Traffic tracers in a suburban location in northern Spain: relationship between carbonaceous fraction and metals

PM10 and black smoke were monitored at a suburban sampling station located in the northern Spanish city of Gijn. Thirty-two metals and total carbon (TC) (i.e., organic carbon (OC) and elemental carbon (EC)) were analyzed over a year. The study of air-mass origin based on 5-day back trajectories was carried out to assess its influence on the recovery data. Different strategies were implemented to infer the influence of traffic in the area. On average, TC accounted for 29 % of the PM10 fraction, with OC forming 77 % of this TC. The influence of traffic was clearly reduced during intense Atlantic advection episodes, when OC and EC decreased up to 0.39 and 0.22 mu g C/m(3), respectively. In contrast, the highest values were reported during regional episodes, exceeding 10 mu g C/m(3) of OC and 2 mu g C/m(3) of EC. The correlation between EC and OC was found to notably improve when considering the days with high traffic flow (from R-2 = 0.46 to R-2 = 0.74). This pattern was also reproduced by black smoke and EC (from R-2 = 0.49 to R-2 = 0.59). Cu and Sn were found to be reliable traffic tracers given their high dependence on EC (R-2 = 0.82 and R-2 = 0.79, respectively). Nevertheless, Sn, Ba, and Sb showed a better correlation with Cu than EC, suggesting a common origin. In the case of Sn, R-2 improved from 0.79 to 0.91. The Cu/Sb ratio had a mean value of 6.6 which agrees with diagnostic criterions for brake wear particles. The relationships and ratios between EC, Cu, Sb, Sn, Ba, and Bi pointed out to non-exhaust emissions, playing a significant role in the chemical composition of PM10. Brake wear was presented as the most likely origin for Cu, Sb, and Sn.