For more information about National Park Service air resources, please visit

Sources of Air Pollution

Air pollution, harmful gases and particles in the air, comes from sources. Sources of air pollution can impact National Park Service (NPS) areas even though the vast majority of air pollution is created outside park boundaries. Learn more about air pollution sources and transport by exploring the tabs below.

  • Types of Sources
  • Transport
  • Parks

Where does pollution come from?

There are four main types of air pollution sources:

  • mobile sources – such as cars, buses, planes, trucks, and trains
  • stationary sources – such as power plants, oil refineries, industrial facilities, and factories
  • area sources – such as agricultural areas, cities, and wood burning fireplaces
  • natural sources – such as wind-blown dust, wildfires, and volcanoes

Mobile sources account for more than half of all the air pollution in the United States and the primary mobile source of air pollution is the automobile, according to the Environmental Protection Agency. Stationary sources, like power plants, emit large amounts of pollution from a single location, these are also known as point sources of pollution. Area sources are made up of lots of smaller pollution sources that aren't a big deal by themselves but when considered as a group can be. Natural sources can sometimes be significant but do not usually create ongoing air pollution problems like the other source types can.

Graphic of Air Pollution Pathways
Mobile, stationary, area, and natural sources all emit pollution into the air.

Pollution on the move

Most pollution affecting NPS areas comes from outside the parks.

Pollution from human-generated and natural sources is created in one place, transported through the air—and sometimes changed by chemical reactions—before being deposited, occasionally in national park units. The effects of this pollution can be seen as haze and through negative biological effects. Learn more about the visibility and ecological effects of air pollution.

Graphic of Air Pollution Pathways
Wind can move air pollutants short or very long distances before they cause harmful impacts.

Fire and Air Quality

Emissions from fire, especially large wildfires, can contribute significantly to air pollution affecting human health and visibility in parks. However, fire also plays an important role in many forest ecosystems. As a result of past fire suppression, many wildland areas now have too much fuel, are filled with nonnative plants, and have increased risk of insect infestations and disease. Protecting human health and air quality while restoring fire-dependent forest ecosystems to their natural, wilderness character is a management challenge. More on smoke management »

The influence of sources on parks

Location and even the time of year can determine which pollution sources are most important to each park. Parks downwind of power plants that lack modern pollution controls can have increased smog. Tailpipe emissions from cars and trucks, as well as industrial processes such as oil and gas development, give rise to elevated ozone concentrations. Summertime wildfires can also reduce visibility in a park. There are even examples of pollutants arriving at parks that originated from other countries and were transported thousands of miles. The effects of this pollution can be seen as haze and through negative biological effects.

Learn more about the visibility and ecological effects of air pollution.

What can parks do?

New development of power plants, industry, and agriculture outside park boundaries has the potential to generate more emissions that can impact NPS areas. The NPS works with States and developers to protect parks from emissions from new or modified sources. NPS staff review permit applications for these proposed new sources. For more information about the NPS new source review program, please visit our Permit Applications web page.

Most air pollution that impacts park resources is emitted from sources outside of the parks. However, air pollution is also emitted directly inside parks, for example, by automobiles, wildfires, and construction. The National Park Service (NPS) is committed to complying with all environmental laws and applying the highest standards of environmental stewardship to its own operations.

To help meet this commitment, the NPS develops air emission inventories for NPS areas. The NPS quantifies in-park emissions in order to:

  1. Determine the magnitude of in-park emissions relative to those from the surrounding area,
  2. Identify strategies to reduce in-park emissions, and
  3. Evaluate and ensure compliance with local, state, and federal air pollution regulations.
Emissions inventories are part of the NPS Climate Friendly Parks program:

Related Links

Last Updated: January 10, 2013