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NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
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Emission Factors for Visibility Impairment from Fugitive Dust Emissions
H. Moosmüller, R. Varma, W. P. Arnott, J. Walker, H. D. Kuhns, V. Etyemezian, and J. A. Gillies
Desert Research Institute, University of Nevada System, Reno, NV
The U.S. EPA´s 1999 Regional Haze Rule sets the stage for a 65-year effort to return visibility to its natural state at 156 national parks and wilderness areas. Visibility impairment is mostly caused by light scattering from suspended particles, with important contributions from both fine (e.g., sulfate, carbonaceous particles) and coarse size fractions (e.g., entrained mineral dust). Current particulate emission factors quantify emissions of particulate matter (PM) mass and are used in conjunction with the U.S. EPA´s health-based PM2.5 and PM10 standards. For visibility applications, we propose to use emission factors quantifying the flux of PM scattering cross sections, which are directly relevant to visibility impairment. Such emission factors are useful for non-hygroscopic particles available for long-range transport, where the flux of scattering cross section is largely conserved during mixing and transport.
As an example, we have measured scattering cross section emission factors for mineral dust entrained by military vehicles from an unpaved road in Ft. Bliss, TX. A novel nephelometer with an enhanced capability for accurately measuring scattering from large particles is used to determine the scattering coefficients in vehicle dust plumes 100 m downwind of the unpaved road at a height of 5.7 m above ground. Fluxes and emission factors for scattering cross section are calculated from these data in conjunction with vertical plume concentration and wind velocity data. The resulting scattering cross section emission factors are stratified as function of vehicle weight and speed.