Fast response in situ particle measurements within the Kuwait oil smoke plume showed that about 70% of the particles are cloud condensation nuclei (CCN) active at about 1% supersaturation. The CCN size range included the entire measured particle size range between 0.024 and 1 μm. The portion of the aerosol spectrum below 0.1 μm appeared to be internally mixed (various compositions within each particle), while the larger particles tended to be externally mixed (various compositions for different particles but homogeneous composition within each particle). The majority of the CCN are very water soluble (critical supersaturations below 0.2%). This significant CCN source could have important climatic effects by altering cloud albedo and precipitation. However, cloud scavenging will reduce the atmospheric lifetimes of the particles, which is an important consideration in large-scale atmospheric injections such as nuclear winter scenarios. ¿ American Geophysical Union 1992