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Modeling Reduced Nitrogen Deposition in Regulatory Context
Citation:
Napelenok, S., R. Pinder, R. Scheffe, AND S. Roselle. Modeling Reduced Nitrogen Deposition in Regulatory Context. ITM 2018 - 36 th International Technical Meeting on Air Pollution Modelling and its Application, Ottowa, CANADA, May 14 - 18, 2018.
Impact/Purpose:
CMAQ model solves the physical and chemical transformations of air pollutants in the aqueous phase through the cloud module. This module was modified to preserve the ambient ratios of particulate and gas phase reduced nitrogen before dissolution into water droplets and applying this ratio to the resulting deposition total. Preserving the ambient reduced nitrogen phase before dissolving this mass in cloud water droplets results in lower particulate NH4+ deposition quantities and higher (NH3). More stringent controls are required on total particulate mass emissions than standard air quality models suggest in order to achieve desired reduction in reduced nitrogen loading to terrestrial and aquatic systems through existing PM NAAQS.
Description:
Wet and dry deposition of gas phase ammonia (NH3) and particulate ammonium (NH4+) contribute substantially to adverse ecological impacts (e.g., eutrophication) from additional nitrogen loading to terrestrial and aquatic systems. Mitigating ecosystem damage from reduced nitrogen deposition requires complete understanding of sources, both in terms of quantity and distribution of emissions and also in terms of compound phase - gaseous versus particulate. Here, we focus on quantifying the relative amounts of wet and dry deposition of NH3 and NH4+ from common sources using the latest version of the Community Multiscale Air Quality (CMAQ) model. Currently, particulate NH4+ is regulated in the U.S. as a component of total PM mass through the National Ambient Air Quality Standards (NAAQS) while NH3 is not. Therefore, it is important to reliability estimate the source phase of deposited reduced nitrogen.
