2000 Volume 44 Pages 73-78
In order to investigate the acidification of cloud droplets due to rainout (in cloud scavenging) of air pollutants, the characteristics ofthe acidification of the growing single cloud droplet by the rainout of SO2(g) are simulated numerically with use of a mathematical model. The mathematical modelis constituted from the conservation equations, the state equation for ideal gas and the equation of drop phase chemidal reactions.(NH4) 2SO4 is selected forthe cloud condensation nucleus (CCN), which is produced from NH3(g) and SO2(g) via gas phase chemical reaction in the atmosphere. With use of the model non-steady pH, droplet radius, temperature and concentrations of chemicals are simulated. The major driving force for both of the droplet growth and the absorption of SO2(g) is the difference of the concentration of (NH4) 2SO4 between droplet and water vapor. It is shown that the salt concentration of CCN controls rainout of pollutants, although little is known about rainout compared with washout (below cloud scavenging).
