The oxidation regime and SOA composition in limonene ozonolysis: roles of different double bonds, radicals, and water

Abstract

Abstract. Volatile organic compounds play an important role in air quality and climate change, largely because they contribute to the formation of oxidizing compounds and secondary organic aerosol (SOA). In this study, a series of products, including peroxides and carbonyl compounds in both gaseous and particulate phases, were simultaneously detected to investigate the oxidation regime and SOA composition in limonene ozonolysis. The roles of different double bonds (DBs), radicals, and water were also examined. In our first investigation, we focused on representative oxidizing compounds produced in limonene ozonolysis, including stabilized Criegee intermediates (SCIs), OH radicals, and peroxides. The dependence of H2O2 and hydroxymethyl hydroperoxide (HMHP) formation on RH demonstrates that the reaction with water is an important reaction pathway for limonene SCIs, and the lower limit SCI yields of endocyclic and exocyclic DBs were estimated to be ∼0.24 and ∼0.43, respectively. The OH yield was determined by adding sufficient amounts of an OH scavenger, and the OH yields of endocyclic and exocyclic DBs were ∼0.65 and ∼0.24, respectively. These results indicate that in limonene ozonolysis the endocyclic DB is inclined to generate OH radicals through the hydroperoxide channel, while the exocyclic DB has a higher fraction of forming SCIs. Additionally, other gas-phase and particle-phase peroxides were also studied in this work. The formation of performic acid (PFA) and peracetic acid (PAA) was promoted significantly by increasing RH and the degree of oxidation, and the discrepancy between the experimental and model results suggested some missing formation pathways. Considerable generation of H2O2 from SOA in the aqueous phase was observed, especially at a high [O3] ∕ [limonene] ratio, which was mainly attributed to the hydration and decomposition of unstable peroxides in SOA such as peroxycarboxylic acids and peroxyhemiacetals. Different DBs and OH scavengers had a large impact on the particulate peroxides, and their stability indicated that the types of peroxides in SOA changed under different conditions. As for the contribution of peroxides to SOA, the results demonstrated that the mass fraction of particulate peroxides in limonene SOA was less than 0.2 at a low [O3] ∕ [limonene] ratio, while the mass fraction was 0.4–0.6 at a high [O3] ∕ [limonene] ratio. The partitioning behavior of peroxides showed that multi-generation oxidation helped produce more low-volatility peroxides, which partially explained the higher SOA yield. The partitioning behavior of carbonyls was also examined and the experimental partitioning coefficients (Kp) were found to be typically several orders of magnitude higher than the theoretical values. This study provided new insights into the oxidation regime and SOA composition in limonene ozonolysis, and limonene showed its specificity in many aspects when both endocyclic and exocyclic DBs were ozonated. We suggest that the atmospheric implications of terpenes containing more than one DB and the SOA composition, especially particulate peroxides, need further study.

Partitioning of hydrogen peroxide in gas-liquid and gas-aerosol phases

“…(S1) to (S4) in the Supplement (Levine and Schwartz, 1982;Kumar, 1985). The concentration of H 2 O 2 in the droplet at the ground (C d aq ) can a These parameters are calculated based on equations in Gunn and Kinzer (1949), Levine and Schwartz (1982), Kumar (1985), and Seinfeld and Pandis (2006). b u is the terminal fall velocity of a raindrop.…”

Quantification of the role of stabilized Criegee intermediates in the formation of aerosols in limonene ozonolysis

“…In the ozonolysis of alkenes, the presence of water changes the reaction pathways of SCIs, while the yields of products, such as peroxides and carbonyls, formed from SCI reactions with water have been reported to vary widely (Berndt et al, 2003;Huang et al, 2013;Li et al, 2016). Furthermore, the dependences of these products on relative humidity (RH) have been a point of controversy (Anglada et al, 2002;Hasson et al, 2001Hasson et al, , 2003Ma et al, 2008;Tillmann et al, 2010). In an ozonolysis system examining the effects of the addition of compounds that could be oxidized by SCIs, the presence of water had different effects on the consumption of these added reactants (Newland et al, 2018;Sipilä et al, 2014;Ye et al, 2018).…”

Carboxylic acids from limonene oxidation by ozone and hydroxyl radicals: insights into mechanisms derived using a FIGAERO-CIMS

“…(Brown et al, 1994;Langer et al, 2008) as well as subsequent SOA formation (Youssefi and Waring, 2014). The total global forest emission of limonene has been estimated at 11.4 Tg yr −1 , placing it in the top four among monoterpenes (Guenther et al, 2012). A high aerosol yield and the two chemically different double bonds, an endocyclic and an exocyclic double bond, make limonene ozonolysis of specific interest (Koch et al, 2000;Saathoff et al, 2009;Chen and Hopke, 2010;Gong et al, 2018).…”