Articles | Volume 16, issue 4
Research article
03 Mar 2016
Research article |  | 03 Mar 2016

Properties of cloud condensation nuclei (CCN) in the trade wind marine boundary layer of the western North Atlantic

Thomas B. Kristensen, Thomas Müller, Konrad Kandler, Nathalie Benker, Markus Hartmann, Joseph M. Prospero, Alfred Wiedensohler, and Frank Stratmann

Abstract. Cloud optical properties in the trade winds over the eastern Caribbean Sea have been shown to be sensitive to cloud condensation nuclei (CCN) concentrations. The objective of the current study was to investigate the CCN properties in the marine boundary layer (MBL) in the tropical western North Atlantic, in order to assess the respective roles of inorganic sulfate, organic species, long-range transported mineral dust and sea-salt particles.

Measurements were carried out in June–July 2013, on the east coast of Barbados, and included CCN number concentrations, particle number size distributions and offline analysis of sampled particulate matter (PM) and sampled accumulation mode particles for an investigation of composition and mixing state with transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDX).

During most of the campaign, significant mass concentrations of long-range transported mineral dust was present in the PM, and influence from local island sources can be ruled out. The CCN and particle number concentrations were similar to what can be expected in pristine marine environments. The hygroscopicity parameter κ was inferred, and values in the range 0.2–0.5 were found during most of the campaign, with similar values for the Aitken and the accumulation mode. The accumulation mode particles studied with TEM were dominated by non-refractory material, and concentrations of mineral dust, sea salt and soot were too small to influence the CCN properties. It is highly likely that the CCN were dominated by a mixture of sulfate species and organic compounds.

Short summary
We have investigated the cloud condensation nuclei (CCN) properties in the trade wind marine boundary layer of the western North Atlantic during the dust season. Little is known about the CCN influencing cloud optical properties in that region. High mass concentrations of mineral dust were observed, but the number concentrations of mineral dust and sea salt were not high enough to influence CCN properties, and the CCN were likely to be dominated by a mixture of sulfates and organic species.
Final-revised paper