On-Road Emission Performance of Late Model Diesel and Gasoline Vehicles as Measured by Remote Sensing
A newly developed remote sensing instrument with NO2 and NOX measurement capability was operated in the fall of 2016 over 19 workdays in Gothenburg, Sweden, to measure real driving emissions from a large number light- and heavy-duty vehicles. From more than 30,000 registered vehicle passages, a final QA/QC-reviewed dataset consisting of about 15,000 paired records containing emissions, driving condition and detailed vehicle information data, was used to evaluate the real-world emission performance of in particular Euro 5 and Euro 6 diesel vehicles. More than 9,000 records were of diesel vehicles, of which about 5,500 were of Euro 5 vehicles and about 2,600 of Euro 6 vehicles. The following conclusions were made from the evaluation:
- Measurements on more than 6,000 diesel passenger cars reveal that the real driving emissions of NOX from Euro 6 diesel cars on average have been reduced by about 60% from pre-Euro 6 levels, e.g. Euro 5. This may be considered a major breakthrough, since the real-world NOX emissions from diesel passenger cars have been virtually unchanged between Euro 2 and Euro 5, although the NOX emission standard has been significantly lowered from Euro 2 to Euro 5. Still, Euro 6 diesel passenger car real-world NOX emissions are roughly more than 5 times higher than the Euro 6 standard, as well as than the measured average on-road NOX emissions from Euro 6 gasoline passenger cars.
- For NOX emissions, an almost identical pattern as for diesel passenger cars was observed for both diesel light-duty commercial vehicles and diesel heavy-duty vehicles (trucks and buses), i.e. virtually no change in real-world emissions between Euro 2 and Euro 5, followed by a major drop in emissions for Euro 6.
- Primary NO2 emissions from diesel light-duty vehicles (both PC and LCV) have been reduced from Euro 4 through Euro 6, implying that the emission ratio of NO2 to NOX has also been reduced, but the ratio is still as high as about 25% for both Euro 5 and Euro 6 (compared to about 15% for Euro 2). The opposite pattern exists for heavy-duty vehicles, for which the NO2/NOX-ratio increased from about 10% for Euro 4-5 to ≈35% for Euro 6.
- For all categories of diesel vehicles, real-world PM emissions have dropped steadily from Euro 2 through Euro 6 – reductions are in the order of 90% for Euro 6 compared to Euro 2.
- For Euro 4, 5 and 6 diesel passenger cars, real-world emissions of both NOX and NO2 increase with decreasing ambient air temperature. The temperature dependence appears to be strongest for Euro 5 cars. At 25-30 degrees C average Euro 5 NOX on-road emissions are around 15 g/kg fuel burned, rising to 20-25 g/kg fuel burned at around 10 degrees C.
- Large differences in the on-road NOX emission performance were observed between different makes, models, as well as individual vehicles among Euro 5 and Euro 6 diesel passenger cars.
- For the first time, remote sensing measurements were combined with air quality measurements and dispersion calculations in an urban street canyon. Calculated average concentrations of NO2, NOX and PM based on HBEFA 3.2 were comparable with corresponding measured concentrations, but the discrepancy increased with increasing concentrations, with calculated concentrations being lower than measured. The latest version of the HBEFA emission model (version 3.3), launched in May 2017, provided a good match with the remote sensing measurements for both NOX and NO2 as well as exhaust PM, but at the same time tended to lead to an overestimation of street canyon concentrations of NO2 and NOX in dispersion calculations carried out in this study.