ENV-09-19 Forthcoming NAAQS Changes and Implementation for PM2.5, SO2, and NO2

Description:

The authors have been following National Ambient Air Quality Standards (NAAQS) developments for PM2.5, SO2, and NO2, and have provided public comments to EPA's Clean Air Science Advisory Committee (CASAC) panels reviewing EPA's analyses supporting the development of new standards. This paper addresses implementation developments for PM2.5, including PSD increments, and anticipated major changes for the SO2 and NO2 NAAQS. We have also reviewed and commented on EPA’s proposal for PM2.5 PSD increments. For both SO2 and NO2, it is very likely that probabilistic-based one-hour standards will be established. For PM2.5, upon completion of the court-mandated review, it appears likely at this time that EPA will propose that the annual standard be lowered. In addition, PSD increments and Significant Impact Levels will be designated for PM2.5 in 2010. These anticipated changes to the NAAQS and PSD increments will pose a number of additional dispersion modeling challenges. Modeling issues and possible approaches to refined modeling that may be needed to demonstrate future air quality compliance are discussed.