西安城市不同功能区街道灰尘磁学特征及环境污染分析

Magnetic Characteristics and Environmental Pollution Analysis of Street Dust in Different Functional Zones of Xi'an City

为了解西安城市不同功能区的环境现状,通过采集西安城市不同功能区街道灰尘的样品,进行系统的环境磁学实验分析并结合扫描电子显微镜研究表明,街道灰尘中磁性矿物含量相对较高,多畴和假单畴的低矫顽力软磁性矿物为主要的载磁矿物,还含有赤铁矿等高矫顽力的硬磁性矿物.磁化率、饱和等温剩磁、低矫顽力软磁性矿物和非磁滞剩磁磁化率与饱和等温剩磁比值等磁性参数揭示出街道灰尘的磁学特征在西安城市不同功能区的差异以及污染的主要来源,根据污染程度划分为重度污染区、中度污染区和轻度污染区并对应西安市7个城市功能区:浐灞生态区(F区)为重度污染区,磁性物质含量较高,表明环境污染相对较重,污染的主要来源为'工业+交通';高新技术产业开发区(A区)和中心商务区(B区)磁性物质含量相对较高,粗颗粒物质相对较少,是中度污染的区域,其污染源分别为'工业'和'交通';经济技术开发区(C区)、科教商业区(D区)、科教文化产业区(E区)和教育科技产业区(G区)城市主要功能具有相似性,是轻度污染的区域,污染源主要为'交通'.

Urban environmental pollution can be revealed by the magnetic characteristics of street dust. Environmental magnetic measurements were carried out for the 151 samples of street dust collected in different functional zones of Xi＇an city. Magnetic susceptibility varied within the range between 169. 5 × 10- 8m3·kg（-1）and 977. 48 × 10- 8m3·kg（-1）,and the χlfaverage value was415. 66 × 10- 8m3·kg（-1）,which was 10 times higher than that of the background value. Isothermal remanent magnetization varied within the range between 2 005. 31 × 10- 5A·m2·kg（-1）and 10 897. 64 × 10- 5A·m2·kg（-1）,and the SIRM average value was 5 105. 99 × 10- 5A·m2·kg（-1）. The average value of frequency-dependent magnetic susceptibility was 1. 30,which was extremely low. The SIRM curve was consistent with χlfcurve. The results indicated a high concentration of magnetic minerals in street dust. The magnetic minerals were mainly low-coercivity ferrimagnetic（ magnetite and maghemite） and anti-ferromagnetic minerals（ hematite）,which contributed to the magnetic susceptibility. The main domains of magnetic minerals were composed of multiple domain（ MD） and pseudo-single domain（ PSD） ferrimagnetic minerals demonstrating the pollution of environment. According to the spatial distribution of magnetic properties of street dust and the different functional zones of Xi＇an city,seven districts（ A,B,C,D,E,F and G areas） were divided,which were summarized as three pollution types： heavily polluted,moderately polluted and lightly polluted. In the ecological district of Baqiao（ F area） which was heavily polluted,χlf,SIRM and soft values were all the highest in the seven areas,and the main pollution sources were industry and vehicle emission. χlf,SIRM and soft values were slightly higher in the high-tech industrial district（ A area） and the central business and commerce district（ B area）,which was moderately polluted by industry and vehicle emission.However,the magnetic parameters were relatively low in the functional zones of education,tourism and culture（ C,D,E and G area）,demonstrating that these areas were only slightly polluted by vehicle emission.