阿拉善沙漠高原降水化学特征与离子来源判别

Chemical Characteristics and Major Ion Sources of Precipitation in the Alxa Desert Plateau

为查明我国北方沙漠地区降水化学组成及来源,在阿拉善沙漠高原阿右旗气象站采集了2013—2015年的降水样品,测定了降水p H、EC(电导率)及主要离子当量浓度.结果表明:阿拉善沙漠阿右旗气象站降水p H和EC的范围分别为6.66~8.05和35~1 237μS/cm;Ca^(2+)、SO_4^(2-)、Na^+和Cl^-为降水中的主要离子,其总和占总离子的85%以上.降水p H、EC和主要离子当量浓度是反映空气质量的基本参数,较高的降水p H反映出当地降水具有明显的碱性特征.与其他地区相比,该地区降水的EC和可溶性离子日均湿沉降通量也较高,且随月份有较大的变化,表明干旱沙漠粉尘对当地降水水化学的贡献较大.根据离子来源相对贡献的计算结果发现,降水中92.8%的SO_4^(2-)和98%的NO_3^-来自人为源,98.8%的Ca^(2+)和88.7%的K^+为陆地来源,55%的Mg^(2+)为海洋源,24.8%的Na^+来自矿物风化,极少部分Cl^-为人为源.研究显示:除降水中的NH_4^+外,其他主要离子之间的相关性表明各种成因物质在风力作用下同时进入了大气;基于[NH_4^+](NH_4^+的当量浓度)与[K^+](K^+的当量浓度)相关性分析,降水中的NH_4^+来自生物质燃烧、肥料使用、动物粪便等.

In order to determine the chemical composition and source of precipitation in the desert areas of northern China, precipitation samples collected at the Ayouqi weather station in the Alxa Desert Plateau during 2013-2015 were analyzed for pH, EC （electrical conductivity）, and the major ion concentrations. The results show that the pH and EC values of precipitation vary from 6.66 to 8.05 and from 35 to 1237 μS /cm,respectively. Ca^2＋ , SO4^2- , Na^＋ and Cl^- are the dominant in precipitation, accounting for more than 85% of the total ion concentration. The pH, EC values and the major ions are the basic parameters of air quality. The high pH values reflect the alkaline characteristics of local precipitation. The EC values and wet deposition fluxes in the Alxa Desert Plateau are higher than that in other places and vary with months. These results show that mineral dust from arid deserts contributes greatly to the chemistry of local precipitation. According to the calculations of the ion source contributions, 92.8% SO4^2- and 98% NO3^- in precipitation were from the anthropogenic pollution, 98.8% Ca^2＋ and 88.7% K^＋ originated from the terrestrial sources, 55% Mg^2＋ was of marine origin, 24.8% Na^＋ came from mineral weathering and a tiny part of Cl^- was related to the anthropogenic input. The overall results suggest that the good correlations among the major ions, except NH 4 ＋, in the precipitation, indicating that various types of materials were synchronously carried into the atmosphere by wind. The good correlation of NH 4^＋ with K^＋ in the precipitation indicated that NH4^＋ probably resulted from biomass burning, fertilizer usage, animal manure and so on.