We use balloon-borne measurements of aerosol size distribution (ASD) made by the University of Wyoming (UW) to derive distributions which are representative of the ASDs that underlie measurements made by the Stratospheric Aerosol and Gas Experiment II (SAGE II). A simple single-mode log-normal distribution has in the past been used to derive ASD from SAGE II data; here we derive bimodal log-normal distributions, reproducing median aerosol properties measured by UW.