EPA Finalizes the Secondary National Ambient Air Quality Standards for NO2 and SO2

On March 20, 2012, the Environmental Protection Agency (EPA) finalized the secondary National Ambient Air Quality Standards (NAAQS) for NO2 and SO2. As proposed, EPA retained the existing standard and opted not to set a novel joint secondary standard for NO2 and SO2 at this time. After reconsidering its initial proposal, EPA declined to adopt a new set of secondary standards identical to the primary 1-hour NO2 and SO2 standards. Even in the proposed rule, EPA recognized that setting this additional standard was not ecologically relevant but would “directionally” benefit the environment. In the final rule (and in response to many comments on this point), the Administrator concluded that there is “no basis to make a reasoned judgment as to what levels of 1-hour NO2 and SO2 standards would be requisite to protect public welfare, such that EPA cannot demonstrate a reasoned basis for judging that the proposed standards would be sufficient but not more stringent than necessary to protect against adverse deposition-related effects to sensitive ecosystems.” EPA continues to maintain that the current standard is inadequate to appropriately protect public welfare and will implement the proposed five-year pilot program to collect and analyze data that can be used to support a new standard based on the Aquatic Acidification Index (AAI). In the preamble to the rule, EPA recognized that there are a number of data limitations and model uncertainties associated with the AAI standard. Despite these shortcomings, EPA continues to believe that the collection of additional data and participation of stakeholders through the pilot program will eliminate these uncertainties and guide the development of a more protective multi-pollutant standard.