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This NASA handout image obtained 23 March, 2005 shows a grey veil of haze covering the Po River Valley of northern Italy and stretching out over the Adriatic Sea in this satellite image from 17 March. The snow-capped Alps to the north help to restrict air flow between northern Italy and the rest of continental Europe, meaning that air pollution in the northern part of the country often gets trapped and can take days to disperse. Many of Italy's major cities and industrial centers are located in this valley, further adding to the problem. AFP PHOTO/HO/NASA (Photo by HO / NASA / AFP)