Automobile Emissions: an Overview
U.S. ENVIRONMENTAL PROTECTION AGENCY OFFICE OF MOBILE SOURCES
EPA 400-F-92-007
Automobile Emissions: An Overview
Cars and Pollution
Emissions from an individual car are generally low, relative to the smokestack image many people associate with air pollution. But in numerous cities across the country, the personal automobile is the single greatest polluter, as emissions from millions of vehicles on the road add up. Driving a private car is probably a typical citizen’s most “polluting” daily activity.
Sources of Auto Emissions
The power to move a car comes from burning fuel in an engine. Pollution from cars comes from by-products of this combustion process (exhaust) and from evaporation of the fuel itself.
• Evaporative Emissions • Refueling Losses
• Exhaust Emissions
The Combustion Process
Gasoline and diesel fuels are mixtures of hydrocarbons, compounds which contain hydrogen and carbon atoms. In a “perfect” engine, oxygen in the air would convert all the hydrogen in the fuel to water and all the carbon in the fuel to carbon dioxide. Nitrogen in the air would remain unaffected. In reality, the combustion process cannot be “perfect,” and automotive engines emit several types of pollutants.
FACT SHEET OMS-5 August, 1994
Automobile Emissions: An Overview
“Perfect” Combustion
FUEL (hydrocarbons) + AIR (oxygen and nitrogen) CARBON DIOXIDE + water + unaffected nitrogen
Typical Engine Combustion
FUEL + AIR UNBURNED HYDROCARBONS + NITROGEN OXIDES + CARBON MONOXIDE + CARBON DIOXIDE + water
Exhaust Pollutants
• HYDROCARBONS Hydrocarbon emissions result when fuel molecules in the engine do not burn or burn only partially. Hydrocarbons react in the presence of nitrogen oxides and sunlight to form ground-level ozone, a major component of smog. Ozone irritates the eyes, damages the lungs, and aggravates respiratory problems. It is our most widespread and intractable urban air pollution problem. A number of exhaust hydrocarbons are also
EPA 400-F-92-007
Automobile Emissions: An Overview
Cars and Pollution
Emissions from an individual car are generally low, relative to the smokestack image many people associate with air pollution. But in numerous cities across the country, the personal automobile is the single greatest polluter, as emissions from millions of vehicles on the road add up. Driving a private car is probably a typical citizen’s most “polluting” daily activity.
Sources of Auto Emissions
The power to move a car comes from burning fuel in an engine. Pollution from cars comes from by-products of this combustion process (exhaust) and from evaporation of the fuel itself.
• Evaporative Emissions • Refueling Losses
• Exhaust Emissions
The Combustion Process
Gasoline and diesel fuels are mixtures of hydrocarbons, compounds which contain hydrogen and carbon atoms. In a “perfect” engine, oxygen in the air would convert all the hydrogen in the fuel to water and all the carbon in the fuel to carbon dioxide. Nitrogen in the air would remain unaffected. In reality, the combustion process cannot be “perfect,” and automotive engines emit several types of pollutants.
FACT SHEET OMS-5 August, 1994
Automobile Emissions: An Overview
“Perfect” Combustion
FUEL (hydrocarbons) + AIR (oxygen and nitrogen) CARBON DIOXIDE + water + unaffected nitrogen
Typical Engine Combustion
FUEL + AIR UNBURNED HYDROCARBONS + NITROGEN OXIDES + CARBON MONOXIDE + CARBON DIOXIDE + water
Exhaust Pollutants
• HYDROCARBONS Hydrocarbon emissions result when fuel molecules in the engine do not burn or burn only partially. Hydrocarbons react in the presence of nitrogen oxides and sunlight to form ground-level ozone, a major component of smog. Ozone irritates the eyes, damages the lungs, and aggravates respiratory problems. It is our most widespread and intractable urban air pollution problem. A number of exhaust hydrocarbons are also