Use of a Dynamic Air Quality Model to Reduce the Uncertainties of Seasonal and Annual Atmospheric Depositions for Mercury TMDLs
Abstract:A state-of-the-science dynamic air quality model and current knowledge have been applied to reduce the uncertainties of dry, wet and total atmospheric deposition fluxes which accounted for nearly all of the nonpoint-source allocations for reservoir mercury TMDLs. Currently, the uncertainties of mercury allocations in these TMDLs are often resulted from an over-simplified methodology, such as the linear regression or interpolation method, used in estimating the temporal and spatial variations of mercury depositions at particular land and water areas. In addition, the air and water chemical transformations of mercury in gas and particulate phases are often ignored in these TMDLs due to the lack of simulation capabilities for mercury and other airborne pollutants emitted from anthropogenic and natural sources. Furthermore, a number of factors particularly important to the successful implementation of mercury TMDLs were not addressed explicitly in the past. For example, the accuracy and representativeness of the meteorological and emission inventory changes for foreseeable policy-driven future years, and the treatment of urban areas in both the source and receptor areas in site-specific TMDL locations.
This paper will discuss a three-dimensional, grid-based dynamic air quality model that addresses the uncertainty issues of mercury TMDLs and will propose a good-science-based source-tracking methodology and a flexible nested-grid system configuration for a better understanding of the distributions, sources, and removal processes related to fine particles and other soluble acidic components and toxics involved in mercury TMDLs. The simulated air deposition results are based on a source tagging method and a 4-km fine-grid resolution. Liberty Reservoir in Maryland has been used to demonstrate the applicability of this approach. It is believed that this proposed cutting-edge methodology and modeling system will help TMDL stakeholders develop a more realistic and implementable TMDL plan that better accounts for site-specific topographical characteristics, meteorological conditions and man-induced air sources of mercury.
Document Type: Research Article
Publication date: January 1, 2005
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