The Fe/Cu ratio has been used to characterise road traffic
emissions. However, the ratios (median value of Fe/Cu in
PM10 = 21) obtained from most tunnel and busy road
experiments (Pio et al., 2013, and references therein) are
significantly higher than the mean value of 4.82 found in
Liberdade tunnel. Ba/Cu and Fe/Cu presented the highest values
among all ratios. While the Ba/Cu ratio tends to decrease with
increasing particle aerodynamic diameter, the highest Fe/Cu
ratioswere observed for PM1 and PM2.5. Aiming at providing an
elemental composition profile of brake wear emissions in
Europe, Hulskotte et al. (2013) analysed 65 brake pads and 12
brake discs. The researchers concluded that the ratios as
measured in brake pads cannot fit observed concentrations at
traffic sites. A mean Fe/Cu ratio of 2.0 was measured in brake
pads. The brake disc wear samples were composed almost