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Atmospheric Modeling and Analysis Research

Linking Air Quality to Aquatic and Terrestrial Ecosystems

Ecosystem exposure occurs when stressors and receptors occur at the same time and place. In order to model the exposure, models for different media (e.g. air, water, land) must be linked together. Linkages between models for air, water, and land can occur through the use of consistent input data such as land use and meteorology and through the appropriate exchange of data at relevant spatial and temporal scales.

Improved spatial distribution of terrestrial receptors

Dry deposition velocity varies with underlying vegetation type due to differences in leaf area index, canopy height, and plant characteristics such as minimum stomatal resistance. Version 4.7 of EPA's Community Multiscale Air Quality model (CMAQ) relies on the 1992 National Land Cover Dataset (NLCD) to identify the location of land cover types. USGS 2001, NLCD 2001 to 2006, and NOAA coastal lands (C-CAP) databases provide higher resolution information.

The Spatial Allocator Raster Tool can be used to compute CMAQ modeling domain gridded land use information based on these input image data. As an example, the figures below illustrate our improved ability to identify the extent of deciduous forest cover areas in North Carolina over current information. Colors indicate the percentage of each 1 kilometer rectangular grid containing deciduous trees.

The second stage of this spatial improvement is to update the 1 kilometer resolution Biogenic Emissions Landcover Database, version 3 (BELD3) dataset agricultural species distributions. The current distribution is based on 1995 National Agricultureal Statistics Service (NASS) surveys. These estimates are being updated to reflect 2001 crop distributions in combination with the 2001 NLCD imagery. At present the BELD3 data are used to determine bioemission input for CMAQ. We anticipate its more extensive use in the estimation of species-specific exposure to atmospheric nitrogen and mercury deposition.

Improved estimates of receptor-specific atmospheric deposition

The deposition velocity calculation for CMAQ version 4.7 is a combination of processes modeled in the meteorological model and the chemical transport model. Since CMAQ is a grid-based model, the influence of the different land covers that comprise a grid cell are averaged in the meteorological model for use in the deposition velocity calculations. These grid-average values are carried forth from the meteorological model to the chemical transport model where chemical specific deposition velocity calculations are done.

Ecological applications need information regarding the amount of deposition to the individual land cover categories. In order to provide this information without modifying the meteorological model, EPA is implementing an approach in CMAQ that separates these grid-average values within CMAQ to allow output of deposition estimates for each land cover type within a grid in a manner consistent with meteorological model flux calculations. The figures below illustrate deposition velocity dependence on vegetation type.

O3 deposition velocities to croplands
O3 deposition velocities to croplands

O3 deposition velocities to forested ecosystems
O3 deposition velocities to forested ecosystems

 

Contacts: Ellen Cooter, Robin Dennis, Donna Schwede

Related Publications:
  • Schwede, D., R. Dennis, M. Bitz. The Watershed Deposition Tool: A tool for incorporating atmospheric deposition in water-quality analyses. J. American Water Resources Association (2009).(abstract) Exit EPA Disclaimer

  • Dennis, R.L., R. Haeuber, T. Blett, J. Cosby, C. Driscoll, J. Sickles, and J.M. Johnston. Sulfur and Nitrogen Deposition on Ecosystems in the United States. EM: Air and Waste Management Association Magazine for Environmental Managers. December, pp 12-17, (2007).
  • Ran, L. and A. Eyth, NLCD Landuse Processing Tools and Projection Issues in Modeling, Center for Environmental Modeling for Policy Development, Institute for the Environment (database).

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