Almost three quarters of Europeans live in cities. The air quality in our cities is therefore of significant importance to the health of Europeans. Considerable
progress has been made in the past twenty years in improving urban air quality, but issues remain. A number of different air pollutants such as nitrogen dioxide, particulate matter, and ozone remain above regulated levels, posing a threat to human health. This report describes a European pilot project to help identify and address the reasons underlying this 'gap' in implementation of air quality policy
in 12 European cities, and thereby draw lessons of wider relevance.