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

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


Atmospheric chemistry and physics. Discussions 11 (2011), No.5, pp.15119-15155
ISSN: 1680-7367
Journal Article
Fraunhofer ITEM ()

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 + hv; and <10 % NO2* + H2O) to our unkno wn 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.