Science. 1984 Jul 27;225(4660):407-9. doi: 10.1126/science.225.4660.407.
Hydrogen ions in precipitation are correlated much more closely with sulfate than with nitrate, whereas ammonium ions are correlated more closely with nitrate than with sulfate. Target loadings of 14 to 16 kilograms of wet sulfate deposition per hectare per year, instead of 20 as suggested hitherto, are probably necessary to produce average pH values of 4.6 to 4.7, the approximate boundary levels for damage to aquatic ecosystems. Cluster analysis reveals that there are three linked groups of ions related to air pollution, agriculture, and sea spray.
降水的氢离子与硫酸盐的相关性远高于硝酸盐，而铵离子与硝酸盐的相关性高于硫酸盐。每年每公顷湿沉降硫酸盐的目标负荷量可能需要达到 14 到 16 公斤，而不是迄今建议的 20 公斤，才能产生平均 pH 值为 4.6 到 4.7，这是对水生生态系统造成损害的近似边界水平。聚类分析显示，与空气污染、农业和海水喷雾有关的离子有三个相关联的组。
