Research Measuring Exhaust Emissions of Heavy Duty Vehicles in Real Traffic Using “Plume Chasing”

23 February 2026

The main causes of poor air quality include nitrogen oxides as well as particulate matter and black carbon emitted by vehicles. The legislature does regulate emissions at the EU level through various emission standards that specify the amount of emissions harmful to the environment and human health that may be released. However, the technical solutions built into vehicles for exhaust-aftertreatment are either inadequate and error-prone or easily tampered with, according to Heidelberg environmental physicist Christina Schmidt. In addition, some of the pollutants in question have not been subject to exhaust emission inspections due to complexity and costs. This is where Plume Chasing comes in. Emissions are checked during driving using a specially equipped measurement vehicle.

During the mobile measurements, the exhaust gases of the vehicle in front are sucked in through a hose and analyzed directly on board the measurement vehicle. During a total of eleven multi-day field campaigns, the international research team carried out exhaust gas tests in Germany, Austria, Denmark, Belgium, the Czech Republic, and Slovakia between 2016 and 2023. Campaigns focused on heavy duty vehicles – mostly trucks – of Euro V and Euro VI emission standards, and the researchers checked nearly 5,000 vehicles. To calculate the emissions and classify the vehicles in real time, a measurement system including a so-called ICAD NOx instrument with software developed in cooperation with Heidelberg University spin-off Airyx was used. Measurements concentrated on nitrogen oxides and to a lesser extent on particulate matter and black carbon.

The data analysis shows that the average emissions vary considerably between countries, influenced by factors such as the origin and emission standard of the vehicles and the year of measurement. One other important factor for these differences was the extent to which the exhaust systems of heavy duty vehicles were monitored in the various countries. In addition, a comparatively small number of especially “dirty” vehicles made up a disproportionately large percentage of total measured emissions. Depending on the country and pollutant, ten percent of vehicles can account for more than half of total emissions from heavy duty vehicles. Inspections of the vehicles classified as high emitters – conducted by in-country authorities – indicated that high emissions of pollutants were caused by technical defects as well as deliberate tampering with hardware and software, such as bypassing exhaust-aftertreatment systems in diesel vehicles to save operating costs.

“Our multi-year study proves that the Plume Chasing method can be used with excellent results as a simple, cost-effective, and reliable process of emission monitoring under real-world conditions. This form of mobile measurement is therefore also a suitable instrument for authorities in implementing the emission standards of the European Union,” emphasizes study lead Prof. Dr Ulrich Platt from the Institute of Environmental Physics at Heidelberg University. “Quickly ridding the streets of vehicles with manipulated or defective exhaust systems would already help improve air quality,” states Christina Schmidt, who is preparing her dissertation in Prof. Platt’s team. According to the researchers, a prerequisite for sustainable reduction of harmful emissions is better legislation, so that authorities throughout Europe are able to easily enforce thresholds.

The research was part of the City Air Remote Emission Sensing (CARES) project, which was funded by the European Union within the framework of Horizon 2020. Researchers from Austria, the Netherlands, and the Czech Republic also contributed to the study. The results were published in the journal “Science of the Total Environment”.