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| Titel |
Photolysis of Nitrate in Greenland Snow |
| VerfasserIn |
Carl Meusinger, Joel Savarino, Matthew Johnson |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250045933
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| Zusammenfassung |
| Nitrate concentrations undergo drastic changes in the first tens of centimeters in the snow
layer at both Arctic and Antarctic low accumulation sites [1]. Those changes go along with
elevated gaseous NOx levels above the snow pack. A thorough description of these
post-depositional effects is still not at hand, so that nitrate and NOx data from field
campaigns can’t serve quantitatively to interpret the oxidation state of the (past)
atmosphere.
At the moment, the most promising candidates for explaining this behavior of nitrogen
compounds are the photolysis of nitrate in the snow and its re-evaporation [5]. While several
attempts have been made to quantify the photolysis [2-4], obtained results could not explain
field data fully [6]. Laboratory experiments were criticized due to their use of specific lamps,
synthetic snow and non-flow conditions leading to accumulation of NOx above the
snow layer [6]. A new experiment is set up that studies the photochemistry of real
snow collected on field campaigns in our newly designed freezer-photoreactor at
CCAR.
Inside a commercial freezer that operates down to -25ºC, UVA and UVC lamps are
installed to induce photolysis. The snow is kept in 2-port-teflon bags that allow maintaining a
constant flow of air over the sample in order to avoid the accumulation of NO2. Before it
enters the freezer, this air passes through a chilled water tank, which is kept at the same
temperature as the freezer. This gives the flowing air a constant water vapor pressure to
ensure steady atmospheric conditions inside the bag (so the snow doesn’t freeze more or
melts). After the freezer, the released NOx is sampled in a cold trap, while the photolyzed
snow will be analyzed in Joël Savarino’s group (Grenoble) using Nitrogen mass
spectrometry.
We will present the characterization of the setup along with initial results; implications
are discussed.
1. Röthlisberger, R., et al. 2000, J. Geophys. Res., AGU, Vol. 105.
2. Blunier, T., et al. 2005, Geophys. Res. Let., Vol. 32.
3. Jacobi, H.-W., et al. 2006, J. Photochemistry and Photobiology, Vol. 179.
4. Honrath, R. E., et al. 2000, Geophys. Res. Let., Vol. 27.
5. Frey, M. M., et al. 2009, Atmos. Chem. Phys., Vol. 9. |
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