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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2018-54
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
28 Feb 2018
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Ship-borne aerosol profiling with lidar over the Atlantic Ocean: From pure marine conditions to complex dust-smoke mixtures
Stephanie Bohlmann1,2, Holger Baars1, Martin Radenz1, Ronny Engelmann1, and Andreas Macke1 1Leibniz Institute for Tropospheric Research, Permoserstraße 15, 04318 Leipzig, Germany
2now at: Finnish Meteorological Institute, P.O. Box 1627, 70211, Kuopio, Finland
Abstract. The multiwavelength Raman lidar PollyXT have been regularly operated aboard the research vessel Polarstern on expeditions across the Atlantic Ocean from North to South and vice versa. The lidar measurements of the Polarstern cruises PS95 from Bremerhaven to Cape Town (November 2015) and PS98 from Punta Arenas to Bremerhaven (April/May 2016) are presented and analysed in detail. The latest setup of PollyXT allows improved coverage of the marine boundary layer (MBL) due to an additional near-range receiver.

Three case studies provide an overview of the detected aerosol over the Atlantic Ocean. In the first case, marine conditions were observed near South Africa on the autumn cruise PS95. Values of optical properties (depolarisation ratios close to zero, lidar ratios of 23 sr at 355 nm and 532 nm) within the MBL indicate pure marine aerosol. A layer of dried marine aerosol, indicated by an increase of the particle depolarisation ratio to about 10 % at both wavelengths and thus confirming the non-sphericity of these particles, could be detected on the top the MBL. On the same cruise, an almost pure Saharan dust plume was observed near the Canary Islands, presented in the second case. The third case deals with several layers of Saharan dust partly mixed with biomass-burning smoke measured on PS98 near the Cape Verde Islands. While the MBL was partly mixed with dust in the pure Saharan dust case, an almost marine MBL was observed in the third case. A statistical analysis showed latitudinal differences in the optical properties within the MBL, caused by the down-mixing of dust in the tropics and anthropogenic influences in the northern latitudes whereas the optical properties of the MBL in the southern hemisphere correlate with typical marine values. The particle depolarisation ratio of dried marine layers ranged between 4–9 %.

Night measurements from PS95 and PS98 were used to illustrate the potential of aerosol classification using lidar ratio, particle depolarisation ratio and Ångström exponent. Lidar ratio and particle depolarisation ratio have been found to be the main indicator for the particle type, whereas the Ångström exponent is rather variable.

Citation: Bohlmann, S., Baars, H., Radenz, M., Engelmann, R., and Macke, A.: Ship-borne aerosol profiling with lidar over the Atlantic Ocean: From pure marine conditions to complex dust-smoke mixtures, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-54, in review, 2018.
Stephanie Bohlmann et al.
Stephanie Bohlmann et al.

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Short summary
Lidar measurements of two expeditions across the Atlantic Ocean aboard the research vessel Polarstern are presented. Besides Saharan dust layers and complex dust-smoke mixtures, pure marine conditions with enhanced particle depolarisation ratios on top of the marine boundary layer could be observed. A statistical analysis shows latitudinal differences in the optical properties within the marine boundary layer and illustrates the potential of these properties for aerosol classification.
Lidar measurements of two expeditions across the Atlantic Ocean aboard the research vessel...
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