An MCM modeling study of nitryl chloride (ClNO2) impacts on oxidation, ozone production and nitrogen oxide partitioning in polluted continental outflow
Links to Fileshttps://acp.copernicus.org/articles/14/3789/2014/
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Type of Work12 pages
Citation of Original PublicationRiedel, T. P., Wolfe, G. M., Danas, K. T., Gilman, J. B., Kuster, W. C., Bon, D. M., Vlasenko, A., Li, S.-M., Williams, E. J., Lerner, B. M., Veres, P. R., Roberts, J. M., Holloway, J. S., Lefer, B., Brown, S. S., and Thornton, J. A.: An MCM modeling study of nitryl chloride (ClNO2) impacts on oxidation, ozone production and nitrogen oxide partitioning in polluted continental outflow, Atmos. Chem. Phys., 14, 3789–3800, https://doi.org/10.5194/acp-14-3789-2014, 2014.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Nitryl chloride (ClNO₂) is produced at night by reactions of dinitrogen pentoxide (N₂O₅) on chloride containing surfaces. ClNO₂ is photolyzed during the morning hours after sunrise to liberate highly reactive chlorine atoms (Cl·). This chemistry takes place primarily in polluted environments where the concentrations of N₂O₅ precursors (nitrogen oxide radicals and ozone) are high, though it likely occurs in remote regions at lower intensities. Recent field measurements have illustrated the potential importance of ClNO₂ as a daytime Cl· source and a nighttime NOx reservoir. However, the fate of the Cl· and the overall impact of ClNO₂ on regional photochemistry remain poorly constrained by measurements and models. To this end, we have incorporated ClNO₂ production, photolysis, and subsequent Cl· reactions into an existing master chemical mechanism (MCM version 3.2) box model framework using observational constraints from the CalNex 2010 field study. Cl· reactions with a set of alkenes and alcohols, and the simplified multiphase chemistry of N₂O₅, ClNO₂, HOCl, ClONO₂, and Cl₂, none of which are currently part of the MCM, have been added to the mechanism. The presence of ClNO₂ produces significant changes to oxidants, ozone, and nitrogen oxide partitioning, relative to model runs excluding ClNO₂ formation. From a nighttime maximum of 1.5 ppbv ClNO₂, the daytime maximum Cl· concentration reaches 1 × 10⁵ atoms cm⁻³ at 07:00 model time, reacting mostly with a large suite of volatile organic compounds (VOC) to produce 2.2 times more organic peroxy radicals in the morning than in the absence of ClNO₂. In the presence of several ppbv of nitrogen oxide radicals (NOx = NO + NO₂), these perturbations lead to similar enhancements in hydrogen oxide radicals (HOx = OH + HO₂). Neglecting contributions from HONO, the total integrated daytime radical source is 17% larger when including ClNO₂, which leads to a similar enhancement in integrated ozone production of 15%. Detectable levels (tens of pptv) of chlorine containing organic compounds are predicted to form as a result of Cl· addition to alkenes, which may be useful in identifying times of active Cl· chemistry.
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