Formation of hydroxymethyl hydroperoxide and formic acid in alkene ozonolysis in the presence of water vapour

Ozonolysis experiments of a series of terminal alkenes were performed to study the products formed in the presence of water vapour. Alkenes investigated were ethene, propene, isobutene and isoprene. Concentrations of the reactants were 4–6 ppmv alkene and 2 ppm ozone. The concentration of water vapour was varied from 0.5 ppmv to 17,000 ppmv. Hydroxymethyl hydroperoxide (HMHP) was found to be the sole product in the reactions of the stabilized Criegee biradical CH2OO with water vapour. The yield of HMHP relative to ozone consumption was measured to be 42% ethene, 14% propene, 13% isobutene and 30% isoprene in the presence of 9,000–18,000 ppmv H2O. HMHP was not stable under the experimental conditions and decomposed to HCOOH and water, presumably via a heterogeneous process. The atmospheric fate of HMHP and the relative rate constants of the CH2OO Criegee biradical with H2O, HCOOH and NOx are discussed.