U.S. ENVIRONMENTAL PROTECTION AGENCY EPA 4oo-F-92-ooS
OFFICE OF MOBILE SOURCES
Automobiles and Ozone
What Is Ozone?
Ozone is a form of molecular oxygen that consists of three oxygen atoms linked
together. Ozone in the upper atmosphere (the "ozone layer") occurs naturally and
protects life on earth by filtering out ultraviolet radiation from the sun. But
ozone at ground level is a noxious pollutant. It is the major component of smog
and presents this country's most intractable urban air quality problem.
Why Is Ozone a Public Health Problem?
Ozone is a severe irritant. It is responsible for the choking, coughing, and sting-
ing eyes associated with smog. Ozone damages lung tissue, aggravates respira-
tory disease, and makes people more susceptible to respiratory infections. Chil-
dren are especially vulnerable to ozone's harmful effects, as are adults with
existing disease. But even otherwise healthy individuals may experience im-
paired health from breathing ozone-polluted air.
Elevated ozone levels also inhibit plant growth and can cause widespread dam-
age to crops and forests.
Unhealthy ozone levels are a problem across the United States, with nearly 100
cities exceeding the U.S. Environmental Protection Agency (EPA) National Am-
bient Air Quality Standard. The standard is based on the highest ozone exposure
sensitive persons can tolerate. Nine cities, home to 57 million people, are consid-
ered "severely" polluted, experiencing peak ozone levels that exceed the standard
by 50% or more.
How Is Ozone Formed?
Ozone is not emitted directly but is formed in the atmosphere through a complex
set of chemical reactions involving hydrocarbons, oxides of nitrogen, and sun-
light. The rate at which the reactions proceed is related to both temperature and
intensity of the sunlight. Because of this, problematic ozone levels occur most
frequently on hot summer afternoons.
Hydrocarbons and nitrogen oxides come from a great variety of industrial and
combustion processes. In typical urban areas, at least half of those pollutants
come from cars, buses, trucks, and off-highway mobile sources such as construc-
tion vehicles and boats.
FACT SHEET OMS-4
January, 1993
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Automobiles and Ozone
What's Been Done to Control Ozone Levels?
The Clean Air Act of 1970 gives primary responsibility to state and local govern-
ments for regulating pollution from power plants, factories, and other "station-
ary sources." EPA has primary responsibility for regulating "mobile sources,"
which include cars, trucks, buses, and aircraft.
The EPA vehicle emission control program has achieved considerable success in
reducing both nitrogen oxide and hydrocarbon emissions. Cars coming off today's
production lines typically emit 70% less nitrogen oxides and 80% to 90% less
hydrocarbons over their lifetimes than their uncontrolled counterparts of the
1960s. The improvement came about in response to stringent regulations, which
required auto manufacturers to develop systems capable of capturing excess
gasoline vapors and cleansing tailpipe emissions.
Why Aren't Ozone Levels Dropping?
Ozone levels in many cities have come down with the introduction of lower vola-
tility gasoline and as newer cars with improved emission control systems re-
placed older models. But although there has been significant progress since 1970
in reducing emissions per mile traveled, the number of cars on the road — and
the miles they travel almost doubled in the same time frame.
A second reason that ozone levels remain high is that emission control systems
do not always perform as designed over the full useful life of the vehicle. Routine
aging and deterioration, poor state of tune, and emission control tampering can
all increase vehicle emissions. In fact, a major portion of ozone-forming hydrocar-
bons can be attributed to a relatively small number of "super-dirty" cars whose
emission control systems are not working properly.
Unless we dramatically reduce the amount of pollution vehicles emit in actual
use, or drastically cut back on the amount we drive, smog-free air will continue
to elude many cities.
Promising Solutions
EPA believes that control of hydrocarbon and nitrogen oxide emissions is the
most promising strategy for reducing ozone levels in most urban areas. Toward
that end, the federal government will establish more stringent limits on gasoline
volatility, control hydrocarbon vapors that evaporate during vehicle refueling,
tighten tailpipe emission standards, and require improvements in Inspection
and Maintenance programs. EPA also is developing requirements for "warning
systems" on all cars to alert drivers when the emission controls malfunction.
In the most polluted cities, however, these measures will not be sufficient. The
only way to ensure healthy air is to markedly reduce our use of cars or to switch
to fuels that are inherently cleaner than conventional gasoline.
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Automobiles and Ozone
Cars are getting cleaner, but people are driving more,
offsetting progress in ozone pollution control
20 T -r 4000
15 4
10 -
B -•
Av*«g» P»r-V»hiel» Emissions
(grams hydrocarbon p»r mil*)
Vehicle MH«s Trav.led
(in billions)
--
-- 2000
H-- 1000
A large amount of hydrocarbon pollution conies from
relatively few cars with "dirty" exhaust
Percent of Fleet Percent of
Emissions
! Normal Imfttors
High Emitters
Super-High Emitters
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Automobiles and Ozone
Clean-Fueled Vehicles and Potential Ozone Reductions In a Typical City
Vehicle Emissions
of Ozone-Forming
Hydrocarbons
Gasoline Vehides
Transitional Clean
Fuel Vehicles
Optimized Clean
Fuel Vehicles
1995
2000
2005
2010
2015
2020
* Assuoiii 9 pri gasoline «nd vehicles equipped with advanced pollution control systems
This chart shows the projected effect of substituting methanol, ethanol, or natu-
ral gas fuel for conventional gasoline in a typical large city. Use of electricity
would result in somewhat greater reductions in ozone-forming hydrocarbons;
propane in somewhat smaller reductions; and reformulated gasoline in consider-
ably smaller reductions, relative to methanol, ethanol, or natural gas fuel.
Because of continued growth in the number of vehicles and miles traveled, hy-
drocarbon emissions from conventional gasoline vehicles will begin to increase
after 2005, despite continued improvements in emission control systems.
If "transitional" vehicles (capable of running on a cleaner fuel, or gasoline) are
phased in beginning in 1995, ultimately dominating the fleet by 2020, ozone-
forming hydrocarbons will remain relatively constant. But if an aggressive clean
fuels program is adopted, overall hydrocarbon emissions will continue to decline
dramatically. Such a program would entail a more rapid phase-in of transitional
vehicles starting in 1995, followed by the introduction of "optimized" vehicles
(designed specifically for optimal performance on one clean fuel) beginning in
2000.
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Automobiles and Ozone
Possible Clean Fuels
Some fuels are inherently cleaner than gasoline because they emit less nitrogen
oxides or hydrocarbons, and because the hydrocarbons they do emit are less
likely to react in the atmosphere to form ozone. These fuels include:
• ALCOHOLS: Methanol (made from natural gas, coal, or biomass) and
ethanol (made from grains or sugar) are high-octane liquid fuels. Cars designed
to run on pure alcohol fuels have the potential to emit 80% to 90% less reactive
hydrocarbons than advanced-technology gasoline cars.
• ELECTRICITY: Battery-powered cars have the potential for zero
tailpipe and evaporative hydrocarbon and nitrogen oxide emissions, though
power plant emissions must be accounted for. Today's electric vehicle technology
is limited, but promising recent developments may lead to more widespread use
in the future.
• NATURAL GAS: Compressed natural gas is also an excellent automo-
tive fuel, particularly for fleet vehicles where long driving range is not impor-
tant. Natural gas vehicles have the potential to emit 85% to 95% less reactive
hydrocarbons than advanced-technology gasoline vehicles.
LIQUID PETROLEUM GAS (PROPANE): Propane is a
byproduct of petroleum refining and natural gas production. Propane vehicles
emit considerably less ozone-forming hydrocarbons than do vehicles fueled with
conventional gasoline.
REFORMULATED GASOLINE: The petroleum industry is study-
ing ways to change refinery procedures to make a cleaner-burning gasoline. A
number of "clean" gasolines have recently been introduced into the marketplace,
and research is continuing to develop even cleaner fuels. Reformulated gasoline,
capable of reducing hydrocarbon emissions by at least 15%, will be required in
some high ozone areas beginning in 1995.
For Further information:
The EPA National Vehicle and Fuel Emissions Laboratory is the national center
for research and policy related to auto pollution. To reguest fact sheets on other
mobile source issues, write to us at 2565 Plymouth Road, Ann Arbor Ml 48105, or
call 313/668-4333.
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Automobiles and Ozone
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