The atmospheric oxidation of hydroxyacetone: Chemistry of activated and stabilized CH3C(O)CH(OH)OO• radicals between 252 and 298 K

Abstract

AbstractThe products of the Cl‐atom‐initiated oxidation of hydroxyacetone (HYAC, CH3C(O)CH2OH) have been examined under conditions relevant to the earth's lower atmosphere. Over the range of temperatures studied (252‐298 K), in the absence of NOx, methylglyoxal (CH3C(=O)CH=O, MGLY) was formed with a primary yield >84% (96 ± 9% at 298 K), while in the presence of elevated NOx, MGLY and formic acid were both formed as major primary products. In contrast to a previous study, acetic acid was not identified as a major primary product under the conditions studied. The results are quantitatively interpreted from a consideration of the formation of a stabilized CH3C(O)CH(OH)OO• radical, either in a ≈50% yield from the addition of O2 to CH3C(O)CH•(OH) or in 100% yield from the addition of HO2 to MGLY. At high temperature and low NOx, decomposition of the stabilized CH3C(O)CH(OH)OO• radical to MGLY is favored, while lower temperatures and conditions of high NOx favor bimolecular reactions of the stabilized radical, with subsequent production of formic acid. Analysis of the data allows for a semiquantitative determination of K3 = (2.9 ± 0.4) × 10−16 cm3 molecule−1, for the HO2 + MGLY ↔ CH3C(O)CH(OH)OO• equilibrium process at 298 K and a roughly order of magnitude increase in K3 at 252 K.