There are four major pollutants that come from cars:
A car emits carbon monoxide when the carbon in fuel doesn't burn completely.
A car's exhaust emits hydrocarbons, a toxic compound of hydrogen and carbon.
When fuel burns, nitrogen and oxygen react with each other and form nitrogen oxides (NOx).
Particulate matter -- small particles of foreign substances -- in the air contribute to atmospheric haze and can damage people’s lungs.
Pollutants from cars contribute to various types of air pollution. When hydrocarbons and NOx combine in sunlight, they produce ozone. High in the atmosphere, ozone protects us from the sun’s ultraviolet rays. When holes in the atmosphere's ozone layer allows ozone to come closer to Earth, it contributes to smog and causes respiratory problems.