Which of the following is NOT considered a criteria pollutant under the Clean Air Act?

Hydrogen sulfide is not considered a criteria pollutant under the Clean Air Act. The Act identifies six specific criteria pollutants: carbon monoxide, lead, nitrogen oxides, sulfur dioxide, ozone, and particulate matter. These pollutants are closely monitored because they have well-documented adverse effects on human health and the environment, and their levels must be maintained below standards set to protect public health and welfare.

In contrast, hydrogen sulfide is classified as a toxic air contaminant rather than a criteria pollutant. While it can cause health issues at elevated levels, it does not fall within the six criteria pollutants due to its different regulatory framework and nature of impacts. Understanding this distinction is essential for environmental professionals, as it helps clarify the focus areas for air quality monitoring and regulation under the Clean Air Act.