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

研究了1994 ~ 1996年库菊火山喷发区附近雨水的化学特征及其酸化范围。雨水收集采用露天式雨水收集器，分布在11个不同的地点，最远距离火山爆发区7公里，每隔两周采样一次。发酵区附近的pH值在2.5 ~ 4之间，随距离的增加而升高。在离富酚区1.5km范围内，Cl^-和SO_4^<2->浓度占总阴离子浓度的90%以上，H^+浓度占阳离子浓度的主导地位。利用各收集期Cl浓度的面积分布和降水持续时间计算的沉积HCl总量，估算了火山喷气孔排放HCl气体的排放速率。1995年7月，在10月11日开始喷发活动之前，计算出的HCl排放量从2 t/d迅速增加到6.3 t/d。这一现象表明，在火山喷发前两个半月，火山深处的岩浆活动有所增加。采用具有吸酸能力的赤叶土制成土柱，进行了酸雨入渗及与土壤的化学反应试验。向塔内提供pH3人工酸雨，降水强度为11.5 mm/h，总量相当于4000mm。在整个实验过程中，柱内排出的水pH值均大于5.5，说明酸雨在向柱内流动的过程中被中和，酸雨阴离子主要成分硫酸盐离子主要被土壤吸附，且随着离柱顶距离的增加，其吸附量迅速减少。

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.