In order to address road traffic emissions, studies need to be performed under realistic driving conditions where the input from other sources is minimised. Measurements in traffic tunnels have been used for quantifying emissions, but so far no study has established emission factors (EFs) for Southern Europe. To fill this gap, a sampling campaign was carried out for one week in the Liberdade Avenue tunnel (Braga, Portugal). The campaign included the monitoring of gaseous pollutants (CO2, CO, NOx) and suspended particulate matter (PM) at two sites, one in the tunnel