Demonstration of connection between pollutant dispersal and atmospheric boundary layers by use of magnetic susceptibility mapping, St. Jacob (Austria)

The relationship between spatial airborne pollutant dispersal and atmospheric boundary layers was studied by means of magnetic susceptibility mapping of topsoils, in a narrow mountain valley with a suspected point emission source. The horizontal and vertical distribution of magnetic susceptibility of soils in the St. Jacob area was recorded, and magnetic phases were subsequently identified. A significant correlation between magnetic susceptibility and the concentration of heavy metals Cd, Pb and Fe was observed. The pattern of magnetic susceptibility anomalies corresponds with the main wind direction and the orientation of the valley, and the main susceptibility anomaly is situated in the region around the emission source. The magnetic particles responsible for the main susceptibility anomaly consist of Fe-rich combustion spherules up to a size of 20 mum. These magnetic particles also carry part of the heavy metal load. The relationship between the spatial dispersal of pollutants and atmospheric boundary layers was investigated by means of a comparison of the pattern of magnetic anomalies with the climate map of the valley. The distribution of pollutants is confined by an atmospheric boundary layer at about 200 m above the bottom of the valley. This relationship is particularly conspicuous north and south of the emission source, because the spread of pollutants is prevented by the steep northern and southern slopes of the valley. The area west of the suspected emission source was contaminated more heavily due to prevalence of downslope winds during the winter, which occur by night-time radiational cooling when the frequent presence of inversions and atmospheric boundary layers leads to a nearly uniform deposition of pollutants. The results confirm the applicability of magnetic susceptibility mapping as a method to investigate the influence of atmospheric processes in pollutant deposition. (C) 2004 Elsevier Ltd. All rights reserved.