大气降尘磁学特征对城市污染源的指示

本文应用环境磁学方法研究了兰州市区大气自然降尘的磁学特征。结果表明:兰州市大气降尘中磁性矿物含量较高,主要含有磁铁矿和磁赤铁矿,并伴有少量赤铁矿,磁性矿物颗粒较粗,为准单畴颗粒;兰州市自然粉尘背景值较高,但市区污染物仍以人为源为主,尤其在冬季采暖期间最为显著,且在春、夏季节,兰州市的污染仍以人为源为主,与通常认为兰州市污染冬季以燃煤为主,春、夏季以粉尘为主的模式有较大差异。

Magnetic Characteristics of Urban Dustfall and the Implications on Pollution Origins

A set of environmental magnetic parameters(Xlf,Xfd%,Xarm,SIRM,HIRM,SOFT and back field IRM) of the monthly-collected dustfall samples,which were collected 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),were analyzed.Results demonstrated that the main magnetic minerals in the dustfall were magnetite and maghaemite with some haematite.Cross plots of Mrs/Ms vs.Bcr/Bc and Xfd % vs.Xarm/SIRM indicated that the main magnetic grain sizes in street dust were pseudo single domain(PSD).The high concentration of magnetic minerals in the dust fall indicated that Lanzhou was serious polluted.The main pollution sources are anthropogenic activities and nature dust.The former poses a great threat during the whole year,which is different from the general opinion that the natural dust is main pollution in summer.The research also revealed that as a simple,rapid and accurate technology,environmental magnetism would be a valuable tool in pollution study.