Profiles of average concentrations are illustrated in Fig. 2. In this study, lower molecular weight PAHs, i.e. three rings PAHs, are abundant both at the tunnel entrance and exit, while the most abundant were four rings (pyrene and benzo(a)anthracene) and six rings (dibenzo-pyrenes) PAHs, as found in several other studies (Chen et al., 2013; El Haddad et al., 2009; Ho et al., 2009). Dibenzopyrene isomers are considered to be potential human