A 700 year sediment record of black carbon and polycyclic aromatic hydrocarbons near the EMEP air monitoring station in Aspvreten, Sweden

In view of poor constraints on historical combustion emissions, past environmental loadings of black carbon (BC) and polycyclic aromatic hydrocarbon (PAH) were reconstructed from dated lake sediment cores collected 70 km south of Stockholm, Sweden. Compared to several dramatic variations over the recent 150 years, the preindustrial loading were steady within +/-50% through the entire medieval with BC fluxes of 0.071 g m(-2) yr(-1) and PAH fluxes of 6 mu g m(-2) yr(-1). In the wood-burning dominated century leading up to the industrial revolution around 1850, increasing BC fluxes were leading PAH fluxes. BC fluxes reached their millennial-scale maximum around 1920, whereas PAH fluxes increased exponentially to its record maximum around 1960, 50-fold above preindustrial values. For 19201950, BC fluxes consistently decreased as PAH fluxes kept increasing. Coal and coke represented >50% of the Swedish energy market in the 1930s. Combined with sharply decreasing (1,7-)/(1,7-+2,6-dimethylphenanthrene), indicative of diminishing wood combustion, and decreasing methylphenanthrenes/phenahthrene, indicative of higher-temperature combustion (coal instead of wood), the sediment archive suggests that the relative BC/PAH emission factors thus are lower for coal than for wood combustion. For the first time, both BC and PAH fluxes decreased after 1960. This trend break is a testament to the positive effects of decreasing reliance on petroleum fuels and a number of legislative actions aimed at curbing emissions and by 1990, the loading of BC was back at preindustrial levels, whereas that of PAH were the lowest since the 1910s. However, for the most recent period (1990-2004) the BC and PAH fluxes are no longer decreasing, putatively reflecting a slight increase in diesel consumption and a doubling of softwood-pellet burners for home heating.