It’s no secret that diesel emissions contribute significantly to air pollution.

But a new study claims emissions from diesel vehicles cause tens of thousands of premature deaths a year worldwide, many of them in China.

One major reason: the inadequate testing of those vehicles.

CGTN’s Hendrik Sybrandy reports.

Follow Hendrik Sybrandy on Twitter @hsybrandy

They’re the vehicles you see belching black smoke as they rumble down the street. Yet it’s gases you can’t see coming out of the tailpipes of diesel cars, trucks and buses that are particularly harmful.

“I do think that diesel emissions have been under reported and under-appreciated in terms of their impacts,” says Ray Minjares, a program leader at the International Council on Clean Transportation (ICCT).

Minjares says invisible nitrogen oxide—also known as NOx—takes a heavy toll on human health. A new study his organization co-led claims the failure of diesel vehicles to comply with emission standards makes the problem much, much worse.

Daven Henze, an Associate Professor at the University of Colorado Boulder’s Environmental Engineering program, contributed to the findings, published recently in the journal Nature.

“Under present day emissions, there are about 38,000 premature deaths every year owing to excess Diesel NOx,” Henze says.

He points out that diesel trucks and buses, in particular, perform very differently in the real world than they do during testing.

“They tend to test vehicles at speeds that are much higher than average driving speed in the city, and vehicles have poor performance at low speeds.”

Poor vehicle maintenance and the use of software to evade emission controls, as happened during the recent Volkswagen scandal, also contribute to the emissions gap.

The study found Europe, India, and China have suffered the greatest health impact from those excess emissions in the form of heart disease, lung cancer, and asthma, just to name three. Nitrogen oxide caused nearly 11,000 premature deaths in China in 2015.

The authors of the study say tighter rules for commercial trucks and buses and measures to improve compliance are badly needed.

“We’re addressing a problem that is big, and we have a solution that can be implemented very rapidly,” says Minjares.

China plans to adopt the so-called Euro 6 standard beginning in 2020, a move that Henze thinks would have a significant impact.

“[The] adoption and implementation of Euro 6 standards in China will be one of the biggest steps we can take globally towards reducing the health impacts of excess diesel NOx emissions,” he explains.

The alternative, according to the study, is bleak. By 2040, it projects, more than 180,000 people around the world will die prematurely each year unless governments act.