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Norikura山顶附近（观测点高度：2770m）对雾水的化学成分进行了检测，同时对气体和颗粒物质进行了化学分析。在本实验中，雾水被划分为4个大小类别，并在大量雾水采样的基础上，使用新制作的串状云收集器进行采样。酸度测定表明，夏季多形成酸性雾，雾水最小pH值达3.30。还发现pH的变化是液滴大小的函数，最小液滴（平均直径[]SY.simeq.[）3.6um)的最小pH值为3.03。雾水中阴离子以硫酸盐和硝酸盐为主，随着雾滴粒径的减小，雾水中多种组分的浓度普遍升高。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，我们假设雾水中的铵来源于被雾滴捕获的气溶胶。根据假设，在最小的雾滴中，由于吸收二氧化硫而产生的硫酸盐超过了硫酸盐的50%。根据我们的观察，提出了酸雾形成的三个过程：酸性颗粒如硫酸铵的成核，雾滴中产生的硫酸盐和硝酸蒸汽的吸收。

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.