The capture of airborne particles by water drops and simulated snow crystals

Abstract

SUMMARYCollection efficiencies of falling water drops ranging from -& to 1 mm in radius for spores of Lycoperdon (mean radius i: = 2.25 p), spores of black rust (i: = 2.6 p), and grains of Paper Mulberry pollen (i: = 6.4 p) have been determined. The experimental results are in fair agreement with calculations based on the assumption of potential flow around the larger drops. With both kinds of small spore the collection efficiencies reach maximum values for drops of about 400 p radius and fall sharply for smaller drops. In this latter regime, where the potential flow solution is inappropriate and the viscous flow solution gives zero values, a sharp fall in collection efficiency is to be expected. Aggregates of two or three spores are collected slightly more efficiently than single spores, but the results show very similar trends in all cases.Some preliminary results have been obtained on the collection of pollen grains by circular, hexagonal and star-shaped paper discs that simulate snow crystals. The collection efficiencies, as deduced from the numbers of particles caught on their leading faces, are usually < 0.05, but the appearance of similar numbers of particles on the trailing faces suggests that particle capture in the wake of the disc is important at these Reynolds numbers of about 100.

Experimental Study of Collection Efficiencies between Submicron Aerosols and Cloud Droplets

“…Figure 2 shows a detailed schematic with the major features of the chamber. Overview of previous experimental studies carried out with different instruments to determine the collection efficiency of droplets with aerosol particles at RH , 100% (Starr and Mason 1966;Beard 1974;Wang and Pruppacher 1977;Lai et al 1978;Leong et al 1982;Byrne and Jennings 1993;Pranesha and Kamra 1996;Vohl et al 2001). Each section is 20 cm in length and 10 cm wide with a distance of 1 cm between the plates.…”

Laboratory studies of collection efficiency of sub-micrometer aerosol particles by cloud droplets on a single-droplet basis

“…This process is known as "collection" or "coagulation". The collection process is considered an important mechanism that can "scavenge", and thereby remove, aerosol particles from the atmosphere (Starr and Mason, 1966;Owe Berg et al, 1970;Hampl and Kerker, 1972;Pranesha and Kamra, 1996). Collection can also affect cloud dynamics, the precipitation process and cloud lifetime, and thereby change the global radiation budget (Rasch et al, 2000;Croft et al, 2009).…”

Inertial Deposition of Small Particles On a Sphere at Intermediate and High Reynolds Numbers: A Time Dependent Study

“…Experimental research on inertial deposition on a sphere was performed by Ranz and Wong, 5 Walton and Woolcock, 6 Star and Mason, 7 Beard and Prupacker, 8 and others. Recently, Kerker and coworkers published a number of papers on the subject in the Journal of Atmospheric Science (1974), 9 but in these works inertial deposition seemed to be less important as compared to diffusional and electrical effects.…”