Abstract:  Motor vehicles are one of the important sources of NH₃ emissions in cities and have an important impact on PM_2.5 formation. In this study, 8-day mobile observations of on-road NH₃ emissions was conducted in the mega-city of Shanghai using a mobile measurement method, and the NH₃ emission ratios and their distributions of on-road motor vehicles were obtained empirically. The results show that the average ΔNH₃/ΔCO₂ emission ratio of actual road motor vehicles is 0.44 ppbv/ppmv, and there are significant differences between different types of traffic functional areas, with relatively high emission ratios for motor vehicles on roads in port areas and central urban areas, and relatively low emission ratios on highways. Traffic conditions have an important influence on NH₃ emissions from actual roads. The NH₃ emission ratio of motor vehicles under low-speed congestion is 2-3 times higher than that under medium-speed conditions, and NH₃ emissions will rise again when the vehicle speed increases further. The study found that traffic control measures have a positive effect on reducing NH₃ emissions from motor vehicles through aerial measurements during the China International Import Expo (CIIE), and the related research results can provide an important reference for NH₃ emissions control from motor vehicles in urban areas.