Brown carbon (BrC), as an important light-absorbing aerosol, significantly impacts regional and global climate. Vehicle emission is a nonnegligible source of BrC, but the optical properties of BrC emitted from vehicles remain poorly understood.
This study evaluates the absorption Ångström exponent (AAE) of traffic-related light-absorbing aerosols (i.e., AAEBrC) and the absorption emission factor (EFabs) of vehicular BrC via chassis dynamometer tests and a road tunnel measurement. These values are important for accurately interpreting aerosol optical depth (AOD). The AOD is applied to estimate the direct climate forcing of BrC. The EFabs of black carbon, which is one of the main light-absorbing aerosols, were also evaluated for comparison.
The AAE of vehicular BrC (AAEBrC) is 3.83 ± 0.092 for on-road vehicle fleet. The BrC EFabs of on-road vehicle fleet at 370 nm wavelength are 0.081 ± 0.0058 m2 kg−1 for mixed fleet, 0.074 ± 0.018 m2 kg−1 for gasoline vehicles (GVs), and 1.66 ± 0.71 m2 kg−1 for diesel vehicles (DVs) in the tunnel measurement. EFabs of vehicular BrC for GVs are lower than those from biomass burning and coal combustion emission. The vehicular BrC EFabs are lower than most biomass burning and coal combustion. The vehicular EFabs for DVs is higher than most biomass burning and coal combustion. The light absorption of BrC from GVs and DVs accounts for 7.2 ± 2.1% and 1.5 ± 0.77% of total traffic-related absorption at 370 nm, respectively.
The results have been published in the journal "Environmental Pollution" under the title of "Optical properties of vehicular brown carbon emissions: Road tunnel and chassis dynamometer tests" (https://doi.org/10.1016/j.envpol.2023.121037).
