Pollutants in the air can also reduce visibility, obscuring the majestic vistas in national parks such as Grand Canyon and Shenandoah. Air toxics include metals, particles and certain vapors from fuels or other sources. For six pollutants, EPA has established air quality standards designed to protect the health and welfare of people, plants and animals, as well as buildings, monuments, water resources, e tc. These pollutants are ozone, carbon monoxide, nitrogen dioxide, particulate matter, sulfur dioxide and lead. Levels of concern vary from pollutant to pollutant.
Air pollution has many sources.
The table that follows presents EPA information on major pollutants, their many sources and their potential effects. Click here to learn even more about the effect of pollutants on human health and the environment. Ozone A colorless gas that is the major constituent of photochemical smog at the Earth's surface. Ozone is formed in the lower atmosphere as a result of chemical reactions between oxygen, volatile organic compounds and nitrogen oxides in the presence of sunlight, especially during hot weather. Sources include vehicles, factories, electric generating plants, landfills, industrial solvents and many small sources such as gas stations, farm and lawn equipment, etc.