Kinetics and Product Yields of the OH Initiated Oxidation of Hydroxymethyl Hydroperoxide

Abstract

Hydroxymethyl hydroperoxide (HMHP), formed in the reaction of the C₁ Criegee intermediate with water, is among the most abundant organic peroxides in the atmosphere. Although reaction with OH is thought to represent one of the most important atmospheric removal processes for HMHP, this reaction has been largely unstudied in the laboratory. Here, we present measurements of the kinetics and products formed in the reaction of HMHP with OH. HMHP was oxidized by OH in an environmental chamber; the decay of the hydroperoxide and the formation of formic acid and formaldehyde were monitored over time using CF₃O⁻ chemical ionization mass spectrometry (CIMS) and laser-induced fluorescence (LIF). The loss of HMHP by reaction with OH is measured relative to the loss of 1,2-butanediol [k1,2-butanediol+OH = (27.0 ± 5.6) × 10⁻¹² cm³ molecule⁻¹s⁻¹]. We find that HMHP reacts with OH at 295 K with a rate coefficient of (7.1 ± 1.5) × 10⁻¹² cm³ molecule⁻¹s⁻¹, with the formic acid to formaldehyde yield in a ratio of 0.88 ± 0.21 and independent of NO concentration (3 × 10¹0 – 1.5 × 10¹³ molecules cm⁻³). We suggest that, exclusively, abstraction of the methyl hydrogen of HMHP results in formic acid, while abstraction of the hydroperoxy hydrogen results in formaldehyde. We further evaluate the relative importance of HMHP sinks and use global simulations from GEOS-Chem to estimate that HMHP oxidation by OH contributes 1.7 Tg yr⁻¹ (1–3%) of global annual formic acid production.