New research finds that 38,000 people a year are dying as a result of the global failure of diesel vehicles to meet NOx official limits in real-world conditions.

Vehicles meet mandatory emission limits but in the real world produce 2.3 times NOx emission limits for light-duty diesel vehicles.

The research, carried out by the International Council on Clean Transportation and Environmental Health Analytics LLC and published in Nature, finds that laboratory-certified vehicles meet mandatory emission limits but in the real world produce 2.3 times NOx emission limits for light-duty diesel vehicles and 1.45 times limits for heavy-duty diesel vehicles, on average.

“The consequences of excess diesel NOx emissions for public health are striking,” said Susan Anenberg, co-lead author of the study and co-founder of Environmental Health Analytics LLC. “In Europe, the ozone mortality burden each year would be 10% lower if diesel vehicle NOx emissions were in line with certification limits.”

The authors said that reasons for the discrepancy may range from details of the engine calibration to equipment failure, inadequate maintenance, tampering by vehicle owners, the deliberate use of defeat devices, or simply deficient certification test procedures.

However, a report published earlier this year by the ICCT found latest heavy goods vehicles emit less than half the NOx of diesel passenger cars, despite significantly higher fuel consumption, with the findings attributed to the use of urea-based exhaust after-treatment systems used on all HGVs – known as selective catalytic reduction (SCR) – and the lean NOx traps still utilised by many lighter-duty vehicles.

The research indicated that after-treatment systems for Euro 6 HGVs are 10 times more effective at removing NOx from exhaust emissions than a Euro 6 diesel passenger car, although SCR is set to become more common among passenger cars with the latest Euro 6c standard, which comes into force this September.

The study predicts that more stringent tailpipe emission standards for heavy-duty vehicles, combined with strengthened compliance for light-duty vehicles and next-generation standards could prevent 174,000 premature deaths annually by 2040.