ACID RAIN DISSOLVED WITH VOLCANIC GASES AND ITS CHEMICAL REACTION WITH SOIL

1994 ~ 1996年，对九州岛火山喷发区附近的雨水化学特征及其酸化的区域扩展进行了研究。雨水收集使用雨水收集器的露天型设置在11个不同的网站，从tumoric区7公里，并采样间隔两周。在不同的pH值附近的沼泽区的范围从2.5到4，并随着距离的增加而上升。在距湿地1.5km范围内，Cl^-和SO_4^-的浓度<2->占总阴离子浓度的90%以上，H^+的浓度占主导地位。通过计算各集雨期内Cl浓度的区域分布和降水持续时间，估算了沉积HCl总量，并计算了各集雨期内HCl气体的排放速率。在1995年10月11日火山爆发前，HCl的计算排放速率从2 t/d迅速增加到1995年7月的6.3t/d。这种行为意味着，在喷发前两个半月，深部岩浆活动增加。利用具有吸酸能力的赤穗土制作土柱，进行了酸雨入渗及与土壤化学反应的实验研究。以11.5mm/h的降水强度向柱中供应pH为3的人工酸雨，总量相当于4000 mm。试验期间，柱出水pH值均高于5.5，说明渗透酸雨在沿柱向下流动时被中和，硫酸根离子是酸雨中主要的阴离子组分，主要被土壤吸附，且吸附量随离柱顶距离的增加而迅速减少。

Chemical characteristics of rain water and areal extension of its acidification in the vicinity of fumarolic area at Kuju volcano were studied between 1994 and 1996. Rain water was collected using rain collectors of open air type set at eleven different sites as far as 7km from the fumarolic area, and sampled at intervals of two weeks. The pH values in the vary vicinity of the fumarolic area ranged from 2.5 to 4, and rose with an increase in distance. Within 1.5km from the fumarolic area, concentrations of Cl^- and SO_4^<2-> occupied more than 90% out of the total anion concentration, and H^+ concentration dominated the cation. Discharge rate of HCl gas emitted from the fumaroles were estimated using the total amount of deposited HCl calculated from areal distributions of Cl concentration and the duration of precipitation during each rain collecting periods. Calculated discharge rate of HCl quickly increased from 2 t/d to 6.3 t/d in July 1995 prior to the eruptive activity started on October 11,1995. This behavior implies that activity of magma at depth has increased two and half months before the eruption. Experiments on acid rain infiltration and chemical reaction with soil was carried out using soil column made with Akahoya soil having acid adsorption capacity. Artificial acid rain of pH3 was supplied to the column at a precipitation intensity of 11.5 mm/h for the total amount of being equivalent to 4000mm. Discharged water from the column showed pH values higher than 5.5 throughout the period of experiment, indicating infiltrated acid rain was neutralized while flowing down the column, Sulphate ion being a dominant anion component of acid rain was mostly adsorbed by soil and adsorbed amount of the ion decreased quickly with distance from the top of the column.