Black carbon aerosols in China: Spatial-Temporal variations and lessons from long-Term atmospheric observations

Black carbon (BC) significantly influences climate, air quality, and public health, and long-Term observations are essential for understanding its adverse effects. While previous studies have primarily focused on spatiotemporal variations, deeper insights from such datasets remain uncovered. Using 13 years (2008-2020) of continuous measurements of equivalent black carbon (eBC) in China, this study reported the spatial-Temporal variations of eBC and its sources, including solid fuel (eBCsf) and liquid fuel combustion (eBClf). The results showed that eBC and its sources exhibited higher concentrations in eastern and northern China compared to western and southern China. Seasonal variations of eBC and eBCsf generally showed lower values during summer and higher values during winter at most stations. Long-Term trends indicated that eBC and eBClf decreased most rapidly at urban stations, while eBCsf declined faster at rural stations. Comparisons of eBC concentrations and trends between this study and global observations revealed higher eBC levels but lower reduction rates in China. These long-Term observations showed that the model simulations performed well in simulating spatial distribution but poorly in capturing inter-Annual variations. The weather-normalized eBC concentrations showed potential for adjusting emission estimates. The normalized results also suggested that emission control was the dominant driver of the BC reduction. This decrease was primarily driven by reductions from solid fuel combustion at rural and background stations. This study provides insights for reducing uncertainties in black carbon emission inventories and improving model performance in simulating surface concentrations.