Water-soluble ions and source apportionment of PM2.5 depending on synoptic weather patterns in an urban environment in spring dust season

Abstract

Emission sources and meteorological conditions are key factors affecting the intensity and duration of air pollution events. In the current study, using the daily concentrations of PM2.5 (particulate matter with a diameter ≤ 2.5 μm) and the water-soluble ions thereof in Lanzhou from March 1, 2021, to May 31, 2021, we investigated the contributions of emission sources and locations of potential sources through positive matrix factorization and potential source contribution function analysis. In addition, synoptic weather patterns affecting pollution were typed using T-model principal component analysis. The results revealed that the average concentrations of PM2.5 for the entire spring, dust storm days, and normal days were 54.3, 158.1 and 33.0 μg/m3, respectively. During dust storm days, sulfate produced from primary emissions was mainly present in the form of K2SO4, Na2SO4, MgSO4, and CaSO4, and nitrate was mainly produced through secondary conversion and took the form of NH4NO3. Dust, industrial entities, biomass combustion, metal smelting, secondary aerosol, and sea salt contributed to 32.0, 29.8, 13.4, 11.2, 10.8 and 2.7% of the spring PM2.5, respectively, in Lanzhou. The main potential sources of PM2.5 during the normal days were in the western parts of Lanzhou. Dust storms entered Lanzhou through the Hexi Corridor from several dust sources: southeastern Kazakhstan, Mongolia, the Kurbantungut Desert, and the Badain Jaran Desert. The northwest high-pressure; northern strong high-pressure and southwest low-pressure; northwest high-pressure and southwest high-pressure synoptic weather circulation types were prone to dust storms. Our results may provide a basis for local environmental governance.