Observations in Germany, France, and Great Britain during eruptions of the Eyjafjallajokull volcano in 2010
Résumé
In spring 2010 the Icelandic volcano Eyjafjallajokull erupted high loads of pyroclastic material into the atmosphere. The eruption cloud reached heights between 4 and 7 km. The volcanic ash advisory centre London, the responsible institution for making forecasts of ash coming to Europe, decided the complete shut down of the air traffic over wide parts of Europe for a sequence of days. From April 13th to 20th there was a stable high pressure system over the Atlantic Ocean. Thus, a rather constant air flow from north-west to south-east prevailed over Europe in the upper and middle troposphere. Due to that the volcanic ash was transported from Iceland over the UK to Central Europe. Furthermore, the weather conditions were sunny, dry, and stable, preventing the ash from being mixed throughout the atmosphere or from being washed out by precipitation. These weather conditions led not only to long range ash transport but also to high PM10 concentrations in the boundary layer from other sources. Thus the question arises whether the volcanic ash contributed to the high PM10 levels near ground or if the reason for the high PM10 concentrations measured by the ground based stations has to be found elsewhere. The aim of this paper is to give a review of some of the findings of the ground based measurements, model calculations, and remote sensing in Central Europe during the volcanic event two years ago, with focus on Germany, France, and Great Britain. A large variety of modelling results on the dispersion of the Eyjafjallajokull plume over Europe can be found in the recent literature. They all showed that the ash plume reached the air space over Central Europe and these findings compare rather nicely to satellite pictures, Lidar measurements, and measurements from aircrafts. In the present paper as an example EURAD and Chimere model simulations will be presented. With regard to lidar and satellite measurements, we will concentrate on the findings by the German Weather Service, the Met Office and of the volcanic ash advisory centre in Great Britain. As an example for the ground based measurements, we will show the findings of Germany and France. To figure out whether and to what extend the elevated PM10 concentrations are influenced by the transported volcanic ash the PM10 samples were analysed for heavy metals, chloride, nitrate, sulphate, and ammonium. The composition was compared with the one of the erupted material as measured by Óskarsson (2010). An additional indicator for volcanic material is the occurrence of elevated SO2 concentrations and of unusual particle shapes that can be detected by scanning electron microscope analyses. The results of the ground based observations in Germany and France are quite similar. There was volcanic ash that reached the surface, especially at the Black Forest as well as in the Alsace region (Colette et al., 2011, LUBW, 2010), where part of the sampled particles have the same chemical composition than the erupted material. Thus about 25 µg/m3 of the PM10 can be ascribed to volcanic ash there, in good agreement with long-range transport modelling studies. Nevertheless in other places, for example in North Rhine-Westphalia (LANUV), the volcanic ash fraction contributed merely about 5 µg/m3 to the PM10 burden in the latter regions. This shows that a combination of all existing methods and a close collaboration should be used to predict the impact of future events.