Ozone is a secondary air pollutant formed by the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight.

Particulate matter can cause a variety of health problems, including cancer, heart disease, and respiratory problems such as asthma and bronchitis.

Mercury is a hazardous air pollutant, but it is not a criteria air pollutant regulated by the Clean Air Act.

The NAAQS for ozone is 0.070 ppm, averaged over an 8-hour period.

Trees are not a source of air pollution, but they can help to improve air quality by removing pollutants from the air.

The purpose of the Clean Air Act is to protect human health and the environment from air pollution.

Criteria pollutants are a type of air pollutant regulated by the Clean Air Act, but they are not a type of air pollutant in general.

Nitrogen dioxide can cause a variety of respiratory problems, including asthma, bronchitis, and emphysema.

Volcanoes are not a source of particulate matter, but they can emit ash and other particles into the air.

The NAAQS for PM2.5 is 12 µg/m³, averaged over a 24-hour period.

Driving less is not a strategy for reducing air pollution, but it can help to reduce traffic congestion and improve air quality.

The NAAQS for sulfur dioxide is 0.030 ppm, averaged over a 1-hour period.

Improved cognitive function is not a health effect of air pollution, but it is a health benefit of reducing air pollution.

The NAAQS for carbon monoxide is 9 ppm, averaged over an 8-hour period.

Oxygen is not a greenhouse gas, but it is an essential component of the Earth's atmosphere.