Paris (AFP) - "Excess" diesel truck and car emissions claimed about 38,000 lives worldwide in 2015, said a study Monday that sought to quantify deaths due to pollution that carmakers sought to hide.

Four-fifths of these additional premature deaths due to nitrogen oxide (NOx) pollution occurred in three regions -- the European Union, China and India, researchers reported in the journal Nature.

NOx are poisonous gases that contribute to acid rain and combine with ammonia to create particles that can penetrate deep into the lungs and cause cancer, chronic breathing problems and premature death.

Until recently, estimates of deaths attributable to NOx pollution was based on levels reported by vehicle makers.

Since 2015, however, it has become clear that Volkswagen and other manufacturers used so-called "defeat devices" to disguise the true extent of diesel engine emissions, which are far higher on the road than in laboratory testing.

The new study of 11 major car markets -- the others are Australia, Brazil, Canada, Japan, Mexico, Russia, South Korea and the United States -- revealed that diesel vehicles spewed at least 50 percent more NOx under real-world driving conditions than their makers claimed.

That translates to 38,000 deaths due to "excess" emissions, out of an estimated total of 107,000 lives foreshortened to diesel car and truck fumes in 2015, the researchers found.

The study focused on how NOx emissions contribute to air pollution in the form of ozone and fine particulate matter.

Long-term exposure is linked to disability and premature death due to stroke, heart disease, lung cancer, and chronic obstructive pulmonary disease (COPD) -- a degenerative condition of the lungs.

The elderly are especially vulnerable.

"The consequences of excess diesel NOx emissions for public health are striking," said lead author Susan Anenberg, co-founder of Environment Health Analytics, a policy research group based in Washington DC.

- Text-evading software -

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Commercial trucks and buses are by far the biggest culprit worldwide, accounting for more than three-quarters of excess NOx output.

Ninety percent was emitted in just five countries or regions -- Brazil, China, the EU, India and the United States.

For light-duty vehicles -- small trucks, cars and vans -- the EU produced nearly 70 percent of global excess NOx emissions, the study found.

A earlier study calculated that pollution from 2.6 million Volkswagen cars equipped with test-evading software and sold in Germany from 2008 to 2015 will cause more than 1,200 premature deaths in Europe.

But defeat devices are not the only cause of additional NOx emissions, according to the new research.

Others included faulty engine calibration, poor maintenance, tampering by vehicle owners, and sub-standard certification testing.

To estimate damage caused by NOx emissions, the study combined data from vehicles used in real-world conditions, computer modelling of the atmosphere, satellite observations, along with health and climate models.

The researchers calculated that diesel NOx pollution will cause more than 183,000 premature deaths per year by 2040.

"Globally, the single-most important action to reduce the health impacts of excess diesel NOx emissions is for countries to implement and properly enforce" European standards for heavy vehicles, said co-author Ray Minjares, a researcher at the International Council on Clean Transportation, a Washington-based research group.

Experts not involved in the research said it was likely conservative in its conclusions.

"The study may well underestimate the full consequences for public health," said Roy Harrison, a professor of environmental health at the University of Birmingham in England.