Gasoline cars produce more carbonaceous particulate matter (PM) emissions than diesel cars equipped with diesel particle filters (DPFs) and catalysts, according to initial laboratory tests published in a study in Scientific Reports. The authors note that emissions from vehicles are sensitive to the sampling location, fleet age and ambient temperature, and they suggest that further studies that calculate an aggregate of emissions are required.

Carbonaceous PM consists of black carbon, primary organic aerosols (including solid particles from combustion) and secondary organic aerosols (produced via the atmospheric ageing of organic compounds released during combustion), and is a toxic component of vehicle exhausts. However, the relative contributions of diesels equipped with DPFs and gasoline cars to these emissions have not been quantified.

In laboratory investigations, Andre Prevot and colleagues quantified carbonaceous PM from 11 gasoline and 6 diesel cars equipped with DPFs at 22°C and -7°C. The authors found that gasoline cars emitted on average ten times more carbonaceous aerosol at 22°C and 62 times more at -7°C compared to the diesel cars. They also found that the diesel cars tested produced no detectable secondary organic aerosols.

The authors note that compared to the cars tested, PM emissions are much higher from diesel cars that do not have a DPF, which will produce the largest fraction of PM emissions for some time.