Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 56, Issue 20, Pages 14249-14261Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.2c02090
Keywords
secondary organic aerosol; ?-pinene oxidation; acylperoxy radicals; stabilized Criegee intermediates; dimers; formation mechanisms
Categories
Funding
- National Natural Science Foundation of China
- Shanghai Pujiang Program
- Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning
- [22022607]
- [22076119]
- [21806104]
- [20PJ1407600]
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This study provides experimental evidence for the important role of acyl organic peroxy radicals (RO2) and stabilized Criegee intermediates (SCIs) in the formation of particle-phase dimers during the ozonolysis of alpha-pinene. It contributes to reducing uncertainties in future atmospheric modeling of secondary organic aerosol (SOA) budget, properties, and health and climate impacts.
High molecular weight dimeric compounds constitute a significant fraction of secondary organic aerosol (SOA) and have profound impacts on the properties and lifecycle of particles in the atmosphere. Although different formation mechanisms involving reactive intermediates and/or closed-shell monomeric species have been proposed for the particle-phase dimers, their relative importance remains in debate. Here, we report unambiguous experimental evidence of the important role of acyl organic peroxy radicals (RO2) and a small but non-negligible contribution from stabilized Criegee intermediates (SCIs) in the formation of particle-phase dimers during ozonolysis of alpha-pinene, one of the most important precursors for biogenic SOA. Specifically, we find that acyl RO2-involved reactions explain 50-80% of total oxygenated dimer signals (C15-C20, O/C >= 0.4) and 20-30% of the total less oxygenated (O/C < 0.4) dimer signals. In particular, they contribute to 70% of C15-C19 dimer ester formation, likely mainly via the decarboxylation of diacyl peroxides arising from acyl RO2 cross-reactions. In comparison, SCIs play a minor role in the formation of C15-C19 dimer esters but react noticeably with the most abundant C9 and C10 carboxylic acids and/or carbonyl products to form C19 and C20 dimeric peroxides, which are prone to particle-phase transformation to form more stable dimers without the peroxide functionality. This work provides a clearer view of the formation pathways of particle-phase dimers from alpha-pinene oxidation and would help reduce the uncertainties in future atmospheric modeling of the budget, properties, and health and climate impacts of SOA.
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