Monitoring of the Eyjafjallajökull volcanic aerosol plume over the Iberian Peninsula by means of four EARLINET lidar stations

Abstract

Lidar and sun-photometer measurements were performed intensively over the Iberian Peninsula (IP) during the eruption of Eyjafjallaj ¨ okull volcano (Iceland) in April–May 2010. The volcanic plume hit all the IP stations for the first time on 5 May 2010. A thorough study of the event is conducted for the period 5–8 May. Firstly the spatial and temporal evolution of the plume is described by means of lidar and sun-photometer measurements supported with backtrajectories. The volcanic aerosol layers observed over the IP were rather thin (< 1000 m) with a top height up to 11–12 km. The mean optical thicknesses associated to those layers were rather low (between 0.013 and 0.020 over the whole period). Punctually on 7 May the optical thickness reached peak values near 0.10. Secondly the volcanic aerosols are characterized in terms of extinction and backscatter coefficients, lidar ratios, A° ngstro¨m exponents and linear particle depolarization ratio. Lidar ratios at different sites varied between 30 and 50 sr without a marked spectral dependency. Similar extinction-related A° ngstro¨m exponents varying between 0.6 and 0.8 were observed at different sites. The temporal evolution of the backscatter-related A° ngstro¨m exponents points out a possible decrease of the volcanic particle size as the plume moves from west to east. Particle depolarization ratios on the order of 0.06–0.08 confirmed the coexistence of both ash and non-ash particles. Additionally profiles of mass concentration were obtained with a method using the opposite depolarizing effects of ash particles (strongly depolarizing) and non-ash particles (very weakly depolarizing), and sun-photometer observations. In Granada the ash mass concentration was found approximately 1.5 higher than that of non-ash particles, and probably did not exceed the value of 200 μgm−3 during the whole event.