Magnetic characteristics of atmospheric dustfall in a subtropical monsoon climate zone of China and its environmental implications: A case study of Nanjing

Abstract

Nanjing is located in the subtropical monsoon climate zone of China. In this study, a series of monthly collections of atmospheric dustfall was performed in different directions from a high-rise building in Nanjing from February 2015 to March 2016. A series of magnetic parameters including χ, χfd%, χARM, SIRM, magnetic hysteresis loops, high-temperature κ-T curves and SEM images was measured from atmospheric dustfall samples. The research shows that the type and size of magnetic minerals within atmospheric dustfall samples in Nanjing are similar to those found in northern cities in China, but the atmospheric dustfall samples in Nanjing have higher magnetic mineral concentrations. Coarse-grained magnetite dominated magnetic minerals. The peak concentrations of magnetic minerals contained from atmospheric dustfall of Nanjing occurred in summer. The relationship between magnetic parameters and meteorological data shows that the high values are mainly influenced by precipitation rather than by wind direction. Combined with results of the SEM images and the weak relationship between magnetic parameters and the data of PM 2.5 and PM10, all these indicate that the atmospheric dustfall of Nanjing is mainly from near-source polluted dustfall rather than from long-distance dustfall. This research suggests that environmental magnetism as a simple, economic and nondestructive technology, will be a useful tool in atmospheric dustfall research.