Clean air logo mobile sources

emissions from automobiles, trains, and airplanes


Mobile sources of air pollution are the most difficult to pinpoint because they are constantly moving. The government cannot distinguish a definite amount of mobile sources in a given area because these automobiles; whether they be cars, trucks, airplanes, trains, or any number of vehicles; freely move across borders and in and out of areas. These sources, as difficult as they are to track, have been the origin of about half of the air pollution in the United States.



Cars and other motorized vehicles have been the source of about half of the air pollution in the United States. This pollution originates in both direct tailpipe emissions and in the mechanical wear of different parts of the vehicle. The major emissions from automobiles include carbon monoxide, hydrocarbons, nitrogen oxides, lead, and particulate matter.

carbon monoxide (CO): This is a colorless, odorless gas that causes serious, possibly fatal, health problems. Motor vehicles emit massive amounts of carbon monoxide; however, its half life is very short causing it to break down quickly and not remain in the atmosphere in this form.

hydrocarbons (HC): Emitted because of incomplete gasoline combustion, these combine with nitrogen oxides in the presence of sunshine to form ozone (O3) which has adverse health effects.

nitrogen oxides (NOx): These compounds pose problems mostly in the form of nitrogen oxide (NO) and nitrogen dioxide (NO2). The compound combines with hydrocarbons and other volatile organic compounds (VOCs) in the presence of ultraviolet sunlight to produce photochemical smog, mainly ozone (O3), which has adverse health effects.

lead (Pb): These emissions originate from the combustion of leaded gasoline. Alkyl lead compounds are used as fuel additives in larger vehicles to control engine knocking. Enough lead in the atmosphere can cause lead poisoning and other health concerns.

Bach, Julie S. and Lynn Hall, The Environmental Crisis: Opposing Viewpoints, (St. Paul, MN: Greenhaven Press, 1986), p. 216.

particulate matter (PM10): These minuscule particles are emitted by exhausts and by mechanical wear, such as, break lining or rubber tires.


standards and deadlines

The government has found it difficult to deal with this issue, and it has encountered confusion in trying to control mobile emissions on the state level. If each state were allowed to set its won standards, then automobile industries would need to meet fifty different sets of standards. Also, automobiles, trains, and airplanes travel freely from state to state; therefore, there would not be any efficient way to enforce these different standards. Washington, therefore, has decided to deal with this issue at a federal level. The following is a series of events outlining the standards and deadlines for mobile emissions.

California sets the first tailpipe emission standards.

Senate Public Works Subcommittee on Air and Water Pollution, during hearings, realized the inadequacy of the amount of attention they have focused on automobile emissions.

Motor Vehicle Air Pollution Control Act (amendments of the Clean Air Act) set the first federal emission standards beginning with the 1968 models (which were the same standards California had set for their 1966 models. These standards were reductions from the 1963 emissions: 72% reduction for hydrocarbons (HC), 56% reduction for carbon monoxide (CO), and 100% reduction for crankcase hydrocarbons.

1968, 1969
Tests showed that more than half of the cars for these model years failed to meet the emission standards.

State legislatures, such as California, New Jersey, and Illinois, pass laws enforcing the cleanup of aircraft engine emissions.

The new Clean Air Act amendments limited HC and CO emissions 90% from what they emitted in 1970 to be effective by the 1975 models. They also limited nitrogen oxides (NOx) emissions 90% from what they emitted in 1971 to go into effect by the 1976 model year. In order to enforce these standards, the Environmental Protection Agency (EPA) was required to perform compliance tests, enforce performance warranties from manufacturers, and impose a $10,000 per vehicle fine for those that violated the standards.
The Department of Transportation and the Department of Health, Education, and Welfare met with major airlines and agreed on installing smoke reduction devices on aircraft engines to control pollution which was to be "substantially completed" by the close of 1972.

EPA granted a one year extension for HC (now 1976), CO (now 1976), and NOx (now 1977) standards to be met.

EPA granted another one year extension for HC (now 1977), CO (now 1977), and NOx (now 1978) standards to allow motor vehicle manufacturers more time to improve fuel economy.

EPA granted another one year extension for HC and CO emissions which set the deadline at 1978 for both compounds.

The Clean Air Act was amended granting another extension on the deadline for HC (now 1980), CO (now 1980) emissions to meet their standards. The NOx standard was increased from .4 grams per mile (g/mi.) to 1.0 g/mi., and the deadline was extended to 1981 or later.
EPA also set standards for lead, allowing refiners to add, at the most, .8 grams of lead per gallon of gasoline (g/gal). Small refiners, as the exception, could add up to 2.65 g/gal until October 1, 1982, when they needed to comply with the .8 g/gal standard.

EPA lowered the lead standard to .5 g/gal.
EPA set standards to limit diesel particulate emissions for the 1982-1984 model years.
EPA also required a 90% reduction in CO emissions for heavy-duty trucks to be effective for the 1984 model year.

National Commission on Air Quality decided that deadlines for emission standards needed to be extended and that these standards needed to be lowered. The deadlines have since been extended well into the 1990s.
EPA proposed diesel particles standards for heavy-duty trucks hoping they would be finalized in 1982 (these standards were never resolved).

EPA allowed the October 1, 1982 deadline for small refiners to be extended indefinitely.
EPA also delayed the deadlines for diesel particulates until the 1987 model year.
EPA granted a one year extension on CO reduction for heavy-duty trucks.

The Clean Air Act was again amended, and these amendments sought to limit tailpipe emissions and develop clean fueled vehicles. EPA called for a 40% HC reduction and a 60% NOx reduction by the turn of the century. These new controls were required to remain effective for 10 years or 100,000 miles.

EPA was required to set emission standards for benzene and formaldehyde.

EPA was required to introduce standards for new locomotives and their engines.
A 50% particulate matter reduction was mandatory for urban transit buses.

In order to achieve these standards, automobile manufacturers as well as individual scientists introduced a number of possible solutions. The first attempt to clean tailpipe emissions was an afterburner which would complete the burning of CO and HC, but tests proved that it ultimately led to more NOx emissions. Other changes which suggested to improve existing engines included exhaust gas recirculation and air pumps; however, scientists believed that a new engine needed to be created. The device which has made the most improvement so far has been the catalytic converter. This device transforms harmful pollutants into benign compounds, and it requires unleaded gasoline which will decrease the atmospheric lead concentration. Electric automobiles were introduced as a solution; however, the batteries need frequent recharging of power which would come from the power companies, in turn, creating more stationary source emissions. Experts now believe that the best way to reduce harmful emissions is to use clean fuels, such as natural gas, or oxygenated fuels based on methanol and ethanol. The easiest way, however, to keep this problem under control now is to require periodic emission inspections and simply to promote carpools to reduce the amount of pollutants.

Cars were not the only concern of environmentalists; engine exhaust from airplanes was also a substantial mobile source for pollution. Airplane engines emitted hydrocarbons, carbon monoxide, and nitrogen oxides just as automobiles did. Also, aircraft emissions of particulate matter were incredible--in Los Angeles, these daily emission levels were equal to that of one million cars. Finally, in the Air Quality Act of 1967, Congress ordered the Secretary of Health, Education, and Welfare to conduct research on aircraft emissions and control began in the early 1970s. (what has happened since then?)



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