There are thousands of different air pollutants, defined as any gas or particle found in concentrations in excess of what is of natural origin. While some are relatively benign, others may be found in concentrations high enough to cause health or environmental impacts. Almost any gas or particle in high enough concentrations will cause some type of health response. Generally, air pollutants of most concern can be broken into three categories: the criteria pollutants, regulated toxic air pollutants (or hazardous air pollutants), and greenhouse gases.
Under the federal Clean Air Act, EPA has identified six air pollutants as the "criteria air pollutants.” In some cases these pollutants are found at concentrations high enough to cause adverse effects on public health and the environment. The criteria pollutants consist of ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, particulate matter, and lead. EPA has set National Ambient Air Quality Standards for each of these criteria pollutants to protect public health and the environment.
Regulated toxic air pollutants (RTAPs) consist of over 180 federally defined compounds that may be emitted at high enough rates to cause localized health or environmental impacts. RTAPs include toxic air pollutants that may have direct impacts, as well as persistent bioaccumulative toxics such as mercury and dioxins that build up in the body before impacts are noticeable.
Greenhouse gases are gases (and particles) that have an affinity for trapping solar energy and retaining heat. While there are a number of greenhouse gases, the most focus is placed on carbon dioxide and methane (see link for Climate Change under Related Programs).
Further information about each pollutant, such as specific issues, rules, fact sheets, and reports, can be found under each specific pollutant listed below.
- Criteria Pollutants
- Regulated Toxic Air Pollutants (RTAPs)
- Greenhouse Gases