An international team working through the Paul Scherrer Institute in Switzerland studied diesel and gasoline emissions from various engines. They found that modern diesel cars with particulate filters emit less carbonaceous material than do similar gasoline-powered cars. Carbonaceous PM is made up of black carbon, primary organic aerosol (POA) and—especially—secondary organic aerosol (SOA), which is known to contain harmful reactive oxygen species and can damage lung tissue.
Experiments were performed at the Vehicle Emissions Laboratory (VELA) of the European Commission Joint Research Centre. Results were published as open source in Scientific Reports.
The findings are synopsized in this chart:
Carbonaceous emissions/secondary organic aerosol formation from modern diesel and gasoline passenger cars. (a) Aerosol emission factors (g kg−1 fuel) measured in the study. Diesel vehicles did not produce measurable OA so gravimetric PM is given. For comparison the average and standard deviation of PM emission factors from non-DPF medium duty diesels is shown.
(b) Average ratio of diesel/gasoline emission factorsfor OA, BC, PM, methane (CH4), total hydrocarbon (THC), aromatic hydrocarbons (Ar. HC), NOx and carbon monoxide (CO) at 22 °C and −7 °C. Euro 5 values are obtained using the NEDC, while US LEV2 and DPF-equipped vehicles use the US unified driving cycle, UC3. While a true ratio cannot be calculated for OC and BC, a maximum can be, based on detection limits, highlighted by the red asterisks (*). In contrast to CO and especially NOx, PM and hydrocarbon emissions from gasoline cars are higher than from diesel cars.
(c)Averaged THC-normalized exhaust composition (temperature in parentheses) in the smog chamber with uncharacterized emissions in grey. The single largest fraction of gasoline THC consists of methyl benzenes present in the fuel, while the rest likely consists of surviving linear/branched, saturated/unsaturated hydrocarbons. Meanwhile, diesel emissions mainly comprise pyrolysis products, including small carbonyls (formaldehyde, acetaldehyde) and carboxylic acids (formic, acetic), which are not efficient SOA precursors. Pratt et al. (2017)