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Stable isotopes in the atmosphere


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Poster describing why and how the Atmospheric Physics and Chemistry group of the IMAU studies the isotopic composition of atmospheric trace gases. With thanks to the rest of the group.

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Stable isotopes in the atmosphere

  1. 1. Stable isotopes in the atmosphereIsotopes Mass spectrometryIsotopes are atoms with the same number of protons, but a di erent The amount of a stable isotope in a gas can be determined with annumber of neutrons, and therefore a di erent mass. Some heavy Isotope Ratio Mass Spectrometer (IRMS). Usually, compounds haveisotopes, like 3H and 14C, are radioactive and decay over time. Others, to be puri ed before injection into the 2H and 13C, are stable and do not radiate. The IMAU focuses onstable isotopes.Isotopes of the same element have the same chemical properties andform the same molecular species. However, the mass di erencebetween them causes subtle di erences in the isotopic composition of Ion beam accelerationcompounds that are produced by di erent processes; they have a Ion source in electric elddi erent `isotopic ngerprint’. De m ag ec Puri ed gas ne tio tic n in el d - - + n + General principle of an IRMS. 1 H (H) 2 H (D) Detection of ions by Faraday cups Light ions Heavy ions The simplest example of isotopes are H (`ordinary’ hydrogen), with just a proton, and 1 2 H (`deuterium ‘), with a proton and a neutron. Isotope signatures of the different CH4 sources Methane (CH4) 0 Natural sources Natural Gas • A potent greenhouse gas -50 Anthropogenic sources • >150 % increase since preindustrial times • Increase rate not constant -100 D(CH4) (‰ vs SMOW) • Causes not well understood: future increase Coal uncertain -150 Geological sources The IMAU studies the processes that produce -200 and destroy CH4. As the di erent CH4 sources Biomass burning produce methane with di erent `isotopic TODAY -250 ngerprints’, we can use measurements of 2H Photochemical degradation and 13C in CH4 to learn more about these Ruminants sources. -300 Rice T. wetlands Waste The relative amount of 2H in the CH4 (δD(CH4)) plotted against the B. wetlands -350 relative amount of 13C in the CH4 (δ13C(CH4)) for di erent sources of -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 atmospheric CH4 13C(CH ) (‰ vs VPDB) 4 Molecular hydrogen (H2) • Promising clean alternative to fossil fuels • Risks of H2 leakage for atmosphere uncertain. • H2 cycle not studied much before. The IMAU analyzes samples from weather stations around the globe for H2 concentration (m(H2)) and 2H content (δ(D,H2)). These data give information about the seasonal cycle of H2, its spatial distribution and the sources and sinks.H2 concentrations (blue) and relative 2H content (red) plotted against sampling date of the analyzed samples from Alert, Arctic Canada. Here the seasonal cycles can be seen quite well.