PNNL

Abstract

If the aerosol size distribution and composition below cloud are uniform the vertical profile of cloud condensation nuclei concentration can be retrieved entirely from surface measurements, thus providing the potential for long-term measurements. We have used a combination of aircraft, surface in situ, and surface remote sensing measurements to test various aspects of the retrieval scheme. Our analysis leads us to the following conclusions. The CCN retrieval works better than expected if in situ measurements of extinction are used. The retrieval works better for supersaturations of 0.1% than for 1%, because CCN concentrations at 0.1% are controlled by the same particles that control extinction and backscatter. The retrieval of the vertical profile of the humidification factor is not the major limitation of the CCN retrieval scheme. The performance of the retrieval varies significantly from day to day, particularly at 1% supersaturation. Vertical structure in the aerosol size distribution and composition is the dominant source of error in the CCN retrieval.