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Modeling Heterogeneous CINO2 Formation, Chloride Availability, and Chlorine Cycling in Southeast Texas
Citation:
SIMON, H., Y. Kimura, G. McGaughey, D. ALLEN, S. S. Brown, D. Coffman, J. Dibb, H. D. Osthoff, P. Quinn, J. M. Roberts, G. Yarwood, S. Kemball-Cook, D. W. BYUN, AND D. Lee. Modeling Heterogeneous CINO2 Formation, Chloride Availability, and Chlorine Cycling in Southeast Texas. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 44(40):5476-5488, (2010).
Impact/Purpose:
National Exposure Research Laboratory′s (NERL′s) Atmospheric Modeling Division (AMD) conducts research in support of EPA′s mission to protect human health and the environment. AMD′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. AMD 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 AMD 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:
Nitryl chloride (ClNO2) mixing ratios above 1 ppbv have been measured off the coast of Southeast Texas. ClNO2 formation, the result of heterogeneous N205 uptake on chloride-containing aerosols, has a significant impact on oxidant formation for the Houston area. This work reports on the modeling of CINO2 formation and describes the sensitivity of CINO2 formation to key parameters. Model sensitivity analyses found that: (1) Chloride availability limits the formation of nitryl chloride at ground level but not aloft; (2) When excess particulate chloride was assumed to be present at ground level through sea salt, ClNO2 concentrations increased in some locations by a factor of 13, as compared to cases where sea salt chloride was assumed to be limited; (3) Inland formation of ClNO2 seems feasible based on chloride availability and could have a large impact on total ClNO2, formed in the region; and (4) ClNO2 formation is quite sensitive to the assumed yield of ClNO2 from N2O5 uptake. These results demonstrate that there is a need for further field studies to better understand the geographic extent of ClNO2 formation and the atmospheric conditions which control partitioning of chloride into the particle phase. In addition, this work examined the role of ClNO2 in the cycling of chlorine between chloride and reactive chlorine radicals. The modeling indicated that the majority of reactive chlorine in Texas along the Gulf coast is cycled through ClNO2, demonstrating the importance of including ClNO2 into photochemical models for this region.
URLs/Downloads:
Atmospheric Environment
Modeling Heterogeneous CINO2 Formation, Chloride Availability, and Chlorine Cycling in Southeast Texas (PDF, NA pp, 7700 KB, about PDF)