Shunsaku Yagi

Acidification of Growing Cloud Droplet by Rainout of SO2(g)

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

Condensational Growth Of Cloud Droplet On Atmospheric (NH4)2 SO4, Particle

In order to investigate the acidification process of cloud drops (i.e., acid rain formation) due to rainout (in cloud scavenging) of gaseous pollutants as 882 (g) and NOx(g)> the non-steady characteristics of the growth of single cloud droplet by condensation of the atmospheric water vapor is simulated numerically with use of a mathematical model. The mathematical model is constituted by the conservation laws of water mass and heat energy and the state equation of ideal gas. The time variation of droplet heat Qw is very fast compared with that of droplet mass m^. Therefore, usually droplet temperature Ta can be treated as in quasi-steady state. The equilibrium droplet size â is approximately dependent on the 3/2 power of the initial radius OgQ of cloud condensation nucleus (NĤ SĈ . Because for large condensation nuclei it takes considerably long time compared with the lifetime of cloud to grow up to its equilibrium radius, the conventional Kohler equation may bring about not a little error in the estimation of cloud drop size.

Effect Of Electric Field Induced Within Rain Drops OnAcid Rain Formation

In order to take account of the effect of the electric potential induced by charged chemical species in rain drops on acid rain formation, a new mathematical model, which contains the electro-migration term in addition to the conventional terms, has been constructed. The electric field in rain drops is brought about by the movement of ions which is produced by the absorption of acidic atmospheric pollutant. The ions undergo the electric force caused by the electic field in rain drops and they move toward the certain direction depending on their charge. The numerical simulations by the new model developed here discloses that: (1) the electro-migration of ions makes H+ concentration higher than that estimated neglecting the electro-migration; (2) the distibution of H+ concentration tends to uniform under the elecric potential field; and (3) the electric potential is higher at the drop center than at the drop surface.