Atmos. Chem. Phys. Discuss., 12, 12885-12934, 2012
© Author(s) 2012. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Impact of HONO on global atmospheric chemistry calculated with an empirical parameterization in the EMAC model
Y. F. Elshorbany1, B. Steil1, C. Brühl1, and J. Lelieveld1,2
1Max-Plank Institute for Chemistry, Atmospheric Chemistry Department, Mainz, Germany
2The Cyprus Institute, Nicosia, Cyprus, and King Saud University, Riyadh, Saudi Arabia

Abstract. The photolysis of HONO is important for the atmospheric HOx (OH+HO2) radical budget and ozone formation, especially in polluted air. Nevertheless, owing to the incomplete knowledge of HONO sources, realistic HONO mechanisms have not yet been implemented in global models. We investigated measurement data sets from 15 field measurement campaigns conducted in different countries worldwide. It appears that the HONO/NOx ratio is a good proxy predictor for HONO mixing ratios under different atmospheric conditions. From the robust relationship between HONO and NOx, a representative mean HONO/NOx ratio of 0.02 has been derived. Using a global chemistry-climate model and employing this HONO/NOx ratio, realistic HONO levels are simulated, being about one order of magnitude higher than the reference calculations, which only consider the reaction OH+NO-> HONO. The resulting enhancement of HONO significantly impacts HOx levels and photo-oxidation products (e.g, O3, PAN), mainly in polluted regions. Furthermore, the relative enhancements in OH and secondary products were higher in winter than in summer, thus enhancing the oxidation capacity in polluted regions, especially in winter, when the other photolytic OH sources are of minor importance. Our results underscore the need to improve the understanding of HONO chemistry and its representation in atmospheric models.

Citation: Elshorbany, Y. F., Steil, B., Brühl, C., and Lelieveld, J.: Impact of HONO on global atmospheric chemistry calculated with an empirical parameterization in the EMAC model, Atmos. Chem. Phys. Discuss., 12, 12885-12934, doi:10.5194/acpd-12-12885-2012, 2012.
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