Identification of high emitting heavy duty vehicles using Plume Chasing: European case study for enforcement

The real-world emissions of almost 5000 heavy-duty vehicles (HDVs), determined by the Plume Chasing method in different European countries from 2016 to 2023, are presented. NO_x emission factors are provided for all assessed vehicles, while solid particle number (PN) and black carbon (BC) emission factors are reported for over 1100 HDVs. A real-time processing software, used in most campaigns, classified vehicles as suspect or high emitters according to Euro emission standards, usually in less than a minute. Several of the identified suspicious and high emitters were stopped and inspected by authorities, revealing causes of the high emissions such as tampering, defects, or cold SCR. The inspections provided further evidence of the merits of the Plume Chasing method to authorities for a reliable pre-identification of malfunctions of the emission systems. We found that average emissions are highly dependent on the country, the national emissions enforcement and the year of measurement. In 2023, in Slovakia and Czechia the share of suspicious and high emitters was substantial at 34% and 41% respectively, while in Germany, only 8% of HDVs were identified as such. Looking back to 2019, around 28% of HDVs measured on German highways were identified as suspicious or high emitters. In countries with strict regulations and more inspections, such as Denmark, the proportion is lower than in other countries over the same period (16% in 2020). The impact of high emitters on the overall fleet performance was assessed and we show that high emitters are responsible for more than a doubling of the average HDV NO_x emissions, while for particulate matter emissions the impact of high emitters is even greater. 4-14% of the dirtiest vehicles are responsible for 50% of the BC and PN emissions.