[Seasonal Variations, Size Distributions, and Sources of Chemical Components of Submicron Particulate Matter in...

Size-segregated particulate matter (PM) samples were collected in different seasons from 2016 to 2017 at the Xianlin Campus of Nanjing University. Mass concentrations of water-soluble inorganic ions, carbonaceous components, and elements were analyzed for PM with an aerodynamic diameter ≤ 1.1 μm (PM_1.1; <0.4 μm, 0.4-0.7 μm, and 0.7-1.1 μm). The results showed that PM_1.1, OC, NO₃^-, SO₄^2-, and NH₄⁺ exhibited higher ambient levels in fall-winter than those in spring-summer, which was attributed to the changes in local diffusion conditions, evaporation, and decomposition of non-refractory components. Elemental carbon (EC) reached its maximum concentration[(1.87±0.98) μg·m^-3]in spring due to the increase in industrial and road dust resuspension. According to the characteristic ratio between bulk components, the anions in PM_1.1 were dominated by NO₃^-, SO₄^2-, and Cl^- in Nanjing, and the carbonaceous components were mainly from fossil fuel combustions and associated aging processes. As the ambient temperature increased, the size distributions of thermo-unstable components including NH₄⁺, NO₃^-, and OC shifted towards finer particles, whereas EC became more enriched in coarse particles, possibly due to the increase in emission intensity of motor vehicles and fugitive dust contributions. Since high relative humidity (>70%) is often accompanied by high temperature (>20℃) and improved diffusion conditions, a relative humidity of 60%-70% was more conducive to the formation of secondary inorganic ions in PM_1.1. Source apportionment results based on the speciation data of PM_1.1 showed that secondary formation processes[(66.6±18.3)%]and dust resuspension[(16.8±14.8)%]were the main contributors to PM_1.1 in Nanjing, and further control of the emissions of gaseous precursors and dust is necessary.