Response to comment SC2 by Barbara Nozière

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. Published by Copernicus Publications on behalf of the European Geosciences Union. β-Hydroxyalkyl HOCH 2 CH 2 O 2 8.7 c propene-derived 9.5 c,d but-1-ene-derived 9.6 c,e CH 3 CH(OH)CH(O 2)CH 3 9.4 c methylpropene-derived 9.6 c,f Hydroxyalkenyl buta-1,3-diene-derived 8.8 c,g isoprene-derived 8.8 a,c,h Oxoalkyl CH 3 C(O)CH 2 O 2 8.0 a,i Hydroxy-oxyalkyl methacrolein-derived 9.3 j,k methyl vinyl ketone-derived 8.4 j,l Hydroxy-dioxa-bicyclo 1,3,5-trimethylbenzene-derived 7.7 m Acyl CH 3 C(O)O 2 7.5 −290 20 a C 2 H 5 C(O)O 2 6.7 −340 21 a CH 2 =CH(CH 3)C(O)O 2 8.7 −290 23 n C(O)(OOH)CH 2 CH 2 CH 2 CH(OOH)C(O)O 2 34 o Comments: a IUPAC Task Group recommendation (http://iupac.pole-ether.fr/, last access: January 2019). b Based on Eberhard and Howard (1996, 1997), Eberhard et al. (1996). c Based on Miller et al. (2004). d Mixture of CH 2 (OH)CH(O 2)CH 3 and CH 2 (O 2)CH(OH)CH 3. e Mixture of CH 2 (OH)CH(O 2)C 2 H 5 and CH 2 (O 2)CH(OH)C 2 H 5. f Mixture of CH 2 (OH)C(O 2)(CH 3) 2 and CH 2 (O 2)C(OH)(CH 3) 2. g Mixture of CH 2 (OH)CH(O 2)CH=CH 2 , CH 2 (OH)CH=CHCH 2 O 2 and CH 2 (O 2)CH(OH)CH=CH 2. h Mixture of CH 2 (OH)C(O 2)(CH 3)CH=CH 2 , CH 2 (OH)C(CH 3)=CHCH 2 O 2 , CH 2 (O 2)C(CH 3)(OH)CH=CH 2 , CH 2 (OH)CH(O 2)C(CH 3)=CH 2 , CH 2 (OH)CH=C(CH 3)CH 2 O 2 and CH 2 (O 2)CH(OH)C(CH 3)=CH 2. i Based on Sehested et al. (1998). j Based on Hsin and Elrod (2007). k Mixture of CH 2 (OH)C(O 2)(CH 3)CHO and CH 2 (O 2)C(OH)(CH 3)CHO. l Mixture of CH 2 (OH)CH(O 2)C(=O)CH 3 and CH 2 (O 2)CH(OH)C(=O)CH 3. m Elrod (2011). Mixture of two complex radicals of molecular formula HOC 9 H 12 [OO]O 2 , although with one isomer likely dominant. n De Gouw and Howard (1997). o Berndt et al. (2015). Inferred to be the complex oxo-di-hydroperoxy acyl peroxy radical shown, on the basis of its molecular mass and a proposed mechanism.