Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction

Abstract

Organic peroxy radicals (RO 2 ), formed from the degradation of hydrocarbons and other volatile organic compounds (VOCs), play a key role in tropospheric oxidation mechanisms. Several competing reactions may be available for a given RO 2 radical, the relative rates of which depend on both the structure of RO 2 and the ambient conditions. Published kinetics and branching ratio data are reviewed for the bimolecular reactions of RO 2 with NO, NO 2 , NO 3 , OH and HO 2 ; and for their self-reactions and cross-reactions with other RO 2 radicals. This information is used to define generic rate coefficients and structure-activity relationship (SAR) methods that can be applied to the bimolecular reactions of a series of important classes of hydrocarbon and oxygenated RO 2 radicals. Information for selected unimolecular isomerization reactions (i.e. H-atom shift and ring-closure reactions) is also summarized and discussed. The methods presented here are intended to guide the representation of RO 2 radical chemistry in the next generation of explicit detailed chemical mechanisms.Under tropospheric conditions, a given RO 2 radical may have several competing reactions available, the relative rates of which are dependent both on the prevailing ambient conditions and on the structure of RO 2 . These include a series of bimolecular reactions (i.e. with NO, NO 2 , NO 3 , OH and HO 2 ; and the self-reaction and cross-reactions with the multitude of other RO 2 radicals present in the atmosphere), which are generally available for all RO 2 radicals; and specific unimolecular isomerization reactions (i.e. H-atom shiftPublished by Copernicus Publications on behalf of the European Geosciences Union.

Aerosol mass yields of selected biogenic volatile organic compounds – a theoretical study with nearly explicit gas-phase chemistry

“…As NO concentrations exceed 1ppb the first-generation RO 2 is scavenged by NO, thereby reducing the concentration of organonitrate HOM (Ehn et al, 2014), possibly affecting SOA yields. The MCM contribution also decreases with increasing NO concentra-tions mostly due to the formation of more volatile organonitrates (Jenkin et al, 2019).…”

CRI-HOM: A novel chemical mechanism for simulating Highly Oxygenated Organic Molecules (HOMs) in global chemistry-aerosol-climate models

“…In addition, TNCARB26 (closed shell carbonyl species) and RCOOH25 (pinonic acid) arise from the reaction of Criegee intermediates with water. RN18AO2 goes on to react with standard peroxy radical reaction partners; 195 HO2 forming hydroperoxides; NO and NO3 forming alkoxy radicals; and the peroxy radical pool forming alkoxy radicals, carbonyls and alcohols, as described in (Jenkin et al, 2019a).…”

“…The first order rate constants for autoxidation can vary over several orders of magnitude (~10 -6 -10 2 s -1 ) depending on nearby functional groups (Bianchi et al, 2019, Crounse et al, 2013, Xu et al, 105 2018, Kurten et al, 2015. Autoxidation rates also exhibit a significant positive temperature dependence (Jenkin et al, 2019a, Bianchi et al, 2019 and HOM yield has been observed to be highly temperature dependent (Quéléver et al, 2019). Thus, the overall competitiveness of autoxidation is dependent on the background atmospheric composition and ambient temperature as well as the molecule undergoing oxidation.…”

“…In addition to autoxidation, the formation of HOM accretion products (also called dimers (Kurten et al, 2016, Bianchi et al, 2019) by reactions between two peroxy radicals has been observed to be significant with large peroxy radicals (Kirkby et al, 2016, Berndt et al, 2018a, Berndt et al, 2018b, Jenkin et al, 2019a, Molteni et al, 2019. These species are predicted to be more involatile than 10-carbon HOMs (also termed monomers (Kurten et al, 2016)) with important implications for new particle formation and contribution to SOA.…”

“…3) and alkoxy radicals ("C10RO" and "C5RO") (Eq. 4) which isomerise or fragment (Jenkin et al, 2019a). 10 2 + 10 2 → 20 + 2 (1) 150 10 2 + 5 2 → 15 + 2 (2) 10 2 + 10 2 → 10 + 5 + 2 (3) 10 2 + 10 2 → 10 + 5 + 2 (4) 155…”