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Assessment of Emission Inventories and Exposure for Air Toxics Using an Automated Grid Modeling System

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The AIRPACT program has developed an automated air quality modeling system to produce daily forecasts of pollutant concentrations for Puget Sound. This system employs MM5 meteorological forecasts coupled with dynamic emissions processing and the CALMET/CALGRID photochemical models. During the summer, 2001, the system was used to produce detailed ozone and ozone precursor forecasts, and during the past winter, the system was used to predict concentrations of diesel particulate emissions. As a result of the automated daily operation, the project team compiled an archived data set of predicted diesel particulate concentrations with 4 km horizontal grid resolution and one hour temporal resolution. Similar information has been compiled from the summertime operations where the focus is on ozone, ozone precursors and other photochemical products (i.e. formaldehyde). In both cases, available monitoring data are used to evaluate the accuracy of the model simulations. The project team proposes to expand this modeling system to predict ambient concentrations of a number of specific air toxics, and to expand the modeling domain to encompass the metropolitan areas of Seattle, WA and Portland, OR. As an option, they also propose converting the system from CALGRID to CMAQ. For the primary work, the specific approach will involve several steps. First, they will develop gridded emission inventories for a number of key air toxics. The list of compounds will be determined in collaboration with all of the partners. They expect the initial list to include diesel particulate, benzene, 1,3-butadiene, formaldehyde, chromium, and chloroform. This step will build on the foundation that is already have in place using gridded emissions for ozone precursors and diesel particulate. It will also build on recently compiled county level air toxics emission inventories in Puget Sound and Portland. Second, they will revise the chemical mechanism in CALGRID to allow treatment of the specific air toxic compounds. They have already done this for particulate diesel so this will be a straightforward step. Third, they will expand the model domain to encompass both Puget Sound and the Portland/Vancouver metropolitan area. There are currently air toxic monitoring programs in place in both areas so they can take advantage of these data for model evaluation.

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