Arable land can have a negative impact on air quality

The directive on particulate matter has been in force in the European Union since 2005. As a consequence, there is a comprehensive air monitoring network in the member states designed to monitor compliance with the limit values. With quick, unbureaucratic assistance from a total of 15 state environmental agencies it was possible to analyse particulate data from 360 stations in five countries. It quickly became apparent that the particulate matter was coming from the east because the concentration increased noticeably towards Slovakia. But where exactly had the cloud come from" What the situation was like the other side of the EU’s eastern border was a matter for speculation because of a lack of air monitoring data. So the researchers combed satellite pictures and came across what they were looking for on a EUMETSAT picture. This showed a noticeable red patch over southern Ukraine on 23 March which expanded rapidly. The researchers estimated the total mass of the dust cloud to be at least 60,000 tons. That is equivalent to more than 600 wagonloads of sand. The actual mass was probably much greater still, since the measuring devices register only those particles that are smaller than 10 microns (0.01 mm). Czech geologists estimated the total dust load must be about 3 million tons because this Ukrainian "plume" contained also bigger particles till size of 0.5mm. The last remaining doubts about the origin of the dust cloud were cleared up by a team led by Dr Jindrich Hladil at the Institute of Geology of the Czech Academy of Sciences in Prague. They compared the dust samples from the air with dust samples taken directly from the Ukrainian soil. The lead isotope ratio showed that the dust had indeed come from the Black Sea region. “The mineralogical-petrological fingerprinting of the solid particles over 10 micrometre size can say a lot about the geologically specific source areas”, says Jindrich Hladil. Moreover, the researchers in Prague, who were investigating the mystery completely independently of their counterparts in Leipzig, discovered in their samples pollen grains that were typical for the Ukraine. These included relatively large quantities of ragweed pollen, which is regarded as extremely allergenic. This also ruled out a dust storm from the Mediterranean coast of Libya, which had caught the scientists’ attention in the meantime. The rapid transport of the air and the presence of a temperature inversion, which acted like a lid, ensured that the dust cloud was unable to escape upwards or sideways – this was shown by data from a LIDAR remote sensing system in Leipzig and from weather balloons. It was swept to Germany as if through a pipe at speeds of up to 70 kilometres per hour, and was even detected in Britain. "At the end of the day, it was the combination of dry, vulnerable soil, strong gusts of wind and fast transport within a dry, stable boundary layer that made this a freak dust event in Central Europe," explains Wolfram Birmili.

A foretaste of the consequences of climate change