The effect of the impaction scavenging efficiency on the wet deposition by a convective warm cloud

To study the influence of the impaction scavenging efficiency in a cloud, we have reevaluated our 2-D dynamical cloud model. This model, which includes spectral microphysics and scavenging was previously applied to a warm precipitating convective cloud at Day 261 (18 September 1974) of the GATE campaign. The original computation used a table for the impaction scavenging efficiency depending on drop radius, particle radius and relative humidity. The re-evaluation used an impaction scavenging efficiency of unity. For both cases the results show general deposition properties that lie within the observed range for marine clouds. Thus, for the simulations of average clouds at a given location the detailed knowledge of the impaction scavenging efficiency is not required. If, however, the calculations are used to simulate the distributions of the pollutant concentration across the rain drop spectrum of a specific cloud, then the detailed knowledge of the impaction scavenging efficiency in addition to the detailed knowledge of the vertical distribution of the pollutants are essential since they determine the deviation from the well mixed spectral concentration distribution produced inside the cloud through collision and coalescence processes.