Based on a three-year study of toxic and environmentally relevant pollutants from gasoline direct injection (GDI) engines, Swiss researchers have concluded that some GDI engines emit just as many soot particles as unfiltered diesel cars did in the past. Further, the GDI particles carry numerous carcinogenic substances. Based on this current data, they recommend that particulate filters be mandatory for GDI engines.
In the spring 2014, the GasOMeP project (Gasoline Vehicle Emission Control for Organic, Metallic and Particulate Non-Legislative Pollutants) got underway. The Paul Scherrer Institute (PSI), Bern University of Applied Sciences, the University of Applied Sciences and Arts Northwestern Switzerland, several industrial partners and Empa were all involved. The project was funded by the ETH Domain’s Competence Center for Energy and Mobility (CCEM) and coordinated by Empa chemist Norbert Heeb, who has made a name for himself in the last 25 years by analyzing diesel emissions and studying filter systems.
The results of the GasOMeP project were presented during a conference held at the Empa Academy in late March.
For the study, the team selected seven direct-injection gasoline 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 Pro-cedure), which will be mandatory for newly licensed models as of September 2017.
The results were sobering: every tested gasoline car emitted ten to 100 times more fine soot particles than the diesel Peugeot. Under the microscope, the particles from the gasoline engines were similar in size to the soot particles 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.—Norbert Heeb
The evidence shows that they can penetrate the membrane of human alveoli in the lungs and thus get into the bloodstream. However, the particles are not the only problem. Heeb notes 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 like a Trojan horse.
Maria Munoz, a colleague of Heeb’s from Empa’s Advanced Analytical Technologies lab, took a closer look at the exhaust emissions from the vehicles tested in the GasOMeP project and discovered the combustion product benzo(a)pyrene, a known carcinogenic substance also found in cigarette smoke.
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.
Once again, the diesel vehicle with particle filter fared much better: in the test, the Peugeot emitted only 45 nanograms of carcinogenic substances—6 times less than the best one of the analyzed gasoline cars.