Characterization of Eyjafjallajökull volcanic aerosols over Southeastern Italy
Authors: Perrone M. R. , De Tomasi F. , Stohl A. , Kristiansen N. I. 
Published: June 2012

Abstract. Volcanic aerosols resulting from the Eyjafjallajökull eruption have been detected in Southeastern Italy from 20 to 22 April 2010, at a distance of approximately 4000 km from the volcano site, and have been characterized by lidar, sun/sky photometer, and in-situ measurements. Numerical simulations by the FLEXPART dispersion model, meteorological synoptic maps, and analytical backtrajectories confirm the advection of volcanic aerosols to the monitoring site. However, both the peak concentrations as well as the total column loadings of volcanic ash simulated by FLEXPART were about one order of magnitude lower than corresponding values simulated over Central Europe on 16 April. This suggests that the volcanic ash over Southeastern Italy was strongly diluted. Nevertheless, volcanic particles added to the pre-existing aerosol load and the integrated use of FLEXPART simulations and experimental measurements has allowed to clearly identifying the impact of volcanic particles on the aerosol vertical distribution, the aerosol size distribution, and the ground-level particulate-matter concentrations. Lidar measurements performed at the Physics Department of the University of Salento (40.4° N; 18.1° E) within EARLINET (European Aerosol Research LIdar NETwork EARLINET) have revealed the first arrival of volcanic aerosols on the afternoon of 20 April. In particular, lidar measurements have shown that at 18:30 UTC of 20 April, lidar ratios (LRs) at 355 nm varied from 65 to 71 sr inside the volcanic aerosol layer located between 2.5–3.5 km from the ground level and were characterized by smaller values (=~45 sr) in the underlying layer. The LR dependence on altitude has decreased with time as volcanic particles also reached ground level. Then, LRs varied between 41 and 60 sr all over the aerosol column at 02:30 UTC of 21 April. The time evolution of the aerosol optical depth from lidar measurements was similar to that of the ash-total-column mass concentration from FLEXPART simulations after midday of 21 April, for the larger contribution of volcanic particles to the whole aerosol load. Sun/sky photometer measurements performed within AERONET, have revealed that the mass size distribution of volcanic particles retrieved from measurements performed on 21 April was in reasonable accordance with the volcanic-ash mass size distribution from FLEXPART simulations. Volcanic particles with radius r > 0.5 μm have mainly been advected over Southeastern Italy and the contribution of coarse volcanic particles has increased from 20 to 22 April. The aerosol fine mode fraction from sun-sky photometer measurements varied between 0.85 and 0.94 on 20 April, but decreased to values between 0.25 and 0.82 on 22 April. Surface measurements of particle size distributions have also supported the advection of coarse volcanic particles. More specifically, mass concentrations of daily PM1 and PM2.5 samples revealed that the PM1/PM2.5 mass ratios were 0.69, 0.66, and 0.60 on 20, 21, and 22 April, respectively, indicating an increasing fraction of super-micron particles. Finally, measurements from the Regional Air Quality Agency have revealed enhanced PM10 and SO2 mass concentrations on 20, 21 and/or 22 April, 2010 all over the ~400 km long Apulia Region. The estimated enhancement of PM10 from volcanic particles was ~6 μg m−3 on 21 April at the monitoring site of this study, in satisfactory accordance with FLEXPART simulations.