Magnetic characteristics of atmospheric particulate matter and its indication of atmospheric pollution during winter in Lanzhou, NW China

Abstract

In order to elucidate the significance of environmental magnetic methods in monitoring atmospheric particulate matter pollution, this study conducted an analysis of the magnetic and chemical properties of PM10 and PM2.5 samples collected during winter in Lanzhou City. The magnetic measurements revealed significant variations in the saturation isothermal remanent magnetization (SIRM) values between daytime and nighttime, with higher SIRM values during nighttime. The magnetic properties were dominated by low-coercivity ferrimagnetic minerals exhibiting multidomain and pseudo-single domain characteristics. SIRM exhibited a significant correlation with the mass concentration of particulate matter. The correlation indicated that during the day, the SIRM of PM2.5 showed a significant correlation with elements such as Zn, Pb, Cl−, K+, K, and organic carbon (OC). Additionally, the SIRM of PM10 was also related to Mg2+, Ca2+, and some crustal elements. During nighttime, the SIRM of PM10 and PM2.5 was primarily associated with Cl−, K+, K, and OC. By comparing the magnetic and chemical properties of particulate matter under clean and non-clean air conditions, similar trends were observed between SIRM and indicators such as NO3−/SO42−, As/Pb, K+/K, and Ca2+, which are commonly associated with traffic emissions, biomass burning, and construction dust sources. Factor analysis was applied to further investigate the sources of magnetic particles, unequivocally demonstrating that traffic emissions constituted the primary source of magnetic particles in both PM10 and PM2.5 during daytime, whereas biomass burning emerged as the predominant source during nighttime. Consequently, our study highlights the innovative use of magnetic parameters as reliable indicators for assessing atmospheric particulate pollution and discerning the sources of particulate matter.