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Atmospheric Modeling and Analysis Research

CMAQ Ecosystem Exposure Studies at National Scale

Over the past century, human intervention in the nitrogen cycle and use of fossil fuels has led to substantial increases in production of reactive nitrogen (Nr) and in human and ecosystem exposure to Nr. The amount of Nr applied to the nation’s landscape and released to the nation’s air and water has reached unprecedented levels. These increases in Nr pollution are accompanied by increased environmental and human health problems. To assess and map environmental effects from the input of excess nitrogen it is necessary to map the inputs from atmopheric deposition across the landscape.

National Atlas

Mapping at the national scale of Community Multi-Scale Air Quality Model (CMAQ) outputs is being developed with an initial focus on selected studies of nitrogen inputs to the landscape. This work is being conducted in a collaborative manner with the Mapping Team of the Sustainable and Health Communities research program (SHC). The SHC Mapping Team is taking the lead on creating the layers, while the CMAQ Ecosystem Team will provide data, model outputs and will contribute to designing the mapping approach. Three major Nr inputs and transfers have been selected as initial cases for the national mapping: fertilizer input, atmospheric deposition, and nitrogen transfer from land to water.

Atmospheric deposition of sulfur, oxidized nitrogen, reduced nitrogen, and ozone will be simulated by CMAQ for a 12km grid size for the continental US. Typical compilations of deposition are monthly and annual accumulated deposition amounts. A base year of 2002 is available to represent current conditions. CMAQ simulations for 2006 will also be available in FY2013, upon completion of new CMAQ simulations. CMAQ projections of deposition for 2020 that represent the implementation of nitrogen oxide controls to meet health standards for ozone and PM2.5 under the 1990 Clean Air Act Amendments will be available for mapping as well. Such projections show a significant reduction in oxidized-N deposition across the eastern US. The 12-km CMAQ grid can be mapped to 12-digit HUCs or any other desired set of polygons.

The CMAQ data will be augmented by National Atmospheric Deposition Program (NADP) wet deposition data in the mapping exercise. The use of CMAQ dry deposition combined with precipitation-corrected and NADP-augmented CMAQ wet deposition will be examined for the national mapping of nitrogen deposition.

Critical Loads or Tipping Points

CMAQ with Bi-Directional NH3
2002 Annual total nitrogen deposition (wet and dry oxidized and reduced species.

The critical loads or tipping points approach can provide a useful lens through which to assess the results of current policies and programs and to evaluate the potential ecosystem-protection value and ecosystem services value of proposed policy options.

A major stressor of concern with serious consequences for freshwater aquatic and terrestrial systems is acidification from atmospheric deposition of reactive nitrogen and sulfur. Several federal agencies are working together on regional pilot projects across the U.S. to explore the possible role a critical loads (or tipping point) approach can have in air-pollution control policy in the U.S. CMAQ deposition outputs and NADP data will be used to provide deposition inputs to the ecosystem models used in these projects.

The use of CMAQ dry deposition combined with precipitation-corrected and NADP-augmented CMAQ wet deposition will be used for the national mapping of nitrogen and sulfur deposition for the critical loads studies. CMAQ projections to 2020 and beyond of deposition will also be used to assess vulnerable ecosystems. Major players in the critical loads studies are the EPA, the National Park Service), and the US Forest Service.

2002 annual acidifying dry deposition of sulfer, oxidized- and reduced-nitrogen
2002 Annual acidifying dry deposition of sulfer, oxidized- and reduced-nitrogen (eq ha-1 yr-1)



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