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.
Air pollutants emitted from cars are believed to cause cancer and contribute to such problems as asthma, heart disease, birth defects and eye irritation.
Emissions from cars increase the levels of carbon dioxide (CO2) and other greenhouse gases in the atmosphere. At normal levels, greenhouse gases keep some of the sun’s heat in the atmosphere and help warm the Earth. That said, many scientists believe that burning fossil fuels such as gasoline causes greenhouse gas levels to spike, leading to global warming.
Scientists use sophisticated instruments to measure concentrations of harmful substances in the air, but it’s tough to say exactly what percentage of air pollution comes from cars. This makes sense, because many other human activities contribute to air pollution as well. In fact, the production of electricity by coal-fired power plants and other sources can cause more pollution than most cars. If that wasn't enough, we pollute the air when we heat our homes and public buildings with fuels other than electricity -- just as we do when we drive our cars. Even people who don’t drive add to pollution when they buy goods and services that involve fuel when they're made or delivered.