PNNL

Abstract

A method of retrieving vertical profiles of cloud condensation nuclei (CCN) concentration from surface measurements is proposed. Surface measurements of the CCN concentration are scaled by the ratio of the backscatter (or extinction) vertical profile to the backscatter (or extinction) at or near the surface. The backscatter (or extinction) profile is measured by Raman lidar, and is corrected to dry conditions using the vertical profile of relative humidity (also measured by Raman lidar) and surface measurements of the dependence of backscatter (or extinction) on relative humidity. The method assumes the surface aerosol size distribution and composition are representative of the vertical column. Aircraft measurements of aerosol size distribution are used to test the dependence of the retrieval on the uniformity of aerosol size distribution. The retrieval is found to be robust for supersaturations less than 0.02%, but breaks down at higher supersaturations if the vertical profile of aerosol size distribution differs markedly from the distribution at the surface. Such conditions can be detected from the extinction/backscatter ratio.