A method and a measuring system for determining exhaust gas emissions from a moving vehicle by a remote optical measuring technique. The model and/or type of the vehicle under examination is identified, and the driving situation of the vehicle in question is determined at the moment of measurement. A calculatory vehicle model is used to determine a case-specific estimate for the carbon dioxide concentration of the exhaust gas plume depending on the vehicle in question and its driving situation. The accuracy of determining the concentrations of the actual emission gases is improved by eliminating the inaccuracy of the carbon dioxide concentration values.