Lab tests of harmful nitrogen oxide (NOx) emissions from diesel vehicles underestimate the real-world emissions by as much as 50%, a new study led by researchers from the International Council on Clean Transportation (ICCT) and Environmental Health Analytics (EHA) has shown.
Cars, trucks and buses worldwide emit 4.6 million tons more harmful NOx than standards allow, according to the new study. Image credit: Arsi Warrior.
Dr. Susan Anenberg, an expert in assessing the health benefits of mitigating air pollution and climate change at EHA, ICCT researcher Dr. Josh Miller and co-authors examined 11 major vehicle markets (Australia, Brazil, Canada, China, the European Union, India, Japan, Mexico, Russia, South Korea and the United States), representing approximately 80% of global diesel vehicle sales.
Of these markets, the researchers found vehicles emitted 13.2 million tons of NOx under real-world driving conditions, which is 4.6 million tons more than the 8.6 million tons expected from vehicles’ performance under official lab tests.
“Heavy-duty vehicles (HDV), such as commercial trucks and buses, were by far the largest contributor worldwide, accounting for 76% of the total excess gas emissions,” said Dr. Miller, lead co-author of the study.
“Five of the 11 markets that we looked at, Brazil, China, the European Union, India, and the United States, produced 90% of that.”
“For light-duty vehicles (LDV), such as passenger cars, trucks, and vans, the European Union produced nearly 70% of the excess diesel NOx emissions.”
“This study shows that excess diesel NOx emissions effect crop yields and a variety of human health issues,” said co-author Dr. Chris Malley, from the Stockholm Environment Institute at the University of York, UK.
“We estimate that implementing Next Generation standards could reduce crop production loss by 1-2% for Chinese wheat, Chinese maize, and Brazilian soy, and result in an additional 4 million tons of crop production globally.”
“A lot of attention has been paid to defeat devices, but our work emphasizes the existence of a much larger problem,” said co-author Dr. Daven Henze, an associate professor of mechanical engineering at the University of Colorado Boulder.
“It shows that in addition to tightening emissions standards, we need to be attaining the standards that already exist in real-world driving conditions.”
NOx emissions by scenario and region: (a) from on-road diesel vehicles in 11 major vehicle markets annually; (b) in 2015 from all emission sources globally, on-road diesel HDV and LDV globally, and on-road diesel vehicles in the 11 markets; (c) in 2015 from on-road diesel vehicles in excess of theoretical compliance with certification limits by region. Image credit: Anenberg et al, doi: 10.1038/nature22086.
NOx are a key contributor to outdoor air pollution. Long-term exposure in humans can lead to a range of adverse health outcomes, including disability and reduced life expectancy due to stroke, heart disease, chronic obstructive pulmonary disease, and lung cancer.
The study estimates that excess diesel vehicle NOx emissions in 2015 were also linked to approximately 38,000 premature deaths worldwide, mostly in the European Union, China, and India.
“The consequences of excess diesel NOx emissions for public health are striking,” said Dr. Anenberg, lead author of the study.
“In Europe, the ozone mortality burden each year would be 10% lower if diesel vehicle NOx emissions were in line with certification limits.”
At a global level, the study estimates that the impact of all real-world diesel NOx emissions will grow to 183,600 early deaths in 2040, unless something is done to reduce it.
In some countries, implementing the most stringent standards — already in place elsewhere — could substantially improve the situation.
“Tighter vehicle emission standards coupled with measures to improve real-world compliance could prevent hundreds of thousands of early deaths from air pollution-related diseases each year,” Dr. Anenberg said.
This research was presented in a paper published in the journal Nature on May 15, 2017.
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Susan C. Anenberg et al. Impacts and mitigation of excess diesel-related NOx emissions in 11 major vehicle markets. Nature, published online May 15, 2017; doi: 10.1038/nature22086
