Why it Matters
EPA sets NAAQS for six common and harmful pollutants: carbon monoxide, lead, PM, ozone, nitrogen dioxide, and sulfur dioxide. The NAAQS are based solely on public health and welfare protection, meaning that the agency must not consider the cost of revising a standard if the current science demands a standard be tightened to protect public health or welfare. The Clean Air Act (CAA) requires that EPA review the NAAQS every five years to ensure their adequacy. The review process is a multi-stage, robust review of the current science that requires significant expert input conducted by the Clean Air Science Advisory Committee (CASAC), which is an independent expert committee that assists EPA in reviewing the NAAQS. After CASAC makes formal recommendations, EPA reviews and finalizes standards for the pollutants. If a standard is tightened, there is a cascading effect on air quality policies and programs across the country. States and local regions must ensure that the sources of pollution in their jurisdiction decrease their emissions so that the region can be on track to meet the new, more stringent national standard.
We only track ozone and PM NAAQS since the others are either regulated more extensively under other Clean Air Act (sulfur dioxide) or no longer a major air issue (carbon monoxide and lead).