Importance of Oxidants and Temperature in the Formation of Biogenic Organosulfates and Nitrooxy Organosulfates

Daniel J Bryant,Erin White,Xinming Wang,Stefan Swift,Wei Deng,Sainan Wang,Yanli Zhang,Mike Newland,Atallah Elzein,Jacqueline F Hamilton,Amy Watkins,Andrew R Rickard,Wei Song

doi:10.1021/acsearthspacechem.1c00204

Abstract

Biogenic secondary organic aerosol (BSOA) makes up a significant proportion of organic aerosol, and its formation chemistry, composition, and physical properties can be influenced by anthropogenic emissions, especially in urban areas. Organosulfates (OSs) are an important class of tracers for BSOA and have been well-studied over the past decade, although detailed ambient studies of diurnal variations are still lacking. In this study, fine particulate matter samples were collected eight times a day across summer and winter campaigns at an urban site in Guangzhou, China. Guangzhou is heavily influenced by both biogenic and anthropogenic emissions, allowing for biogenic–anthropogenic interactions to be studied. Individual OSs and nitrooxy OSs (NOSs) species derived from monoterpenes and isoprene were analyzed using ultrahigh-performance liquid chromatography tandem mass spectrometry (UHPLC–MS2) and quantified using three authentic and proxy standards. The observations show strong diurnal variations of monoterpene derived OSs and NOSs, which peaked during the night, with concentrations increasing from the early evening, highlighting the role of NO3-oxidation chemistry. Isoprene derived OSs/NOSs showed strong seasonal profiles, with summer and winter average concentrations of 181.8 and 69.5 ng m–3, respectively, with exponential increases observed at temperatures above 30 °C. Low-NO formation pathways were dominant in the summer, while high-NO pathways became more important in the winter. Isoprene OS formation was strongly dependent on the availability of particulate sulfate (SO42–), suggesting an extensive heterogeneous chemistry of oxidized isoprene species. Overall, this study provides further insights into biogenically derived OS and NOS formation within highly anthropogenically influenced environments.

Highlights

Organosulfates (OSs) are key contributors of atmospheric secondary organic aerosol and have been detected in ambient aerosols in both clean and polluted sites around the world.[1−10]OSs have been shown to make up significant portions of organic 2.5 μm aerosol (OA) in diameter) amnadssP,1M1−21.53(particulate matter less with isoprene derived than OSs accounting for up to 8% of organic matter.[14]
Ambient aerosol filter samples were collected in Guangzhou, China at the Guangzhou Institute for Geochemistry (GIG) as part of the Natural Environmental Research Council’s (NERC) NITRO-PM project
OSMT showed a limited correlation to potential reactants but showed a strong correlation toward NOSMT species, especially during the summer, suggesting a potential NOSMT to OSMT degradation route

Summary

Introduction

Organosulfates (OSs) are key contributors of atmospheric secondary organic aerosol and have been detected in ambient aerosols in both clean and polluted sites around the world.[1−10]OSs have been shown to make up significant portions of organic 2.5 μm aerosol (OA) in diameter) amnadssP,1M1−21.53(particulate matter less with isoprene derived than OSs accounting for up to 8% of organic matter.[14]. Chamber studies have shown the formation of particlebound OSs from gas-phase oxidation of biogenic volatile organic compounds (VOCs) such as isoprene,[20−22] monoterpenes,[7,21] sesquiterpenes,[23] and green leaf volatiles[24] via OH, NO3, and O3 oxidation pathways in the presence of sulfate aerosol or SO2. Many of the species identified in these chamber studies have been detected in ambient samples, with isoprene derived OSs as some of the most abundant biogenic OS markers quantified.[4,25] It should be noted that while these OS and NOS species are termed as BSOA due to their VOC precursors they are formed through interactions with anthropogenic pollutants. Several other routes have been proposed such as sulfate radical addition to an unsaturated precursor in the aqueous phase,[29,30] direct sulfate esterification of an alcohol precursor,[21] or the replacement of nitrate groups within organonitrate species with sulfate.[31,32] Recent studies have reported the formation of OSs both directly and indirectly from the reaction of unsaturated species

Methods

Results

Conclusion