In this paper we present a mobile system for air quality and pollution measurement suited for the urban environment. We designed, tested and built a reliable measurement device that can acquire information about the air quality of its surroundings, store it in a temporary memory buffer and periodically relay it to a central on-line repository. Real-time gathered data can be freely accessed by the public through an on-line web interface. Users can select and view different gases and concentrations overlapped on a map of the city.