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.