United States
             Environmental Protection
             Agency
Office ;of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
 September 1995

EPA-454/F-95-003
& EPA  Air  Quality Trends

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AIR
QUALITY
TRENDS
 The overall quality of our nation's air continues to improve.
 This brochure highlights the United States Environmental
 Protection Agency's (EPA's) most recent analysis of trends
 in air pollution emissions and air quality concentrations.

 Highlights include:

   • Emissions of the six principal pollutants increased
     significantly between 1900 and 1970.  However, since
     1970 (the year the Clean Air Act was signed into law),
     emissions of all but one of these pollutants have
     declined, in some cases dramatically.

   • Economic growth and  environmental protection can
     go hand-in-hand.  Between 1970 and  1994, total
     emissions of the six principal pollutants decreased
     while gross domestic product, population, and total
     vehicle miles traveled all increased significantly.
   • Between 1985 and 1994,  air quality continued to
     improve as monitored concentrations of each of the
     six pollutants declined.
   • Short-term trends between 1993 and 1994 showed
     slight increases in monitored concentration levels of
     nitrogen dioxide and carbon monoxide.   Monitored
     concentration levels of lead, ozone, and sulfur dioxide
     continued to decrease, while particulate matter
     remained unchanged.  During this same 1 -year period,
     emissions of carbon monoxide, nitrogen oxides,
     particulate matter, and volatile organic compounds also
     increased.

   •  Despite the improvements to date in air quality since
     1970, approximately 62 million people lived in
     counties where air quality levels exceeded the national
     air quality standards for at least one of the six
     principal pollutants in 1994.-
   •  Toxic air emissions from sources such as organic
     chemical plants, oil refineries, dry cleaning operations,
     and aerospace manufacturing are decreasing as
     federal air toxic regulations take effect.


Background
Air pollution comes from many different sources.
"Stationary sources" such as factories, power plants, and
smelters — "mobile sources" including cars, buses,
planes, trucks and trains — and "natural sources" such as
wildfires, windblown dust and volcanic eruptions —
contribute to air pollution in the United States. The Clean
Air Act provides the principal framework for  State, tribal,
national and local  efforts to protect air quality.  Under the
Clean Air Act, which was last amended in 1990, EPA has a
number of responsibilities, including:
   •  Setting National Ambient Air Quality Standards
     (NAAQS) for pollutants considered harmful to public
     health and the environment.

   •  Ensuring that these air quality standards are met or
     attained (in cooperation with States) through national
     standards and strategies to control air emissions from
     sources such as automobiles and factories.
   •  Ensuring that sources of toxic air pollutants are well
     controlled.

The Clean Air Act  established two types of national air
quality standards.  Primary standards set limits to protect
public ihealth, including the  health of "sensitive"
populations such as asthmatics, children, and  the elderly.
Secondary air quality standards set limits to  protect public
welfare, including protection against decreased visibility,
damage to animals, crops, vegetation, and buildings.

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EPA has set national air quality standards for six principal
pollutants (referred to as "criteria" pollutants):  carbon
monoxide (CO), lead (Pb), nitrogen dioxide (NC>2), ozone (O3),
partteulate matter (PM-10), and sulfur dioxide (SO2). [Note:
The pollutant ozone is not emitted directly to the air, but is
formed by sunlight acting on emissions of nitrogen  oxides
(NOX) and volatile organic compounds (VOC).

For the past 22 years, EPA has examined air pollution trends
of each of the six principal pollutants in this country.  EPA
examines changes in  air pollution levels over time  and
summarizes the current air pollution status.  Each year, EPA
publishes a comprehensive technical document titled
"National Air Quality and Emissions Trends Report."  The
1994 report is scheduled for publication in late October
1995. This brochure  is a summary of trends in the nation's
air quality for the last  10 years.

Emissions of some particulate matter and some volatile
organic compounds,  as well as other chemicals, may be
more dangerous and  have  been designated as toxic  air
pollutants.  The Clean Air Act contains  requirements for
reducing air toxics.  EPA has responsibility for developing
regulations to  control  toxic air pollutants from industrial
factories and other sources. This brochure also provides an
overview of trends in toxic air pollution, sources of toxic air
emissions and the process EPA has developed for controlling
toxic air pollution.


Long-Term Emissions Trends
Before the Clean Air Act was signed into law in 1970, the
20th century witnessed a significant, continued increase in
air pollution levels. Although efforts made during the 1960's
by State and local air pollution agencies in particular  polluted
cities in the Northeast did help reduce pollution in some local
areas, emissions continued to increase on a national level.
Between 1900 and 1970, emissions of nitrogen oxides
Increased  690 percent, volatile organic compounds
increased 260 percent, and sulfur dioxide increased 210
percent. Emissions of these pollutants have decreased
significantly since the 1970 Clean Air Act was passed.
Without passage of the Clean Air Act in 1970, emissions
would have continued to increase as illustrated in the charts.
          Without the passage of the Clean Air Act in 1970,
          emissions would have increased at a higher rate.
           Without the passage of the Clean Air Act in 1970,
           emissions would have continued to increase.
         Without the passage of the Clean Air Act in 1970,
         emissions would have continued to increase.
^	T,:;:.rfWI,


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Summary of Air Quality and Emissions Trends
The 1994 Trends Report tracks two kinds of trends: air
concentrations based on actual measurements of
pollutant concentrations in the air at selected sites
throughout the country, and emissions based on
engineering estimates of the total tonnage of these
pollutants released into the air annually.

Each year, EPA gathers and analyzes air quality
concentration data from more than 4,000 monitoring
stations around the country.  Monitoring stations are
operated by State, tribal, and local government agencies
as well as some federal agencies, including EPA. Trends
for 1994 are derived by averaging direct measurements
from these monitoring sites. During the last 10 years
(1985 through 1994), air quality has continued to improve
as shown in the  chart below. The most notable
improvements were an 86  percent decrease in lead
concentrations and a 28 percent decrease in carbon
monoxide concentrations.  Improvements in measured
concentrations were also noted for the other principal
pollutants including nitrogen dioxide, ozone, particulate
matter and sulfur dioxide during this timeframe.
 PERCENT DECREASE IN CONCENTRATIONS
                  (1985-1994)
CO
Lead
N02
Ozone
PM-10
S02
28%
86%
12%
20%
25%
developments, fuel consumption, vehicle miles of travel,
and other activities that cause air pollution. Emissions
trends also reflect changes in air pollution regulations and
installation of emissions controls. Over the last 10-year
period (1985 through 1994), air emissions have shown
improvement (decreased) for all pollutants except nitrogen
oxides as shown in the chart below. The slight emissions
increase (3 percent) observed for nitrogen oxides can be
attributed to increased processing or manufacturing by
industry and increased amounts of fuels burned by electric
utility plants.
     PERCENT DECREASE IN EMISSIONS
                  (1985-1994)*
CO
Lead
VOC
PM-10
S02
,15%
75%
10%
12%
9%


*

                                                          Unlike the other pollutants, NOX emissions increased 3 percent.
EPA estimates nationwide air emissions trends based on
engineering calculations of the amounts and types of
pollutants emitted by automobiles, factories, and other
sources. Emission trends are based on many factors,
including the level of industrial activity, technology

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As illustrated in the following charts, since
1970, the combined emissions of the six
principal pollutants decreased 24 percent,
while U.S. population increased 27 percent,
vehicle miles traveled increased 111 percent,
and gross domestic product increased 90
percent. These dramatic improvements in
emissions and air quality occurred
simultaneously with significant increases in
economic growth and population. The
improvements are a direct result of effective
implementation of clean air laws and
regulations.
                Comparison of 1970 and 1994 Emissions
                     (24% decrease for all pollutants)
Million Tons/Year                                         Thousand Tons/Year
    30
                                                    —       50
                    NOX
                   (+14%)
                                                                            VOC
                                                                            (-24%)
PM-10
(-78%)
 S02
(-32%)
                                                          Although some areas of the United States are experiencing air quality
                                                          problems, overall air quality continues to show improvement, despite
                                                                            extensive national growth.


     Total U.S. Population                        Vehicle Miles Traveled                      Gross Domestic Product
,  ' (27% increase, 1970-94)
                                          (90% increase, 1970-94
                                                     (111% increase, 1970-94)
                         rfaam&it ..... srsiiaai mfratOHoninivetirwiqMnHnrwiMCWmhmainiri
                         200    250    300       0    500   1000  1500   2000   2500
    0  --.50    100    t50
                         le                       Vehicle Miles Traveled (Billions Miles              Gross Domestic Product (Billions Dollars)
                                                                         		"	
                                                                Since 1970, the United States has experienced extensive national growth.
         PM-10
     AnyNAAQS
          Lead
         Ozone
                    10     20     30     40     50     60     70
                               Millions of People
                 Despite great progress in air quality improvement, in
                 1994 approximately 62 million people nationwide lived
                 in counties with air quality levels above the primary
                 national air quality standards.

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Six
PRINCIPAL
POLLUTANT
 CARBON MONOXIDE (CO)
 Nature and Sources of the Pollutant: Carbon
 monoxide is a colorless, odorless, poisonous gas formed
 when carbon in fuels is not burned completely. It is a by-
 product of motor vehicle exhaust, which contributes more
 than two-thirds of all CO emissions nationwide. In cities,
 automobile exhaust can cause as much as 95  percent of
 all CO emissions. These emissions can result in high
 concentrations of CO, particularly in local areas with heavy
 traffic congestion.  Other sources of CO emissions include
 industrial processes and fuel combustion in sources such
 as boilers and incinerators. Despite an overall downward
 trend in concentrations and emissions of CO, some
 metropolitan areas still experience high levels of CO.

 Health and Other Effects:  Carbon monoxide enters
 the bloodstream and reduces oxygen delivery to the
 body's organs and tissues. The health threat from CO is
 most serious for those who suffer from cardiovascular
 disease. Healthy individuals are also affected, but only at
 higher levels of exposure.  Exposure to elevated CO  levels
 is associated with visual impairment, reduced work
 capacity, reduced manual dexterity, poor learning ability,
 and difficulty in performing complex tasks. EPA's health-
 based national air quality standard for CO is 9 parts per
 million (ppm) [measured over 8 hours].

 Trends in Carbon Monoxide Levels: Long-term
 improvements continued between 1985 and 1994.
National average CO concentrations decreased 28 percent
while CO emissions decreased 15 percent.  Long-term air
quality improvement in CO occurred despite a 32 percent
increase in vehicle miles traveled in the U.S. during the
past TO years.  Between 1993 and 1994, national average
CO concentrations increased 2 percent while total CO
emissions increased 4 percent. Transportation sources
now account for 78 percent of the nation's total CO
emissions. The observed increase in CO emissions
between 1993 and 1994 is attributed to two sources:
transportation emissions (up 2%) and wildfire emissions
(up 160%).
                                                                          CO CONCENTRATION TRENDS
                                                               15
          1985-94: 28% decrease
          1993-94: 2% increase
                             90% of monitor sites had
                             concentrations less than this line
       1985 1986  1987  1988  1989  1990 1991  1992  1993 1994
                  CO EMISSIONS TRENDS
                  Fuel Combustion E3 Industrial Processing
                  Transportation   Q Miscellaneous
     20
    •-0
       1985 1986 1987  1988 1989 1990  1991  1992  1993  1994

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LEAD (Pb)
Nature and Sources of the Pollutant:  Smelters and
battery plants are the major sources of the pollutant "lead" in
the air. The highest concentrations of lead are found in the
vicinity of  nonferrous smelters and other stationary sources of
lead emissions.

Health Effects: Exposure to lead mainly occurs through
inhalation of air and ingestion of lead in food, paint, water,
soil, or dust. Lead accumulates in the body in blood, bone,
and soft tissue. Because it is not readily excreted, lead can
also affect the kidneys, liver, nervous system, and other
organs. Excessive exposure to lead may cause anemia,
kidney disease, reproductive disorders, and neurological
impairments such as seizures, mental retardation, and/or
behavioral disorders. Even at low doses, lead exposure is
associated with changes in fundamental enzymatic, energy
transfer, and other processes in the body.  Fetuses and
children are especially susceptible to low doses of lead, often
suffering central nervous system damage or slowed growth.
Recent studies show that lead may be a factor in high blood
pressure and subsequent heart disease in middle-aged white
mates. Lead may also contribute to osteoporosis in post-
menopausal women.  EPA's health-based national air quality
standard for lead is 1.5 micrograms per cubic meter (|j.g/m3)
[measured as a quarterly average].

Trends In Lead Levels: Between 1985 and 1994, average
lead concentrations in urban areas throughout the country
decreased 86 percent while total lead emissions decreased
            LEAD CONCENTRATION TRENDS
 1.5
      NAAQS
            1985-94:  86% decrease
            1993-94:  20% decrease
 Q 5 L   90% of monitor sites had concentrations
        less than this line
                 Average for all sites
   1985  1986  1987  1988 1989  1990  1991  1992  1993 1994
               LEAD EMISSIONS TRENDS
25,000 -
20,000
              I Fuel Combustion H Industrial Processing
              I Transportation
             1985-94:  75% decrease
             1993-94:  No Change
                                                                       1985 1986  1987 1988  1989 1990 1991  1992 1993  1994


                                                              75 percent. These reductions are a direct result of the use of
                                                              unleaded gasoline in automobiles. The large reduction in lead
                                                              emissions from transportation sources has changed the
                                                              nature of the air quality problem for lead in the U.S.
                                                              Violations of the lead air quality standard still occur, but tend
                                                              to occur near large industrial complexes such as lead
                                                              smelters. Between  1993 and 1994, lead emissions remained
                                                              unchanged while national average lead concentrations
                                                              decreased 20 percent.
                                                          6

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NITROGEN DIOXIDE (NO2)
Nature and Sources of the Pollutant: Nitrogen
dioxide belongs to a family of highly reactive gases called
nitrogen oxides (NOX). These gases form when fuel is
burned at high temperatures, and come principally from
motor vehicle exhaust and stationary sources such as
electric utilities and industrial boilers. A suffocating,
brownish gas, nitrogen dioxide is a strong oxidizing agent
that reacts in the air to form corrosive nitric acid, as well as
toxic organic nitrates.  It also plays a major role in the
atmospheric reactions that produce ground-level ozone (or
smog).

Health and Other Effects:  Nitrogen dioxide can irritate
the lungs and lower resistance to respiratory infections
such as influenza. The effects of short-term exposure are
still unclear, but continued or frequent exposure to
concentrations that are typically much higher than those
normally found in the ambient air may cause increased
incidence of acute respiratory illness in children. ERA'S
health-based national air quality standard for NC>2 is 0.053
ppm (measured as an  annual average). Nitrogen oxides
are important in forming ozone and may affect both
terrestrial and aquatic ecosystems.  Nitrogen oxides in the
air are a potentially significant contributor to a number of
environmental effects such as acid rain and eutrophication
in coastal waters like the Chesapeake Bay. Eutrophication
occurs when a body of water suffers an increase in
nutrients that reduce the amount of oxygen in the water,
producing an environment that is destructive to fish and
other animal life.
                 NO2 CONCENTRATION TRENDS
     0.06
     0,05
     0.04
    0.03
    0.02
    0.01 -
       1985  1986 1987  1988  1989  1990  1991  1992  1993 1994
                   NOX EMISSIONS TRENDS
     30
     25
     20
     15
     10
                  I Fuel Combustion E3 Industrial Processing
                  § Transportation  0 Miscellaneous
                 1985-94:  3% increase
                 1993-94:  1% increase
Trends in Nitrogen Dioxide Levels:  Nationally, annual
NC>2 concentrations remained relatively constant through-
out the 1980's, followed by decreasing concentrations in
the 1990's. Average NC>2 concentrations in 1994 were 9
percent lower than the levels recorded in 1985.  National
total NOX emissions increased 3 percent since 1985. The
two primary sources of the NOX emissions in 1994 were
fuel combustion (50 percent) and transportation (45
percent). Since 1985, emissions from highway vehicles
decreased 7 percent while fuel combustion emissions
       1985  1986 1987
                              1990 1991  1992 1993  1994
increased 8 percent.  Between 1993 and 1994, NOX
emissions and NO2 concentrations increased. The
emissions increases are attributed to increased emissions
from off-highway vehicles and wildfires.  Even with an
increase in NOX emissions, 1994  is the third year in a row
that all monitoring locations across the nation, including
Los Angeles, met the federal NC>2 air quality standard.

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                      OZONE CONCENTRATION TRENDS
it^lOZONE(°3)
     HI   Nature and Sources of the Pollutant: Ground-level ozone
           (the primary constituent of smog) is the most complex, difficult
           to control, and pervasive of the six principal pollutants. Unlike
           other pollutants, ozone is not emitted directly into the air by
           specific sources. Ozone is created by sunlight acting on NOX
           and VOC emissions in the air.  There are literally thousands of
           sources of these gases.  Some of the more common sources
           include gasoline vapors, chemical solvents, combustion
           products of various fuels, and consumer products. They can
           originate from large Industrial facilities, gas stations, and small
           businesses such as bakeries and dry cleaners. Often these
           "precursor" gases are emitted in one area, but the actual
           chemical reactions, stimulated by sunlight and temperature,
           take place in another. Combined emissions from motor vehicles
           and stationary sources can be carried hundreds of miles from
           their origins, forming high ozone concentrations over very large
           regions. Approximately 50 million people lived in counties with
           air quality levels above EPAfe health-based national air quality
           standard in 1994. The highest levels of ozone were recorded in
           Los Angetes.  High levels also persist in other heavily populated
           areas Ike the Texas Gulf Coast and much of the Northeast.

           Health and Other Effects:  Scientific evidence indicates that
           ground-level ozone not only affects people with impaired
           respiratory systems (such as asthmatics), but healthy adults and
           children as well. Exposure to ozone for 6 to 7 hours, even  at
           relatively tow concentrations, significantly reduces lung function
           and induces respiratory inflammation in normal, healthy people
           during periods of moderate exercise. It can be accompanied by
           symptoms such as chest pa'n, coughing, nausea, and
           pulmonary congestion. Recent studies provide evidence of an
           association between elevated ozone levels and increases in
           hospital admissions for respiratory problems in several U.S.
           cities. Results from animal studies indicate that repeated
           exposure to high levels of ozone for several months or more can
           produce permanent structural damage in the lungs. EPA's
           health-based national air quality standard for ozone is 0.12 ppm
           (measured at the highest hour during the day). Ozone is also
           responsible for several billion dollars of agricultural crop yield
           toss in the U.S. each year. Ozone also damages forest eco-
           systems in California and the eastern U.S.

           Trends in Ozone Levels:  Ground-level ozone has been a
           pervasive pollution problem throughout the U.S. Ozone
            0.25
            0.20
            0.15
                        1985-94:  12% decrease
                        1993-94:  1% decrease
                                       90% of monitor sites had
                                       concentrations less than this line
                                                 NAAQS
            0.05
            0.00
              1985  1986  1987 1988  1989 1990  1991  1992  1993  1994

                          VOC EMISSIONS TRENDS
      >•
      S.
            30
             25
             20
             15
             10 H
             5 -t
                         I Fuel Combustion  H Industrial Processing
                         1 Transportation   Q Miscellaneous

              1985  1986  1987 1988  1989 1990  1991  1992  1993  1994

    concentration trends are influenced by year-to-year changes in
    meteorological conditions as well as emission reductions from
    ongoing control measures. Although meteorological conditions
    in 1994 were conducive to ozone formation (especially in the
    Southeast), national ozone levels were 12 percent lower than
    those in 1985. Levels in 1994 are the second lowest national
    average for the period between 1985 and 1994. The lowest
    level was recorded in 1992, and the highest in 1988.  Recent
    control measures include regulations to reduce evaporation of
    fuel and limit NOX and VOC emissions from tailpipe exhaust.
    Emissions of VOCs (which contribute to ozone formation)
    decreased 10 percent between 1985 and 1994, despite a slight
    increase between 1993 and 1994.
8

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                                                                          PM-10 CONCENTRATION TRENDS
 PARTICULATE MATTER (PM-10)
 Nature and Sources of the Pollutant: Particulate
 matter is the term for solid or liquid particles found in the air.
 Some particles are large or dark enough to be seen as soot
 or smoke. Others are so small they can be detected only
 with an electron microscope. Because particles originate
 from a variety of mobile and stationary sources (diesel
 trucks, wood stoves, power plants, etc.), their chemical and
 physical compositions vary widely.

 Health and Other Effects:  In 1987, EPA replaced the
 earlier Total Suspended Particulate (TSP) air quality standard
 with a PM-10 standard. The new standard focuses on
 smaller particles that are likely responsible for adverse health
 effects because of their ability to reach the lower regions of
 the respiratory tract. The PM-10 standard includes particles
 with a diameter of 10 micrometers or less (0.0004 inches or
 one-seventh the width of a human hair).  EPA's health-based
 national air quality standard for PM-10 is 50 ng/m3
 (measured as an annual average) and 150 |j,g/m3
 (measured as a daily average).  Major concerns for human
 health from exposure to PM-10 are: effects on breathing
 and respiratory systems, damage to lung tissue, cancer, and
 premature death. The elderly, children, and people with
 chronic lung disease, influenza, or asthma, tend to be
 especially sensitive to the effects of paniculate matter.
Acidic PM-10 can also damage manmade materials and is a
 major cause of reduced visibility in many parts of the U.S.

Trends in PM-10 Levels: Air monitoring networks were
changed in 1987 to measure PM-10 (replacing the earlier
TSP monitors). Between 1988 and 1994, average PM-10
                                                                '70-
 60
1988-94:  2O% decrease
1993-94:  No change
                        NAAQS
0.00
  1988    1989    1990    1991    1992    1993   1994

             PM-10 EMISSIONS TRENDS
             Fuel Combustion H Industrial Processing
              ransportation
  1988
        1989
               1990
                      1991
                             1992
                                    1993
                                           1994
                                                          concentrations decreased 20 percent, while PM-10
                                                          emissions decreased 12 percent.  Particulate matter
                                                          emissions from sources such as fuel combustion, industrial
                                                          processes, and transportation decreased 17 percent since
                                                          1985.  Emissions from residential wood combustion
                                                          decreased 50 percent in the past 10 years. Although not
                                                          included in the above chart, fugitive emissions (such as
                                                          those from construction) are also a significant source of
                                                          particulate matter in the air.  Between 1993 and 1994, PM-
                                                          10 concentrations remained unchanged. Between 1993
                                                          and 1994, emissions of PM-10 increased 1 percent due to
                                                          emissions from transportation, industrial sectors, and
                                                          wildfire's.
                                                      9

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SULFUR DIOXIDE (SO2)
Nature and Sources of the Pollutant: Sulfur dioxide
belongs to the family of sulfur oxide gases (SOX). These
gases are formed when fuel containing sulfur (mainly coal and
oil) is burned, and during metal smelting and other industrial
processes.

Health and Other Effects: The major health concerns
associated with exposure to high concentrations of SC>2
Include effects on breathing, respiratory illness, alterations in
pulmonary defenses, and aggravation of existing
cardiovascular disease. Major subgroups of the population
that are most sensitive to SO2 include asthmatics and
individuals with cardiovascular disease or chronic lung
disease (such as bronchitis or emphysema) as well as
children and the elderly.  EPA's health-based national air
quality standard for SO£ is 0.03 ppm (measured on an annual
average) and  0.14 ppm (measured over 24 hours). Emissions
of SO2 also can damage the foliage of trees and agricultural
crops. Together, SC>2 and NOX are the major precursors to
acid rain, which is associated with the acidification of lakes
and streams, accelerated corrosion of buildings and
monuments, and reduced visibility.
                                                                              SO2 CONCENTRATION TRENDS
  0.035
  0.030
  0.025
E- 0.020
  0.015
  0.010
  0.005
         NAAQS
1985-94:  25% decrease
1993-94:  4% decrease
         90% of monitor sites had concentrations
         less than this Bne       I
      1985  1986  1987  1988  1989  1990  1991  1992 1993  1994
    30
    25
                                                                   20
                  SO2 EMISSIONS TRENDS
                 I Fuel Combustion  H Industrial Processing
                 1 Transportation
                                                                   15 -I
                                                                   10
                                                                               1985-94:  9% decrease
                                                                               1993-94:  2% decrease
                                                                     1985  1986 1987  1988 1989  1990 1991  1992 1993  1994

                                                              Trends in Sulfur Dioxide Levels: Between 1985 and
                                                              1994, SC>2 emissions decreased 9 percent while national
                                                              SC>2 concentrations decreased 25 percent. Between 1993
                                                              and 1994, national SC>2 concentrations decreased 4 percent
                                                              and SC>2 emissions decreased 2 percent.  EPA's Acid Rain 	
                                                              Program calls for major reductions of SC>2 and NOX, the
                                                              pollutants that cause acid rain. The program sets a
                                                              permanent cap on the total amount of SC>2 that may be
                                                              emitted by electric utilities nationwide, about one-half the
                                                              amount emitted in 1980..

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VISIBILITY
  Nature and Sources of the Problem: Visibility
  impairment is caused by the presence of particles in the air.
  It is most simply described as the haze which obscures the
  clarity, color, texture, and form of what we see, and is
  actually a complex problem that relates to several
  pollutants. Visibility impairment is primarily a result of fine
  particles (even smaller than PM-10) in the air.  These
  particles cause light to be scattered or absorbed, thereby
  reducing visibility.

  Long Term Trends:  Visibility impairment has been
  analyzed using data collected since 1960 at 280 monitoring
  stations located at airports across the country. At these
  stations, measurements of visual range (the maximum
  distance at which  an observer can discern the outline of an
  object) were recorded.  Long-term records of visual range
  (derived from weather data) help reveal trends in visibility.
  The following maps display U.S. visibility trends derived
  from such data.

  The maps show the amount of haze during the summer
  months of 1970,1980, and  1990.  The greater the haze,
  the poorer the visibility.  The dark blue color represents the
  best visibility and red represents the worst visibility. Overall,
  these maps show  that visibility impairment in  the eastern
  U.S. increased greatly between 1970 and 1980, and
  decreased slightly  in  1990. This follows the overall trends
  in SOX emissions during these periods.  Sulfur oxides are a
  major source of fine particles.
New Monitoring Network: EPA and the National Park
Service established a long-term visibility monitoring
program at locations throughout the U.S. The effort has
been expanded to incorporate other federal and regional
monitoring programs.  The network is the largest in the
country devoted to fully characterizing visibility. Sulfates are
.the largest single contributor to haze,  or visibility reduction,
in many parts of the U.S.  Data from this monitoring
network reveals that sulfates account  for 68 percent of the
visibility reduction in the Appalachian Mountains in the East.
Organic carbon, the next-largest contributor, causes 16
percent of visibility reduction.  In most areas of the western
U.S. and Alaska, sulfates and  organic particles contribute
equally to haze.  In southern California, nitrate particles are
the greatest contributor to haze.
  Best
                                                                  Map of haze from airport visual data (July-September).
                                                         11

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Programs to Improve Visibility: In April 1994, EPA
announced development of its new regional haze program to
address visibility impairment in national parks and wilderness
areas. This program will introduce new approaches to
monitoring and modeling regional haze as well as define a policy
for achieving "reasonable progress" toward the reduction  of
visibility impairment. The program will build on efforts of the
Grand Canyon Visibility Transport Commission which was
established to address visibility impairment in the region around
the Grand Canyon National Park. This commission is in the
process of developing recommendations for EPA regarding
protection of the national park areas on the Colorado Plateau in
the western United States. In addition, it is expected that better
controls for sources of pollutants such as sulfur oxides as a
result of the Acid Rain Program will also lead to improvements
Invisibility.
Toxic  AIR
POLLUTANTS
 Nature and Source: Toxic air pollutants are those pollutants
 known to or suspected of causing cancer or other serious
 health effects such as birth defects or reproductive effects.
 Examples of toxic air pollutants include dioxins, benzene,
 arsenic, beryllium, mercury, and vinyl chloride.  The Clean Air
 Act lists 189 toxic air pollutants to be regulated by EPA. They
 are emitted from all types of sources, including motor vehicles
 and stationary sources such as factories.  Control of toxic air
 pollutants differs in focus from control of the six principal
pollutants for which EPA has established national air, quality
standards (discussed earlier). For the six principal pollutants,
a variety of control strategies are used in geographic areas
where the national air quality standards have been violated.
In contrast, for toxic air pollutants, EPA has focused on
identifying all major sources that emit these pollutants and
developing national technology-based performance
standards to significantly reduce their emissions. The
objective is to ensure that major sources of toxic air pollution
are well controlled regardless of geographic location.

The air toxics program and the  NAAQS program
complement each other. Many air toxics are emitted in the
form of particulates or as volatile organic compounds.
Control programs to meet the NAAQS for ozone and PM-10
also reduce toxic air emissions. Likewise, emission
requirements under the toxic air pollutant program can
significantly reduce emissions of the six principal pollutants
for which EPA has national ambient air quality standards.
For example, EPA's final toxic air pollutant regulation for
organic chemical manufacturing is expected to reduce VOC
emissions (which form ground-level ozone or smog) by an
amount equivalent to removing  millions of cars from the road.

The toxic air pollutant program  is especially important in
reducing air emissions at or near industrial locations and in
controlling pollutants that are toxic even when emitted in
small amounts. Companies handling toxic chemicals are
required by EPA to develop plans to prevent accidental
releases and to contain any releases in the event they should
occur.

Health and Other Effects: At sufficient concentrations   .
and exposure durations, human health effects from toxic air
pollutants can include cancer, poisoning, and rapid onset of
sickness such as nausea and difficulty in breathing. Other
less measurable effects include immunological, neurological,
reproductive, developmental, and respiratory effects.  Toxic  .
air pollutants may also be deposited onto soil or into lakes
and streams, thereby affecting ecological systems and
eventually human health through consumption of
contaminated food (mainly freshwater fish).

Trends in Toxic Air Pollutants: In 1993, industrial sources
emitted toxic air pollutants totalling 1.2 billion pounds
                                                         12

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nationally, as reported in EPA's toxic release inventory (TRI).
Reporting under TRI is required for manufacturers handling
toxic chemicals and represents only a subset of total
nationwide emissions.  This total represents a decrease of
approximately 600 million pounds (or 33 percent) from 1989
levels and reduction of 110 million pounds (or 8 percent)
from 1992 levels.

These downward trends in emissions are expected to
continue. The 1990 Clean Air Act Amendments greatly
expanded the number of industries that will be affected by
national air toxic emission  controls. The emission
reductions from these controls are just beginning to be
realized for some industries. Large industrial complexes
such as chemical  plants, oil refineries, aerospace
manufacturers, and steel mills are some of the industries
being controlled for toxic air pollution. It is necessary to
control smaller sources of toxic air pollution such as dry
cleaning operations, solvent cleaning, and chrome plating.
Within the next 10 years, the air toxics program is projected
to reduce emissions of toxic air pollutants by at least 1
billion pounds.
 CONCLUSIO
 Since EPA was established in 1970, air quality in the U.S.
 has improved tremendously.  Many of these improvements
 can be attributed to pollution control programs instituted
 by EPA, State and local agencies and industry. Because
 air pollution problems continue in many parts of the
 country, EPA and states are actively seeking innovative
 and more cost-effective programs to further reduce
 emissions.  Market-based programs like emissions trading
 provide incentives for industry to develop new pollution
 control technologies or pollution prevention approaches.
 Through continued interaction with the regulated
 community, environmental groups, State, tribal, and local
governments, and concerned citizens, EPA is working to
develop effective common-sense control strategies to
improve our nation's air quality.

For Further Information:

Call   (919)541-5285
       National Air Pollutant Emission Trends,
       1900-1994 (EPA-454/R-95-011)

       (919)541-5558
       National Air Quality and Emissions Trends,
       1994 (EPA-454/R-95-014) -

Internet Users: EPA Homepage "at:
(http://www.epa.gov/docs/oar/oarhome.html)
      !
Technology Transfer Network (TTN) Users:
   • Access by modem, dial: (919) 541-5742
   • Access by Internet, use telnet address:
    (ttnbbs.rtpnc.epa.gov)
ACRONYMS
Principal Pollutants:
   CO	Carbon Monoxide
   Pbj	Lead
   NO2, NOX	Nitrogen Dioxide, Nitrogen Oxides
   03	!.. .. Ozone
   PM-10	Particulate Matter
   SO2, SOX	Sulfur Dioxide, Sulfur Oxides
EPA .,	Environmental Protection Agency
NAAQS	National Ambient Air Quality Standard
TRI	Toxic Release Inventory
TSP.
VOC.
. Total Suspended Particulates
. Volatile Organic Compounds
                                                     13

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