PM Filters Should be Mandatory for GDI Cars, Researchers Say

05.24.17 | Blog | By:

Are new gasoline cars environmentally friendly? Not always, says a new study by Swiss scientists at the research organization, Empa. Some gasoline direct-injection (GDI) engines emit just as much PM as unfiltered diesel cars did in the past, and they “carry” numerous carcinogenic substances. Particle filters could remedy this situation, they say, and should be mandatory on all GDI vehicles.

The researchers selected seven GDI cars, including a Mitsubishi Carisma (2001 model, exhaust emission standard Euro 3). The other vehicles were all built between 2010 (VW Golf, Euro 4) and 2016 (Citroën C4, Euro 6b). By way of comparison, a current Peugeot 4008 (2013, Euro 5b) with a diesel engine and a particle filter was also included. All the vehicles were tested based on the WLTP cycle (Worldwide Light-Duty Vehicles Test Procedure), which will be mandatory for newly licensed models as of September 2017.

The researchers found that every single one of the tested GDI cars emitted 10 to 100 times more fine PM than the diesel Peugeot. Under the microscope, the PM from the GDI cars were similar in size to the PM that had given diesel a bad name: primary particles measuring ten to 20 nanometers in size, which congregate into particle agglomerates measuring 80 to 100 nanometers before leaving the exhaust. “Once inhaled, these particles remain in the body forever,” said one of the lead researchers of the study. The evidence shows that they can penetrate the membrane of human alveoli in the lungs and thus get into the bloodstream.

Another issues is that liquid or solid chemical toxins from the combustion process, including polycyclic aromatic compounds, accumulate on the surface of the particles, which can then smuggle these substances into the bloodstream. The combustion product benzo(a)pyrene, a known carcinogenic substance also found in cigarette smoke, was found.

The World Health Organization (WHO) considers even the tiniest dose of benzo(a)pyrene harmful. The EU settled on an air limit of one nanogram per cubic meter. Levels in exhaust emissions were found to be as much as 1,700 times above this limit. Or to put it another way, one cubic meter of exhaust gas transforms up to 1,700 cubic meters of clean air into a mixture deemed carcinogenic according to the EU standard.

The diesel vehicle with a PM filter fared much better: in the test, the Peugeot emitted only 45 nanograms of carcinogenic substances – six times less than the best one of the analyzed GDI cars. The researchers say these filters should be mandatory on all GDI vehicles.


Tammy Klein is a consultant and strategic advisor providing market and policy intelligence and analysis on transportation fuels to the auto and oil industries, governments, and NGOs. She writes and advises on petroleum fuels, biofuels, alternative fuels, automotive fuels, and fuels policy.

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