Abstract
Abstract. A natural emissions inventory for the continental United States and surrounding territories is needed in order to use the US Environmental Protection Agency Community Multiscale Air Quality (CMAQ) Model for simulating natural air quality. The CMAQ air modeling system (including the Sparse Matrix Operator Kernel Emissions (SMOKE) emissions processing system) currently estimates non-methane volatile organic compound (NMVOC) emissions from biogenic sources, nitrogen oxide (NOx) emissions from soils, ammonia from animals, several types of particulate and reactive gas emissions from fires, as well as sea salt emissions. However, there are several emission categories that are not commonly treated by the standard CMAQ Model system. Most notable among these are nitrogen oxide emissions from lightning, reduced sulfur emissions from oceans, geothermal features and other continental sources, windblown dust particulate, and reactive chlorine gas emissions linked with sea salt chloride. A review of past emissions modeling work and existing global emissions data bases provides information and data necessary for preparing a more complete natural emissions data base for CMAQ applications. A model-ready natural emissions data base is developed to complement the anthropogenic emissions inventory used by the VISTAS Regional Planning Organization in its work analyzing regional haze based on the year 2002. This new data base covers a modeling domain that includes the continental United States plus large portions of Canada, Mexico and surrounding oceans. Comparing July 2002 source data reveals that natural emissions account for 16% of total gaseous sulfur (sulfur dioxide, dimethylsulfide and hydrogen sulfide), 44% of total NOx, 80% of reactive carbonaceous gases (NMVOCs and carbon monoxide), 28% of ammonia, 96% of total chlorine (hydrochloric acid, nitryl chloride and sea salt chloride), and 84% of fine particles (i.e., those smaller than 2.5 μm in size) released into the atmosphere. The seasonality and relative importance of the various natural emissions categories are described.
Highlights
Air quality modeling as practiced in the United States is often done to support air pollution management decisions that result in controls on anthropogenic pollutant sources
The reasons for this are usually associated with expectations that such emissions are not important when compared to anthropogenic emissions, or the emissions processes themselves are complex and not as well characterized as emissions that are typically modeled
This paper describes the first part of an effort to incorporate a greater diversity of natural emissions into an air quality model that is widely used for air management studies
Summary
Air quality modeling as practiced in the United States is often done to support air pollution management decisions that result in controls on anthropogenic pollutant sources. There are several categories of natural emissions that are currently not assimilated into many regional air quality models. The reasons for this are usually associated with expectations that such emissions are not important when compared to anthropogenic emissions, or the emissions processes themselves are complex and not as well characterized as emissions that are typically modeled. Neglected emissions may, at some times and in some places, play significant roles in the photochemical evolution of the atmosphere even in the presence of anthropogenic emissions. This paper describes the first part of an effort to incorporate a greater diversity of natural emissions into an air quality model that is widely used for air management studies. Later papers will describe changes to an air quality model necessitated by the introduction of new emission sources and simulation results from that model
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