Emissions and light absorption of carbonaceous aerosols from on-road vehicles in an urban tunnel in south China

With changing numbers, compositions, emission standards and fuel quality of on-road vehicles, it is imperative to accordingly characterize and update vehicular emissions of carbonaceous aerosols for better understanding their health and climatic effects. In this study, a 7-day field campaign was conducted in 2019 in a busy urban tunnel (>30,000 vehicles day⁻¹) in south China with filter-based aerosol samples collected every 2 h at both the inlet and the outlet for measuring carbonaceous aerosols and their light absorbing properties. Observed fleet average emission factor (EF) of total carbon (TC) was 13.4 ± 8.3 mg veh⁻¹ km⁻¹, and 17.4 ± 11.3 mg veh⁻¹ km⁻¹ if electric and LPG-driven vehicles were excluded; and fleet average EF of organic carbon (OC) and elemental carbon (EC) was 8.5 ± 6.6 and 4.9 ± 2.6 mg veh⁻¹ km⁻¹ (11.0 ± 8.8 and 6.3 ± 3.6 mg veh⁻¹ km⁻¹ if excluding electric and LPG vehicles), respectively. Regression analysis revealed an average TC-EF of 319.8 mg veh⁻¹ km⁻¹ for diesel vehicles and 2.1 mg veh⁻¹ km⁻¹ for gasoline vehicles, and although diesel vehicles only shared ~4% in the fleet compositions, they still dominate on-road vehicular carbonaceous aerosol emissions due to their over 150 times higher average TC-EF than gasoline vehicles. Filter-based light absorption measurement demonstrated that on average brown carbon (BrC) could account for 19.1% of the total carbonaceous light absorption at 405 nm, and the average mass absorption efficiency of EC at 635 nm and that of OC at 405 nm were 5.2 m² g⁻¹ C and 1.0 m² g⁻¹ C, respectively.