Carbonaceous aerosols in an urban tunnel

Abstract Particulate matter in the Mount Victoria Tunnel, an urban road tunnel 623 m in length with an average traffic volume of 2070–2300 vehicles per hour located in Wellington, New Zealand, was studied to gain an understanding of carbonaceous species emitted from motor vehicles. The average PM 2.5 concentration during peak hours in the tunnel was found to be 67.6 ± 19.4 μg m −3 . Analysis of carbonaceous species present (OC, EC, TC) was performed by both the NIOSH and IMPROVE thermal/optical protocols and carbonaceous species were found to make up 63–73% of the total PM in the tunnel. Comparison of TC concentrations obtained from each protocol revealed that no significant difference was present between the two protocols. Black carbon (BC), also used as a measure of EC, was determined using light reflection and BC values did not differ significantly from EC concentrations determined using the NIOSH and IMPROVE protocols. TC was also determined using EA/IRMS and it was found that TC concentrations from EA/IRMS directly correlated with TC results obtained using the NIOSH protocol. Stable isotope analysis of the PM 2.5 yielded δ 13 C values from −24.7 to −28.3‰, typical of motor vehicles. Analysis of particle-phase PAHs by thermal desorption GC/MS revealed an average total PAH concentration of 70.0 ± 4.1 ng m −3 and PAHs were found to contribute 0.10% of total PM 2.5 in the tunnel. PAH emissions in the tunnel were found to be enriched in low molecular weight PAHs, indicative of emissions from diesel-fueled vehicles. Analysis of individual particle composition and morphology revealed that most particles were carbonaceous species that formed large, amorphous agglomerates made up of smaller spherules.