According to a new study co-authored by University of Colorado Boulder researchers, and published in Nature, cars, trucks and buses worldwide emit 4.6 million tons more harmful nitrogen oxide (NOx) than standards allow, and these excess emissions lead to 38,000 premature deaths annually worldwide, including 1,100 deaths in the United States.
Testing inefficiencies, maintenance inadequacies are the reasons
The study said the reason behind emission of more harmful gas is testing inefficiencies, maintenance inadequacies and other factors. The study findings highlight major inconsistencies between what vehicles emit during testing and what they emit on the roads, said the researchers. Federal regulators had, in 2015, discovered Volkswagen had been fitting millions of new diesel cars with defeat devices. "A lot of attention has been paid to defeat devices, but our work emphasizes the existence of a much larger problem," said Daven Henze, an associate professor of mechanical engineering at CU Boulder who, along with postdoctoral researcher Forrest Lacey, contributed to the study. "It shows that in addition to tightening emissions standards, we need to be attaining the standards that already exist in real-world driving conditions."
Heavy-duty vehicles were by far the largest contributor
The researchers, for the study assessed 30 studies of vehicle emissions under real-world driving conditions in 11 major vehicle markets representing 80 percent of new diesel vehicle sales in 2015. Those markets include Australia, Brazil, Canada, China, the European Union, India, Japan, Mexico, Russia, South Korea and the United States. The scientists found that in 2015, diesel vehicles emitted 13.1 million tons of NOx, a chemical precursor to particulate matter and ozone and had the emissions met standards, the vehicles would have emitted closer to 8.6 million tons of NOx. Exposure in humans can lead to different health problems including heart disease, stroke and lung cancer. Heavy-duty vehicles, such as commercial trucks and buses, were by far the largest contributor worldwide, accounting for 76 percent of the total excess NOx emissions.