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Multi-decadal (1990-2019) trends and source contributions to atmospheric nitrogen and sulfur deposition across the Northern Hemisphere
Citation:
Mathur, R., C. Hogrefe, J. Xing, Keith Appel, J. Bash, K. Foley, R. Gilliam, B. Henderson, W. Hutzell, D. Kang, B. Murphy, S. Napelenok, J. Pleim, G. Pouliot, H. Pye, G. Sarwar, AND F. Sidi. Multi-decadal (1990-2019) trends and source contributions to atmospheric nitrogen and sulfur deposition across the Northern Hemisphere. American Geophysical Union Fall Meeting, San Francisco, CA, December 11 - 15, 2023.
Impact/Purpose:
Multi-decadal trends in atmospheric deposition of reactive nitrogen and sulfur are simulated and analyzed to (1) characterize the space and time changes in this key atmospheric removal processes, (2) quantify changing impacts on sensitive ecosystems and (3) assess relative contributions of different source regions and sectors to atmospheric deposition and their changes in response to heterogeneous emission changes.
Description:
Understanding the fate of airborne reactive nitrogen (NOy and NHx) and sulfur (SOx) compounds is desirable given their role in determining tropospheric acidic substances and particulate matter budgets and potential altering of sensitive ecosystems resulting from their atmospheric deposition. Removal by wet scavenging and dry deposition is the primary sink for atmospheric SOx, NOy and NHx, which lead to a variety of environmental effects including altering net primary production, acidification, eutrophication and other nutrient loading effects. Gas-particle partitioning of airborne reactive nitrogen regulates its transport distance, since dry deposition velocity for fine particles is comparatively low, and their primary atmospheric sink is wet scavenging. Changes in NOx, NH3, and SO2 emissions over time have altered both their atmospheric transport distances as well as deposition patterns and amounts. We examine the multi-decadal trends in wet and dry deposition amounts of reactive nitrogen and sulfur through detailed analysis of two sets of long-term simulations using the Community Multiscale Air Quality model (CMAQ) driven with the Weather Research and Forecast model (WRF): (1) for the 1990-2010 period and (2) 2002–2019 dataset from EPA’s Air QUAlity TimE Series (EQUATES) project. WRF-CMAQ simulations were conducted over a domain covering the northern hemisphere discretized with a 108km horizontal grid spacing. Long-term trends in model wet deposition, relative amounts of oxidized and reduced nitrogen, and relative amounts of wet and dry deposition of N and S, are assessed and compared with those inferred from available measurements. The impacts of spatially heterogeneous emission changes across the northern hemisphere, on changing deposition amounts over terrestrial and aquatic ecosystems are analyzed and suggest that critical load threshold exceedances have decreased at many locations in North America and Europe but have increased across Asia. The relative contributions of different source regions and sectors to atmospheric deposition and their changes will be discussed.
