GROWTH OF CLOUD DROPLET DUE TO CONDENSATION OF WATER VAPOR ON PARTICULATE ATMOSPHEREIC POLLUTANT

摘要

Cloud droplet formation is an important process in water cycle between the earth and the atmosphere. In order to investigate the nonsteady growth of cloud droplets due to the condensation of the atmospheric water vapor on (NH_4)_2SO_4 particles, a mathematical model has been constructed and the nonsteady growth has been simulated numerically with use of the model. The model is constituted by the conservation laws of water mass and heat energy and the state equation of ideal gas. As the time variation of droplet heat Q_w is very fast compared with that of droplet mass m_w, droplet temperature T_a can be treated as in quasi-steady state. The equilibrium droplet size a_e is dependent on the 3/2 power of the initial radius a_(s0) of (NH_4)_2SO_4. The larger a_(s0) is, the more the droplet grows in its equilibrium size a_e. It takes much time for the cloud droplet condensed on large (NH_4)_2SO_4 to attain its equilibrium size a_e. It also has been cleared that Kelvin's equation is not always applicable to estimate the cloud droplet size.