Component characteristics and source analysis of fine particulate matter PM2.5 in autumn and winter in Urumqi, China

This study offers a comprehensive examination of fine particulate matter (PM2.5) pollution observed in Urumqi during the autumn and winter seasons of 2021-2022, with an emphasis on the characteristics and origins of PM2.5 components. The results illustrate that sulfate ions (SO4^2-) and nitrate ions (NO3-) are the prevailing components in this setting. In particular, the concentration of SO4^2- reached 32.0 µg/m3, making up 23% of the PM2.5, whereas the concentration of NO3- was recorded at 29.2 µg/m3, representing 22% of the PM2.5. Ammonium ions (NH4+) were identified at a concentration of 20.7 µg/m3, or 16%, which is marginally lower than the concentrations of SO4^2- and NO3-. Cumulatively, the levels of SO4^2-, NO3-, and NH4+ surpassed 60%, highlighting a considerable effect from secondary sources throughout the autumn and winter periods. Evaluating data from Midongjcfz and Ganquanbao shows that the concentrations of chloride ions (Cl-) and sulfate ions (SO4^2-) within PM2.5 are significantly elevated, coupled with a low NO3-/SO4^2- ratio, indicating a considerable contribution from coal combustion in this area. Conversely, at the Dawan survey station, the content of elemental carbon (EC) is markedly higher, with the organic carbon to elemental carbon (OC/EC) ratio at its lowest and a relatively high NO3-/SO4^2- ratio. Among secondary sources, the share of secondary nitrate is greater than that of secondary sulfate, cumulatively accounting for 53.1%. As for primary sources, coal burning emerges as the predominant contributor, with a concentration of 32.1 µg/m3, constituting 25.6% of PM2.5. In contrast, biomass burning is the least contributing factor, adding merely 2.5%. The analysis concludes that secondary inorganic salt formation is the main contributor to PM2.5 levels during the autumn and winter seasons in Urumqi, representing up to 53% of the overall total.