PAH content in size-fractionated PM samples, per sampling location. The PAHs have been grouped according to their molecular weight as schematically shown on the rightmost panel for all four sampling locations. Note the logarithmic scale on the x-axis. The highest PAH concentrations were found for samples collected in the tunnel. Interestingly, the concentration of heavier PAHs is higher in the gasoline-only tunnel bore while the PAH profile is shifted to relatively lighter components in the mixed gasoline-diesel bore.