Which of the following is a criteria air pollutant for which the EPA must set National Ambient Air Quality Standards?

• A. Carbon Monoxide
• B. Mercury
• C. Ammonia
• D. Benzene

Answer: (A)

The EPA sets National Ambient Air Quality Standards for pollutants designated as criteria pollutants because these are the pollutants chosen for nationwide ambient-air limits due to their widespread presence and well-established health and welfare effects. Carbon monoxide is one of these criteria pollutants, so the EPA has established ambient standards to protect public health from CO exposure. Mercury, ammonia, and benzene are regulated under different parts of the Clean Air Act: mercury and benzene are hazardous air pollutants (HAPs) managed by technology-based controls, while ammonia isn’t a criteria pollutant with an NAAQS. So carbon monoxide is the correct choice because it falls under the criteria pollutant category that requires NAAQS.