Which listing represents criteria air pollutants?

• A. sulfur dioxide, nitrogen dioxide, carbon monoxide, lead, ozone, particulate matter
• B. water vapor and carbon dioxide only
• C. radon and methane
• D. ammonia and chlorine

Answer: (A)

Criteria air pollutants are the six pollutants for which the EPA established National Ambient Air Quality Standards to protect public health and welfare. These six are sulfur dioxide, nitrogen dioxide, carbon monoxide, lead, ozone, and particulate matter. Each has well-defined health or environmental effects and specific exposure standards. The other substances listed don’t fall into this set: water vapor and carbon dioxide are greenhouse gases, not regulated as criteria pollutants under the Clean Air Act; radon and methane are significant pollutants in other contexts but aren’t part of the criteria pollutant list; ammonia and chlorine are pollutants but not included among the six. So the best answer is the group of sulfur dioxide, nitrogen dioxide, carbon monoxide, lead, ozone, and particulate matter.