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REGIONAL MODELING OF THE ATMOSPHERIC TRANSPORT AND DEPOSITION OF ATRAZINE
Citation:
Cooter, E J. AND W T. Hutzell. REGIONAL MODELING OF THE ATMOSPHERIC TRANSPORT AND DEPOSITION OF ATRAZINE. Presented at Society of Environmental Toxicology and Chemistry 21st Annual Meeting, Nashville, TN, November 12-16, 2000.
Impact/Purpose:
The goal of this research is to develop and test appropriate chemical and physical mechanisms for use in EPA's Models-3 chemical/transport models. These models will be addressing issues of tropospheric photochemistry, fine particles, toxic and semi-volatile substances, and acid deposition. As such, scientifically credible mechanisms for atmospheric gas- and aqueous-phase chemistry as well as heterogeneous chemistry, applicable to the particular pollutant regimes must be included in Models-3.
Description:
A version of the Community Multiscale Air Quality (CMAQ) model has been developed by the U.S. EPA that is capable of addressing the atmospheric fate, transport and deposition of some common trace toxics. An initial, 36-km rectangular grid-cell application for atrazine has been developed for the United States and southern Canada for a continuous 120 day period during the Spring and Summer of 1995. The principle focus of the analysis is Lake Michigan and its surrounding watershed. Grid-cell average model results are compared to total ambient atmospheric measurements reported by the U.S. EPA Lake Michigan Mass Balance (LMMB) Study and the USGS National Weather Quality Assessment program for 1995. Grid-averaged weekly and monthly aggregate wet deposition model results are compared to observations reported by the LMMB, USGS and Environment Canada. Special attention is given to gas/particle partitioning mechanisms when modeling ambient atmospheric concentration since expected partitioning behavior, based only on direct particle sorption, does not appear to adequately explain most field observations. Inclusion of additional sorption mechanisms (i.e., liquid film and film pH) results in model estimates that more closely resemble reported values. In the future, a second, 12 km rectangular grid domain, centered over Lake Michigan itself, will be nested within the larger model domain for a sub-set of the 120 day period to obtain more spatially resolved wet and dry chemical deposition patterns over the Lake surface.