Detection and characterization of volcanic ash plumes over Lille during the Eyjafjallaj?kull eruption

摘要

Routine sun-photometer and micro-lidar measurements were performed in Lille,northern France, in April and May 2010 during the Eyjafjallaj?kullvolcanic eruption. The impact of such an eruption emphasized significance ofhazards for human activities and importance of observations of the volcanicaerosol particles. This paper presents the main results of a jointmicro-lidar/sun-photometer analysis performed in Lille, where volcanic ashplumes were observed during at least 22 days, whenever weather conditionspermitted. Aerosol properties retrieved from automatic sun-photometermeasurements (AERONET) were strongly changed during the volcanic aerosolplumes transport over Lille. In most cases, the aerosol optical depth (AOD)increased, whereas ?ngstr?m exponent decreased, thus indicatingcoarse-mode dominance in the volume size distribution. Moreover, the non-sphericalfraction retrieved by AERONET significantly increased. The real part of thecomplex refractive index was up to 1.55 at 440 nm during the eruption,compared to background data of about 1.46 before the eruption. Collocatedlidar data revealed that several aerosol layers were present between 2 and5 km, all originating from the Iceland region as confirmed bybackward trajectories. The volcanic ash AOD was derived from lidarextinction profiles and sun-photometer AOD, and its maximum was estimatedaround 0.37 at 532 nm on 18 April 2010. This value was observed at analtitude of 1700 m and corresponds to an ash mass concentration (AMC)slightly higher than 1000 μg m?3 (±50%). An effective lidarratio of ash particles of 48 sr was retrieved at 532 nm for 17 April duringthe early stages of the eruption, a value which agrees with several otherstudies carried out on this topic. Even though the accuracy of theretrievals is not as high as that obtained from reference multiwavelengthlidar systems, this study demonstrates the opportunity of micro-lidar andsun-photometer joint data processing for deriving volcanic AMC. It alsooutlines the fact that a network of combined micro-lidars andsun photometers can be a powerful tool for routine monitoring of aerosols,especially in the case of such hazardous volcanic events.