Carbon Monoxide | Hydrocarbons
Nitrogen Oxides | Particulate Matter

Photo of SUV's stuck in traffic

Air pollution in the United States comes from many types of engines, industries, and commercial operations. Pollution sources that move, such as trucks, snowblowers, bulldozers, and trains, are known as “mobile sources.” Examples of all other (non-mobile) sources of air pollution include power plants, factories, and manufacturing processes.

Mobile sources pollute the air through combustionand fuel evaporation. These emissions contribute greatly to air pollution nationwide and are the primary cause of air pollution in many urban areas. Learn more about how mobile sources contribute to four significant air pollutants and how these pollutants affect human health and the environment in the following pages:

Mobile sources also produce several other important air pollutants, such as air toxics and greenhouse gases. Nationwide, mobile sources represent the largest contributor to air toxics. Air toxics are pollutants known or suspected to cause cancer or other serious health or environmental effects. Greenhouse gases, such as carbon dioxide (CO2), trap heat in the Earth’s atmosphere, contributing to global climate change.