Criteria Pollutants

The Clean Air Act requires EPA to set National Ambient Air Quality Standards for six common air pollutants. These commonly found air pollutants (also known as "criteria pollutants") are found all over the United States. They are particle matter pollution (PM), ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. Of these, ozone and particulate matter are the pollutants of greatest concern with regards to wildland fire.

Ozone (O3) is a gas composed of three oxygen atoms. It is not usually emitted directly into the air, but at ground-level is created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ground-level ozone also can reduce lung function and inflame the linings of the lungs. Repeated exposure may permanently scar lung tissue. Under conditions favorable to the formation of ozone, there is evidence indicating that emissions of VOCs from vegetation burning (e.g., wild land or wild fire burning) can further contribute to ozone formation.

Particulate matter or PM, is a complex mixture of extremely small particles, sometimes combined with liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:

Numerous scientific studies have linked particle pollution exposure to a variety of problems, including irritation of the airways, coughing or difficulty breathing, decreased lung function, aggravated asthma, development of chronic bronchitis, irregular heartbeat, nonfatal heart attacks, and premature death in people with heart or lung disease.

Carbon monoxide (CO) is a colorless, odorless gas emitted from incomplete combustion processes. CO can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death. Incomplete combustion of fuels during forest fire events can lead to the formation of high concentrations of CO. This pollutant is a concern in areas which lie in close proximity to the fire.

The following criteria pollutants are addressed by the NAAQS, but are not linked to wildland fire.

Source: U.S. Environmental Protection Agency. 2012. What Are The Six Common Air Pollutants. Accessed on 9 September 2013. Available at

U.S. Environmental Protection Agency. 1999. Handbook for criteria pollutant inventory development: a beginner's guide for point and area sources. EPA-OAQPS-454-037. Research Triangle Park, NC. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards.