Anthropogenic Activities Increase the Proportion of Soot in Black Carbon Particles and Thereby Intensify Atmospheric Radiative Forcing

Black carbon (BC) is a continuum of combustion products, encompassing char-BC and soot-BC, exhibits variations in particle size and radiative forcing (RF), which critically influence its role in the atmospheric radiative balance. However, the understanding of its long-term compositional changes and responses to natural and anthropogenic factors remains limited, and few atmospheric radiative modeling studies have specifically examined the distinct contributions of char-BC and soot-BC components. In this study, we trace the compositional changes of BC over the past ∼500 years using sediments from Huguangyan Maar Lake, China and separately quantify the impacts of char-BC and soot-BC on the RF of atmospheric BC. Our findings reveal that the proportion of soot-BC in BC has increased by 2.5 times since 1950 CE. In earlier periods, wildfires driven by the East Asian summer monsoon were the primary contributors to the dominance of char-BC in BC. However, the contribution of human activities to the rise in soot-BC has progressively increased from approximately 10% around 1950 CE to 80% by around 2010 CE, significantly altering BC composition and leading to a 5-fold increase in atmospheric BC RF. These results suggest that ongoing human activities will likely continue to alter BC composition and the atmospheric radiative balance, emphasizing the importance of distinguishing BC components in atmospheric models.