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Atmospheric ammonia and particulate inorganic nitrogen over the United States
Citation:
Heald, C., J. Collett, T. Lee, K. Benedict, F. Schwander, Y. Li, L. Clarisse, D. Hurtmans, M. VanDamme, C. Clerbaux, P. Coheur, S. Philip, R. Martin, AND H. Pye. Atmospheric ammonia and particulate inorganic nitrogen over the United States. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, Germany, 12(21):10295-10312, (2012).
Impact/Purpose:
The National Exposure Research Laboratory′s (NERL′s)Atmospheric Modeling Division (AMAD) conducts research in support of EPA′s mission to protect human health and the environment. AMAD′s research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the Nation′s air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Description:
We use in situ observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring Project, 11 surface site campaigns as well as Infrared Atmospheric Sounding Interferometer (IASI) satellite measurements with the GEOS-Chem model to investigate inorganic aerosol loading and atmospheric ammonia concentrations over the United States. IASI observations suggest that current ammonia emissions are underestimated in California and in the springtime in the Midwest. In California this underestimate likely drives the underestimate in nitrate formation in the GEOS-Chem model. However in the remaining continental United States we find that the nitrate simulation is biased high (normalized mean bias >= 1.0)year-round, except in Spring (due to the underestimate in ammonia in this season). None of the uncertainties in precursor emissions, the uptake efficiency of N2O5 on aerosols, OH concentrations, the reaction rate for the formation of nitric acid, or the dry deposition velocity of nitric acid are able to explain thisbias. We find that reducing nitric acid concentrations to 75% of their simulated values corrects the bias in nitrate (as well as ammonium) in the U.S. However the mechanism for this potential reduction is unclear and may be a combination of errors in chemistry, deposition and sub-grid near-surface gradients. This “updated” simulation reproduces PM and ammonia loading and captures the strong seasonal and spatial gradients in gas-particle partitioning across the United States. We estimate that nitrogen makes up 15-35% of inorganic fine PM mass over the U.S., and that this fraction is likely to increase in the coming decade, both with decreases in sulfur emissions and increases in ammonia emissions.
URLs/Downloads:
Atmospheric ammonia and particulate inorganic nitrogen over the United States (PDF, NA pp, 5258 KB, about PDF)Atmospheric Chemistry and Physics
