Experimental and theoretical studies of novel HOx-NOx reactions in the atmosphere

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This is a proposal for research into key reactions that substantially impact on atmospheric chemistry. By combining experiment and theory a number of reactions which couple the HOx and NOx radical families of the lower and middle atmosphere and profoundly modify photochemical ozone production will be fully characterised:HO2 + NO + M → HNO3 + M (R1b)NO2* + H2O → OH + HONO (R2b)NO3* + H2O → OH + HNO3 (R3b)OH + HNO3 → NO3 + H2O (R4)The kinetic/mechanistic database for these reactions is in poor shape. Advanced experimental techniques and theoretical methods will be employed in particular to verify the recent suggestion of HNO3 formation in the reaction between HO2 and NO (R1b), and the formation of OH radicals via non-dissociative photo-excitation of NO2 and NO3 in the presence of water-vapour (R2b, R3b). The rate coefficient for R4 is highly uncertain at low temperatures. A fundamental understanding of the mechanisms of these reactions is to be obtained and reliable kinetic data for atmospheric modeling will be provided.