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

• Published in: Atmospheric chemistry and physics Vol. 11; no. 20; pp. 10433 - 10447
• Main Authors: M. Martinez, Z. Hosaynali-Beygi, H. Harder, A. Held, H. Fischer, F. Drewnick, J.-M. Diesch, H. Bozem, E. Regelin, M. Sörgel, C. Zetzsch
• Format: Journal Article
• Language: English
• Published: Copernicus Publications 01.01.2011
• ISSN: 1680-7316; 1680-7324
• DOI: 10.5194/acp-11-10433-2011

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.