Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 6 2006 10.5194/acpd-6-13225-2006 http://www.atmos-chem-phys-discuss.net/6/13225/2006/ http://www.atmos-chem-phys-discuss.net/6/13225/2006/acpd-6-13225-2006.html http://www.atmos-chem-phys-discuss.net/6/13225/2006/acpd-6-13225-2006.pdf 13225 13250 2006-12-15 Daytime tropospheric loss of hexanal and trans-2-hexenal: OH kinetics and UV photolysis E. Jiménez B. Lanza E. Martínez J. Albaladejo Departamento de Química Física, Facultad de Ciencias Químicas, Universidad de Castilla-La Mancha, Avda. Camilo José Cela, s/n, 13071 Ciudad Real, Spain The ultraviolet (λ=250–370 nm) photolysis and the OH-initiated oxidation of hexanal and trans-2-hexenal, which are relevant atmospheric processes, have been investigated at room temperature and as a function of temperature (T=263–353 K), respectively. This kinetic study as a function of temperature is reported here for the first time. Absolute absorption cross sections (σλ) were obtained using a recently built system operating in the UV region. This work represents the first reported σλ for trans-2-hexenal. The obtained σλ allowed the estimation of the photolysis rates (J) of hexanal and trans-2-hexenal across the troposphere. Kinetic measurements of the gas-phase reaction of hydroxyl radicals (OH) with hexanal and trans-2-hexenal were performed by using the laser pulsed photolysis/laser-induced fluorescence technique. Rate coefficients kOH for both aldehydes were determined at temperatures between 263 and 353 K at 50 Torr in helium or argon bath gases. The temperature dependence of kOH for both aldehydes was found to be slightly negative. The tropospheric lifetime of hexanal and trans-2-hexenal due to the chemical removal by OH radicals has been estimated across the troposphere. The loss rate due to the OH chemical removal was compared with the estimated photolysis rates. 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