Vehicular Emission Factor of Gases and Particulate Matter Measured in Two Road Tunnels in São Paulo, Brazil

Abstract

In this paper we show measurements of air pollutants for a mixed vehicle fleet, heavy and light duty vehicles (HDV, LDV), in the Rodoanel and Janio Quadros tunnels in the Metropolitan Region of Sao Paulo (MRSP) in May-July 2011. Measurements of carbon dioxide (CO₂), carbon monoxide (CO), nitrogen oxides (NO_x) and Particle Matter (PM₁₀) were performed by the air quality monitoring net from CETESB (Environmental Agency of Sao Paulo State). High concentrations correlated with high density traffic (approximately 3,000 ± 1,000 vehicles per hour), especially during weekdays, and have a characteristic diurnal pattern with two peaks: at morning (06:00–9:00 h) and at afternoon (16:00–19:00 h).

The emission factors (EFs) of pollutant species were heavily influenced by the pollutant species loads, so the total vehicle traffic and the fraction of HDV. The EF values for HDV were 3.5 ± 1.5 g/km, 1,427 ± 1,178 g/km, 9.2 ± 2.7 g/km, 0.290 ± 0.248 g/km, for CO, CO₂, NO_x and PM₁₀ respectively, and for a temperature inside the tunnel of 20–25 °C. These values could be directly applicable to outside tunnel conditions because they are derived from pollutant species mass concentrations that are roughly a factor of only 2.5–3.5 higher than São Paulo typical urban concentrations. EF values of 5.8 ± 3.8 g/km, 219 ± 165 g/km, 0.3 ± 0.2 g/km, 0.178 ± 0.143 g/km, for CO, CO₂, NO_x and PM₁₀ respectively, were obtained for LDV, assuming constant ratios between concentration increments of pollutant species x and trace CO and considering than the EF(CO)_LDV were 1.5 times higher than the EF(CO)_HDV. In the methodology used to determine inside tunnel EF estimates, parameters such as velocity of the air, cross section area and length of the tunnel and vehicles passing at one hour time interval were considered, and sensitivity analyses was done.