Empirical estimates of CCN from aerosol optical properties at four remote sites

This study presents an empirical method to estimate the CCN concentration as a function of percent supersaturation. The aerosol optical properties, backscatter fraction and single scatter albedo, function as proxies for the aerosol size and composition in a power law relationship to CCN. This method is tested at four sites with aged aerosol: SGP (Oklahoma, USA), FKB (Black Forest, Germany), HFE (Hefei, China) and GRW (Graciosa, Azores). Each site represents a different aerosol type and thus demonstrates the method robustness and limitations. Good agreement was found between the calculated and measured CCN with slopes between 0.81 and 1.03 and correlation coefficients (r2 values) between 0.59 and 0.67. The fit quality declined at low CCN concentrations.