Simultaneous airborne measurements of cloud condensation nuclei and sodium‐containing particles over the ocean

Abstract

AbstractSimultaneous airborne measurements have been made over the Pacific Ocean of the concentrations of cloud condensation nuclei (CCN) active at 0.5 per cent supersaturation and the concentrations and size‐spectra of sodium‐containing particles (SCP) over a wide range of sizes. The concentrations of SCP decreased sharply with increasing height above the ocean and it is likely that most of them originated from the ocean. However, even at altitudes as low as 50 ft above the surface of the ocean, and over surf, the measured concentrations of SCP were only a few per cent of the concentrations of CCN at G.5 per cent supersaturation. Also the average concentrations of CCN did not change significantly with altitude up to at least 10,000 ft. These observations indicate that sea‐salt particles were not the major source of the CCN.It is suggested that the production of sulphates in cloud droplets, followed by the release of these particles when the droplets evaporate, is an important mechanism for increasing the efficiency of CCN in the air.