In this paper an on-road network of monitoring stations for the air quality is organized in order to provide data with high spatial resolution in a wide urban area. On this purpose a dedicated experimental set-up was developed in order to be installed on board of DHL courier vans. The monitoring station is completely automated and transmit continuously environmental data and positions during the daily route of the van. In order to aggregate data, the city map is partitioned into a grid of 1 km2. The system is tested by comparing average concentrations with those of a fixed monitoring station.