United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
August 1980
v>EPA
Carbon Monoxide
Proposed
NAAQS Revisions
SSI*5*
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-Text and graphic arts
prepared by Northrop Services, Inc.
Research Triangle Park, NC
Bottom photo, cover,
courtesy of the
Daily Tar Heel
UNC-Chapel Hill
North Carolina
All other photos
from EPA Collection
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National Ambient
Air Quality Standards
(~ I £,
The U.S. Environmental Protection Agency (EPA),
under the provisions of the Clean Air Act, is author-
ized to develop a comprehensive national program
for curtailing air pollution and improving air quality.
With these clean air goals in mind, EPA has estab-
lished ambient air quality standards for the seven
major or "criteria" pollutants: carbon monoxide,
ozone, particulate matter, sulfur oxide, hydro-
carbons, nitrogen oxides, and lead. A National
Ambient Air Quality Standard (NAAQS) is the
maximum amount of pollutant that is permitted in
the ambient (surrounding) air in order to protect the
public health and welfare.
These NAAQS consist of primary and secondary
standards. A primary standard is intended to protect
the health of the general public, as well as sensitive
population groups, with an adequate margin of
safety. A secondary standard is one set to protect
public welfare, which includes such things as soil,
crops, water, vegetation, and other similar con-
siderations.
Primary standards are established to protect public
health; secondary standards protect wildlife, crops,
and other similar considerations.
Carbon monoxide (CO) is one major air pollutant for
which EPA has set primary and secondary ambient
air quality standards. In accordance with Clean Air
Act Provisions, EPA recently reviewed the current
NAAQS for CO and, on the basis of data made
available since the standards were initially published
in 1971, has proposed revisions for these NAAQS.
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Revising NAAQS
to Meet Clean Air Act
Requirements
The existing primary and secondary standards for
CO were established by EPA in April 1971, and re-
flect the human health and welfare effects data
available at that time. The primary and secondary
standards are currently set at 9 parts per million
(ppm), averaged over an 8-hour period, and at 35
ppm, averaged over a 1-hour period, not to be ex-
ceeded more than once per year.
The proposed revisions would tighten the 1-hour
primary standard, so that the average hourly CO
concentration could not exceed 25 ppm on more
than one day per year on average. The 8-hour
primary standard would remain at 9 ppm. EPA's
proposed revisions would rescind the secondary
standards, since no adverse impacts on vegetation,
materials, or soils have been associated with existing
ambient CO concentrations.
Compliance with NAAQS is primarily the respon-
sibility of the States, who must incorporate CO
pollution controls into their State Implementation
Plans (SIPs). The 1977 Amendments to the Clean
Air Act require that States demonstrate attainment
of the standards by the end of 1982.
EPA must review the scientific basis for each NAAQS
by the end of 1980, and at least once every five
years thereafter. Results of numerous studies for
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determining CO's harmful effects on public health
and welfare are summarized in the Air Quality Cri-
teria Document for Carbon Monoxide.*
Public participation is a key factor in the develop-
ment of air pollution laws that establish NAAQS
and other standards. This material, which presents
pertinent facts and issues associated with the pro-
posed NAAQS revisions, is intended to inform mem-
bers of public and private sectors who may wish to
contribute to EPA's rule making by participating in
public hearings, and in the public comment process.
Carbon Monoxide A colorless, odorless, and generally unreactive gas,
CO is usually formed when carbon-containing fuels
are incompletely burned, and is emitted from some
natural processes as well. Forest fires, methane ox-
idation, and certain biological activities contribute
to a nearly constant CO background concentration
of about 0.044 ppm. When this amount is combined
with emissions from urban and industrial sources,
global background concentration of CO increases to
0.18 ppm in the northern hemisphere, and to 0.05
ppm in the southern hemisphere.
Through its conversion by natural processes to harm-
less carbon dioxide, any significant CO buildup is
usually prevented. But in congested urban areas
where the ambient standard is being violated, and
where industrial sources and heavy vehicular traffic
exist in close proximity, CO pollution may reach
unsafe levels of 50-200 ppm.
Nationwide, more than 103 million metric tons of
CO enter the atmosphere each year. According to
figures realeased in the most recent EPA Emissions
*EPA-600/8-79-022 (October 1979)
An earlier edition was published in 1971 when the
original NAAQS were adopted.
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Trends Report,** transportation - including high-
way and non-highway vehicles — contributes over
83 percent of total CO emissions. Industrial pro-
cesses such as primary metal, carbon black, and
maleic anhydride production contribute about 8
percent of the total. Miscellaneous combustion
such as agricultural burning and forest fires account
for 4.8 percent; solid waste incineration, 2.5 per-
cent; and electric power and heat generation, 1.2
percent.
Industrial
Processes
Forest Fires and
Agricultural Burning
Solid Waste
_jj. Incineration
Sources of CO Pollution
Environmental Effects
Most forms of plant life metabolize and produce CO
through photosynthesis. This may explain why only
very high CO concentrations have detrimental effects
on plant life. One study has reported that the thres-
hold exposure for significant effects on vegetation
occurs at 100 ppm CO for 3 to 34 days, resulting in
reduced nitrogen fixation in plants. Such studies,
however, give little indication of the effects occur-
ring at ambient levels, since the test exposures are
much greater than those recorded in urban areas.
**National Air Quality, Monitoring, and Emission
Trends Report, 1977, EPA-450/2-78-052.
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Because observed CO pollution levels have not been
shown to adversely affect crops, wildlife, or other
aspects of public welfare, EPA is proposing that the
existing secondary standard for CO be eliminated.
CO levels required by the primary standards are
expected to provide adequate protection for public
welfare.
Health Effects Exposure to carbon monoxide concentrations that
exceed levels set by the primary standards results in
pronounced adverse effects on the human body. CO
has a strong affinity for hemoglobin, the blood's
oxygen-carrying protein. Blood hemoglobin is 200
times more likely to bond with CO than with oxygen.
When CO and hemoglobin combine, carboxyhemo-
globin (COHb) is produced in the blood.
Some COHb is formed through natural processes,
(i.e; the body's own metabolic breakdown of hemo-
globin and other heme-containing materials) resulting
in a normal background (or endogenous) COHb level
of between 0.3 and 0.7 percent. Significant amounts
of inhaled CO can raise COHb levels dramatically,
triggering hypoxemia, a deficient oxygenation of the
blood. Hypoxemia occurs when hemoglobin bonded
with CO is no longer available to transport adequate
amounts of oxygen throughout the body. In addi-
tion, high COHb levels inhibit oxygen release from
"free" hemoglobin. This oxygen starvation asso-
ciated with hypoxemia can have detrimental con-
sequences for the cardiovascular, pulmonary, central
nervous, and other body systems.
CO exposure producing elevated COHb levels of 2.5
to 3.0 percent can aggravate angina pectoris, a car-
diovascular disease where low level oxygen depri-
vation results in chest pressure and pain.
Aggravation of angina may cause cardiovascular
damage that current medical technology is incapable
of measuring. In addition, symptoms triggered by
increased COHb levels may be the first in a series of
progressively more serious symptoms that accompany
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coronary insufficiency, myocardial infarction (heart
attack) and other cardiovascular diseases. For in-
dividuals with more serious forms of heart disease,
the consequences of relatively low-level CO ex-
posure may have more immediate, serious health
implications.
Studies have indicated that short-term, high level
exposure to CO can produce a "bolus effect", where
a portion of the blood supply becomes essentially
devoid of oxygen. Life-threatening consequences
may result when this portion of blood reaches the
heart. The 1-hour and 8-hour standards are intended
to provide reasonable protection against this con-
dition.
Finally, some studies have suggested that carbon
monoxide exposures resulting in blood COHb levels
of 3.0 6.5 percent can produce "decrements in-
vigilance," or the ability to detect small changes in
one's environment that take place at unpredictable
times. Blood COHb levels of 4.0 to 5.0 percent can
result in decrements invisual function and sensitivity-
important functions that are components of more
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Protecting
Sensitive Groups
complex tasks like driving. Thus, reduced alertness
or visual sensitivity may lead to increased accidents.
Revisions proposed forthecarbon monoxide NAAQS
are intended to provide an adequate margin of safety
for the nearly 8 million Americans who have cardio-
vascular or peripheral vascular disease. Available
health effects data indicate that, for members of this
"sensitive population," the accumulation of relatively
low COHb levels may trigger the onset of symptoms
associated with angina or other cardiovascular
diseases.
In determining what margin of safety the revised
standards should provide, EPA also considered CO's
effects on other sensitive groups, including persons
with central nervous system defects, pregnant wo-
men (fetuses), older persons, children, persons
living at high altitudes, persons under medication,
and anemics (who have higher endogenous COHb
levels).
Attaining Levels
Set by NAAQS
The Clean Air Act allows maximum participation
by state and local agencies in achieving NAAQS.
States must submit to EPA State Implementation
Plans (SIPs) that outline in detail their approaches
towards attainment and maintenance of the CO
standards. In non-attainment areas where the CO
standards are exceeded, SIPs must be revised to
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Public Participation
include control strategies that will insure attainment
of the standards by December 31, 1982. In areas
where the CO pollution problem is so severe that
attainment cannot be achieved through implementing
reasonably available control measures, the deadline
can be extended to 1987.
Federal programs like the Federal Motor Vehicle
Emissions Program (FMVCP) have been implemented
to lower CO pollution levels. The FMVCP focuses
on controls for automobiles, trucks, and other mobile
sources. States can achieve compliance with the CO
standard by establishing automobile inspection and
maintenance (I/M) programs, and by establishing
other reasonable strategies for reducing air pollution.
Other control strategies might include transportation
control measures (TCMs) for reducing vehicle miles
travelled and alleviating traffic flow problems.
The cost of implementing I/M and TCM programs to
meet the proposed standards is expected to be ap-
proximately $450 million per year. Total costs of
CO emission control are estimated at about $2.9
billion annually; nearly $2.4 billion of that amount
is linked to the FMVCP.
The criteria document developed by EPA reflects
consideration given to public comments solicited by
the Agency; EPA will continue to solicit public com-
ments prior to final decision making for revisions to
this air quality standard, which was proposed in the
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Federal Register on August 18, 1980 (45FR55066).
Public meetings on the NAAQS revisions are sched-
uled for October 2, 1980, at the U.S. Environmental
Protection Agency Headquarters, Room 3906-3908,
401 M Street, SW, Washington, DC. A public
meeting is also scheduled for October 10, 1980 at
the U.S. Post Office Building Auditorium, Denver,
Colorado.
Written comments on the proposed regulation must
be received in duplicate no later than November 10,
1980, and must be addressed to: Central Docket
Section (A-130), Environmental Protection Agency,
Attn: Docket No. OAQPS 79-7, 401 M Street SW,
Washington, DC 20460.
Docket No. OAQPS 79-7, containing material rele-
vant to the proposed rulemaking, is available for
public inspection during the Agency's normal work-
ing hours.
Documents generated as part of the NAAQS review
and revision, such as the Control Techniques Docu-
ment, Regulatory and Community Impact Analysis,
Exposure Analysis, and Environmental Impact
Statement can be obtained from the EPA Library
(MD-35), Research Triangle Park, NC 27711, tele-
phone (919) 541-2777.
The Air Quality Criteria Document for carbon mon-
oxide is available from: Environmental Criteria and
Assessment Office (MD-52), U.S. Environmental
Protection Agency, Research Triangle Park, NC
27711, Attn: Dr. David McKee. The criteria docu-
ment also may be received by calling (919) 541-
3746 (FTS 629-3749).
For further information on the proposed rulemaking
contact: Michael Jones, Strategies and Air Stan-
dards Divisions (MD-12), Office of Air Quality
Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC
27711, telephone (919) 541-5231 (FTS 629-5231).
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