An episode of extremely high PM concentrations over Central Europe caused by dust emitted over the southern Ukraine

Abstract

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 30ms−1. Along the pathway of the plume, maximum particulate matter (PM10) mass concentrations between 200 and 1400µgm−3 occurred in Slovakia, the Czech Republic, Poland, and Germany. Over Germany, the dust plume was characterised by a volume ex- tinction coefficient up to 400Mm−1 and a particle optical depth of 0.71 at wavelength 0.532µm. In-situ size distri- bution measurements as well as the wavelength dependence of light extinction from lidar and Sun photometer measure- ments confirmed the presence of a coarse particle mode with diameters around 2–3µm. Chemical particle analyses sug- gested 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 burn- ing was ruled out. The reasons for the high particle con- centrations 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 1.4–1.8km height, and could therefore neither expand nor dilute effi- ciently. 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. Al- though such plumes from Southern Eurasia seem to occur rather infrequently in Central Europe, its unexpected fea- tures highlights the need to improve the description of dust emission, transport and transformation processes needs, par- ticularly when facing the possible effects of further anthro- pogenic desertification and climate change.