硫酸根三氧同位素激光氟化-质谱仪在线测试技术及应用于珠江河水硫酸根示踪研究

Sulfate is the major component in Chinese aerosol and hydrosphere, which rising several problems in surface critical zone, such as water acidification and enhancing catchment chemical weathering. Sulfate in the river is affected by atmospheric deposition, evaporites dissolution, and oxidization from mineral, soil and chemical fertilizer. Sulfate Δ17O is a more accurate tool than traditional isotopes (δ34S and δ18O) for tracing the sulfate sources in river. There is no mature technical method for sulfate triple oxygen isotopes measurement by online laser fluorination system coupled with isotopic ratio mass spectrometer (LF-IRMS) in China, the sulfate purified method need test, and there is no study on the riverine sulfate triple oxygen isotopes. Pearl River locates in wet-warm South China with serious acid rain, intensive chemical weathering and mining activity, therefore the study of riverine sulfate sources is important. The proposal aims are 1) develop a complete method for barium sulfate purification and online analysis for sulfate triple oxygen isotopes on LF-IRMS; 2) use sulfate Δ17O together with other sulfate isotopes (δ34S and δ18O) and geochemical compositions in better tracing riverine sulfate sources study (especial for determining the atmospheric contributions) in Pearl River. This study can constrain the sulfate sources and cycles in typical major rivers in China, which provide information to strategic management and treatment to sulfate.

硫酸根是我国气溶胶及水体最主要的成分之一，它引起表生关键带诸多问题，如水体酸化，增加流域化学风化等。河流硫酸根受到大气沉降、蒸发岩溶解、硫化物矿/土壤和化肥的氧化的影响。硫酸根Δ17O比传统的δ34S和δ18O能更好地示踪中河水硫酸根的来源。目前我国尚未建立完善的硫酸根三氧同位素激光氟化-质谱仪（LF-IRMS)在线测试技术，硫酸根纯化也需要验证，也尚未开展河流硫酸根三氧同位素的应用研究。珠江处于湿润温暖的华南，受到较严重的酸雨、强烈的化学风化及矿山活动影响，因此河水硫酸根的来源研究意义重大。本项目拟开展1）建立完善的方法用于硫酸根纯化及LF-IRMS在线测定其三氧同位素；2）硫酸根Δ17O,结合δ34S和δ18O，及其他地球化学组成能更好地研究珠江河水硫酸根来源(尤其是用Δ17O获得大气源的贡献)。这项研究将更好地掌握我国大型流域硫酸根的来源及迁移转化，为流域管理，硫酸根治理提供决策。

我们地表水体依然面临着人类活动引起硫酸盐排放（大气，工业废水甚至农业活动）胁迫。本项目主要利用三氧同位素及硫同位素研究珠江三大主要支流硫酸盐的季节变化特征，结合大气源，蒸发盐来源及自然氧化源的同位素特征来定量追溯不同来源的贡献。首先我们分析了广州一年的周分辨率PM2.5硫酸盐的δ34S和δ18O，得到全年平均值分别为2.6±1.2和10.1±2.3, 表明近年来大气颗粒物的硫酸盐来自生物质硫的贡献增加。同时分析了广州少量屋顶灰尘及空调灰（多年来混合值）的硫酸盐三氧同位素，得到δ34S，δ18O和Δ17O平均值分别为5.0±1.6，8.0±2.0及0.56±0.11，表明过去数年大气颗粒物中硫主要来自燃煤，而大气氧化过程主要以H2O2为主。还发现西江河水Δ17O普遍偏负，认为是硫化物的自然氧化及蒸发盐（石膏）淋滤是主要贡献者。发现酸性矿山废水的硫酸盐Δ17O可以低至-0.41，认为主要受到溶解氧的氧化过程，结合河水硫酸盐δ34S和Δ17O可以用来研究酸性矿山废水对周围水体的影响。