Figure 6 shows the strong positive correlation found between BC and CO concentrations, r2 = 0.721 at Centro and r2 = 0.670 at Miravalle, also with significant p values (< 0.05) at both sites. This confirms common sources for the two species, both produced in the combustion of fossil fuels and biomass burning and both have a relatively long atmospheric lifetimes (BC = 6–10 days and CO = 1–3 months), that varies with season and location (Zhou et al., 2009;Edwards et al., 2004). Consequently, no significant chemical reactions and transformations are expected to change the BC and CO concentrations during their transport between the emission sources and sampling sites.