On-road vehicle Nox-emission measurements using plume chasing. Results of a plume-chase measurement campaign in the Netherlands

Throughout the years, road vehicle emission regulations have become more stringent, and pollutant emissions from on-road vehicles have gradually reduced due to better exhaust gas aftertreatment systems and the ingrowth of electric vehicles in the fleet. Emissions from the remaining internal combustion engine (ICE) vehicle fleet will however remain relevant even after the foreseen stop on new ICE vehicles in 2035 due to aging effects of the existing fleet. A large share of automotive emissions is currently already caused by a small fraction of high-emitters due to poor maintenance or tampering, rather than due to the lack of capable exhaust gas aftertreatment systems. This has been shown in previous work [1] [2] where 6% of petrol vehicles on Dutch roads were found to be responsible for 36% of the total NOx -emissions in the petrol vehicle fleet. The sample size is however still small, measuring and monitoring of a larger set of vehicles is crucial to generate better (statistically significant) insight in the real-world emissions on Dutch roads and to support effective policy making. The fleet emissions statistics have traditionally been established using extensive emission testing of individual vehicles with on-road measurements using a portable emission measurement system (PEMS). This method provides detailed insight into the emission behaviour of a specific vehicle, but often requires multiple days of work, including vehicle instrumentation and testing. The plume-chasing remote-sensing method provides a less detailed but much faster method for measuring on-road NOx-emissions of multiple vehicles without the need for extensive installation of individual vehicles. A typical measurement of a single vehicle takes between 2 to 5 minutes, with 10 to 15 vehicles being measured per hour in practice.