NO2 NAAQS Implementation Status Quo (For Now)

U.S. EPA has posted its responses to states’ initial designation recommendations for the new 1-hour nitrogen dioxide (NO2) National Ambient Air Quality Standard (NAAQS). Determining which areas are attaining or not attaining the 1-hour NAAQS will require the operation of a new network of near roadway ambient monitors that will not be in place until 2013. As such, states submitted their initial designation recommendations as “unclassifiable” or “attainment.” In response, U.S. EPA has recommended designating the entire country as “unclassifiable/attainment” with respect to the new 1-hour NAAQS since the enhanced ambient monitoring is not yet available and no existing ambient monitor is measuring ambient levels in excess of the NAAQS. U.S. EPA also recommended that states consider the geographic extent of how they separate their air basins to manage air quality. 

For now, there is no indication that U.S. EPA will utilize air dispersion modeling as a strategy to determine NO2 NAAQS attainment status. There was some concern that U.S. EPA would use dispersion modeling in a similar fashion to their current sulfur dioxide (SO2) attainment designation strategy, particularly once the atmospheric chemistry approaches to model NO2 using AERMOD had been solidified. As of yet, only the originally proposed near roadway ambient monitoring network is being mentioned. Stay tuned for additional updates as the 1-hour NO2 NAAQS implementation process continues.