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Quantification of black carbon in soils and sediments

Quantification of black carbon in soils and sediments. Basil Thalmann & Eleanor Cato 20.11.12. Contents. What is Black Carbon? Chemical composition Sources and role in the carbon cycle Reasons of interest Methods of Analysis Sampling Reference standards CTO-375

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Quantification of black carbon in soils and sediments

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  1. Quantification of black carbon in soils and sediments Basil Thalmann & Eleanor Cato 20.11.12

  2. Contents • What is Black Carbon? • Chemical composition • Sources and role in the carbon cycle • Reasons of interest • Methods of Analysis • Sampling • Reference standards • CTO-375 • Differential Scanning Calorimetry • FFF • Electronmicroscopy

  3. What is Black Carbon? • Black carbon (BC) is described as a continuum of substances ranging from charred plant material to soot and graphite. • Types of BC differ in stoichiometry and aromaticity. • Charred biomass often retains enough of its original character to identify its source, unlike soot. • Heavy particles are mainly stored in soil but lighter particles can remain in the atmosphere for some time. Schmidt and Noack, 2000

  4. Black Carbon and the Environment • BC can spend between 2,400 and 13,900 years in sediment or soils stores. (Masiello et al) • Considered refractory but this depends on the type of BC. • Time spent in the atmosphere depends on particle size.

  5. Black Carbon and the Environment • Potentially the 2nd largest contributor to global warming. • In the atmosphere, soot particles absorb light and radiate heat, causing localised warming. • When particles fall out they can accelerate snow melt. • The relatively short atmospheric lifetime means that effects are generally experience closed to the source.

  6. Health Concerns World Health Organisation Inhalation of soot particles can lead to lung tissue damage and smaller particles can enter the bloodstream. Black carbon may be able to act as a carrier for harmful substancestothelungs Carbon nanotubes with similarities to asbestos fibres have caused concerns about inhalation risks although there are no conclusive studies so far.

  7. Sorption ofOrganic Chemicals Adsorption of organic chemicals by the combination of BC, coal and kerogen can exceed that of amorphous organic matter by 10 times. Poly aromatic hydrocarbons (PAHs), poly chlorinated biphenyls, chlorobenzenes, and pesticide diuron. BC therefore plays an important role in soil toxicology

  8. Reference Materials • Standards: • Urban dust – 1649a NIST • Marine sediment – 1941b NIST • Vertisol • Chernozem • N-hexane soot • Diesel soot – 1650 NIST • Graphite – Erne Chemie • Interference: • Shale • Bituminous coal • Lignite

  9. Methods of AnalysisOverview Samples are prepared by drying and grinding. BC is separated from organic and inorganic carbon by one of three methods; The remaining material generallyclassedas BC andquantified.

  10. Methods of AnalysisChemo-Thermal-Oxidation at 375°C (CTO-375) 3 Stages: • Removal of inorganic carbon by acidification. • Removal on non-pyrogenic organic material using a furnace. • Quantification of BC using CHN elemental analyser. • Sample is dried and ground to a fine powder – typically 10 mg with 200 µg of carbon. • Microacidification using 1 M HCl. • 18 hrs in a tube furnace at 375 oC. • LOD approx. 2 µg

  11. Methods of AnalysisDifferential Scanning Calorimetry DSC measured the heat flow of a sample compared to a reference as a function of temperature. Types of BC can be identified using typical combustion patterns, with temperatures greater than 520 oC. For organic carbon and most potentially interfering materials thermal oxidation begins below 520 oC. The exception is bituminous coal. Leifeld, J. Thermal stability of black carbon characterised by oxidative DSC. 2006

  12. Non–dispersive IR Thermal method used for Total Organic Carbon quantification Advantage that it measured carbon dioxide directly 2350 cm-1 IR absorption band is monitors as the carbon is oxidised

  13. Methods of Analysis13C NMR http://www.waite.adelaide.edu.au/NMR/quant.html Used as a quantification method CP/MAS NMR Cross polarization used to increase the signal intensity Magic Angle Spinning used to improve resolution – vital for distinguishing between different types of BC Disadvantages for BC analysis include the lack of hydrogen atoms and the underestimation of some functional groups

  14. Method of SeparationField Flow Fractionation (FFF) • Liquid chromatography without stationary phase • Separation is suitable for dispersions • Separation takes place in a laminar flow • A field of force causes the separation • Range of separation: 1 nm to several µm

  15. Method of SeparationField Flow Fractionation (FFF)

  16. Method of SeparationField Flow Fractionation (FFF) Asymmetric Field Flow Field Fractionation (AF4)

  17. Method of SeparationAsymmetric Field Flow Field Fractionation (AF4) Injection Inlet Outlet Source: Wyatt Technology Europe GmbH

  18. Methods of AnalysisElectron Microscope Qualitative analysis of total sample or fractions from FFF Fractions with bigger particles can be analyzed by SEM Diesel soot Charcoal

  19. Methods of AnalysisTransmission Electron Microscope HRTEM resolution down to 0.05 nm Additionally energy dispersive X-ray spectroscopy can be used MWNTs

  20. SEM

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