In situ physical and chemical characterisation of the Eyjafjallajökull aerosol plume in the free troposphere over Italy

Abstract. Continuous measurements of physical and chemi- cal properties at the Mt. Cimone (Italy) GAW-WMO (Global Atmosphere Watch, World Meteorological Organization) Global Station (2165 m a.s.l.) have allowed the detection of the volcanic aerosol plume resulting from the Eyjafjalla- jökull (Iceland) eruption of spring 2010. The event affected the Mt. Cimone site after a transport over a distance of more than 3000 km. Two main transport episodes were detected during the eruption period, showing a volcanic fingerprint discernible against the free tropospheric background condi- tions typical of the site, the first from April 19 to 21 and the second from 18 to 20 May 2010. This paper reports the modification of aerosol characteristics observed during the two episodes, both characterised by an abrupt increase in fine and, especially, coarse mode particle number. Analysis of major, minor and trace elements by differ- ent analytical techniques (ionic chromatography, particle in- duced X-ray emission–particle induced gamma-ray emission (PIXE–PIGE) and inductively coupled plasma mass spec- trometry (ICP-MS)) were performed on aerosols collected by ground-level discrete sampling. The resulting database allows the characterisation of aerosol chemical composition during the volcanic plume transport and in background con- ditions. During the passage of the volcanic plume, the fine fraction was dominated by sulphates, denoting the secondary origin of this mode, mainly resulting from in-plume oxida- tion of volcanic SO2. By contrast, the coarse fraction was characterised by increased concentration of numerous ele- ments of crustal origin, such as Fe, Ti, Mn, Ca, Na, and Mg, – Published: 29 January 2014 which enter the composition of silicate minerals. Data analy- sis of selected elements (Ti, Al, Fe, Mn) allowed the estima- tion of the volcanic plume’s contribution to total PM10, re- sulting in a local enhancement of up to 9.5 μg m−3, i.e. 40 % of total PM10 on 18 May, which was the most intense of the two episodes. These results appear significant, especially in light of the huge distance of Mt. Cimone from the source, confirming the widespread diffusion of the Eyjafjallajökull ashes over Europe.