Despite tighter nitrogen oxides (NO_x) emission norms for diesel cars, buses and trucks in several countries, the actual amount of NO_x emitted by diesel vehicles is far more during on-road driving conditions than under laboratory testing carried out at the time of certification. As a result, the excess NO_x emitted over certification limits caused nearly 38,000 premature deaths in 2015 in the European Union, China and India; India alone had 9,400 deaths due to excess NOx emissions. Over and above the deaths caused by excess NO_x emissions, increased air pollution from diesel NO_x caused 107,600 premature deaths globally in 2015.

Diesel vehicles in the 11 major markets (Australia, Brazil, Canada, China, the EU, India, Japan, Mexico, Russia, South Korea, and the U.S.) emitted 13.2 million tonnes of NO_x under on-road driving conditions, which is 4.6 million tonnes more than the vehicles’ performance under official laboratory testing. Compared with certification testing, the average on-road NO_x emission is 2.3 times higher for light-duty diesel vehicles and 1.45 times the limit for heavy-duty diesel vehicles. Diesel vehicles sold in the 11 markets account for about 80% of global sales.

Adopting and enforcing the stricter Euro VI emission norms could “nearly eliminate” on-road diesel-related NO_x emissions and avoid nearly 174,000 premature deaths in 2040, says a study published in Nature on May 15. NO_x is a key contributor to outdoor air pollution in the forms of ground-level ozone and fine particulate matter of less than 2.5 micrometre size (PM2.5).

Under the current Euro IV diesel emission norms, there is a wide gap between on-road NO_x emissions and certification limits. The excess NO_x emissions coming from diesel vehicles gained worldwide attention when 11 million Volkswagen vehicles that contained defeat devices that controlled emissions only at the time of emission testing became known. But what is less known is that the current certification procedure adopted for diesel cars, buses and trucks “legally permits higher” vehicle emissions under normal driving conditions than the certification limits.

Euro VI emission norms have in-service testing, in-use emission monitoring, expanded driving conditions and independent verification.

Heavy diesel vehicles accounted for 86% of on-road emissions and over 75% of excess on-road diesel NO_x emissions in 2015, about 90% of which is from China and India, the EU, Brazil and the U.S. In the case of diesel cars, the on-road emissions were 130% more than the certification limits.