Atmos. Chem. Phys. Discuss., 13, 1891-1947, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Retrieving volcanic, desert dust, and sea-salt particle properties from two/three-component particle mixtures after long-range transport using UV-VIS polarization Lidar and T-matrix
G. David1, B. Thomas1, T. Nousiainen2, A. Miffre1, and P. Rairoux1
1Institut Lumière Matière,~UMR5306 Université Lyon 1, CNRS, Université de Lyon, 69622 Villeurbanne cedex, France
2Department of Physics, P.O. Box 48, 00014, University of Helsinki, Helsinki, Finland

Abstract. During transport by advection, atmospheric nonspherical particles, such as volcanic, desert dust or sea-salt particles experience several chemical and physical processes, leading to a complex vertical atmospheric layering at remote sites where intrusion episodes occur. In this contribution, a new methodology is proposed to analyze this complex vertical layering in the case of a two/three-component particle external mixtures after long-range transport. This methodology relies on a precise analysis of the spectral and polarization properties of the light backscattered by atmospheric particles. It is based on combining a sensitive and accurate UV-VIS polarization Lidar experiment with accurate T-matrix numerical simulations and air mass back-trajectories. The Lyon UV-VIS polarization Lidar is used to efficiently partition the particle mixture into its nonspherical components, while the T-matrix algorithm is used for computing backscattering and depolarization properties specific to nonspherical volcanic, desert dust and sea-salt particles, the latter being described in the cubic shape approximation. It is shown that, after long-range transport, the particle mixtures' depolarization ratio δp differs from the nonspherical particles' depolarization ratio δns due to the presence of spherical particles in the mixture. Hence, after identifying a tracer for nonspherical particles, particle backscattering coefficients specific to each nonspherical component can be retrieved in a two component external mixture. For three-component mixtures, the spectral properties of light must in addition be addressed by using a dual-wavelength polarization Lidar. Hence, for the first time, in a three-component external mixture, the nonsphericity of each particle is taken into account in a so-called 2β + 2δ formalism. Applications of this new methodology are then demonstrated in two case studies carried out in Lyon, France, related to the mixing of Eyjafjallajökull volcanic ash with sulphate particles (case of a two-component mixture) and to the mixing of dust with sea-salt and water-soluble particles (case of a three-component mixture). This new methodology, which is able to provide separate vertical profiles of mixed atmospheric dust, sea-salt and water-soluble particles, may be useful for accurate radiative forcing assessments.

Citation: David, G., Thomas, B., Nousiainen, T., Miffre, A., and Rairoux, P.: Retrieving volcanic, desert dust, and sea-salt particle properties from two/three-component particle mixtures after long-range transport using UV-VIS polarization Lidar and T-matrix, Atmos. Chem. Phys. Discuss., 13, 1891-1947, doi:10.5194/acpd-13-1891-2013, 2013.
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