Abstract
Abstract. Ozonolysis of monoterpenes is an important source of atmospheric biogenic secondary organic aerosol (BSOA). While enhanced BSOA formation has been associated with sulfate-rich conditions, the underlying mechanisms remain poorly understood. In this work, the interactions between SO2 and reactive intermediates from monoterpene ozonolysis were investigated under different humidity conditions (10 % vs. 50 %). Chamber experiments were conducted with ozonolysis of α-pinene or limonene in the presence of SO2. Limonene SOA formation was enhanced in the presence of SO2, while no significant changes in SOA yields were observed during α-pinene ozonolysis. Under dry conditions, SO2 primarily reacted with stabilized Criegee intermediates (sCIs) produced from ozonolysis, but at 50 % RH heterogeneous uptake of SO2 onto organic aerosol was found to be the dominant sink of SO2, likely owing to reactions between SO2 and organic peroxides. This SO2 loss mechanism to organic peroxides in SOA has not previously been identified in experimental chamber studies. Organosulfates were detected and identified using an electrospray ionization–ion mobility spectrometry–high-resolution time-of-flight mass spectrometer (ESI-IMS-TOF) when SO2 was present in the experiments. Our results demonstrate the synergistic effects between BSOA formation and SO2 oxidation through sCI chemistry and SO2 uptake onto organic aerosol and illustrate the importance of considering the chemistry of organic and sulfur-containing compounds holistically to properly account for their reactive sinks.
Highlights
Secondary organic aerosol (SOA) is formed from condensation of low-volatility products from atmospheric oxidation of volatile organic compounds (VOCs) and comprises a major fraction of atmospheric organic aerosol (Jimenez et al, 2009)
Liu et al (2017) demonstrated that SOA yields of cyclohexene photooxidation were lower at atmospherically relevant concentrations of SO2, implying that SO2 may indirectly decrease SOA formation when the acid-catalyzed SOA enhancement is insufficient to compensate for the loss of OH reactivity towards VOCs
Synergistic effects were observed between Limonene SOA (LSOA) formation and SO2 oxidation, as SO2 was consumed on the same timescales as the formation of LSOA
Summary
Secondary organic aerosol (SOA) is formed from condensation of low-volatility products from atmospheric oxidation of volatile organic compounds (VOCs) and comprises a major fraction of atmospheric organic aerosol (Jimenez et al, 2009). Liu et al (2017) demonstrated that SOA yields of cyclohexene photooxidation were lower at atmospherically relevant concentrations of SO2, implying that SO2 may indirectly decrease SOA formation when the acid-catalyzed SOA enhancement is insufficient to compensate for the loss of OH reactivity towards VOCs. SO2 can directly influence VOC oxidation mechanisms through reactions with stabilized Criegee intermediates (sCIs) formed from olefin ozonolysis (Huang et al, 2015a; Welz et al, 2012). Field observations suggested that SO2+ sCIs reactions may contribute up to 50 % of the total gaseous sulfuric acid production in the forest atmosphere, which is comparable to that from gas-phase oxidation by OH (Mauldin III et al, 2012). Results in this study provide a better mechanistic understanding of BSOA formation and atmospheric SO2 oxidation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
