This ISA focused on ecological effects resulting from current deposition of compounds containing N and S. Acidification, N-nutrient enrichment, and effects of sulfate on methylation of mercury (Hg) are highlighted in the document. Both S and N contribute to acidification of ecosystems. Deposition of N contributes to N-nutrient enrichment and eutrophication. An assessment of the complex ecological effects of atmospheric N deposition requires consideration of many different chemical forms of reactive N. For this reason, the ISA includes evaluation of data on the most common reduced inorganic forms of N, ammonia and ammonium; on oxidized inorganic forms including nitric oxide and nitrogen dioxide, nitrate, nitric acid, and nitrous oxide; and on organic N compounds including peroxyacetyl nitrate.
Other welfare effects addressed in the ISA include effects of sulfate deposition on Hg methylation, along with evidence related to direct exposure to gas-phase oxides of N and S. E&S is also assisting EPA, through a subcontract with RTI International, to prepare the ISA for the 2018 NAAQS review.
Project completion was December 2008.