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. The power to move a car comes from burning fuel in an engine. The Combustion Process Gasoline and diesel fuels are mixtures of hydrocarbons, compounds which contain hydrogen and carbon atoms. Nitrogen in the air would remain unaffected. 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 toxic, with the potential to cause cancer. Under the high pressure and temperature conditions in an engine, nitrogen and oxygen atoms in the air react to form various nitrogen oxides, collectively known as NOx. Nitrogen oxides, like hydrocarbons, are precursors to the formation of ozone. They also contribute to the formation of acid rain.