A 300 Years Record of Polycyclic Aromatic Hydrocarbons in Lake Botanisk, Copenhagen: A Historical Reconstruction of Combustion Processes in a Scandinavian Urban Lake
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Date
2013-02-04
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Abstract
Lake Botanisk, a small isolated body of water in Copenhagen, Denmark, has remained relatively undisturbed for four centuries, making its sediments an excellent historical archive of past deposition rates of atmospheric contaminants. The concentrations and composition of polycyclic aromatic hydrocarbons (PAHs) measured in a sediment core of Lake Botanisk assisted in reconstructing the historical combustion activities for that region. Source diagnostic ratios indicate that PAHs were primarily derived from pyrogenic rather than petrogenic sources throughout the entire core. Marked increases in PAH concentrations during the pre-industrial era (<1860) trace major geopolitical events of the period (e.g. bombing of Copenhagen by British Navy in late 1700s). A significant rise in combustion-derived PAHs was observed with the start of the industrial revolution, which corresponds to the start of coal imports in Denmark (1860s). The ratio of Retene/(Retene+Chrysene) demonstrates that until ~1860, Copenhagen’s combustion sources were dominated by wood burning. The shift to coal consumption starting in 1860 leads to simultaneous increases in pyrogenic PAHs and isomer ratios (Benzo[b]fluoranthene/Benzo[k]fluoranthene) typical of coal usage. Variations in PAH concentrations and ratios during the 20th Century track the shifts in energy sources (coal to oil, oil to natural gas), major political events such as the oil embargo of 1970s (oil back to coal), as well the implementation of air quality standards and improvements in combustion technologies in recent decades (>1980s). In spite of significant decreases in PAH concentrations since the early-20th century peak, levels still remain 10-fold above preindustrial values in recent decades suggesting an impact from the growth in urban development.
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Polycyclic aromatic hydrocarbons, Black Carbon, Copenhagen, Denmark, Sediment, PAH diagnostic ratios