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Regional Trends and Sources of Nitrogen Deposition in the United States from 2002-2018
Citation:
Benish, S., J. Bash, K. Foley, S. Napelenok, C. Hogrefe, Keith Appel, AND L. Linker. Regional Trends and Sources of Nitrogen Deposition in the United States from 2002-2018. AGU Fall Meeting, Virtual, LA, December 13 - 17, 2021.
Impact/Purpose:
Over the past century, human activity has doubled the amount of reactive nitrogen available in the global environment. Despite documented adverse consequences of deposition, the total (wet+dry) nitrogen and sulfur budgets remain uncertain, particularly for compounds not routinely measured and in areas with sparse measurements. In this presentation, we investigate spatial and temporal trends of total inorganic nitrogen and sulfur deposition across climatically compatible regions within the contiguous United States over a period of large emission reductions. By employing multiyear Community Multiscale Air Quality (CMAQ) model version 5.3.2 simulations from the EPA’s Air QUAlity TimE Series (EQUATES) project, we assess trends of deposition from 2002 to 2018 using a consistent modeling framework with a unified set of emissions.
Description:
Over the past century, human activity has doubled the amount of reactive nitrogen available in the global environment. Despite documented adverse consequences of deposition, the total (wet+dry) nitrogen and sulfur budgets remain uncertain, particularly for compounds not routinely measured and in areas with sparse measurements. In this presentation, we investigate spatial and temporal trends of total inorganic nitrogen and sulfur deposition across climatically compatible regions within the contiguous United States over a period of large emission reductions. By employing multiyear Community Multiscale Air Quality (CMAQ) model version 5.3.2 simulations from the EPA’s Air QUAlity TimE Series (EQUATES) project, we assess trends of deposition from 2002 to 2018 using a consistent modeling framework with a unified set of emissions. First, we compare measurements from the National Atmospheric Deposition Program (NADP) and Clean Air Status and Trends Network (CASTNET) to the model simulations. A measurement-model fusion approach is used to precipitation- and bias-correct the modeled wet deposition, improving the overall agreement. Next, we investigate temporal and spatial changes in deposition throughout nine climate regions, as defined by the National Oceanic and Atmospheric Administration (NOAA), quantifying the relative fractions of wet verses dry deposition. Lastly, we explore important nitrogen and sulfur sources resulting to heavy nutrient loading within the Chesapeake Bay Watershed, a region sensitive to atmospheric nutrient deposition due to its geography and home to over 18 million residents. We use the Integrated Source Apportionment Method (ISAM) in CMAQ to evaluate the relative importance of seven emission source types from eight regions within the Chesapeake Bay Watershed, an area of 64,000 square miles that encompasses 6 states. Preliminary results suggest the importance of mobile emissions to total oxidized nitrogen deposition and emissions from animal production to total reduced nitrogen deposition. This study demonstrates how modeling platforms with state-of-the-art science can be leveraged to understand changes in atmospheric deposition to inform emission reduction strategies for decreasing atmospheric nutrient loadings.
