Characterization and Quantification of Particle-Bound Criegee Intermediates in Secondary Organic Aerosol

The ozonolysis of alkenes contributes substantially to the formation of secondary organic aerosol (SOA), which are important modulators of air quality and the Earth's climate. Criegee intermediates (CIs) are abundantly formed through this reaction. However, their contributions to aerosol particle chemistry remain highly uncertain. In this work, we present the first application of a novel methodology, using spin traps, which simultaneously quantifies CIs produced from the ozonolysis of volatile organic compounds in the gas and partide phases. Only the smallest CI with one carbon atom was detected in the gas phase of a beta-caryophyllene ozonolysis reaction system. However, multiple particle-bound CIs were observed in beta-caryophyllene SOA. The concentration of the most abundant CI isomer in the partide phase was estimated to constitute similar to 0.013% of the SOA mass under atmospherically relevant conditions. We also demonstrate that the lifetime of CIs in highly viscous SOA particles is at least on the order of minutes, substantially greater than their gas-phase lifetime. The confirmation of substantial concentrations of large CIs with elongated lifetimes in SOA raises new questions regarding their influence on the chemical evolution of viscous SOA particles, where CIs may be a previously underestimated source of reactive species.

Automated summary

The ozonolysis of alkenes is responsible for the formation of significant amounts of Criegee intermediates (CIs), but their contributions to aerosol particle chemistry remain uncertain. In this study, a novel methodology using spin traps was used to simultaneously quantify CIs produced from the ozonolysis of volatile organic compounds in the gas and particle phases. The results showed that only the smallest CI with one carbon atom was detected in the gas phase, while multiple particle-bound CIs were observed in the secondary organic aerosol (SOA). Furthermore, it was found that CIs have a longer lifetime in highly viscous SOA particles compared to the gas phase.