Insights into the seasonal characteristics of single particle aerosols in Chengdu based on SPAMS

To investigate the seasonal characteristics in air pollution in Chengdu, a single particle aerosol mass spectrometry was used to continuously observe atmospheric fine particulate matter during one-month periods in summer and winter, respectively. The results showed that, apart from O₃, the concentrations of other pollutants (CO, NO₂, SO₂, PM_2.5 and PM₁₀) were significantly higher in winter than in summer. All single particle aerosols were divided into seven categories: biomass burning (BB), coal combustion (CC), Dust, vehicle emission (VE), K mixed with nitrate (K-NO₃), K mixed with sulfate and nitrate (K-SN), and K mixed with sulfate (K-SO₄) particles. The highest contributions in both seasons were VE particles (24%). The higher contributions of K-SO₄ (16%) and K-NO₃ (10%) particles occurred in summer and winter, respectively, as a result of their different formation mechanisms. S-containing (K-SO₄ and K-SN), VE, and BB particles caused the evolution of pollution in both seasons, and they can be considered as targets for future pollution reduction. The mixing of primary sources particles (VE, Dust, CC, and BB) with secondary components was stronger in winter than in summer. In summer, as pollution worsens, the mixing of primary sources particles with 62 [NO₃]⁻ weakened, but the mixing with 97 [HSO₄]⁻ increased. However, in winter, the mixing state of particles did not exhibit an obvious evolution rules. The potential source areas in summer were mainly distributed in the southern region of Sichuan, while in winter, besides the southern region, the contribution of the western region cannot be ignored.