A case of extreme particulate matter concentrations over Central Europe caused by dust emitted over the southern Ukraine

On 24 March 2007, an extraordinary dust plume was observed in the Central European troposphere. Satellite observations revealed its origins in a dust storm in Southern Ukraine, where large amounts of soil were resuspended from dried-out farmlands at wind gusts up to 30 m s(-1). Along the pathway of the plume, maximum particulate matter (PM10) mass concentrations between 200 and 1400 mu g m(-3) occurred in Slovakia, the Czech Republic, Poland, and Germany. Over Germany, the dust plume was characterised by a volume extinction coefficient up to 400 Mm(-1) and a particle optical depth of 0.71 at wavelength 0.532 mu m. In-situ size distribution measurements as well as the wavelength dependence of light extinction from lidar and Sun photometer measurements confirmed the presence of a coarse particle mode with diameters around 2-3 mu m. Chemical particle analyses suggested a fraction of 75% crustal material in daily average PM10 and up to 85% in the coarser fraction PM10-2.5. Based on the particle characteristics as well as a lack of increased CO and CO2 levels, a significant impact of biomass burning was ruled out. The reasons for the high particle concentrations in the dust plume were twofold: First, dust was transported very rapidly into Central Europe in a boundary layer jet under dry conditions. Second, the dust plume was confined to a relatively stable boundary layer of 1.4-1.8 km height, and could therefore neither expand nor dilute efficiently. Our findings illustrate the capacity of combined in situ and remote sensing measurements to characterise large-scale dust plumes with a variety of aerosol parameters. Although such plumes from Southern Eurasia seem to occur rather infrequently in Central Europe, its unexpected features highlights the need to improve the description of dust emission, transport and transformation processes needs, particularly when facing the possible effects of further anthropogenic desertification and climate change.