Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 14107-14130, 2016
https://doi.org/10.5194/acp-16-14107-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
15 Nov 2016
Aerosol arriving on the Caribbean island of Barbados: physical properties and origin
Heike Wex1, Katrin Dieckmann1,a, Greg C. Roberts2,3, Thomas Conrath1, Miguel A. Izaguirre4, Susan Hartmann1, Paul Herenz1, Michael Schäfer1,b, Florian Ditas1,c, Tina Schmeissner1, Silvia Henning1, Birgit Wehner1, Holger Siebert1, and Frank Stratmann1 1Leibniz Institute for Tropospheric Research, Experimental Aerosol and Cloud Microphysics, Leipzig, Germany
2Centre National de Recherche Scientifique, Meteo France, Toulouse, France
3Scripps Institution of Oceanography, Center for Atmospheric Sciences, La Jolla, USA
4Meteorology and Physical Oceanography, University of Miami RSMAS, Miami, USA
anow at: Eurofins GfA GmbH, Münster, Germany
bnow at: Leipzig Institute for Meteorology, University of Leipzig, Leipzig, Germany
cnow at: Max Planck Institute for Chemistry, Mainz, Germany
Abstract. The marine aerosol arriving at Barbados (Ragged Point) was characterized during two 3-week long measurement periods in November 2010 and April 2011, in the context of the measurement campaign CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados). Through a comparison between ground-based and airborne measurements it was shown that the former are representative of the marine boundary layer at least up to cloud base. In general, total particle number concentrations (Ntotal) ranged from as low as 100  up to 800 cm−3, while number concentrations for cloud condensation nuclei (NCCN) at a supersaturation of 0.26 % ranged from some 10 to 600 cm−3. Ntotal and NCCN depended on the air mass origin. Three distinct types of air masses were found. One type showed elevated values for both Ntotal and NCCN and could be attributed to long-range transport from Africa, by which biomass burning particles from the Sahel region and/or mineral dust particles from the Sahara were advected. The second and third type both had values for NCCN below 200 cm−3 and a clear minimum in the particle number size distribution (NSD) around 70 to 80 nm (Hoppel minimum). While for one of these two types the accumulation mode was dominating (albeit less so than for air masses advected from Africa), the Aitken mode dominated the other and contributed more than 50 % of all particles. These Aitken mode particles likely were formed by new particle formation no more than 3 days prior to the measurements. Hygroscopicity of particles in the CCN size range was determined from CCN measurements to be κ  =  0.66 on average, which suggests that these particles contain mainly sulfate and do not show a strong influence from organic material, which might generally be the case for the months during which measurements were made. The average κ could be used to derive NCCN from measured number size distributions, showing that this is a valid approach to obtain NCCN. Although the total particulate mass sampled on filters was found to be dominated by Na+ and Cl, this was found to be contributed by a small number of large particles ( >  500 nm, mostly even in the super-micron size range). Based on a three-modal fit, a sea spray mode observed in the NSDs was found to contribute 90 % to the total particulate mass but only 4 to 10 % to Ntotal and up to 15 % to NCCN. This is in accordance with finding no correlation between Ntotal and wind speed.

Citation: Wex, H., Dieckmann, K., Roberts, G. C., Conrath, T., Izaguirre, M. A., Hartmann, S., Herenz, P., Schäfer, M., Ditas, F., Schmeissner, T., Henning, S., Wehner, B., Siebert, H., and Stratmann, F.: Aerosol arriving on the Caribbean island of Barbados: physical properties and origin, Atmos. Chem. Phys., 16, 14107-14130, https://doi.org/10.5194/acp-16-14107-2016, 2016.
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Short summary
Aerosol arriving in the eastern Caribbean after passing the Atlantic is characterized, based on ground-based and airborne measurements. We describe the repetitive occurrence of three different types of air masses and relate them to their origin from either Africa or the Atlantic and also draw conclusions about the particle composition. The length of the data series is unprecedented. By a comparison with other studies, we also suggest that the organic fraction in the aerosol depends on season.
Aerosol arriving in the eastern Caribbean after passing the Atlantic is characterized, based on...
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