The main scientific goal of this project is to develop tools for estimating a diffusive field, such as the concentration of gases over a certain area, using a set of mobile sensors. The envisioned application proposed here is pollution monitoring in the city of Lisbon based on measurements taken by the fleet of public urban buses (Carris). This approach could significantly increase the density of sampling across the city with only a modest investment in infrastructure, thus providing a much more detailed picture of air quality than using the current small network of fixed measurement stations. A prototype system will be developed, comprising a few sensing/computing units installed on buses, a central station (CS) where data on the reconstructed pollution field will be made available, and all necessary components to convey readings or computed variables via an ad-hoc wireless network. The latter will link buses and a set of gateway nodes that interface to the internet, through which the CS is reached. The system output will include pollution maps with fine spatial and temporal resolution.