On-road emissions of Euro 6d-TEMP passenger cars on Alpine routes during the winter period

Abstract

The transport sector is an important source of air pollution. Seasonal studies have shown that, in some urban areas, pollution episodes often take place during the cold season. This study investigates how sub-zero ambient temperatures (between −8 °C and −1 °C) and high altitudes (from 1300 to 2000 m above sea level) impact the on-road emissions of NOx, CO, PN and CO₂ from three Euro 6d-TEMP certified vehicles—one diesel, one gasoline and one plug-in hybrid gasoline–electric vehicle (PHEV). In comparison to tests performed at moderate altitude and ambient temperatures, CO, NOx and PN emissions increased under sub-zero temperature, high-altitude conditions for all three vehicles tested. In particular, cold-start emissions from all tested vehicles substantially increase as temperature decreased. Nevertheless, the emissions of NOx and PN met the Euro 6d-TEMP on-road emission requirements of the Real Driving Emissions (RDE) test procedure. CO emissions from the diesel and the gasoline vehicles were low. The PHEV had consistently low NOx emissions (ranging from 4 to 33 mg km⁻¹), but emissions of CO (1010–1849 mg km⁻¹) and PN (3.5 × 10¹¹ to 1.0 × 10¹² # per km) were high in some cases. Our results add to the body of evidence indicating that, following the introduction of the RDE in the EU, more efficient emission control technologies are being used to reduce the emissions of NOx and PN—the pollutants covered by this test procedure—particularly NOx from diesel vehicles. However, the emissions of PN from the two gasoline vehicles were high (>1 × 10¹² # per km) under certain experimental conditions. This result is a reason for concern, because PN emissions from vehicles using the fuel injection technology (PFI, port fuel injection) investigated in this study are not limited by the current Euro 6 regulation. This underlines the need for technology- and fuel-neutral approaches to vehicle emission standards, whereby all vehicles must comply with the same emission limits for the same pollutants regardless of the technologies or fuels employed.