WASHINGTON, D.C.–Diesel-engine nitrogen oxide (NOx) emissions as measured in the lab are one thing; real-world emissions quite another. That’s the gist of a new study just published in the science journal Nature.

And in response to the revelation, Allen Schaeffer, the executive director of the non-profit Diesel Technology Forum, called for “real-world vehicle-testing standards and increased adoption of new diesel technology to replace older diesels.

“Diesel engine, truck and equipment makers today produce diesel engines that are certified by various government agencies to achieve near-zero levels for emissions of both nitrogen oxides and particulate matter,” Schaeffer said. 

“Laboratory tests are not designed to replicate all real-world conditions that a vehicle and driver may encounter or create.  It is common knowledge that manufacturers and regulators in the E.U. and the U.S. have been working together to develop more representative tests for in use vehicle and engine performance, and that work is ongoing.

“The primary sources of NOx emissions on a global basis are not diesel engines.  The portion of nitrogen oxide emissions–the primary focus of this study–attributed to on-road diesel engines makes up less than 20% of all global NOx emissions.” 

Schaeffer said the engine industry would welcome the investment in new technology clean diesel engines on a global basis.  Essential to that, he said,  would be the availability of ultra-low sulfur diesel fuel.

“Older technology engines met the standards in place at the time, and as this study points out, standards have become progressively more stringent.  Some study areas find that diesel engine popularity in the marketplace grew very fast while the adoption of new emissions control requirements and emissions reducing technology development were taking longer to implement.” 

Schaeffer says that in the U.S., new-technology diesel trucks and buses have reduced NOx emissions by more than 95% compared to older models and it would take 60 new diesel trucks to equal the same emissions as one pre-1988 truck.

“NOx emissions are just one of several contributors to air pollution, including ground level ozone.  There are many sources of NOx emissions, including power plants, industrial activity and mobile sources like cars, trucks and off-road equipment. 

According to the U.S.-based Environmental Protection Agency (EPA), emissions of oxides of nitrogen have fallen by 61% since 1980. In 2016, the EPA reviewed the current NO2 national ambient air quality standards and in its policy assessment, recommended that no changes to the health-protective standard are needed as existing control measures continue to contribute to declining NO2 emissions.