Pollution-free air is composed primarily of nitrogen and oxygen, with trace amounts of carbon dioxide, argon, and water vapor. Air pollution is considered to be any substance released into the atmosphere in harmful amounts. Air pollution can be dust, fumes, chemicals, or microorganisms. Air pollution is likely the most widespread and noticeable type of pollution.

Some major air pollutants include:

1. Particulates
2. Sulfur Oxides
3. Nitrogen Oxides
4. Tropospheric (ground-level or low-level) ozone
5. Greenhouse Gases
   

In the past, chlorofluorocarbons (CFCs) were considered a major pollutant as well; however, adherence to international laws and regulations banning the use of CFC's has reduced their impact on the global atmosphere.

The following video describes some of the sources of particulate matter in the atmosphere over Alaska. Some of the particulate pollution is natural (from sand, sea salt, and soil), but some of it is man-made. For example, sulfur oxides, which come from the burning of fossil fuels, are a major component of the brown, hazy smog over Alaska.