THE EFFICIENCY WITH WHICH DRIZZLE AND PRECIPITATION SIZED DROPS COLLIDE WITH AEROSOL-PARTICLES

Values of collision efficiency and scavenging rates for drops interacting with aerosol particles are presented using more accurate flow fields than previous work and for a much greater number of drops than hitherto obtained. All calculations are performed at an ambient temperature of 10-degrees-C and atmospheric pressure of 900 mb. Computations of collision efficiency are performed for a drop radius range from 50 to 500 micrometre (mu-m), for particle radius from 0.005 to 10-mu-m, for relative humidity values of 50, 75, 95 and 100%, and for particle density of 1, 1.5, 2.0 and 2.5 x 10(3) kg m-3. In addition the collision efficiency was also calculated for electric charges on the drop and particle, and for an electric field, representative of typical thundercloud values. Combined use is made of a rigorous trajectory model together with a flux model and comparison is made between them in the overlap size region. Precipitation scavenging rates and the percentage of aerosol particles scavenged by precipitation drops described by Marshall-Palmer size distributions is also calculated.