C.J,
EPA
United States April 1979
Environmental Protection OPA 3/9
Agency
Air
Ozone
Its Effects
and Control
•*•
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lational. 333 Ra
Under provisions of the Federal Clean Air
Act, the U.S. Environmental Protection
Agency (EPA) has issued National Ambient
Air Quality Standards (NAAQS). These
standards are set at a level to protect sen-
sitive people and to protect the general
public with an adequate margin of safety.
A secondary standard is also set to protect
vegetation, materials, and properly. When
the standards are found to be exceeded in
any location, the Act requires that steps be
taken to reduce emissions to levels that will
insure attainment of the standard.
Ozone is an air pollutant for which EPA
has issued a standard to protect the public
health and welfare. Frequent and wide-
spread violations of the standard have been
recorded and extensive remedial measures
are now required. Current efforts to
mobilize the Nation to solve the problem,
however, are hampered by the complexity
of the issues and controversy regarding ap-
propriate solutions.
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Introduction
By the Clean Air Amendments of 1970,
Congress gave the U.S. Environmental Pro-
tection Agency (EPA) the responsibility for
setting air quality standards. As an out-
growth of studies relating photochemical
oxidants to health effects and damage to
plants and materials, EPA in 1971 issued a
standard for photochemical oxidants.
A primary standard, to protect public
health, was set at 0.08 parts of oxidant per
million parts of air as a one-hour average
not to be exceeded more than once in any
given year. The level of the standard, as re-
quired by law, was based on health criteria
with an adequate margin of safety to pro-
tect the sensitive population. The secon-
dary standard to protect public welfare was
also set at 0.08 parts per million.
In 1976, EPA began a re-evaluation of
the standard in the light of the most recent
scientific and health data available on ox-
idants. These findings, with special em-
phasis on "what is an adequate margin of
safety," were subject to public comment.
The results led the Agency in January 1979
to revise the primary standard to a one-
hour average concentration of 0.12 ppm
not to be exceeded more than an average
of once per year. The chemical designation
of the standard also was changed from
photochemical oxidant to ozone because
ozone is the only oxidant which can be
measured reliably. The secondary standard
was set at 0.12 ppm.
The 1977 Amendments require that the
States take steps to achieve the standard
by 1987 at the latest, and by 1982 where
feasible. The States are required to revise
their State Implementation Plans and to
present proposed solutions to the public
before formally submitting those plans to
EPA for approval.
Ozone pollution is substantial, wide-
spread and harmful to both health and wel-
fare. Extensive measures will be required to
reduce the pollutant to standard level. It is
important, therefore, that local decision-
makers and the public know and under-
stand the issues and become involved in
the process of developing needed air pollu-
tion control measures.
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The following information was prepared
to help you better understand the evolving
issues related to oxidant pollution and its
control and to help you to participate in the
decisions which must be made in your
community to improve air quality.
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Definitions, Effects, and
Standards
What are The term oxidants describes a complex
photochemical group of compounds found in the ambient
oxidants? air. The term "photochemical" indicates
that most of these particular oxidants are
formed in the air by chemical reactions re-
quiring the presence of sunlight. Oxidants
were first associated with undesirable ef-
fects on human health and welfare three
decades ago, when they were found to be
major constituents of southern California
"smog." Since that time, much more has
been learned about the photochemical ox-
idants and their effects on public health,
vegetation, certain ecosystems, and mate-
rials. Ozone—the most abundant, and most
reliably measured oxidant—has been
singled out for special concern from a
public health and welfare standpoint.
Are oxidants Numerous studies have been undertaken
harmful? over the last 30 years to determine how
harmful oxidants are to public health and
welfare. The results are in an EPA publica-
tion, Air Quality Criteria for Ozone and
Other Photochemical Oxidants. * There has
not been sufficient study of the synergistic
effects of ozone or other air contaminants
to determine their significance to the public
health and welfare. The most significant
known effects of oxidants are:
Public Health
• The mechanical function of the lung is
affected by exposure to ozone for periods
on the order of two hours. The effect is
pronounced at concentrations of 0.37 ppm
or more; evident but less pronounced at
concentrations from 0.25 to 0.37 ppm, and
some studies suggest that this effect may
occur at concentrations in the range of 0.15
to 0.25 ppm.
• Studies have reported that asthma at-
tacks occur more often when ambient con-
centrations of ozone reach 0.25 ppm for a
one-hour period. For some asthmatics and
other sensitive people, there is a likelihood
of effect at concentrations from 0.15 to
0.20 ppm.
*EPA-600/8-78-004 (April 1978). An earlier edition
was published in 1971 when the original NAAQS
was adopted.
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• Ozone exposures in the range of 0.15 to
0.25 ppm for an hour or so have resulted in
reports of coughs, chest discomfort and
headaches.
• There is evidence of impairment of
physical performance (athletic performance)
at ozone concentrations as low as 0.15
ppm.
• Vigorous exercise is likely to increase the
risk of health effects from ozone.
Public Welfare
• Ozone reduces the yields of citrus, cot-
ton, potatoes, soy beans, wheat, spinach,
and other sensitive crops.
• Ozone causes visible injury to a variety of
plant species.
• Ozone affects entire ecosystems, as
evidenced by damage to mixed conifer
forests in California, reduction in the fruit
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and seed diet of small mammals, and
alterations in species composition and
wildlife habitat.
• Ozone accelerates the deterioration of
rubber, textile dyes and fibers, and certain
paints and coatings.
Both health and welfare effects have
severe economic impacts, which can be
measured in terms of monetary losses
totalling hundreds of millions of dollars
each year.
How clean Under the provisions of the Clean Air Act,
should the air EPA is charged with setting standards for
be? the cleanliness (quality) of the ambient air.
Ambient air is the outdoor air to which
people, structures, plants, and animals are
exposed. A standard is a combination of
the amount of pollutant in the air and the
maximum length of exposure permitted in
the interest of public health and welfare.
Standards are set by the EPA after careful
consideration of effects and an adequate
margin of safety. Separate standards are
authorized by the Clean Air Act for protec-
tion of public health (primary standards)
and for protection of public welfare (secon-
dary standards).
In April 1971 EPA published a primary
(and secondary) standard for photochemi-
cal oxidants of 0.08 ppm as a one-hour
average not to be exceeded more than
once in any given year. The human health
effect category of most concern is aggrava-
tion of chronic lung disease and the basic
work documenting the effect is the
Schoettlin and Landau* asthma study. This
was a key study in determining the level of
the existing standard. Based on a reevalua-
tion of this study, the current criteria docu-
ment attributes an increase in asthmatic at-
tacks to a level of 0.25 ppm and not 0.10
ppm as presumed when the existing stan-
dard was promulgated. The revised 0.12
standard anticipates a few excesses in
some years, balanced by years with no ex-
cesses at all to give an average of one or
less per year.
"C.E. Schoettlin and E. Landau, "Air Pollution
and Asmathic Attacks in the Los Angeles Area,"
Public Health Reports 1976, pps. 545-48, 1961.
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The Ozone Problem
Where does Unlike many other pollutants, ozone is not
ozone come introduced directly to the air by man or
from? nature, but forms in the air by chemical
reaction. The compounds called "precur-
sors," that eventually react to form ozone
may be natural constituents of the at-
mosphere (as are oxygen and nitrogen), or
may be introduced directly as pollutants, or
may be formed (as is ozone itself) by
chemical reaction
High in the upper atmosphere, large
amounts of ozone are produced by sunlight
from the oxygen present in the air. Near
the ground, ozone is produced primarily
from man-made compounds. While many
different compounds are involved, two
basic precursor classes control the ozone
production process: volatile organic com-
pounds (VOC) and oxides of nitrogen
(NOx). VOC enters the air from a variety of
human activities, among them fossil fuel
combustion (primarily in auto exhaust),
chemical processing, fuel storage and
handling and solvent usage (such as paint-
ing or degreasing). They also enter the air
from natural sources, such as biological
decay and the vegetative growth process.
Oxides of nitrogen, a compound in the
photochemical process, is primarily emitted
to the atmosphere from the burning of
fossil fuels.
Which sources Because air moves readily from one loca-
contribute tion to another, the air we breathe at a
most to ozone given place and time will contain ozone
problems? from natural as well as man-made sources.
Measurements have shown, however, that
ozone concentrations in and near large ur-
ban centers, are from man-made sources.
How does the Ultraviolet radiation from sunlight is re-
weather affect quired for the photochemical process,
ozone Ozone episodes, therefore, typically occur
pollution? on sunny days in spring, summer, and fall,
when the sun is high enough to provide
sufficient ultraviolet radiation. On cloudy
days and during the winter months, ozone
levels rarely exceed the federal standard.
Sluggish air movement aids in ozone pro-
duction by allowing air parcels to remain
longer over the source areas and permitting
large amounts of precursors to accumulate
and ozone to form. Temperature inversions
(i.e., layers of warm air several hundred
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meters above the cooler air nearer the
ground) frequently trap the pollutants near
the ground. Warm temperatures have
always been associated with ozone
episodes, although the precise role of
temperature in ozone production has not
been adequately defined.
How serious is Measurements indicate that ozone levels
the ozone that exceed the standard occur in virtually
problem in the every part of the United States. Ozone
United States? problems have been found in rural as well
as urban areas. The highest concentrations
of ozone are usually found a few miles
downwind of large urban centers. The
ozone standard is exceeded frequently in
and near these urban centers, as often as
100 or more days per year in some loca-
tions. Concentrations exceeding 0.2 ppm
are not uncommon and concentrations as
high as 0.5 ppm have occurred in a few
communities. The seriousness of the prob-
lem is highlighted by the fact that the
ozone standard has been exceeded in vir-
tually every area where measurements have
been taken, except for a few predominantly
rural locations.
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Ozone and the Law
Under the Clean Air Act, States must sub-
mit to EPA State Implementation Plans
(SIPs), detailing approaches toward attain-
ment and maintenance of all air-quality
standards. In areas where the ozone stan-
dard has not yet been attained (nonattain-
ment areas), the State Plan must be revised
to include control strategies to achieve the
standards by December 31, 1982. In areas
where attainment cannot be demonstrated
by implementing reasonably available con-
trol measures, the deadline can be ex-
tended (up to 5 years) until 1987. Imple-
mentation plans for nonattainment areas
must be included in the SIP revision sub-
mitted to EPA.
While EPA bears ultimate responsibility for
enforcing requirements of the Clean Air
Act, the law provides for maximum par-
ticipation of State and local governments in
forming and implementing the clean air
plans and strategies. Each State must pro-
vide for implementation, maintenance, and
enforcement of primary and secondary air
quality standards in designated areas. Since
many control measures for ozone reduction
strongly affect local jurisdictions, the Act
provides that air quality plans be prepared,
where possible, by an organization of
elected local officials in the affected areas
certified by the State for this purpose.
Otherwise, a State agency must prepare
the plan. The plan must demonstrate that
necessary requirements, timetables, and
compliance schedules are legally enforce-
able and that the agency or organization
responsible for carrying out the plan is
committed to the implementation and en-
forcement of appropriate plan elements.
Clean air plans must be developed with the
continuing cooperative, and comprehensive
transportation planning process mandated
by federal law and with the general air-
quality maintenance planning process of
the State Plan. Attainment planning re-
quires a coordinated effort and includes
local agencies responsible for transportation
and maintenance planning. In carrying out
any requirements of the Act that bear upon
the perogatives of local government, the
States must provide a satisfactory process
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for consulting with local governments and
the designated organizations of their
elected officials.
What are the One of the principal penalties for inade-
penalties for quate State planning affects the construc-
non- tion or modification of major stationary
compliance? sources, such as industrial facilities. After
June 30, 1979, no new construction that
would raise emission levels above the
health-related standard will be permitted
unless an adequate plan for air quality at-
tainment exists. In addition, unless there is
an adequate plan no projects and grants for
transportation or air quality can be autho-
rized under the United States Code, other
than for safety, mass transit, or transpor-
tion improvement related to air quality im-
provement or maintenance.
EPA is required to enforce any require-
ment of a State Plan if the State has failed
to enforce the plan effectively. Enforcement
against a source may be an order to com-
ply to a civil action.
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What can be
done?
10
Approaches to Control
Since the ozone problem results primarily
from chemical reaction of man-made VOC
and NOx, control of these precursors is
necessary to reduce ambient ozone levels.
Laboratory studies suggest that control
of VOC is an effective approach to lowering |
ozone levels. Significant downtrends in
ozone pollution have been recorded in the
Los Angeles Basin and the San Francisco
Bay Area, where VOC control programs
have been underway for some time.
Studies suggest that control of NOx may
not be as effective in reducing ozone in ur-
ban areas. Because of the demonstrated ef-|
fectiveness the current EPA strategy for
reducing the oxidant problem is focused
primarily on VOC control. EPA's Federal
Motor Vehicle Control Program, however,
reduces, emission of both VOC and NOx.
Rural areas also suffer from ozone pollution!
from urban pollutants—that can travel con-f
siderable distances at relatively high con-
centrations. Because the chemical composi-|
tion of rural air differs from that of urban
areas, NOx control may be more effective i|
controlling rural ozone problems. For this
reason, NOx control has received greater
attention in recent years both for rural
areas and for those urban areas which af-
fect rural areas through transport.
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On the whole, studies indicate that a
more effective program for reducing urban
ozone concentrations should emphasize the
control of VOC. Additional emphasis on
NOx control may be required, however, at
a later date.
What State Plans for areas which have not at-
measures are tained the NAAQS for ozone, must contain
appropriate? limitations on the amount of ozone precur-
sors that enter the air and timetables for
compliance with such limitations. Other
measures may be necessary, also, including
(as a minimum) transportation controls, in-
spection and maintenance plans for autos
when a State has requested an extension
beyond 1982, and preconstruction review of
direct sources of air pollution. State Plans
may (but are not required to) contain provi-
sions for land use controls, preconstruction
review of indirect* sources of air pollutants,
and other such measures as may be appro-
priate.
How much Maximum ozone levels found in and around
control will be major urban centers are typically above the
necessary? federal ambient standard. Assuming a
direct proportion between VOC and ozone
reductions, VOC emissions in these areas
will have to be reduced considerably since
studies have indicated that reductions in
VOC yield less than proportional reduc-
tions in ozone concentration. When ozone
contribution from natural sources (including
vegetation and particularly upper atmo-
spheric ozone intrusion) is considered,
an even greater reduction in the contribu-
tion from man-made activities may be re-
quired.
Methods for estimating needed degree of
control have been and are being developed.
Although no single currently available
model is satisfactory in every respect,
evidence from a variety of modeling tech-
niques indicates that there must be sub-
stantial control in many areas. Research is
continuing at EPA to develop improved
models to aid in determining the most ef-
fective approaches to ozone control.
*An indirect source is a facility such as a parking
lot that tends to increase air pollution from
mobile sources (e.g., cars).
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How should Most urban and many rural areas now have
controls be ozone concentrations greater than the na-
applied? tional standard. Since attainment of the
ozone standard will be costly, it is impor-
tant to seek the most equitable distribution
of the burden and the most efficient control
program. One of the most sensitive issues
at present is the division of control respon-
sibility when a local ozone problem results
from pollutants transported from other
areas. This is especially sensitive where
transported pollutants from adjacent urban
centers accumulate under stagnant weather
conditions to form a regional "blanket" of
background ozone.
At present it is difficult to partition
responsibility for ozone control. Consider-
ing the degree of control that will be re-
quired to attain the standard, it is reason-
able, until more information is at hand, for
everyone to exert maximum effort toward
local control of VOC emissions. Coopera-
tive efforts among the States should
minimize any gross inequities.
Who should be
involved?
The ozone problem affects every individual.
Few urban areas are free of ozone pollu-
tion. None is free of sources of pollution
which cause ozone which makes virtually
everyone subject to adverse health and
welfare effects associated with the pro-
blem. And because ozone is a regionwide
problem with a full spectrum of sources
and causes, everyone will bear some por-
tion of the cost for ozone control. For
these reasons, all citizens are urged to be
aware of the solutions being considered for
their areas and to take an active role in the
planning and implementation of control
measures in their States and communities.
\
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EPA is charged by Congress to protect the Nation's land, air and water
systems. Under a mandate of national environmental laws focused on air
and water quality, solid waste 'nanagement and the control of toxic
substances, pesticides, noise and radiation, the Agency strives to formulate
and implement actions which lead to a compatible balance between human
activities and the ability of natural systems to support and nurture life.
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