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Aerosol properties were measured during two transects over the North Atlantic between Halifax (Nova Scotia, Canada) and the Moroccan coast. Measurements of the chemical composition of total aerosol, of the black carbon concentration and of the number size distributions with particle diameter D(p) in the range 16 nm to 1 um were made. The e-folding lifetime of the black carbon aerosol, coming from the northeast American continent and transported eastward over the ocean, was estimated to be 15 hours. The nonsea salt (NSS) fraction of the sulphate concentrations encountered during this campaign spans a 3 order of magnitude range and shows a high correlation with black carbon. The measured bimodal aerosol size distributions were analysed in order to yield number concentrations of the nuclei and the accumulation mode (ACM), the latter being interpreted as cloud processed particles and thus as cloud condensation nuclei (CCN). A strong positive correlation was found between ACM number concentration and NSS sulphate load over the whole concentration range. Regression between NSS-sulphate and ACM number concentration also agrees well with results from other investigators where CCN or cloud droplet concentrations were related to NSS sulphate at a variety of geographical locations and degrees of pollution. The composite data set shows that the NSS sulphate-CCN relationship from baseline conditions to anthropogenically conditioned aerosol, happens via smooth transition which can be described by a linear regression on a logarithmic scale.

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Authors: VAN DINGENEN R, JRC Ispra, (IT);RAES F, JRC Ispra, (IT);JENSEN N R, JRC Ispra, (IT)
Bibliographic Reference: Article: Journal of Geophysical Research, Vol. 100 (1995) No. D10, pp. 21057-21067
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