Light absorption of black and brown carbon in eastern China

Black carbon (BC) and brown carbon (BrC) are important light-absorbing components of carbonaceous aerosols in the atmosphere. While BC concentrations and properties have been widely studied, BrC concentrations and its radiative balance have been rarely studied due to the lack of information on the light-absorbing properties. In this study, a novel Bayesian inference model (BI) and conventional BC and BrC models were both applied to systematically study the BC and BrC properties at a roadside site in Yantai based on the data from a 7-wavelength aethalometer and total carbon (TC) analyzer. TC was resolved into BC, BrC and white carbon (WtC) by the BI model, in which BC dominates the TC (43.4 %), followed by WtC (29.5 %) and BrC (27.1 %) during autumn and winter. Significant agreements in BC and b_{abs, BC} (880) (R > 0.95) were achieved by BI and traditional BC model. BC source apportionment shows a clear contribution of biomass burning in cold seasons, especially on cold winter nights. Further separations of b_{abs, BrC} (370) shows distinct seasonal variations of b_{abs, BrC, pri} (370) and b_{abs, BrC, sec} (370). While b_{abs, BrC, pri} (370) diel distribution was similar across different seasons, b_abs,BrC,sec(370) shows a significant contribution in winter, especially during nighttime, possibly due to the enhanced nighttime NO₃ chemistry via aqueous reactions. Hourly resolved mass absorption efficiency (MAE) shows a clear BrC photobleaching process during noontime. Unlike HKUST where clear darkening-photobleaching BrC process was observed, the morning darkening-photobleaching processes were interfered by traffic emissions, suggesting that the formation/emission process of BrC surpassed the photobleaching process in the morning.