Diesel cars, trucks, and other vehicles in more than 10 countries around the world produce 50 percent more nitrogen oxide emissions than lab tests show, according to a new study. The extra pollution is thought to have contributed to about 38,000 premature deaths in 2015 globally.

In the study, published today in Nature, researchers compared emissions from diesel tailpipes on the road with the results of lab tests for nitrogen oxides (NOx). The countries where diesel vehicles were tested are Australia, Brazil, Canada, China, the European Union, India, Japan, Mexico, Russia, South Korea, and the US, where more than 80 percent of new diesel vehicle sales occurred in 2015. The researchers found that 5 million more tons of NOx were emitted than the lab-based 9.4 million tons, according to the Associated Press.

tiny soot particles and smog

Nitrogen oxides are released into the air from motor vehicle exhaust or the burning of coal and fossil fuels, producing tiny soot particles and smog. Breathing in all this is linked to heart and lung diseases, including lung cancer, according to the International Council on Clean Transportation, which took part in the research. Governments routinely test new diesel vehicles to check whether they meet pollution limits. The problem is that these tests fail to mimic real-life driving situations, and so they underestimate actual pollution levels.

The researchers estimate that the extra pollution is linked to about 38,000 premature deaths worldwide in 2015 — mostly in the European Union, China, and India. (The US saw an estimated 1,100 deaths from excess NOx.) The findings are not too surprising. A report in January found that modern diesel cars in Europe produce more toxic emissions than trucks and buses, because cars have less strict regulations, and even if they meet lab tests, they emit more NOx when driven on actual roads. The research comes in the wake of the Volkswagen emissions cheating scandal that broke in September 2015, opening up a heated discussion about exhaust emissions of NOx from vehicles.

A way to avoid the extra pollution is to implement more stringent regulations and testing, according to the study authors. That could prevent 174,000 premature deaths annually by 2040, the study says.