The Clean Air Act (CAA) requires the establishment of National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to public health and the environment. There are two types of NAAQS: 1) primary standards, which protect public health; and 2) secondary standards, which protect public welfare. The CAA also requires periodic review and, if appropriate, revision of the NAAQS.

As part of the current review process of the NAAQS for particulate matter (PM), EPA has recently published a “Policy Assessment for the Review of the National Ambient Air Quality Standards for Particulate Matter, External Review Draft”. The policy assessment evaluates the potential policy implications of the available scientific evidence and the potential implications of the available air quality, exposure, or risk analyses. This assessment is intended to help “bridge the gap” between EPA's scientific assessments, quantitative technical analyses, and the judgments required in determining whether it is appropriate to retain or revise the NAAQS.

According to the draft policy assessment, EPA's preliminary conclusion is that, based on the available scientific evidence, air quality analyses and the risk assessment, the current primary annual standard for PM2.5 (12 µg/m3) may not be adequate. The draft policy assessment discusses how various levels as low as 8 µg/m3, and alternative standards could be supported. Nevertheless, it does mention uncertainties and limitations in the evidence and analyses.

With respect to the primary standard for PM10 as well as the secondary standards for both PM2.5 and PM10, EPA's preliminary conclusion is that the available evidence does not call into question whether the current primary standard for PM10 or the secondary standards for PM2.5 and PM10 are adequate. As such, the draft policy assessment appears to support retaining the current standards.

As published in the Federal Register on September 11, 2019, EPA is requesting comments on the draft policy assessment by November 11, 2019. A copy of the draft policy assessment can be found on EPA's website. For more information, please contact your local Trinity office at (800) 229-6655.