d Slates
Environmental Protection
                                                            March 1977



A Little
"The Nation's
 ' commitment to clean
air has taken many
forms. But over the past
several years, the
evolution of Federal
legislation and regulation
has shaped and
increased a cooperative
effort among Federal and
State control agencies,
industry, and a
concerned and informed
public. Especially as a
result of the  1970 Clean
Air Amendments, a
considerable expenditure
of time, material, and
funds has been brought
to bear on  solutions to
the technological and
social problems  needed
to assure protection of
public health and welfare
from the adverse effects
of air pollution.

The States, backed by
Federal assistance, have
developed  wide-ranging
regulatory, enforcement,
and administrative
programs to reduce
emissions of air  pollution
from a great variety of
sources. These
abatement efforts have
been augmented by
direct Federal regulation
and enforcement of
control measures
directed toward certain
types of pollutants and
industrial sources, as
well as the Federal
program to reduce air
pollution emissions from
new motor vehicles.

As more and more
information becomes
available, it also
becomes possible to
assess with increasing
assurance what the
success of these
programs has been and
to describe more fully
and accurately the trends
in the quality of the
Nation's air. Based on  a
study by the
Environmental  Protection
Agency, National Air
Quality and Emissions
Trends Report, 1975, we
can provide some
reasonable answers to
the question, "What has
all of this effort

And the answer quite
simply is that the quality
of the Nation's air has
improved. Over the past
five years considerable
progress has been made
toward achieving the
National Ambient Air
Quality Standards
established by the
Environmental Protection
Agency, under the 1970
Clean Air Amendments,
to protect our public
health and welfare.

In the remaining pages,
we shall present, in
simplified form, some of
the information from the
study. (Those desiring to
review the full, detailed
technical and statistical
analysis,  may obtain a
copy from the U.S.
Environmental Protection
Agency, Office of Air
Quality Planning and
Standards, Research
Triangle Park, N.C. 27711.)

An analysis of special
interest, done for the
first time,  is an estimate
of changes in population
exposed to high air
pollution  levels. This has
been done for the
country for particulate
matter where more
information was
available, and for
selected areas for other

The Air Quality
                            • The
^yieasurements of
'^'actual air pollution
levels in the air are made
throughout the country
by State and local
agencies. The  number of
locations where these
measurements are made
varies with different State
and metropolitan areas;
also some pollutants are
measured at fewer
locations than others,
and have been measured
for fewer years.

Using the information
provided by the States,
changes were  studied for
those pollutants for
which EPA has set air
quality standards—total
suspended particulates,
sulfur dioxide,
photochemical oxidants,
carbon monoxide, and
nitrogen dioxide. Trends
in the levels of these
pollutants were
determined on a national
basis and on a regional
basis. Most of the
information covers the
period 1971-1975,
although other time
periods were considered
in some cases where
more, or less, information
may have been available.

Following the general
results, some additional
detail is provided for
particulates, sulfur
dioxide, carbon
monoxide, and oxidants.
(Not enough information
is yet available to provide
detail for nitrogen
dioxide in a non-
technical fashion, and
the reader is referred to
the original study for that
• In 1975, 28 million
  fewer people
  throughout the country
  were exposed to
  particulate levels
  above the health-
  related air quality
  standard than had
  been exposed in 1970.
  This is a decrease of
  38 percent.

• In the greater New
  York Metropolitan area,
  7 million fewer people
  in 1974 were  exposed
  to particulate levels
  above the health-
  related standard than
  had been exposed in

• By 1975,  average sulfur
  dioxide levels in urban
  areas had dropped 30
  percent since 1970.
  This improvement
  took place most rapidly
  in the 1970-1973
  period. Since then,
  with much of the
  emission reduction
  having been
  accomplished, and
  with some movement
  toward greater use of
  high sulfur fuels where
  possible, without
  exceeding the air
  quality standard, trends
  have tended  to level off.

• Long-term oxidant data
  for much of the
  country  is  somewhat
  limited.  But short-term
  trends for the eastern
  part of the United
  States for 1973-1975

  show some decline in
  levels exceeding the
  air quality standard.

• In the Los Angeles Air
  Basin, there has been
  a considerable
  reduction in the
  number of days on
  which the health-
  related oxidant
  standard has been
  exceeded.In the mid-
  60's, people in the
  Basin were exposed to
  levels above the
  standard on an average
  of 176 days a year.  By
  the mid-70's, this
  exposure was down to
  an average of 105 days
  a year.

• Some 80 percent of the
  locations where carbon
  monoxide is measured
  across the Nation
  show improvements in
  levels of this auto-
  related pollutant, with
  the rate of
  improvement more
  pronounced in
  California where auto
  emission standards
  have been somewhat
  more stringent than
  the Federal standards.

• Trends in nitrogen
  dioxide levels were
  mixed. Levels in the
  Los Angeles Basin
  declined between  1971
  and 1975. but in other
  parts of the country
  where information is
  available, levels have
  declined in some
  locales, increased in
  others, and show no
  particular trend for still

Some  Details . .  .
About Particulates
Trends in particulate
 ' levels since 1970 show
a general improvement at
a rate of four percent per
year, with the result that
38 percent fewer people
throughout the country
now are exposed to
levels higher than the
health-related air quality

Improvement rates have
differed in various parts
of the country, with
higher rates being found
in  the Northeast and
Great  Lakes areas, and
more level rates in some
western States where
natural particulate matter
poses problems.

Despite the
improvements, total
suspended particulates
still remain a problem.
Approximately 28  percent
of the Nation's
population are still living
in  areas where the annual
standard is exceeded.
Because of this, some
States may be required
to adopt new measures
to take care of problems
that still exist.

Measurements have been
made of levels of
particulate  matter in the
air for more locations
and for a longer time
than any other air
pollutant. Thus, there is
enough information
available to make  it
possible to estimate
nationwide trends in
population  exposure.
The information available
was sufficient to allow
such an analysis to be
made for most areas of
the country, covering
some 165 million of the
total population.

In 1970, 74 million people
were exposed to levels
above the health-related
air quality standard for
particulate matter. By
1975 this number had
dropped to  46 million —
an improvement of 28
million fewer people, or
38 percent,  exposed to
levels above the

Moreover, as would be
expected from the trends
in measured air quality
levels, reduced
exposures generally
occurred at all
concentration levels.

In the greater New York
Metropolitan area,
measurements have been
made of particulate
matter at a  large number
of locations extending
back over many years.
Thus, it is possible to
make especially detailed
studies of trends in
population  exposures to

   National Trends, Yearly Average Particulate Levels, 1971 -1975
 Year   1971
                LJere we see the year-by-year
                  'change in the levels
                measured throughout the
                country. The bottom red line
                shows typical average levels for
                the cleaner  locations, the white
                line shows the overall average,
                and the top red line shows
                the typical average levels for the
                dirtier locations. A general
                improvement can be seen for all
                categories. The cleaner
                locations, while improving, are
                not doing so at as great a rate.
                The overall average shows
                greater improvement. The dirtier
                areas show  the greatest
                improvement. This is consistent
                with planned pollution control
                programs. Those locations
                where the yearly average air
                quality control  standards
                already were met are not so
                much concerned with further
                reductions,  but rather with
                maintaining air quality. Those
                with the greatest problems,
                because of previously
                uncontrolled sources, have
                needed, and achieved, greater
                emissions reductions and
                greater rates of air quality
   Trend in National Population Exposure to Particulate Matter Levels
   Above the Health-Related Standard
Represents 8.2 million people
 (5% of Base =  165 million)

Between 1971 and 1974,
annual average levels
were reduced 25  percent
resulting in 71 percent
fewer people living in
areas exposed to levels
in excess of the health-
related air quality
standard. And the
number of  repeated
exposures  to high daily
levels also was reduced.

The numbers of those
more likely  to be
adversely affected by
high air pollution levels—
the elderly and the
school aged — living  in
the high pollution area—
also dropped sharply.
Although a  slightly
higher proportion of the
elderly population lives in
areas of elevated
paniculate levels, the
overall rates of
improvement are similar
for the total population,
for the school aged,and
for the elderly.
Number of People Living
in Areas of New York
Exceeding the Annual
Particulate Standard

              §    §   ol
              •^   ^n   *- t/>
              J2    ® •- T3 •=





                 New York Population Exposure to Daily Particulate

                                                       Areas where daily TSP
                                                       concentrations exceed
                                                       secondary NAAQS
                                                  < 5% ol the time

                                                           I 20 - 30%

                                                           I >30%

Area,  1971 and 1974

      Nole Isoplelh maps are based on spalial interpolation Irom data
      measured al 103 monitoring sites Local TSP may vary because ol
      meteorology, topography, and emissions

Levels, 1971 and 1974

                                                          In  1971, 19 percent of
                                                          ' the land area was
                                                          exposed to levels higher
                                                          than the health-related air
                                                          quality standard. But, in
                                                          1974, less  than four
                                                          percent was blanketed by
                                                          air  containing levels this
                                                          "The percent of people
                                                          ' exposed to daily
                                                          particulate levels in the
                                                          New York area are  shown
                                                          here for 1971 and 1974.
                                                          With much smaller areas
                                                          blanketed by high levels
                                                          in 1974, many fewer people
                                                          were exposed to the higher
                                                          levels.  For example, in
                                                          1971, some 58 percent of
                                                          the  total population lived
                                                          in areas where levels
                                                          exceeded the welfare
                                                          related standard. But, by
                                                          1974, this had dropped to
                                                          15 percent.

Some Details . .  .
About Sulfur  Dioxide
I  evels of sulfur dioxide
'—in the air over the
Nation's urban areas
have decreased by an
average of 30 percent
from 1970 to 1975. Most
of this improvement took
place rapidly in the
1970-1973 period.  Since
then, levels have been
fairly constant because
many areas had reached
levels that met the
ambient air quality
standard  and  because of
some movement toward
greater use of high
sulfur fuels where
possible,  without
exceeding the air
quality standard.

In some few cases, there
seem to have been slight
increases during 1975
because of changes in
fuel use patterns. In Los
Angeles,  for instance,
even though sulfur
dioxide levels are low,
there has been an
increase because of
recent changes in fuel
use associated with a
curtailment of the use of
natural gas for industrial
purposes in that area.
Similar patterns appear in
parts of the Northeast.

From a national
viewpoint, the urban
sulfur dioxide problem
has diminished so that
only a small number of
areas now exceed the air
quality standard for
sulfur dioxide. But, of
course, continued
vigilance will be required
to maintain this favorable

On the other hand, a
number of single sources
of sulfur dioxide still
exist outside of major
urban areas. These
individual sources, such
as smelters, pose  the
greatest threat to  the air
quality standards for
sulfur dioxide at the
present time.

National Trends in Yearly Sulfur Dioxide Levels, 1971-1975
                                            Llere we see the year-by- year
                                            ''changes in the levels of
                                            sulfur dioxide levels measured
                                            at all individual locations  in the
                                            country. The bottom red line
                                            shows the typical average level
                                            for the cleaner locations,  the
                                            white line shows the overall
                                            average, and the top red line
                                            shows the typical average for
                                            the more polluted locations. A
                                            general improvement can  be
                                            seen. Improvement at the
                                            cleaner locations is much less
                                            evident, while the overall
                                            average shows greater
                                            improvement, and the more
                                            polluted locations show the
                                            greatest improvement. This
                                            pattern is to be expected
                                            because the cleaner areas did
                                            not have as  far to go, while
                                            those areas  needing the
                                            greatest improvement show the
                                            greatest improvement.

               Some Details .
               About Carbon
                The primary source for
                ' emissions of carbon
                monoxide in most U.S.
                cities is the automobile.
                Nationally, some three-
                fourths of the carbon
                monoxide comes from
                transportation sources.
                But in some urban areas,
                transportation can be
                responsible for as much
                as 99 percent of the
                emissions, and any city
                with heavy enough traffic
                may have a potential
                problem from carbon
                monoxide. In some
                cases, the problem may
                be highly localized —
                affecting perhaps only
                the area around a few
                street corners. In other
                cases, the problem may
                be spread throughout the
                center-city area and near
                major commuter
                corridors. In any event,
                improvements in levels of
                carbon monoxide in the
                air will almost always be
                directly related to control
                of emissions from

                Throughout the country,
                carbon monoxide levels
                have not been measured
                at as many locations and
                for as long a period of
                time as'particulates and
                sulfur dioxide. This
                means that it is not as
                easy to determine
                national trends in carbon
                monoxide levels in the
                air. California, however
                has been making such

extensively for a longer
time, so trends there can
be checked more easily.
And these can be
compared with those in
other parts of the country
to see whether they

When this is done, the
overall picture clearly
shows improvement.

In California, over a
three-year period, lower
carbon monoxide levels
were measured at 81
percent of the sampling
locations. For the
remainder of the country,
this improvement was
found at 78 percent of
the locations.

In California, carbon
monoxide levels
decreased at a rate of
about 7 percent per year.
In the rest of  the country,
the decrease was at a
rate of about 5 percent a
year. Because California
has more stringent
automobile control
regulations, this
difference should be

Some Details . .
About Oxidants
   Qxidants (or
oxidants) are not emitted
directly into the air from
air pollution sources.
This group of chemicals
is formed in the air by
chemical reactions
between hydrocarbons—
such things  as gasoline
vapors and cleaning
solvents—and nitrogen
oxides—which are
formed from the nitrogen
and oxygen  in  the air
whenever any kind of
burning takes place. The
reactions producing
oxidants are strongly
stimulated by sunlight,
but however formed,
oxidants are an important
air pollutant having
adverse effects on public
health and welfare.

Oxidants have  long been
a major air pollution
problem in Los Angeles,
and other parts of
California. They have
become increasingly
important in other parts
of the country as motor
vehicle traffic —a major
source of hydrocarbons
and nitrogen oxides —has
increased, and as  levels
of other contaminants
have dropped. However.
because oxidants —
outside of California—
have been recognized as
a serious problem only
during  recent years, there
is not enough
information on levels in
the air extending far
enough  back to allow
national trends to be
determined, although
some clues can be

Summertime oxidant
levels in eastern cities
seem to be lower over
the past three years.

In California, there has
been a general
improvement. A decline
has occurred in San
Francisco over the past
ten  years. In San Diego,
levels declined by some
40 percent over the past
ten  years. Most of this
decline occurred during
the  first five years of the
period, but recent
patterns have been
mixed, so that there  has
been no net change  over
the  past five years.

In the Los Angeles area,
measurements of
oxidants have been made
at a large number of
locations, over a long
period of time. This
allows for a more
detailed examination of
trends in air quality
levels and, even more
usefully, in  changes in
the exposure of the
population to high levels
of this contaminant.

Over a 10-year period,
people in the Los
Angeles Basin
experienced a dramatic
decline  in the number of
days they were exposed
to oxidant levels above
the health standard. In
the two-year period
1965/66  people were
exposed an average of
176 days a year. By
1969/70, this had dropped
to 144 days a year. And
by 1973/74 this exposure
was down to 105 days a
year. Not only did the
number of days
decrease—so also did
the total time during
which a person  was
exposed. In terms of total
hourly exposure, people
in Los Angeles were
exposed to  oxidant levels
above the health-related
standard an average of
1050 hours a year in
1965/66, but by 1973/74
this exposure had fallen
to an  average 525 of
hours a year—a
reduction in exposure of

             Percent of Days on
             Which Oxidants
             Exceeded the Health-
             Related Standard in
             Los Angeles
             LJere we see the trend
               ' in the percentage of
             days in the Los Angeles
             area on which the health-
             related air quality
             standard was exceeded.
             In 1965/66, more than half
             of the Basin was
             blanketed with air
             exceeding the standard
             on more than half of the
             days of the year. By
             1973/74, this has been
             reduced to only  a small
             area. This small  area
             remains as the result of a
             combination of two
             factors. A significant
             reduction in emissions of
             hydrocarbons  that react
             rapidly has taken place in
             the Los Angeles Basin.
             This has resulted in
             sizeable improvements in
             oxidant air quality in the
             general vicinity of where
             the reductions occurred.
             On the other hand, there
             still exist emissions of
             sizeable quantities of
             hydrocarbons  that react
             more slowly. Movement
             of these slower reacting
             materials toward the
             eastern portions of the
             Basin, coupled with
             population growth in
             these areas, has resulted
             in increased high levels
             in some eastern  parts of
             the Basin. An area where
             the standard was
             exceeded on fewer than
             20 percent of the days
             has emerged and grown.

Trends in Population
Exposure to Oxidants
in Los Angeles,
                                                    LJere we see what
                                                    ** percent of the Los
                                                    Angeles population was
                                                    exposed to various levels
                                                    ot oxidant above the
                                                    health-related standard
                                                    for various amounts of
                                                    time. For example, in
                                                    1965/66, a little over 50
                                                    percent (53%) were
                                                    exposed to levels above
                                                    the standard  on at least
                                                    50 percent of the  days. In
                                                    1973/74, the percentage
                                                    of the population  with
                                                    the same exposure was
                                                    down to less  than five

                                                    The standards still are
                                                    being exceeded for
                                                    virtually the entire
                                                    population for a least
                                                    some small fraction of
                                                    days, so there still is
                                                    much work to be done.
                                                    But, the improvements
                                                    are an encouraging
                                                    testimonial to the efforts
                                                    that everyone has made.
                                                       - 50%


                                                      •  20°--
      \  \  %  '<$  %
         1 x standard

The Emissions
• Results
 A nother way of
** measuring pollution
control progress is to
estimate the changes in
amounts of pollution
being put into the air.
Measures of the levels in
the air relate  most
directly to people and to
the effects that air
pollution has on health
and welfare. Estimates of
amounts emitted relate
more directly to the
sources,  and  can show
where control has been
most effective and what
sources still need most

Estimates are made for
five major pollutants:
particulate  matter, sulfur
oxides, oxides of
nitrogen, hydrocarbons,
and carbon monoxide.
Since oxidants are not,
for the most part, emitted
directly, estimates of
these would be
meaningless. But since
hydrocarbons are a major
ingredient in  the
formation of oxidants,
estimates of these
emissions provide
important information in
determining the
effectiveness of control
P\uring the period 1970
'-'through 1975, for the
Nation —

• Particulate emissions
  from all sources are
  down by 33 percent.
• Sulfur oxides
  emissions from all
  sources are down by 4
• Nitrogen oxides
  emissions from all
  sources are up by 7
• Hydrocarbon
  emissions from all
  sources are down by 9
• Carbon monoxide
  emissions from all
  sources are down by
  15 percent.
   These figures do not take
   into account the fact that
   all emissions would have
   been higher had there
   been no pollution
   controls in effect.
Summary of National Emission Estimates
Millions of Tons a Year
1970  26.8  34.2  22.7  33.9   113.7

1971  24.9  32.3  23.4  33.3   113.7
                         1972  23.4  36.7  24.6  34.1  115.8

                         1973  21.9  35.6  25.7  34.0  111.5

                         1974  20.3  34.1  25.0  32.9  103.3

                         1975  18.0  329  24.2  30.9   96.2

Darticulate emissions
'were reduced mainly
by installation of control
equipment on industrial
processes, because of
less coal burning by non-
utility stationary sources,
by installation of control
equipment by electric
utilities  that burn coal,
and because of a
decrease in  the burning
of solid  waste. The
extent of emission
reductions by industrial
processing also was
increased as a result of
economic recessions
that curtailed production
by some industries. This
is particularly evident
from 1974 to 1975.

Sulfur oxides emissions
declined slightly from
1972 through 1975.
Although not shown,
emissions from electric
power generating plants
increased somewhat
through 1973, and then
levelled  off.  In spite of
the overall relatively
slight declines in
emissions, the air quality
trends showed us that
levels in the air over
urban areas  have
decreased considerably
over the past few years.
This difference arises
because high sulfur fuels
have been shifted from
use in urban areas  to use
in a growing number of
sources outside of
densely populated  areas,
where fewer people live
and there are fewer other
Nitrogen oxides
emissions have increased
mainly because of
increased emissions
from electric utilities and
from mobile sources.
Emissions from electric
utilities rose because of
increased electric
generation, which
requires the use of more
fuel. Nitrogen oxides
emissions from mobile
sources have increased
due to increases in the
number of vehicle miles
travelled by all highway
vehicles. For the
automobile portion of the
highway vehicles,
emissions have been
essentially constant
since 1972 because
Federal emission
standards that went into
effect with the 1972 cars
have tended to balance
the increase in total
miles travelled.
Hydrocarbon emissions
have gone down only
slightly. Significant
reductions have been
obtained from highway
vehicles as a result of
the Federal emission
standards. But these
reductions have been
partially offset by
increases in industrial
process emissions and
losses of gasoline and
other hydrocarbon vapors
from evaporation at
filling stations and other
points in the marketing
chain, and from the use
of various solvents. The
increases reflect a
general increase in the
consumption of these

Carbon monoxide
emissions have
decreased mostly
because of the Federal
emission standards on
motor vehicles and
because of less burning
of solid waste. Some
industrial emissions also
have been reduced
because of decreases in
production, and the
phasing-out  of some
obsolete processes.
                All photos in this publication from
                EPA's Documerica collection

                U S GOVfMNMfNl PRIN1INC Off ICC 1971 O -??! 430

  Calculated Total Emissions of Criteria Pollutants by Source Category,
  1970 through 1975
    Particulate Matter                          Hydrocarbons
     Nitrogen Oxides
                                           Carbon Monoxide
    70     71     72     73     74    75
I       Industrial
• '    South  Di
          Illinois   606CW