Air quality is an increasing concern, particularly in densely populated urban areas. Indeed, large European cities have seen pollutant concentrations exceed World Health Organization thresholds, with a significant portion of NOx emissions originating from road transportation. Studies have shown that less than five percent of the vehicle fleet, often including vehicles with defective after-treatment systems, is responsible for a disproportionate share of these emissions. This highlights the importance of not solely relying on the gradual renewal of vehicle fleets to mitigate health risks associated with air pollution. This research, funded by the French Agency for the Ecological Transition (ADEME), introduces an experimental methodology aimed at controlling emissions from vehicles already in circulation. Aramis Group, a European specialist of refurbishment and online sales of used cars, provided several refurbished used vehicles for testing, directly taken from its workflow. These vehicles were tested using REAL-e, a lightweight Smart Emission Measurement System developed by IFP Energies nouvelles, along a short round trip near the refurbishment site. The methodology adjusts measured emissions values – CO, NOx, and PN23 – based on driving behavior indicators to mitigate the variability caused by traffic and driving conditions in a procedure called contextualization. Furthermore, a new environmental evaluation score for used vehicles is proposed, based on the Green NCAP rating procedure. The results demonstrate that the proposed contextualization is most effective for vehicles with higher emissions (e.g., older vehicles) and aggressive driving behavior – validating the methodology for the current sample of used vehicles but highlighting the need for future after-treatment system technologies. The observed emission levels in the tested vehicle sample strongly correlate with the evolution of emissions standard, validating the use of REAL-e for such experimental campaigns. Finally, the calculated scores show that 4 vehicles out of the 28 tested received the lowest score, while none achieved the highest score – an expected outcome for used vehicles. Future research will focus on refining the methodology to enhance contextualization and exploring the broader application of REAL-e.