Continental Surface Measurements of CCN Flux

Abstract

Systematic spatial variations in CCN concentrations point to a major source near continental surfaces of the same magnitude as the removal rate by precipitation. Various theories of production point to either 1) a source at the surface, or 2) a diffuse source throughout the mixing layer (?1 km). The work presented here is an attempt to test the validity of the first hypothesis by using a micrometeorological technique to determine the vertical flux of CCN. A very high degree of precision in measuring CCN and a very high counting rate are required to apply this technique. A pair of continuous flow diffusion cloud chambers (Hudson and Squires, 1976) were developed for this purpose. The experiment was performed at four different locations in three distinct types of terrain. At all locations the concentrations were consistently greater at higher levels (?10 m above ground) than at lower levels (?1 m above ground) indicating surface deposition rather than surface production.