U.S. ENVIRONMENTAL PROTECTION AGENCY EPA 400-F-92-006

OFFICE OF MOBILE SOURCES

FACT SHEET OMS-4

January, 1993

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 stinging eyes associated with smog. Ozone damages lung tissue, aggravates respiratory disease, and makes people more susceptible to respiratory infections. Children are especially vulnerable to ozone’s harmful effects, as are adults with

existing disease. But even otherwise healthy individuals may experience impaired health from breathing ozone-polluted air.

Elevated ozone levels also inhibit plant growth and can cause widespread damage 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 Ambient Air Quality Standard. The standard is based on the highest ozone exposure

sensitive persons can tolerate. Nine cities, home to 57 million people, are considered “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 sunlight. 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 construction vehicles and boats.
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What’s Been Done to Control Ozone Levels?

The Clean Air Act of 1970 gives primary responsibility to state and local governments for regulating pollution from power plants, factories, and other “stationary 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 volatility gasoline and as newer cars with improved emission control systems replaced 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 hydrocarbons 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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This chart shows the projected effect of substituting methanol, ethanol, or natural 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 considerably smaller reductions, relative to methanol, ethanol, or natural gas fuel.

Because of continued growth in the number of vehicles and miles traveled, hydrocarbon 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, ozoneforming 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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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 automotive fuel, particularly for fleet vehicles where long driving range is not important. 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 studying 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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