  We suggest a model of rain scavenging of soluble gaseous pollutants in the
atmosphere. It is shown that below-cloud gas scavenging is determined by
non-stationary convective diffusion equation with the effective Peclet number.
The obtained equation was analyzed numerically in the case of log-normal
droplet size distribution. Calculations of scavenging coefficient and the rates
of precipitation scavenging are performed for wet removal of ammonia (NH3) and
sulfur dioxide (SO2) from the atmosphere. It is shown that scavenging
coefficient is non-stationary and height-dependent. It is found also that the
scavenging coefficient strongly depends on initial concentration distribution
of soluble gaseous pollutants in the atmosphere. It is shown that in the case
of linear distribution of the initial concentration of gaseous pollutants
whereby the initial concentration of gaseous pollutants decreases with
altitude, the scavenging coefficient increases with height in the beginning of
rainfall. At the later stage of the rain scavenging coefficient decreases with
height in the upper below-cloud layers of the atmosphere.
