Cars powered by synthetic fuel produce the same amount of nitrogen oxide (NOx) emissions as cars burning conventional gasoline, according to the environmental group Transport & Environment (T&E).
That conclusion is based on tests conducted by research organization IFP Energies Nouvelles on behalf of T&E, according to a group press release. The tests compared three synthetic fuel blends with the E10 fuel (a mix of 90% gasoline and 10% ethanol) dispensed from most European Union pumps.
Testing also found much higher levels of carbon monoxide and ammonia emissions from the synthetic fuels, according to T&E. Particulate emissions were lower than conventional gasoline, but still quite significant, the group said.
NOx emissions of synthetic fuels versus E10 gasoline (via T&E)
T&E previously cautioned EU regulators about including synthetic fuels, which some automakers have rallied for, saying that ownership costs for synthetic-fueled vehicles will be much higher than for gasoline ones.
That's not the only potential drawback to synthetic fuels. While they are supposed to be carbon neutral, a study published earlier this year found that synthetic-fueled vehicles may cause more carbon emissions than battery-electric vehicles, in part because producing synthetic fuels requires more electricity than charging a fleet of EVs.
Synthetic fuels also require similar infrastructure to fossil fuels for production and transportation, making the process of getting into a car's fuel tank inherently less efficient than charging an EV.
Rendering of Porsche-backed Haru Oni synthetic fuel pilot plant.
Yet some automakers are looking to synthetic fuels as a way for keep the internal-combustion engine alive, for high-end sports cars, at least.
BMW last year invested in Prometheus Fuels, which claims to have a process to create synthetic fuel by removing carbon dioxide from the atmosphere.
Porsche claims synthetically-fueled cars can be as clean as EVs. It's working on a pilot plant in Chile and has started testing synthetic fuel in race cars.