Air pollution is an environmental issue of major concern in Europe, as highlighted by the EU Thematic Strategy for air quality (COM 2005 446) and Directive 2008/50/EC on ambient air quality and cleaner air for Europe.

Despite the legislation, some regions in Europe produce or maintain pollutant levels that threaten human health and ecosystems. This is the case in the Po Valley, Italy, where the combination of high population densities, high emission densities and poor meteorological dispersion lead to adverse impacts on the population from high levels of fine particulate matter (PM2.5) and on ecosystems because of high levels of ozone and eutrophication.

Although less dramatic, air pollution problems are also encountered in Central Europe. For example, in Alsace, France, where factors – e.g. the high population density in the Upper Rhine valley, high levels of border traffic across France, Germany and Switzerland, as well as the presence of important industrial areas (the Ruhr region in the north-east and the Basel area in the south) – have led to a deterioration of air quality with measurements frequently in excess of the maximum values for particulate matter and ozone compounds.