Organosulfate Formation in Biogenic Secondary Organic Aerosol

Abstract

Organosulfates of isoprene, alpha-pinene, and beta-pinene have recently been identified in both laboratory-generated and ambient secondary organic aerosol (SOA). In this study, the mechanism and ubiquity of organosulfate formation in biogenic SOA is investigated by a comprehensive series of laboratory photooxidation (i.e., OH-initiated oxidation) and nighttime oxidation (i.e., NO3-initiated oxidation under dark conditions) experiments using nine monoterpenes (alpha-pinene, beta-pinene, d-limonene, l-limonene, alpha-terpinene, gamma-terpinene, terpinolene, Delta(3)-carene, and beta-phellandrene) and three monoterpenes (alpha-pinene, d-limonene, and l-limonene), respectively. Organosulfates were characterized using liquid chromatographic techniques coupled to electrospray ionization combined with both linear ion trap and high-resolution time-of-flight mass spectrometry. Organosulfates are formed only when monoterpenes are oxidized in the presence of acidified sulfate seed aerosol, a result consistent with prior work. Archived laboratory-generated isoprene SOA and ambient filter samples collected from the southeastern U.S. were reexamined for organosulfates. By comparing the tandem mass spectrometric and accurate mass measurements collected for both the laboratory-generated and ambient aerosol, previously uncharacterized ambient organic aerosol components are found to be organosulfates of isoprene, alpha-pinene, beta-pinene, and limonene-like monoterpenes (e.g., myrcene), demonstrating the ubiquity of organosulfate formation in ambient SOA. Several of the organosulfates of isoprene and of the monoterpenes characterized in this study are ambient tracer compounds for the occurrence of biogenic SOA formation under acidic conditions. Furthermore, the nighttime oxidation experiments conducted under highly acidic conditions reveal a viable mechanism for the formation of previously identified nitrooxy organosulfates found in ambient nighttime aerosol samples. We estimate that the organosulfate contribution to the total organic mass fraction of ambient aerosol collected from K-puszta, Hungary, a field site with a similar organosulfate composition as that found in the present study for the southeastern U.S., can be as high as 30%.

Organosulfates from Pinene and Isoprene over the Pearl River Delta, South China: Seasonal Variation and Implication in Formation Mechanisms

“…Previous chamber studies have demonstrated that both OH-photooxidation and NO 3 dark reactions can form pinene-derived nitrooxy-organosulfates (pNOSs) on acidic particles. 9 The pNOSs were only detected in nighttime samples in northeastern Bavaria, Germany, suggesting a role for nighttime NO 3 chemistry in pNOS formation. 15 However, if acidic aerosols are required by the NO 3 pathway, 9 what is the explanation for the phenomena that neutralized aerosols coincided with the high overnight concentrations of pNOSs?…”

“…35 For pNOSs, additional MS/MS product ions with m/z 247 (loss of HNO 2 ) and m/z 231 (loss of HNO 3 ) were detected. 9 The structures of three pNOS isomers with MW 295 (pNOS a , pNOS b , pNOS c ) were identified by comparing the detected spectra (Figure S2c−e) with those provided by Surratt et al 9 The isomer pNOS a was identified by extremely low intensity of m/z 231 ions and high intensity of m/z 220 (loss of CO and NO 2 ) in MS2 spectra ( Figure S2c); while the isomer pNOS c was identified by significant intensity of m/z 142 ( − OSO 3 NO 2 ) ( Figure S2e). Due to the lack of commercial standard, OSs were quantified using camphor sulfonic acid.…”

“…In contrast, pNOSs are formed by heterogeneous reactions on acidic particles. 9,34,57 High sulfate levels would promote pNOSs' formation. 26 Since there was no significant difference in aerosol acidity between summer and fall (p > 0.05), aerosol acidity should not be the major factor leading to the seasonal differences in correlations between terpenoic acids and pNOSs.…”

“…To further check the relative contributions of OH-initiated and NO 3 -initiated chemistry to the formation of the pNOS c isomer, we employed the Master Chemical Mechanism (MCM) to explore the formation of hydroxynitrates (MW 215) (http://mcm.leeds.ac.uk/MCM/browse.htt?species= APINENE) during daytime and nighttime, following the mechanisms proposed by Surratt et al 9 As shown in Scheme 1, the first step for hydroxynitrate formation is the reaction of α-pinene with OH to form a hydroperoxy radical or with NO 3 radical to form a nitroperoxy radical. 62 resulting in an α-pinene lifetime of ∼4.5 min, given a rate constant for NO 3 + α-pinene of 6.21 × 10 −12 cm 3 molecules −1 s −1 with (k 1 ).…”

Real Time In Situ Detection of Organic Nitrates in Atmospheric Aerosols

“…Interferences due to evaporative loss from the filters or heterogeneous reactions on the filters during sampling are known issues and difficult to quantify. Individual large multifunctional nitrates have been observed in ambient aerosol samples collected on filters using electrospray ionization mass spectrometry (23,24). However the most widely used methods for aerosol chemical characterization including Aerosol Mass Spectrometry (AMS) have had limited success.…”