Po River Valley Smog, Italy Fall/Winter 1997 The snow capped higher elevations of the Italian, Swiss, and French Alps mountains provide a natural barrier to the outward migration of smog shown here filling the Po River Valley of northern Italy. This southwest-looking view shows a dense sea of air pollution (extensive, lighter colored area-center of image) that is trapped from time to time by air stagnation in the heavily industrialized Po River Valley. The picture shows that air pollution even infiltrates the numerous mountain valleys that surround this river basin. The smog appears to be less dense towards the eastern side of the basin where the terrain is visible though the hazy-looking atmosphere. A small section of the Rhone River Valley can be traced through the Swiss Alps near the right edge (middle) and the small patch of whiteness along the right edge (middle) is a low deck of clouds over Lake Geneva