Radical oxidation of methyl vinyl ketone and methacrolein in aqueous droplets: Characterization of organosulfates and atmospheric implications

Abstract

In-cloud processing of volatile organic compounds is one of the significant routes leading to secondary organic aerosol (SOA) in the lower troposphere. In this study, we demonstrate that two atmospherically relevant α,β-unsaturated carbonyls, i.e., but-3-en-2-on (methyl vinyl ketone, MVK) and 2-methylopropenal (methacrolein, MACR), undergo sulfate radical-induced transformations in dilute aqueous systems under photochemical conditions to form organosulfates previously identified in ambient aerosols and SOA generated in smog chambers. The photooxidation was performed under sun irradiation in unbuffered aqueous solutions containing carbonyl precursors at a concentration of 0.2 mmol and peroxydisulfate as a source of sulfate radicals (SO) at a concentration of 0.95 mmol. UV-vis analysis of solutions showed the fast decay of unsaturated carbonyl precursors in the presence of sulfate radicals. The observation confirms the capacity of sulfate radicals to transform the organic compounds into SOA components in atmospheric waters. Detailed interpretation of high-resolution negative ion electrospray ionization tandem mass spectra allowed to assign molecular structures to multiple aqueous organosulfate products, including an abundant isoprene-derived organosulfate CHSO detected at m/z 199. The results highlight the solar aqueous-phase reactions as a potentially significant route for biogenic SOA production in clouds at locations where isoprene oxidation occurs. A recent modelling study suggests that such processes could likely contribute to 20-30 Tg year production of SOA, referred to as aqSOA, which is a non-negligible addition to the still underestimated budget of atmospheric aerosol.

Molecular Characterization of Organosulfates in Highly Polluted Atmosphere Using Ultra‐High‐Resolution Mass Spectrometry

“…The specific reason was shown in the chemical mechanism in Figure 4a and further explored below. In addition, C 5 H 11 O 3 SO 4 − and C 4 H 7 O 3 SO 4 − could also be produced through the sulfate radical‐induced oxidation of MVK and MACR (Noziere et al, 2010; Schindelka et al, 2013; Wach et al, 2019). This fact could be confirmed by strong correlations ( r ≥ 0.59, p < 0.01) between isoprene‐derived OSs and oxidation products (MVK + MACR) in summer (Figure S6).…”

Organosulfates in atmospheric aerosols in Shanghai, China: seasonal and interannual variability, origin, and formation mechanisms

“…The C5H7O7Sand C5H9O7Sspecies can be produced by photooxidation of isoprene (Surratt et al, 2008;Nestorowicz et al, 2018) and/or the oxidative aging of methyltetrol sulfate (Hettiyadura et al, 2015). The C4H7O6Scan be generated both from sulfate radical reaction with MACR/MVK (Noziè re et al, 2010; Schindelka et al, 2013;Wach et al, 2019) and isoprene photooxidation (Surratt et al, 2007a;Lin et al, 2013;Nestorowicz et al, 2018). The C5H7O7Sand C4H7O6Sare also consistent in molecular formula with the OS species formed https://doi.org/10.5194/acp-2020-784 Preprint.…”

Thermodynamic properties of isoprene- and monoterpene-derived organosulfates estimated with COSMO&lt;i&gt;therm&lt;/i&gt;

“…Multiple laboratory studies have shown that organosulfates are formed in the condensed phase from reactions between organic molecules and either a sulfate ion (SO 2− 4 ) (Iinuma et al, 2009;Minerath and Elrod, 2009) or a sulfate radical (SO •− 4 ) (Schindelka et al, 2013;Wach et al, 2019). Organosulfates have been seen to form, for instance, from oxidation products of monoterpenes (Surratt et al, 2008) and pinonaldehyde (Liggio and Li, 2006) in the presence of acidified sulfate seed and from isoprene-derived organosulfates in the presence of sulfate (Darer et al, 2011).…”