Chemical nature and predominant sources of PM10 and PM2.5 from multiple sites on the Silk Road, Northwest China

Abstract

We analyzed particulate matter (PM10 and PM2.5) from 4 urban sites (Wuwei, Zhangye, Jiuquan and Dunhuang) located on the Silk Road of Northwest China in summer and winter of 2018 for water-soluble ions, carbonaceous aerosols and heavy metals. The focus was to examine patterns in mass concentration, chemical nature and predominant sources. The average concentrations of PM10 and PM2.5 in this region were in the range of 112–152 μg/m3 and 70–81 μg/m3, respectively, and water-soluble inorganic ions (WSIIs) and mineral dust were the two main species of PM. PM10 and PM2.5 showed a relatively homogeneous spatial distribution in this area. The ratios of chemical composition and the enrichment factors of heavy metals were also analyzed. Four sources were identified by the positive matrix factorization (PMF) model. Dust and secondary inorganic aerosols were the dominant PM10 and PM2.5 contributors, respectively, accounting for 32.2% for PM10 and 34.7% for PM2.5. The contribution of dust and factory combustion emission sources to PM2.5 in this region was higher than that in the North, East and South regions of China, while that of secondary inorganic aerosol sources was relatively lower than in these other areas. The backward-trajectory model revealed that high PM pollution was related to the air masses from adjacent polluted regions in Inner Mongolia and was characterized by high PM contributions from secondary aerosols.