Magnetic particles greatly contribute to atmospheric particulate matter (PM) pollution. The concentration, particle size, and component changes in different functional areas of a city and during different seasons can be detected by environmental magnetic indicators. However, the regularity of changes in magnetic particles and their sources with increasing height indoors are unclear, and whether magnetic parameters can directly indicate atmospheric PM pollution is unclear. Therefore, we investigated indoor dustfall in a high-rise building in Xuzhou and then combined the experimental results with existing data from Lanzhou for further research. Here, we showed that in these industrial cities, there are two prevalent pollution zones. One is close to the ground at ∼5–18 m (lower pollution zone), and the other is located above ∼42.2 m (high-level pollution zone). We found that the lower pollution zones in both Xuzhou and Lanzhou contained coarse ferrimagnetic particles (mainly magnetite), which are likely related to vehicular emissions and some industrial activities. However, the high-level pollution zone in Xuzhou was dominated by fine-grained ferrimagnetic particles (with a small amount of hematite) from industrial combustion processes rather than coarse magnetic particles from natural sources, while in Lanzhou, these two types of magnetic particles yielded combined effects. An ultrafine magnetic particle pollution zone resulting from vehicle emissions occurred only in Xuzhou, indicating that this source is not prevalent in the industrial cities of northern China. Moreover, our results demonstrated that the changes in the size and composition of magnetic particles are closely related to the different atmospheric PM types.

中文翻译：

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北方工业城市室内降尘大气PM中磁性粒子的垂直变化

磁性颗粒对大气颗粒物（PM）污染有很大影响。通过环境磁指示器可以检测城市不同功能区、不同季节的浓度、粒径和成分变化。然而，随着室内高度增加，磁性颗粒及其来源的变化规律尚不清楚，磁性参数是否可以直接指示大气PM污染尚不清楚。因此，我们对徐州某高层建筑室内降尘进行了调查，并将实验结果与兰州现有数据相结合进行进一步研究。在这里，我们表明在这些工业城市中，存在两个普遍的污染区。一处靠近地面约 5~18 m（低污染区），另一处位于约 42.2 m 上方（高污染区）。我们发现徐州和兰州的低污染区含有粗大的亚铁磁性颗粒（主要是磁铁矿），这可能与车辆排放和一些工业活动有关。然而，徐州的高污染区主要是工业燃烧过程中产生的细粒亚铁磁性颗粒（含有少量赤铁矿），而不是来自天然来源的粗粒磁性颗粒，而在兰州，这两类磁性颗粒产生了综合效应。仅徐州出现了汽车尾气超细磁粉污染带，说明该污染源在北方工业城市并不普遍。此外，我们的结果表明，磁性颗粒的尺寸和成分的变化与不同的大气PM类型密切相关。