A Product Yield Study of the Reaction of HO₂ Radicals with Ethyl Peroxy (C₂H₅O₂), Acetyl Peroxy (CH₃C(O)O₂), and Acetonyl Peroxy (CH₃C(O)CH₂O₂) Radicals

Abstract

The reaction between HO2 and RO2 radicals represents an important chemical sink for HO x radicals in the atmosphere. On the basis of a few product yield studies, these reactions are believed to form hydroperoxides almost exclusively (R8a), although several different reaction channels may be thermodynamically accessible (R8a−d): RO2 + HO2 → ROOH + O2 (R8a); RO2 + HO2 → ROH + O3 (R8b); RO2 + HO2 → RO + OH + O2 (R8c); and RO2 + HO2 → R‘CHO + H2O + O2 (R8d). Branching ratios for reaction R8 were measured for three organic peroxy radicals: ethyl peroxy (C2H5O2), acetyl peroxy (CH3C(O)O2), and acetonyl peroxy (CH3C(O)CH2O2) radicals. Product yields were measured using a combination of long-path Fourier transform infrared spectroscopy and high-performance liquid chromatography with fluorescence detection. Measured branching ratios for the reaction of the three organic peroxy radicals with HO2 are as follows: ethyl peroxy, Y 8a - ETH > 0.93 ± 0.10, Y 8b - ETH = Y 8c - ETH = Y 8d - ETH = 0; acetyl peroxy, Y 8a - ACT = 0.40 ± 0.16, Y 8b - ACT = 0.20 ± 0.08, Y 8c - ACT = 0.40 ± 0.16, and Y 8d - ACT = 0; acetonyl peroxy, Y 8a - ACN = 0.33 ± 0.10, Y 8b - ACN = Y 8d - ACN = 0, and Y 8c - ACN = 0.67 ± 0.20. The atmospheric implications of these branching ratios are discussed.

Observations of elevated formaldehyde over a forest canopy suggest missing sources from rapid oxidation of arboreal hydrocarbons

“…Recent studies proposed that a new channel of PA + HO 2 reaction can be important with a branching ratio of 0.4 Hasson et al, 2004;Jenkin et al, 2007), through which CH 3 O 2 is produced, and therefore this new finding can be a potential HCHO source. We added the new HCHO producing channel of PA + HO 2 reaction in the HCHO production calculation (Eq.…”

“…The HCHO production mechansim via CH 4 oxidation is described in detail by Fried et al (1997). The lifetime of CH 4 at 298K with 6 × 10 6 molecule cm −3 OH is ∼10 months (Atkinson et al, 2006), and hence it is assumed that CH 4 is homogeneously distributed throughout the boundary layer at a concentration of 1.774 ppm (IPCC, 2007 Grosjean and Grosjean (1995) Fantechi et al (1999), 0.29 from Alvarado et al (1999), and 0.36 from Grosjean and Grosjean, 1995 al., 2006; Klotz et al, 2001;Koch and Moortgat, 1998;LaFranchi et al, 2009;Orlando et al, 1999;Tuazon and Atkinson, 1989 Hasson et al, 2004;Jenkin et al, 2007), which, upon decomposition and reaction with O 2 forms CH 3 O 2 (Reactions R13-R15 in Appendix C). We assume that CH 3 O 2 is rapidly converted into HCHO.…”

Direct measurements of OH and other product yields from the HO<sub>2</sub> + CH<sub>3</sub>C(O)O<sub>2</sub> reaction

“…Hasson et al (2004) observed, using chamber studies and measuring stable products, that certain peroxy radical + hydroperoxy radical reactions such as the title reaction of acetylperoxy, CH 3 C(O)O 2 , can lead to the formation of OH radicals through a third channel (Reaction R5c). Previous studies had assumed radical termination through Reaction (R5a) (α (R5a) = k (R5a) /k (R5) = 0.8) and Reaction (R5b) (α (R5b) = k R5b /k R5 = 0.2) (Lightfoot et al, 1992;Moortgat et al, 1989;Crawford et al, 1999).…”

“…Orlando and Tyndall (2003) were able to demonstrate that an underestimated IR cross-section for peracetic acid, CH 3 C(O)OOH (Reaction R5a), had led to the assignment of α (R5a) 3 times too high. Based on this revised cross-section, Hasson et al (2004) measured yields of (0.40 ± 0.16) : (0.20 ± 0.08) : (0.40 ± 0.16) for α (R5a) : α (R5b) : α (R5c) . In equivalent reactions of the alkyl peroxy radical, C 2 H 5 O 2 , with HO 2 , only channel (Reaction R4a) producing C 2 H 5 OOH + O 2 was observed.…”

Atmospheric photochemistry of aromatic hydrocarbons: OH budgets during SAPHIR chamber experiments

“…The differences of the ratios could also be caused by additional OH recycling via HO 2 + RO 2 reactions that gain importance under low-NO conditions. Such radical-radical reactions that are usually thought to produce non-radical products can lead to enhanced OH recycling as shown by recent laboratory studies for reactions of carbonyl-containing RO 2 radicals with HO 2 (Hasson et al, 2004(Hasson et al, , 2012Jenkin et al, 2007Jenkin et al, , 2008Jenkin et al, , 2010Dillon and Crowley, 2008;Groß et al, 2014). Recently also OH formation for the reaction of HO 2 with bicyclic peroxy radicals from aromatic precursors was proposed with a rate constant k 9 as used in the previous section.…”