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Quantification of the unknown HONO daytime source and its relation to NO(2)

: Sorgel, 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 11 (2011), No.20, pp.10433-10447
ISSN: 1680-7316
ISSN: 1680-7324
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 NO(2), j(NO(2)) as a proxy for j(HONO). This allowed us to calculate values of the unknown HONO daytime source. This unknown HONO source, normalized by NO(2) mixing ratios and expressed as a conversion frequency (% h(-1)), showed a clear dependence on j(NO(2)) 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 NO(2) conversion on soot surfaces and the reaction of electronically excited NO(2)* with water vapour, with the result that these two reactions normally contributed less than 10% (<1% NO(2) + soot + hv; and <10% NO(2)* + H(2)O) 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((1)D)) integrated over the day.