Air pollution is essentially harmful materials that are present in the air. It is considered an air pollutant if it is harmful to humans and/or the environment. The vast majority of pollution in the air is produced by human activities. This includes both indoor pollutants, which are pollutants present in homes and buildings, as well as outdoor pollutants, present in open spaces.
Pollutants are produced by a variety of sources in three main categories:
Stationary sources of air pollution are fixed. They are considered point source polluters, and much like water point pollution sources, they are easier to monitor and control. Examples of stationary sources would be a coal-fired power plant, oil refinery, or gas station.
The third source comprises natural causes such as volcanoes or forest fires, like the one depicted below. Smog created by volcanoes can lead to acid rain, while forest fires like this one can produce carbon monoxide and nitrogen oxides, which contribute to air pollution and negative human health impacts.
There are many major outdoor air pollutants, which include the following.
|Outdoor Air Pollutants||Description|
|Greenhouse Gasses||Greenhouse gases -- such as carbon dioxide and methane -- which contribute to the greenhouse effect and climate change. These pollutants come primarily from coal, oil, and natural gas consumption.|
|Chlorofluorocarbons||Chlorofluorocarbons, or CFCs, come from aerosol sprays and refrigerators.|
|Sulfur and Nitrogen Oxide||Sulfur and nitrogen oxide come from coal, oil, and natural gas. In the United States, 60% of sulfur dioxides come from power plants.|
|Particulate Matter||Particulate matter, or PM, come from industry and manufacturing combustion of fossil fuels and their waste.|
|Ozone||While naturally-created ozone protects the earth from solar radiation high in the atmosphere in what is called the ozone layer, ground-level ozone can damage human health. Ground-level ozone comes from burning fossil fuels in lawnmowers, construction vehicles, and automobiles.|
|Lead and Heavy Metals||Lead and other heavy metals are other types of outdoor air pollution, and they come from burning fossil fuels.|
|Carbon Monoxide||Carbon monoxide is another type of air pollution, and it comes from burning fossil fuels as well. Approximately 60% of carbon monoxide emissions come from mobile non-road sources and highway vehicles.|
Nationally in the United States, the type and amount of pollution vary from region to region and state to state.