Aethalometer measurements in a road tunnel: A step forward in the characterization of black carbon emissions from traffic.

ABSTRACT

A sampling campaign was conducted in the Liberdade Avenue tunnel (Braga, Portugal) during a week (with 56,000 vehicles) to monitor black carbon (eBC-equivalent black carbon) by means of an Aethalometer AE-31, and gaseous pollutants (CO2, CO, NOx). Inside the tunnel, the mean eBC mass concentration was 21 ±â€¯10 µg m-3, reaching a maximum hourly value of 49.0 µg m-3. An hourly and weekday-weekend study was carried out. Regarding the Absorption Ångström exponent (AAE), a mean value of 0.97 ±â€¯0.10 was obtained, for a source of practically pure traffic. There was a positive significant correlation between eBC and the number of light vehicles (r = 0.47; p < 0.001) and between eBC and the gaseous emissions CO (r = 0.67; p < 0.001), CO2 (r = 0.71; p < 0.001), NO (r = 0.63; p < 0.001) and NO2 (r = 0.70; p < 0.001). The mean black carbon emission factors (EFBC) inside the tunnel were 0.31 ±â€¯0.08 g (kg fuel)-1 and 0.11 ±â€¯0.08 mg veh-1 km-1, similar to those found in other studies for gasoline and diesel vehicles in road tunnels.