Characteristics, formation, and sources of PM_2.5 in 2020 in Suzhou, Yangtze River Delta, China

Here we present seasonal chemical characteristics, formations, sources of PM_2.5 in the year 2020 in Suzhou, Yangtze River Delta, China. Expectedly, organic matter (OM) found to be the most dominant component of PM_2.5, with a year-average value of 10.3 ± 5.5 μg m^-3, followed by NO₃^- (6.7 ± 6.5 μg m^-3), SO₄^2- (3.3 ± 2.5 μg m^-3), NH₄⁺ (3.2 ± 2.8 μg m^-3), EC (1.1 ± 1.3 μg m^-3), Cl^- (0.57 ± 0.56 μg m^-3), Ca²⁺ (0.55 ± 0.91 μg m^-3), K⁺ (0.2 ± 1.0 μg m^-3), Na⁺ (0.18 ± 0.45 μg m^-3), and Mg²⁺ (0.09 ± 0.15 μg m^-3). Seasonal variations of PM_2.5 showed the highest average value in spring, followed by winter, fall, and summer. Meanwhile, the formation mechanisms of the major PM_2.5 species (NO₃^-, SO₄^2-, and OM) varied in seasons. Interestingly, NO₂ may have the highest conversion rate to NO₃^- in spring, which might be linked with the nighttime chemistry due to the high relative humidity. Moreover, OM in summer was mainly produced by the daytime oxidation of volatile organic compounds, while local primary organic aerosols might play a significant role in other seasons. Source apportionment showed that the more-aged PM_2.5 contributed significantly to the PM_2.5 mass (42%), followed by the dust-related PM_2.5 (38%) and the less-aged PM_2.5 (21%). Potential contribution source function (PSCF) results indicated that aged PM_2.5 were less affected by transportation than dust-related PM_2.5.