Acidification of growing cloud droplet by rainout of SO2(g)

Growing cloud droplets absorb such atmospheric gaseous pollutani as SO2(g), condensing atmospheric water vapor into themselves. Then, the cloud drople ts are acidified by absorption of SO2(g) during condensational growth on cl oud condensation nuclei (CCN). Characteristics of this process, which is a part of rainout, have not been made clear yet. In order to estimate the con tribution of rainout to acid rain formation, the acidification of growing c loud droplets is investigated numerically, using a mathematical model. The numerical simulations show that: (1) the time to attain the equilibrium sta tes for mass transfer (acidity and growth) and heat transfer (temperature) is much longer than the time for disappearance of CCN; (2) time variation o f acidity and temperature of cloud droplets are greatly dependent on the ex istence of undissolved CCN; and (3) there seems to be a close correlation b etween the time variation of the acidity and that of the temperature.