Organosulfates in Humic-like Substance Fraction Isolated from Aerosols at Seven Locations in East Asia: A Study by Ultra-High-Resolution Mass Spectrometry

Abstract

Humic-like substances (HULIS) in ambient aerosols collected at seven locations in East Asia were analyzed using electrospray ionization (ESI) coupled with an ultra-high-resolution mass spectrometer (UHRMS). Locations included a 3 km high mountaintop site in Taiwan, rural, suburban, and urban locations in the Pearl River Delta (PRD), South China, and in Taiwan. Organosulfates (OS) in the HULIS fraction were tentatively identified through accurate mass measurements and MS/MS spectra interpretation. In the two mountaintop samples collected in regional background atmosphere, little OS were detected, while a few hundred OS formulas were identified in the six samples taken in Taiwan and PRD. Many of the OS ions were among the most intense peaks in the negative ESI-UHRMS spectra, and their elemental formulas were identical to OS derived from biogenic volatile organic compounds (BVOCs) (e.g., monoterpenes) that have been identified in chamber studies. With OS having less than 6 carbon atoms too hydrophilic to be effectively retained in the HULIS fraction, OS containing 10 carbon atoms were the most abundant, indicating monoterpenes as important precursors of OS in the HULIS fraction. Clear spatial variation in abundance of OS was found among different atmospheric environments, with enhanced coupling of BVOCs with anthropogenic acidic aerosols observed in the PRD samples over the Taiwan samples. The double bond equivalent (DBE) values indicate the majority of OS (>90%) in the HULIS fraction are aliphatic. The elemental compositions of OS compounds containing N atoms (defined as CHONS) indicate that they are probably nitrooxy OS. Some insights into OS formation mechanisms are also gained through examining the presence/absence of perceived reactant-product formula pairs in the mass spectra. The results suggest the dominant epoxide intermediate pathway for formation of OS compounds without N atoms (defined as CHOS) and confirm the more readily hydrolyzed characteristics of the --ONO₂ group than the --OSO₃ group. There is a lack of evidence for the epoxide pathway to account for the formation of OS in the CHONS subgroup.

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

“…In the Amazon, Kourtchev et al (2016) previously found a similar subset of these unidentified CHOS compounds in SOA samples, suggesting a biogenic influence. Many organosulfates and nitrooxy-organosulfates, previously reported in laboratory studies, ambient aerosols, and cloud water as derived from monoterpene oxidation (Boone et al, 2015;Hamilton et al, 2013;Iinuma et al, 2007aIinuma et al, , b, 2009Kristensen et al, 2016;Kristensen and Glasius, 2011;Lin et al, 2012;Mazzoleni et al, 2012;Nguyen et al, 2012b;Nozière et al, 2010;O'Brien et al, 2014;Pratt et al, 2013;Stone et al, 2012;Surratt et al, 2008), were detected in the biogenic-influenced cloud water samples (Table 2), also consistent with monoterpene emissions along the air mass trajectories (Guenther et al, 2006). In this study, the required solid-phase extraction step precluded the detection of isoprene-derived organosulfates, which would have been removed prior to analysis.…”

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

“…A solution of camphor sulfonic acid (Sigma-Aldrich, USA) was used to optimize ionization and fragmentation parameters to gain high intensity of [M−H] − , the resulting ionization voltage was 4 kV and the fragmentor was 120 V. 34 S-containing isotopic peaks coincident with the target ions provided an additional confirmation of 32 Scontaining formulas. 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).…”

The effects of isoprene and NO<sub><i>x</i></sub> on secondary organic aerosols formed through reversible and irreversible uptake to aerosol water

“…These species do not partition to dry particles (Kroll et al, 2005;Nguyen et al, 2014), so their condensed-phase products are called aqueous SOA (aqSOA; Ervens et al, 2011). IEPOX uptake also depends on the inorganic composition and acidity of the seed particles (Surratt et al, 2010;Gaston et al, 2014;Budisulistiorini et al, 2017;Lin et al, 2012;Riedel et al, 2015). A body of work indicates that the uptake of water-soluble organic gases into atmospheric waters (clouds, fogs, and aerosol water) is an important pathway for SOA formation (Ervens et al, 2011).…”