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SEASONAL NH3 EMISSION ESTIMATES FOR THE EASTERN UNITED STATES BASED ON AMMONIUM WET CONCENTRATIONS AND AN INVERSE MODELING METHOD
Citation:
Gilliland, A B., R L. Dennis, S J. Roselle, AND T E. Pierce Jr. SEASONAL NH3 EMISSION ESTIMATES FOR THE EASTERN UNITED STATES BASED ON AMMONIUM WET CONCENTRATIONS AND AN INVERSE MODELING METHOD. JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES 108(D15):ACH20-1-ACH 20-11, (2003).
Impact/Purpose:
The goal of this task is to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the Models-3 system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not validated. Both performance and diagnostic evaluation together with sensitivity analyses are needed to establish credibility and build confidence within the client and scientific community in the simulations results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.
Description:
Significant uncertainty exists in the magnitude and variability of ammonia (NH3) emissions. NH3 emissions are needed as input for air quality modeling of aerosols and deposition of nitrogen compounds. Approximately 85% of NH3 emissions are estimated to come from agricultural non-point sources. We suspect a strong seasonal pattern in these NH3 emissions; however, current NH3 emission inventories lack intra-annual variability. If NH3 emissions are distributed evenly over a year, a default approach that has been used with air quality models, it can adversely affect model-predicted concentrations of nitrogen-containing compounds. In this paper, we apply a Kalman filter inverse modeling technique to deduce monthly 1990 NH3 emissions for the eastern United States. The United States Environmental Protection Agency (USEPA) Community Multiscale Air Quality (CMAQ) model and ammonium (NH4+) wet concentration data from the National Atmospheric Deposition Program (NADP) network are used. The results illustrate the strong seasonal differences in NH3 emissions that were anticipated, where NH3 emissions are considerably smaller during the colder seasons fall and winter and peak during summer. The results also suggest that the current USEPA 1990 National Emission Inventory (NEI) for NH3 may be too high. This is supported by a recent USEPA study of emission factors that proposes lower emission factors for cattle and swine, which are two of the largest sources of NH3 emissions in the inventory.
This paper has been subjected to U.S. Environmental Protection Agency peer review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.