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.

1. Stable isotopes
in the atmosphere
Isotopes Mass spectrometry
Isotopes 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 an
number of neutrons, and therefore a di erent mass. Some heavy Isotope Ratio Mass Spectrometer (IRMS). Usually, compounds have
isotopes, like 3H and 14C, are radioactive and decay over time. Others, to be puri ed before injection into the IRMS.
like 2H and 13C, are stable and do not radiate. The IMAU focuses on
stable isotopes.
Isotopes of the same element have the same chemical properties and
form the same molecular species. However, the mass di erence
between them causes subtle di erences in the isotopic composition of Ion beam acceleration
compounds that are produced by di erent processes; they have a Ion source in electric eld
di erent `isotopic ngerprint’.
De
m
ag ec
Puri ed gas ne tio
tic n
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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.