中国降水酸度和离子浓度的时空分布

The Geographical Distribution of Ion Concentration in Precipitation over China

１９９１～１９９５年在全国进行了酸雨观测，建立了覆盖全国的具有区域代表性的酸沉降监测网，含２７１个测站。降水的ｐＨ值和电导率在现场采样后立即测量，降水样品的化学分析则在实验室里进行。主要离子ＳＯ２－４，ＮＯ－３，ＮＨ＋４，Ｃａ２＋浓度的加权均值分别为１２５８６，１９９６，６７８９和８０４１μｅｑ／Ｌ。由离子浓度地理分布图看出，这些离子浓度地理分布状况因离子而异。值得注意的是降水中ＳＯ２－４和ＮＯ－３浓度，北方非酸雨区甚高于南方酸雨区，这说明降水的酸度并不简单地决定于降水中ＳＯ２－４和ＮＯ－３的绝对浓度，而决定于这些离子对于Ｃａ２＋和ＮＨ＋４的相对浓度。发现了降水年均ｐＨ值低至４的一些地区，此值可能是目前世界年降水酸性最强的地区。文中还对代表性地区１９８６～１９９３年降水化学特征进行了分析，结果表明降水的酸度仍在升高。

The precipitation chemistry over China had been studied on a nation-wide monitoring network from 1991 to 1995. Precipitation samples and other meteorological data were collected at the National Acid Deposition Monitoring Network with 271 sample sites over the country. Precipitation pH and electro-conductivity were measured in the field and the chemical analysis of collected samples were conducted in the laboratory. The annual precipitation weighted concentrations of SO 2- 4, NO - 3, NH + 4 and Ca 2+ are 125.86, 19.62, 67.89 and 80.41μeq/L, respectively. The geographical distribution of these ion concentrations in precipitation shows that the scenarios vary from ion to ion. It is interesting to point out that the SO 2- 4 concentrations in the northern non-acid rain areas are generally much higher than that in the southern acid rain areas. It means that the rain acidity is not only determined by the absolute concentrations of SO 2- 4 and NO - 3, but by the relative concentration of basic and acid ions in precipitation. It is found that the rain pH has a minimum annual average value which is lower than 4.0 in some areas, and it is probably the lowest pH in precipitation in the world. The characteristics of chemical deposition of rain water for typical areas were analyzed, and results showed that the rain acidity is still increasing over China.