Light absorption of biomass burning and vehicle emission-sourced carbonaceous aerosols of the Tibetan Plateau

Abstract

Carbonaceous aerosols over the Tibetan Plateau originate primarily from biomass burning and vehicle emissions (BB and VEs, respectively). The light absorption characteristics of these carbonaceous aerosols are closely correlated with the burning conditions and represent key factors that influence climate forcing. In this study, the light absorption characteristics of elemental carbon (EC) and water-soluble organic carbon (WSOC) in PM_2.5 (fine particulate matter smaller than 2.5 μm) generated from BB and VEs were investigated over the Tibetan Plateau (TP). The results showed that the organic carbon (OC)/EC ratios from BB- and VE-sourced PM_2.5 were 17.62 ± 10.19 and 1.19 ± 0.36, respectively. These values were higher than the ratios in other regions, which was primarily because of the diminished amount of oxygen over the TP. The mass absorption cross section of EC (MAC_EC) at 632 nm for the BB-sourced PM_2.5 (6.10 ± 1.21 m².g⁻¹) was lower than that of the VE-sourced PM_2.5 (8.10 ± 0.98 m².g⁻¹), indicating that the EC content of the BB-sourced PM_2.5 was overestimated because of the high OC/EC ratio. The respective absorption per mass (α/ρ) values at 365 nm for the VE- and BB-sourced PM_2.5 were 0.71 ± 0.17 m².g⁻¹ and 0.91 ± 0.18 m².g⁻¹. The α/ρ value of the VEs was loaded between that of gasoline and diesel emissions, indicating that the VE-sourced PM_2.5 originated from both types of emissions. Because OC and WSOC accounts for most of the carbonaceous aerosols at remote area of the TP, the radiative forcing contributed by the WSOC should be high, and requires further investigation.

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