Water droplet growth in a carbon dioxide atmosphere: A case for small sticking coefficient

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Abstract
Water droplet growth was measured in a CO2 atmosphere using an expansion cloud chamber. Sufficient pressure and temperature data were obtained in order to calculate droplet growth which was compared to the experimentally measured growth curves. As the droplets increased in size, it was found that the rate of change of the growth rate was not constant. The sticking coefficient in the droplet growth theory was treated as a parameter, but no single value of this coefficient would yield agreement between theory and experiment over the whole observational period. When the droplets are smaller than about 2.0 μ, a sticking coefficient value between 1.0 and 0.1 yields best agreement. For droplets of larger radius, it was found that an even smaller value of this coefficient, as small as 0.036, was required. The dehydration of the bicarbonate ion appears to be responsible for the lower value of the sticking coefficient.