Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

Abstract

Abstract. Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85–1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV–visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

“…Aqueousphase methylglyoxal reaction products are expected to remain largely in the aerosol phase upon cloud droplet evaporation (Heaton et al, 2009;Loeffler et al, 2006). Syringol (2,6-dimethoxyphenol) and guaiacol (2-methoxyphenol) are also emitted in significant quantities from biomass burning, and previous studies have examined the bulk aqueous-phase photooxidation of syringol and guaiacol (Yu et al, 2014(Yu et al, , 2016, showing production of several CHO compounds that were also observed in the wildfire-influenced cloud water studied here (Table 3). Notably, aqueous SOA formation from phenolic compounds has been shown to enhance light absorption in the UV-visible region (Yu et al, 2014), suggesting that these brown carbon compounds in the cloud water may be important upon cloud droplet evaporation.…”

“…In addition, observations of likely dinitroaromatics during all air mass influences, potentially from aqueous nitration of nitroaromatic compounds, have important implications because of their light-absorbing and mutagenic properties (Purohit and Basu, 2000;Zhang et al, 2011Zhang et al, , 2013. During wildfire influence, the cloud water showed evidence of aqueous SOA formation, including oligomer formation involving methylglyoxal Yasmeen et al, 2010) and aqueousphase reactions of syringol and guaiacol (Yu et al, 2014(Yu et al, , 2016. Monoterpene-derived organosulfates and organonitrates (Surratt et al, 2008) were observed in the cloud water during all air mass influences, similar to previous cloud water studies (Boone et al, 2015;Pratt et al, 2013).…”

Particulate matter, air quality and climate: lessons learned and future needs

“…The coating of BC has been estimated to enhance its absorption by 50-200 %, depending on the relative sizes of the BC core and the coating (Bond et al, 2013). The optical properties of OA can also change due to atmospheric processing, due to aqueous phase reactions, as well as chemical reactions in the organic phase that can lead to the formation of absorbing species (Kitanovski et al, 2014;Yu et al, 2014). Such changes can lead to more scattering or absorption by aerosols and hence modify their direct radiative effect due to the scattering and absorption of incoming solar radiation.…”

Mixing state of oxalic acid containing particles in the rural area of Pearl River Delta, China: implications for the formation mechanism of oxalic acid

“…A number of ground-based and airborne field studies have found a close correlation between oxalic acid and sulfate in ambient particles and cloud droplets, relating aqueous-phase chemistry to the formation of oxalic acid in aerosols and cloud droplets (Yao et al, 2002(Yao et al, , 2003Yu et al, 2005;Sorooshian et al, 2006Sorooshian et al, , 2007aMiyazaki et al, 2009;Wonaschuetz et al, 2012;Wang et al, 2016). In recent years, several model and laboratory studies have suggested that the aqueous-phase oxidation of highly water-soluble organics like glyoxal, methylglyoxal and glyoxylic acid can efficiently produce oxalic acid in aerosol particles and cloud droplets (Lim et al, 2010;Myriokefalitakis et al, 2011;Ervens et al, 2014;Yu et al, 2014;McNeill, 2015). Recent stable carbon isotope studies and field observations have also suggested that oxalic acid forms through aqueous-phase reactions (Wang et al, 2012;Cheng et al, 2015).…”