Deposition and 14C-based source apportionment of black carbon in a small lake in southern Sweden since 1450 CE

Black carbon (BC) is produced by incomplete combustion of biomass and fossil fuels and is released as aerosols to the atmosphere with effects on the climate, environment, and human health. Current BC emissions are well monitored in many parts of the world. However, the geographical coverage is limited, and historical records of BC accumulation are still scarce. Here we present a quantification of soot BC (SBC) concentrations in sediments deposited in a small lake in southern Sweden during recent centuries. The SBC was quantified using chemical and thermal oxidation at 375°C (CTO375). The SBC concentrations are low (c. 3 mg/g) in the preindustrial sediments older than 1650 CE and reached maximum concentrations (c. 8.5 mg/g) after 1900 CE. The increase in SBC accumulation started before the major phase of industrialisation of Sweden in the 19th century, probably related to local emission sources from increased biomass burning or coal extraction in the region that expanded from the second half of the 17th century. The effect of industrialisation is seen as an increase in SBC concentration and accumulation from around 1875 CE. The maximum accumulation of SBC was observed between 1950 CE and 2005 CE. The fraction of the SBC derived from fossil fuels was estimated using radiocarbon-based source apportionment. Biomass was the main source of SBC throughout the studied period. The maximum contribution from fossil fuel was observed between 1970 CE and 1990 CE, amounting to 26 −28 % of the total SBC. From 2000 CE the SBC deposition was dominated by biomass sources, probably because of a transition from fossil fuels to biomass as the dominant source of heating in Sweden.