| Lanzhou has been one of the most seriously polluted cities in the world due to its special geographical location and weather conditions, which make it an ideal place for urban pollution studies. A set of environmental magnetic parameters (χlf,χfd%,χARM, SIRM, HIRM, SOFT and back field IRM) of the street dust sampled in Lanzhou during spring and summer 2005 were analyzed. These samples were collected along a main street across the urban area and a mountain route from foot to the top. Results demonstrate that the main magnetic minerals in the street dust are magnetite, maghaemite and haematite with some paramagnetic minerals. Plots of Mrs/Ms vs. Bcr/Bc and χfd % vs. χARM/SIRM indicate that the main grain size of magnetic minerals in the street dust are pseudo single domain (PSD). The results reveal that the Lanzhou city is more polluted in spring than in summer. The main pollution sources are anthropogenic activities (81.9%) and natural dust (18.1%), especially the former. The spatial distribution of pollution is controlled by the topography and weather conditions. |
