[Magnetic properties of indoor dustfall at different heights in Lanzhou].

Environmental magnetic measurements were carried out on the samples of indoor dustfall collected from Qiyun building at different heights in Lanzhou University. The results indicate a high concentration of magnetic minerals in indoor dustfall, dominated by pseudo-single domain (PSD) and multiple domain (MD) ferrimagnetic minerals which are mainly from air pollution. The concentration and granulometry of magnetic minerals decrease with the increase of the height within 24 m near surface. We call it near surface blowing model dominated by low pollution sources. Within 10 m near the top of the building, the concentration and granulometry of magnetic mineral show the synchronous change with the increase of height and that is called building damping model dominated by high pollution sources. The concentration of magnetic minerals can reflect particulate matter pollution in Lanzhou. The results show the pollution is relatively slight from 20-30 m and can provide a scientific basis for atmospheric dust management and improvement at the same time.