Vertical transport of atmospheric pollutants over the foothills of the Alps

During the EU-VOTALP II (Vertical ozone transports in the Alps) project, aircraft and other measurements of gaseous pollutants were performed in the Alpine foothills near Lake Como, Italy. It could be shown that vertical air motion induced by the hills caused an increase of pollutant concentrations at altitudes well above the hill crests. Substantial concentration increases were observed for formaldehyde, nitrogen oxides aerosol number and other species down-wind of the hilly area at altitudes which were higher than the mixed planetary boundary layer over the Po Basin. This suggests that vertical pollution transport not only occurs in deep valleys as previously shown for the Mesolcina valley but also over Alpine foothills. (authors)