Atmospheric Chemistry and Physics, vol. 13, issue 7 (2013) pp. 3705-3720 Published by Copernicus GmbH
Routine sun-photometer and micro-lidar measure-ments were performed in Lille, northern France, in April and May 2010 during the Eyjafjallajökull volcanic erup-tion. The impact of such an eruption emphasized significance of hazards for human activities and importance of observa-tions of the volcanic aerosol particles. This paper presents the main results of a joint micro-lidar/sun-photometer anal-ysis performed in Lille, where volcanic ash plumes were observed during at least 22 days, whenever weather condi-tions permitted. Aerosol properties retrieved from automatic sun-photometer measurements (AERONET) were strongly changed during the volcanic aerosol plumes transport over Lille. In most cases, the aerosol optical depth (AOD) in-creased, wherea Angström exponent decreased, thus indi-cating coarse-mode dominance in the volume size distri-bution. Moreover, the non-spherical fraction retrieved by AERONET significantly increased. The real part of the com-plex refractive index was up to 1.55 at 440 nm during the eruption, compared to background data of about 1.46 be-fore the eruption. Collocated lidar data revealed that several aerosol layers were present between 2 and 5 km, all origi-nating from the Iceland region as confirmed by backward trajectories. The volcanic ash AOD was derived from lidar extinction profiles and sun-photometer AOD, and its maxi-mum was estimated around 0.37 at 532 nm on 18 April 2010. This value was observed at an altitude of 1700 m and corre-sponds to an ash mass concentration (AMC) slightly higher than 1000 µg m −3 (±50 %). An effective lidar ratio of ash particles of 48 sr was retrieved at 532 nm for 17 April dur-ing the early stages of the eruption, a value which agrees with several other studies carried out on this topic. Even though the accuracy of the retrievals is not as high as that obtained from reference multiwavelength lidar systems, this study demonstrates the opportunity of micro-lidar and sun-photometer joint data processing for deriving volcanic AMC. It also outlines the fact that a network of combined micro-lidars and sun photometers can be a powerful tool for routine monitoring of aerosols, especially in the case of such haz-ardous volcanic events.
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