National Ambient Air Quality Standards (NAAQS)

E&S Environmental Chemistry, Inc. was contracted by the U.S. EPA to draft a synthesis report on ecological effects of atmospheric deposition of oxides of sulfur (S) and nitrogen (N). E&S assembled a team of leading scientists from government, industry, and academia to conduct this work. This Integrated Science Assessment (ISA) was a synthesis and evaluation of the most policy-relevant science that formed the scientific foundation for the 2008 review of the secondary (welfare-based) national ambient air quality standards (NAAQS) for oxides of nitrogen (NOx) and oxides of sulfur (SOx). The Clean Air Act definition of welfare effects includes, but is not limited to, effects on soils, water, wildlife, vegetation, visibility, weather, and climate, as well as effects on man-made materials, economic values, and personal comfort and well-being.

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.