Abstract
Abstract. Organosulfates are important components of atmospheric organic aerosols, yet their structures, abundances, sources and formation processes are not adequately understood. This study presents the identification and quantitation of benzyl sulfate in atmospheric aerosols, which is the first confirmed atmospheric organosulfate with aromatic carbon backbone. Benzyl sulfate was identified and quantified in fine particulate matter (PM2.5) collected in Lahore, Pakistan, during 2007–2008. An authentic standard of benzyl sulfate was synthesized, standardized, and identified in atmospheric aerosols with quadrupole time-of-flight (Q-ToF) mass spectrometry (MS). Benzyl sulfate was quantified in aerosol samples using ultra performance liquid chromatography (UPLC) coupled to negative electrospray ionization triple quadrupole (TQ) MS. The highest benzyl sulfate concentrations were recorded in November and January 2007 (0.50 ± 0.11 ng m−3) whereas the lowest concentration was observed in July (0.05 ± 0.02 ng m−3). To evaluate matrix effects, benzyl sulfate concentrations were determined using external calibration and the method of standard addition; comparable concentrations were detected by the two methods, which ruled out significant matrix effects in benzyl sulfate quantitation. Three additional organosulfates with m/z 187, 201 and 215 were qualitatively identified as aromatic organosulfates with additional methyl substituents by high-resolution mass measurements and tandem MS. The observed aromatic organosulfates form a homologous series analogous to toluene, xylene, and trimethylbenzene, which are abundant anthropogenic volatile organic compounds (VOC), suggesting that aromatic organosulfates may be formed by secondary reactions. However, stronger statistical correlations of benzyl sulfate with combustion tracers (EC and levoglucosan) than with secondary tracers (SO42− and α-pinene-derived nitrooxy organosulfates) suggest that aromatic organosulfates may be emitted from the combustion sources or their subsequent atmospheric processing. Further studies are needed to elucidate the sources and formation pathways of aromatic organosulfates in the atmosphere.
Highlights
M aerosol samples using ultra performance liquid chromatography (UPLC) coupled to negative electrospray ionization Atmospheric aerosols absorb and scatter solar radiation triple quadrupole (TQ) mass spectrometry (MS)
Benzyl sulfate was not detected in this sample, suggesting that benzyl sulfate was not formed during aerosol extraction, which is consistent with a prior study that showed that the reaction between alcohol and H2SO4 is not feasible even under most acidic conditions observed in the atmosphere (Minerath et al, 2008)
The synthesized benzyl sulfate was standardized by 1H NMR
Summary
Fine particulate matter (PM2.5) samples were collected on the campus of the University of Engineering and Technology in Lahore, Pakistan, as described in a previous publication (Stone et al, 2010). An eight-channel mediumvolume PM2.5 and PM10 sampler (URG-3000ABC, Chapel Hill, NC, USA) was placed on the rooftop of the Institute for Environmental Engineering and Research at the height of 10 m (31◦15 , 31◦45 N and 74◦10 , 74◦39 E). Filter samples were collected on pre-baked quartz-fiber substrates Pall Life Sciences, East Hill, NY, USA) for the duration of 24 h, with sample collection beginning at 11:00 LT. Samples were collected from January 2007 to January 2008 at a rate of one-in-six days, yielding 63 samples. The PM2.5 samples were analyzed in this study
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