Atmospheric chemistry of ketones: Reaction of OH radicals with 2-methyl-3-pentanone, 3-methyl-2-pentanone and 4-methyl-2-pentanone

Highlights: • Room temperature rate constants are determined for the reactions of 2M3P, 3M2P and 4M2P with OH radicals; • This work constitutes the first temperature dependence study of the reactions of OH with 2M3P and 3M2P; • OH-initiated oxidation products of the studied ketones have been investigated under atmospheric conditions; • Mechanistic degradation schemes of the investigated ketones are proposed mainly based on the experimental data; • The new kinetic and mechanistic information enabled to discuss the atmospheric fate of the studied ketones. This work reports new kinetic and mechanistic information on the atmospheric chemistry of ketones. Both absolute and relative rate methods were used to determine the rate constants for OH reactions with 2-methyl-3-pentanone (2M3P), 3-methyl-2-pentanone (3M2P) and 4-methyl-2-pentanone (4M2P), three widely used compounds in the industry. This work constitutes the first temperature dependence study of the reactions of OH with 2M3P and 3M2P. The following rate constants values are recommended at 298 K (in 10⁻¹² cm³ molecule⁻¹ s⁻¹): k_OH+2M3P = 3.49 ± 0.5; k_OH+3M2P = 6.02 ± 0.14 and k_OH+4M2P = 11.02 ± 0.42. The following Arrhenius expressions (in units of cm³ molecule⁻¹ s⁻¹) adequately describe the measured rate constants for OH reactions with 2M3P and 3M2P in the temperature range 263–373 K: k_2M3P = (2.33 ± 0.06) × 10⁻¹² exp((127.4 ± 18.6)/T) and k_3M2P = (1.05 ± 0.14) × 10⁻¹² exp((537 ± 41)/T). Products studies from the reactions of OH with the investigated ketones were conducted in a 7.3 m³ simulation chamber using PTR-ToF-MS, UHPLC-MS and GC–MS. A series of short chain carbonyl compounds including formaldehyde, acetone, acetaldehyde, 2-butanone and 2-methypropanal were observed as products. Combining the yields of carbonyls measured with those estimated from the SAR method, we propose various mechanistic degradation schemes of the investigated ketones initiated by reaction with OH radicals.