Alkaline earth metals act as dominating acid-neutralizing species in atmosphere and hence, regulate the rain water chemistry significantly. In this contribution, concentrations of these metals (Mg, Ca, Sr and Ba) and other major ions in rain water samples, collected during south-west monsoon of year 2017, from a coastal location (Berhampur) in eastern part of India have been analyzed to trace their provenances and controlling factors. The chemical compositions of rain water reveal oceanic and continental supply of Mg and Sr to the site, whereas Ca and Ba are pre-dominantly supplied through continental sources. The dominancy of continental fluxes at this coastal site is mainly due to particulate fluxes from regional lithologies and favorable wind pattern for long-range transport from south-western/western directions. An inverse model involving chemical mass balance between rain water composition and its possible sources have been adopted in this study to quantify the source(s) contributions. These model results show that the continental Mg is mainly derived from long-range transport of mafic minerals from Deccan Traps (40 ± 21%) with sub-ordinate contribution (15 ± 6%) from regional lithologies. On average, about 70% of rain water Ca at Berhampur is derived from carbonates, whereas most of the Ba (~95%) is supplied from regional silicates (charnockites and khondalites). Owing to faster dissolution kinetics of these silicates with higher Ba content, the silicates contribute most of the rain water Ba concentration over this region. The median Ba content (29 nM) at this location is systematically higher than available literature Ba data for rain water worldwide (1-22 nM). The observed higher concentrations of Ba, a micronutrient, in rain water emphasize important role of regional lithology in the biogeochemical cycling of nutrients over the region via wet deposition.

中文翻译：

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印度东海岸雨水中钡浓度升高：区域岩性的作用

碱土金属在大气中充当主要的酸中和物种，因此显着调节雨水化学。在此贡献中，这些金属（Mg、Ca、Sr 和 Ba）和其他主要离子在 2017 年西南季风期间从印度东部沿海地区 (Berhampur) 收集的雨水样品中的浓度为分析以追溯其来源和控制因素。雨水的化学成分揭示了该地点的 Mg 和 Sr 的海洋和大陆供应，而 Ca 和 Ba 主要通过大陆来源供应。该沿海站点的大陆通量的主导地位主要是由于来自区域岩性的颗粒通量和从西南/西部方向进行远程传输的有利风型。本研究采用了涉及雨水成分与其可能来源之间的化学质量平衡的逆模型来量化来源的贡献。这些模型结果表明，大陆镁主要来源于德干圈闭（40±21%）的镁铁质矿物的长距离输运，次要来自区域岩性的贡献（15±6%）。平均而言，Berhampur 大约 70% 的雨水 Ca 来自碳酸盐，而大部分 Ba（~95%）来自区域硅酸盐（charnockites 和 khondalites）。由于这些具有较高 Ba 含量的硅酸盐的溶解动力学更快，硅酸盐在该区域贡献了大部分雨水 Ba 浓度。该位置的平均 Ba 含量 (29 nM) 系统地高于全球可用的雨水文献 Ba 数据 (1-22 nM)。在雨水中观察到的较高浓度的 Ba 是一种微量营养素，强调了区域岩性通过湿沉积在该区域营养物质的生物地球化学循环中的重要作用。