Multi-Elemental Characterization of PM_0.4–0.7 and PM_1.1–2.1 in the Ambient Air of Isfahan (Iran) Complemented by the Speciation of Mn and Cr Using SR-XANES

In the present paper, we seek to study the interaction of desert dust and urban pollution in the particulate matter (PM) of an urban area of Isfahan, Iran, where anthropogenic and natural emission sources substantially contributed to the urban emission inventory. We used an eight-stage Anderson Cascade Impactor (ACI) for size-segregated sampling from the Isfahan PM for autumn 2017. According to the gravimetric analysis results, our study concentrated on the fractions with the largest mass concentrations, i.e. aerosols with sizes from 0.4 to 0.7 µm (PM_0.4–0.7) and from 1.1 to 2.1 µm (PM_1.1–2.1). We then employed chemical and optical methods for the multi-elemental characterization of the size-segregated particles and analyzing the interactions between the desert dust and urban pollution. The absorption-near-edge-structure (XANES) spectroscopy technique was also applied here for the speciation of Mn and Cr in the studied fractions. Our results showed that PM_1.1–2.1 dominated by the dust particles, and particles originated by the fuel combustion have a significant contribution to the fraction PM_0.4–0.7. The mass concentration of the iron element in the PM_0.4–0.7 was higher than that in the PM_1.1–2.1. The significant contribution of iron-rich particles to both studied fractions demonstrates that anthropogenic sources play an important role in the air quality degradation of the city. The interaction of desert dust and urban pollution was notably achieved in the fraction PM_0.4–0.7, but the fraction PM_1.1–2.1 is comprised predominantly of regular-shaped particles with the origin of natural sources (desert dust). XANES results argued that Cr and Mn species exist mainly in the trivalent and divalent oxidation states in the studied area, respectively. The weathering and surrounding conditions of the city could moderately develop the oxidation states of Cr and Mn.