A mobile vehicle-borne monitoring system,passive differential optical absorption spectroscopy which is based on natural light sources,has been explored and applied successfully in the experiment of traffic air pollution monitoring in Hefei. The system uses passive zenith-sky scattered light differeential optical absorption spectroscopy (DOAS) to sample and analysis the air on the top of the road,combining with real-time GPS receiver to acquire latitude and longitude coordinates. According to the GPS positioning coordinates in the Hefei traffic map and the NO2 vertical column density retrieved from the spectrum,a overall air quality map will be produced. The difference of NO2 vertical column density between the monitoring road section and the background (IEE of CPLA) is 6.4 × 1014 molecule/cm2 -1.96 × 1016 molecule/cm2. Due to the effects of vehicle type,traffic and other factors,the overall average concentration of northeast section is higher than southwest.