Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance

Abstract

Organic peroxy radicals (often abbreviated RO(2)) play a central role in the chemistry of the Earth's lower atmosphere. Formed in the atmospheric oxidation of essentially every organic species emitted, their chemistry is part of the radical cycles that control the oxidative capacity of the atmosphere and lead to the formation of ozone, organic nitrates, organic acids, particulate matter and other so-called secondary pollutants. In this review, laboratory studies of this peroxy radical chemistry are detailed, as they pertain to the chemistry of the atmosphere. First, a brief discussion of methods used to detect the peroxy radicals in the laboratory is presented. Then, the basic reaction pathways - involving RO(2) unimolecular reactions and bimolecular reactions with atmospheric constituents such as NO, NO(2), NO(3), O(3), halogen oxides, HO(2), and other RO(2) species - are discussed. For each of these reaction pathways, basic reaction rates are presented, along with trends in reactivity with radical structure. Focus is placed on recent advances in detection methods and on recent advances in our understanding of radical cycling processes, particularly pertaining to the complex chemistry associated with the atmospheric oxidation of biogenic hydrocarbons.

Role of the reaction of stabilized Criegee intermediates with peroxy radicals in particle formation and growth in air

“…For example, RO 2 radicals can also react with NO, HO 2 , and other RO 2 in the atmosphere, with the relative importance depending particularly on the NO concentration. 5,45,92 Vereecken et al 45 suggested that in a tropical forest area (e.g., Suriname) the RO 2 + SCI reactions accounted for only 0.1% of RO 2 losses, assuming a rate constant of 5 Â 10 À12 cm 3 molecules À1 s À1 . However, they point out that this rate constant was a conservative estimate and it could be on the order of 10 À11 cm 3 molecules À1 s À1 .…”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Broadly speaking, the RO2 + NO reaction can be classed as the most important of the RO 2 loss reactions to include for modelling O 3 production in the troposphere. The products of the reaction between RO 2 and HO 2 depend strongly on the structure of the RO 2 (Orlando and Tyndall, 2012). Traditionally the reaction between RO 2 and HO 2 has been thought of as a radical sink, hence limiting the propagation of RO 2 + NO reactions and so reducing the potential O 3 production.…”

“…Significant use of the review of Orlando and Tyndall (Orlando and Tyndall, 2012) is made and for further details we refer the reader to their work.…”

Stochastic methods for aerosol chemistry: a compact molecular description of functionalization and fragmentation in the heterogeneous oxidation of squalane aerosol by OH radicals

“…Indeed, gas phase product studies of RO2 selfreactions show that alcohols and ketones are formed in equal yields. [13][14][15] Later condensed phase studies of the oxidation of alkanes showed that the reaction actually favored ketones over alcohols at room temperature as in (R1), with more ketones at lower temperatures and more alcohols at higher temperatures. 18 These results suggested that the one to one ratio of ketones and alcohols observed by Russell 17 was a special case and that the ratio could vary depending on molecular structure.…”

“…10 Furthermore, the "branching ratio" between these two pathways was found to be dependent on molecular structure, with more branched and more oxidized hydrocarbons undergoing more fragmentation than functionalization. 11,12 For both of these oxidation pathways, the central intermediate is an organic peroxy radical (RO2), formed from the addition of molecular oxygen to the alkyl radical formed via hydrogen abstraction by OH as shown in Figure 1.. Peroxy radicals undergo several possible self-reactions [13][14][15] to form alcohols, ketones, and alkoxy radicals. While all of these peroxy reactions will result in functionalized products, β-scission of an alkoxy radical (R6) is the only known pathway that leads to fragmentation products.…”