Evaluation of automotive polycyclic aromatic hydrocarbon emissions

Report no. 4/05: CONCAWE has measured PAH emissions from a range of vehicles and fuels. For diesel vehicles, the relationship between fuel poly-aromatics content and PAH in exhaust emissions has been examined. The programme focused on the US EPA’s Priority Pollutant list of 16 polycyclic aromatic hydrocarbons (PAH) and both particulate-bound and vapour phase PAH were measured.In older technology diesel vehicles, reducing fuel poly-aromatics content gave lower PAH emissions, although reducing fuel poly-aromatics content even to zero would not eliminate PAH emissions, as a significant proportion of the total PAH emissions is combustion derived.

The improvements with advanced emissions control systems were impressive. Modern three-way catalyst (TWC) gasoline cars all gave very low PAH emissions. In the newer technology diesel vehicles with effective exhaust after-treatment, either oxidation catalysts or diesel particulate filters, PAH emissions were so low that there was no longer any sensitivity to fuel poly-aromatics content. The advances in exhaust after-treatment, which are being implemented for the control of total hydrocarbon and particulate emissions, are clearly effective in also controlling PAH emissions.