Measurement and source apportionment of ubiquitous soot black carbon in sediments
Abstract: The pyrogenic particles formed from incomplete combustion of organic matter are often termed black carbon (BC) and they partake in many important biogeochemical processes. For instance, BC in water and sediment affects the solid-water partitioning of hydrophobic organic pollutants reducing their bioavailability.The key objective of this thesis was to test the chemothermal oxidation method (CTO) to quantify soot-BC in sediments. In the CTO method, sedimentary BC is isolated by removing non-pyrogenic organic matter through thermal combustion at 375°C under active airflow and subsequent removal of inorganic carbonates by adding hydrochloric acid. The CTO method was here shown to work well for quantifying the thermally more stable soot-BC phase.Another objective was to study sediment samples to measure the historical and spatial distribution of combustion products. First, historical fluxes of BC and polycyclic aromatic hydrocarbons (PAH) were investigated in a Swedish lake sediment. Increasing fluxes of BC and PAH were seen in sediment dated to the industrial revolution in the 1850s, the high coal usage in the early 1900s lead to a 5 time increase in BC flux relative to the pre-industrial flux, and the switch from coal to oil usage in the 1950s lead to a 46 time increase in PAH flux relative to the pre-industrial flux. Further, lower fluxes came from stricter emission controls in the 1960s, improvements in combustion technology and the usage of catalytic filters from mid-1980s. Modern sediment measured 20% lower BC flux and 5 times higher PAH flux relative to the pre-industrial fluxes.Secondly, the spatial distribution and sources of sedimentary soot-BC were studied in rivers in the Arctic region. The estimated BC flux was highest in the McKenzie (99 kton yr-1) whereas it was lowest in Yukon (1.1 kton yr-1). Contemporary biomass-derived BC was detected for the Yenisey, whereas fossil fuel derived BC was found for the Lena, Yukon and McKenzie.
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