The rate and mechanism of the gas-phase oxidation of hydroxyacetone

The rate and mechanism for gas-phase destruction of hydroxyacetone, CH3C(O) CH2OH, by reaction with OH, Cl-atoms, and by photolysis have been determine d. The first quantitative UV absorption spectrum of hydroxyacetone is repor ted over the wavelength range 235 to 340 nm; the spectrum is blue-shifted b y about 15 nm relative to that of acetone and peaks at 266 nm, with a maxim um absorption cross section of (6.7 +/- 0.6) x 10(-20) cm(2) molecule(-1). Measurable absorption extends out to about 330 nm. The quantum yield for ph otolysis of hydroxyacetone in the region relevant to the troposphere (lambd a, > 290 nm) was found to be significantly less than unity. Rate coefficien ts for the reaction of hydroxyacetone with OH radicals and CI-atoms were de termined at 298 K using the relative rate technique. The rate coefficient f or reaction with OH was found to be (3.0 +/- 0.7) x 10(-12) cm(3) molecule( -1) s(-1), while the rate coefficient for reaction with Cl-atoms was found to be (5.6 +/- 0.7) x 10(-11) cm(3) molecule(-1) s(-1). Both values agree w ell with previous studies. The data were used to determine the lifetime of hydroxyacetone in the troposphere. Reaction with OH is the major gas-phase destruction mechanism for this compound,limiting its lifetime to about 4 da ys, while photolysis is found to be only of minor importance. (C0) 1999 Els evier Science Ltd. All rights reserved.