Assessment of heavy metal contamination of dustfall in northern China from integrated chemical and magnetic investigation

Magnetic phases are a common component of dustfall samples and mineral magnetic studies have been increasingly exploited for air quality studies in recent years to assess the source and spatial-temporal distribution of anthropogenic magnetic particulates and associated heavy metals. Here we report a comparative study of magnetic and chemical properties of atmospheric particulate deposits from rural areas of Inner Mongolia and urban regions of Hebei and Beijing. The sample sets were collected at 13 monitoring stations by the gravimetric method between April 2009 and March 2010. At the rural sites paramagnetic clays, complemented by hematite and goethite recognized by Isothermal Remanent Magnetism (IRM) and Diffuse Reflectance Spectra (DRS) investigations, accompany fine grained magnetite as an important fraction. Although present as a residual phase in samples from the urban regions, coarse-grained magnetite of anthropogenic origin dominants the magnetic signatures in these latter environments. Systematic variations with local anthropogenic activity including traffic, the mining of ores and a range of industrial emissions are identified, together with a seasonal signature in the Beijing area. We use correlations between magnetic concentration-related parameters, notably magnetic susceptibility, and the Pollution Load Index to demonstrate how magnetic parameters can be used as a practical tool for mapping degrees of heavy metal pollution and tracing the sources of pollutants in dustfall samples.