Variability of the relationship between particle size and cloud-nucleating ability

Cloud condensation nuclei (CCN) are characterized by their critical supersaturation (S-c), which is a function of particle size and chemistry, namely water solubility. Measurements that relate particle size to Sc can thus be used to determine CCN solubility. A sufficiently small degree of variability of size-S-c measurements has been cited as evidence that CCN can be deduced from particle size measurements alone. Since particle size is so much easier to measure than particle chemistry or CCN this would have significant advantages for investigations of the largest climate uncertainty, the indirect aerosol effect; e. g., remote sensing of CCN. However, we present size-S-c measurements with a greater range of variability, which appears to at least limit or cast doubts on the practicality of deducing CCN from particle size measurements.