Abstract
Abstract. Organosulfates are secondary organic aerosol (SOA) products that form from reactions of volatile organic compounds (VOC), such as isoprene, in the presence of sulfate that is primarily emitted by fossil fuel combustion. This study examines the anthropogenic influence on biogenic organosulfate formation at an urban site in Atlanta, Georgia (GA) in the southeastern United States (US). Organosulfates were analyzed in fine particulate matter (PM2.5) collected during August 2015 in Atlanta using hydrophilic interaction liquid chromatography (HILIC), tandem mass spectrometry (MS/MS), and high-resolution time-of-flight (ToF) mass spectrometry. By their MS/MS response, 32 major organosulfate species were identified, selected species were quantified, and other species were semi-quantified using surrogate standards. Organosulfates accounted for 16.5 % of PM2.5 organic carbon (OC). Isoprene-derived organosulfates were the most abundant, dominated by methyltetrol sulfate which accounted for 12.6 % of PM2.5 OC. Together, the isoprene-derived organosulfates accounted for the majority of the isoprene-derived SOA that had been previously observed in Atlanta, but had not been identified at the molecular level. Other major species included seven monoterpene-derived organosulfates, five diesel and/or biodiesel-derived organosulfates, and three new organosulfates that are also expected to derive from isoprene. Organosulfate species and concentrations in Atlanta were compared to those in a rural forested site in Centreville, Alabama (AL) during summer 2013, which were also dominated by isoprene-derived organosulfates. In Atlanta, isoprene-derived organosulfate concentrations were 2–6 times higher and accounted for twice as much OC. The greatest enhancement in concentration was observed for 2-methylglyceric acid sulfate whose formation is enhanced in the presence of nitrogen oxides (NO and NO2; NOx) and is a tracer for isoprene high-NOx SOA. The isoprene-derived organosulfates indicated a stronger influence of NOx in Atlanta compared to Centreville. Overall, these results suggest that SOA in the southeastern US can be reduced by controlling NOx and SO2 emissions from fossil fuel combustion. This study gives insights into the major organosulfate species that should be targets for future measurements in urban environments and standard development.
Highlights
Organosulfates are components of atmospheric secondary organic aerosol (SOA) that contain a sulfate ester functional group
As fossil fuel combustion is the major source of sulfate aerosols in the atmosphere (Wuebbles and Jain, 2001; Hidy et al, 2014; Carlton et al, 2010), biogenic volatile organic compounds (VOC) derived organosulfates are useful as tracers of anthropogenically influenced biogenic SOA (Hettiyadura et al, 2018)
Organosulfates have been detected among the SOA generated from diesel and biodiesel fuel emissions (Blair et al, 2017) and in SOA produced from aromatic VOC such as naphthalene and methylnaphthalene (Riva et al, 2015) as well as long chain n-alkanes (Riva et al, 2016b)
Summary
Organosulfates are components of atmospheric secondary organic aerosol (SOA) that contain a sulfate ester functional group This class of compounds has been detected in ambient aerosols around the world, including rural, urban, forested, and coastal sites in the United States (US), China, and/or Europe (Hansen et al, 2014; He et al, 2014; Kristensen and Glasius, 2011; Lin et al, 2012; Stone et al, 2012; Ma et al, 2014). As fossil fuel combustion is the major source of sulfate aerosols in the atmosphere (Wuebbles and Jain, 2001; Hidy et al, 2014; Carlton et al, 2010), biogenic VOC derived organosulfates are useful as tracers of anthropogenically influenced biogenic SOA (Hettiyadura et al, 2018). This study provides insights into the composition, abundance, sources, and formation pathways of organosulfates, which are useful as tracers for anthropogenically influenced SOA
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