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

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.

Heavy truck restrictions and air quality implications in São Paulo, Brazil.

This study quantified the effects of traffic restrictions on diesel fuel heavy vehicles (HVs) on the air quality of the Bandeirantes corridor using hourly data obtained by continuous monitoring of traffic and air quality at sites located on this avenue. The study addressed the air quality of a city impacted by vehicular emissions and that PM10 and NOX concentrations are mainly due to diesel burning. Data collection was split into two time periods, a period of no traffic constraint on HVs (Nov 2008 and 2009) and a period of constraint (Nov 2010, 2011 and 2012). We found that pollutants on this corridor, mainly PM10 and NOX, decreased significantly during the period from 2008 to 2012 (28 and 43%, 15.8 and 86.9 ppb) as a direct consequence of HV traffic restrictions (a 72% reduction). Rebound effects in the form of increased traffic of light vehicles (LVs) during this time had impacts on the concentration levels, explaining the differences between rates of reduction in HV traffic and pollutants. Reductions in the number of trucks resulted in longer travel times and increased traffic congestion as a consequence of the modal shift towards LVs. We found that a 51% decrease in PM10 (28.8 µg m-3) was due to a reduction in HV traffic (vehicle emissions were estimated to be 71% of total sources, 40.1 µg m-3). This percentage was partially offset by 10% more PM10 emissions related to an increase in LV traffic, while other causes, such as climatic conditions, contributed to a 13% increase in PM10 concentrations. The relationships analyzed in this research served to highlight the need to apply urban transport policies aimed at decreasing pollutant concentrations in São Paulo, especially in heavily congested urban corridors on working days.