Characterisation and source apportionment of chemical components in fine particulate matter from atmosphere in two districts of Lanzhou City

Environmental context Exploring the characterisation and sources of the chemical composition of fine particulate matter in the atmosphere is critical to human health. The main sources of PM2.5 in Lanzhou City are dust, secondary pollution, industry, biomass burning, traffic and coal combustion. In Chengguan District, dust sources are the most significant contributors, whereas secondary pollution sources are dominant in Xigu District. This provides directions and ideas for future local ecological environment management, especially air pollution. Rationale The characterisation and sources of the chemical composition of fine particulate matter in the atmosphere are of critical importance to the environment and human health. As the capital of Gansu Province with a population of more than 4 million people, and being one of important industrial cities in western China, it is of importance to study the characterisation and sources of atmospheric fine particulate matter chemical constituents in Lanzhou City. Methodology In this study, monitoring was carried out from January 2018 to June 2022 in Chengguan and Xigu Districts, and a total of 702 valid samples were collected. Measurements included PM2.5 mass concentrations, water-soluble ions, metals, metalloids and polycyclic aromatic hydrocarbons (PAHs) in both districts. Results The results showed that PM2.5 mass concentrations in both districts exhibited a decreasing trend throughout the study period, with seasonal variations characterised as high in winter and spring, and low in summer and autumn. The concentration of water-soluble ions follows the order of SO42- > NO3- > NH4+ > Cl-, with a seasonal distribution pattern of winter > autumn > spring > summer (P < 0.05). The concentrations of metals and metalloids were higher in Xigu District than in Chengguan District, following a seasonal pattern of spring > winter > autumn > summer (P < 0.05). PAHs concentrations were significantly higher in Chengguan District than in Xigu District (P < 0.05), with a seasonal pattern of being high in winter and low in summer (P < 0.05). Discussion The main sources of PM2.5 in Lanzhou City comes from dust, secondary pollution, industry, biomass burning, traffic and coal combustion. Dust sources were the most significant contributors in Chengguan District (37.6%), whereas secondary pollution sources were predominant in Xigu District (40.9%). This provides the latest research evidence exploring feasible pollution reduction pathways for Lanzhou to achieve cleaner skies. The results provide valuable insights and a scientific basis for the prevention and control of atmospheric PM2.5 pollution in Lanzhou City.