Schaeffer Disputes Study on Impacts and Mitigation of NOx Emissions


Improved “real-world” vehicle testing standards and increased adoption of new diesel technology to replace older diesels would play a major role in helping to reduce nitrogen oxide (NOx) emissions, according to Allen Schaeffer, the executive director of the Diesel Technology Forum.

Schaeffer made his comments in response to a new study’s findings that diesel vehicles emitted higher amounts of NOx in real-world driving conditions than in current laboratory certification testing. 

“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. “Emissions certification tests conducted in laboratory settings are the standard established by government, and have always been recognized as an imperfect measure, but it is the governing system. 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 percent of all global NOx emissions. Emissions inventories are themselves estimates, and subject to wide ranges of uncertainty of the fleet composition and operating characteristics. The contribution of NOx emissions to ozone formation itself is influenced by constantly changing meteorological conditions and other factors. The accuracy to which one can project benefits or impacts foreword three decades or more based on many assumptions and models, each with its own uncertainty, seems questionable.

“Industry would certainly welcome the investment in new technology clean diesel engines on a global basis. Essential to that would be the availability of ultra-low sulfur diesel fuel. It’s important to understand that diesel has been a technology of continuous improvement, meaning that today’s generation of new diesel technology is lower in emissions and more efficient than one built 10 or even five years ago. 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.  

“In the U.S., new technology diesel trucks and buses have reduced NOx emissions by more than 95 percent compared to older models. Today, it would take 60 new diesel trucks to equal the same emissions from 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 U.S. EPA, emissions of oxides of nitrogen have fallen by 61 percent since 1980. In 2016 U.S. 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,” Schaeffer concluded.