Monoterpene Photooxidation in a Continuous-Flow Chamber: SOA Yields and Impacts of Oxidants, NOx, and VOC Precursors

Monoterpene photooxidation plays an important role in secondary organic aerosol (SOA) formation in the atmosphere. The low-volatility products can enhance new particle formation and particle growth and thus influence climate feedback. Here, we present the results of alpha-pinene and Delta-3-carene photooxidation experiments conducted in continuous-flow mode in an environmental chamber under several reaction conditions. The roles of oxidants, addition of NO, and VOC molecular structure in influencing SOA yield are illustrated. SOA yield from alpha-pinene photooxidation shows a weak dependence on H2O2 concentration, which is a proxy for HO2 concentration. The high O/C ratios observed in the a-pinene photooxidation products suggest the production of highly oxygenated organic molecules (HOM). Addition of ozone to the chamber during low-NOx photooxidation experiments leads to higher SOA yield. With the addition of NOx the production of N-containing HOMs is enhanced and the SOA yield shows a modest, nonlinear dependence on the input NO concentration. Carene photooxidation leads to higher SOA yield than a-pinene under similar reaction conditions, which agrees with the lower volatility retrieved from evaporation kinetics experiments. These results improve the understanding of SOA formation from monoterpene photooxidation and could be applied to refine the representation of biogenic SOA formation in models.

Automated summary

Monoterpene photooxidation plays an important role in the formation of secondary organic aerosols (SOA), and this study investigates the factors influencing SOA yield from alpha-pinene and Delta-3-carene photooxidation. The results show that oxidation conditions, addition of NO, and the molecular structure of volatile organic compounds (VOCs) can all affect SOA formation. The study also reveals that the composition of the photooxidation products and the SOA yield differ between alpha-pinene and Delta-3-carene.