Anthropogenic effects on Δ3-carene photooxidation: Different oxidants induce significant changes of secondary organic aerosol formation mechanisms

Elucidating the effects of anthropogenic pollutants on the formation mechanism of secondary organic aerosol (SOA) is crucial for the improvement of atmospheric models toward the development of effective control strategies. It is extremely challenging to precisely clarify the impacts of concentrations of anthropogenic pollutants on the molecular compositions and particle number/mass concentrations of SOA under complicated conditions. Here, we report a series of the studies on the effects of anthropogenic pollutants (NO 2 and SO 2 ) on the photooxidation of a representative monoterpene , Δ 3 -carene, by using the scanning mobility particle sizer spectrometer, recently-developed vacuum ultraviolet free electron laser (VUV-FEL) photoionization aerosol mass spectrometry , and quantum chemical calculations . The results indicated that with the increase of NO 2 concentration, the SOA yields increased under low-NO 2 conditions but decreased under high-NO 2 conditions. The OH radical was found to be the primary oxidant under low-NO 2 conditions, whereas O 3 became the dominant oxidant under high-NO 2 conditions. SO 2 substantially enhanced the formation of highly oxidized molecules via the acid-catalyzed pathway. A series of new compounds (i.e., organic peroxides , organic nitrates, and organosulfates) were observed and their formation mechanisms were proposed. The present findings highlight the critical role of anthropogenic pollutants in the photooxidation of monoterpene under low and high pollution environments and also open new avenues toward systematic studies of a broader class of volatile organic compounds .