Real Scale Cloud Experiments in a Long Vertical Shaft -A Study on the Oxidation Process of Sulfur Dioxide

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In a 430m-long vertical shaft of Kamaishi Mine, Iwate Prefecture, artificial clouds were formed by raising a humid updraft of about 1m/s using an electric fan placed at the top of the shaft, and the following experiments were carried out :1. In order to investigate the dissolution of sulfur dioxide into cloud droplets and subsequent oxidation, this gas was emitted into the air stream at the bottom of the shaft. Then by utilizing an elevator, cloud droplets and aerosol particles were separately sampled through multistage impactors. Sulfur dioxide was also collected by sodium carbonate impregnated filters. As the collection media for the impactor, filter paper impregnated with formaldehyde was used to suppress the oxidation of sulfurous acid ; this procedure enabled one to quantify S (IV) and S (VI) separately. Main results are (1) Immediately above the cloud base. S (IV) in droplets was found to be already in equilibrium with the gas-phase sulfur dioxide. This implies that the rainout o … More f sulfur dioxide is a rapid process, and (2) The concentration ratio S (VI)/S (IV) in droplets stayed almost constant through the updraft. From this result it is concluded that the thermal oxidation reaction of sulfur dioxide by dissolved oxygen is slow.A distinct feature of cloud chemistry is that the reaction sites (i.e droplets) are appearing and disappearing elusively. Therefore it is essential to understand the droplet formation processes. Accidentally, in the second year of this project, the stoppage of the elevator made it impossible to trace the in-cloud reactions. In these circumstances. the study was turned to focus on the formation and growth of cloud droplets. Along this line, the following results were obtained :2. By means of a laser ranging device, the cloud base height was observed, and it was found to fluctuate with the spacial and temporal scales of 100m and 10s, respectively.3. Aqueous solutions of inorganic salts such as sodium chloride and lithium chloride were atomized at the bottom of the shaft. As a result, conspicuous increase was observed in the number concentration of droplets and their sizes were found to be inflated. However, the mode of the size distribution remained constant. It was also found that the time between the start of the atomization and the onset of the concentration increase depended on the droplet size, and the droplet growth rate was estimated from this dependence. Less