Abstract
Abstract. Although secondary organic aerosol (SOA) is a major component of PM2.5 and organic aerosol (OA) particles and therefore profoundly influences air quality, climate forcing, and human health, the mechanism of SOA formation via Criegee chemistry is poorly understood. Herein, we perform high-level theoretical calculations to study the gas-phase reaction mechanism and kinetics of four Criegee intermediate (CI) reactions with four hydroxyalkyl hydroperoxides (HHPs) for the first time. The calculated results show that the consecutive reactions of CIs with HHPs are both thermochemically and kinetically favored, and the oligomers contain CIs as chain units. The addition of an −OOH group in HHPs to the central carbon atom of CIs is identified as the most energetically favorable channel, with a barrier height strongly dependent on both CI substituent number (one or two) and position (syn- or anti-). In particular, the introduction of a methyl group into the anti-position significantly increases the rate coefficient, and a dramatic decrease is observed when the methyl group is introduced into the syn-position. These findings are expected to broaden the reactivity profile and deepen our understanding of atmospheric SOA formation processes.
Highlights
Alkenes are the most abundant volatile organic compounds (VOCs) in the atmosphere after methane and primarily originate from anthropogenic and biogenic sources (Lester and Klippenstein, 2018; Guenther et al, 2000)
Alkene ozonolysis produces a carbonyl oxide and a carbonyl moiety (Donahue et al, 2011a; Aplincourt and Ruiz-López, 2000; Johnson and Marston, 2008; Welz et al, 2012; Criegee, 1975; Taatjes et al, 2013), which is thought to be an important source of radicals, whose subsequent reactions lead to the formation of hydroperoxides, organic peroxides, and secondary organic aerosol (SOA) (Donahue et al, 2011a; Becker et al, 1990; Kroll and Seinfeld, 2008; Hallquist et al, 2009; Tobias and Ziemann, 2001)
The carbonyl oxides considered in this work (CH2OO, synand anti-CH3CHOO, and (CH3)2COO) are anticipated upon the ozonolysis of ethylene, propylene, isobutene, and 2,3dimethyl-2-butene, while the investigated hydroxyalkyl hydroperoxides (HHPs) are assumed to arise from bimolecular reactions with water vapor in the troposphere
Summary
Alkenes are the most abundant volatile organic compounds (VOCs) in the atmosphere after methane and primarily originate from anthropogenic and biogenic sources (Lester and Klippenstein, 2018; Guenther et al, 2000). Wang et al (2016) investigated the heterogeneous ozonolysis of oleic acid (OL) using an aerosol flow tube and found that reactions of particulate SCIs generate highmolecular-weight oligomers with low volatility that are preferentially partitioned into the particle phase to promote SOA formation They confirmed that the SCI-based mechanism is the dominant pathway in the formation of high-molecularweight oligomers. We mainly focus on the gas-phase oligomerization reaction of carbonyl oxides with HHPs, leading to the formation of high-molecular-weight oligomers under atmospheric conditions This reaction represents the initial step of oligomer formation and growth during alkene ozonolysis and needs to be extensively characterized to gain deeper insights into the fundamental chemical composition of these oligomers in the atmosphere. The carbonyl oxides considered in this work (CH2OO, synand anti-CH3CHOO, and (CH3)2COO) are anticipated upon the ozonolysis of ethylene, propylene, isobutene, and 2,3dimethyl-2-butene, while the investigated HHPs are assumed to arise from bimolecular reactions with water vapor in the troposphere
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