Chemical characteristics and source apportionment of fine particulate matters at a typical suburban site in Nanjing, China

Abstract

Regional atmospheric pollution events still occur frequently in China despite the decline in PM_2.5 concentrations in recent years. In order to investigate the chemical composition and pollution characteristics of atmospheric fine particulate matters measured by off-line soot particle aerosol mass spectrometer in Nanjing during the cold seasons, this study presented a comprehensive analysis of PM_2.5 diurnal samples from October 10 to December 31 in the year 2020, which collected at a typical suburban site in Nanjing. Results showed that water-soluble inorganic ions dominated PM_2.5 mass, with NH₄⁺ primarily forming NH₄NO₃, (NH₄)₂SO₄ and NH₄Cl through secondary reactions. Excess NO₃^- was found in the form of Ca(NO₃)₂ and Mg(NO₃)₂. Emissions from vehicle exhaust significantly contributed to the inorganic component, and both organic and inorganic analyses indicated that biomass burning was a more significant primary source during the night. In terms of water-soluble organic components (WSOM), the average O/C, H/C, N/C, and organic matter to organic carbon ratio (OM/OC) were 0.48, 1.38, 0.03, and 1.79, respectively. Four OA factors were identified in WSOM: hydrocarbon-related OA from traffic emissions (HOA), mixed primary OA (MPOA), low oxidized OA (LO-OOA), and more oxidized OA (MO-OOA). Their daytime contributions were 10.6%, 25.6%, 35.5%, and 28.8%, while nighttime contributions were 9.7%, 33.5%, 32.9%, and 23.9%, respectively. Potential source contribution function (PSCF) analysis showed that Yangtze River Delta, North China, and Mongolia were major potential sources of PM_2.5, highlighting the importance of coordinated measures to reduce PM_2.5 in Nanjing.