Challenging the paradigm – diesel cars cleaner than gasoline, study claims

Modern diesel cars emit less pollution in general than cars that run on gasoline, according to a new international study published in the journal Scientific Reports.

According to Patrick Hayes, a scientist at University of Montreal who worked on the research, the results of the study suggest that environmental regulators should increasingly shift their focus to gasoline powered cars and other sources of air pollution, particularly because diesel can be produced in much cleaner ways than ever before.

"Diesel has a bad reputation because you can see the pollution, but it's actually the invisible pollution that comes from gasoline in cars that's worse," said Hayes.

"The next step should be to focus on gasoline or removing old diesel vehicles from the road. Modern diesel vehicles have adopted new standards and are now very clean, so attention needs to now turn to regulating on-road and off-road gasoline engines more. That's really the next target."

Led by researchers in Switzerland and Norway, with help from scientists in the US, France and Italy, the study looked at carbonaceous particulate matter (PM) emitted from the tailpipes of cars. Carbonaceous PM is comprised of the black carbon, primarily organic aerosol, which is known to contain harmful reactive oxygen species and can damage lung tissue.

Analysis of emissions at the Paul Scherrer Institute, near Zurich, showed that on average gasoline cars emitted 10 times more carbonaceous PM at 22°C and 62 times more at -7°C compared to diesel cars, the researchers note in their study.

"These results challenge the existing paradigm that diesel cars are associated, in general, with far higher PM emission rates, reflecting the effectiveness" of engine add-ons like DPFs (diesel particle filters) to stem pollution,” the study notes.

The study notes that older diesel cars, without DPFs, do pollute more than gasoline ones, and in general diesel cars emit more nitrogen oxides, causing acid rain and smog. Nevertheless, when it comes to carbonaceous PM, the stereotype of diesel cars being worse than gasoline is no longer true.