Temporal Distribution and Source Apportionment of Composition of Ambient PM_2.5 in Urumqi, North-West China

Abstract

In order to identify the pollution characteristics and sources of PM2.5 in Urumqi, fine particulate matter samples were collected from September 2017 to August 2018, and the water-soluble ions (WSIs), organic carbon (OC), elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs), and metal elements were analyzed. The results indicate that the annual mass concentration of PM2.5 in Urumqi was 158.85 ± 15.11 μg/m3, with the highest seasonal average in autumn (180.49 ± 87.22 μg/m3) and the lowest in summer (148.41 ± 52.60 μg/m3). SO42− (13.58 ± 16.4 μg/m3), NO3− (13.46 ± 17.5 μg/m3), and NH4+ (10.88 ± 12.2 μg/m3) were the most abundant WSIs, and the secondary inorganic ions (SNA = SO42− + NO3− + NH4+) accounted for 87.23% of the WSIs. The NO3−/SO42− ratio indicates that the contribution of stationary sources was dominant. The annual concentrations of OC and EC were 12.00 ± 4.4 µg/m3 and 5.00 ± 3.5 µg/m3, respectively, the OC/EC ratios in winter (2.55 ± 0.7), spring (3.43 ± 1.3), and summer (3.22 ± 1.1) were greater than 2, and there was the formation of secondary organic carbon (SOC). The correlation between OC and EC in spring in Urumqi (R2 = 0.53) was low. In the PM2.5, Al and Fe were the most abundant elements. The highest mass concentration season occurred in autumn, with mass concentrations of 15.11 ± 10.1 µg/m3 and 8.33 ± 6.9 µg/m3, respectively. The enrichment factor (EF) shows that most of the metal elements come from natural sources, and the Cd element mainly comes from anthropogenic sources. PAHs with a middle molecular weight were the main ones, and the annual average annual mass concentration of the PAHs was 451.35 ng/m3. The positive matrix factor model (PMF) source analysis shows that there are five main sources of PM2.5 in Urumqi, including crustal minerals, biomass combustion, coal combustion, vehicular transport, and secondary aerosols. The distribution percentages of these different sources were 19.2%, 10.2%, 12.1%, 8.2%, and 50.3%, respectively.

Keywords

• PM_2.5
• PAHs
• metals
• positive matrix factorization
• Urumqi