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Changing chemical composition of precipitation in Wilmington, North Carolina, USA: Implications for the continental USA

机译：美国北卡罗莱纳州威尔明顿市降水化学成分的变化：对美国大陆的启示

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摘要

The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation. The concentrations of H+(aq) and DOC are highly correlated primarily because small organic acids contribute to both DOC and H+(aq) in precipitation. Ammonium ion concentrations in precipitation have increased due to increased agricultural activities, and this also affects precipitation pH. The reduction of SO2 emissions in 1995 imposed by the Clean Air Act Amendment, better control of emissions of volatile organic compounds, and the increase in ammonia emissions all contribute to the decreasing H+(aq) in precipitation nationwide. These compositional changes in precipitation have many environmental implications, such as decreased acid deposition to lakes, changing speciation for trace metals in precipitation, increased ammonium deposition to coastal waters, and decreased DOC transport to the open ocean.
机译：在前二十年中，北卡罗来纳州威尔明顿市的H +（aq）浓度下降了约50％，与全国范围内的趋势相似。酸度的降低很重要，因为溶液的pH值在大气反应中起关键作用，而且变化很大。这项研究是对降水中溶解有机碳（DOC）水平的首次长期研究，该研究表明北卡罗来纳州威尔明顿市的DOC中的DOC浓度降低了约一半。 H +（aq）和DOC的浓度高度相关，主要是因为小的有机酸对降水中的DOC和H +（aq）都有贡献。由于农业活动的增加，降水中的铵离子浓度增加，这也影响降水的pH。 1995年通过的《清洁空气法修正案》减少了SO2排放，更好地控制了挥发性有机化合物的排放，以及氨气排放的增加，都导致全国降水中H +（aq）的减少。降水的这些组成变化具有许多环境影响，例如减少的酸向湖泊的沉积，改变降水中痕量金属的形态，增加向沿海水域的铵沉积以及向公海的DOC传输减少。

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