Atmospheric non-spherical particles optical properties from UV-polarization lidar and scattering matrix
Résumé
In this contribution, the optical backscattering properties of atmospheric non-spherical particles are analyzed after long-range transport with a highly sensitive and accurate UV-polarization lidar. Far from the source region, the aerosol cloud is considered as a mixture of spherical (s) and non-spherical (ns) particles. Aerosols UV-depolarization serves as an independent means to discriminate ns from s-atmospheric particles. Vertical profiles of aerosols backscattering coefficient βa and UV-depolarization ratio δa are provided for two ns-particles case studies, on volcanic ash and desert dust, in the troposphere of Lyon (45.76°N, 4.83°E, France). Achieved polarization-sensitivity and accuracy allows tracing different atmospheric layers with a 75 m-altitude resolution. The depolarization ratio δa of the mixed (a) = s, ns aerosol cloud is then analyzed in the frame of the scattering matrix formalism. Observed δa-values, which range from a few to 38.5% (19.5%) for volcanic ash (desert dust) particles, only equal the intrinsic depolarization ratio of ns-particles when there is no detectable s-particle, and in the presence of s-particles, δa is always below δa,ns. By coupling our accurate lidar measurements with scattering matrix, we retrieved vertical profiles of backscattering coefficient, specific to ash (dust) particles, which is new. This ash (dust) specificity is then discussed within our error bars. We hence developed a methodology giving access to the number concentration vertical profile of specific particulate matter in the troposphere.