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

by M. Sörgel, E. Regelin, H. Bozem, J.-M. Diesch, F. Drewnick, H. Fischer, H. Harder, A. Held, Z. Hosaynali-Beygi, M. Martinez, C. Zetzsch show all authors
Atmospheric Chemistry and Physics ()


During the DOMINO (Diel Oxidant Mechanism In relation to NitrogenOxides) campaign in southwest Spain we measured simultaneously all quantities necessary to cal- culate 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 reac- tion 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 unknownHONOdaytime source. OHproduction from HONO photolysis was found to be larger (by 20%) than the “classical” OH formation from ozone photolysis (O(1D)) in- tegrated over the day. Corres

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