The atmospheric oxidation of hydroxyacetone: Chemistry of activated and stabilized CH<sub>3</sub>C(O)CH(OH)OO• radicals between 252 and 298 K
John J. Orlando, Geoffrey S. Tyndall
Abstract
Abstract The products of the Cl‐atom‐initiated oxidation of hydroxyacetone (HYAC, CH 3 C(O)CH 2 OH) 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 NO x , methylglyoxal (CH 3 C(=O)CH=O, MGLY) was formed with a primary yield >84% (96 ± 9% at 298 K), while in the presence of elevated NO x , 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 CH 3 C(O)CH(OH)OO• radical, either in a ≈50% yield from the addition of O 2 to CH 3 C(O)CH•(OH) or in 100% yield from the addition of HO 2 to MGLY. At high temperature and low NO x , decomposition of the stabilized CH 3 C(O)CH(OH)OO• radical to MGLY is favored, while lower temperatures and conditions of high NO x favor bimolecular reactions of the stabilized radical, with subsequent production of formic acid. Analysis of the data allows for a semiquantitative determination of K 3 = (2.9 ± 0.4) × 10 −16 cm 3 molecule −1 , for the HO 2 + MGLY ↔ CH 3 C(O)CH(OH)OO• equilibrium process at 298 K and a roughly order of magnitude increase in K 3 at 252 K.