Raman lidar observations of aerosol emitted during the 2002 Etna eruption

Results of a lidar measurement campaign performed at IMAA-CNR (Potenza, Italy) during the 2002 Etna volcano eruption, are reported. With combined Raman elastic-backscatter lidar, independent measurements of aerosol extinction and backscatter coefficients at 355 nm are retrieved, whereas aerosol backscatter coefficient at 532 nm is retrieved from elastic lidar signal. A volcanic aerosol layer has been observed in the free troposphere on 1-2 November. AVHRR images show direct plume transport from Etna to Potenza. Optical depth of 0.1 and lidar ratio of 55 sr at 355 nm have been observed at the moment of direct transport. For the first time, a measurement of the lidar ratio for tropospheric volcanic aerosol has been performed. This lidar ratio value and the estimation of the wavelength dependence of the aerosol backscatter coefficient of 2.4 indicate the presence of young sub-micron sulfate particles, a low soot content, and the absence of large ash particles.