Investigation of the Gas-Phase Photolysis and Temperature-Dependent OH Reaction Kinetics of 4-Hydroxy-2-butanone

Abstract

Hydroxyketones are key secondary reaction products in the atmospheric oxidation of volatile organic compounds (VOCs). The fate of these oxygenated VOCs is however poorly understood and scarcely taken into account in atmospheric chemistry modeling. In this work, a combined investigation of the photolysis and temperature-dependent OH radical reaction of 4-hydroxy-2-butanone (4H2B) is presented. The objective was to evaluate the importance of the photolysis process relative to OH oxidation in the atmospheric degradation of 4H2B. A photolysis lifetime of about 26 days was estimated with an effective quantum yield of 0.08. For the first time, the occurrence of a Norrish II mechanism was hypothesized following the observation of acetone among photolysis products. The OH reaction rate coefficient follows the Arrhenius trend (280-358 K) and could be modeled through the following expression: k4H2B(T) = (1.26 ± 0.40) × 10(-12) × exp((398 ± 87)/T) in cm(3) molecule(-1) s(-1). An atmospheric lifetime of 2.4 days regarding the OH + 4H2B reaction was evaluated, indicating that OH oxidation is by far the major degradation channel. The present work underlines the need for further studies on the atmospheric fate of oxygenated VOCs.

Kinetics of the photolysis and OH reaction of 4-hydroxy-4-methyl-2-pentanone: Atmospheric implications

“…An overall QY of 0.15 was obtained for the atmospheric windows, in good agreement with the estimation of Magneron et al (2003) of <0.20. This QY is somewhat larger than those determined previously for 3H3M2B (0.10) (Bouzidi et al, 2014) and 4H2B (0.08) (Bouzidi et al, 2015).…”

“…As for the similar b-hydroxyketone 4H2B (Bouzidi et al, 2015) proposed in a previous work of the same laboratories, a Norrish II photodissociation pathway may also be expected implying an intramolecular rearrangement with H-atom transfer as displayed on Scheme 1. In this proposed mechanism, two molecules of acetone are produced by each molecule of 4H4M2P photolyzed, i.e.…”

“…Therefore, 4H4M2P photolysis may represent up to 20% of the gasphase degradation of this compound in the atmosphere. Comparing with 4H2B (4-hydroxy-2-butanone) and 3H3M2B (3-hydroxy-3- methyl-2-butanone) for which lifetimes of 26 and 4e5 days towards photolysis were calculated (Bouzidi et al, 2014(Bouzidi et al, , 2015, respectively, emphasizes the role of the molecular structure and absorption properties on the atmospheric fate of hydroxyketones. Hence, the present results underline the need for a precise knowledge of hydroxyketone photolysis under real conditions to better constrain atmospheric chemistry models.…”

“…Conversely, for 4-hydroxy-2-butanone (4H2B), photolysis is negligible and OH initiated oxidation represents the main fate (Bouzidi et al, 2015), due to both a higher OH reactivity and a lower photo-activity compared to 3H3M2B. In their analysis of summertime photochemistry during the measurement campaign CAREBeijing in 2007, Liu et al (2012) reported that the photolysis of oxygenated volatile organic compounds is the largest primary peroxy radical source in Beijing urban atmosphere.…”

Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling

“…We also note that the ratio of O( 1 D) exp / OH exp in the OFR is actually much lower than in the troposphere (Monks, 2005), except under some riskier conditions. It is believed that the contribution of O( 1 D) to VOC destruction in the atmosphere should be negligible (Calvert et al, 2002), and their relative importance is even lower under most OFR conditions. Reactions with O( 3 P) are small or negligible contributors to VOC consumption except under extreme riskier conditions.…”