Automobile Emissions: An Overview

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.

 

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. Pollutants also escape into the air through fuel evaporation

 

FUEL (hydrocarbons) + AIR (oxygen and nitrogen) ==>> CARBON DIOXIDE + water + unaffected nitrogen

 

FUEL + AIR ==>> UNBURNED HYDROCARBONS + NITROGEN OXIDES +

+ CARBON MONOXIDE + CARBON DIOXIDE + water