The undisclosed emissions spewing from Volkswagen vehicles may be closer to the rule than the exception, with a comprehensive new study published this week finding that real-world emissions from diesel vehicles have been underestimated by as much as 50 percent. The pollutant in question, nitrogen oxide, is linked to thousands of premature deaths, with the scientists calling for stricter regulations to limit further damage.

In 2014, scientists from the International Council for Clean Transportation (ICCT) and West Virginia University carried out a real-world emissions tests and discovered elevated levels of nitrogen oxide (NOx) coming from Volkswagen's diesel vehicles. This would lead to the company famously admitting it had used "defeat devices," sophisticated software that detects when the vehicle is undergoing official emissions testing and turns on full emissions controls only during that test. These same real-world emissions tests have now revealed that the problem is much more widespread.

An international team of researchers drew on more than 30 of these in-use vehicle emission studies, examining 11 markets that represented more than 80 percent of new diesel vehicle sales in 2015. These studies, the paper's lead author Susan Anenberg explains, use both portable measurement systems (PEMs) to track tailpipe emissions and roadside monitors to track emissions from traffic as it passes.

"The PEMS method gives you a sense for how individual vehicles perform across a range of driving conditions, while the roadside remote sensing method measures emissions from a large number of vehicles for a snapshot of time and in one driving condition where the monitors are located, for example a highway," she tells New Atlas.

Comparing this data on real-world emissions to the official laboratory tests reveals an alarming disparity. The researchers found that the vehicles emitted 13.2 million tons of NOx on the road, 4.6 million tons more than the 8.6 million expected from the laboratory testing.

"Heavy-duty vehicles, such as commercial trucks and buses, were by far the largest contributor worldwide, accounting for 76 percent of the total excess gas emissions," says Josh Miller, researcher at the International Council on Clean Transportation (ICCT). "Five of the 11 markets that we looked at, Brazil, China, the EU, India, and the US, produced 90 percent of that. For light-duty vehicles, such as passenger cars, trucks, and vans, the European Union produced nearly 70 percent of the excess diesel nitrogen oxide emissions."

Nitrogen oxides are a family of poisonous gases that form when fuel is burned at high temperatures. They are strong oxidizing agents that react with volatile organic compounds in the atmosphere to play a major role in the smog that often shrouds cities like Beijing and Los Angeles. They can lead to respiratory problems, headaches, eye irritation and over the long-term have been linked to stroke, heart disease and lung cancer. The World Health Organization classified diesel engine fumes as a Group 1 carcinogenic in 2012.

The study estimates that the excess NOx was associated with 38,000 premature deaths in 2015. And looking forward, the numbers get really scary. The scientists project that unless something is done to clamp down on NOx emissions, this number could balloon to around 180,000 early deaths in 2040.

"The problem of excess diesel NOx extends beyond defeat devices and results in part from emission certification testing cycles that do not reflect the full range of real-world driving conditions," Anenberg tells us.

So it seems clear that current emissions testing for diesel vehicles isn't up to scratch, so what's the answer? The researchers point to the Euro 6 standard as their guiding light. Introduced in September 2015, this standard targeted diesel vehicles specifically, cutting the maximum allowable NOx emissions from 180 mg/km to 80 mg/km.

The researchers believe that implementing these standards for heavy duty vehicles elsewhere would go a long way to improving the situation. But they would like to see things taken even further, stating that stricter "next generation" regulations could help to avoid most of the projected 180,000 premature deaths in 2040.

The paper was published in the journal Nature.