Characterization of organosulfates from the photooxidation of isoprene and unsaturated fatty acids in ambient aerosol using liquid chromatography/(−) electrospray ionization mass spectrometry

Abstract

In the present study, we have characterized in detail the MS(2) and MS(3) fragmentation behaviors, using electrospray ionization (ESI) in the negative ion mode, of previously identified sulfated isoprene secondary organic aerosol compounds, including 2-methyltetrols, 2-methylglyceric acid, 2-methyltetrol mononitrate derivatives, glyoxal and methylglyoxal. A major fragmentation pathway for the deprotonated molecules of the sulfate esters of 2-methyltetrols and 2-methylglyceric acid and of the sulfate derivatives of glyoxal and methylglyoxal is the formation of the bisulfate [HSO(4)](-) anion, while the deprotonated sulfate esters of 2-methyltetrol mononitrate derivatives preferentially fragment through loss of nitric acid. Rational interpretation of MS(2), MS(3) and accurate mass data led to the structural characterization of unknown polar compounds in K-puszta fine aerosol as organosulfate derivatives of photooxidation products of unsaturated fatty acids, i.e. 2-hydroxy-1,4-butanedialdehyde, 4,5- and 2,3-dihydroxypentanoic acids, and 2-hydroxyglutaric acid, and of alpha-pinene, i.e. 3-hydroxyglutaric acid. The deprotonated molecules of the sulfated hydroxyacids, 2-methylglyceric acid, 4,5- and 2,3-dihydroxypentanoic acid, and 2- and 3-hydroxyglutaric acids, showed in addition to the [HSO(4)](-) ion (m/z 97) neutral losses of water, CO(2) and/or SO(3), features that are characteristic of humic-like substances. The polar organosulfates characterized in the present work are of climatic relevance because they may contribute to the hydrophilic properties of fine ambient aerosol. In addition, these compounds probably serve as ambient tracer compounds for the occurrence of secondary organic aerosol formation under acidic conditions.

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

“…Unlike our observation in the PRD, high levels of pNOSs were observed in the nighttime and early morning in Antwerp, Belgium, 12 K-puszta, Hungary, 60 northeastern Bavaria, Germany, 15 the Sierra Nevada Mountains, California, 26 and Shanghai. 37 Nighttime NO 3 chemistry was proposed to account for the high levels of nighttime pNOSs.…”

Reactive intermediates revealed in secondary organic aerosol formation from isoprene

“…S1. Extracted ion chromatograms (EICs) of selected ions corresponding to particle-phase IEPOX, as well as the previously characterized C 5 -alkene triols (20), 2-methyltetrols (5), hemiacetal dimers (12), organosulfate derivatives of the 2-methyltetrols (16,17), and organosulfate derivatives of the hemiacetal dimers (18) are shown in Fig. 1G-L, respectively.…”

“…Enhancement of isoprene SOA mass with increasing aerosol acidity observed in laboratory chamber studies (12,14,15), including increased mass concentrations of the 2-methyltetrols (14, 15), organosulfates of isoprene (i.e., hydroxy sulfate esters) (15), and high-molecular weight (MW) SOA constituents (15), has been explained by acid-catalyzed particlephase reactions. Although a linear correlation between the SOA mass formed and measured aerosol acidity (i.e., nmol H þ m −3 ) has been found under dry conditions [approximately 30% relative humidity (RH)] (15), the actual acid-catalyzed particle-phase reactions responsible for these observed enhancements in isoprene SOA formation remain unclear, especially because previously proposed reactions, like that of organosulfate formation by alcohol sulfate esterification (16)(17)(18), appear to be kinetically unfavorable at atmospheric conditions (19).…”

Secondary organic aerosol (SOA) formation from reaction of isoprene with nitrate radicals (NO<sub>3</sub>)

“…It should be noted that the data presented in Table 2 are also applicable to all other types of experiments conducted in this study; however, none of the organosulfates are observed in the nucleation experiments, consistent with previous work (Liggio et al, 2005;Liggio et al, 2006;Surratt et al, 2007a,b;Iinuma et al, 2007a,b). Surprisingly, previously characterized organosulfates of the 2-methyltetrols and the 2-methyltetrol mono-nitrates detected at m/z 215 and m/z 260 (not listed in Table 2), respectively, which are produced from the photooxidation of isoprene in the presence of acidified sulfate seed aerosol (Surratt et al, 2007a,b;Gómez-González et al, 2007), are also observed in the acid seed experiment shown in Fig. 10, suggesting that nighttime oxidation of isoprene in the presence of acidic seed may also be a viable pathway for these known ambient tracer compounds.…”