Author(s)

S Shiba, Y Hirata & S Yagi

Abstract

In order to investigate the acidification of raindrops due to washout (below cloud scavenging) of air pollutants, the characteristics of interactive mass transfer between raindrops and the atmosphere is simulated numerically with use of a mathematical model. This is based on the idea that the chemical species concentration of not only the raindrop but also the atmosphere controls washout of pollutants interactively. The model equations are derived from the mass conservation of chemical species in liquid phase (raindrops) and gas phase (the atmosphere), taking account of the time and space variations of the atmospheric concentration due to the interactive mass transfer, which is usually not considered for simplicity. The numerical results show that: (1) the distribution feature of the atmospheric concentration varies considerably with the physical properties of chemicals; (2) the later the raindrop falling is, the lower the raindrop H+ concentration becomes and the less the raindrop is acidified; and (3) the acidity prediction error due to neglecting the interactive mass transfer grows more and more with passage of time.

Keywords