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

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) cm(3) 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 cm(3) 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) x 10(-12) exp((127.4 +/- 18.6)/T) and k(3M2P) = (1.05 +/- 0.14) x 10(-12) exp((537 +/- 41)/T). Products studies from the reactions of OH with the investigated ketones were conducted in a 7.3 m(3) 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. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study provides new kinetic and mechanistic information on the atmospheric chemistry of ketones by investigating the reactions of OH radicals with three widely used compounds (2M3P, 3M2P, and 4M2P). The temperature-dependent rate constants were determined and Arrhenius expressions were proposed to describe the reactions. The products studies revealed a series of carbonyl compounds, leading to proposed mechanistic degradation schemes initiated by OH reactions.