Jos Lelieveld of the Max Planck Institute for Chemistry in Hohenpeissenberg, Germany, and his colleagues studied pollution data collected during the summer of 2001. Land and aircraft sensors measured levels of a variety of man-made pollutants, including carbon dioxide, ozone precursors and particulate matter. The team found that levels of key pollutants were two to 10 times higher in the Mediterranean basin than in other areas far from urban centers. In the lowest levels of the atmosphere, winds carried pollution from eastern and western Europe in concentrations higher than typical air-quality standards allow, the researchers determined. The level of ozone on the remote island of Crete, for instance, exceeded the limits set by the European Union by 10 percent, on average. In the layer of the atmosphere four to six kilometers above the earth's surface, most of the contaminants came from Asia and North America, whereas in the highest layers of the atmosphere, monsoon currents brought Asian pollutants into the region. According to the authors, this convergence of wind currents into one region carries "large pollution loads over the Mediterranean, and the negative effects extend far beyond the region. International efforts are called for to reduce these atmospheric environmental stresses and to further investigate the links between Mediterranean and global climate change."