New international study finds lab testing of diesel NOx emissions underestimates real-world levels by up to 50%
A new international study has found that laboratory tests of nitrogen oxide emissions from diesel vehicles significantly underestimate the real-world emissions by as much as 50%. A paper on the work is published in the journal Nature.
The research, led by the International Council on Clean Transportation and Environmental Health Analytics, LLC., in collaboration with scientists at the University of York’s Stockholm Environment Institute (SEI); University of Colorado; and the International Institute for Applied Systems Analysis, assessed 30 studies of vehicle emissions under real-world driving conditions in 11 major vehicle markets representing 80% 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.
Of these markets, they found vehicles emitted 13.2 million tons of NOx under real-world driving conditions—4.6 million tons more than the 8.6 million tons expected from vehicles’ performance under official laboratory tests.
|Real-world NOx emission factors by vehicle emissions standard in key regions. a, Passenger cars; b, heavy heavy-duty trucks; and c, buses. Error bars indicate high and low estimates. Anenberg et al. Click to enlarge.|
Heavy-duty vehicles, such as commercial trucks and buses, were by far the largest contributor worldwide, accounting for 76% of the total excess gas emissions. Five of the 11 markets that we looked at, Brazil, China, the EU, India, and the US, produced 90% of that. For light-duty vehicles, such as passenger cars, trucks, and vans, the European Union produced nearly 70% of the excess diesel nitrogen oxide emissions.—Josh Miller, researcher at the International Council on Clean Transportation (ICCT)
Daven Henze, an associate professor of mechanical engineering at CU Boulder, used computer modeling and NASA satellite data to simulate how particulate matter and ozone levels are, and will be, impacted by excess NOx levels in specific locations. The team then computed the impacts on health, crops and climate.
Chris Malley, from the SEI, University of York, said that the study showed that excess diesel nitrogen oxide emissions effect crop yields and a variety of human health issues.
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 four million tonnes of crop production globally.—Chris Malley
The study also estimates that excess diesel vehicle nitrogen oxide emissions in 2015 were also linked to approximately 38,000 premature deaths worldwide—mostly in the European Union, China, and India.
China suffers the greatest health impact with 31,400 deaths annually attributed to diesel NOx pollution, with 10,700 of those deaths linked to excess NOx emissions beyond certification limits. In Europe, where diesel-passenger cars are common, 28,500 deaths annually are attributed to diesel NOx pollution, with 11,500 of those deaths linked to excess emissions.
The consequences of excess diesel NOx emissions for public health are striking. In Europe, the ozone mortality burden each year would be 10% lower if diesel vehicle nitrogen oxide emissions were in line with certification limits.—Susan Anenberg, co-Founder of Environmental Health Analytics, LLC
At a global level, the study estimates that the impact of all real-world diesel nitrogen oxide 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, according to the researchers.
The authors say emission certification tests, both prior to sale and by vehicle owners, could be more accurate if they were to simulate a broader variety of speeds, driving styles and ambient temperatures. Some European countries now use portable testing devices that track emissions of a car in motion.
Susan C. Anenberg, Joshua Miller, Ray Minjares, Li Du, Daven K. Henze, Forrest Lacey, Christopher S. Malley, Lisa Emberson, Vicente Franco, Zbigniew Klimont & Chris Heyes (2017) “Impacts and mitigation of excess diesel-related NOx emissions in 11 major vehicle markets” Nature doi: 10.1038/nature22086