,
the possibility of some risks at lower exposures should be considered.
2) Carcinogenesis - Cigarette smoking generally is recognized as the
major determinant of lung cancer. The available epidemiological evidence
-------
Ill
does not unequivocally show that current particle exposures contribute
to cancer nor does it rule out the possibility of some small contribution.
The presence of mutagens in organic particulate fractions from unidentified
sources and the potential interaction between these, as well as inert
particles, and carcinogens from cigarettes or occupational exposures
(Appendix B, Section E), suggest some need for caution and further study.
3) Premature Mortality - Regression analyses of long-term mortality
(Table B-ll) have been used to suggest effects of sulfur containing particulate
pollution. The criteria document discusses a number of inherent difficulties
and inconsistencies that preclude quantitative conclusions and limit their
qualitative use.
The available information does not suggest major risks for these effect
categories at current ambient particle levels in most U.S. areas. Nevertheless,
the risk that both fine and coarse mode particles may produce these responses
supports the need to limit long-term levels of TP for a variety of aerosol
compositions.
D. Summary of Staff Conclusions and Recommendations
The major staff conclusions and recommendations made in Section
VI. A-C above are briefly summarized below:
1. A separate general particulate standard remains a reasonable
public health policy choice.
2. The current TSP standard directs control efforts towards particles
of lower risk to health because of its inclusion of larger
particles which can dominate the measured mass concentration, but
which are deposited only in the extrathoracic region. A new
particle indicator representing those particles capable of
penetrating the thoracic regions (thoracic particles, TP)
-------
112
is recommended. The size range should include those particles
less than a nominal 10 ym and sampler performance criteria should
be related to respiratory tract deposition data.
3. Both short-term (24-hour) and annual arithmetic mean standards
are recommended. The short term standard should be expressed in
statistical form, the decision on allowable number of exceedances
should be made in conjunction with establishing a level for
the standard.
4. Based on a staff assessment of the short-term epidemiological data,
3
the range of 24-hour TP levels of interest are 150 to 350 yg/m .
Under the conditions prevailing during the London studies, the
upper end of the range represents levels at which effects are
likely in the sensitive populations studied. Given the uncertainties
in translating these results to U.S. conditions and the seriousness
of the potential health effects, the upper end of the above range
contains no identifiable margin of safety and should not be
considered as an appropriate standard alternative. The uncertainties
and the nature of the potential effects are important margin-of-
safety considerations. Neither the studies used to derive the
range nor more qualitative studies of effects in other sensitive
population groups (e.g. asthmatics, children), or effects in
controlled human or animal studies provide scientific support for
health risks of consequence below 150 yg/m . These qualitative
data as well as factors such as aerosol composition and exposure
characteristics should also be considered in evaluating margins
of safety associated with alternative standards in the range of
3 3
150 yg/m to something below 350 yg/m .
-------
113
5. Based on a staff assessment of the long-term epidemiological
data, the range of annual TP levels of interest are 55 to
•3
110 yg/m . The upper end of this range overlaps the somewhat
uncertain "effects levels" derived from these studies. Due to
q
these uncertainties, the upper end of the range (110 yg/m )
may not include any margin of safety, and should not be considered
as an appropriate standard alternative. The lower end (55 yg/m )
represents a level where some risk of symptomatic effects might
remain but no detectable differences in pulmonary function or
marked increases in respiratory diseases are expected. Increases
in symptomatic effects at the lower levels are uncertain and small
in comparison to baseline rates.
When evaluating margins of safety for an annual standard, it
is particularly important to examine the results of qualitative
data from a number of epidemiological, animal, and air quality
studies. These^suggest concern for effects not directly evaluated
in the studies used to develop the ranges. Such effects include
damage to lung tissues contributing to chronic respiratory
disease, cancer, and premature mortality. The available scientific
data do not suggest major risks for these effects categories at
current ambient particle levels in most U.S. areas. Nevertheless,
the risk that both fine and coarse particles may produce these
responses supports the need to limit long-term levels of TP for
a variety of aerosol compositions.
-------
Because of different form, averaging procedures and size range,
precise comparisons between the above ranges of TP standards and the
current primary TSP standards are not possible.* The lower bounds, taken
together, result in standards roughly equivalent in stringency to the
current standards. In general, the rest of the ranges represent varying
degrees of relaxation as compared with the current standards. At the
lower concentrations in the ranges much of the relaxation would result
because only smaller particle sizes would be collected. Thus, a city
where exceedance of the TSP standard was largely dominated by coarse
mode dust (with substantial mass of particles greater than 10 urn) would
be less likely to violate a comparable TP standard than would an area where
exceedance of the TSP standard was dominated by particles smaller than
10 urn. At higher concentrations in the above ranges, standards would
permit increased levels for TP as well as for larger particles.
*By applying observed TP/TSP ratios and other factors,3crude comparisons
can be made. The current annual TSP standard (75 ug/nu, geometric mean)
is roughly equivalent to an arithmetic mean of 50 ug/m as TP. The
numerical value of the 24 hour TSP standard (260 ug/m ) is roughly equivalent
to 140 yg/m TP, but this does not account for differences between the
arithmetic (current standard) and recommended statistical form.
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115
VII. CRITICAL ELEMENTS IN THE REVIEW OF THE SECONDARY STANDARD
This section discusses information drawn from the criteria document
that appears most relevant in the review and possible revision of secondary
standards for particulate matter. Four major categories of welfare effects
are examined. Within each category, the paper presents 1) a brief summary
of relevant scientific information, 2) an evaluation of potential quantitative
relationships between atmospheric particles and effects, and 3) a staff
assessment of whether the available information suggests consideration of
secondary standards that differ from the recommended primary standards.
Where applicable, preliminary staff recommendations are presented on the
most appropriate pollutant indicator and form of standards, in the event
the Administrator determines such standards are warranted.
A. Visibility and Climate
1. Nature of Effects
a) Visibility
i) Categories and Extent of Perceived Effects
Impairment of visibility is perhaps the most noticeable and best
documented effect of particles in current U.S. atmospheres. Although
often equated with "visual range" as measured by airport weather observers,
visibility in a broader context relates to visual perception of the environment
and involves color and contrast of viewed objects and sky, atmospheric
clarity, and the psychophysics of the eye-brain system (CD, p. 9-43 to 9-46).
For present purposes, it is useful to classify pollution-derived
effects on visibility into two categories: 1) regional haze and 2) visible
plumes. The nature and extent of these effects are determined largely by
the distribution and characteristics of anthropogenic and natural particles
-------
116
and, to a lesser extent, by NCL. Salient features of both categories are
outlined below.
Regional haze is relatively homogeneous, reduces visibility in every
direction from the observer, and can occur on a geographic scale ranging
from an urban area to multistate regions. Increased haze reduces contrast
causing more distant objects to disappear. Nearby objects can appear
"flattened" and discolored, the horizon sky is whitened, and scattered
light is perceived as a grey or brown haze (Charlson ejt a]_., 1978). When
urban light and haze combine at night, the contrast between the night sky
and the stars is reduced, markedly limiting the number of stars visible
in the night sky (Leonard et aj_., 1977).
Visual range (visibility) measurements at airports are a useful
indicator of the extent and intensity of regional haze. Analyses of
airport visibility trends from 1948 to 1972 suggest that while visibility
in some urban areas improved or stayed the same during the winter months,
the occurrence of episodic eastern U.S. regional haze with visibilities
less than seven miles appears to have increased. This later occurrence
has been most notable during the summer months (Husar et al_., 1980).
Since 1972, regional visibility in both the East and West apparently has
improved slightly but not to pre-1960 levels (Sloane, 1980; Marians and
Trijonis, 1979). Whether this recent improvement is related to more
favorable meteorology or reduced regional particle and sulfur oxide
emissions is not known with certainty, but such reductions are reflected
in emissions inventories in both East and West. Regional differences in
visibility are illustrated in Figures 7-la and 7-lb. As indicated by suburban
and non-urban airport data, visibilities in the East are substantially
-------
117
P: Based on photographic
photometry data
N: Based on nepAelonefry 4*ta
*: Based on uncertain extrapolation of
visibility frequency distribution
P: Based on photographic
photometry data
N: Based on nephelonetry data
*: Based on uncertain extrapolation of
visibility frequency distribution
Figure 7-1. Median 1974-76 visibilities(miles) and visibility isopleths for
suburban/nonurban airports: a) yearly and b) summertime (Trijonis and Shapland,
1979). Data are subject to uncertainties associated with suburban airport
observations, but show general regional patterns. The clear differences between
East and West are parallelled by regional humidity'(CD, Figure 1-17) and nonurban
fine particle levels. Summertime fine mass averaged from 22 to 25 iag/nr at 12
eastern nonurban sites (Watson et al., 1981) and about 4 ng/m3 for 40 Rocky Mountain
and southwest background sites "(Snelling, 1981).
-------
118
lower than in most of the West. Some of the difference between East and
West may be related to the lower regional humidity in the West, but a more
important difference is the generally higher regional particle loading in
the East. Based on: 1) long-term historical data in the northeast from 1889
to 1950 (Husar and Holloway, 1981); 2) examination of airport visibility
trends after deleting data possibly influenced by obvious natural sources
(fog, precipitation, blowing dust) (CD, p. 9-75); and 3) current assessments
of natural sulfur sources and regional fine particle levels (Galloway and
Whelpdale, 1980; Stevens et al_., 1980; Pierson et al_., 1980, Ferman et
al.. 1981), anthropogenic particulate pollution would appear to dominate
eastern regional haze. Relying on the analysis of Ferman jjt aj_. (1981),
the criteria document estimates that, in the absence of anthropogenic
sources, summertime visibility in the Shenandoah Valley would range between
60 and 80 km (36 - 50 miles) (CD, p. 9-63). The median daytime visual
range actually observed during the one month study at this site was 4 to 5
times lower (9 miles).
Visible plumes of smoke, dust, or colored gas obscure the sky or
horizon relatively near their source of emission (EPA, 1979). Black,
gray, or bluish plumes are caused by particles. Brownish plumes may be
carused by N02 or particles. Perception of plumes (and regional haze) is
strongly influenced by factors such as viewing angle, sun angle, and
background objects (CD, p. 9-46). Because visible particle plumes often
are subject to state and local opacity regulations and because it is
difficult to specify air quality standards to deal with elevated plumes,
the focus here will be on urban and larger scale regional haze.
-------
119
ii) Evaluation of Visibility
Visibility impairment may adversely affect public welfare in
essentially two areas: 1) the subjective enjoyment of the environment
(aesthetics, personal comfort and well-being); and 2) transportation
operations. As discussed in the criteria document, evidence on the
effects is drawn from studies of social perception and awareness of air
pollution, economic studies, and visibility/air transportation requirements.
These studies are discussed and evaluated in Appendix C. Key findings are
summarized in Table 7-1 and discussed below.
1) Early studies of social awareness (e.g., Schusky, 1966) have
found that as particulate pollution levels increase, an increasing
portion of the population is aware of air pollution and considers
it a nuisance. A more recent Los Angeles study (Flachsbart and
Phillips, 1980) found that of nine pollutant indices, only two,
visibility and ozone, were consistently and significantly related
to perceived air quality for all averaging times.
2) Economic approaches to evaluation of visibility include "iterative
bidding" and property value studies. Despite their limitations
for providing quantitative estimates, iterative bidding studies
(see Table C-l) suggest that visibility is of substantial
economic value in both urban and natural settings. Although
the value of visibility in other areas may vary significantly
from that suggested for the areas studied to date (chiefly the
rural southwest and Los Angeles), no a priori reason exists to
suggest that visibility is of little value in heavily populated
eastern urban areas or in widely visited eastern recreational
areas. The Los Angeles iterative bidding study (Brookshire et al..
1979) suggests that about 2/3 of the estimated willingness
-------
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121
to pay for visibility improvement was related to concern over
potential health effects.
3) Property value studies are less useful indicators of visibility
values, but when combined with perception and bidding studies,
the data suggest that visibility may have tangible effects on
property values in urban areas.
4) The available information indicate that the major effects of
visibility on transportation are related to air traffic,
particularly when visibility falls below three miles and FAA
restricts visual flight (VFR) operations. The data show that
episodic regional haze over large segments of the East tends to
curtail some segments of general aviation aircraft and slow
commercial, military, and other instrument flight (IFR) operations
on the order of 2-12% of the time during the summer. The
extent of any delays varies with airport. Reduced visibility
also may tend to increase risks associated with aircraft
operations in the mixing layer, but quantitative assessments
are not available.
b) Climate
The presence of particles that scatter and absorb light also may
affect climate. Principal effects of concern include:
1) Reduction of net solar radiation to the earth's surface—this
may lead to small local or regional reductions in temperature
and ultimately affect climate. Trends in atmospheric turbidity
(a measure of the reduction in the intensity of direct sunlight
reaching the ground) are qualitatively similar to those for
visibility (CD, Figure 9-37).
2) Enhanced cloud and fog formation, and possible increased preci-
pitation (CD, p. 9-95). Enhanced fog formation would add to the
adverse visibility effects discussed above.
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122
Because available information as summarized in the criteria document
does not permit quantitative assessment of the relationship between the
presence of particles and effects on climate, such effects, although poten-
tially of significance, cannot form the principal basis for a secondary
particle standard at this time. Nevertheless, because effects of particles
on climate and on visibility both appear to be dominated by fine particles,
the potential climatic effects would tend to provide support for decisions
based on visibility criteria.
2. Mechanisms and Quantitative Relationships
The more important studies in the criteria document on mechanisms by
which particles impair visibility and quantitative relationships between
particles and visibility are evaluated and discussed in Appendix C.
Key conclusions are summarized below.
1) Visibility impairment is caused by light scattering and absorption
by atmospheric particles and gases. Theoretical and empirical
results provide strong evidence that visual range reduction in
urban and regional haze normally is controlled by fine particles
(<2.5 ym). The only important situations where larger particles
dominate are some naturally occurring phenomena including
precipitation, fog, and dust storms.
2) The relative importance of scattering and absorption by particles
and the extinction (scattering and absorption) efficiency per
unit mass of fine particles vary with chemical composition and,
to some extent, humidity. Scattering dominates regional haze,
but absorption can be important in urban settings. As humidity
increases from 70 to 90%, fine particle scattering can increase
by a factor of about two.
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123
3) Two fine particle components, hygroscopic sulfates and elemental
carbon, generally tend to be the most important in reducing
visibility. Sulfate compounds with associated water often
dominate fine mass and light scattering, particularly in the
East, while elemental carbon accounts for most particle absorption
in urban areas.
4) Within reasonable limits, the Koschmieder equation (Equation C-l)
can be used to relate visual range and fine particle concentration.
To do this, the Koschmieder constant (K) must be estimated.
Available data (CD, p. 9-9) suggest that due to imperfect
techniques and observers, reported K varies from the commonly
used value of 3.9 (ranging from 1.7 to 3.6). Figure 7-2 illustrates
the Koschmieder equation for the standard K = 3.9 and a representative
range of fine particle extinction efficiency per unit mass
(Y). Cases are detailed in Appendix C.
3. Staff Recommendations
a) Rationale for Consideration of a Secondary Standard
Impairment of visibility over urban to multistate regions is
clearly an effect on public welfare as specified in the Clean Air Act.
The relationship of fine particles to visibility impairment in such cases
is known well enough to permit quantitative predictions of the ranges of
visibilities for given fine particle levels. Of initial concern is whether
the range of recommended primary standards would provide adequate protection
against these welfare effects. Rough estimates of visibilities associated
with alternative primary standards are listed in Table 7-2.
Precise comparisons of predicted visibility associated with primary
standard attainment with current airport visibility information are
difficult. It would appear, however, that none of the alternative
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60
30
ui
O
I
I
10
VISUAL RANGE - 3.9/c.,,,
AEROSOL. <80%RHO I
AEROSOL. 90X RH M m2A|)
AEROSOL. 90% RH (10 m2/|l
20
10
GO
75
100
126
160
FINE MASS CONCENTRATION. pg/mj
range as a function of fine mass concentration
Figure 7-2. Visual
(determined from equilibrated filter) and Y, assuming the "standard"
K = 3.9. Because K is commonly lower in non-ideal application,
results from this relationship should not be compared directly to
airport visibility data.
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TABLE 7-2. VISIBILITY ASSOCIATED WITH ALTERNATIVE PRIMARY STANDARDS
TP (< 10 um)
Standard
24-Hour
Annual
150
250
300
55
75
100
Range of Visibility (miles)*
1.9 -
1.1 -
1.0 -
8.4 -
6.2 -
5.2 -
6.2
3.8
3.1
16
12
10
*Range derived from application of relationship in Figure 7-2 with K =
3.9 and Y = 4 to 8 m /g. Comparable visibilities reported by airports
would be lower. For 24 hour cases fine mass/TP mass ratios are assumed
to range from 0.6 - 1. For annual cases the ratio was fixed at 0.6.
Primary standards are assumed to be just met throughout the viewing
distance. Because primary standards usually are directed at maximum
point measurements, this assumption tends to understate visibility
resulting from primary standard attainment. Nevertheless, it is not
clear whether control strategies directed at attaining TP standards
would reduce the fine fraction responsible for visibility impairment by
the same proportion as total TP mass is reduced. The effect of 24-hour
standard on annual visibilities was not evaluated. The annual values
are made less certain because natural impairment (fog, rain) is not
included and because the arithmetic mean particle mass was used to
derive visibility. These errors tend to be in opposite directions. The
visibility estimates for the annual standards are, therefore, best
interpreted as representative of "typical" days rather than as annual
averages.
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126
primary standards would materially improve regional visibility over current
levels unless attainment strategies included regional fine particle controls,
With the exception of the lower half of 24 hour values, most of these
alternative standards might permit some decrease in visibility, even in
the East.
The question then arises as to whether a separate secondary standard
is needed to limit further impairment of visibility or improve visibility
over levels permitted by the primary standards and other applicable
regulations. Unfortunately, reliable quantitative information on the
value of visibility on a national level is not available. Taken together,
however, the qualitative benefits of improving or maintaining visibility
summarized in Table 7-1 suggest that visibility values, although of
uncertain magnitude, are important in a variety of contexts. Because
of this, and the uncertainty as to whether the recommended primary standards
would provide adequate protection of public welfare with respect to these
values, the staff recommends that a visibility-related particle standard
be considered.
b) Factors to Be Considered in Selecting a Standard
In the event the Administrator decides to propose a secondary
standard, decisions will be necessary on the most appropriate pollutant
indicator, averaging time, form, and level of the standard. Preliminary
staff recommendations in each of these areas follow.
i) Pol 1utant Indicator
The indicator for the current secondary particle standard is TSP.
The available information shows that TSP is a poor indicator for particles
that impair visibility. The current secondary standard tends to focus
controls on coarse particles with little resulting benefit for visibility.
Alternative indicators for a visibility related secondary standard include:
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1) Direct measurements of visibility and long-path extinction through
a) human observers/photography
b) telephotometers
c) transmissometers
2) Measurement of the optical properties of the aerosol
a) Light scattering (nephelometer)
b) Light absorption (carbon analysis or transmittance)
3) Measurement of fine particles
a) Fine mass
b) Specific chemical components
Direct measurement of visibility is attractive in that it is directly
related to the effect, responds to changes in humidity (unlike heated
nephelometers), and provides long-path integration of pollutant impacts.
However, such measurements are labor-intensive, vary with observer, target
and atmospheric conditions, and are affected by natural phenomena such as
dust and fog as well as N0?. These limitations would make specifying
reference methods incorporating such approaches in support of particle-
based air quality standards difficult. Thus, direct visibility measurements
are not recommended as the principal indicator for standard compliance.
Measurement of the optical properties of the aerosol has a number of
advantages. Nephelometers are available and provide continuous readings
of light scattering by particles. The high correlation between fine mass
and light scattering suggests the nephelometer is a good indicator of fine
mass, and one that is somewhat sensitive to changes in composition that
tend to affect scattering. Although routine measurements for light
absorption are not yet available, promising methods are under development.
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In the case of regional haze, however, absorption is generally small and
measurements may be unnecessary.
Despite the advantages of nephelometers, it might not be wise to
recommend these as the principal measurement method at this time. To
date, they have been used principally by trained researchers. Large-scale
networks with routine quality assurance programs have not been tested.
Moreover, companion measurements of fine mass and composition probably would
be needed for source assessment. If, however, short-term (<24 hour)
average times become important, measurement of scattering by automated
nephelometer might be the most appropriate particle indicator.
Although fine particle mass measurements are less directly related to
visibility than scattering on an absolute basis, the two measurements are
highly correlated at most sites. Furthermore, the relationship between
fine particle mass and visibility is relatively straightforward. Fine
particle instruments are available and long-term (1 year) data exist from
at least three major networks (Pace e_t aj_., 1981; Cahill ejt aJL, 1981;
Watson et_ a]_., 1981). Compositional analyses of mass measurements provide
important insights as to the sources of the haze. Some obvious natural
sources (coarse dust, fog) are excluded by such measurements.
Because sulfates and carbon are often the most significant fine
particle components contributing to extinction, some consideration might
be given to their use as standard indicators. A sulfate standard would
direct control towards eastern regional visibility impairment, but have
little impact in most western urban areas. Carbon standards would direct
control towards urban areas, with little regional impact. Neither indicator
would include other fine particles. If all fine particles are to be
accounted for, specific substance indicators might be unnecessarily complex.
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Considering the practical constraints associated with large monitoring
networks and because fine mass may be better related to other welfare
effects of fine particles (e.g., soiling, materials damage), than optical
measurements, the staff recommends fine mass as the principal pollutant
indicator. On both practical and empirical grounds, the commonly used
DCQ of 2.5 pm for fine mass is acceptable. Fine mass measurements could,
in some cases, be supplemented by "equivalent" extinction measurements.
Because fine mass (and light scattering) instruments provide point
measurements, it is recommended that concentrations from several instruments
(three or more) be spatially averaged to provide a more reliable indication
of the long-path concentrations that are more directly related to visibility.
Separation of instruments should be on the scale of the desired visual
range.
Spatial averaging tends to minimize the chance of singling out point
source or urban "hot spots" of maximum concentration that are unimportant
on a regional scale. Addressing regional scale visibility problems
will require a fundamentally different control approach than has been used
in the past for TSP. Available information on composition, extinction, and
transport suggests that multistate regional scale control of the gas
phase precursors (notably SCL) of secondary aerosols would be considerably
more important than additional controls on traditional local primary
particle emitters (Lodge et a]_., 1981). A spatially averaged pollutant
indicator should facilitate focusing on the more important sources.
ii) Averaging Times
As indicated in Table 7-1, visibility impairment can be of
importance for hourly to annual (or longer) time scales. Although close
control of appropriate and practical short- and long-term averaging times
is important in establishing standards for protecting public health with
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an adequate margin of safety, it is less clear that multiple averaging
times are necessary for welfare effects such as visibility.
For control purposes, longer averaging times are desirable in that
effects of extreme weather and source conditions tend to be dampened.
To the extent that long-term average visibilities correlate with the
occurrance of the best and worst daily visibilities, a single long-term
standard may be sufficient. This indeed seems to be the case. The
evaluation of eastern airport visibility trends by Trijonis ejt jil_. (1978a,b)
and Trijonis and Shapland (1979) indicates similar trends in best tenth
percentile, worst tenth percentile, and median visibility. Figure 7-3
shows representative cumulative frequency plots for visibility. This
nearly linear relationship is found at most Eastern and Western sites
evaluated by Trijonis and co-workers (1978a,b). It thus appears that a
single averaging time for visibility should provide a reasonable index
for all averaging times. Spatially averaged fine particle levels may
follow different, but still predictable, distributions. Thus, if the
rationale for the standard were derived largely from a short-term effect
(e.g., airport operation) a longer term standard could be specified to
provide adequate protection within predictable statistical limits.
A seasonal averaging time may represent the most reasonable indicator
of both long-term and short-term visibility values. Additional supporting
factors include: 1) visibility in the eastern U.S. has a strong seasonal
character; 2) the greatest impacts on recreation and transportation
occur in the summer months; and 3) regional models currently under
development can deal with seasonal averages better than with daily
averages. The staff therefore recommends a calendar quarterly (three
month) averaging time for a secondary visibility based standard. The
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15 —
uo
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132
standard should be expressed in statistical form such that seasonal
(quarterly, e.g., summer) values are compared for multiple years. This
tends to smooth variability due to natural fluctuations in seasonal
meteorology from year to year.
i i i) Level of the Standard
The available data on the value of visibility (both aesthetic and
transportation related) provide no clear guidance for an acceptable level
of a standard. In arraying the elements of the decision, it is helpful
to focus on those aspects of visibility impairment where national air
quality standards appear most useful.
A major difficulty in selecting a national standard is evidence
that both the extent of visibility impairment and the value people place ^
on visibility vary widely with affected populations, region of the
country, and settings within each region. Therefore an air quality
standard cannot reasonably address all facets of the visibility problem <
equally. In particular, a standard that would maintain current visibility
levels in the rural West (< 3-5 ug/m ) might require lower than natural
background levels in the East. Fortunately, other Clean Air Act mechanisms I
directly and indirectly address visibility.* These clearly provide the
Administrator with the flexibility to deal directly with visibility in
sensitive non-urban areas of the West. Thus, the level of any secondary 4
fine particle standard might best be directed at establishing desirable
visibility goals for those regions in the East affected by large scale
*The prevention of significant deterioration (PSD) provision of the CAA establishes
limits on particle (and other pollutant) increases over "baseline" conditions.
Certain "class I" areas (e.g., national parks, wilderness areas) where
visibility is an important value receive special PSD and visibility protection.
The interaction among these and other CAA regulatory mechanisms that affect
visibility is further discussed in Chapter 7 of Protecting Visibility: Ajri^ <
EPA Report to Congress (EPA, 1979).
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regional haze of multistate origin and those major western urban centers
affected by haze predominately of local origin.
The level of any standard must be based on the judgment of the
Administrator after considering the available evidence on both aesthetic
and transportation effects as well as other welfare effects associated
with fine- particles. Long or short-term visibility impacts of alternative
seasonal fine mass standards can be estimated using the relationships
and assumptions outlined previously. Empirical boundaries for standards
can be estimated from the available technical data. One reasonable
upper bound might be derived from the desire to ensure that eastern
regional visibility does not become significantly degraded over current
levels. Based on measurements from 12 non-urban eastern sites (Watson
e_t al_. , 1981) as well as estimates based on typical summer time visibility
(Figure 7-lb), spatially averaged seasonal fine particle levels
of 22-25 yg/m would tend to maintain the status quo. Typical urban
scale fine particle levels are about 5 yg/m higher in the East (see Table
4-3). Due to the limited number of sites and years of data, these
estimates obviously are uncertain. Available summertime fine particle
levels from non-urban sites of three research networks are depicted in
Figure 7-4.
An absolute, but unattainable, lower bound can be derived from the
criteria document's estimate of natural background visibility in the
East. Based on the assumptions in the criteria document (CD, p. 9-63)
and the data of Ferman et^ al_. (1981) estimated natural background fine
3
particle levels in the East are 6-10 yg/m . As noted earlier, this
corresponds to visibilities of 60 - 80 km, or 3 - 5 times greater than
current levels. These estimates are quite uncertain, but the basic
assumptions do not appear likely to underestimate natural contributions.
o
The mid-point (8 yg/m ) might serve as a single lower bound.
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135
The upper and lower bounds for a seasonal (three month) fine particle
3
standard thus derived are 8-25 yg/m, spatially averaged over distances
on the order of 16 - 50 km. The range is perhaps surprisingly narrow.
Nevertheless, as illustrated in Figure 7-2, visibility is extremely
sensitive to fine particle levels in this range. If visibility benefits
were proportional to "typical" annual visual range, then marginal benefits
would increase with decreases in fine particle concentrations.
B. Materials Damage and Soiling
1. Description of Effects
The deposition of airborne particles can become a nuisance, degrade
aesthetics and material usage through soiling and may contribute directly,
or in conjunction with other pollutants, to structural damage by means of
corrosion or erosion. The nature of these effects is discussed below
and the relative importance of particle size, composition, and other
environmental factors such as moisture, temperature, sunlight, and wind
also is considered.
a) Materials Damage
Particles affect structural materials principally by promoting and
accelerating the corrosion of metals, the degradation of paints, and the
deterioration of building materials such as concrete and limestone.
Particles exhibit these effects because of their electrolytic, hygroscopic,
and/or acidic properties, and their ability to sorb corrosive gases. Our
review suggests that only chemically active fine mode or hygroscopic coarse
mode (mainly sea or road salt) particles materially contribute to such
effects (CD, p. 10-41).
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136
While particles have been qualitatively associated with damage to
paints and building materials, there are insufficient data at present to
relate such effects to specific pollutant levels. With respect to the
corrosion of metals, field studies (Mansfield, 1980; Haynie and Upham,
1974; and Upham, 1967) have not established a quantitative relationship
between particles and corrosion (CD, p. 10-41). This may be explained by the
presence of sulfur dioxide which, in combination with sufficient moisture,
dominates the corrosion rate to such extent that an independent effect of
particles is not evident (Yocom and Grappone, 1976). The available data
do not clearly suggest major effects of particles on materials for
concentrations at or below the ranges recommended for the primary health
standards, but to the extent damages occur, they are more likely associated
with active fine particles. Potential materials damage effects thus may
provide ancillary support for a fine particle secondary standard.
b) Soiling
Soiling is the accumulation of particles on the surface of an exposed
material resulting in the degradation of its appearance. When such
accumulations produce sufficient changes in reflection from opaque
surfaces and/or reduce light transmission through transparent materials, the
surface will become perceptibly dirtier to the human observer. At higher
loadings, the effect will be detectable by touch. In a subjective
perception/values study, Hancock ert al_. (1976) determined that "dirtiness"
for a flat surface would occur when the accumulation of dust particles is
sufficient to cover 0.7% of the material's surface under conditions of
maximum contrasts (e.g., black on white or vice versa). Similar studies
have not been reported for other soiling effects.
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137
Despite the numerous observations that airborne particles soil a
wide range of man-made materials, there is only limited information
available with respect to the size and composition of the culpable parti-
cles. In general, the soiling of fabrics and vertical surfaces
has been ascribed to fine particles, particularly dark carbonaceous
materials. Soiling of horizontal surfaces may result from deposition of
a wide range of particles, including coarse mode dusts.
Theoretically, coverage of horizontal surfaces will be related to
particle surface area and deposition velocity. Particle surface area per
unit mass decreases linearly with diameter (assuming spherical particles),
while, under quiescent conditions, deposition velocity increases with
the square of the diameter. Under such conditions, large particles would
result in more soiling than an equivalent mass of smaller particles. Although
second order effects may enhance fine particle deposition relative to larger
particles, the deposition velocity data in Chapter 6 of the criteria document
still suggest substantially higher deposition on horizontal surfaces for
particles larger than 10 pm than for smaller particles.
The increasing soiling potential associated with increased particle
size is mitigated by lighter particle color, smaller transport distance
from sources, and markedly lower penetration of larger particles to indoor
surfaces (relative to smaller particles). Alzona et^ al_. (1979) concluded,
on the basis of their study of indoor/outdoor element ratios, that indoor
exposure to outdoor dust would be reduced by two-thirds with the doors and
windows partially closed (CD, p. 5-127). Because these conflicting factors
have not been quantitatively evaluated, it is not possible to make clear
particle size divisions with respect to soiling of horizontal surfaces.
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138
The time interval that it takes to transform horizontal and vertical
surfaces from a clean to a perceptibly dirty state is generally determined
by particle composition and the rate of deposition. This process also is
influenced by the location and spatial alignment of the material, the
texture and color of the surface relative to the particles, and meteoro-
logical variables such as moisture, temperature, and wind speed.
2. Quantitative Associations
a) Soiling/Property Values
The effect of particles on aesthetic quality depends in part on human
perception of pollution. The reduction of aesthetic quality may arise from
the soiling of buildings or other objects of historical or social interest
or by the mere dirty appearance of the neighborhood. A number of studies
have indicated that such perceptions of neighborhood degradation are
revealed indirectly through effects on the value of residential property.
That is, when residential properties similar in other respects are com-
pared, the properties in the more highly polluted areas typically have
lower value.
Freeman (1979a), reporting on 14 property value studies that used
particulate matter or dustfall as one of their pollutant measures, noted
that the results generally supported the premise that property values are
affected by the full range of particle pollution. He cautioned, however,
that direct comparison of the monetary results is not possible since the
studies cover a number of cities, use different data bases, empirical
techniques, and model specifications.
The extent to which the city specific results represent soiling as
opposed to perceptions of the effects of particles on health and visibility
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139
is not clear. Therefore, the results of studies such as those described
above cannot provide reliable quantitative estimates of the effects of
soiling on property values.
b) Soiling/Household Cleaning
Airborne particles soil a wide range of materials in all sectors of
the economy. Assuming that these sectors are not as well off in a dirtier
state as a cleaner one, soiling will result in an economic cost to society.
While the household sector has been examined by a number of investigators,
their results have been questioned because of methodological problems and
their failure to appropriately address particle size, composition, and
deposition rates. As a result, no single study has produced a completely
satisfactory estimate of soiling costs for the household sector. It is
unfortunate that little or no effort has been expended to account for
soiling costs in the commercial, manufacturing, or public sectors. For
example, preliminary results from Manuel e_t jil_. (1981) suggest that the
omission of the manufacturing sector alone could result in a significant
understatement of soiling costs due to particle pollution.
In its review of effects of household soiling, the criteria document
relied principally on Booz, Allen, Hamilton (1970), Watson and Jaksch
(1978, 1982), and Freeman (1979b) to derive estimates for both household
soiling costs in 1970 and the benefits that accrued in 1978 as the
result of reduced total suspended particulate (TSP) levels. For the year 1970,
the estimate for amenity loss due to exterior household soiling was estimated
to range from 1 to 3.5 billion dollars (1978 dollars). The 14 yg/m reduction
in U.S. annual TSP levels between 1970 and 1978 was estimated to have
resulted in an annual benefit for the year 1978 of 0.2 to 0.7 billion
dollars or 14 to 50 million dollars for each yg/m3 of reduction (CD, p. 10-73).
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140
These estimates obviously are rough and mainly provide an indication
that substantial costs may be associated with particle related soiling.
Some of the important limitations include:
1) The exclusion of interior household soiling costs from these
estimates would tend to bias the results downward since the
analysis did not address the soiling effects of those smaller
particles that readily penetrate the indoor environment (CD, p.
5-131).
2) Even for estimating exterior soiling costs, the use of TSP may be
a poor pollutant indicator. As noted earlier, the soiling of
vertical surfaces generally have been ascribed to fine particles
while the soiling of horizontal surfaces may result from the
deposition of a wide range of particles, including coarse
dusts. Moreover, national average TSP readings may be a poor
surrogate for actual exposures.
3) The basic data on costs and frequency of performing household
cleaning and maintenance tasks used in the studies relied on
were derived for Philadelphia and may not be readily transferable
to other parts of the country.
4) The studies relied on had both positive and negative biases which
cannot be assumed to cancel out, thus adding additional uncertainty
to the final estimates.
3. Staff Recommendations
It is clear that at high enough concentrations, the full size range of
particles including dustfall can contribute to soiling, become a nuisance
and result in increased cost and decreased enjoyment of the environment.
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141
The available data are limited, however, and do not permit any definitive
findings with respect to the economic costs or other response functions
associated with particle soiling or provide clear quantitative relationships
between ambient loadings and soiling. The limited data do suggest, however,
that soiling costs can be significant.
The key question is whether the recommended range of primary standards
would provide adequate protection against these effects. Much of the range
of primary standards would appear to permit increases in TSP loadings.
Thus, the staff recommends consideration of the economic and other effects
associated with soiling and nuisance when determining whether a secondary
standard for TP or for TSP or other large particle indicator is desirable
to supplement whatever soiling benefits accrue from the primary health
standards. Because fine particles are a significant contributor, soiling
effects also should be considered in determining whether a fine particle
secondary standard is needed. Given the uncertainties in the data,
recommendations on ranges of interest are not appropriate at this time.
C. Vegetation Damage
1. Description of Effects/Relationships
Controlled laboratory and crop field studies indicate that current
levels of "general" particulate matter are relatively unimportant from the
standpoint of vegetation damage. Controlled laboratory studies have
associated vegetation damage only with very high particle dustfall rates
of insoluble particles (Lerman and Darley, 1975; NAS, 1977a). Field
studies near emission sources have reported injury to vegetation following
exposures to high dustfall rates of general particulate matter or specific
phytotoxic substances that may be found in particulate matter (EPA,
1975a; Lerman and Darley, 1975; NAS, 1977a).
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142
Controlled exposure studies of insoluble dusts (e.g., cement dust)
indicate that the accumulation of particulate matter on leaf surfaces can
result in damage to vegetation when particle dustfall rates are very high.
Although some leaf injury from insoluble particles may result from reduced
light transmission to the leaf surface following heavy particle accumulation
on leaf surfaces, the more likely cause of leaf injury from insoluble
particles is from particle lodging/penetration in stomatal apertures.
Partial stomatal occlusion by particles could alter normal gas exchange
patterns resulting in reduced carbon dioxide uptake during the day when
plants fix carbon dioxide into carbohydrates. Since most stomatal apertures
are less than 10 ym long and 4 urn wide when open (Esau, 1960), particle
lodging/penetration should become more efficient as particle sizes approach
2
those that can fit into stomatal apertures. Plant exposure to 0.6 g/m /day
2
(~500 tons/mi /mo) of cement dust ("most" of the dust represented particles
less than 10 urn) for 8-10 hours/day is the lowest exposure regime reported
to produce a physiologic response (a reduction in carbon dioxide uptake).
Foliar injury was reported at higher exposure regimes in this study (Darley,
1966).
Field studies of the effects of cement dust on citrus trees have
reported foliar injury, damage to fruit, and reduced yield at high
2
dustfall rates (about 290 tons/mi/mo) that were observed around 1900
(Parish, 1910). Since deposition rates substantially less than about 75
2
tons/mi /mo have generally been observed even in the more polluted urban
areas of the United States in the 1960's (DHEW, 1969), it is unlikely
that plants would be injured by the lower particle deposition likely to
be found today. Exceptions could occur in proximity to strong point
sources.
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143
Plants have, however, been shown to respond to exposure from relatively
high concentrations of specific phytotoxic substances that are sometimes
found in particulate matter. The entrance of such particles into plant
tissues is facilitated when such particles are small enough to penetrate
stomatal apertures or when soluble materials are deposited in the soil
and absorbed by plant roots (Brady, 1974). In addition, some components
of particulate matter (especially soluble fractions) that are deposited
on leaf surfaces could subsequently penetrate to the leaf interior.
Substance specific toxicity has been reported in plants following exposure
to arsenic (Linzon, 1977), boron (Kupra and Kohut, 1976), fluorides (Lerman
and Parley, 1975), soot (Lerman and Darley, 1975), zinc (Yopp ejt al.,
1974), and other substances.
2. Staff Recommendations
Recognizing that specific toxic particulate substances that may affect
public welfare generally are found only in trace quantities except near specific
sources, regulatory mechanisms other than the national ambient air quality
standards (e.g., section lll(d)) are used to regulate specific toxic substances.
The effects of fine acid aerosols on vegetation should be considered as a
part of the acidic deposition phenomenon.
In view of the lack of any clear effect of particle exposure that
is not composition specific on plants at current particle levels, the
staff concludes that a secondary particle standard is not needed to
protect vegetation.
D. Personal Comfort and Well-Being
Because the effects of thoracic deposition, including the production
of health related symptoms causing discomfort, are incorporated in the
primary standard discussion and recommendations, this assessment will focus
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144
on direct effects of extrathoracic and extra-respiratory particle deposition
on personal comfort.
1. Description of Effects, Quantitative Data
A controlled exposure study found that discomfort is proportional to the
concentration of dust and that symptoms can be produced by "inert" (carbon
impregnated plastic) particles deposited in the nose and throat (Andersen
ejt al_., 1979). Subjects were young, healthy adults characterized as nose
breathers, and were at rest during exposure. Symptoms from extrathoracic
particle deposition included dryness of the nose, pharynx, and throat and other
mild symptomatic responses. Particle size was about 9-11 pm (MMAD) with 30% of
the mass larger than 12.4 ym. The lowest reported concentration associated with
o
symptomatic effects was 2 mg/m (Andersen ejt al_., 1979). Although the sympto-
matic response to dust exposure was noted one to two hours following the
beginning of the dust exposure, available subjective information indicates that
discomfort was mild.
In high enough concentrations, large particles such as wind blown dust
or cinders also might cause discomfort through impact!on on the eye or
skin (extra-respiratory deposition). The scientific literature summarized
in the criteria document, however, provides no basis for evaluating the
concentrations at which such effects might occur.
2. Staff Recommendations
The available information suggests that particles might affect personal
comfort at total particle concentrations in excess of 2 mg/m for short
exposure (2 hour) periods. The data are, however, extremely limited, and
not unequivocally associated with larger particles. Although it is reasonable
to suggest that high dust concentrations are a nuisance that affects personal
comfort, the available data provide no clear evidence as to what concentrations
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145
of larger particles not included in the primary standards might be of
concern. The data in the criteria document in this area thus provide
little support for a TSP or other large particle indicator secondary standard
based on soiling and nuisance effects discussed in Section VII.B.
E. Acidic Deposition
On August 20-21, 1980, the Clean Air Act Scientific Advisory Committee
(CASAC) concluded that the issue of acidic deposition was so complex and
important that a significantly expanded and separate document would be
necessary if NAAQS were to be selected as a regulatory mechanism for control
of acidic deposition. CASAC noted that a fundamental problem of addressing
acid deposition in a criteria document is that acidic deposition is pro-
duced by several pollutants (including oxides of nitrogen, oxides of sulfur,
and acidic fine particles). Consequently, a document on acidic deposition
would include various pollutants contributing to wet and dry deposition.
The Committee also recommended that a revised version of the acidic deposition
chapter be retained in PM/SO and NOV criteria documents. In response to
A X
these recommendations, EPA is in the process of developing an acidic deposi-
tion document that will provide a more comprehensive treatment of this
subject. Thus, the issue will not be directly addressed in this staff
paper.
F. Summary of Staff Conclusions and Recommendations
Major staff conclusions and recommendations made in Section VII.A-E
are summarized below:
la) Impairment of visibility by fine particles over urban to multi-
state regions clearly affects public welfare. Fine particles or
major constituents thereof also are implicated in climatic
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146
effects, materials damage, soiling, and acid deposition. Neither
the current TSP secondary standard nor the recommended ranges of
TP standards will protect visibility in an effective manner. The
staff, therefore, recommends consideration of a fine particle
secondary standard, based primarily on the relatively well defined
quantitative relationships between fine mass and visibility.
b) If a fine particle standard is selected, a seasonal (calendar
quarter) averaging time could provide a statistically stable target
and yet achieve most short or long-term visibility goals. Considera-
tion should be given to specifying a spatial average of three
or more monitors placed at distances on the order of 16-50 km.
c) Despite the fact that the public is concerned about visibility
and is willing to pay something for clean air, quantitative bases
for evaluating visibility goals have not been established. Therefore,
the level of any standard must be based on the judgment of the
Administrator after consideration of aesthetics, transportation,
as well as non-visibility related effects. The staff recommends
that any national standards focus on welfare effects associated
with multistate eastern regional (and western urban) haze. Such
standards would not of themselves protect sensitive scenic areas
of the West, but these areas are directly and indirectly addressed
by other provisions of the Clean Air Act.
d) Empirical ranges for standards can be derived from approximate
estimates of eastern natural background and current summertime fine
particle levels. The range thus derived is 8-25 ug/m , seasonal
and spatial average. The upper portion of the range would tend to
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147
maintain the status quo in the East. Because the lower
portion of the range approaches natural background levels,
standards set at the lower levels would be, in all practicality,
unattainable in most of the Eastern U.S.
e) Because regional fine particles in the East appear to be
influenced most strongly by sulfates, adoption of a fine particle
standard would trigger a substantial departure from current approaches
to particle control strategies. The evidence suggests that multistate
control of regional sulfur oxide emissions might be needed to reduce
fine particle levels. Thus, fine particle/visibility-climate effects
are linked to acid deposition, and these problems would likely be
ameliorated by similar control strategies. Addressing these
welfare effects with a common standard or control strategy is likely to
be more efficient than establishing separate control approaches for
»
each. Appropriate scientifically based targets and control
strategies for acid deposition are not yet available.
2) Although potential effects on climate support the consideration of
a fine particle standard, quantitative relationships are not well
enough developed to provide the principal basis for selecting the
level of the standard.
3) Consideration should be given to soiling and nuisance effects in
determining whether a secondary standard for TP or for TSP or some
other large particle indicator is desirable to supplement the
primary health and secondary fine particle standards. The available
data base on such effects is, however, largely qualitative.
Therefore, the basis for selecting a particular level for a
secondary TP or TSP standard is a matter of judgment.
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148
4) While chemically active fine mode and hygroscopic coarse mode
particles have been qualitatively associated with materials damage,
the available data do not clearly suggest major effects of particles
on materials for concentrations at or below the ranges recommended
for the primary health and secondary visibility standards. Therefore,
a secondary standard based solely on materials damage is not
recommended.
5) The staff concludes that a secondary particle standard is not
needed to protect vegetation.
6) The acid deposition issue will not be addressed directly in the
review of the particulate matter standards.
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APPENDIX A. FACTORS THAT INFLUENCE DEPOSITION AND CLEARANCE OF PARTICLES
This material briefly summarizes subject related and environmental
factors that affect deposition and clearance of particles, and supports the
discussion in Section V A.1 of this paper.
A. Inhalation Patterns
The most important aspects of inhalation pattern are flow rate,
breathing frequency, and whether breathing is through nose, mouth, or
both. Nasal breathing results in nearly complete extrathoracic deposition
for all particles larger than about 10 pm, with removal efficiency
decreasing to less than 10% for particles less than 1 urn (CD, p. 11-23).
In contrast, extrathoracic deposition of 10 pm and 1 ym particles for
mouth breathing is about 65% and 2%, respectively (CD, p. 11-23). As
illustrated in Figure 5-1, mouth breathing enhances the availability of
> 1 pm particles for deposition in the alveolar and tracheobronchial
regions. Because the mouth can release substantial quantities of
endogenous ammonia, mouth breathing may provide partial protection from
airborne acids by ammonia neutralization (Larson et_ ajL, 1977).
Except in the case of blockage of the nasal passages by mucus or other
obstruction, typical "mouth" breathing is better characterized as "oronasal"
breathing, since the larger portion of the inspired air does pass through
the nasal passages. Therefore, experimental deposition studies as summarized
in Figure 5-1 that use mouth piece only breathing may tend to overestimate
thoracic deposition for oronasal breathing at rest. Approximately 15% of the
population are habitual oronasal or mouth only breathers (Saibene et aj_., 1978;
Niinimaa et. aj_., 1981). Anyone may shift to oronasal breathing during
conversation, singing, illness related congestion, and exercise. Most
-------
A-2
people shift to oronasal breathing at flow rates greater than 30-35 I/minute
(Ninnimaa e_t al_., 1981), which is equivalent to moderate exercise as in walking
briskly or bicycling (Cotes, 1979). At these flows, the quantity of air
passing through the mouth is greater than that used in resting, mouth only
deposition studies. Thus, results of such studies might not overestimate
deposition for exercising conditions with oronasal breathing.
Increased flow rates also increases impaction related deposition in
all regions and apparently speeds mucuciliary clearance (Wolff et^ al_., 1975).
The generally increased extrathoracic and tracheobronchial deposition
efficiency in the 2-10 ym range, reduces the alveolar deposition efficiency
in this same range (Heyder et_ a]_., 1980; Stahlhofen £t al_., 1980). Nevertheless,
because of increased intake, as well as a shift to mouth breathing, total
dose to the alveolar region may increase with exertion related increases
in flow rate. For example, Heyder et_ al_. (1980) found that the alveolar
deposition efficiency (mouth breathing) for a 5 ym particle was about
3
0.4 at a flow rate of 250 cm. At three times the flow rate, with constant
breathing frequency, the efficiency dropped to 0.3, but alveolar dose/unit
time would be increased by a factor of about 3 x 0.3/0.4 = 2.2.
B. Subject Airway Dimensions, Disease State
Size, shape and branching of the airways and other airspaces markedly
affect deposition of particles (Palmes and Lippmann, 1977). Evaluation of
available data reproducibility of individual deposition curves (Chan and
Lippmann, 1980) and studies of identical twins (Bohning et_ al_., 1975) suggest
that much of the variability observed in various deposition studies is largely
due to anatomical differences among subjects. Among normal adults total
respiratory deposition can vary by a factor of 4 (lowest to highest)
(Giacomelli-Matoni et al., 1972). Although the criteria document
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A-3
reports no deposition studies on children, it is reasonable to expect
that the smaller airway dimensions in children would result in rela-
tively greater impaction related deposition in the tracheobronchial and
extrathoracic regions than in normal adults.
Disease states or other conditions that constrict, inflame, or cause
mucous build-up in the airways can substantially increase tracheobronchial
deposition (Lippmann et_ aj_., 1971). Otherwise normal cigarette smokers
have somewhat increased bronchial deposition (Lippmann et_ al_., 1971), and
greatly enhanced bronchial deposition was seen in chronic bronchitics and
asymptomatic asthmatics (Albert «rt al_., 1973). Over a size range of 1.5 to 6
urn, deposition was up to a factor of 5 greater than the upper bound of the
normal range.
Clearance rates for deposited materials also varies substantially among
normal healthy adults (Yeates et_ aK, 1975). Studies of bronchial clearance
in patients with chronic lung disease have reported transport rates
which were faster, slower, and similar to those of healthy adults (NAS,
1977a). Within the tracheobronchial region the nature of the branching
airways also results in nonhomogeneous deposition patterns. Of par-
ticular significance are the observations and calculations indicating
increased deposition at "hot spots" located around the carina of airway
bifurcations (Bell and Fried!ander, 1973; Schlesinger and Lippmann,
1978). The latter authors were able to demonstrate a correlation of
upper airway deposition patterns and reported incidence of bronchogenic
carcinoma. Effects at the bifurcations also may be enhanced due to
potentially slower clearance rates (Hilding, 1957).
C. Aerosol Composition
Aerodynamic diameter, chemical composition, and shape are among the
more important particle specific parameters affecting deposition. The
-------
A-4
importance of initial aerodynamic diameter is illustrated in Figure 5-1.
A substantial fraction of ambient aerosol consists of hygroscopic acids or
salts (e.g., sulfuric acid and sulfates, sea salt). As noted in Section IV,
as humidity increases, these substances accumulate water and increase in
size. The respiratory tract humidity of inspired air nears 100% in the
vicinity of the nasopharyngeal cavity, and the residence time of smaller
aerosols is sufficient to allow growth by a factor of 2 to 4 (Perron, 1977;
Tang, 1980). Evidence of such growth is provided by Utell et al_. (1981)
who measured total respiratory tract deposition after oral inhalation of
several sulfates and sodium chloride, initially of 0.5-1.0 ym aerodynamic
diameter. Total deposition efficiency (.55 - .65) was much higher than
expected for the initial size, and was in the range expected for 2-4 urn
particles (Figure 11-4, CD).
Growth of ambient hygroscopic aerosols in the fine mode would be
expected to enhance deposition in all three regions of the respiratory
tract. Because total deposition increases rapidly with sizes above
about 1-2 um, increased deposition resulting from hygroscopic growth of
a factor of 2 to 4 would be most important for accumulation mode particles
larger than about 0.4 um. Neutralization of acid aerosols by endogenous
ammonia decreases with larger particle size (Larson ejt al_., 1982).
Gaseous components of pollutant atmospheres, as well as irritant particles
can affect particle deposition by causing bronchoconstriction (Lippmann, 1977).
As noted above, airway constriction tends to markedly increase tracheobronchial
deposition. Among the more prevalent irritant gases that occur in combination
with particles in U.S. atmospheres are ozone, sulfur dioxide, nitrogen
dioxide, and formaldehyde. As discussed in Section V.A., a number of
particulate substances may cause bronchoconstriction.
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APPENDIX B. EVALUATION OF EVIDENCE FOR EFFECTS OF CONCERN
This section discusses and evaluates the key studies providing evidence
on the kinds of effects that might reasonably be anticipated to result from
exposure to atmospheric particles. As outlined in Section V-B, the principal
effects of concern include:
1) Respiratory mechanics and symptoms;
2) Aggravation of existing respiratory and cardiovascular disease;
3) Clearance and other host defense mechanisms;
4) Morphological alterations;
5) Carcinogenesis; and
6) Mortality.
Because of the complexity of the data base and lack of clear quantitative
relevance to general populations, the criteria document lists but does
not discuss a number of occupational studies and reviews that may be of
qualitative interest. The staff has evaluated a number of these documents
and has selected those of interest for discussion in this section.
These results are illustrative of the kinds of responses that can be
elicited in groups usually characterized as normal, adult healthy males
after prolonged high exposures to a variety of different "inert" dusts
and reactive particle classes. Although significant weight is not given
to these studies in the following discussions, they are listed in Table
B-l as supportive material.
A. Respiratory Mechanics and Symptoms
A number of functional measurements are used to indicate altered mechanical
and flow attributes of the respiratory tract following pollutant exposures.
Effects on respiratory mechanics and function can range from mild transient
changes of little direct health significance to incapacitating impairment of
breathing. Mild effects in normal subjects may indicate potentially more
-------
B-2
TABLE B-l. RESPIRATORY DISEASES AND RELATED IMPAIRMENTS
ASSOCIATED WITH OCCUPATIONAL EXPOSURE TO PARTICLES
Biological Endpoint
1. Deterioration of lung capacity/
Pulmonary Function Decrement
2. Bronchitis
3. Asthma
4. Pneumoconiosis
4a. Si li cos is
4b. Sili cosis and Mycobacterial
Infection (e.g., Tuberculosis)
5. Pulmonary Fibres is
6. Byssinosis
7. Mesothelioma and Respiratory
Cancer
Particle
Coal Dust
Carbon Black
Cotton, Flax and
Hemp Dust
Grain Dust
"Coal Dust
Grain Dust
Grain Dust
Coal Dust
Slate Dust
Free Silica Dust
(sandblasting)
Kaol i n
Mica and Quartz
(slate)
Free Silica Dust
Granite Dust
Asbestos
Cotton, Flax and
Hemp Dust
Asbestos
Arsenic
Coke Oven
Emissions
Reference
Lapp et al ., 1972
Morgan, T9~78
Valic et al.. 1975
NIOSH, 1975b
Dosman et al. , 1980
Morgan, 1978
Dosman et. al. , 1980
Dosman et. sK , 1980
Morgan, 1978
Glover et al. , 1980
Ziskind et al., 1976
Ziskind et aj_. , 1976
Ziskind et aj_., 1976
Ziskind et al., 1976
Craighead and
Vallyathan, 1980
NIOSH, 1976
NIOSH, 1975b
NIOSH, 1977
NIOSH, 1975a
NAS, 1972
-------
B-3
serious responses in more sensitive subjects. Symptomatic effects such as
coughing, wheezing, or bronchospasm also vary in severity, but at minimum
are indicative of a biological response. This section discusses the effects
of specific particulate components and community aerosols on respiratory
mechanics and symptoms.
1. Sulfates and Other Water Soluble Aerosols
Sulfate compounds are among the most widely tested particulate components
in animal and human controlled exposure studies. Studies of these and
other soluble aerosol substances provide some clues to their relative
irritant potential and factors that affect responses.
Unfortunately, animal studies of sulfur-containing acid aerosols
(sulfuric acid, ammonium bisulfate) may be seriously compromised by the
presence of high chamber ammonia which may partially or fully neutralize
the acidity. The problem of neutralization is most serious in long-term
studies where both exhalation (Larson et_ a_l_., 1977) and the accumulation
of excrement (Malanchuk et_ aJL , 1980) contribute to chamber ammonia.
Short or long term studies that do not explicitly deal with this problem
by measurement or other approaches do not provide reliable quantitative
assessments of the effects of acid aerosols alone. In some short term
studies, neutralization may be reduced to some extent by systems that
use head only exposures and should not be compromised by excrement
ammonia (e.g., Amdur and Mead, 1955). Even in well designed studies,
however, it is difficult to determine the reliability of reported
sulfuric acid and bisulfate levels, due to possible differences in
exhaled ammonia between animals and people (Larson et jil_., 1977).
A number of experiments have been conducted in guinea pigs to rank
the relative respiratory irritancy potential (as measured by airway
-------
B-4
resistance) of sulfuric acid and other sulfates by size and species.
Amdur and co-workers report that the relative irritancy increases as
particle size decreases but only at lower concentrations (Amdur, 1958).
However, observations of animal response at higher concentrations than
in this study indicate that increases in airway resistance are greater
for 2.5 than for 0.8 ym diameter particles. Other investigators comparing
the relative irritancy of 2.7 and 0.8 pm sulfuric acid aerosol report
that death rates are higher for larger particles (Rattle e_t al_., 1956).
Amdur and co-workers (1978a) report that the irritancy potential of various
sulfates roughly follows their acidity, with the exception that NH.HSO* was
less irritant than (NH.KSO.. Clear distinctions between these substances
are difficult to resolve because of differences in particle size and
concentrations and the potential neutralization problem. Although Amdur
and co-workers (1978b) report changes in pulmonary mechanics following a
3
single hour of exposure as low as 100 yg/m HUSO,, other investigators have
not been able to produce similar changes in guinea pigs, dogs, sheep,
and donkeys below at least 1,200 ug/m (Sackner et_ a]_., 1978; Schlesinger
ejt al_., 1978; Silbaugh et_ al_., 1980). Differences in animal susceptibility
(CD, p. 12-79) and experimental techniques may be responsible for these observed
differences. Within Amdur's studies, some guinea pigs were apparently more
susceptible than others. One interesting feature of the Amdur work is the
apparently linear dose response curve for some sulfate species (Figure B-l).
No evidence exists for a "threshold" of response in this animal model.
A number of recent studies have examined human respiratory mechanical
responses to sulfuric acid and other sulfates (Table B-2). In essence, no
-------
B-5
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B-7
direct changes in respiratory function have been reported for short term
exposure to normals and asthmatics at levels below 350 yg/m , and only one
study has reported symptomatic responses in these groups at levels below
1000 yg/m3.
3
Both normals and asthmatics exposed to 1000 yg/m of sulfuric acid,
ammonium bisulfate, ammonium sulfate, and sodium bisulfate responded
with small but significant reductions in maximum expiratory flow volume
at 60% total lung capacity (TLC) and partial expiratory flow-volume at
40% and 60% TLC (Utell e_t al_., 1981). At this concentration, sulfuric acid
and ammonium bisulfate also produced significant reductions in airway
conductance and forced expiratory volume at 1 second. All sulfates also
enhanced the response of normals and asthmatics to subsequent bronchoconstrictor
challenge. In the two asthmatics most sensitive to sulfate at 1000
ug/m , sulfuric acid potentiated the effect of bronchoconstrictor on
airway conductance and flow rates at the lowest dose tested, 100 yg/m .
In this test, the irritant potency more or less followed the acidity of
the sulfates (H2S04 > NH4HS04 > (NH4)2$04). This is somewhat different
than the irritant potential ranking indicated by guinea pig experiments
discussed above.
The positive results of Utell et_ aj_. (1981) are in obvious contrast to
the negative findings of other investigators at similar levels (Sackner
e_t al_., 1978; Avol e_t aj_., 1979). The authors offer four possible explanations:
1) Utell's group selected asthmatics according to carbachol reactivity;
they should have been more homogeneous in terms of airway reactivity
and, as a group, they may have been inherently more sensitive than
other asthmatics tested;
-------
B-8
2) Unlike the Avol subjects, Utell's subjects breathed orally;
3) Sackner's group studied asthmatics using daily medication to control
bronchospasm. This medication may have reduced any response;
none of Utell's subjects used medication; and
4) The parameters used by Utell may have been more sensitive
to respiratory changes than those of the other investigators.
Of the above explanations, 1, 3, and 4 appear most plausible. Like Utell,
Sackner employed oral only exposure, making the second point less pertinent.
Perhaps a more important difference between Avol and Utell is that the former
did not test bronchial reactivity. There was some suggestion of airway resistance
changes in two of AvoTs asthmatics. Sackner reportedly generated very small
particles (= 0.1-0.2 ym) compared to the 0.5-1.0 ym particles of Utell. Considering
hygroscopic growth in the respiratory tract, deposition of the larger aerosols
on the sensitive receptors in the tracheobronchial region could have been
substantially greater for similar initial concentrations. Moreover, the smaller
aerosols used by Sackner would undergo more rapid neutralization by respiratory
tract ammonia (Larson et ail_., 1977). The aerosols used by Utell should have more
closely matched typical ambient size distributions.
The greater effectiveness of larger particle sizes (as well as longer exposure
durations) may also be responsible for the increased respiratory symptoms reported
by Horvath et al. (1981). Subjects were exposed for 2 hours to 0.9 ym
sulfuric acid aerosol. Reports of sore throat, irritation and dryness increased
at 220 yg/m (3 of 9 subjects), again at 420 yg/m3 (5 of 9 subjects), and at
940 yg/m (8 of 9 subjects). Reports of cough paralleled those for the other
symptoms. Other investigators reporting equivocal results or an absence of symptoms
usually used smaller particle sizes and/or substantially shorter exposure periods.
A recent study on influenza patients indicates that bronchial reactivity
to another soluble aerosol, sodium nitrate, (NaNO.,) is increased during
infectious disease. In this study, Utell et aj_. (1980) examined influenza
-------
B-9
3
patients exposed to aerosols of NaN03 or NaCl (7,000 yg/m , ^ 0.5 urn
MMAD, a =1.7). Patients were exposed to both aerosols at the onset
of sickness and at 1, 3, and 6 weeks after the initial exposure. Alternate
exposures of NaCl or NaNO., lasted 16 minutes and were separated by 3
hours. Specific airway conductance and maximum expiratory flow at 60%
of total lung capacity were significantly diminished following NaN03
exposure (but not NaCl) at the onset of sickness and exposure one week
later, but no differences betweeen NaCl and NaNO., exposure treatments
could be resolved after 3 weeks. The authors suggest several possible
explanations for the increased sensitivity of the influenza patients.
For example, epithelial damage exposing and sensitizing reflex receptors
is postulated to result from viral infection.
Long term animal studies of effects of sulfuric acid or other soluble
aerosols have produced either no lasting mechanical response or the reported
respiratory functional measurements are of less interest than the results
of direct examination of the damaged lung tissues. These studies are
discussed in Section B.4.
2. Insoluble "Inert" Aerosols
Few animal studies have examined the effect of non-sulfur containing
particles at levels approaching those observed in the ambient air. Studies
in Amdur's laboratory of guinea pig exposures to fine oil mists, (^ < 2.6 ym
AED) spectrographic and activated carbon (< 1 ym CMD), MnO? (< . 5 ym AED),
open hearth dust (2 ym AED), and iron oxide (0.3 ym AED) have only found
changes at relatively high concentrations (Amdur and Underhill, 1968,
1970; Costa and Amdur, 1979)*. These non-hygroscopic fine substances were
apparently less irritating than sulfuric acid in this animal model.
Most of the controlled human exposure work involving insoluble
*Aerodynanric Equivalent Diameters (AED) reported here were calculated based
on reported geometric count mean diameters (CMD). For these studies CMD's
were < 1 ym.
-------
B-10
particles was conducted before 1970. Using a variety of particle types
and sizes (< .5 to over 12 pm), investigators have studied effects on
adult workers and other subjects of high concentrations (2 to over 50
mg/m ) for very short (2-10 minutes) to moderate (4-5 hoars) duration.
Even with differences among studies, the following findings appear to be
relatively consistent:
1) Although there is variability among individual subjects, changes
in pulmonary mechanics are concentration-dependent (Dubois and
Dautrebande, 1958; McDermott, 1962; McKerrow, 1964).
2) Changes in pulmonary mechanics are most pronounced during the
first few minutes and generally appear to diminish with time
(Dubois and Dautrebande, 1958; McDermott, 1962; McKerrow, 1964).
3) The relative irritant potential of the various particulate
substances (coal dust, carbon, calcium carbonate, iron hydroxide,
india ink, charcoal and carbon) is difficult to compare due to
differences in techniques, subjects, and exposures regimes.
4) The effects in polydisperse aerosol studies cannot be ascribed to
fine particles alone. McDermott (1962) and McKerrow (1964) studied
O
the effects of coal dust (9-50 mg/m , size < 7 urn), found increases in
airway resistance following a 4 hour exposure and concluded that
"significant increases in airway resistance occurred and the response
was correlated to the weight of coarse particles between 3.6 and
7 urn." The lowest level tested in these healthy at rest subjects
(9 mg/m3) produced no significant responses, but all higher levels
tested (> 19 mg/m3) did.
-------
B-ll
5) Symptomatic effects (tightness of the chest, dyspnea, cough and
wheeze) may be observed concurrently even when broncoconstriction
is clearly insignificant (Dubois and Dautreband, 1958). Similar
studies comparing normal subjects and subjects with chronic lung
disease (asthma, bronchitis, and emphysema) indicate that relative
changes in respiratory mechanics can be similar in various
diseased and normal groups following exposure to insoluble
dusts. Some investigators have suggested that because many
individuals with chronic lung disease have compromised pulmonary
mechanics, the bronchoconstriction produced by particle exposure
may place serious stress on such individuals at levels that should
be easily tolerated in normal subjects (Constantine et aj_., 1959;
Morris and Bishop, 1966).
3
A more recent study indicates that exposure to 2 mg/m of "inert"
polydispersed plastic dust containing carbon black (MMD was 9-12 urn, 30%
mass > 12.5 ym) decreases forced expiratory volume at 1 second and forced
expiratory flow in normal resting subjects (Andersen et a]_., 1979). Unlike
the change in pulmonary mechanics, discomfort was proportional to the
concentration of dust and was not immediate, lagging almost 2 hours behind
changes in dust concentration. While the symptomatic effects may have
caused personal discomfort, the noted results do not appear to be of
substantial health import for resting normal healthy adults after 2-4 hour
exposures. Exercise, oronasal breathing, or the presence of illness would
increase the possibility of more significant responses for short term peak
levels of such particles, perhaps at lower levels.
-------
B-12
3. Particles and Pollutant Gases
The interaction of particles and gases has been reported to produce
responses on respiratory mechanics and symptoms sometimes exceeding those
attributable to the two agents administered separately. Enhanced responses
may arise from deposition and combined action of gases and particles in
various respiratory sites, physical sorption of gases on particles permitting
enhanced respiratory tract penetration of the gas, and chemical reactions
to form more irritant pollutants. The combination of SQ~ and particles
has been most widely studied.
Based on the work of McJilton et al_. (1976) and Snell and Luchsinger
(1969), water or salt droplet aerosols may potentiate the effect of SCL by
increased penetration, but probably not by oxidation to sulfuric acid.
Amdur's work suggests the possibility that chemical transformation may
occur within exposure chambers to enhance irritant potential of combinations
of SQp and soluble, but not insoluble, aerosols (Amdur and Underhill,
1968). In some cases, stable sulfite-particle complexes might be implicated
(Hansen et aj_., 1974); in others, sulfuric acid may be formed. Andersen ejt al
(1981) examined the combination of the dry "inert" carbon containing
plastic dust described previously and sulfur dioxide. Effects were at most,
additive. These combinations will be discussed more fully in the sulfur
oxides staff paper.
Various particles also may enhance penetration and effects of other
soluble gases, notably formaldehyde (LaBelle et al_., 1955), and presumably,
may increase effects on respiratory mechanics and symptoms.
-------
B-13
4. Community Air Pollution
Changes in respiratory mechanics, or lung function, provide a sensitive
and objective index of respiratory health status and have been employed
in combination with respiratory symptom questionnaires to assess long-term
alterations in populations exposed to air pollution. A number of community
epidemiological studies have attempted to demonstrate an association between
long-term exposure to particulate matter and impairments in respiratory
mechanics and symptoms.
Table B-3 summarizes studies derived from the criteria document
that best describe this relationship and are at minimum judged to be
useful for qualitative comparisons. A few studies failed to show an
association or show only a marginal one; they appear to compare populations
with similar exposures to relatively low levels of particles. In general,
populations living in areas with higher particulate pollution tend to have
a higher prevalence of respiratory symptoms and lower lung function capability
compared with other groups in areas with less particulate pollution. Many
of the studies suffer from the design or methodological flaws associated
with most cross sectional epidemiological studies (CD, p. 14-2 to 4).
In addition, these studies rely on lung function tests that use devices
and techniques subject to various methodological errors (e.g., calibration,
seasonal effects, technician). Table B-3 indicates where these deficiences
further limit a study's utility or reliability. In most studies, high
levels of other pollutants, notably S02, were also present. These and other
considerations, outlined in Chapter 14 of the criteria document, also apply
to the epidemiological studies discussed in Sections B-F that follow.
In summarizing the studies of long-term (chronic) effects of particles
and related pollutants on respiratory mechanics and symptoms, a clear and
-------
B-14
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B-16
consistent association emerges for higher exposures that applies to
children as well as adults. Long-term occupational exposures to various
particles at high concentrations also have been implicated in the prevalence
of airway obstruction, as indicated in Table B-l. These findings qualitatively
support the evidence from community studies which indicate that an
association exists between respiratory mechanical impairments and long-
term exposures to elevated particle levels.
In contrast, the information on acute effects of ambient particles
on respiratory mechanics is limited to two studies, also summarized in
Table B-3. Lebowitz ert al_. (1974) suggests that the observed pulmonary
function decrements in exercising children and adolescents exposed to
southwest U.S. urban aerosols may be linked to short-term exposures to
particles at high temperature and that the mechanism for chronic effects
might be mediated by acute insults to the respiratory tract. Dockery et_
al. (1981) reported on preliminary studies of acute respiratory mechanical
changes in children exposed to higher concentrations of particulate
matter in Steubenville. The investigators found that children exposed
to sudden increases of TSP and SCL concentrations had declines of 1 to
2% in forced expiratory volume in 1-second (FEV-, Q). These changes were
considered small relative to sampling variability and marginally significant.
The authors concluded that this study provides suggestive but inconclusive
evidence concerning the relationship between short-term changes in air
pollution concentration and the level of FEV The long-term significance
of these effects remains to be determined.
A somewhat unique controlled study of community air pollution also
supports these acute effects associations. Toyama (1964) exposed 10 healthy
-------
B-17
males to high levels (10 mg/m ) of resuspended dust collected by deposition
in a Japanese urban area. Exposures were brief, consisting of 20 deep
breaths. The dust ranged from 0.5 to 10 pm (MMD ^2.0 urn) and was composed of
crustal material (64% as Si02, A1302, CaO, MgO), sulfates (10%), and volatile
material (19%). Bronchoconstriction effects as measured by airway resistance
varied with individual, ranging from no response (one subject) to a 70%
increase. The response appeared to be mediated by a reflex reaction to
mechanical irritation and was said by the authors to be consistent with
insoluble dust studies (see Subsection B.l.b. above). Subsequent experiments
suggested a greater than additive effect of resuspended dust and S02 (> 3 ppm).
B. Aggravation of Existing Respiratory and Cardiovascular Disease
Because bronchoconstriction is one of the major mechanisms by which
particles may aggravate existing respiratory disease, many of the animal
and human studies most relevant to this issue have been discussed in the
preceeding section; this section will focus on the results of community
epidemiological studies.
The epidemiological evidence suggesting an association between particles
and aggravation of the various states of respiratory illness and associated
cardiovascular disease is summarized in Table B-4.
Evidence from the "smog" episodes of Donora, London, and New York
City, in the 1950-60's indicate that individuals with pre-existing respiratory
and cardiac illness are especially vulnerable to sudden increases in air
pollution. Furthermore, the acute changes or aggravations of their
conditions provide a more sensitive index of the effects of air pollution
than do day-to-day changes in relatively healthy individuals.
-------
B-18
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-------
B-19
Based on the possible responses to particle deposition in the tracheo-
bronchial and alveolar regions as outlined in Section V.A, and the suscepti-
bility of cardiopulmonary patients to stress from infections or increased
airway obstruction (Fishman, 1976), the observed associations are biologically
plausible.
Effects of ambient particles on asthmatics are also to be expected.
Asthma is a disease characterized by a high degree of airway reactivity, with
a plurality of causes (allergy, inflammation, irritation, temperature changes,
etc.) and a wide variation of physical manifestations. These factors make
asthmatics an important and difficult group to study. Despite these diffi-
culties, and the limitations in assessing personal exposures inherent in
epidemiological research, some studies have attempted to delineate relationships
between aggravation of asthma and particulate matter. Although the results
are equivocal, there is an indication that an association may exist, especially
when the particle pollution contains dusts derived from biologic matter
(e.g., grain dust). Due to their apparent sensitivity to SCL (Sheppard e_t
a!., 1981; Koenig ejt a]_., 1981) epidemiological studies of asthmatics where
high SCL levels were present (e.g., Cohen et al_., 1972), cannot be used as
qualitative support for an association with particulate matter.
It must be emphasized that in most of the studies of acute exacerbations
of chronic or acute respiratory conditions, the effect of particles cannot
be distinguished from other pollutants, usually SOp. However, clear evidence
emerges from the body of epidemiological literature that implicates particles
in aggravating disease among bronchitics, asthmatics, cardiovascular patients
and people with influenza.
-------
B-20
C. Alterations in Host Defense Mechanisms—Clearance and Infection
1. Clearance
The effects of particulate exposure on clearance have been examined
using several different types of particles. Studies of exposures to
cigarette smoke and sulfuric acid have received more attention than other
particulate types. These studies have focused on mucociliary clearance in
various regions of the respiratory tract.
As indicated in Table B-5, the exposure-dependent response of mucociliary
clearance rates to particle exposure can be complex. Observations in humans
indicate that a single exposure to as little as 100 yg/m of sulfuric acid
for 1 hour can accelerate bronchial clearance rates in some individuals.
Leikauf et, aj_. (1981) note that as sulfuric acid concentrations are increased,
mucociliary clearance rates are progressively reduced. Although donkeys
exposed by the same investigators do not appear to show any change in
2
mucociliary clearance rates below about 200 yg/m sulfuric acid (1 hour),
depressions in mucociliary clearance rates have been reported in donkeys
following repeated exposures of 100 yg/m sulfuric acid for repeated 1 hour
exposures (5 days/week for 6 months). Two (of four) donkeys in this experiment
developed grossly abnormal clearance times during the fourth through sixth
months of exposure and remained so for at least three months after exposure
was ended (Schlesinger et a]_., 1979).
Lippmann and co-workers (1981) have stressed several similarities
between the above effects of sulfuric acid on clearance and those of cigarette
smoke: 1) transient accelerations of clearance are produced by low dose
o
exposures (100 ug/m sulfuric acid for 1 hour or 2 to 7 cigarettes); 2) a
transient slowing of clearance follows high dose exposure (1 mg/m sulfuric
acid for 1 hour or > 15 cigarettes); and 3) alterations in clearance rates
-------
B-21
TABLE B-5. EFFECTS OF SULFURIC ACID, CARBON EXPOSURE ON MUCOC1LIARY CLEARANCE
Clearance Region Pollutant Exposure
Sulfuric Acid
Tracheobronchial Ten healthy adults
exposed for one
hour (via nasal
face mask) to:
a) 110 ug/nr H-SO.
(0. 5 um MMAD,
o. » 1.91
b) 330 p"g/mf
c) 980 ug/m
Tracheobronchial Four donkeys ex-
posed for 1 hour
(via nasal cathe-
ters) tOi
194 wg/m3 H,SO.
(0.3 - 0.6 &» *
MMAD, og - 1.5)
Trachea Eight dogs ex-
posed for 1 hour
(via nasal face
mask) to:
500 ug/m^ H.-SO
(0.9 urn MMAD,
"o * ^-3)
9
Tracheobronchial Four donkeys ex-
posed for 1 hour per
day; 5 days per week
for 6 months- 122 ex-
posures (via nasal
catheters) to:
105 »g/mj H,SO.
B" Z 4
Trachea Hamsters exposed for
3 hours to:
1 . 1 mg/mj H,SO.
(0.12 uml and/or
1.5 mg/m carbon
(0.3 um)
Time After
Exposure
0-10 hours
0-24 hours
a) 30 min-
utes
b) 1 week
a) 1 week
b) 6-9 mos.
Immediate
Effect(s)
a) Acceleration in
bronchial mucoclllary
clearance
b) Varied
c) Depression In
bronchial mucoclllary
clearance rates
Depression in bron-
chial mucoclllary
clearance
a) No group change
b) Depression in
tracheal mucus
flow rate
Bronchial clearance
becomes erratic
Varied
Ciliary beat frequency
depressed by both
H2S04 exposures
Comment
Six of ten healthy non-smoking adults
exhibited increases in bronchial
clearance half times that were
greater than 25% of control values.
As a group, a significant (P<0.02) 40%
decrease in mean bronchial clearance
half times was observed.
Three persons showing substantially
faster clearance than in the control
test and three persons showing sub-
stantially slower clearance than in
the control test.
As a group, the mean rate of clearance
was significantly depressed (P<0.03)
with mean bronchial clearance half
times being about 150% of control
values.
Transient increase in bronchial clearance
half time in one of four donkeys.
Transient increases in two other animals
were observed at higher concentrations.
Persistent alterations in clearance
produced in two animals.
One dog (16) showed an increase in
tracheal mucus velocities of about
300% of control values at 30 minutes
after exposure.
A significant depression (P<0.05) was
observed for the group. One dog (#6)
showed an increase in tracheal mucus
flow rate unlike the rest of the group.
The bronchial clearance half times became
significantly different from controls on
many test days.
Two animals sustained impairment of clear
ance towards the end of the 6-month
exposure period and continued to have
erratic clearance during a 3-month
follow-up period.
Morphological damage was greatest for the
H2S04 and carbon exposure
Reference
Leikauf et al..
1981
Schlesinger
et aj_.. 1978
Wolff et al..
1981
Schlesinger
et aj.. , 1979
Schiff et al.,
1979
-------
B-22
that can persist for several months following multiple exposures (> 6 one
3
hour exposures at 200-1000 yg/m sulfuric acid, 6 months of daily exposure
3
to 100 yg/m sulfuric acid for 1 hour/day, and/or 4 to 8 months of 30
cigarettes for 3 times/week).
Based on these similarities, together with the well established role of
cigarette smoking in the development of chronic bronchitis in humans, it is
suggested that sulfuric acid exposure may play a role in the etiology of
chronic bronchitis (Lippmann et_ jil_., 1981). Significantly, although these
sulfuric acid levels are perhaps a factor of two or more of peak U.S. levels,
they are in the range of peak levels of sulfuric acid during London episodes
as reported by Commins and Waller (1967). Even in London, however, such
levels apparently were rare.
Several clearance studies have also been conducted using carbon or
carbon/SOp mixtures. Camner ejt al_. (1973) reported that brief but extremely
high exposure to 11 ym carbon particles usually accelerated clearance. In
contrast to the studies on tracheobronchial clearance, normal subjects
have not shown changes in nasal mucous clearance rates following exposure to
polymerized plastic dust containing carbon black below 25 mg/m (Andersen et^
al... 1979).
2. Infection
As indicated above, changes in mucociliary clearance are the most
studied effects on host defense systems. No controlled human exposure
studies have evaluated the effect of particulate exposure on other mechanisms
affecting susceptibility to infection. Table B-6 lists animal studies high-
lighted in the criteria document. Animal exposure studies indicate that
single or repeated exposures to high levels of toxic metal salts increases
-------
B-23
TABLE B-6. EFFECT OF PARTICIPATE MATTER ON HOST DEFENSE SYSTEMS
Concentration
Observation
Reference
Acute exposures; Infactivity Model
Mice exposed for 2 hours to:
0.075 - 1.94 mg/m3 CdCl9
(94-99* <1.4 urn)
0.1 - 0.67 mg/m3 NiCl,,
(94-99% <1.4 urn) *
0.5-5 mg/m Mn.,0
(94-99% <1.4 y
Increased mortality at .1 mg/m
Cd following bacterial challenge
(Streptococcus pyogenes)
Increased mortality at 0.5 mg/m
Ni following bacterial challenge
(S. pyogenes)
Increased mortality at 1.55 mg/rrf
Mn following bacterial challenge
($._ pyogenes)
Gardner et al.,
1977b
Adkins et al.,
1979
Adkins ejt al.,
1980
Mice exposed for 3 hours to:
0.1 ppm 03 followed by 2
'jours at 6.9 mg/m H~SO,
(0.23 vm AED, o = 2f4r
Increased susceptibility
to infection by !S^ pyogenes.
Neither pollutant alone produced
an effect. Order of exposure
(ozone first) was important.
Gardner et
al., 1977a
Chronic Exposures
Mice exposed for 100 hours per
week for 192 days to:
0.56 mg/m carbon
(1.8 to 2.2 ym MMD)
and/or 5.24 mg/m (2 ppm) S02
Immunological (and morphological)
alterations in the lungs.
Systemic immune system affected
after 192 days. S02 + carbon and
carbon alone were more effective
than S02 alone.
Zarkower,
1972
Mice exposed for 3 hours per day for
5 days per week for 20 weeks to:
1.4 mg/nr H2$0. (0.12 pin/nT)
- and/or -
1.5 mg/m carbon (0.3 pm/m )
or
2.9 mg/m H9SOA coated carbon
(0.4 pm). ^ 4
Increased mortality and pulmonary
consolidation following exposure
to virus in the acid coated carbon.
No change in resistance to
Klebsiella pneurnoniae (a bacteria).
Immunological changes were similar
to those observed by Zarkower, 1972.
Fenters ejt
al., 1979
-------
B-24
the rate of mortality resulting from induced bacterial infection (Maigetter
et al_., 1976; Gardner et al..> 1977b; Adkins et al_., 1979, 1980). Using the
same model, however, no increased mortality rates were observed in animals
exposed to sulfuric acid, ammonium sulfate, iron oxide, and carbon black
(Gardner et al_., 1977a; Gardner, 1981; Ehrlich et al.., 1978; Ehrlich, 1979).
Sulfuric acid and ozone, however, increased mortality even though neither
pollutant alone produced an effect. Long-term studies of combinations
suggest that high levels of carbon or carbon plus S02 or sulfuric acid may
affect the immune system (Zarkower, 1972; Renters et a]_., 1979).
The mouse studies in Table B-6 suggest that high levels of particles
and gas (CL, S02)—particle combinations may increase susceptibility to a
bacterial or viral challenge and produce immunological changes. The rele-
vance of many of these high dose results to real world exposures can,
however, be questioned. Of similar interest are in vitro and in vivo studies
of various particles on alveolar macrophages which are the primary defense
cells of the lungs. A variety of trace elements, minerals, fibrous materials,
and other particles have been observed to damage macrophages to varying
degrees (CD, Section 12.3.4.2).
3. Clearance and Infection - Community Air Pollution
The first part of Table B-7 summarizes the studies that demonstrate the
influence of particulate pollution on acute infections in populations.
Insults to the respiratory tract such as acute infections in childhood
may be important in the subsequent development of obstructive airways
disease, where exposure to adverse environmental factors changes a relatively
minor infection into one that produces permanent changes in the respiratory
tract (Colley et al_., 1973; Kiernan et a]_., 1976).
-------
B-25
Because the impact of ambient pollutants on respiratory illness may
have important consequences for the subsequent development of functional
abnormalities, and a substantial proportion of these illnesses in very young
children involve the lower respiratory tract (Speizer ejt al_- > 1980) and
particularly the small airways (Tager and Speizer, 1976), the studies in the
second part of Table B-7 relating chronic exposures to pollution to childhood
respiratory infection are especially significant.
Based on animal and clinical data, episodic infection with a variety of
microbial agents might be an important risk factor in the evolution of mucus
hypersecretion and chronic obstructive airways disease. (Speizer and Tager,
1979). It is thought that upon irritation, excessive mucus is secreted
into the airways, causing airway blockage and reduced mucus clearance. This
damage predisposes the individual to infection, particularly in the lower
airways. At this stage, characterized by cough and phlegm production, the
effect may be reversible. Chronic irritation, however, may allow infections
to persist in the airways, ultimately producing irreversible obstruction.
Thus, impaired mucus clearance appears to be an important indicator in the
evolution of obstructive diseases such as bronchitis.
Studies of normal population groups, with comparable smoking and age
distributions suggest a greater prevalence of symptoms of mucus hypersecre-
tion (e.g., runny nose, persistent cough, phlegm production) in subjects
living in more polluted environments (Holland and Reid, 1965; Holland et a!.,
1969; Lambert and Reid, 1970; Rudnik et ^]_., 1978). To the extent that
the longitudinal study of Fletcher et al_. (1976) is related to air
pollution, it distinguishes the effect of particles from SCL with regard
-------
B-26
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B-28
to impaired mucus clearance and is consistent with the evidence that
suggests that particles, with and without S02, have acute and long-term
impacts on the respiratory system that may increase its susceptibility
to infection.
D. Morphological Damage
Damage to respiratory tract tissues has been associated with exposure
to a variety of different types of particles, including direct acting
irritants (sulfuric acid) and insoluble dusts. Because detection of such
damage normally requires invasive techniques, evidence for these effects is
derived from controlled animal tests and autopsy studies of individuals
characterized as having long-term exposures to urban, rural, or occupationally-
related particles. As such, evidence for morphological damage is mainly
qualitative.
1. Sulfuric Acid/Combinations
Table B-8 summarizes a variety of studies examining the effects of
sulfuric acid and fly ash alone or in combination with other pollutants. As
discussed earlier, a serious complication of all animal acid aerosol expo-
sure studies is the potential neutralization by chamber ammonia. In the
absence of special precautions, chamber ammonia concentrations may average
up to 25 ppm (Malanchuk e_t al_., 1980). Thus, the sulfuric acid exposure
studies listed may actually have examined ammonium sulfates/sulfuric acid
mixtures, even where frequent cage cleanings may have reduced contamination.
Nevertheless, some morphological effects have been observed in some studies.
The chronic exposure of beagle dogs provide several interesting findings
(Hyde et aQ_., 1978; Gillespie, 1980). Distinct, pathological changes in
structure and pulmonary mechanics were found (by electron microscopy) at
-------
B-29
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B-30
exposure levels that were considerably lower than those used in earlier
experiments. As discussed in the criteria document (CD, p. 12-60), the
evidence suggests that pathological changes continued to become progressively
more severe with time after exposure had been terminated, highlighting the
importance of post-exposure follow-up studies. The authors consider the
morphological changes to be analagous to an incipient stage of emphysema.
In applying these beagle dog studies to real world exposures, the
following points should be considered:
1) The alternating exposure/clean air system was useful, but
does not simulate repeated short-term peaks or lower long-term
averages more likely to be experienced in the ambient air.
2) Based upon the information presented in the studies, it is difficult
to determine whether the particle size was representative of that
normally found in ambient air.
3) Actual sulfuric acid exposures were probably lower due to unknown
chamber levels of endogenous ammonia. Neutralization is faster
for smaller particles.
4) It seems reasonable to attribute most of the deep lung changes to
the sulfuric acid or acid/ammonium sulfate mixture, based on the
probability of deep lung deposition. Sulfuric acid aerosols are
unlikely to absorb SCL and increase penetration, although ammonium
sulfate aerosols might.
5) If the two sets of dog studies can be directly compared, they
indicate that morphological effects of the SO mixture are more
A
pronounced with extended lower level exposure. This is in con-
trast to acute bronchoconstrictive responses for these substances,
-------
B-31
where higher concentrations appear more important than exposure
duration. Although the time integrated dose (concentration x
time) in the Hyde ejt aj_. study was lower than in the Lewis work,
morphological effects were apparently much more pronounced,
suggesting time integrated dose is not necessarily a good indicator
of morphological damage.
The Alarie e_t aj_. (1975) studies also suggest that sulfuric acid (between
0.1-1 mg/m ), may affect bronchial morphology; in two cases, sulfuric acid
was more potent when combined with SC^. in one case it was not. Fly ash
accumulated in the lungs but apparently (using light microscopy) did not
affect morphology, even in combination with SOo- Although 3-5 urn fly ash
can be efficiently deposited in mouth breathing humans, the alveolar
penetration in guinea pigs and small monkeys might well be significantly
lower. Pulmonary function testing suggested possible effects for most
2
sulfuric acid combinations tested (0.1 - 1 mg/m ), but the differences in
response to these levels were not large and interpretation difficult
due to anomalous trends in the control group. In view of the beagle
dog studies, (Gillespie, 1980), it is unfortunate that post-exposure
follow-up studies were not conducted.
2. Insoluble Particles
As indicated earlier, slowly cleared insoluble particles may accumulate
in the alveolar region of the lung. Controlled animal exposures and in vitro
studies have typically been conducted at unrealistically high concentrations
and are most useful in identifying mechanisms. (NIOSH, 1974; White and
Kuhn, 1980; Ziskind et^ aj_., 1976). Besides accumulation in lung tissue
-------
B-32
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B-33
and macrophages, insoluble particles (most notably various free silica
minerals) may indirectly produce fibresis through macrophage damage.
Autopsies of both humans and animals naturally exposed to various
kinds and amounts of fugitive crustal material have found changes in
many ways similar to the morphological responses produced in controlled
studies (see Table B-9). The occurrence of silicosis in workers exposed
to high levels of silica in occupations of sandblasting and granite
mining is well documented (Ziskind et aj_., 1976; NIOSH; 1974). Evidence
for varying degrees of penumoconiosis has recently begun to appear in
the literature for animals and people exposed to crustal dust near or
not far above ambient levels. Silicate pneumoconiosis has been reported
in zoo animals (Brambilla e_t al_., 1979), farm workers (Sherwin et al.,
1979), desert dwellers (BarZiv and Goldberg, 1974), and residents of the
southwestern United States (Brambilla et al_., 1979).
Routine examination of over 11,000 San Diego zoo animals exposed to
ambient particulate matter indicated the presence of crystalline material
in 20% of the cases (Brambilla et _al_., 1979). Accumulation of crystal-laden
macrophages was the only lesion in about 50% of the cases, but more
serious lesions were observed in some animals. Macrophages and birefringent
particles had accumulated in pulmonary lymphatics. Crystals from lung tissues
were lamellar, 1-10 urn long and 0.5-7 urn wide, and were chemically and
physically similar to those found in local air samples as determined by
electron microscopy and X-ray analyses. The authors noted that they had
observed similar accumulations and responses in autopsies of various
human residents of this area, apparently not related to occupation.
-------
B-34
Sherwin ejt al_. (1979) found fibrotic lesions in 6 vineyard workers and
one farm housewife. Particles measuring up to 3 by 12 ym were found in the
lungs and were minerologically similar to local soil samples. The deaths of
these subjects were apparently related to respiratory difficulties, but the
role of high soil particle loadings cannot be unequivocally separated from
possible pesticide contamination, organic dusts, and in some cases, smoking.
Nevertheless, these coarse particles apparently produced responses in lung
tissues, since in most cases interstitial deposits of particles were associated
with areas of chronic inflammation and fibrosis.
A study of Bedouin desert dwellers identified several degrees of accumu-
lation and response (see Table B-9) associated with exposure to desert dust
of undetermined particle size (Bar-Ziv and Goldberg, 1974). Accumulation
tended to increase with age and probable degree of exposure to higher
concentrations. In some cases mild focal emphysema was present in areas
surrounding dust nodules. The authors suggest this was not of clear clinical
significance. A number of pathological conditions were noted in the 54 lung
specimens examined, but effects were not necessarily related to dust accumula-
tion. More advanced nodules characteristic of classical occupational
silicosis were not observed. The authors suggest that the limited fibrotic
response might be explained by the reduced activity of aged desert dust
compared to freshly generated particles. Cigarette consumption or other
personal particle exposure unrelated to desert dusts were not evaluated.
Although the findings are difficult to ascribe to particulate air
pollution, Ishikawa et_ al_- (I969) found that the prevalence and severity of
emphysema was greater in smokers, but, for all degrees of smoking, emphysema
was worse in residents of St. Louis than those in less polluted Winnipeg,
Canada.
-------
B-35
Because the accumulation of particulate matter typically results in
pigmentation in lungs, several studies have evaluated the pigmentation and
particle deposition of lungs in urban air. Pratt and Kilburn (1971) examined
the degree of lung pigmentation and found it was affected by both smoking
and urban pollution. Another study found dust (Sweet et a]_t, 1978) and
accumulation in urban dwellers. These studies provide evidence for the
longer lifetime of soluble particles in the alveolar region.
These autopsy studies, particularly the more recent work in Table B-9,
suggest that deposition of ambient coarse particles in the alveolar region is
a matter of some concern. Unfortunately, they provide no basis for reliable
quantitative assessment of potential health effects or risk factors.
E. Cancer
The relationship between particulate air pollution and cancer has been
approached in essentially three ways:
1) Whole animal (in vivo) and or in vitro tests of collected ambient
particulate and extracts;
2) Animal and occupational epidemiologic studies of specific substances
found in ambient particles; and
3) Retrospective community epidemiology.
1. Toxicological Studies of Ambient Particles
A number of early studies examined the carcinogenicity of combustion
emissions, ambient air and extracts (e.g. Campbell, 1939; Leiter et a!.,
1942; Kotin et a\_., 1954). These studies have generally found that
organic extracts were more potent tumor producers or promoters than
whole samples and that, based on the size distribution of such organics,
-------
B-36
much of the tumor producing activity should be found in the fine fraction.
A notable exception is the observation of McDonald and Woodhouse (1942),
who found dust from a freshly tarred road was carcinogenic to animals.
Early studies of extracts of particles from atmospheres dominated by coal
combustion and industrial emissions also found the aromatic (neutral)
fraction of organics dominate tumorogenicity (Stern, 1968; Wynder and
Hoffman; 1965). This fraction contains polycyclic aromatics such as BaP.
More recent studies on current U.S. aerosols have focused on the mutagenic
potential of airborne particles as indicated by Ames and other in vitro
tests (Pitts etal_., 1977; Huisingh, 1981; Daisey, 1980). Mutagenic
extracts have been found by preliminary studies in a number of urban areas
and, to a lesser extent, non-urban particles (Kolber et al_., 1981; Pitts
ejt a]_., 1978). As in earlier tumorogenesis studies, organic extracts and
smaller particles tend to dominate activity. The neutral fraction, however,
does not appear to be most potent on a unit-mass basis (e.g. Figure B-2).
Moreover, the coarse fraction contains some mutagenic activity (Kolber
et^ jil_., 1981). These animal and in vitro studies of particles are
useful in identifying potential problems but are limited by sampling
artifacts, questions on the bioavailability of the extracts, and their
relationship to human exposures.
2. Studies of Specific Particulate Carcinogens
A number of particulate substances, normally present in ambient air in
trace amounts have been found to be carcinogenic in animal and occupational
studies. Examples include several polycyclic organics, compounds of trace
elements such as chromium, arsenic, nickel, and beryllium and minerals (e.g.
asbestos) (See NIOSH, NAS documents on these substances). Inorganic
-------
B-37
Bacterial Mutagenic Activity of Respirable Particulate Organic Matter (Rev.//ig)
S typhimunum TA-98, no microsomal activation
5.0
=,40
-5-
V
1 3-°
'H
1 2.0
i
% 1.0
n
— New York C
ty Moderately
— Sterling Forest Polar Fraction
-
- Non-Pol
i-T
or Fraction
ITT
Tl
Polar Fraction
i— 1
18
Date
Figure B-2. Bacterial mutagenicity of three organic fractions of size
specific participate matter (<3.5 urn) collected in New York City and
Sterling Forest (The latter site is in Tuxedo, N.Y., about 70 km
northwest of Manhattan, Daisey, 1980). The moderately polar fraction
is a more potent direct acting mutagen than the PAH containing neutral
fraction. All fractions show somewhat more activity in the winter.
The polar fraction accounts for over half of the organic mass followed
by- the non-rpolar and polar fraction respectively (Daisey et_ al_., 1980).
-------
B-38
materials (iron ore, carbon, asbestos) have been found to potentiate the
oncogenic effect of BaP in intratracheal instillations in rodents (Pylev
and Shabad, 1973; Stenback et al_., 1976; Safflot! et a].., 1968).
These insoluble particles may act as carriers for carcinogens (Stenback
et_ ^1_., 1973) or delay lung clearance (Hilding, 1957) which would increase
the contact time between the carcinogen and bronchial mucous membranes.
This is especially important considering that most lung tumors occur at
the carina or bifurcations of the larger airways (Schlesinger and Lippmann,
1978) where deposition is high and particles tend to accumulate (see Section
V-A).
3. Community Epidemiology
Due to the apparent lag between exposure and onset of cancer, available
community epidemiological evidence reflects more the polluted conditions
in U.S. and British cities in the 1950's and 1960's. The data indicate
that cigarette smoking is the dominant cause of respiratory cancer, but
that some carcinogenic risk related to air pollution may be present. A
higher incidence of lung cancer morbidity and mortality among smokers and
non-smokers in urban compared with rural areas, suggests that differences in
smoking habits and specific occupational exposures cannot account for all of
the urban excess in cancer rates. Several observations implicate particulate
matter as contributing to this urban/rural gradient.
As evaluated in several review articles (Higgins, 1976; Holland et al.,
1979; Doll, 1978), reductions in particulate matter in London (1954-70)
were followed by a reduction in male lung cancer mortality in that city for
1960-1970 (Higgins, 1976). Lung cancer mortality in other urban areas
remained constant and increased in rural areas. Although changes in cigarette
-------
B-39
tar content or consumption may have been responsible, Higgins (1976) con-
cludes that reductions in ambient smoke levels may have been partly responsi-
ble. Support is provided by cross-sectional studies that have found weak
associations between BS levels and lung cancer in England, after adjusting
for cigarette smoking (Higgins, 1976).
Analyses of differential cancer rates between areas are usually limited
by a lack of social class, occupational, smoking and mobility information,
indirect estimates of exposure to air pollutants, and the long induction
time of cancer. Associations between lung cancer and specific indicators
(BaP) (MAS, 1972) are not reliable in the context of current exposures.
These difficulties preclude any quantitative relationships to be drawn
from community studies of particulate matter and cancer.
d) Summary of Evidence on Carcinogeneses
Cigarette smoking generally is considered to be the major determinant
of lung cancer (Doll, 1978). The high particulate air pollution of the
1940-60's contained carcinogens and may have potentiated or otherwise
contributed to elevated cancer rates in urban areas. Based on filter
chemical analyses, levels of polycyclic organics and some inorganic
carcinogens have declined since that time and hence carcinogenic risk
from these substances has been reduced (Section IV). Studies of current
U.S. air suggest mutagenicity of particulate extracts is dominated by
other organic particle fractions that may not have been of significance
in historical settings. Epidemiological evidence relating to current
exposures will not be available for years.
In essence, available evidence does not unequivocally show that current
particle exposures contribute to cancer. Neither do they disprove any
-------
B-40
effect. Because lung cancer is the leading cause of cancer-related deaths,
the risk of a small effect could assume some importance. The presence
of mutagens in organic participate fractions from unidentified sources
and the potential interaction between these or other particles and carcinogens
from cigarettes or occupational exposures suggest some need for caution
and further study.
F. Mortality
1. Acute Studies
Community epidemiological studies linking acute particle exposure
to mortality are listed in Table B-10. During the "killer fog" episodes
in Europe and the U.S., mortality rates rose far above their expected
levels, coincident with several days of extremely high levels of particulate
and sulfur oxide pollution presumably (Firket, 1936; Schrenk, 1949; Ministry
of Health, 1954). Subsequent deaths and chronic disease attributed to
severe illnesses during one such episode has also been reported (Ciocco
and Thompson, 1961).
Other episodes, though less dramatic, have been reported in London
(see CD, Table 14-1) and New York City (Greenburg et al_., 1962, 1967).
As noted in Section 14.3 of the criteria document much smaller estimates of
excess mortality were reported for the New York episodes (at most 4 to 20%)
compared to the 15 to 350% death rate increases during the London episodes.
Several factors could account for these differences, for example: 1) extremely
dense fog associated with the higher levels of sulfuric acid in London (see
Section IV); 2) differences in diurnal patterns of pollution levels and in
-------
B-41
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Increase in dally mortality above 15-day moving average.
especially among Individuals with preexisting cardio-
resplratory disease. Bronchitis, but not pneumonia ,
mortality significantly correlated with pollution. Peak
mortality occurred during an Influenza epidemic on • day
with peak pollution levels. Meteorological variables do
not confound associations.
ly
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ality and da
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Clear ass
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Apparent Increase In dally mortality above 15-day moving
age and 5-year dally average on days with high CoH
SO. levels. SO. most strongly correlated with
ality. Data from one central monitoring station .
to estimate city-wide exposure levels. Mortality
temperature, but not other environmental variables,
sted. 'Some Internal Inconsistencies, relation-
clear only for 1963. See follow-up NYC analyses
w.
ave
and
mor
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and
adju
hip
elow
shi
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Consistent association between smokeshade and dally
mortality. Reduction In SO, levels were not accom-
panied by decreased mortality rates. SO. not sig-
nificant In multiple regression. Temperature
strongly correlated with mortality. Data from one
central monitoring station used to estimate city-wide
exposure levels. Demographic changes not considered.
Clear association between dally mortality and PH bu
not SO.. Seasonal and temperature effects controll
Preliminary results from ongoing study. Improved
exposure estimates but complex terrain limits for
quantitative purposes.
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B-42
the duration of inversions between the two cities, and; 3) differences in
exposure patterns, e.g., London residents typically were exposed to higher
levels of indoor pollution.
Studies of two London winters, one being particularly foggy, have
shown consistent relationships between particles in the presence of SCL, and
daily variations in mortality (Martin and Bradley, 1960; Martin, 1964).
These studies, and reanalyses by Ware e_t afL (1981) are discussed more
fully in Sections V-D and VI-C. An exploration of the relationship
between daily levels of pollution to daily mortality in London, extended
to 14 winters, 1958-59 to 1971-72, (Mazumdar et al_., 1981) is also discussed
in these sections.
The attempt of Mazumdar et_ aj_. (1981) to separate SCL and particles
is of particular interest. Based on quartile and multiple regression
analyses, a strong association between daily mortality and daily pollution,
primarily smoke and not SOp, was found for 1) all days in the data set,
q
2) episodic days (days when smoke values exceeded 500 yg/m plus the
seven days adjacent on either side), and 3) non-episodic days (the remaining
days). No synergistic effects between the pollutants could be shown.
Advanced analytical techniques were applied in this study in an
attempt at separating the effects of S02 from smoke and to eliminate the
confounding influences of meteorological variables, seasonal and yearly
trends, and the strong correlation between the two pollutants. The
complexity of the mathematical approach, however, requires cautious
interpretation of the results. For instance, there may have been over-
adjustment for weather influences, mortality being regressed on seven
-------
B-43
weather variables. Therefore, it is not clear whether the effects of
S02 and BS were truly separated. Despite the limitations, the study's
superior data base, the attempt at specifying the most appropriate
model, and the internal consistency of results add validity to the
analyses. The ongoing year by year analyses of this data base should
provide additional insights into the potential relationships.
The series of studies that analyzed daily mortality variations in
New York City from 1960-1976 also attempted to separate the effects of
SCL from particulate pollution by calculating the partial correlation
coefficients between individual pollutants and health measures. Glasser
and Greenburg (1971) reported that SCL, (based on hourly readings from a
single monitoring station) was associated most strongly with daily
mortality during the 5 year period, 1960 to 1964. Although the analysis
was adjusted for temperature and seasonal variability in mortality
rates, no adjustment was made for other environmental variables.
Schimmel and Murawski (1976) and Schimmel (1978) analyzed daily New
York City mortality data using time series techniques (e.g., "pre-
filtering, nested quartile analysis), refined subsequently by Mazumdar
e_t al_. (1981). They concluded that particles, as measured by coefficient
of haze (CoHs), were associated with mortality and that S02 is merely an
index variable for other unmeasured extraneous variables and is not a
cause of mortality. Buechley (1975) employed similar techniques for
approximately the same time period and reached similar conclusions after
allowing for many factors (e.g., heat waves, annual mortality cycles,
influenza epidemics). This approach, however, unlike Schimmel's, depends
upon the specification of the adjustment variables and cannot avoid
confounding between the air pollution variables and other components of
mortality.
-------
B-44
These analyses, like Mazumdar et_ _al_. (1981), represent methodological
advances over similar epidemiological studies, particularly in their
explicit recognition of the time series structure of the data and the
requirements this imposes on analysis and conclusions. A number of
limitations should be recognized, however, for example: 1) the effect
of temperature which was great in NYC, in contrast to London, was treated
by a linear analysis, although a nonlinear treatment might have been
more appropriate, 2) as in the London study (Mazumdar et^ al_., 1981),
changes in the demographic profile in the New York City population
during the study period were not considered, 3) as in the London study,
the many coefficients studied and the intercorrelations among variables
make the standard errors of the coefficients liable to be large, and
4) it is doubtful that measurements from a single monitoring station in
central New York City could generate representative exposure estimates
for the entire metropolitan area (Goldstein and Landovitz, 1975; 1977a;
1977b). In contrast, Mazumdar et al_. (1981), like Martin and Bradley
(1960), used pollution data measured at seven stations, which represented
the London metropolitan area relatively well (CD, p. 14-19).
Based on a preliminary time-series analyses similar to that of
Mazumdar et_ aj_. (1981), Mazumdar and Sussman (1981) found that daily levels
of particulates (as measured by CoH at three monitoring stations), but not
S02, were associated with daily mortality in Pittsburgh, Pennsylvania.
Another approach was developed by Lebowitz (1973) who, using a stimulus-
response model, showed that daily mortality in New York (1962-1965),
Philadelphia (1963-1964), Los Angeles (1962-1965) and Tokyo (1966-1969)
was associated with high concentrations of S02 and particles as measured
by TSP (Los Angeles, Philadelphia) and by CoH (New York, Tokyo).
-------
B-45
In summary, these acute studies, both episodic and time-series,
indicate that high levels of particulate matter, in combination with SO,,
increase mortality rates among individuals with cardiorespiratory disease
and influenza. The analyses of daily mortality in London show that the
associations may be stronger for particles in some cases, however, SOp
cannot be clearly excluded. The evidence from New York City analyses is
less clear, mainly because of inadequate aerometric data and the confounding
influences of temperature.
2. Long-Term Regression Analyses
A number of retrospective regressions analyses have examined
the relationship between mortality and sulfur-containing particulate
matter as indicated by sulfates. These studies have assumed some prominence
in policy analyses and risk assessment of coal combustion (e.g., Wilson
e_t aL, 1980). A listing of cross-sectional geographic comparisons is
given in Table B-ll.
The most widely quoted of these studies are the analyses of Lave
and Seskin (1977), which have consistently indicated an association
between both sulfates and particulates and mortality. They failed to
find a consistent association between non-pollution related effects,
such as suicides, venereal diseases, and crime, and sulfates or TSP and
hence concluded that the pollution variables were not acting as surrogates.
The study's validity in demonstrating a causal association between
mortality and TSP and sulfate is limited because of several factors, for
example: 1) the omission of important variables (e.g., smoking, diet),
2) aggregate analysis of inadequate data (e.g., minimum sulfate levels),
3) estimation methods which possibly make inefficient use of the information
-------
B-46
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B-48
contained in the data, 4) the failure to consider inherent simultaneous
relationships, making interpretation of the estimated coefficients
difficult, or even meaningless, and 5) internal inconsistencies that were
not adequately addressed. (See CD, p. 14-36 to 14-43).
The original Lave and Seskin model was refined and re-estimated using
1974 data (Chappie and Lave, 1981) and although the results were qualitatively
similar to those for 1960 and 1964, the particulate variables were not
significant. A consistent and statistically significant association
between sulfates and mortality persisted. The authors attempted to respond
to past criticisms by adding variables for smoking, alcohol consumption,
medical care and nutrition, by using city or county instead of SMSA data,
by using a generalized least squares estimator instead of ordinary least
squares, and by testing a simultaneous equation framework. However, the
major criticism of their results owing to the inherent limitations in the
mortality and exposure data bases, cannot be removed.
Some cross-sectional regression analyses and critiques of Lave and
Seskin's work, have found similar relationships (Thibodeau ejt aj_., 1980;
Christainsen and Degen, 1980; Schwing and MacDonald, 1976; Mendelson and
Orcutt, 1979). Others have demonstrated a much smaller influence of
sulfur-containing particles and other particle pollutant indicators (Crocker
et al_., 1979; Lipfert, 1980), while Gerking and Schulze (1981) found a
negative, though non-significant, association.
In general, like any epidemiological studies, these models can only be
approximately correct; the surrogate explanatory variables can never lead
to an adequately adjusted analysis, and separating associations between
mortality rates and pollutant and confounding variables is impossible (Ware
et^l_., 1981). Thus, these studies deal with unknown levels of exposure of
-------
B-49
ill-defined groups of individuals to unspecified pollutants for unstated
periods of time, and fail to control for many variables known to affect
health status. As such, this group of cross-sectional mortality studies,
although suggestive, do not provide reliable quantitative evidence on
effects of particulate matter and sulfur oxides. They are, however, not
inconsistent with the evidence from acute studies which suggests that a
linkage between mortality and pollution may occur at levels below these
observed in the more extreme episodes.
-------
APPENDIX C. VISIBILITY—EFFECTS, MECHANISMS AND QUANTITATIVE RELATIONSHIPS
This appendix discusses and evaluates the key studies in the
criteria document that provide evidence on the effects associated with
reduced visibility, and on both mechanisms and quantitative relationships
linking reduced visibility to atmospheric particles.
A. Evaluation of Visibility
Visibility impairment may adversely affect public welfare in essentially
two areas: 1) the subjective enjoyment of the environment (aesthetics,
personal comfort and well-being); and 2) transportation operations. As dis-
cussed in the criteria document, the aesthetic aspects of visibility values
can be categorized according to: 1) social/political criteria, community
opinions and attitudes held in common about visibility; 2) economic criteria,
the dollar cost/benefit associated with visibility; and 3) psychological
criteria, the individual needs and benefits resulting from visibility.
These categories are not exclusive, but relate to different approaches for
measuring somewhat intangible values.
1. Aesthetic Effects
Assessment of the social, economic and psychological value of
various levels of visibility is difficult. The criteria document, an EPA
report to Congress (EPA, 1979), Rowe and Chestnut (1981), and Fox, Loomis,
and Greene (1979) discuss and evaluate several approaches that have been
used or proposed towards this end. In particular, the criteria document
indicates that preliminary studies of social awareness/perception and the
economic value of visibility in urban and non-urban areas support the
notion that visibility is an important value in both settings.
-------
C-2
Early social awareness studies (Schusky, 1966; DHEW, 1969, p. 100-102;
Wall, 1973) conducted in polluted urban areas have generally shown that at
higher pollution levels an increasing portion of the population is aware
of air pollution and considers it a nuisance. In St. Louis, a linear
2
relationship was observed between annual particle levels (50 - 200 ug/m
3
TSP) and public awareness and concern. At 80 ug/m annual geometric mean
TSP, about 10% of those surveyed reported air pollution as a nuisance
(Schusky, 1966). Although it is reasonable to attribute more of these and
other perception results to particulate matter than to gaseous pollutants
(Barker, 1976; Wall, 1973), the relative importance of visibility degradation
by plumes and haze as compared to dustfall was not clearly addressed in
these studies. A more recent study of perception of air pollution in Los
Angeles (Flachsbart and Phillips, 1980) represents the most comprehensive
evaluation of major pollutant indicators and perception to date. Five
gaseous pollutants (03> CO, N02, NO, S02), 4 particle related indices (TSP,
dustfall, CoH, visibility), and 6 averaging times were compared with
perceived air quality as reported by 475 respondents living in 22 residential
areas in Los Angeles County. Only two indices, visibility and ozone, were
consistently significantly related (a = 0.001) to perceived air quality
for all averaging times. The highest correlation coefficient (Kendall's T)
occurred for yearly visibility (T = -.29) and for number of days visibility
was less than 3 miles (T = 0.32).* Of the other particle indices, only
monthly average dustfall was significantly correlated (T = .12) with
perception. Consistent with other studies, the survey also found that air
*KendalVs T is a non-parametric statistic. The negative correlation between
the number of people perceiving poorer air quality and visibility and the
positive correlation with the number of days visibility is less than three
miles are consistent with expectations.
-------
C-3
quality is valued less by minority groups and long-time urban residents
than by whites (all income classes) and those with some history of rural
residence.
The two major approaches to economic valuation of visibility include
1) survey (e.g., iterative bidding) and 2) property value studies. The
major published iterative bidding studies of visibility, conducted in the
rural southwest and in the Los Angeles area (South Coast Air Basin), are
summarized and evaluated in Table C-l. The Four Corners and Lake Powell
studies deal only with single sources and visible plumes, while the Farmington
and Los Angeles studies address haze. The preliminary nature of these
studies makes them useful primarily as qualitative indicators of the economic
value of visibility. Among the more important limitations of the published
results are the following:
1) None of these studies has measured existence values (benefit
of just knowing pristine areas exist, regardless of intent
to use them) or options values (wish to preserve the opportunity to
view an unimpaired vista). Rowe and Chestnut (1981) suggest that
existence values of good visibility in natural settings may be
significantly greater than measured activity values.
2) The studies may be subject in varying degrees to methodological
problems. The Farmington study, in particular, discovered a number
of biases probably related to the credibility of the contingent market.
These biases were not always large but show the difficulty of valuing
visibility through iterative bidding.
3) Even if the available results could be taken at face value, so few
studies have been conducted that results cannot be directly transferred
to other areas of the country. For example, it might be expected that
-------
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C-5
willingness to pay for improved visibility in Los Angeles might be
greater than that for areas in flat terrain without background hills or
mountains.
Despite their limitations, the iterative bidding studies suggest that
visibility is of substantial economic value in both urban and natural settings,
Although the value of visibility in other areas may vary significantly from
that suggested by studies in the rural southwest and Los Angeles, no a priori
reason exists to suggest that visibility is of little value in heavily
populated eastern urban and rural areas. With respect to recreational
settings, of the 23 most heavily used national parks and monuments, 11 were
in the East (NFS, 1981). In 1979 over 90 million visits were recorded in
all eastern National Park Service managed facilities.
A large number of property value studies related to air quality have
been conducted. These have been reviewed by Freeman (1979) and Rowe and
Chestnut (1981). Although a variety of air quality indicators have been used,
the results of awareness/perception studies strongly suggest visibility plays
an important role in air quality related impacts on property values
(Rowe and Chestnut, 1981). This contention is best documented in the case of
the South Coast Air Basin property value survey (Brookshire _et aj_., 1979).
There, the estimated annual benefit of a 25% - 30% improvement in air quality
based on property values was about $500 per household. These results are
qualitatively similar to the companion iterative bidding study (about $300/
household). The bidding study suggests that 22-55% of the bids to improve
visibility were related to aesthetic effects. Both the bidding results and
the perception study (Flachsbart and Phillips, 1980) conducted in the same
area support the possibility of substantial impacts of visibility on Los
Angeles area property values.
-------
C-6
None of the other published property value studies are accompanied by
companion studies that suggest what portion willingness to pay for improved
t
air quality may be due to visibility. Moreover, theoretical problems
remain in relating willingness to pay functions from property value differentials
(Rowe and Chestnut, 1981). No single study has examined all of the variables
that might be important in influencing property values. Because air pollution
tends to be a small influence compared to other variables, earlier studies
that examined a limited number of variables are particularly suspect. In
essence, the available literature suggests that perceived air pollution,
and hence visibility, may have tangible effects on property values in urban
areas such as Washington, Boston, Los Angeles, and Denver (Rowe and Chestnut);
nevertheless, additional theoretical and empirical work is needed before
reliable and transferable quantitative relationships for visibility evalua-
tion can be established.
2. Transportation Effects *
Although all forms of transport may be affected by poor visibility
(e.g., slowing of highway traffic by anthropogenically induced fog), at
current ambient levels, aircraft operations appear to be most sensitive. *
When visibility drops below 3 miles, FAA safety regulations restrict flight
in controlled air spaces to those aircraft and pilots that are certified
for operation under Instrument Flight Rules (IFR) (FAA, 1980a). The most <
severe impact in such cases is usually on non-IFR general aviation aircraft
which are, in effect, grounded or forced to search for alternate landing
sites. In 1979, there were about 210,000 active general aviation aircraft (
which accounted for about 84% of total airport operations. Over 23% of all
general aviation aircraft had no IFR capability (Schwenk, 1981). Estimates
of the percentage of pilots certified for IFR are not available. Commercial, i
military, and other IFR aircraft operation also may be affected by reduced visibility.
-------
C-7
Under IFR conditions, the number of arrivals and departures per hour can be
significantly decreased as compared to Visual Flight Rules (VFR) conditions.
The effect varies with airport, and in some cases, the visual range cutoff
for the most efficient visual approaches (VAPs) may be 5 miles (FAA, 1980b).
For example, the performance standard for one configuration at Boston Logan
International Airport is 109 operations per hour for VAPs (5 miles), 79 operations
per hour for "basic" VFR (3-5 miles), 79 operations per hour for "controllers"
visual approach IFR (2-3 miles), and 60 operations per hour for "category
I" IFR (2 miles). Thus, depending on airport configuration, schedules, and
the extent and duration of haze induced visibility reduction, delays in
commercial and other aircraft operations can occur. In large segments of the
eastern U.S., midday visibilities less than 3 miles with no obvious
natural causes occur 2-12% of the days in the summer and 1 - 5% of the
time during other seasons (CD, Table 9-5, Figure 9-31). Visibilities
less than 5 miles would, of course, be more frequent. Based on typical
eastern summertime diurnal cycles in humidity and light scattering (e.g.,
Ferman et ^1_., 1981), the occurrence of morning visibilities (6-8
a.m.) less than 3-5 miles would be somewhat greater than for midday
visibility, even discounting naturally occurring fog.
Compared with other modes of transport, air travel is generally
considered to be safe. It is not, however, riskfree; based on reasonable
expectations and the available record, air pollution visibility impairment
would tend to increase risks of aircraft operation (U.S. Senate, 1963). Failure
to see and avoid objects and obstructions during flight is one of the ten
most frequent cause factors for general aviation accidents (FAA, 1978).
Another important cause factor is continued VFR flying into adverse weather.
-------
C-8
Although such action is normally attributed to errors in judgment (FAA, 1978),
in some cases, pilots who by choice or necessity fly in the mixing layer,
could fail to distinguish storm fronts or thunderclouds from the prevailing
haze until they are upon the adverse weather. The available data in the
criteria document do not, however, permit any quantitative assessment of
the risks to commercial and general aviation aircraft operation associated
with reduced visibility.
The available information on the effects of visibility on transportation
suggest that episodic eastern regional haze tends to curtail substantial
segments of general aviation aircraft and slow commercial, military, and
other IFR operations on the order of 2-12% of the time during the summer.
The extent of any delays varies with airport. Reduced visibility may also
tend to increase risks associated with aircraft operations in the mixing
layer, but quantitative assessments are not available.
B. Mechanisms and Quantitative Relationships
The mechanisms by which atmospheric pollutants degrade perceived
visibility are reasonably well understood (Middleton, 1952; Friedlander,
1977). Visibility impairment is the result of light scattering and absorption
by the atmospheric aerosol (particles and gases). The "extinction" or
attenuation coefficient (aext) is a measure of aerosol optical properties and
is the sum of blue sky or Rayleigh scattering by air molecules (aD ),
Kg
absorption by pollutant gases (a), and particle scattering (a__) and absorption
ag sp
(a,,,)- Visibility is inversely related to total extinction from these sources.
ap
Blue sky scattering is relatively constant and is significant only under
relatively pristine conditions. Absorption by pollutant gases, notably
N02, usually contributes only a small amount to total extinction (CD, p. 9-
20). Even brown hazes in Denver and Los Angeles formerly attributed solely
-------
C-9
to NCL, are often dominated by particles (Husar and White, 1976; Groblicki
et_ &]_., 1980). Thus atmospheric extinction and visibility impairment are
normally controlled by particulate matter. Important causes include natural
sources (fog, dust, forest fires, sea spray and biologic sources) and
anthropogenic sources of sulfur oxide, soot and other particles, nitrogen
oxides, and volatile organics (EPA, 1979).
Reduction of visual range by particle extinction is normally dominated
by fine particles.* The only important exceptions are some naturally
occurring phenomena including precipitation, fog, and dust storms, where
larger particles control visibility. Theoretical calculations show that
extinction/unit mass efficiencies are substantially greater for fine particles
in the 0.1 to 2.0 pm size range than for larger particles (Faxvog and Roessler,
1978). For most commonly observed size distributions of particulate matter,
the increased extinction efficiency of fine particles results in fine particles
accounting for most of total extinction even though they are only a third
or so of the total mass of particles (Latimer et. a]_., 1978). This theoretical
expectation is borne out by the unique experiment of Patterson and Wagman
(1977) where independent measurement of light scattering and particle size
distributions verified the importance of fine particles in controlling
scattering in New York City. In addition, a number of experiments have
found consistently high correlation (.8 to .98) between light scattering and
fine mass (CD, Table 9-1).
The relative importance of scattering and absorption as well as the
extinction efficiency per unit equibilibrated mass (y) of fine particles
varies with location. On large regional scales, about 80-95% of particle
*For purposes of this document, fine particles include those smaller than
2.5 ym AED.
-------
C-10 •
extinction is due to light scattering (Waggoner ejt al_., 1980; Wolff et al.,
1980), with the remainder due to absorption. In urban areas absorption may
*
account for up to 50% of particle extinction (Waggoner et_ al_., 1980; Weiss,
1978). The particle scattering efficiency/unit mass varies from about
p
3 - 5 m /g at various sites, with higher values tending to occur in eastern
locations (CD, Table 9-1).
The variations in fine particle extinction noted above are due largely to
variations in size, chemical composition and to some extent, relative humidity.
Based on theoretical (Faxvog and Roessler, 1978) and empirical (e.g., Trijonis
et a]_., 1978 a,b; Stevens e_t a]_, 1980; Groblicki et al_., 1980) results, two components,
hygroscopic sulfates and elemental carbon, generally tend to be most significant.
Sulfate, with associated ammonium, and hydrogen ions and water, often dominates
regional fine mass and extinction, particularly in the East, while elemental
carbon accounts for most of the particle absorption observed in urban areas.
The relative importance of sulfates to extinction depends on relative humidity,
both at the site in question and perhaps along the transport path where
secondary formation occurs. Project VISTTA found that sulfates formed in
dry desert air were of relatively low light scattering efficiency, compared *
to sulfates apparently formed in more humid conditions in southern California
and transported to the desert (Macias e_t al_. , 1980). Our understanding of
the role of fine organics and nitrates in light scattering is hindered ^
by the lack of reliable data. In the eastern regional haze these components
are likely to amount to less than half of the sulfate component, but may
dominate scattering in western urban areas such as Denver and Portland •
(Groblicki £t aj_., 1980; Cooper and Watson, 1979). The remainder of fine
mass (soil-related elements, lead and trace species) contributes only a
minor amount to extinction in most U.S. atmospheres (Stevens ejt aj_., 1978). 4
-------
C-ll
Humidity is important to visibility because of the presence of fine
hygroscopic aerosols (e.g., sulfates) which tend to absorb atmospheric
water and thus increase light scattering. Measurements in several areas
suggest that the extinction due to fine particle scattering will increase
by a factor of about two as relative humidity is increased from 70 to 90%
(Covert et^ aj_., 1980). Based on laboratory studies, reduction in humidity
from 90% to 70% might not produce corresponding decreases in scattering
because of hysteresis (Tang, 1980). In essence, the hysteresis effect
means that the aerosol may tend to retain water absorbed at higher humidities
even at lower relative humidities. This effect has not yet been demonstrated
to occur in the ambient air.
Through the Koschmieder equation, the extinction coefficient, measured
or estimated from fine particle levels, may be used to estimate visual range
(CD, p. 9-6). The relationship has the general form:
V = _K_ (C-l)
aext
Where: V = the visual range, the distance at which a large black
object is just visible against the sky.
a . = total extinction, the sum of light scattering and
absorption by air molecules, fine particles, and
N02 (CD, p. 9-19).
K = a function of the intrinsic target brightness and observer
threshold contrast (E). E is a function of the observer
and of target size.
Although a number of factors may limit the applicability of this
relationship, for homogeneous pollution, reliable extinction measurements,
uniform illumination, large dark targets, and moderate visual ranges,
agreement between experiment and theory is rather good. The correlation
-------
C-12
between visual range and the scattering portion of extinction is typically
on the order of 0.9 where comparisons have been made (CD, p. 9-9 to 9-10).
This relationship depends, in part, on human perception of contrast
as well as target size and brightness. For a typical observer with a
reasonable time for observation and large black targets, a "threshold" of 0.02
is commonly assumed and K = 3.9 (CD, p. 9-9). As noted in the criteria
document empirical determinations of K have yielded somewhat lower values,
ranging from 1.7 to 3.6 for studies discussed in the criteria document
(CD, p. 9-9). The most complete analysis (Ferman et al_. , 1981) reported
a value of 3.5 for well mixed periods. The lower values likely arise from
higher threshold contrasts, non-ideal targets, (too bright and/or too
small), and the exclusion of absorption estimates. The available data
also suggest that reported airport visibilities may significantly underestimate
standard visual range. Thus, lower values of K may be more appropriate
for matching airport data with higher values for observations in natural
settings (CD, p. 9-43).
The relationship between extinction due to dry particle scattering
and fine mass is sufficiently stable over a wide range of areas that
reasonably quantitative estimates of fine/particle visibility relationships
can be made where long-term relative humidity is low (<70%) and particle
absorption is small or otherwise known. For such purposes, the Koschmieder
relationship can be written as:
(C-2)
V= K
Where FMC = fine mass concentration, and
* = (o
ap
rti
distance, (e.g., km" )
a = particle absorptioncoefficient (in units of inverse
p "
a = particle scattering coefficient
-------
C-13
a0 = Rayleigh or "blue sky scattering" (Rg - 0.12 km"1)
Kg
a = absorption by gases (usually small in non-urban areas)
ag
Thus, with appropriate K and y derived from available studies, visual
range can be estimated from fine mass. Although less certain, the measurements
of Covert e_t al_. (1980) and regression relationships developed by a number of
investigators can be used to estimate fine particle/visibility relationships
for higher humidities and hygroscopic aerosols. The criteria document
indicates that to correct for the humidity effect, y (as determined by heated
nepholometers and equilibrated filters) should be increased by a factor of
about 1.5 at 80% RH, and about 2 at 90% RH. The Koschmieder relationship
strictly applies for short-term observations. In estimating long-term
(e.g., annual) average visibility from long-term fine mass data, the temporal
distribution of fine particle concentrations (e.g., lognormal) must be specified,
or median values used.
Figure 7-2, adapted from Figure 9-18 of the criteria document, presents
fine particle/visual range relationships for three cases selected as
representative of the range of normal situations encountered in the
eastern U.S. regional haze and in western urban areas:
2
1) Y = 3 m /g; representative of a dry aerosol (CD, Table 9-1) at
<_ 50%2RH. Absorption may be 10% of extinction where a /unit mass =
2.7 m /g. This is close to typical measurements in western
areas but below most eastern data (CD, Table 9-1).
2
2) Y = 6 m /g; representative of the same aerosol as in 1) at 90%
humidity, a increased by a factor of 2.
p
3) Y = 10 m /g, representative of the similar aerosol, but
with absorption accounting for 40% of extinction. Such high
absorbtion (predominately associated with carbon) is likely only in
urban areas.
-------
C-14
Each case may actually be representative of a variety of aerosols. For
example, case 2 closely approximates the aerosol observed by Ferman et al.
(1981) during their month long study in the Blue Ridge Mountains, even
though typical daytime humidities were less than 70%. In this study
p
corrected y = 5.5 m /g as measured by heated nephelometer and when the measured
effect of condensed water is added, y increases. Thus, even though 90% RH
is comparatively rare during the daylight hours, case 2 is likely to be
closer to typical summertime eastern conditions than is case 1.
Figure 7-2 shows the powerful effect of humidity and carbon absorption
on visual range for a given particle level. The curves also indicate that
visibility becomes more sensitive to changes to fine particle levels below
about 100-200 yg/m . Results from this figure should not be compared
directly with airport visibility data. Due to non-ideal targets and
observation conditions, airport visibilities will tend to be lower than
predicted by the Koschmeider relationship with K = 3.9.
-------
APPENDIX D. TERMS USED TO INDICATE PARTICULATE MATTER
A number of terms are used in the staff paper to indicate various
fractions of particulate matter. Table D-l lists the most frequently
used terms and briefly summarizes the relevant size range, definition, and
measurement principles for each. Terms are grouped according to their
discussion in the staff paper. The table is intended as a ready reference
for the reader. A more complete listing of terms and discussion of measurement
can be found in the criteria document.
Because conversion among various indicators may be site and time
specific, conversion factors are not listed in the Table. Approaches for
bounding TP levels from BS readings for certain periods of time in London
are presented on pages 96-99 (Section VI-C) of the main text. The relationships
between TSP and both IP and TP for contemporary US urban areas are summarized
on page 19 (Section IV) and pages 108 and 115 (Section VI).
-------
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APPENDIX E. CASAC CLOSURE MEMORANDUM
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E-2
\
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON. D.C. 20460
January 29, 1982
OFFICE OF
THE ADMINISTRATOR
Subject: CASAC Review and Closure of the OAQPS Staff
Paper for Particulate Matter /V
From : Sheldon K. Friedlander, Chairman
Clean Air Scientific Advisory Committee
To : Anne M. Gorsuch
Administrator
The Clean Air Scientific Advisory Committee (CASAC)
recently completed its second and final review of the document
entitled Review of the National Ambient Air Quality Standards
for Particulate Matter; Assessment of Scientific and Technical
Information, OAQPS Staff Paper. The Committee notes with
satisfaction the improvements made in the scientific quality
and the completeness of the staff paper. It has been modified
in accordance with the recommendations made by CASAC in July
and November 1981. This document is also consistent in all
significant respects with the scientific evidence presented
and interpreted in the combined criteria document for sulfur
oxides and particulate matter. It has organized the data
relevant to the establishment of particulate primary and
secondary ambient air quality standards in a logical and
compelling way, and the Committee believes that it provides
you with the kind and amount of technical guidance that will
be needed to make appropriate revisions to the standards.
CASAC has prepared this closure memorandum to inform you
more specifically of its major findings and conclusions
concerning the various scientific issues and studies discussed-
in the staff paper. In addition, the Committee's review of the
scientific evidence leading to the particulate standard revision
leads to a discussion of its own role in the process for setting
the standard.
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E-3
CASAC Conclusions and Recommendations on Major Scientific Issues
and Studies Associated With the Development of Revised NAAQS for
Particulates
1. Based upon the review of available scientific
evidence/ a separate general particulate standard remains a
reasonable public health policy choice.
2. CASAC reaffirms its initial recommendation of July 1981
to establish a 10 micrometer cut point for a revised primary
particulate standard. This recommendation is based upon a
recognition of the periodic, and sometimes frequent, tendency of
both healthy and sensitive populations to breathe through their
mouths and/or oronasally. This practice increases the amount of
particulate matter that can penetrate into the thorax because
the larger particles are not filtered in the oronasal passages.
Deposition of particulates into this region is of special
concern to those individuals with pre-existing respiratory
problems and children. In addition, the collection of particles
of less than 10 micrometer diameter size more closely resembles
particles passing into the thoracic region of the human
body than the collection of larger sized particles. Furthermore,
monitors equipped for a 10 micrometer cut are less wind dependent
and can provide a more accurate profile of the contemporary
ambient air than samplers which measure total suspended particles.
CASAC1s recommended size cut is also similar to proposals
of other scientific associations. For example, 88% of the national
members of the Air Quality Committee of the International Standards
Organization recently voted for a particulate cut point at
10 micrometers for sampling particles which can deposit in the lungs.
The CASAC recommendation is based upon available scientific
data. Other individuals and groups have discussed the
possibility of establishing a revised particulate standard
at a size cut considerably less than 10 micrometers. However, for
the current revision of the standard, the scientific data more
readily support a 10 micrometer size cut.
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E-4
3. CASAC reached several major conclusions concerning the
revision of the 24-hour and annual particulate standards. At
the upper bound of the proposed ranges of 150-350 ug/m3 for the
24-hour and 55-110 ug/m3 for the annual averages, detectable
health effects occur in the.populations evaluated in the epi-
demiological studies. Since the upper end of these ranges contain
little or no margin of safety, it would be appropriate to consider
lower values for revising the 24-hour and annual standards. In
addition, the stated ranges are based solely on quantitative
evidence reported in epidemiological studies. A final decision
on a revised standard should also incorporate information generated
through controlled human, animal toxicology, and from other less
quantitative epidemiological studies discussed in the criteria
document.
There is an absence of a clearly definable exposure-response
relationship for particles, as amply discussed in the criteria
document and the staff paper. In addition, because airborne
particles are heterogeneous in composition, the potential
toxic effects of individual constituents should be considered
in setting the standard. Thus, compared to margins of safety
set for pollutants such as ozone and carbon monoxide, where
exposure-response relationships are better established and
small margins of safety are more justifiable, CASAC believes you
should consider a revised standard with a wider margin of
safety.
4. The Committee reached general agreement that the
annual particulate standard should consist of an arithmetic
mean. It is recommended that the 24-hour standard include a
statistical form and that the number of exceedences is set
in relation to the revised standard level.
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E-5
5. During the past decade, the link between visibility and
fine particle mass concentrations has been convincingly documented.
Visibility is a sensitive indicator of accumulated man-made
pollutants in the ambient-air. The public cares about visibility
and is willing to pay something for clean air. However, the
quantitative basis for establishing a psychological, economic,
transportation or any other welfare cost associated with
visibility impairment has not been established. In addition,
controls required to achieve a given visibility standard are
not known due to the complexities of pollutant transport and
transformation.
Defining acceptable levels of visibility is a social/
policy judgment as well as a scientific decision, but science
can provide some guidance. The upper end of the 8-25 ug/m^
range for fine particles (those particles with a diameter
size of less than 2.5 micrometers) would tend to maintain
the status quo for the eastern United States and some western
urban areas, but would permit air quality degradation for large
areas in the west including national parks. Also, it is highly
uncertain that the recommended thoracic particle ranges for the
primary standard will protect visibility. The S-25 ug/m^
range for fine particles suggested for visibility protection
is a seasonal and spatial average, unlike peak values which
will be recommended for the primary standard.
The strongest case for a visibility related standard is
one that links emissions of nitrogen oxides and sulfur dioxide
with the interrelated aspects of acidic deposition, possible
climatological effects, and visibility. Each of these three
air quality issues is related to the fine particles which
originate both as primary particulate emissions and as
secondary aerosols from atmospheric conversions of sulfur
dioxide and nitrogen oxides emitted as vapors. In terms of a
control strategy to protect public welfare, it may be more
efficient to consider a common standard linked to fine
particles than to establish a separate set of controls for
each of these problems and pollutants.
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E-6
6. The Committee's evaluation of scientific data and
studies in the criteria document and the staff paper lead it
to conclude that there is no scientific justification for the
establishment of a particulate standard for the specific
protection of vegetation.
7. The Committee discussed what effect elimination of a
Total Suspended Particulate (TSP) standard would have on the
environment. The soiling and nuisance aspects of TSP are
essentially local air quality problems because such coarse
particles are not transported great distances. This contrasts
with visibility or oxidant related problems which are
distinctly issues of long range pollution transport.
Individuals who serve on the Committee made various recommenda-
tions regarding retention or elimination of a secondary
standard for TSP, but no clear consensus evolved.
The Processfor Setting the Ambient Particulate Standard
In its report of September 21, 1981, CASAC made several
major recommendations relating to the process for setting
ambient air standards. The Committee is aware that your
staff is analyzing its report and is awaiting a response.
A major underlying assumption of the Committee's recommen-
dations was the need to make more explicit the relationship
between the scientific evidence in the criteria document and the
staff paper and the eventual selection of a numerical level for
individual standards. The Committee strongly believes in the
need to clarify the standard setting process by identifying
the key studies that will shape the determination of a standard.
Intensive evaluation of such studies by CASAC and the public
will considerably increase your ability to set a scientifically
supportable standard.
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E-7
The Committee is greatly encouraged by your decision to
improve the format and content of OAOPS scientific issue staff
papers. In the Draft Staff Paper for Particulate Matter
key studies are identified a.nd their implications for setting
primary and secondary standards are discussed. More importantly,
the inclusion of numerical ranges and their supporting rationale
enabled the Committee and the public to critically examine the
staff's proposed use of the studies. This led to a marked
improvement in the quality of the public dialogue concerning
the scientific basis for revising the standard. CASAC commends
your effort and recommends that all staff papers developed
for ambient air standards contain numerical ranges.
CASAC recognizes that your statutory responsibility to
set standards requires public health policy judgments in
addition to determinations of a strictly scientific nature.
While the Committee is willing to further advise you on the
particulate standard/ we see no need, in view of the already
extensive comments provided, to review the proposed particulate
standards prior to their publication in the Federal Register.
In this instance, the public comment period will provide
sufficient opportunity for the Committee to provide any
additional comment or review that may be necessary.
-------
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1.
4.
7.
9.
12
15
16
REPORT NO.
EPA-450/5-82-001
2.
TITLE AND SUBTITLE
Review of the National Ambient Air Quality
for Particulate Matter: Assessment of Scie
Technical Information - OAQPS Staff
AUTHOR(S)
PERFORMING ORGANIZATION NAME AND ADDRESS
Office of Air, Noise and Radiation
Office of Air Quality Planning and Standar
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 277
. SPONSORING AGENCY NAME AND ADDRESS
. SUPPLEMENTARY NOTES
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
Standards January 1982
ntific and 6- PERFORMING ORGANIZATION CODE
Paper
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
dS 11. CONTRACT/GRANT NO.
11
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
. ABSTRACT
This paper evaluates and interprets the available scientific and technical infor-
mation that the EPA staff believes is most relevant to the review of primary (health)
and secondary (welfare) National Ambient Air Quality Standards for Particulate Matter
(PM) and presents staff recommendations on alternative approaches to revising the
standards. The assessment is intended to bridge the gap between the scientific review
in the EPA criteria document for particulate matter and sulfur oxides and the judge-
ments required of the Administrator in setting ambient air quality standards for
particulate matter.
The major recommendations of the staff paper include the following:
1) that TSP be replaced by a new particle indicator that includes only those
particles less than a nominal 10 ym (thoracic particles or PM-i0);
2) that the levels of both 24-hour and annual standards be revised;
3) that the statistical form of the standard should be changed;
4) consideration of a fine particle (<2.5 urn) secondary standard recognizing the
advantages of combining any action with later decisions on acid deposition programs;
and
5) consideration of secondary standards related to soiling and nuisance.
17.
a
DESCRIPTORS
KEY WORDS AND DOCUMENT ANALYSIS
Parti culate Matter
Aerosols
Air Pollution
Sulfur Oxides
18
DISTRIBUTION STATEMENT
Release to Public
b. IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air Quality Standards
19. SECURITY CLASS (This Report) 21. NO. OF PAGES
Unclassified 276
20 SECURITY CLASS (This page) 22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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