AIR QUALITY CRITERIA
FOR
PARTICULATE MATTER
SUMMARY AND CONCLUSIONS
U S DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Consumer Protection and Environmental Health Service
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RESUME
In addition to health considerations, the economic and aesthetic
benefits to be obtained from low ambient concentrations of particulate
matter as related to visibility, soiling, corrosion, and other effects
should be considered by organizations responsible for promulgating
ambient air quality standards. Under the conditions prevailing in areas
where the studies were conducted, adverse health effects were noted when
the annual mean level of particulate matter exceeded 80 ug/m . Visibility
n
reduction to about 5 miles was observed at 150 pg/m , and adverse effects
3
on materials were observed at an annual mean exceeding 60 ug/m . It is
reasonable and prudent to conclude that, when promulgating ambient air
quality standards, consideration should be given to requirements for
margins of safety which would take into account long-term effects on
health and materials occurring below the above levels.
. This statement, and the following text, are reprinted from
Air Quality Criteria for Particulate Matter, issued in February, 1969,
by the National Air Pollution Control Administration, 801 N. Randolph
Street, Arlington, Va. 22203.
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SUMMARY AND CONCLUSIONS
Page
A. SUMMARY 12-2
1. General 12-2
2. Effects on Health 12-5
3. Effects on Climate Near the Ground 12-8
4. Effects on Visibility 12-9
5. Effects on Materials 12-11
6. Economic Effects of Atmospheric Particulate Matter 12-13
7. Effects on Vegetation 12-13
8. Effects on Public Concern 12-15
9. Suspended Particles as a Source of Odor 12-16
B. CONCLUSIONS 12-16
1. Effects on Health 12-17
2. Effects on Direct Sunlight 12-19
3. Effects on Visibility 12-19
4. Effects on Materials 12-19
5. Effects on Public Concern 12-19
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A. SUMMARY
1. General
The particulate matter commonly found dispersed in the atmosphere is
composed of a large variety of substances. Some of these—fluorides, beryllium,
lead, asbestos, for example—are known to be directly toxic, although not neces-
sarily at levels routinely found in the atmosphere today. The evidence suggests
that there may very well be others whose toxic effects have not yet been recog-
nized. To evaluate fully the effects on health and welfare of the presence of
each of these substances in the air requires that they be given individual atten-
tion, or attention as classes of similar substances. Such evaluations will be
made in separate documents.
This document considers the effects on man and his environment of
undifferentiated particulate matter. These effects oftentimes are produced by
a combination of particulate and gaseous pollutants, the contributions of which
are difficult to distinguish. Moreover, laboratory studies have shown that a
combination of particulates and gases may produce an effect that is greater
than the sum of the effects caused by these pollutants individually.
Particles in the atmosphere, whatever their individual characteristics,
exhibit a number of similar properties, which are for the most part dependent
on the particle size. Most of the available studies on the effects of particulate
air pollution, however, do not specify particle size, and this document is
limited to treating particulate matter as a whole, and to considering the effects
which are generally associated with the presence of particles in the air.
Particulate air pollution, as used in this document, refers to any matter
dispersed in the air, whether solid or liquid, in which the individual particles
are larger than small molecules but smaller in diameter than 500 (j.. (One |j.
is one millionth of a meter.) Particles in this size range stay in the air any-
where from a few seconds to several months.
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Generally speaking, particles smaller than 1 p. in diameter originate in
the atmosphere principally through condensation and combustion, while larger
particles, with the exception of rain, snow, hail, and sleet, arise principally
from comminution. Particles larger than 10 p. in diameter result from mechan-
ical processes such as wind erosion, grinding and spraying, and the pulverizing
of materials by vehicles and pedestrians. Particles between 1 PL and 10 p. in
diameter usually include local soil, process dusts and combustion products
from local industries, and, for maritime locations, sea salt. Combustion
products and photochemical aerosols make up a large fraction of the particles
in the range 0.1 p. to 1 p. in diameter, and, although particles below 0. Ip. in
diameter have not been extensively identified chemically, the typical urban
increase over natural levels of particles in this size range seems to be entirely
due to combustion.
Particles of a size less than 0.1 p. in diameter are characterized by
random motions produced by collisions with gas molecules. They are highly
concentrated, move rapidly, collide frequently, and through sorption and
nucleation of gas molecules and adhesion with other particles grow larger
quickly. Particles larger than 1 p. have significant settling velocities, and
their motions may deviate significantly from the motion of the air.
Measurements of dustfall are commonly used to indicate the mass con-
centration of the settleable portion of particulate air pollution. Typical
2 2
values for cities are 10 to 100 tons/mile -month; as high as 2, 000 tons/mile -
month have been measured in the vicinity of especially offensive sources.
Levels of dustfall have apparently declined in some American cities, and
dustfall measurements are probably not useful as an index of overall particu-
late air pollution. However, dustfall itself constitutes a nuisance, and its
measurement can be used as an index of the dirtiness of air pollution.
Several methods are available for measuring suspended particulate
concentrations. The most commonly used device is the high-volume sampler,
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which consists essentially of a blower and a filter, and which is usually operated
in a standard shelter to collect a 24-hour sample. The sample is weighed to
determine concentration, and is usually analyzed chemically. The hi-vol is
considered a reliable instrument for measuring the weight of total particulatc
matter. Chemical analysis of the hi-vol sample, however, may be limited:
the filter material may contaminate the sample; different substances in the
sample may react with each other; and losses may occur through volatilization
of material. Tape samplers, which collect suspended particulate matter on
filters and analyze the sample optically, are also in common use. While these
samplers are inexpensive and rugged, they yield data which cannot always be
easily interpreted in terms of particulate mass concentration. Other techniques
available for measuring particulate pollution include optical systems, which
provide an indication of concentration without requiring that a sample be taken.
The averaging time used for measuring suspended particulates is not as
significant a factor as it is for gaseous pollutants. The basic unit of time is
24 hours. Values taken over this period may be combined into weekly, monthly,
seasonal, and annual means as required. The relationships between daily and
other longer time periods in the United States is known with some degree of
precision, as data exist for a 10-year period.
Most of the data on mass concentrations of suspended particulates come
from the National Air Surveillance Networks (NASN), which uses the high-
votume sampler. NASN currently operates some 200 urban and 300 nonurban
stations, and is supplemented by State and local networks. From the NASN
data, the annual geometric mean concentrations of suspended particulate
3 3
matter in urban areas range from 60 p.g/m to about 200 p.g/m . The maximum
24-hour average concentration is about three times the annual mean, but values
of seven times the annual mean do occur. Mean particulate concentrations
correlate, in general, with urban population class, but the range of concentra-
tions for any class is broad, and many smaller communities have higher
12-4
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concentrations than larger ones. For nonurban areas the annual geometric
3 3
mean is typically between 10 (j.g/m and 60 |ag/m .
2. Effects on Health
For the most part, the effects of particulate air pollution on health are
related to injury to the surfaces of the respiratory system. Such injury may be
permanent or temporary. It may be confined to the surface, or it may extend
beyond, sometimes producing functional or other alterations. Particulate
material in the respiratory tract may produce injury itself, or it may act in
conjunction with gases, altering their sites or their modes of action.
Laboratory studies of man and other animals show clearly that the depo-
sition, clearance, and retention of inhaled particles is a very complex process,_
which is only beginning to be understood. Particles cleared from the respira-
tory tract by transfer to the lymph, blood, or gastrointestinal tract may exert
effects elsewhere. Few studies have investigated the possibility of eye injury
by particles in the air; only transient eye irritation from large dust particles
presently is known to be a problem.
The available data from laboratory experiments do not provide suitable
quantitative relationships for establishing air quality criteria for participates.
The constancy of population exposure, the constancy of temperature and humid-
ity, the use of young, normal, healthy animals, and the primary focus on
short-term exposures in many laboratory studies make extrapolation from
these studies of limited value for the general population, and singularly risky
for special risk groups within the population. These studies do, however,
provide valuable information on some of the bioenvironmental relationships
that may be involved in the effects of particulate air pollution on health. The
data they provide on synergistic effects show very clearly that information
derived from single-substance exposures should be applied to ambient air
situations only with great caution.
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Epidemiological studies do not have the precision of laboratory studies,
but they have the advantage of being carried out under ambient air conditions.
In most epidemiological studies, indices of air pollution level are obtained by
measuring selected pollutants, most commonly particulates and sulfur com-
pounds. To use these same studies to establish criteria for individual pollutants
is justified by the experimental data on interaction of pollutants. However, in
reviewing the results of epidemiological investigations it should always be
remembered that the specific pollutant under discussion is being used as an
index of pollution, not as a physicochemical entity.
In epidemiological studies consistency of results at different times and
places is important in determining the significance of observations. However,
while polluted air has many similarities from place to place and from time to
time, it is not identical in all communities or at all times, and complete con-
sistency between epidemiological studies should not be expected. There are
not a large number of suitable epidemiological studies available at present,
but those that are available show some consistency in the levels at which effects
were observed to occur.
Considerable data have been presented on a number of air pollution
episodes in London and in New York City. In reviewing these data it should be
remembered that British air pollution measurements are not entirely compar-
able with American measurements. The only published comparison indicates
that the British method of measuring particulates tends to give somewhat lower
readings than American methods.
Excess deaths and a considerable increase in illness have been observed
3
in London at smoke levels above 750 p-g/m and in New York at a smokeshade
index of 5-6 cohs. Sulfur oxides pollution levels were also high in both cases.
These unusual short-term, massive exposures result in immediately apparent
pathologic effects, and they represent the upper limits of the observed dose-
response relationship between particulates and adverse effects on health.
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3 3
Daily averages of smoke above 300 (ig/m to 400 |o.g/m have been asso-
ciated with acute worsening of chronic bronchitis patients in England. No
comparable data are available in this country. Studies of British workmen
found that increased absences due to illness occurred when smoke levels
3
exceeded 200
Two recent British studies showed increases in selected respiratory
illness in children to be associated with annual mean smoke levels above
3
120 ng/m . Additional health changes were associated with higher levels.
These effects may be of substantial significance in the natural history of
chronic bronchitis. Changes beginning in young children may culminate in
bronchitis several decades later.
The lowest particulate levels at which health effects appear to have
occurred in this country are reported in studies of Buffalo and Nashville. The
Buffalo study clearly shows increased death rates from selected causes in
3
males and females 50 to 69 years old at annual geometric means of 100 jag/m
and over. The study suggests that increased mortality may have been associated
with residence in areas with 2-year geometric means of 80 fj.g/m3 to 100 (j.g/m^.
The Nashville study suggests increased death rates for selected causes at
levels above 1. 1 cohs. Sulfur oxides pollution was also present during the
periods studied. In neither study were the smoking habits of the decedents
known.
Corroborating information is supplied from Fletcher's study of West
London workers between the ages of 30 and 59. The data indicate that with a
3 3
decrease of smoke pollution (yearly mean) from 140 M-g/m to 60 pg/m , there
was an associated decrease in mean sputum volume. Fletcher noted that there
may have been changes in the tar composition of cigarettes during the period
studied; such a change could affect the findings. This study provides one of
the rare opportunities to examine the apparent improvement in health that
followed an improvement in the quality of the air.
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3. Effects on Climate Near The Ground
Particles suspended in the air scatter and absorb sunlight, reducing the
amount of solar energy reaching the earth, producing hazes, and reducing
visibility. Suspended particulate matter plays a significant role in bringing
about precipitation, and there is some evidence that rainfall in cities has
increased as the cities have developed industrially.
Suspended particulate matter, in the concentrations routinely found in
urban areas, considerably reduces the transmission of solar radiation to the
ground, creating an increased demand for artificial light. The effect is more
pronounced in the winter than in the summer, when particulate pollution loadings
are higher, and sunlight must penetrate more air to reach the ground. For
similar reasons the effect is also more pronounced during the workweek than
on weekends, during industrial booms, and in higher latitudes. For a typical
urban area in the United States, with a geometric mean annual particulate
3
concentration of roughly 100 (ig/m , the total sunlight, including that received
directly from the sun and that reflected by the sky, is reduced five percent for
every doubling of particle concentration. The reduction is most pronounced on
ultraviolet radiation.
For urban areas in the middle and high latitudes, particulate air pollution
may reduce direct sunlight by as much as one-third in the summer and as much
as two-thirds in the winter. This effect may have implications for the delicate
heat balance of the earth's atmospheric system. In spite of an increase in the
carbon dioxide content of the atmosphere over the past several decades, which
would presumably bring about an increase in atmospheric temperature, mean
worldwide temperatures have been decreasing since the 1940's. Increased
reflection of solar radiation back to outer space, brought about by increased
concentrations of particulate air pollution, may be more than cancelling out
the climatic effect of the increased carbon dioxide. That worldwide particulate
air pollution has been increasing is evidenced by the fact that in the United States
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and in other countries, turbidity, a phenomenon produced by the back-scattering
of direct sunlight by particles in the air, has increased significantly over the
last several decades.
4. Effects on Visibility
Particles suspended in the air reduce visibility, or visual range, by
scattering and absorbing light coining from both an object and its background,
thereby reducing the contrast between them. Moreover, suspended particles
scatter light into the line of sight, illuminating the air between, to further
degrade the contrast between an object and its background.
The scattering of light into and out of the line of viewing by particles in
the narrow range of 0. l[i to IJJL in radius has the greatest effect on visibility.
Certain characteristics of behavior of these particles make it possible to
formulate a useful approximate relationship between visual range and concen-
trations of particulate matter:
L.a A X 103
G'
3
where G' = particle concentration (fj.g/m ),
Ly = equivalent visual range, and
A = 1.2 ' for L, expressed in kilometers and 0.75 '
0.6" 0. oo
for Ly expressed in miles.
The value 1.2 for A is the mid-range value empirically obtained from observa-
tions in a variety of air pollution situations. The data indicate that the range
0.6 to 2.4 covers virtually all cases studied. The relationship does not hold
at relative humidities above TO percent, nor does it apply to fresh plumes from
stacks, and it may not hold for the products of photochemical reactions. A
companion document, Air Quality Criteria For Sulfur Oxides, discusses a
relationship between levels of sulfur dioxide and visual range at various relative
humidities.
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Within the limitations prescribed, the relationship provides a useful
means of estimating approximate visual range from particulate concentrations.
In addition to aesthetic degradation of the environment, reduced visibility has
serious implications for safe operation of aircraft and motor vehicles. At a
visual range of less than 5 miles, operations are slowed at airports because of
the need to maintain larger distances between aircraft. Federal Aviation
Administration restrictions on aircraft operations become increasingly severe
as the visual range decreases below 5 miles . Using the upper and lower bounds
of the relationship described above, visibility could be 5 miles at a particulate
3 3
loading as high as 300 fig/m or as low as 75 ng/m . However, on the average,
visibility can be expected to be reduced to approximately 5 miles at a particulate
3 3
concentration of 150 (j.g/m . At a level of 100 |JLg/m , visibility is reduced to
7-1/2 miles. This limited distance, however, may be related to particulate
concentrations as low as 50 n-g/m3 and as high as 200
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5. Effects on Materials
Particulate air pollution causes a wide range of damage to materials.
Particulate matter may chemically attack materials through its own intrinsic
corrosivity, or through the corrosivity of substances absorbed or adsorbed
on it. Merely by soiling materials, and thereby causing their more frequent
cleaning, particulates can accelerate deterioration.
Laboratory and field studies underscore the importance of the combination
of particulate matter and corrosive gases in the deterioration of materials.
On the basis of present knowledge, it is difficult to evaluate precisely the
relative contribution of each of the two classes of pollution; however, some
general conclusions may be drawn.
Particulates play a role in the corrosion of metals. In laboratory
studies, steel test panels that were dusted with a number of active hygroscopic
particles commonly found in the atmosphere corroded even in clean air.
Corrosion rates were low below a relative humidity of 70 percent; they
increased at relative humidities above 70 percent; and they greatly increased
when traces of sulfur dioxide were added to the laboratory air.
It is apparent that the accelerated corrosion rates of various metals in
urban and industrial atmospheres are largely the result of relatively higher
levels of particulate pollution and sulfur oxides pollution. High humidity and
temperature also play an important synergistic part in this corrosion
reaction. Studies show increased corrosion rates in industrial areas where
air pollution levels, including sulfur oxides and particulates, are higher.
Further, corrosion rates are higher during the fall and winter seasons
when particulate and sulfur oxides pollution is more severe, due to a
greater consumption of fuel for heating.
Steel samples corroded 3.1 times faster in the spring of the year in
3
New York City, where annual particulate concentrations average 176 ng/m ,
than did similar samples in State College, Pennsylvania, where the average
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3 3
concentrations were estimated to range from 60 (j.g/m to 65 (j.g/m . In the
fall of the year, when particulate and sulfur oxide concentrations in New York
were considerably higher than in the spring, the steel samples in New York
corroded six times faster than the samples at State College. Similar
findings were reported for zinc samples. Moisture may have contributed to
the corrosion.
In Chicago and St. Louis, steel panels were exposed at a number of sites,
and measurements taken of corrosion rates and of levels of sulfur dioxide
andparticulates. In St. Louis, except for one exceptionally polluted site,
corrosion losses correlated well with sulfur dioxide levels, averaging
30 percent to 80 percent higher than losses measured in nonurban locations.
Sulfation rates in St. Louis, measured by lead peroxide candle, also correlated
well with weight loss due to corrosion. Measurements of dustfall in St. Louis,
however, did not correlate significantly with corrosion rates. Over a
12-month period in Chicago, the corrosion rate at the most corrosive site
(mean SO level of 0.12 ppm) was about 50 percent higher than at the least
A
corrosive site (mean SO level of 0.03ppm). Although suspended particulate
£i
levels measured in Chicago with high-volume samplers also correlated with
corrosion rates, a covariance analysis indicated that sulfur dioxide
concentrations were the dominant influence on corrosion. Based on these
data, it appears that considerable corrosion may take place (i.e., from
11 percent to 17 percent weight loss in steel panels) at annual average
sulfur dioxide concentrations in the range of 0.03 ppm to 0.12 ppm, and
although high particulate levels tend to accompany high sulfur dioxide
levels, the sulfur dioxide concentration appears to have the more important
influence.
Particulate air pollution damages electrical equipment of all kinds.
Oily or tarry particles, commonly found in urban and industrial areas,
contribute to the corrosion and failure of electrical contacts and connectors.
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Dusts can interfere with contact closure, and can abrade contact surfaces.
Hygroscopic dusts will absorb water and form thin electrolytic films which
are corrosive.
Particulates soil and damage buildings, statuary, and other surfaces.
The effects are especially severe in urban areas where large quantities of
coal and sulfur-bearing fuel oils are burned. Particles may act as
reservoirs of acids, and thereby sustain a chemical attack that will
deteriorate even the more resistant kinds of masonry. Particles stick to
surfaces, forming a film of tarry soot and grit which oftentimes is not
washed away by rain. Considerable money and effort have been spent in
many cities to sandblast the sooty layers that accumulate on buildings.
Water-soluble salts, commonly found in urban atmospheres, can blister
paint. Other particles may settle on newly painted surfaces, causing
imperfections, thereby increasing the frequency with which a surface
must be painted.
The soiling of textiles by the deposition of dust and soot on fabric
fibers not only makes them unattractive, and thereby diminishes their
use, but results in abrasive wear of the fabric when it is cleaned.
Vegetable fibers, such as cotton and linen, and synthetic nylons are
particularly susceptible to chemical attack by acid components of airborne
particles.
6. Economic Effects of Atmospheric Particulate Matter
It is not possible at the present stage of knowledge to provide accurate
measures of all the costs imposed on society by particulate air pollution.
Selected categories of effects can be quantified; it is obvious that these
estimates represent a significant understatement of the total cost.
7. Effects on Vegetation
Relatively little research has been carried out on the effects of
particulate air pollution on vegetation, and much of the work that has been
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performed has dealt with specific dusts, rather than the conglomerate mixture
normally encountered in the atmosphere. This document reports briefly
on some of these specific particulate studies only to illustrate the possible
mechanisms through which particulate matter may affect vegetation. This
information is not presented for the purpose of establishing air quality
criteria on these specific pollutants.
There is considerable evidence that cement-kiln dusts can damage plants.
A marked reduction in the growth of poplar trees I mile from a cement plant
was observed after cement production was more than doubled. Plugging of
stomates by the dust may have prevented the exchange of gases in leaf tissue
that is necessary for growth and development. Moderate damage to bean
2
plants occurred when the plant leaves were dusted at the rate of 0.47 mg/cm -
2
day (400 tons/m -month) for 2 days and then exposed to natural dew. The
mechanism through which the leaves were damaged is not entirely understood
but the crust formed by the dust and moisture may, again, have plugged
stomates, and may have blocked the light needed for photosynthesis. Direct
alkaline damage to tissues was observed. Cement-kiln dusts may change the
alkalinity of soils to benefit or harm vegetation, depending on the species.
Dust deposits may also eliminate predators, and thereby bring on
increased insect injury to plants; they may interfere with pollen germination;
and they may make plants more susceptible to pathogens.
Fluoride dusts apparently have a difficult time penetrating leaf tissue
in physiologically active form, and they are much less damaging to vegetation
than is gaseous fluoride. Soluble fluoride dusts may be absorbed by the plant,
but the amount is relatively small compared to that which can enter the
plant in gaseous form. The evidence suggests that there is little effect on
2
vegetation at fluoride particulate concentrations below 2 p-g/m . Concentratio
of this magnitude and above can sometimes be found in the immediate vicinity
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of sources of fluoride particulate pollution; they are rarely found in urban
atmospheres.
Ingestion of particles deposited on plants can be harmful to animal health
Fluorosis and arsenic poisoning have been brought on through this medium.
Soot may clog stomates and may produce necrotic spotting if it carries
with it a soluble toxicant, such as one with excess acidity. Magnesium oxide
deposits on soils have been shown to reduce plant growth, while iron oxide
deposits appear to have no harmful effects, and may be beneficial.
8. Effects on Public Concern
Several studies indicate that there is a relationship between levels of
particulate pollution, used as an index of air pollution, and levels of public
concern over the problem. A study conducted in 1963 in the St. Louis
metropolitan region found a direct linear relationship between the fraction
of a community's population who said air pollution was a nuisance, and the
annual mean concentration of particulate air pollution in the community.
The relationship, which was derived from data on communities in the St.
Louis area whose a
was formulated as:
3 3
Louis area whose annual concentrations ranged from 50 fig/m to 200 (Jig/m ,
y = 0.3x- 14
where y = population fraction (%) concerned, and
x = annual geometric mean particle
concentration ((j.g/m ).
It is thought that the reaction to suspended particulates as a nuisance
probably occurs at peak concentrations, and not necessarily at the values
representing annual means. However, the relationship provides a useful
example of how the nuisance effect of air pollution relates to concentrations.
Approximately 10 percent of the study population considered air pollution
a nuisance in areas with suspended particulates at an annual geometric
2
mean concentration of 80 (ig/m . At this same level of pollution, 30 percent
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of the study population was "aware of" air pollution. In areas with 120
(annual geometric mean), 20 percent were "bothered by" and 50 percent
were "aware of" air pollution; in areas with an annual geometric mean of
2
160 (j.g/m , one-third of the population interviewed were "bothered by"
and three-fourths were "aware of" air pollution.
Although data from other studies do not readily lend themselves to
quantitative formulation, they do, in general, support the relationship reported
by the St. Louis study. A study of communities in the Nashville, Tennessee,
metropolitan area in 1957 found that at least 10 percent of the population
expressed concern about the nuisance of air pollution at dustfall levels
2
exceeding 10 tons/mi -month.
9. Suspended Particles as a Source of Odor
Particulate air pollution is not ordinarily considered a significant
source of odors. However, there is evidence that liquid and even solid
particles of some substances may be volatile enough to vaporize in the
nasal cavity, and produce sufficient gaseous material to stimulate the
sense of smell. Further, particles may carry absorbed odorants into the
nasal cavity, and there transfer them to olfactory receptors. A survey
of State and local air pollution control officials revealed that approximately
one-fourth of the most frequently reported odors are those which are
known to be, or are suspected to be, associated with particulate air
pollution. The sources of these odorous particles are diverse, including
diesel and gasoline engine exhausts, coffee-roasting operations, paint
spraying, street paving, and the burning of trash.
B. CONCLUSIONS
The conclusions which follow are derived from a careful evaluation by the
National Air Pollution Control Administration of the foreign and American
studies cited in previous chapters of this document. They represent the Admin-
istration's best judgment of the effects that may occur when various levels of
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pollution are reached in the atmosphere. The da from which the conclusions
were derived, and the qualifications which should be considered in using the
data, are identified by chapter reference in each case.
1. Effects on Health
Analyses of numerous epidemiological studies clearly indicate an associ-
ation between air pollution, as measured by particulate matter accompanied by
sulfur dioxide, and health effects of varying severity. This association is most
firm for the short-term air pollution episodes.
There are probably no communities which do not contain individuals with
impaired health who are particularly susceptible to the adverse effects of
elevated levels of particulate matter and sulfur oxides. However, to show
small changes in deaths associated with coincident higher levels of air pollu-
tants requires extremely large populations. In small cities, these changes are
difficult to detect statistically.
The epidemiologic studies concerned with increased mortality also show
increased morbidity. Again, increases in morbidity as measured, for example,
by increases in hospital admissions or emergency clinic visits, are most
easily demonstrated in major urban areas.
For the large urban communities which are routinely exposed to relatively
high levels of pollution, sound statistical analysis can show with confidence the
small changes in daily mortality which are associated with fluctuation in pol-
lution concentrations. Such analysis has thus far been attempted only in London
and in New York.
The association between longer-term community exposures to particulate
matter and respiratory disease incidence and prevalence rates is conservatively
believed to be intermediate in its reliability. Because of the re-enforcing
nature of the studies conducted to date, the conclusions to be drawn from this
type of study can be characterized as probable.
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The association between long-term residence in a polluted area and
chronic disease morbidity and mortality is somewhat more conjectural. How-
ever, in the absence of other explanations, the findings of increased morbidity
and of increased death rates for selected causes, independent of economic
status must still be considered consequential.
Based on the above guidelines the following conclusions are listed in
order of reliability, with the more reliable conclusions first. Refer to Chapter
11 for cautions to be taken in comparing British and American air quality
measurement data.
a. AT CONCENTRATIONS OF 750 M-g/m3 and higher for particulates
on a 24-hour average , accompanied by sulfur dioxide concentrations of
3
715 (Jg/m and higher, excess deaths and a considerable increase in illness
may occur. (British data; see Chapter 11, Section C-l)
3 3
b. A DECREASE FROM 140 Rg/m to 60 |ig/m (annual mean) in
particulate concentrations may be accompanied by a decrease in mean sputum
volume in industrial workers. (British data; see Chapter 11, Section C-4)
c IF CONCENTRATIONS ABOVE 300 ^g/m3 for particulates persist
on a 24-hour average and are accompanied by sulfur dioxide concentrations
2
exceeding 630 |j.g/m over the same average period, chronic bronchitis
patients will likely suffer acute worsening of symptoms. (British data; see
Chapter 11, Section C-3)
d AT CONCENTRATIONS OVER 200 fjig/m3 for particulates on a 24-
hour average, accompanied by concentrations of sulfur dioxide exceeding
3
250 fig/m over the same average period, increased absence of industrial
workers due to illness may occur. (British data; see Chapter 11, Section C-5)
e. WHERE CONCENTRATIONS RANGE FROM lOOfig/m3 to 130 (Jg/m
and above for particulates (annual mean) with sulfur dioxide concentrations
3
(annual mean) greater than 120 |o.g/m , children residing in such areas are
likely to experience increased incidence^of certain respiratory diseases.
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f. AT CONCENTRATIONS ABOVE 100 [ig/m3 for participates (annual
2
geometric mean) with sulfation levels above 30 mg/cm -mo. , increased death
rates for persons over 50 years of age are likely. (American data; see
Chapter 11, Section C-2)
g. WHERE CONCENTRATIONS RANGE FROM 80fag/tn3 to lOO^g/m3
for particulates (annual geometric mean) with sulfation levels of about
2
30 mg/cm -mo. , increased death rates for persons over 50 years of age may
occur. (American data; see Chapter 11, Section C-2)
2. Effects on Direct Sunlight
AT CONCENTRATIONS RANGING FROM 100 M-g/m3 to 150 pg/m3 for
particulates, where large smoke turbidity factors persist, in middle and high
latitudes direct sunlight is reduced up to one-third in summer and two-thirds
in winter. (American data; see Chapter 2, Section C-2)
3. Effects on Visibility
AT CONCENTRATIONS OF ABOUT 150fjg/m3 for particulates, where
the predominant particle size ranges from 0. 2|j. to 1. Op. and relative humidity
is less than 70 percent, visibility is reduced to as low as 5 miles. (American
data; see Chapter 3, Section E-4)
4. Effects on Materials
AT CONCENTRATIONS RANGING FROM 60 (ig/m3 (annual geometric
3
mean), to 180 M-g/m for particulates (annual geometric mean), in the presence
of sulfur dioxide and moisture, corrosion of steel and zinc panels occurs at an
accelerated rate. (American data; see Chapter 4, Section B)
5. Effects on Public Concern
3
AT CONCENTRATIONS OF'APPROXIMATELY 70 [J.g/m for particulates
(annual geometric mean), in the presence of other pollutants, public awareness
and/or concern for air pollution may become evident and increase proportion-
3
ately up to and above concentrations of 200 ng/m for particulates. (See
Chapter 7, Section B-l)
12-19
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