Organosulfates in Atlanta, Georgia: anthropogenic influences on biogenic secondary organic aerosol formation
2018
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
(PM 2.5 ) 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 PM 2.5 organic carbon
(OC). Isoprene-derived organosulfates were the most abundant, dominated by
methyltetrol sulfate which accounted for 12.6 % of PM 2.5 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 NO 2 ; NO x ) and is a tracer for isoprene
high- NO x SOA. The isoprene-derived organosulfates indicated a stronger
influence of NO x in Atlanta compared to Centreville. Overall, these
results suggest that SOA in the southeastern US can be reduced by controlling
NO x and SO 2 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.
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