When drilling rigs retrieve oil and gases from deep within the Earth, they bring up a host of flammable gases and chemicals that affect life on the surface. Although the list of air polluters is long, the oil, gas and automotive industries and electricity generation are major players. Even natural events, such as dust storms and wildfires, add to air pollution.

Greenhouse Gases

Many industries contribute to greenhouse gases. Electricity, meaning power generation, is responsible for 31 percent of greenhouse gases; transportation, 27 percent; industry, 21 percent; commercial and residential activities, 12 percent; and agriculture 9 percent, according to the Environmental Protection Agency (EPA).

Carbon dioxide makes up a full 82 percent of greenhouse gases. Methane (10 percent), nitrous oxide (5 percent) and fluorinated gases make up the rest. Over a century, however, methane is 21 to 25 times as effective at trapping heat in the atmosphere as carbon dioxide. Oil, gas, coal mining and landfills together produce more than half of U.S. methane emissions, says the EPA.

Oil and Gas

Besides carbon dioxide, oil and gas operations produce nitrogen oxides and hydrogen sulfide, which create smog; and flammable, toxic chemicals called volatile organic compounds (VOCs). Methane is just one VOC. Oil and gas operations also produce hazardous air pollutants (HAPs) such as benzene, toluene, n-hexane and many others, along with tiny particles of soot.

Fracking operations launch health-threatening silica particles into the air as well. Over time, accumulations of silica in the lungs can cause silicosis, a disabling lung disease, and can contribute to tuberculosis. In 2015, the Centers for Disease Control identified tuberculosis as the most "distinctive" cause of death in Texas, whose economy depends heavily on oil and gas production.

Transportation

One 2013 study from the MIT Laboratory for Aviation and the Environment estimated that air pollution causes 200,000 early deaths a year. The chief source of early death by pollution is road transportation -- that is, tailpipe exhaust.

Motor vehicles account for almost half of VOC air pollution, more than half of the nitrogen oxide emissions, and 75 percent of the carbon monoxide emissions, the EPA says. The EPA's master list of chemical compounds released in road transport runs to 1,162 entries, from (1, 1-dimethylethyl)-benzene to hydrogen cyanide.

One fourth of motor-vehicle pollution comes from heavy-duty trucks, which typically get 5 or 6 miles per gallon and account for about 4 percent of traffic. In June 2015, the EPA proposed new rules to increase fuel efficiency by up to 40 percent for any truck larger than a pickup.

Power Plants

Electricity generation is responsible for almost as many early deaths from emissions as road transportation, according to the MIT study.

Almost 40 percent of the carbon dioxide produced in the United States comes from power plants. Coal-fueled plants are the most polluting. The U.S. Energy Information Administration (EIA) states that in 2014, power plants produced 2.04 billion metric tons of carbon dioxide, with 76 percent, or 1.56 billion, coming from coal plants. Coal generated 39 percent of U.S. electricity in 2014, according to the EIA.

Power plant emissions have long been unrestricted. However, in 2014, the EPA proposed new rules to cut plant emissions by 30 percent from 2005 levels by 2030.

Agriculture

Agriculture is known more for water pollution than for air pollution. The EPA, however, considers crop and livestock dust air pollutants, and agriculture produces more than 90 percent of ammonia pollution, which has multiple adverse health effects, from nose and throat irritation to chronic lung disease. The methane that farm animals produce as part of their digestive processes makes up 26 percent of U.S. methane emissions, and manure management adds 10 percent more.