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Changes in the magnitude and spatial pattern of reduced nitrogen deposition due to SOx and NOx reductions in the U.S.
Citation:
Bash, J., J. Kelly, P. Campbell, S. Napelenok, AND D. Schwede. Changes in the magnitude and spatial pattern of reduced nitrogen deposition due to SOx and NOx reductions in the U.S. 2019 AGU Fall Meeting, San Francisco, CA, December 09 - 13, 2019.
Impact/Purpose:
Changes in the atmospheric composition due to SOx and NOx reductions has impacted the magnitude and spatial distribution of reduced nitrogen deposition through the reduction of the atmospheric NH4 aerosol burden. Here we use several model simulations to explore the driven mechanisms of the these changes and the potential ecological implications.
Description:
Atmospheric reduced nitrogen is primarily found as particulate ammonium, priorly associated with nitrate or sulfate, or as gaseous ammonia. Over the past few decades, controls on nitrogen and sulfur oxide emissions, NOx and SOx respectively, have resulted in a large reduction in atmospheric in-organic particulate matter. During this same time-period ammonia emissions have been relatively constant. The reduction in the atmospheric sulfate and nitrate has resulted in a larger fraction of atmospheric reduced nitrogen as gaseous NH3. This change in atmospheric composition has been documented in satellite and surface observations. This composition change has also altered the rate and spatial patterns of nitrogen and ammonia deposition due to the different rates of atmospheric deposition for ammonia and ammonium. Here we explore the impact of SOx and NOx reductions on the atmospheric deposition of reduced nitrogen using the EPA’s Community Multiscale Air Quality (CMAQ) simulations from 2002 to 2012 and a set of brute force sensitivity simulations for 2016. Preliminary results indicate that while total nitrogen deposition is decreasing the reduced fraction of wet deposition is increasing and the dry deposition of reduced nitrogen has increased substantially, ~100%, in areas with large NOx and SOx reductions. Additionally, the atmospheric lifetime of reduced nitrogen has decreased due to the more rapid removal of gaseous ammonia than particulate ammonium from the atmosphere resulting in areas of higher deposition near ammonia emission sources and lower rates of deposition further downwind. The potential impact on ecosystems due to this change in atmospheric composition will be discussed.