Chemical composition and sources of the high Arctic aerosol relevant for cloud formation

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Abstract
The chemical composition, sources, and methods of production of cloud condensation nuclei (CCN) were studied over the pack ice covered Arctic Ocean in summer. After ∼2 days' travel of air over the pack ice, two local CCN sources were identified: particles derived from the bursting bubbles on open water between ice floes (film and jet drops) and particles reaching CCN size by acquisition of oxidation products of dimethyl sulfide. The bubble‐derived particle modes were found to have an exponential dependence on prevailing wind speed. The film drop generation depended less on wind speed and jet drop production depended more on wind speed than particles over open water did. However, the enhanced presence of film drop particles at wind speeds 12 m s−1 to dominate both mass and number. The jet drop mode was composed largely of sea salt, making a significant mass contribution already for wind speeds >5 m s−1. However, the smaller‐sized jet drops were not pure sodium chloride but contained a varied and appreciable organic component. The sulfur‐containing particles dominated the CCN population and mass for the most common wind speeds of 5–12 m s−1. Measured CCN concentrations were on average less than would have been expected from either a sulfate or a sea‐salt composition and the observed particle‐size distribution. It is concluded that other components, probably organic, depressed the nucleating ability of the particles. However, on clear sky days, there were a majority of occasions on which CCN concentrations were more than predicted from a sulfate composition and the measured size distribution.

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