Laboratory photochemical processing of aqueous aerosols: formation and degradation of dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls

Abstract

Abstract. To better understand the photochemical processing of dicarboxylic acids and related polar compounds, we conducted batch UV irradiation experiments on two types of aerosol samples collected from India, which represent anthropogenic (AA) and biogenic (BA) aerosols, for time periods of 0.5 to 120 h. The irradiated samples were analyzed for molecular compositions of diacids, oxoacids and α-dicarbonyls. The results show that photochemical degradation of oxalic (C 2 ), malonic (C 3 ) and other C 8 -C 12 diacids overwhelmed their production in aqueous aerosols, whereas succinic acid (C 4 ) and C 5 -C 7 diacids showed a significant increase (ca. 10 times) during the course of irradiation experiments. The photochemical formation of oxoacids and α-dicarbonyls overwhelmed their degradation during the early stages of experiment except for ω-oxooctanoic acid (ωC 8 ), which showed a similar pattern to that of C 4 . We also found a gradual decrease in the relative abundance of C 2 to total diacids and an increase in the relative abundance of C 4 during prolonged experiment. Based on the changes in concentrations and mass ratios of selected species with the irradiation time, we hypothesize that iron-catalyzed photolysis of C 2 and C 3 diacids controls their concentrations in Fe-rich atmospheric waters, whereas photochemical formation of C 4 diacid (via ωC 8 ) is enhanced with photochemical processing of aqueous aerosols in the atmosphere. This study demonstrates that the ambient aerosols contain abundant precursors that produce diacids, oxoacids and α-dicarbonyls, although some species such as oxalic acid decompose extensively during an early stage of photochemical processing.

Aircraft observations of water-soluble dicarboxylic acids in the aerosols over China

“…2b), which are the major organic compounds produced by the oxidation of anthropogenic cyclohexene and methylenecyclohexane (Hamilton et al, 2006;Muller et al, 2007). Although C 5 and C 6 diacids are the ozonolysis products in smog chamber studies, Pavuluri et al (2015) recently proposed that C 5 and C 6 are produced by photochemical processing of aqueous aerosols from a laboratory study. Such a molecular distri- Table 1 for abbreviations.…”

“…Indeed, from a model study it has been proposed that photochemical oxidation of isoprene and subsequent partitioning of water-soluble photooxidation products into the aqueous phase is a predominant formation pathway of oxalic acid (Myriokefalitakis et al, 2011). Most of the previous studies of diacids and other organic compounds in aerosols have been conducted at ground surface; however, only a few aircraft observations have been conducted over the arctic region (Talbot et al, 1992), the western North Pacific (Narukawa et al, 1999), the western rim of the Pacific Ocean (Kawamura et al, 2003), the coastal marine stratocumulus and cumulus clouds over USA (Crahan et al, 2004;Sorooshian et al, 2013Sorooshian et al, , 2007aWonaschuetz et al, 2012;Prabhakar et al, 2014) and over inland agricultural and urban areas in the western USA (Sorooshian et al, 2015). These aircraft experiments have revealed that water-soluble diacids may be produced by the photochemical oxidation of anthropogenic organic compounds in the atmosphere and thus play an important role in controlling the chemical and physical properties of OA in the troposphere.…”

Large contribution of fine carbonaceous aerosols from municipal waste burning inferred from distributions of diacids and fatty acids

“…Oxidation of organics in atmospheric waters are considered to be an important process that results in high abundance of oxalic (C 2 ) acid (Pavuluri et al 2015b). Such processing of aerosols is significant under strong solar radiation and high humid environment and thus enhances the loading of short-chain diacids and the fraction of total diacids and related compounds to OA (Yang et al 2008, Pavuluri et al 2015b.…”

“…Oxidation of organics in atmospheric waters are considered to be an important process that results in high abundance of oxalic (C 2 ) acid (Pavuluri et al 2015b). Such processing of aerosols is significant under strong solar radiation and high humid environment and thus enhances the loading of short-chain diacids and the fraction of total diacids and related compounds to OA (Yang et al 2008, Pavuluri et al 2015b. Generally, in terrestrial or marine aerosols, C 2 acid was often found as the most abundant species of diacids, followed by malonic (C 3 ) or C 4 acids, whereas in polar aerosols, C 4 acid found to be higher occasionally than that of C 2 , particularly in the samples collected under overcast conditions with brume events Ikushima 1993, Kawamura et al 2005).…”

“…Moreover, some diacid species such as adipic (C 6 ), azelaic (C 9 ) and t-Ph acids are mainly derived from specific compounds originated from fossil fuel combustion, biogenic, and plastic (municipal waste) burning respectively (Kawamura and Gagosian 1987, Kawamura et al 1996. Therefore, distributions of diacids including diurnal changes together with mass ratios of selected species would provide insights on their origins and secondary formation and transformation processes (Pavuluri et al 2015b, Sorathia et al 2018.…”