Tracing the biogenic secondary organic aerosol markers in rain, snow and hail

Heterogeneous Hydroxyl Radical Oxidation of Isoprene-Epoxydiol-Derived Methyltetrol Sulfates: Plausible Formation Mechanisms of Previously Unexplained Organosulfates in Ambient Fine Aerosols

“…Heterogeneous • OH oxidation increases the functionalities and oxygen content of 2-MTS aerosols, as indicated by increased oxygen-to-carbon ratios (O:C) of the oxidation products (Table S2). Both the oxidation state and functionalities will affect the aerosol volatility, viscosity, acidity, morphology, and hygroscopicity. ,− Therefore, these aerosol physicochemical properties are expected to change for aged IEPOX-derived SOA, likely governing its climate-relevant properties by acting as cloud condensation or ice nuclei. , We postulate that 2-MTSs oxidation by • OH may also take place in cloudwater, since 2-MTSs and related OSs ( m / z 199, 211, 213, 229), have been observed in cloudwater, rainwater, and hailstone samples collected over forested areas. − Cloudwater • OH oxidation of 2-MTSs may contribute (in part) to the multifunctional nature of particulate OSs through cloud droplet evaporation. The role of cloud processing on particulate OS composition remains unclear and warrants future investigation.…”

Isoprene Epoxydiol-Derived Sulfated and Nonsulfated Oligomers Suppress Particulate Mass Loss during Oxidative Aging of Secondary Organic Aerosol

“…13 MTSs and other isoprene-derived OSs have also been measured in submicron particles in the upper troposphere, 14−16 cloud water, 17,18 and other forms of precipitation such as hailstones and rain. 19 The low volatility of IEPOXderived OSs is thought to contribute to cloud formation 20,21 and lead to long atmospheric lifetimes of IEPOX-SOA, with removal only by particle deposition. 11,15 Though some atmospheric chemistry models include the formation of IEPOX-SOA, most assume that IEPOX-SOA and its particulate OSs remain unreactive.…”

“…In isoprene-rich regions, the IEPOX-derived methyltetrol sulfates (MTSs) are among the most abundant compounds in PM 2.5 , contributing up to 13% of the total organic carbon in PM 2.5 collected in downtown Atlanta, GA, up to 10% of OA mass at Look Rock, TN, and Manaus, Brazil, and up to 15% of total organic matter collected at Lake Michigan . MTSs and other isoprene-derived OSs have also been measured in submicron particles in the upper troposphere, − cloud water, , and other forms of precipitation such as hailstones and rain . The low volatility of IEPOX-derived OSs is thought to contribute to cloud formation , and lead to long atmospheric lifetimes of IEPOX-SOA, with removal only by particle deposition. , Though some atmospheric chemistry models include the formation of IEPOX-SOA, most assume that IEPOX-SOA and its particulate OSs remain unreactive. − A potential mechanism for the loss of OS-containing particle mass is • OH oxidation and fragmentation of the C 5 isoprene skeleton into lower-molecular-weight (MW) compounds that partition into the gas phase. − If volatilization as a result of heterogeneous • OH oxidation is substantial, it would impact the lifetime and effects of IEPOX-SOA.…”

Organosulfates from Dark Aqueous Reactions of Isoprene-Derived Epoxydiols Under Cloud and Fog Conditions: Kinetics, Mechanism, and Effect of Reaction Environment on Regioselectivity of Sulfate Addition

“…Dissolved organic carbon has long been detected in fogs and clouds, indicating the potential for dilute aqueous solutions to result in appreciable aerosol mass after water evaporation. − Cloud chemistry studies have focused on the quantification of carboxylic acids and carbonyls − resulting from the oxidation of glyoxal, methylglyoxal, and pyruvic acid, − but recent work indicates that epoxides, including IEPOX, may also serve as precursors to the production of low-volatility species in cloudwater. , IEPOX is relatively water-soluble; estimates of the Henry’s Law constant for IEPOX range from 2.7 × 10 6 to 1.7 × 10 8 M atm –1 , ,− rivaling those of glyoxal, methylglyoxal, and pyruvic acid, whose Henry’s Law constants are 0.36–50 × 10 6 , − 0.35–3.2 × 10 4 , − and 3.1 × 10 5 M atm –1 , ,− respectively. Organosulfates have been detected in cloud and fog waters, as well as in precipitation (rain, snow, and hail), ,− including abundant 2-MTS isomers, observed by electrospray ionization mass spectrometry (ESI-MS) as deprotonated ions at mass-to-charge ratios ( m / z ) 215, specifically attributable to IEPOX-derived MTSs, , prompting a question as to whether cloud/fog processing could be a source of IEPOX-derived organosulfates. Although much of the knowledge of IEPOX-derived MTSs originates from chamber and flow tube studies using acidified aerosols, , aerosol formation from IEPOX measured during field campaigns does not universally trend with estimates of aerosol acidity. , This also highlights the possibility of cloudwater formation of IEPOX SOA and has prompted recent studies of acid-catalyzed IEPOX reactions modeled at cloud-relevant aqueous concentrations and experimental OH radical-initiated aqueous oxidation of IEPOX .…”