A comprehensive analysis of the chemical composition of precipitation was performed on rainwater samples collected between 1978 and 2017 over the conterminous US. A total of 86470 data records downloaded from the National Atmospheric Deposition Program were statistically analyzed and assessed in terms of precipitation chemistry. The ion abundance followed the Cl⁻ > Na⁺ > SO₄²⁻ > Ca²⁺ > H⁺ > NH₄⁺ > NO₃⁻ > Mg²⁺ > HCO₃⁻ > K⁺ downward trend, showing that chloride and sodium were the most dominant among anions and cations. Ca²⁺, SO₄^2– and NH₄⁺ concentrations were notable in desert areas or in regions with significant anthropogenic activity. Frequency analysis of pH values showed that the 87.90% of the pH is acidic, exhibiting values under 5.6. According to the acidifying and neutralization potential, rainwater pH is mostly alkaline in the Western region, presenting acidic values in highly industrialized areas, in the Central and Eastern Regions. Fractional acidity showed that in the majority of the studied sampling sites 61% of the acidity in precipitation is neutralized, due to the presence of the main neutralizing agents (NH₄⁺, Ca²⁺, Na⁺), fact sustained by the neutralization factor values. The relationship between acidic and alkaline components was thoroughly examined by ionic ratios and the ammonium availability index. Wet deposition rates of major ions confirmed the dominance of acidic species over neutralizing ones, as well as the significant imprint of regional climate and heavily industrialized areas on the precipitation chemistry. The complex major ion source apportionment, including marine and crustal enrichment factors, sea salt and non-sea salt fractions, Spearman’s rank correlation analysis and Principal Component Analysis, showed that anthropogenic influences are the most significant, including coal-fired power plants, oil refineries, major industries and agricultural activities. Crustal and marine sources also presented a prominent imprint on the rainwater chemistry of the conterminous US.

对1978年至2017年间在美国本土收集的雨水样本进行了降水化学成分的综合分析。从国家大气沉积计划下载的总共86470条数据记录经过了沉淀化学分析和统计分析。的离子丰度遵循的Cl - >Na⁺> SO 4 ² ⁻>的Ca ² ⁺> H +> NH +>NO₃⁻>的Mg ² ⁺>HCO₃⁻> K +下降的趋势，这表明氯离子和钠是属于最主导阴离子和阳离子。Ca 2 ⁺，SO ₄ ^2–和NH ₄ ⁺在沙漠地区或具有明显人为活动的地区浓度显着。pH值的频率分析表明，pH的87.90％是酸性的，其值低于5.6。根据酸化和中和的潜力，西部地区的雨水pH值大多为碱性，在中部和东部地区高度工业化的地区呈酸性。分数酸度表明，在大多数研究的采样点中，由于主要中和剂（NH ₄ ⁺，Ca 2 ⁺，Na ⁺），由中和因子值维持的事实。酸性和碱性组分之间的关​​系已通过离子比和铵离子利用率指数得到了彻底检验。主要离子的湿沉降速率证实了酸性物质优于中和物质，以及区域气候和重工业化地区对沉淀化学的显着影响。复杂的主要离子源分配，包括海洋和地壳富集因子，海盐和非海盐馏分，Spearman秩相关分析和主成分分析，表明人为影响是最重要的，包括燃煤电厂，炼油厂，主要工业和农业活动。