摘要:重金属是影响农田土壤环境质量和农产品品质的主要污染物，大气沉降是农田重金属的来源之一。长期以来，由于观测资料缺乏，对于我国农业区大气重金属的沉降量和来源认识一直不清楚。本研究基于河北典型农田连续1年的外场观测，测试分析了大气气溶胶9个粒径段中25种金属元素的含量，结合干沉降阻抗模型估算了这些金属的干沉降量，并利用PMF模型对其来源进行了解析。结果表明，该区域25种金属元素在细粒子（DP ≤ 2.1 μm，DP为空气动力学直径，下同）、粗粒子（2.1 < DP ≤ 9 μm）和巨粒子（DP>9 μm）中的质量浓度存在较大差异。重金属（如：Zn、Cd和Pb等）主要富集在细粒子，而地壳源的金属（如：Al、Fe和Th等）主要富集在粗粒子。大多数金属元素的浓度呈现冬春季高于夏秋季的变化特征。Cr是细粒子和粗粒子中质量浓度最高的重金属，其次为As、Zn、Pb、V和Sb。重金属中，Cr的大气干沉降量最高，达350.7 mg·m-2·a-1，其次是As、Sb和V，分别为153.4 mg·m-2·a-1、103.1 mg·m-2·a-1和102.3 mg·m-2·a-1。研究区域大气中金属元素的主要来源为道路扬尘、工业、矿尘、燃煤和机动车排放。巨粒子中的金属主要来自矿尘源（62.0%），细粒子中的金属主要来自燃煤、机动车和工业源（67.7%）。颗粒物的粒径越小，人为排放源的贡献越大，重金属的污染风险（富集因子）也越高。农田重金属污染防治需要充分考虑大气沉降的输入及来源的变化。
关键词:农田/
大气干沉降/
重金属/
源解析/
污染控制
Abstract:Atmospheric deposition is a major contributor of heavy metals contaminating the farmland, which endangers the quality of soil as well as agricultural products. Because of the paucity of relevant observational data, the dry deposition flux and sources of atmospheric heavy metals in agricultural areas have for long remained unclear. Based on a year of field observation in a typical farmland in Hebei Province, we measured the content of 25 elements in nine size-segregated particles. The dry deposition flux of atmospheric metal elements was estimated by employing resistance modeling. In addition, the sources of atmospheric metal elements were apportioned using the PMF model. The results indicated that there were large differences in the concentrations of 25 metals between the fine particles (DP ≤ 2.1 μm, aerodynamic diameter, the same below), coarse particles (2.1 < DP ≤ 9 μm), and giant particles (DP>9 μm). Heavy metals (such as Zn, Cd, and Pb) were primarily concentrated in fine particles, whereas the crustal elements (such as Al, Fe, and Th) were primarily concentrated in coarse particles. The concentrations of most metals were higher in spring and in winter rather than in summer and autumn. Annual mean concentration of Cr was the highest among the heavy metals both in fine and coarse particles, followed by As, Zn, Pb, V, and Sb. Regarding the dry deposition flux, Cr also had the highest value of 350.7 mg·m-2·a-1, followed by As, Sb, and V, which were 153.4, 103.1, and 102.3 mg·m-2·a-1, respectively. The primary sources of atmospheric metal elements confined to the study area were road dust, industrial pollution, mineral dust, coal combustion and vehicle emission. The metals in the giant particles were primarily from dust source (62.0%), whereas the metals in the fine particles were primarily from coal, motor vehicles and industrial sources (totally 67.7%). With decrease in particle size, the contribution of anthropogenic pollution increased, thereby increasing the pollution risk (enrichment factor) of heavy metals. In conclusion, the study was critical in considering the input and sources of atmospheric deposition regarding regulation of farmland involving heavy metals.
Key words:Farmland/
Atmospheric dry deposition/
Heavy metals/
Source apportionment/
Pollution control
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