NERL Research Abstract EPA's National Exposure Research Laboratory GPRA Goal 8 - Sound Science APM # 639 Significant Research Findings Studies of Dry Deposition to Forest Ecosystems Purpose Forests cover more than 50 percent of the land in the eastern U.S. and Canada, and comprise some of the more sensitive and important ecosystems. Dry deposition (the deposition of pollutants to the surface and plants by means other than rainfall) constitutes more than half of all pollutant deposition. Dry deposition is measured in the United States by EPA's Clean Air Status and Trends Network (CASTNET), and modeled for both scientific and regulatory purposes by Models-3/Community Multiscale Air Quality Modeling System (CMAQ) and other modeling systems. CASTNET is an "inferential network" (it measures concentration and infers deposition by using a modeled deposition velocity). Both CASTNET and the regional scale models require better models and understanding of the processes that control dry deposition. The purpose of this study was to measure dry deposition to several forests of different structures using "first principle" methods along with ancillary meteorological and biological data, and to use that data to evaluate deposition velocity models. The NERL mobile dry deposition laboratory, which had the capability to directly measure the fluxes of ozone, sulfur dioxide, nitric acid, carbon dioxide, water vapor, heat, and momentum, along with other meteorological and biological measurements, was employed at three forest sites during a three- year field campaign. The sites were a deciduous forest in northwestern Pennsylvania, a pine forest in North Carolina, and a mixed forest in the Adirondack region of New York. Tall towers were built within the canopy so that measurements could be taken over the tops of the trees. The pine forest experiment was a pilot study and lasted two months. The other two studies extended for the full growing season, from leaf-out in spring to after leaf-fall in autumn. This extensive database has allowed for a thorough study of the various weather and biological factors controlling dry deposition. Major The deposition velocity models used in CASTNET and Models-3/CMAQ, Findings while state-of-the-art, fail to account for many of the controlling processes in deposition. They give the right answer in the mean, but fail to match the Research Approach National Exposure Research Laboratory - September 2000 ------- temporal and spatial variations in deposition rates seen in nature. These variations, and the reasons that they occur, have been identified. New models are now being developed that should be much more accurate in defining the rates that pollutants are removed from the atmosphere through dry deposition. Research This research was conducted by the EPA National Exposure Research Collaboration Laboratory's Atmospheric Modeling Division and Human Exposure and Publications Atmospheric Sciences Division at Research Triangle Park, NC, with collaboration from the National Oceanic and Atmospheric Administration's Atmospheric Turbulence and Diffusion Division. The first part of the research, the development of the CASTNET model and a study of deposition to crops, resulted in an award-winning journal article (Meyers et al. - see below). The forest research is being published in a second journal article (Finkelstein et al.) Several papers on this research have been presented in various scientific meetings and workshops. Meyers, T.P., Finkelstein, P.L., Clarke, J., Ellestad, T.G., Sims, P.F. A multi-layer model for inferring dry deposition using standard meteorological measurements. Journal of Geophysical Research D: Atmospheres 103: 22,645-22,661, 1998. Finkelstein, P.L., Ellestad, T.G., Clarke, J.F., Meyers, T.P., Schwede, D.B., Hebert, E.O., Neal, J.A. Ozone and sulfur dioxide dry deposition to forests: Observations and model evaluation. Journal of Geophysical Research. In Press. Future Future research is focusing on the use and analysis of the field measurement Research (jata t0 be^er understand the deposition processes, and to develop improved deposition velocity models for CASTNET and Models-3/CMAQ. Questions concerning dry deposition to forest ecosystems may be directed to: Peter Finkelstein U.S. Environmental Protection Agency National Exposure Research Laboratory (MD-80) Research Triangle Park, NC 27711 Phone: (919)541-4553 E-mail: finkelstein.peter@epa.gov National Exposure Research Laboratory - September 2000 ------- |