【摘要】 通过磁学手段以树木年轮为研究对象,通过多参数磁学研究探讨钢铁厂周围环境污染的历史。研究表明:钢铁厂附近树木年轮样品中磁性矿物为准单畴(其中颗粒偏向于多畴)的磁铁矿,磁性矿物形状各异,粒径大小不一;样品中磁铁矿的含量随年份的不同差异很大;通过树木不同方向上磁性参数尤其是饱和等温剩磁(SIRM)值的差异以及扫描电镜(SEM)和X射线能谱(EDX)分析,发现树木木质部中的磁性颗粒来自于树皮,即大气中颗粒被树皮和树叶表面吸附后,在树木的生长季节通过树皮进入形成层的木质部细胞,然后通过木质化作用被固定在当年生长的树木木质部木材中;另外,朝向钢铁厂方向的树干年轮钻芯样品SIRM值与对应年份钢铁厂年生产量之间高度相关,磁性颗粒在年轮之间不存在横向迁移,树干年轮钻芯的磁性参数(SIRM和部分磁滞参数)可指示该区大气环境污染的历史;污染树木钻芯样品的SIRM随时间的变化曲线说明该研究区大气污染日益严重。更多还原

【Abstract】 Comparing with traditional chemical methods, magnetic method is simple, rapid, precise, low-cost, and non-destructive for monitoring air pollution and has been widely applied. In this paper, with an aim of better monitoring air pollution, we selected tree bark and tree ring core samples(willow, Salix matsudana)close to a smelting industry in northeast Beijing for magnetic studies. With systemic magnetic measurements on these samples, magnetic response mechanism of contamination(e.g. tree bark, tree ring)to long-term environmental pollution has been constructed, and accordingly the pollution range, degree and process of human activities could be assessed. This paper is the first to investigate the relationship of smelting factory activities and magnetic properties of tree rings. Results of magnetic techniques including low-temperature experiment, successive acquisition of IRM, hysteresis loops, and SIRM measurements indicate that magnetic particles are omnipresent in tree bark and trunk, which are predominated by magnetite in pseudo-single domain state. Further comparing confirms that magnetic properties of tree trunk and branch drilling cores collected from different directions and heights on the trees are different. Core samples closer to pollution source contains more magnetic particles than others, indicating that magnetic particles are most likely to be intercepted and collected by tree bark first, then enter into tree xylem tissues during growing season, and finally are enclosed in a tree ring by lignifying. Correlation has been obvious observed between time-dependent SIRM values of tree ring cores and the annual iron production of the smelting factory. Considering dependence of magnetic properties in sampling directions, heights of ring cores, we argue that magnetic particles in the xylem cannot move between tree rings. Accordingly, SIRM and some other magnetic parameters of core samples closer to pollution source could be contributed to historical atmospheric pollution produced by heavy metal smelting activities. We believed that a synthetic magnetic study is an effective method for determining concentration and grain size of ferromagnets in the atmospheric PMs, and thus should be a rapid and feasible technique for monitoring atmospheric pollution.更多还原