The study is based on on-road tests of 15 vehicles—12 certified to the Euro 6 standard and three to the US equivalent (Tier 2 Bin 5) using Portable Emissions Measurement Systems (PEMS), which provide a continuous stream of vehicle data signals including emission rates, velocity, acceleration, road gradient and exhaust temperature.

(The testing of the US-spec vehicles certified to the US Tier 2 Bin 5/California LEV II standard was commissioned to West Virginia University (WVU) by the ICCT.)

The high temporal and spatial resolution of PEMS datasets permitted the analysis to link elevated NO_x mass emission rates to the driving conditions that caused them.

The study covered more than 140 hours and 6,400 kilometers (3,977 miles) of driving, and provides the largest collection of public data on Euro 6 equivalent diesel cars currently available. Diesel vehicles make up about 50% of all new cars in the EU. From September 2014 on, the Euro 6 standard applies to all new passenger car types.

On average, NO_x emissions from the tested vehicles were about seven times higher than the limits set by the Euro 6 standard. If applied to the entire new vehicle fleet, this would correspond to an on-road level of about 560 mg/km of NO_x (compared to the regulatory limit under Euro 6 of 80 mg/km).

On-road emissions of NOx from 15 Euro 6–equivalent diesel passenger cars, as measured by portable emissions measurement systems (PEMS). Source: ICCT. Click to enlarge.

The ICCT team found that in most cases, the exceedances found could not be attributed to “extreme” or “untypical” driving. Instead, they were due to transient increases in engine load typical of everyday driving (e.g., going up a slight incline), or to normal regeneration events in the diesel exhaust aftertreatment systems.

Example visualization of situation-specific emission factors (binning by acceleration*velocity). Source: ICCT. Click to enlarge.

This is compelling evidence of a real-world NO_x compliance issue for recent-technology diesel passenger cars, for both the EU and US test vehicles, the researchers said. The ICCT team also found significant differences among the performance of all the vehicles tested, with a few vehicles performing substantially better than the others.

This supports the notion that the technologies for real-world clean diesels already exist. Policies are needed to ensure that manufacturers will use these technologies and calibrate them to effectively control emissions over the large majority of in-use operating conditions, not just those covered by the current test cycle.

—Dr. Vicente Franco, lead author

The European Commission is currently preparing to require on-road testing as part of the passenger car type-approval process in the EU. According to these plans, vehicle manufacturers from 2017 would have to test new vehicles not only under laboratory conditions but also on the road, using PEMS equipment.

Technical experts from the EU Member States will meet in Brussels on October 15 to discuss further steps and whether the new regulation can be approved at the end of 2014, as originally planned.

NO_x can have serious adverse health effects, causing major respiratory problems and leading to premature death. Diesel vehicles are the single largest contributor to total nitrogen oxide emissions in the EU. Ambient NO_x concentrations in Europe regularly exceed current EU air quality standards (200 μg/m³ one-hour average for nitrogen dioxide, 40 μg/m³ one-year average), especially in urban areas. Some EU Member States are already facing legal actions for persistent air pollution problems.

Unless the appropriate technical measures are adopted, the high on-road emissions of NO_x from the new diesel technology classes of passenger cars could have serious adverse health effects on the exposed population. Regulatory action is urgently required in Europe, where all new diesel passenger cars sold from September 2014 belong to the Euro 6 class and the regional share of diesel vehicles in the passenger car fleet is higher than anywhere else in the world. In this sense, the European RDE-LDV initiative … requiring the inclusion of on-road testing with PEMS as part of the passenger car type-approval process in the EU is a step in the right direction. However, the existence of the real-world diesel NO_x issue must be acknowledged by regulators in its full extent and subsequently addressed in collaboration with vehicle manufacturers and other stakeholders.

—Franco et al.

Resources

• Vicente Franco, Francisco Posada Sánchez, John German, and Peter Mock (2014) “Real-world exhaust emissions from modern diesel cars: A meta-analysis of PEMS emissions data from EU (Euro 6) and US (Tier 2 BIN 5 / ULEV II) diesel passenger cars”