A new study has found that diesel cars are producing 50% more nitrogen oxide emissions under real-world driving conditions, than compared to the official results.

Work carried out by the International Council on Clean Transportation and the University of York among others studied 11 major car markets in 2015, which represented around 80% of new diesel vehicle sales that year.

The results showed that the vehicles studied emitted 13.2 million tons of nitrogen oxide, more than 4.5 million tons more than the 8.6 million tons that could have been expected based on the vehicle’s official laboratory test results.

With air quality an increasingly prominent topic in the news currently, the results will only strengthen demands to tackle air pollution issues, especially those associated with diesel cars.

Chris Malley, from the Stockholm Environment Institute, University of York, said: “This study shows that excess diesel nitrogen oxide emissions effect crop yields and a variety of human health issues.”

Josh Miller, researcher at the International Council on Clean Transportation (ICCT), said: “Heavy-duty vehicles, such as commercial trucks and buses, were by far the largest contributor worldwide, accounting for 76% of the total excess gas emissions.

“Five of the 11 markets that we looked at, Brazil, China, the EU, India, and the US, produced 90% of that. For light-duty vehicles, such as passenger cars, trucks, and vans, the European Union produced nearly 70% of the excess diesel nitrogen oxide emissions.”