Assessing the NO and SO2 pollution impacts on the Δ3-carene photooxidation mechanisms.

Investigating the influences of gaseous pollutants on volatile organic compound photooxidation mechanisms is essential for establishing robust air quality management strategies. Here, a set of well-defined experiments were conducted to elucidate the roles of NO and SO2 in Δ3-carene-derived secondary organic aerosol (SOA) formation. Employing electron ionization time-of-flight aerosol mass spectrometer, we found that high NO concentration significantly inhibited new particle formation (NPF) by reducing the O:C rate of products. With the presence of SO2 pollution, the trend of SOA yield exhibited two distinct regimes governed by SO2 concentration. At low SO2 concentrations ([SO2]0 ≤ 119 ppb), H2SO4 nucleation promoted the NPF and elevated the SOA yields; with the increase of SO2 pollution level (119-178 ppb), the consumption of stabilized Criegee intermediates increased, which reduced particle number concentrations and SOA yields. Significantly, two distinct NPF events were observed in the Δ3-carene photooxidation. Leveraging the unique capabilities of vacuum ultraviolet free electron laser photoionization online aerosol mass spectrometer, we detected the dynamic chemical evolution of SOA across reaction stages and elucidated the differences between such two NPF mechanisms. The results show that the introduction of SO2 progressively accelerated the onset of NPF, with a maximum shift of approximately 1 h H2SO4 formed from SO2 oxidation promoted earlier nucleation, while the generation of particulate formation was dominated by Δ3-carene oxidation. By integrating experimental observations with theoretical calculations, we identified a series of key organosulfates and elucidated their formation mechanisms. These results highlight the NO and SO2 pollution impacts on Δ3-carene photooxidation and advance our understanding of NPF in polluted environments.