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x>EPA
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United States
Environmental Protection
Agency
August
1984
Trends
in the Quality
of the Nation's Air
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Background
Since the mid-1950's, the nation has maintained a
steady commitment to protecting public health from the
adverse effects of air pollution. This commitment
became a federal mandate with enactment of the 1970
Clean Air Act, and through subsequent amendments to
that Act in 1977.
The Act includes several specific requirements and
deadlines for federal and state governments, and for
industry to reduce air pollution. It also provides for
public participation and intergovernmental consultation.
These have fostered cooperative efforts to solve the
technical and political problems involved in cleaning the
nation's air.
Most states have developed a wide range pf
regulatory, enforcement, and administrative programs
to reduce emissions of air pollution. These include
controls on pollution from factories, industries, and
utilities, and motor vehicle emission inspection and
maintenance programs.
The state programs have been augmented by federal
regulations and control measures for reducing
emissions from new motor vehicles and certain
industrial sources. EPA is specifically responsible for
coordinating and approving most state air pollution
plans and programs. The Agency also provides
substantial technical assistance to states ranging from
information on new air pollution control technology to
studies of the health effects of air pollution.
The development of new and improved air pollution
control technology is especially noteworthy. In recent
years, this has involved state governments and industry
in efforts to establish a variety of innovative pollution
control measures that have reduced the cost of
complying with federal requirements while achieving
commensurate reductions of emissions.
The overall goal of these programs is to ensure that
national ambient air quality standards (NAAQS) are
achieved and maintained for several major air
pollutants. A program has also been developed to
protect very clean air in pristine and wilderness areas.
Several major air pollution problems remain to be
fully solved during the coming years. One of the more
complex of these is the phenomenon of acid rain.
Acid rain is the term used to describe a chain of
complex processes that starts with air pollutant
emissions from utilities, industry, and motor vehicles as
well as natural sources. When these emissions interact
with sunlight and vapor in the air, they are changed into
acidic compounds that may be transported long
distances to other areas and subsequently deposited
with rain, snow, or dust.
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A great deal of public concern has been focused on
the harmful effects that acid rain may be having on fish
and other wildlife, lakes, forests, crops, and on
manmade objects such as buildings and statues. While
certain aspects of the acid rain phenomenon are
generally accepted by the scientific community, many
other causes and effects are uncertain. Some of these
include the geographic range of damage from acid rain,
the rate at which acidification takes place, and the
combination of pollutants that are involved in the
formation of acid rain. For example, most attention has
been focused on the contribution of sulfur emissions to
acid deposition, but other pollutants (including oxides of
nitrogen) are also contributors.
Another major air quality issue involves the transport
of ozone and its precursors. This chiefly involves a
process whereby emissions of volatile organic
compounds are transported over long distances from
the sources of emissions. This phenomenon has
complicated the development of control strategies for
some areas of the country and has also compounded
the difficulties of achieving air quality standards for
ozone, one of the major pollutants. This has been a
particularly difficult problem in some large urban areas
and regions of the country.
Finally, there is the issue of hazardous air pollutants
which pose potentially serious but primarily localized
health problems. EPA is focusing research and technical
studies to determine the health effects and the most
feasible control programs for these pollutants.
Despite these problems, the overall trends in the
quality of the nation's air are encouraging. In many
areas, the air quality standards for protecting public
health were achieved for all major air pollutants by the
end of 1982. In some other areas, where higher levels
have existed for one or more pollutants, achievement
of standards appears likely by the statutory deadlines.
The latest publication that documents recent
progress in reducing air pollution is entitled, National Air
Quality and Emissions Trends Report, 1982.
Highlights of that detailed report are presented in this
booklet.
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Summary
,
Approximately 5,000 air monitors across the country
measure and record air pollution levels. This report
covers data accumulated from these stations between
1975 and 1982 for six principal pollutants.
The six are: lead, carbon monoxide, ozone, nitrogen
dioxide, sulfur dioxide, and particuiates. All six are
known or suspected causes of illness or disease, and
they sometimes occur in concentrations that are above
the health standards set by EPA.
In most respects, the air quality data are encouraging
Pollution levels for five of the six pollutants were lower
in 1982 than in 1975.
For example:
• Levels of lead recorded at 46 urban sites decreased
a dramatic 64 percent between 1975 and T982.
• Carbon monoxide levels recorded mainly at traffic
saturated areas in center city locations fell 31 percent in
the same time period.
• Ozone (smog) decreased 18 percent from recordings
taken at almost 200 sites. The reasons for the
reduction appears to be due to a combination of
decreasing emissions from volatile organic compounds,
which are the precursor of ozone, and a change which
occurred in the calibration procedures at the monitoring
sites between 1978 and 1979. To eliminate the
influence of the calibration change, trends for ozone
were examined for the 1979-1982 time period. Ozone
levels improved by 9 percent during this latest 4-year
interval, a period which was not influenced by the
calibration change.
• Nitrogen dioxide levels were the same in I982 as
they were in 1975, but the levels generally declined
between 1979 and 1982 after increasing slightly
between 1975 and 1978.
• Sulfur dioxide in urban areas decreased 33 percent
from 1975 to 1982.
• The level of particuiates in the air decreased 15
percent between 1978 and 1982.
• How Air Quality is Determined
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How Air Quality Is Determined
Most of our information about pollution levels is
determined from data based on three related
measurements: (1) Trends recorded from the
measurements of ambient air quality; (2) Trends
derived from estimates of total national pollution
emissions; and (3) Trends in the number of times an air
quality standard is violated.
National Trends
in Pollutant
Concentrations
National Trends
in Estimated
Total Emissions
National Violation
Trends
Measurements for ambient air quality trends tell us the
amounts and kinds of pollutants that are concentrated
in the air we breathe at a given time and place.
Pollutant concentrations are measured routinely by
monitoring stations operated by State and local
agencies. National trends (1975-1982) in ambient
pollution concentrations are averaged over available
monitoring sites for each of the six major pollutants.
These trends appear in the set of Graph A's on
subsequent pages of this booklet.
National trends in total emissions are the combined
estimates of the amounts and kinds of pollution that
are generated by automobiles, factories, and other
sources based on the best available engineering
calculations. Emissions estimates tell us how many
millions of metric tons of any pollutant were released
into the air over the nation as a whole. Graph B under
each pollutant shows the estimated total national
emissions for each year between 1975 and 1982.
While national air quality and emissions trends show
the overall progress in reducing various pollutants, the
results will have more significance by considering the
impact at the various monitoring sites.
While it would be impractical to list findings from
thousands of sites across the nation, a reasonable
alternative exists in the National Violations Trends (NVT)
which is used in this booklet. The NVT shows the
average number of days that standards for two of the
pollutants (ozone and sulfur dioxide) are violated at all
monitoring sites during the course of a year. In the
case of carbon monoxide, the number of
non-overlapping 8-hour violations of the standard are
examined. There could be as many as three 8-hour
carbon monoxide violations in a single day, although
that is unlikely.
The NVT is denoted as a set of Graph C's throughout
this booklet. It serves as a complementary statistic to
the set of Graph A's that show the national ambient air
quality trends for the three pollutants.
Two final points should be observed. The first is that
three of the principal emissions have names different
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from the pollutants they help to form in the air.
Emissions of sulfur oxides help to form sulfur dioxide
pollution, while nitrogen oxides emissions contribute to
nitrogen dioxide pollution. In addition, emissions of
volatile organic compounds and oxides of nitrogen are
the principal sources for ozone pollution. Lead, carbon
monoxide, and particulates have the same name for
emissions and the pollutants they form in the air
The second point is that the reductions of pollutant
concentration in the air (as a national average) are often
quite different from those of the estimated emissions
which contribute to that pollutant in the ambient
environment.
For example:
<
(1) Average ambient concentration of sulfur dioxide
declined over 33 percent from 1975 to 1982, although
estimated total emissions of sulfur oxides declined only
17 percent. The monitoring stations recording sulfur
dioxide pollution are principally located in urban areas
where low sulfur fuel is used to maintain air quality
standards. High sulfur fuel is more common in rural
areas with fewer monitoring stations, so the emissions
figures account for these sources.
(2) Ambient carbon monoxide concentrations dropped
31 percent between 1975 and 1982, while total
estimated emissions from highway vehicles decreased
only 17 percent. Both figures reflect improvements as a
result of federal emissions standards on newer motor
vehicles. Carbon monoxide levels are generally
monitored in center city areas where motor vehicle
activity was more or less constant between I975 and
I982. The estimated emissions figures takes into
account a 20 percent increase in vehicle miles travelled
nationally. So, while very significant progress was made
in reducing motor vehicle emissions, the improvements
were partially offset by increases in motor vehicle
travel.
(3) Particulate pollution is another area where apparent
discrepancies exist. Dust and soot from natural dust,
road debris, construction, and other activities contribute
to ambient concentrations of particulates. However,
these are not included in the total emissions inventory.
Consequently, between 1975 and 1982 ambient
concentration of particulates declined less than total
paniculate emissions.
The reader will be better able to grasp the variations
as well as the interrelated significance of air pollution
terminology and measurement if these points are kept
in mind.
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Lead
Sources and
Nature of the
Pollutant
Lead gasoline additives, non-ferrous smelters, and
batten/ plants are the most significant contributors to
atmospheric lead emissions. Transportation sources
alone contribute about 80 percent of the annual
emissions
Health
Effects
Lead is physically harmful when ingested or inhaled. It
accumulates in the body in the blood, in bone, and in
soft tissue Because it is not readily excreted, lead also
affects the kidneys, nervous system, and all
blood-forming organs. People who ingest excessive
amounts of lead may show neurological impairment
such as seizures, mental retardation, and/or behavioral
disorders. Infants and children are particularly
susceptible to lead damage to the central nervous
system.
Trends in
Lead Levels
There was a 64 percent decrease in the average
ambient concentrations of lead, measured at 46 sites
between 1975 and 1982. In order to increase the
number of sites and their geographical representation,
lead trends at 214 sites in 21 states were studied for
the period 1979 to 1982. The results showed a decline
of 43 percent at these sites during the four year period.
Complementing the figures for reduced ambient lead
levels are consumption figures on leaded gasoline from
the U. S. Department of Energy and a private
corporation. These show an overall percentage
decrease of 69 percent for consumption of leaded
gasoline between 1975 and 1982.
Further bolstering the conclusion that very dramatic
reductions in lead pollution have occurred is a recent
study on lead levels in blood in the civilian popoulation
by the National Center for Health Statistics. This study
measured the degree of exposure the
nonmstitutionalized population of the country was
subjected to between 1976 and 1980. It showed a 37
percent decrease in the mean blood lead levels from
the first 6 months of 1976 to the last 6 months of
1980.
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The significant decline in
consumption of leaded
gasoline is depicted in this
graph. The consumption drop
of 69 percent is particularly
noteworthy, since there was
an increase of approximately
20 percent in the number of
vehicle miles travelled
nationally during the same
period. The consumption drop
would have been even greater
if some motorists had not
tampered with their
automobiles by using leaded
gasoline in newer vehicles
designed to burn unleaded
fuel.
Blood Lead Levels
1976-1980
(Graph C)
The National Center for Health
Statistics in 1981 examined the
exposure of the U. S civilian
population to ead between 1976
-1980. Graph C shows that a 37
percent reduction in lead levels
in blood occurred. This 37 percent
reduction in blood lead levels
does complement a 48 percent
decrease in ambient lead levels
and a 56 percent decrease in the
consumption of leaded gasoline
during the same 5-year period.
It can reasonably be concluded
that further reductions in lead
pollution will occur as more and
more older vehicles that con-
sume leaded gasoline are phased
out during the coming years.
Reductions in ambient lead con-
centrations will be reduced at an
even greater rate, if people use
the proper gasoline in their
automobiles. Leaded gasoline
should not be used in newer
automobiles with catalytic
control devices.
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Carbon Monoxide
Sources and
Nature of the
Pollutant
Health
Effects
Over two thirds of the carbon monoxide released into
the air comes from motor vehicle exhaust. It is a
colorless, odorless, and poisonous gas produced by
incomplete burning of carbon in fuels. In certain areas,
transportation sources, especially the automobile, are
responsible for 95 percent of these emissions. Any city
with heavy traffic may have a potential problem from
carbon monoxide, and it can reach very high
concentrations in such areas.
Carbon monoxide is also emitted from some
industrial processes, 6.5 percent of the total estimated
emissions. Solid waste, fuel combustion and
miscellaneous emission sources account for the
remaining 21.1 percent of the total emissions.
In some areas, high levels of carbon monoxide from
motor vehicles are isolated to only a few street corners.
In other cities, the problem is spread throughout the
center-city and along major commuter corridors.
When inhaled, carbon monoxide enters the blood
stream and binds chemically to hemoglobin, the
substance that carries oxygen to the cells. This reduces
the amount of oxygen delivered to all tissues of the
body. The adverse impacts of carbon monoxide on
hemoglobin are determined by the amount of air
breathed, the concentration of the pollutant, and the
length of exposure.
Cigarette smoke also contains carbon monoxide.
Therefore, cigarette smokers have a portion of their
hemoglobin inactivated by this source as well as by
external air pollution.
Carbon monoxide weakens the contractions of the
heart, reducing the amount of blood pumped to various
parts of the body. It results in a reduction of oxygen
available to the muscles and various organs. It
diminishes the functioning of even healthy individuals
and can be life threatening to those with heart disease.
Individuals with anemia, emphysema, and other lung
diseases, as well as cigarette smokers and those living
at high altitudes, are likely to be more susceptible to
the effects of carbon monoxide. Even at relatively low
concentrations, carbon monoxide can affect mental
function, visual acuity, and alertness.
Carbon
Monoxide
Trends
Ambient carbon monoxide concentrations, as measured
at 196 urban sites, have steadily decreased. From 1975
to 1982, carbon monoxide levels dropped at a rate of 5
percent per year with an overall reduction of about 31
percent. Improvements were recorded in all regions of
the country and at 88 percent of the monitoring sites.
Estimates of nationwide carbon monoxide emissions
from all sources show an 11 percent decrease since
8
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1975. Highway vehicle emissions, which are the
dominant contributors to ambient levels, decreased 17
percent between 1975 and 1982. The smaller
reductions in estimated emissions than air quality is
largely due to a 20 percent increase in total vehicle
miles travelled since 1975. Since carbon monoxide
monitors are generally located in areas where traffic
saturation has been a chronic problem, the amount of
traffic and vehicle miles of travel they record is rather
constant from year to year. As a result, the carbon
monoxide concentrations at these locations generally
improve at a faster rate than the estimated nationwide
reduction in emissions.
It can be concluded from this that the 31 percent
reduction in ambient carbon monoxide concentration
reflects the reductions in emissions from new cars
brought about by federal standards on vehicle
emissions. The fact that the estimated highway vehicle
emissions only declined by 17 percent is due to the
fact that motor vehicle travel increased by 20 pecent
during the same time period.
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The National Trend in
Carbon Monoxide
Concentrations, 1975-1982
(Graph A)
This graph shows the
year-by-year changes in annual
average carbon monoxide
concentration between 1975
and 1982 The results were
recorded at monitoring stations
at 196 urban sites
It can be seen that carbon
monoxide levels improved at a
rate of 5 percent per year with
an overall reduction of about 31
percent. The improvement
reflects reduced levels at
traffic-saturated monitoring
sites, chiefly in center-city
areas Since motor vehicle
activity has remained relatively
constant in these urban
downtown areas, the lower
ambient levels reflect almost
totally the reductions in
emissions from new cars
brought about by federal
emissions standards
National Trend in
Emissions of Carbon
Monoxide, 1975-1982
(Graph B)
Total carbon monoxide
emissions were 11 percent
lower in 1982 than in 1975
Highway vehicle emissions.
which are the main source of
the pollutant, decreased a full
17 percent. A 20 percent
increase in total vehicle miles
travelled during the period
partially offsets the decrease in
emissions per car achieved by
federal emissions standards.
There was almost no change
in estimated emissions of
carbon monoxide from sources
other than motor vehicles
Emissions from industrial
processes were down slightly,
but there was a small increase
in emissions from solid waste.
fuel combustion, and
miscellaneous sources
National Violation Trends
for Carbon Monoxide
1975-1982
(Graph C)
The average number of times
the 8-hour carbon monoxide
standard was violated
decreased 87 percent, as
measured at 196 monitoring
sites The average number of
times the standard was
violated fell from 34 to under 5
between 1975 and 1982
Although the average number
of days that standards were
violated was less than 5 in
1982, some areas are
exceeding standards at a far
higher number of times than
the average. So while
significant progress continues
to be made in reducing carbon
monoxide concentrations,
additional work is needed to
bring all affected areas into
compliance
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Sources and
Nature of the
Pollutant
Particulates
Total suspended participate matter is the gerera ie?rr
for particles found in the atmosphere They forrr as
solid particles or liquid droplets small erougn to re^a r
suspended in air. Some particles are large erougr to oe
visible as soot or smoke Others are so small ma: :rey
can be detected only with an electron microscope
Some particles may be formed in the air as a resu:: of
various chemical and physical processes, so the
chemical composition of particulates vanes widely
depending upon location and time of year.
Health
Effects
When airborne particles are inhaled, they may irritate
the respiratory system, or damage the clearance
mechanism of the lungs, thereby contributing to acute
respiratory illnesses in much the same way as gaseous
pollutants do. Prolonged inhalation of certain
components of airborne particles may increase the
number of cases and the severity of chronic respiratory
diseases. Certain particulates, including sulfates.
nitrates, and metals, are being studied to determine
what contribution they may be making (if any) to the
adverse health effects that have been observed from
elevated paniculate levels.
Particulate
Trends
Annual average concentrations of total suspended
particulate (largely soot and dust) decreased 15 percent
between 1975 and 1982. Tnis corresponds to a 27
percent decrease in estimated particulate emissions for
the same period.
It's important to note why there is an apparent
discrepancy between reductions in the ambient
concentration of particulates and the decline in
estimated emissions nationwide. Particulate air qual'ty
levels do not improve in direct proportion to estimated
emissions reductions, because particulate levels are
influenced by factors such as natural dust, street dust,
construction work, and other activities that generate
soot and dust. These are not included in the est mate
of total particulate emissions.
In addition, technical problems related to the filters
used throughout the nation at total suspended
particulate monitoring sites probably led to the
recording of higher air quality values in some of the
years than actually existed. In particular, the filters used
in 1979, 1980, and 1981 were found to record higher
concentrations than the filters used in 1978 and 1982
Therefore, although the air quality values for the
1979-1981 are probably biased high, the decreasing
trend between 1978 and 1982 is valid.
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The air quality improvement between 1978 and 1982
is due not only to reductions in particulate emissions,
but also to more favorable meteorology in 1982 An
analysis of meteorological conditions for 1982 indicated
that lower TSP concentrations may have been caused
in part by abnormally high precipitation
Particulate emissions declined between 1975 and
1982 primarily because of reductions in industrial
emissions nationwide This was attributed both to the
installation of control equipment for industrial processes
and to reduced industrial productivity. Also contributing
to lower emissions were reduced coal burning by
non-utility users, the installation of pollution control
equipment by electric utilities that burn coal, and a
decrease in the burning of solid wastes.
All regions of the country showed lower average
particulate concentration in 1982 than in 1975 The
areas with the largest decreases included parts of the
Northeast, the Great Lakes area, and Pacific Coast
states
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National Trend in Average
Paniculate Concentrations
1975-1982
(Graph A)
This graph shows year-by-year
changes in average ambient
participate concentrations
between 1975 and 1982 based
on measurements taken at
1768 monitoring stations
throughout the country These
showed a decline of 15
percent in the 8-year period
The major reductions were
due to the placing of emission
controls on paniculate sources
such as fuel combustion, solid
waste disposal operations, and
industrial processes
Meteorological conditions may
also have accounted for some
of the reductions that were
recorded
National Trend in
Paniculate Emissions
1975-1982
(Graph B)
The 27 percent reduction m
particulate emissions from
1975 to 1982 is rooted in
reductions of industrial
emissions from the installation
of control processes, and from
reduced industrial productivity
Declining coal consumption by
non- utility users, the
installation of control
equipment by electric utilities
that burn coal and a decrease
m the burning of solid wastes.
all caused further reductions
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Sources and
Nature of the
Pollutant
Ozone
Unlike the other pollutants described in this report,
ozone is not emitted directly by specific sources.
Instead, it is formed in the air by chemical reactions
between nitrogen oxides and volatile organic
compounds. These come from sources such as: (1)
vapors of gasoline; (2} chemical solvents; and (3)
combustion products of various fuels.
Since these reactions are stimulated by sunlight,
ozone reaches peak levels in most parts of the country
during the summer. This type of pollution first gained
public attention in the 1940's as Los Angeles "smog."
It has long been a major air pollution problem in that
city as well as in most major metropolitan areas of the
United States. These areas have abundant sunlight and
high emissions from motor vehicle traffic — a major
source of volatile organic compounds and nitrogen
oxides.
Ozone has become increasingly important in most
major urban areas in subsequent years as motor vehicle
traffic has increased.
Health
Effects
Ozone, the mam constituent of photochemical oxidants,
and peroxyacyl nitrates are associated with a number of
health effects in humans. Peroxyacyl nitrates and other
chemicals, such as aldehydes, cause the eye irritation
that is characteristic of photochemical pollution.
Ozone severely irritates the mucous membranes of
the nose and throat. It impairs normal functioning of the
lungs and reduces the ability to perform physical
exercise. Its effects are more severe in individuals with
chronic lung disease. The length of exposure, frequency
of exposure, and ozone concentration are significant
factors in determining the effects. Individuals with
asthma or diseases of the heart and circulatory system
experience symptoms at lower ozone concentrations. It
also appears that ozone in combination with sulfur
dioxide has a greater effect on respiratory function than
either pollutant alone.
Ozone
Trends
Measurements of ozone concentrations nationwide
showed an 18 percent decrease between 1975 and
1982. The reduction is due to a combination of
decreasing emissions from volatile organic compounds
and a change which occurred in the calibration
procedures at the monitoring sites between 1978 and
1979.
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National Trend in Oxone
Concentrations 1975-1982
(Graph A)
This graph compares the
year-by-year changes in ozone
concentration at 193 sites
between 1975 and 1982
There was an average
decrease of 18 percent in
ozone concentrations at all
sites during the 8-year period
The pattern, however, shows
fairly consistent levels from
1975 through 1978. followed
by a rather sharp drop
between 1978 and 1979 due
principally to a change in the
calibration procedure, and
more modest decreases after
1979
National Trend in
Emissions of Volatile
Organic Compounds
1975-1982
(Graph B)
Volatile organic compound
emissions decreased 13
percent in the 8-year time
period of this report. The most
significant feature is the
decline from transportation
sources despite a 20 percent
national increase in vehicle
miles travelled
While emissions from
industrial processes were
about the same in 1982 as
they were in 1975, there was
a decline beginning in 1979
following modest increases
between 1975 and 1978
One conclusion is
abundantly clear from these
data. Federal standards limiting
vehicle emissions have been
the major factor accounting for
the decline in volatile organic
compounds emissions
National Violation Trends
for Ozone, 1975-1982
(Graph C)
Reduced ozone emissions and
ozone levels nationally caused
a sharp reduction in the
average number of days that
standards were violated at the
193 monitoring sites Thee
was an average decline of
about 50 percent from slightly
under 14 days in 1975 to about
7 days in 1982
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Sources and
Nature of the
Pollutant
Nitrogen Dioxide
Nitrogen dioxide is one of a family of nitrogen oxides
The oxides important to air pollution control usually
come from high temperature combustion processes In
1982, nitrogen oxide emissions came equally from
transportation, 48 percent, and from stationary fuel
combustion sources, another 48 percent. Nitrogen
dioxide plays a major role m the atmospheric reactions
which produce photochemical oxidants (smog) and is
primarily responsible for smog's yellow-brown color.
Health
Effects
Nitrogen oxides can irritate the lungs, cause bronchitis
and pneumonia, and lower resistance to respiratory
infections such as influenza. The effects of exposure to
the pollutant for short periods are still being studied,
but continued or frequent exposure to concentrations
higher than have been found in the ambient
atmosphere can cause pulmonary edema.
Nitrogen
Dioxide
Trends
Nitrogen dioxide concentrations were exactly the same
in 1982 as they were in 1975. What occurred within the
time period, however, is far more dynamic. The national
average increased from 1975 to 1978, leveled off
between 1978 and 1979, and then decreased from
1979 to 1982.
Estimated nitrogen oxide emissions showed similar if
somewhat more modest variation during the same time
period. It is interesting to note that the relative trends
in nitrogen oxide emissions from transportation,
industrial processes, solid waste, and miscellaneous
sources closely paralleled one another over the 8-year
period.
While there was a slight increase in emissions from
transportation sources, it is negligible and actually
somewhat encouraging in view of the 20 percent
increase that occurred in vehicle miles travelled
nationally.
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Sources and
Nature of the
Pollutant
Sulfur Dioxide
Sulfur dioxide is one of a number of sulfur- containing
compounds found in the atmosphere It enters the air
primarily from the burning of coal and oil. and from
various other industrial processes
Health
Effects
Studies of serious air pollution episodes have found an
increase in death rates among people with existing
heart and lung disease when high concentrations of
sulfur dioxide are present in combination with high
concentrations of total suspended particulate matter
(see next section). A noticeable increase in acute and
chronic respiratory diseases can also occur at lower
levels.
Sulfur dioxide reacts m the atmosphere to form other
compound such as sulfunc acid, sulfates, and sulfites
These may be even more irritating to the respiratory
system than sulfur dioxide itself Not enough is known
about these pollutants at present to permit EPA to take
any specific regulatory steps other than controlling
sulfur dioxide, which generally lowers the
concentrations of other sulfur compounds.
Sulfur
Dioxide
Trends
Concentration of sulfur dioxide in the air decreased by
33 percent between 1975 and 1982 Declines occurred
in all regions except for parts of the southwestern
United States
Sulfur oxides are emitted mainly by electric utilities
that burn coal or oil. Emissions decreases were mainly
due to the installation of controls at coal- fired electric
generating stations and by reductions in the average
sulfur content of fuels consumed. Emissions from other
sources also declined from decreased combustion of
coal and from emissions controls on nonferrous
smelters and sulfunc acid manufacturing plants.
Nationally, the sulfur dioxide problem has diminished
to the point that air quality standards appear to have
been achieved at almost all sites. In an effort to curb
imports of oil from foreign countries, programs are
underway for converting power plants from oil to coal.
These changes could increase future levels of sulfur
dioxide, although the effects should be mitigated by the
installation of emissions controls and by fuel
conservation measures.
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