Articles | Volume 11, issue 20
Research article
20 Oct 2011
Research article |  | 20 Oct 2011

Quantification of the unknown HONO daytime source and its relation to NO2

M. Sörgel, E. Regelin, H. Bozem, J.-M. Diesch, F. Drewnick, H. Fischer, H. Harder, A. Held, Z. Hosaynali-Beygi, M. Martinez, and C. Zetzsch

Abstract. During the DOMINO (Diel Oxidant Mechanism In relation to Nitrogen Oxides) campaign in southwest Spain we measured simultaneously all quantities necessary to calculate a photostationary state for HONO in the gas phase. These quantities comprise the concentrations of OH, NO, and HONO and the photolysis frequency of NO2, j(NO2) as a proxy for j(HONO). This allowed us to calculate values of the unknown HONO daytime source. This unknown HONO source, normalized by NO2 mixing ratios and expressed as a conversion frequency (% h−1), showed a clear dependence on j(NO2) with values up to 43% h−1 at noon. We compared our unknown HONO source with values calculated from the measured field data for two recently proposed processes, the light-induced NO2 conversion on soot surfaces and the reaction of electronically excited NO2* with water vapour, with the result that these two reactions normally contributed less than 10% (<1% NO2 + soot + hν; and <10% NO2* + H2O) to our unknown HONO daytime source. OH production from HONO photolysis was found to be larger (by 20%) than the "classical" OH formation from ozone photolysis (O(1D)) integrated over the day.

Final-revised paper