What Are the Main Causes of Air Pollution?

The Environmental Protection Agency (EPA) targets six pollutants thought to be the main contributors to air pollution. The agency calls them "criteria pollutants" and in compliance with the Clean Air Act sets the National Ambient Air Quality Standards for them. These air pollutants cause cancer and lung disease. The destruction of the protective ozone layer in the upper atmosphere is caused by these and other pollutants. The pollutants create greenhouse gases that contribute to global warming.

Carbon Dioxide

• Though naturally occurring in the environment, carbon dioxide (CO) is, in excess, the most famous of the criteria pollutants. Motor vehicle exhaust is the main delivery system for CO, accounting for 56 percent of CO emissions nationwide. Another 22 percent comes from other kinds of engines. Metals processing and chemical manufacturing contribute to polluting CO emissions as do wood and gas stoves and cigarettes.

Oxides

• Sulfur dioxide (SO2) and nitrogen dioxide (NO2), are two kinds of reactive gasses that cause air pollution. Seventy-three percent of SO2 comes from the combustion of fossil fuels at power plants and the rest from industrial facilities, and petroleum products used by heavy equipment. Nitrogen dioxide is created by emissions from vehicles, heavy equipment and power plants. NO2 contributes to dangerous ozone at ground level.

Lead

• Lead emissions, too, come from vehicle emissions and industry. Regulation of fuel containing lead has decreased lead in the air. By 2010 lead smelters were the largest contributor, along with waste incinerators, utilities and lead-acid battery manufacturing.

Ozone

• Ozone (O3) in the upper atmosphere is desirable, but at ground level is problematic. Nitrogen (NOx) and "volatile organic compounds" (VOC) combined with sunlight create ground-level ozone. Vehicle and industrial emissions, chemical solvents and fumes are the contributors. Smog is primarily ground-level ozone. The combination of NOx and VOC with heat and sunlight promote harmful ozone in the air.

Particulates

• Particle pollution (PM) is made up of tiny particles and droplets of acids, metals, soil, organic chemicals and dust. Two kinds of particles, "inhalable coarse," and "fine," pollute the air. They come from dust, smoke and haze as in forest fires or gases from power plants, vehicles and industry.