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The excess emissions of harmful nitrogen oxide (NOx) exhaust gases can be linked to 38,000 premature deaths worldwide, according to the new research.

This is in addition to the World Health Organisation’s estimate of 3.7 million deaths caused by outdoor air pollution.

The US scientists argue that there is too little awareness of the impact of “real world” vehicle air pollution.


NOx can damage lung tissue but also reacts with chemicals in the atmosphere to produce ground-level ozone and ultra-fine particles, both of which are harmful.

Ozone irritates the airways and aggravates lung diseases such as asthma and bronchitis, while inhaling fine particles is strongly linked to heart and artery disease.

The study found that diesel vehicles around the world produced 4.5 million tons more NOx than they should do under international emission standards.

Heavy duty vehicles such as lorries and buses were identified as the major culprits.

“The consequences of excess diesel NOx emissions for public health are striking,” says study co-author Susan Anenberg, from the consultancy firm Environmental Health Analytics LLC. Her team analysed data from 30 studies of vehicle emissions under real-world driving conditions around the world.

The impact of excess emissions was strongly felt in Europe, where diesel cars are common. Here, 11,500 of the 28,500 deaths each year attributed to diesel NOx pollution were linked to excess emissions.

Daven Henze, from UC Boulder, says the research exposed a much bigger issue than Volkswagen’s notorious use of “defeat device” sensors that automatically reduce the pollution emissions of vehicles undergoing tests.

“A lot of attention has been paid to defeat devices, but our work emphasises the existence of a much larger problem,” he says. “It shows that in addition to tightening emissions standards, we need to be attaining the standards that already exist in real-world driving conditions.”

Henze’s team used computer modelling and satellite data to simulate the effect of excess NOx pollution on health, crops and the climate.

The scientists predict that in 23 years time diesel vehicles around the world will be causing 183,600 premature deaths each year unless further action is taken to curb their emissions.

Enforcing more stringent emission limits could prevent 174,000 deaths related to fine particles and ozone in 2040, they say.

“This is a rigorous study which highlights the serious consequences which have resulted directly from the irresponsible actions of the motor manufacturers in producing vehicles which meet regulatory requirements under test conditions, but emit far higher pollutant levels during on-road use,” says Roy Harrison, at the University of Birmingham, UK.

“The study may well underestimate the full consequences for public health as it quantifies only the effects of particulate matter and ozone formed in the atmosphere as a result of excess nitrogen ox-ides emissions, but not the direct effects of the oxides of nitrogen themselves.”