兰州市大气降尘环境磁学特征研究

Magnetic Property of Lanzhou Dustfall and Its Implication in Urban Pollution

应用环境磁学方法系统研究了兰州市区大气自然降尘的磁学特征(包括磁化率、无磁滞磁化率、等温剩磁、磁滞回线和热磁曲线)。结果表明:兰州市大气降尘中磁性矿物含量较高,磁参数的贡献主要来自磁铁矿和磁赤铁矿,磁性矿物的粒度较粗,为准单畴颗粒;兰州市大气污染严重,磁化率等磁学参数较好地反映了兰州市大气污染状况;兰州市空气污染防治近年来已取得了一定成效,空气质量有了较大改善,冬季污染在逐年减轻,而夏季污染变化不大。环境磁学作为一种简单、快速且无破坏性的研究手段,可以为城市污染防治研究提供许多有价值的信息。

In this study a set of environmental magnetic parameters （Х^lf, Хfd %, Хarm SIRM, HIRM, SOFT and back field IRM） were measured on the monthly-collected dustfall samples（KLD）, which were collected during April 1997 to May 2000 and November 2004 to October 2005 at Lanzhou University campus. The results demonstrate that the main magnetic minerals in the dustfall are magnetite and/or maghaemite. Cross plots of Mrs/Ms vs. Bcr/Bc and Хfd % vs. Хarm/SIRM indicate that the main magnetic grain sizes in street dust are pseudo single domain （PSD）. With the great efforts of the government and local authority to control the urban environment during the past decades, the air quality in Lanzhou has been improved greatly in winter, but it is not so obvious in summer. This research also reveals that as a simple, rapid and no-distrusting technology, environmental magnetism could be a valuable tool in pollution study.