Joint pollution and source apportionment of PM_2.5 among three different urban environments in Sichuan Basin, China

The PM_2.5 were sampled in three different urban environments: (city of) Chengdu, Leshan, and Dazhou, which are located in Sichuan Basin. 8 types of water-soluble ion and 25 types of metal element were measured in each PM_2.5 sample across the seasons of 2017. The study results suggest that the joint PM_2.5 pollution among the three cities mainly occurred in autumn and winter, and the air quality of Chengdu and Leshan was largely affected by Dazhou. Overall, the mass concentrations of PM_2.5 of these three cities exhibited no statistically significant differences. However, Leshan had the highest level of ionic pollution, and the dominant form of inorganic compound in ambient PM_2.5 was NH₄NO₃, and a competitive relationship between form of NH₄NO₃ and (NH₄)₂SO₄ (NH₄HSO₄) was found as well. High homology between SO₄^2- and NO₃^- has been observed in all the three cities, and the ratio between [SO₄^2-] and [NO₃^-] indicated that the stationary source contributed the most to ambient PM_2.5 in Dazhou. The mass concentrations of the total metal elements from the three cities exhibited similar levels, nevertheless, Dazhou had the highest mass fraction of total metal elements in PM_2.5. The enrichment factor of each element indicated that the natural source was highly contributory to the crustal elements in PM_2.5 of all the three cities, whereas Cr, Cu, Se, Mo, Cd, Tl and Bi were primarily originated from anthropogenic source. In addition, the source apportionment of PM_2.5 suggest that Dazhou had the different factors and factor-contributions comparing with Chengdu and Leshan.