What is a key difference between criteria air pollutants and air toxics pollutants regarding health standards?

The distinction between criteria air pollutants and air toxic pollutants is fundamentally tied to the regulatory framework established by the Environmental Protection Agency (EPA). Criteria air pollutants are those for which the EPA has established specific national ambient air quality standards (NAAQS) aimed at protecting public health and environmental quality. These standards are based on considerable scientific research and are designed to be protective of the general population, including sensitive groups.

In contrast, air toxics, also referred to as hazardous air pollutants (HAPs), do not have the same quantified health-based ambient air quality standards set by the EPA. Instead, air toxics are regulated under the National Emission Standards for Hazardous Air Pollutants (NESHAP), which focus on controlling emissions from specific sources rather than setting broad health standards that apply throughout the ambient air as is done with criteria pollutants. Therefore, while there is rigorous oversight of air toxics, it does not take the form of established minimum health standards comparable to those for criteria pollutants.

This regulation framework indicates that the overall approach to air toxics is more focused on limiting significant sources of hazardous emissions rather than establishing specific acceptable levels in outdoor air quality, hence the absence of minimum standards.