Reaction of Criegee Intermediates with Water VaporAn Additional Source of OH Radicals in Alkene Ozonolysis?

The yields of OH radicals from the ozonolysis of ethene and trans-2-butene under dry and humid conditions (0% and 65% relative humidity, respectively) were measured by the small-ratio relative rate technique. The OH yields from both alkenes are found to be independent of the humidity within the error limits of the experiments. This suggests that the OH yield from the reaction of Criegee intermediates with water is less than 30%. These findings are supported by Master equation calculations that are consistent with the major product from the reaction of Criegee intermediates with water being the hydroxyalkyl hydroperoxide (RCH(OH)OOH), with a smaller contribution from OH. Implications of these results for both the fundamental reaction mechanism of ozone-alkene reactions and the fate of Criegee intermediates in the troposphere are discussed.