Apparently, diesel pollutes the air worse than what was previously thought. Based on a new study co-authored by the University of Colorado Boulder, vehicles like trucks, cars and buses emit more nitrogen oxide (NOx) worldwide.

The result of the study was published in the journal Nature. Harmful use of diesel emits nitrogen oxide (NOx) and lead, which can result to 38,000 premature deaths globally, 1,100 of which are in the U.S.

The alarming data proves that there are inconsistencies between the emission testing and the actual harmful element released in air with the use of diesel. This even led Volkswagen to fit diesel cars with "defeat devices."

Reports say that defeat devices lower NOx emissions during testing in order for the vehicles to comply with government standards. The unrecorded NOx emissions reportedly led to about 50 to 100 deaths in the U.S.

"A lot of attention has been paid to defeat devices, but our work emphasizes the existence of a much larger problem," Daven Henze, an associate professor of mechanical engineering at CU Boulder, said in a statement. "It shows that in addition to tightening emissions standards, we need to be attaining the standards that already exist in real-world driving conditions."

Colorado Boulder researchers worked with the International Council on Clean Transportation, a non-profit organization, and the Environmental Health Analytics LLC to conduct the study.

To collect data, the researchers analyzed 30 vehicle emissions in 11 major markets representing 80 percent of diesel-fueled vehicles in 2015. This is to prove whether diesel indeed pollutes that air much more than what is initially thought.

Based on the data, diesel vehicles emitted 13.1 million tons of NOx in 2015. The emitted toxic chemicals pollute the air that causes serious medical conditions like heart disease, stroke, lung cancer and death. The study also discovered that if the emission stays within the government standard, the total worldwide emissions could have only been 8.6 million tons of NOx.

They also discovered that commercial trucks and buses are the largest contributor of NOx emissions in the world.