Regulation under the Clean Air Act

Because they are harmful to our health, there are limits placed on airborne particles under the Clean Air Act. The U.S. Environmental Protection Agency (EPA) regulates PM_2.5 and PM₁₀ as two of six criteria pollutants that must meet specific concentration-based thresholds known as National Ambient Air Quality Standards (NAAQS), which you may hear pronounced as “the nacks”. The PM₁₀ NAAQS is a 24-hour average mass concentration of 150 μg/m³, not to be exceeded more than three times over three years. There are two PM_2.5 NAAQS: a 24-hour average mass concentration of 35 μg/m³ and a recently revised annual average mass concentration of 9 μg/m³. The NAAQS are set to protect public health, including the health of more sensitive individuals such those with asthma as well as children and elders. That said, there is no known safe level of exposure to particles, with documented health impacts below the NAAQS. To determine NAAQS compliance, PM_2.5 and PM₁₀ must be measured using designated regulatory air monitors by an agency with the authority to do so, which in Virginia is the Virginia Department of Environmental Quality (VA DEQ).