Composition and evolution of volcanic aerosol from eruptions of Kasatochi, Sarychev and Eyjafjallaj?kull in 2008–2010 based on CARIBIC observations

摘要

Large volcanic eruptions impact significantly on climate and lead to ozonedepletion due to injection of particles and gases into the stratospherewhere their residence times are long. In this the composition of volcanicaerosol is an important but inadequately studied factor. Samples ofvolcanically influenced aerosol were collected following the Kasatochi(Alaska), Sarychev (Russia) and also during the Eyjafjallaj?kull(Iceland) eruptions in the period 2008–2010. Sampling was conducted by theCARIBIC platform during regular flights at an altitude of 10–12 km as wellas during dedicated flights through the volcanic clouds from the eruption ofEyjafjallaj?kull in spring 2010. Elemental concentrations of thecollected aerosol were obtained by accelerator-based analysis. Aerosol fromthe Eyjafjallaj?kull volcanic clouds was identified by highconcentrations of sulphur and elements pointing to crustal origin, andconfirmed by trajectory analysis. Signatures of volcanic influence were alsoused to detect volcanic aerosol in stratospheric samples collected followingthe Sarychev and Kasatochi eruptions. In total it was possible to identify17 relevant samples collected between 1 and more than 100 days following theeruptions studied. The volcanically influenced aerosol mainly consisted ofash, sulphate and included a carbonaceous component. Samples collected inthe volcanic cloud from Eyjafjallaj?kull were dominated by the ash andsulphate component (∼45% each) while samples collected inthe tropopause region and LMS mainly consisted of sulphate (50–77%) andcarbon (21–43%). These fractions were increasing/decreasing with the ageof the aerosol. Because of the long observation period, it was possible toanalyze the evolution of the relationship between the ash and sulphatecomponents of the volcanic aerosol. From this analysis the residence time(1/e) of sulphur dioxide in the studied volcanic cloud was estimated to be45 ± 22 days.