Background/Question/Methods The U.S. Environmental Protection Agency (EPA) is currently conducting a joint review of the existing secondary National Ambient Air Quality Standards (NAAQS) for oxides of nitrogen (NOx) and sulfur (SOx). As discussed in the Clean Air Act (CAA), the purpose of a secondary NAAQS is to “protect the public welfare from any known or anticipated adverse effects associated with the presence of such air pollutants in the ambient air” (section 109(b)(2)). Public welfare includes “effects on soils, water…vegetation, animals, wildlife, weather, visibility, and climate; as well as…the effects on economic values and on personal comfort and well-being, whether caused by transformation, conversion, or combination with other air pollutants” (section 302[h]). Adverse public welfare effects are based on an assessment of how negative ecological effects translate into negative impacts on public welfare. While adversity is not explicitly defined in the CAA, it can be inferred that negative ecological effects may have some corresponding impact on the well-being of humans and society through reductions in ecosystem services.
An update on the status of the review will include highlights from the risk assessment, policy-relevant science questions, and current policy options.
Results/Conclusions The risk and exposure assessment focuses on acidification and nutrient enrichment in terrestrial and aquatic ecosystems. Based on several case studies in sensitive ecosystems, ecosystem services can be used to characterize the adversity to public welfare of ecological effects associated with current deposition of N and S. For aquatic acidification, we linked ambient concentrations of NOx and SOx to deposition, then deposition to changes in an ecological indicator (ANC), and finally to changes in fish species richness and its influence on recreational fishing. In simulations of 3,000 New York lakes under business-as-usual (no reductions of N and S deposition) and “zero-out” (anthropogenic sources of NOx and SOx eliminated) scenarios, modeled changes in ANC were used to project improvements in fish species richness through 2100.  A Random Utility economic model was used to describe the behavior of recreational fishers in response to changing lake conditions.  Annualized benefits from the “zero-out” scenario ranged from $4.5-130M per year, depending upon assumptions about the ANC-fish species richness relationship and the discount rate used. By estimating improvements in fish species richness and annualized benefits of enhanced recreational fishing, ecosystem services provide valuable information about the adversity associated with potential ecologically-based secondary standards.