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Long-term trends in sulfur and reactive nitrogen deposition across the Northern Hemisphere and United States
Citation:
Mathur, R., Y. Zhang, C. Hogrefe, AND J. Xing. Long-term trends in sulfur and reactive nitrogen deposition across the Northern Hemisphere and United States. ITM 2018 - 36 th International Technical Meeting on Air Pollution Modelling and its Application, Ottawa, CANADA, May 14 - 18, 2018.
Impact/Purpose:
Emissions of sulfur (SOx) and reactive nitrogen compounds (NOy and NHx) not only impact concentrations of tropospheric particulate matter, acidic substances and oxidants, but also have potential nutrient loading effects in sensitive ecosystems resulting from their and derived species atmospheric deposition. Effective implementation of the National Ambient Air Quality Standards (NAAQS) for ozone and fine particulate matter pollution, thus requires a detailed assessment of both the atmospheric and ecological impacts of emission perturbations. Changing emissions patterns of NOx, SO2, and NH3 have likely altered both their atmospheric transport distances as well as deposition patterns and amounts and this study examines the impacts of contrasting changes in historical emission patterns across the northern hemisphere, i.e., reductions in North America and Europe vs. increases across regions in Asia, on changing deposition amounts over terrestrial and aquatic ecosystems. . This work contributes towards building improved modeling approaches for assessing long-term trends of nitrogen and sulfur deposition, which can assist EPA and its stakeholders in managing and mitigating impairment of sensitive ecosystems.
Description:
A detailed understanding of the distribution and fate of atmospheric sulfur (SOx) and reactive nitrogen compounds (NOy and NHx) is desirable given their role in determining tropospheric acidic substances and particulate matter budgets and potential nutrient loading effects in sensitive ecosystems resulting from their atmospheric deposition. The ultimate fate of airborne SOx, NOy and NHx is removal by wet scavenging and dry deposition, which in turn lead to a variety of environmental effects including altering net primary producton, acification, eutrophication and other nutrient loading effects. The gas-particle partitioning of airborne sulfur and reactive nitrogen regulates their transport distances since dry deposition velocity for fine particles is relatively low, and consequently their primary atmospheric sink is wet scavenging. Changing emissions patterns of NOx, SO2, and NH3 have likely altered both their atmospheric transport distances as well as deposition patterns and amounts. We model the changes in wet and dry deposition amounts of reactive nitrogen and sulfur over the 1990-2010 period using the WRF-CMAQ modeling system. WRF-CMAQ simulations for this 21-year period were conducted over a domain covering the northern hemisphere using a horizontal resolution of 108km and a nested domain over the contiguous U.S. using a grid of 36 km resolution. Long-term trends in model wet deposition amounts, relative amounts of oxidized and reduced nitrogen, and relative amounts of wet and dry deposition of N and S, are compared with those inferred from available measurements. The impacts of contrasting changes in emission patterns across the northern hemisphere, i.e., reductions in North America and Europe vs. increases across regions in Asia, on changing deposition amounts over terrestrial and aquatic ecosystems in these regions will be discussed.
