Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 14199-14217, 2017
https://doi.org/10.5194/acp-17-14199-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
30 Nov 2017
Dry versus wet marine particle optical properties: RH dependence of depolarization ratio, backscatter, and extinction from multiwavelength lidar measurements during SALTRACE
Moritz Haarig1, Albert Ansmann1, Josef Gasteiger2, Konrad Kandler3, Dietrich Althausen1, Holger Baars1, Martin Radenz1, and David A. Farrell4 1Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
2Faculty of Physics, University of Vienna, Vienna, Austria
3Technische Universität Darmstadt, Darmstadt, Germany
4Caribbean Institute for Meteorology and Hydrology, Bridgetown, Barbados
Abstract. Triple-wavelength lidar observations of the depolarization ratio and the backscatter coefficient of marine aerosol as a function of relative humidity (RH) are presented with a 5 min time resolution. The measurements were performed at Barbados (13° N, 59° W) during the Saharan Aerosol Long-range Transport and Aerosol-Cloud interaction Experiment (SALTRACE) winter campaign in February 2014. The phase transition from spherical sea salt particles to cubic-like sea salt crystals was observed with a polarization lidar. The radiosonde and water-vapor Raman lidar observations show a drop in RH below 50 % in the marine aerosol layer simultaneously with a strong increase in particle linear depolarization ratio, which reaches values up to 0.12 ± 0.08 (at 355 nm), 0.15 ± 0.03 (at 532 nm), and 0.10 ± 0.01 (at 1064 nm). The lidar ratio (extinction-to-backscatter ratio) increased from 19 and 23 sr for spherical sea salt particles to 27 and 25 sr (at 355 and 532 nm, respectively) for cubic-like particle ensembles. Furthermore the scattering enhancement due to hygroscopic growth of the marine aerosol particles under atmospheric conditions was measured. Extinction enhancement factors from 40 to 80 % RH of 1.94 ± 0.94 at 355 nm, 3.70 ± 1.14 at 532 nm, and 5.37 ± 1.66 at 1064 nm were found. The enhanced depolarization ratios and lidar ratios were compared to modeling studies of cubic sea salt particles.

Citation: Haarig, M., Ansmann, A., Gasteiger, J., Kandler, K., Althausen, D., Baars, H., Radenz, M., and Farrell, D. A.: Dry versus wet marine particle optical properties: RH dependence of depolarization ratio, backscatter, and extinction from multiwavelength lidar measurements during SALTRACE, Atmos. Chem. Phys., 17, 14199-14217, https://doi.org/10.5194/acp-17-14199-2017, 2017.
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Short summary
The depolarization ratio and the backscatter coefficient of marine particles are correlated with the relative humidity. The measurements were performed under atmospheric conditions with a multi-wavelength lidar system in pure marine conditions over Barbados in February 2014. For RH < 50 % the sea salt particles have a cubic-like shape resulting in an enhanced depolarization ratio of up to 0.15. This agrees with model results of cubic sea salt. The extinction enhancement f(RH) factor was derived.
The depolarization ratio and the backscatter coefficient of marine particles are correlated with...
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