Abstract:
Geophysical magnetometric study on a collection of dust material from playgrounds in the city of Sofia and several sub-urban areas in its vicinity was carried out. The main aims of the study were: 1) evaluation of the degree of anthropogenic pollution at the urban playgrounds in Sofia; 2) tracking out the changes in the quality of environment during different seasons; 3) obtaining new data on the magnetic properties of anthropogenic settled dust. Experimental mineral magnetic data show that the main magnetic minerals are magnetite, maghemite and titanomagnetite. The obtained magnetic results are interpreted in relation to the degree of anthropogenic pollution by local (point) and areal (distant) sources, related to the atmospheric air circulation in the city and the particulate matter (PM) distribution. Magnetic susceptibility of the fine-grained (d < 1mm) dust fraction for the locations, sampled in the autumn 2017 and January 2019 is higher than the susceptibility of the coarse (d > 1mm) fraction. Contrary, playground dust sampled in summer 2019 has magnetic susceptibility of the coarse fraction higher than that of the fine fraction. It is concluded that fine-grained PM pollution dominates during the autumn-winter seasons, while during the summer season local sources (mostly automobile traffic) dominate. Scanning electron microscopy observations on magnetic extracts from playground dusts show abundant presence of anthropogenic particles of irregular shape and spherules formed as a result of high-temperature technological processes. All anthropogenic particles are strongly enhanced in iron oxides. In some of them other chemical elements, like lead, zinc and antimony are also detected.