ACIDIFICATION OF GROWING CLOUD DROPLET DUE TO ABSORPTION OF SO2 (g)

Abstract

In order to investigate the acidification of rain drops due to rainout (in cloud scavenging) of air pollutants, the characteristics of acidification of growing single cloud droplet due to condensation of the atmospheric water vapor and the rainout of SO2 (g) are simulated numerically with use of a mathematical model. It is considered that growth of doud dnplet controls rainout of pollutants, although little is known about rainout compared with washout (below doud scavenging).(NH4) 2SO4 is selected for the condensation nucleus, which is produced from NH3 (g) and SO2 (g) via gas-phase chemical reaction in the atmosphere. The mathematical model is constituted from the conservation equations, the state equation for ideal gas andthe equation of reactions. With use of the lumped model non-steady dropletradius, temperature and concentrations of chemicals are simulated Radus of solid-phase (NH4) 2SO4, which forms the core of droplet, is reduced gradually with condensation of water vapor into droplet. The major driving force for droplet growth and the absorption of SO2 (g) is the difference of the concentration of (NH4) 2SO4 between droplet and water vapor, i. e., the use and fall of the droplet temperature, condensation of vapor and the absorption of SO2 (g) are dependent on the existence of solid-phase (NH4) 2SO4.