Urban environmental problems are of increasing concern. Lanzhou is a large industrial city in North-west China. Street dust samples representing different temporal and spatial scales were collected for magnetic properties study. Magnetic measurements indicate a high concentration of magnetic minerals in Lanzhou street dust, dominated by pseudo-single domain (PSD) magnetite. The concentration of magnetic materials is distinctly high in winter and spring, low in autumn. Similarly, higher concentra-tions associated with heavy industry, concentrated residential development, and vehicular traffic sug-gest mixed contributions of magnetic material from both anthropogenic and natural sources. χ_lf and SOFT% are effective magnetic parameters that denote seasonal differences among magnetic proper-ties in street dust, convenient and economical methods for monitoring street dust pollution.
WANG GuanXIA DunShengLIU XiuMingCHEN FaHuYU YeYANG LiPingCHEN JianHuiZHOU AiFeng
Urban particulate pollutants not only affect urban air quality but also directly threaten public health. Lanzhou has been one of the most seriously polluted cities in the world due to its special geophysical location and weather conditions, which makes it an ideal place for urban particulate pollution study. In this study a set of environmental magnetic parameters (χ_(1f),χ_(fd)%, χ_(ARM), SIRM, HIRM, SOFT and back field IRM) were measured and analyzed for the dustfall samples collected monthly during 1997.4—2000.5 and 2004.11—2005.10 at Lanzhou University campus (KLD and CCS) and at a clear site of Gaolanxian (GLX). Results demonstrate that the main magnetic minerals in the dustfall are magnetite, with some maghaemite and haematite. Cross plots of M_(rs)/M_s vs. B_(cr)/B_c and χ_(fd)% vs. χ_(ARM)/SIRM indicate that the main magnetic grain sizes are pseudo-single-domain (PSD). The high concentration of magnetic minerals in the dustfall indicates that Lanzhou is seriously polluted. The main pollution sources are anthropogenic activities and nature dust, with the former posing a great threat during the whole year, which is different from the general view that the natural dust is the main contributor in summer. With great efforts of the government and local authority in the past decades, the air quality in Lanzhou has been improved in winter, but it is not so obvious in summer. This study also reveals that as a simple, rapid and accurate technology, environmental magnetism could be a valuable tool for urban pollution study.
XIA DunSheng1,2, YANG LiPing2, MA JianYing1, YU Ye1, WANG Guan2 & CHEN FaHu2 1 Key Laboratory of Desert and Desertification, Institute of Cold and Arid Regions Environmental and Engineering, Chinese Academy of Sciences, Lanzhou 730000, China
