Rate of Sulfur Dioxide Removal Artificial Cloud Experiments Utilizing a Long Vertical Shaft

Removal of sulfur dioxide through the absorption into cloud droplets is the initial stage of acid rain formation. We studied this process by forming an artificial cloud with a spatial scale close to the real one. We used a vertical shaft of 430 m in length in an abandoned mine, and operating an electric fan placed at the top of the shaft, generated an updraft of about 1 m s−1 of the air humidified by underground water. This produced an artificial cloud rising about 400m above the cloud base observed at a height of about 35 m from the bottom. At the bottom of the shaft, we emitted SO2 gas into the air stream, and measured its concentration profile by an SO2-meter loaded on an elevator going up and down in the shaft. From the slope of the observed decay curve, we evaluated the rate constant for the absorption to be 0.010 s−1. This value was found to agree in order of magnitude with an estimate derived on the basis of the laminar film model for mass transfer.