Cloud condensation nuclei (CCN) volatility and size versus critical supersaturation Sc measurements are presented for maritime, continental, and urban areas. The measurements included both hemispheres of the globe. Although this was a nonsystematic preliminary survey, some general trends are shown. CCN in cleaner air were smaller, characteristic of completely pure soluble substances, whereas the CCN in dirtier air were larger, characteristic of insoluble and/or different soluble material mixed internally. Volatility was generally characteristic of sulfate (i.e., ammonium sulfate) except in urban areas, where more volatile material was present, which is characteristic of unneutralized acids. ¿ American Geophysical Union 1996