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, Finland
Received: 21 Dec 2012 – Published in Atmos. Chem. Phys. Discuss.: 17 Jan 2013
Abstract. During transport by advection, atmospheric nonspherical particles, such as volcanic ash, 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 paper, a new methodology is proposed to analyse this complex vertical layering in the case of a two/three-component particle external mixtures. This methodology relies on an 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 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 method is used for simulating the backscattering and depolarization properties of nonspherical volcanic ash, desert dust and sea-salt particles. It is shown that the particle mixtures' depolarization ratio δ p 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 exploited 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 sulfate 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 backscattering coefficient for mixed atmospheric dust, sea-salt and water-soluble particles, may be useful for accurate radiative forcing assessments.
Revised: 06 Jun 2013 – Accepted: 07 Jun 2013 – Published: 18 Jul 2013
David, G., Thomas, B., Nousiainen, T., Miffre, A., and Rairoux, P.: Retrieving simulated volcanic, desert dust and sea-salt particle properties from two/three-component particle mixtures using UV-VIS polarization lidar and T matrix, Atmos. Chem. Phys., 13, 6757-6776, doi:10.5194/acp-13-6757-2013, 2013.