Measurement of the Size Distribution and CCN Supersaturation Spectrum of Submicron Aerosols over the Ocean

Abstract

Data on the submicron aerosol size distribution, the supersaturation spectrum, and the relationship between dry size and critical supersaturation taken during a cruise of the USNS Hayes from Norfolk, Virginia, to Piraeus, Greece, are presented. Measured values of the critical supersaturation required to nucleate natural aerosols of known size are given and used to convert the size distribution to the supersaturation spectrum. The supersaturation spectrum derived in this manner shows good agreement with the supersaturation spectrum measured directly. The observed decrease in particles smaller than 0.06 µm in an air mass which moved 100 mi out to sea could be explained by coagulation and mixing with marine air. The absence of particles below about 0.02 µm on most occasions in marine air was consistent with the finding that the number of CCN active at 0.8% was nearly equal to the total CN count.