Characterization of iceland volcanic aerosols by UV-polarization lidar at Lyon, SW Europe

In this paper, a ground-based UV-polarization Lidar is used to characterize the optical properties of volcanic particles that originated from the Eyjafjöll volcano (63.63°N, 19.62°W, Iceland) and advected over Lyon (45.76°N, 4.83°E, France), a distance 2,600 kilometers away. The volcanic origin of the observed particles has been confirmed with 7-days air mass back-trajectories and FLEXPART dispersion model. The measured UV-particle backscattering coefficient is typically equal to 4 × 10^-6 m^-1.sr^-1. UV-depolarization ratios measurements have been performed in the troposphere of Lyon to measure the degree of volcanic particle non-sphericity. Experimental efforts have been done to determine the systematic errors contributing to the retrieved UV-particle depolarization ratio δ_p. The precision on retrieved δ_p-values is hence dominated by the uncertainty on the extinction to backscatter ratio S = 55 ± 10. It follows that the microphysical properties of the observed volcanic aerosols are quite difficult to retrieve from δ_p. However, a main volcanic layer of 2 kilometres width has been observed in the troposphere of Lyon, where measured UV δ_p-values reach up to (30 ±; 10) %, showing that the observed highly dispersed and aged volcanic particles are irregular-shaped particles, even at more than 2,000 km from the Eyjafjöll volcano.