So far, real driving emissions knowledge involves installing Portable Emissions Measurement Systems (PEMS). As a consequence, large scale campaigns of measurement are not feasible. This paper describes an innovative coupling of Information and Communication Technology (ICT) and physical modeling to turn the driver's smartphone into a virtual sensor of pollutant emissions of his/her vehicle. It consists of using the smartphone as a vehicle speed sensor and using cloud computing to make pollutant estimation. Large scale deployment of this approach provides i) decision-makers with precise information about pollutant emissions related to choices of standards or infrastructure ii) car drivers with their real footprint.