Tracing sources of sedimentary soot: The underestimated role of liquid fossil fuels in North China.

Soot emissions significantly impact air pollution and climate change, especially in regions like North China, where industrialization has driven energy shifts. Understanding historical soot sources is crucial for improving emission inventories and developing mitigation strategies. Traditional methods struggle to capture the complexity and temporal shifts in combustion sources. This study uses dual-carbon isotopes (δ¹³C and F¹⁴C) in soot from Gonghai Lake to trace soot emission sources in North China over the past 130 years. The results reveal that after 1949, soot emissions from fossil fuel sources increased from 31.64 % to 67.85 %, with fluxes more than tripling, reflecting a transition from biomass burning to fossil fuel combustion driven by industrialization. Despite pollution control efforts, soot fluxes from both biomass and fossil fuel sources have not shown a significant decline in the 21st century. Notably, since the 1980s, soot flux from liquid fossil fuels has been comparable to that from coal, despite their lower consumption. This suggests that the contribution of liquid fossil fuels to soot emissions may have been underestimated in emission inventories. This study provides a more detailed, quantifiable understanding of historical soot emission sources and highlights the role of geochemical constraints in refining emission inventories and evaluating mitigation effectiveness.