Distribution of magnetic particulates in a roadside snowpack based on magnetic, microstructural and mineralogical analyses

Vehicle traffic is at present one of the major sources of environmental pollution in urban areas. Magnetic parameters are successfully applied in environmental studies to obtain detailed information about concentrations and quality of iron-bearing minerals. A general aim of this research was to investigate the magnetic, microstructural and mineralogical properties of dust extracted from the roadside snowpack accumulated on the side of an urban highway, northern Helsinki. Vertical snow profiles were taken at different distances (5, 10 and 15 m) from the road edge, during winter season 2010-2011. The temporal distribution of mass magnetic susceptibility (chi) of the road dust shows that the concentration of magnetic particles increases in the snowpack during winter. Roadside snowpack preserves a large fraction of the magnetic particulate until the late stages of melting and this could be considered as one of the main factors responsible for the resuspension phenomenon observed in Nordic countries. The vertical distribution of chi and SIRM (saturation isothermal remanent magnetization)/chi ratio may indicate the migration of magnetic particles down in the snowpack during melting conditions. Ultrafine to coarse-grained (superparamagnetic to multidomain) magnetite was identified as the primary magnetic mineral in all the studied road dust samples. The examined road dust contains significant amount of dia/paramagnetic minerals (e.g. quartz, albite, biotite) and the content of magnetite is relatively low (below 1 weight percent, wt%). The roadside snowpack is enriched in anthropogenic particles such as angular and spherical iron-oxides, tungsten-rich particles and sodium chloride. This study demonstrates the suitability of snow as an efficient collecting medium of magnetic particulates generated by anthropogenic activities.