National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2011

Modeling heterogeneous ClNO2 formation, chloride availability, and chlorine cycling in southeast Texas

Simon, H., Y. Kimura, G. McGaughey, D.T. Allen, S.S. Brown, D. Coffman, J. Dibb, H.D. Osthoff, P. Quinn, J.M Roberts, G. Yarwood, S. Kemball-Cook, D. Byun, and D. Lee

44, Air Quality Research Center, UC Davis, 2nd Biennial Conference on Atmospheric Chemistry Mechanisms, Davis, CA, 10-12 December 2008, 5476–5488, doi: 10.1016/j.atmosenv.2009.09.006 (2010)

Nitryl Chloride (ClNO2) mixing ratios above 1 ppbv have been measured off the coast of Southeast Texas ClNO2 formation the result of heterogeneous N2O5 uptake on chloride-containing aerosols has a significant Impact on oxidant formation for the Houston area This work reports on the modeling of ClNO2 formation and describes the sensitivity of ClNO2 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.

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