U.S. ENVIRONMENTAL PROTECTION AGENCY EPA 400-F-92-008

OFFICE OF MOBILE SOURCES

FACT SHEET OMS-6

August, 1994

Clean Fuels: An Overview

What are Clean Fuels?

The most familiar transportation fuels in this country are gasoline and diesel

fuel, but any number of energy sources are capable of powering motor vehicles.

These include alcohols, electricity, natural gas, and propane.

Some vehicle fuels, because of physical or chemical properties, create less pollution than do today’s gasolines. These are called “clean fuels.”

Why Switch to Clean Fuels?

Cars operating on today’s gasolines emit complex mixtures of compounds that

lead to the formation of ground-level ozone; many of these compounds are also

toxic. A lot has been done to reduce automobile pollution, from development of

innovative emission control technologies to establishment of Inspection and

Maintenance programs. But each year sees more cars on the road, traveling

more miles, and the pollution control measures taken so far have not been sufficient to solve the ozone problem in many large cities.

Clean fuels have a number of inherent properties that make them cleaner than

conventional gasoline. In general, these fuels emit less hydrocarbons, and the

hydrocarbons they do emit are less reactive (slower to form ozone) and less toxic.

Emissions from electricity, natural gas, or alcohol-powered vehicles can be as

much as 90 percent lower in toxics and ozone-forming hydrocarbons than emissions from vehicles fueled with conventional gasoline. New gasoline formulations (“reformulated gasoline”) are expected to reduce these emissions up to 25

percent over today’s gasoline.

Use of clean fuels could also help slow atmospheric buildup of carbon dioxide, a

“greenhouse gas” that contributes to the potential for global warming. Combustion of any carbon-based fuel produces carbon dioxide. But the overall impact of

a given fuel on global warming depends on how the fuel is made. In general,

fuels produced from biomass (crops, trees, etc.) and from natural gas result in

less carbon dioxide accumulation than fuels made from petroleum or coal.

Clean fuels have benefits that reach beyond their air quality advantages. New

fuels in the marketplace give consumers new choices and could decrease our

dependence on imported oil.
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Clean Fuels: an Overview

FUEL ADVANTAGES DISADVANTAGES

ELECTRICITY • Potential for zero vehicle emissions

• Power plant emissions easier to control

• Can recharge at night when power demand

is low

• Current technology is limited

• Higher vehicle cost; lower

vehicle range, performance

• Less convenient refueling 

ETHANOL • Excellent automotive fuel

• Very low emissions of ozone-forming

hydrocarbons and toxics

• Made from renewable sources

• Can be domestically produced

• High fuel cost

• Somewhat lower vehicle range

METHANOL • Excellent automotive fuel

• Very low emissions of ozone-forming

hydrocarbons and toxics

• Can be made from a variety of feedstocks,

including renewables

• Fuel could initially be imported

• Somewhat lower vehicle range

(METHANE)

• Very low emissions of ozone-forming

hydrocarbons, toxics, and carbon

monoxide

• Can be made from a variety of feedstocks,

including renewables

• Excellent fuel, especially for fleet vehicles

• Higher vehicle cost

• Lower vehicle range

• Less convenient refueling

PROPANE • Cheaper than gasoline today

• Most widely available clean fuel today

• Somewhat lower emissions of ozone -

forming hydrocarbons and toxics

• Excellent fuel, especially for fleet vehicles

• Cost will rise with demand

• Limited supply

• No energy security or trade

balance benefits

REFORMULATED

GASOLINE

• Can be used in all cars without changing

vehicles or fuel distribution system.

• Somewhat lower emissions of ozone -

 forming hydrocarbons, nitrogen oxides, 

• Somewhat higher fuel cost

• Few energy security or 

trade balance benefits

and toxics

NATURAL GAS

•ELECTRICITY

Battery-powered vehicles give off virtually no pollution and offer one of the best

options for reducing motor vehicle emissions in polluted cities. Power plants

that produce electricity do pollute. But these plants are often in rural areas

where the emissions do not drive pollution levels above health standards. Also,

efficient emission controls can be installed and maintained more easily on

individual power plants than on millions of vehicles. The driving range of

today’s electric cars is limited by the amount of power the battery can provide.

Current batteries take hours to recharge and the cost of electric vehicles is

high. Recent developments in electric vehicle technology show much promise

for the future.

•ETHANOL

Ethanol (“grain alcohol”) is the primary automotive fuel in Brazil, and ethanol/

gasoline blends (known as “gasohol”) have been used in the United States for

many years. Pure ethanol fuel offers excellent performance, plus low hydrocarbon and toxic emissions. It can be produced domestically from corn or other

crops, as well as from cellulosic materials such as wood or paper wastes, potentially minimizing the accumulation of greenhouse gases (since these “renewable” feedstocks draw carbon dioxide out of the atmosphere as they grow). With

current technology and price structures, ethanol is more expensive than gasoline. New technologies offer the hope of significantly reduced costs.
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Clean Fuels: an Overview

• METHANOL

Methanol (“wood alcohol”), like ethanol, is a high-performance liquid fuel that

emits low levels of toxic and ozone-forming compounds. It can be produced at

prices comparable to gasoline from natural gas and can also be produced from

coal and wood. All major auto maufacturers have produced cars that run on

“M85,” a blend of 85 percent methanol and 15 percent gasoline. Cars that burn

pure methanol (M100) offer much greater air quality and efficiency advantages.

Many auto manufacturers have developed advanced M100 prototypes. Methanol has long been the fuel of choice for race cars because of its superior performance and fire safety characteristics.

•NATURAL GAS (METHANE)

Natural gas is abundant and is widely used for home heating and industrial

processes. It is easily transported through pipelines and costs about the same

or slightly less than gasoline. Compressed natural gas (CNG) vehicles emit

low levels of toxics and ozone-forming hydrocarbons. But CNG fuel must be

stored under pressure in heavy tanks, and the cost of accommodating these

tanks must be considered. There are significant tradeoffs for CNG vehicles

among emissions, vehicle power, efficiency, and range; however, natural gas is

already used in some fleet vehicles and appears to have a bright future as a

motor vehicle fuel.

• PROPANE

Propane, or liquefied petroleum gas, is a by-product of petroleum refining and

natural gas production. It burns more cleanly than gasoline but is limited in

supply. Propane-fueled vehicles are already common in many parts of the

world.

• REFORMULATED AND OXYGENATED GASOLINE

The petroleum industry is beginning to market gasoline formulations that emit

less hydrocarbons, nitrogen oxides, carbon monoxide, and toxics than conventional gasoline. These new gasolines can be introduced without major modification to existing vehicles or the fuel distribution system. The Clean Air Act

requires some gasoline modifications to reduce carbon monoxide emissions

beginning in 1992 and use of reformulated gasoline in certain polluted cities

beginning in 1995.

Are Clean Fuels Feasible?

Clean-fueled vehicles are here today and widespread use in the near future is

feasible. To enable the transition, technologies must be refined so vehicles can

achieve optimum performance and emissions characteristics. Consumers must

accept the new vehicles and fuels, and government and industry must cooperate

to ensure their availability. It will take a concerted effort by all sectors of society,

but a switch to clean fuels may be the most viable way for many cities to attain

clean and healthy air.

For More Information:

The Office of Mobile Sources is the national center for research and policy on air

pollution from highway and off-highway motor vehicles and equipment. You

can write to us at the EPA National Vehicle and Fuel Emissions Laboratory,

2565 Plymouth Road, Ann Arbor, MI 48105. Our phone number is (313) 668-4333.