Chemical composition of fog water classified according to their sizes and their formation process.

为了研究酸雾的形成过程，在对云雾水进行化学成分分析的同时，对山顶附近的气态和颗粒物进行了化学分析。纪仓（观测点高度：2770 m）。实验中除大量采集雾水外，还将雾水分为4个粒径级，用新型的绳式集云器采集，酸度测定表明，酸性雾多在夏季形成，雾水的最低pH值可达3.30。还发现pH的变化是液滴尺寸和最小液滴的最小pH的函数（平均直径（）SY.simeq. [）3.6um）为3.03。雾水中的主要阴离子是硫酸根和硝酸根，并且许多成分的浓度随雾滴粒径的减小而增加。另一方面，颗粒物质的化学成分表明，气溶胶颗粒主要由硫酸铵组成。因此，我们认为，在雾水中的铵来源于气溶胶捕获到雾滴。这是根据以下假设估计的：通过吸收二氧化硫在雾滴内产生的硫酸盐超过最小雾滴中硫酸盐的50%。根据我们的观察，提出了酸雾形成的三个过程：硫酸铵等酸性粒子的成核、雾滴中硫酸盐的生成和硝酸蒸气的吸收。

In order to study the formation process of acidic fog, chemical composition of fog water was examined simultaneously with chemical analysis of gaseous and particulate materials near the top of Mt. Norikura (Height of observation site:2770m). In this experiment, fog water was classified into four size classes and sampled with a newly made string-type cloud collector, in addition to bulk fog water sampling.Acidity measurement showed that acidic fogs are often formed in the summer seasons and minimum pH of fog water reached 3.30. It was also found that change in pH is a function of the droplet size and minimum pH of the smallest droplets(mean diameter(] SY.simeq.[)3.6um) was 3.03. Main anions in fog water were sulfate and nitrate and concentration of many constituents increased generally with decreasing fog droplet size. On the other hand, chemical composition of particulate materials suggested that aerosol particles consisted mainly of ammonium sulfate. Therefore, we assumed that ammonium in fog water was originated from aerosols captured into fog droplets. It was estimated from the assumption that sulfate produced within fog droplets by absorption of sulfur dioxide exceed 50 % of sulfate in the smallest fog droplets. Based on our observations, three processes were suggested for the formation of acidic fogs: nucleation of acidic particles such as ammonium sulfate, sulfate produced in fog droplets and absorption of nitric acid vapor.