This study provides an analysis of a five-year time series chemical composition of the bulk deposition (2009–2013), collected within a farm surrounded by industrial and urban settlements in a semi-rural area of the Po Valley, with the aim of characterizing potential emission sources affecting precipitation composition at the site. Most monitoring efforts in this region, recognized as one of the most polluted in the world both due to the intense industrialisation and urbanisation as well as to frequent air stagnation conditions, are presently devoted more to gaseous and particulate pollutants than to precipitation chemistry. The bulk deposition samples were very concentrated in chemical species, both acidic and alkaline, high compared to other polluted sites in the world and to locations in the same district. The mean ions concentrations (in μeq l−1) are: NO3− (243) > SO42− (220) > PO43− (176) > Cl− (153) > NO2− (29) > F− (2.6); NH4+ (504) > Ca2+ (489) > K+ (151) > Na+ (127) > Mg2+ (127). pH data shows a trend toward slightly alkaline conditions attributed to the large presence of ammonium and crustal elements, in spite of high concentrations of nitrates and sulphates. The relevant concentrations of Ca2+ and Mg2+ further suggests that these alkaline conditions might be due to the correspondingly significant concentrations of carbonates/bicarbonates in our dataset. While back-trajectories analysis suggests the stronger importance of local resuspension over long-range transport, statistical analyses on ion composition highlight the key role exerted by agricultural activity, especially in the case of NH4+, K+, Ca2+ and PO43− (especially linked to fertilisation practices and soil resuspension due to mechanical operations). Apart from Na+ and Cl− ions which correlate well as expected, indicating their likely common origin from marine salt, the identification of the origin of the other ions is very complex due to the contribution of diverse local sources, such as industrial and residential settlements.

中文翻译：

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波河谷（意大利）半农村地区大气大量沉积的化学特征

本研究对大堆沉积物（2009-2013 年）的五年时间序列化学成分进行分析，这些沉积物收集在 Po Valley 半农村地区工业和城市定居点周围的农场内，旨在表征影响现场降水成分的潜在排放源。由于强烈的工业化和城市化以及频繁的空气停滞条件，该地区被认为是世界上污染最严重的地区之一，目前该地区的大多数监测工作更多地用于气态和颗粒污染物，而不是降水化学。与世界上其他污染地点和同一地区的地点相比，大量沉积样品非常集中在酸性和碱性化学物质中。平均离子浓度（μeq l−1）为：NO3− (243) > SO42− (220) > PO43− (176) > Cl− (153) > NO2− (29) > F− (2.6)；NH4+ (504) > Ca2+ (489) > K+ (151) > Na+ (127) > Mg2+ (127)。尽管硝酸盐和硫酸盐的浓度很高，但由于铵和地壳元素的大量存在，pH 数据显示了向弱碱性条件的趋势。Ca2+ 和 Mg2+ 的相关浓度进一步表明，这些碱性条件可能是由于我们的数据集中相应显着浓度的碳酸盐/碳酸氢盐。虽然反向轨迹分析表明局部再悬浮对远距离迁移的重要性更大，但离子组成的统计分析强调了农业活动发挥的关键作用，尤其是在 NH4+、K+、Ca2+ 和 PO43-（特别是与施肥实践和由于机械操作导致的土壤再悬浮有关）。除了 Na+ 和 Cl- 离子与预期的相关性很好，表明它们可能来自海盐的共同来源之外，由于工业和住宅定居点等多种当地来源的贡献，其他离子来源的鉴定非常复杂。