Experimental Study of Collection Efficiencies between Submicron Aerosols and Cloud Droplets

Collection efficiency E experiments for aerosol particles scavenged by cloud droplets were carried out in the newly built Collision Ice Nucleation Chamber (CLINCH). Pure water droplets having radii between 12.8 and 20.0 μm were allowed to fall freely and to collide in a laminar flow with lithium metaborate particles having radii between 0.05 and 0.33 μm. At the bottom of the chamber, the droplets and the particles captured were collected using a cup impactor. The collected solution was analyzed for the scavenged aerosol mass by inductively coupled plasma mass spectrometry. Evaporation of droplets was taken into account since the relative humidity inside the chamber was below 100%, resulting in final theoretical droplet sizes between 4.2 and 17.6 μm. The resulting experimental measurements were compared with theoretical values to see their correlation. The authors found an experimental trend similar to theory, as well as the “Greenfield gap” at the particle radius of 0.24 μm (E = 0.038) for the smallest cloud droplet size investigated in this study. The experimental values of collection efficiency found herein agree with those from theory within one order of magnitude, similar to previous studies reported in the literature.