Brown carbon aerosol in urban Beijing: Significant contributions from biomass burning and secondary formation

Atmospheric brown carbon (BrC) has significant impact on Earth’s radiative budget. However, due to our very limited knowledge about the relationship between BrC light absorption and the associated sources, the estimation for radiative effects of BrC is still largely constrained. In this study, we combine ultraviolet−visible (UV−vis) spectroscopy measurements and chemical analyses of BrC samples collected from January to December 2015 in urban Beijing, to investigated the sources of atmospheric BrC. The multiple liner regression model was applied to apportion the contributions of individual primary and secondary organic aerosol (OA) source components to light absorption of BrC. Our results indicated that biomass burning emission and secondary formation are highly absorbing up to 500 nm, and their contributions increased with the wavelengths. In contrast, the contribution of traffic emission and coal combustion to total absorption decreased with the wavelength and the large contributions were mostly found at shorter wavelengths. Then the mass absorption efficiency (MAE) of major light-absorbing components were estimated, which can provide a support to estimate the impact of BrC from these sources on the climate. The positive matrix factorization model were also used to verify the contributions of different source components of BrC absorption at 365 nm. The results consistently demonstrate that the biomass burning and secondary formation contributes significantly to the overall absorption, followed by coal combustion and traffic emission.