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| Titel |
Laboratory studies of VUV photochemistry of thin water ice films: H2O2 production and its implication for Noctilucent Clouds |
| VerfasserIn |
Mikhail Kulikov, Alexander Feigin, Stanislav Ignatov, Petr Sennikov, Thaddaeus Bluszcz, Otto Schrems |
| 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 |
250055739
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| Zusammenfassung |
| Noctilucent Clouds (NLC) are the highest clouds of the Earth’s atmosphere. They are formed
during summer at middle to high latitudes in an altitude range between 80 and
90 km when the air temperature drops below 150K. The particles of NLC consist
primarily of water ice [1] and are formed as a result of water vapor condensation. In
the day time, NLC are subjected to strong solar Lyman - alpha irradiation with
the wavelength of 121.6 nm which penetrates into ice particles and is absorbed
essentially. This leads to photodissociation of H2O molecules and to formation of mobile
and chemically active components in the solid phase which can diffuse inside the
ice, participate in chemical reactions with formation of secondary products (H2O,
HO2, HO3, H2O2, O2, O3), accumulate in the ice matrix and escape into the
gas-phase.
We have carried out first VUV-photolysis laboratory studies of water ice to acquire detailed
knowledge about physicochemical processes inside the NLC particles initiated by solar
irradiation. The experimental set-up used includes a high-vacuum chamber, a gas-inlet
system, a refrigerator-cryostat with temperature controller, a FTIR spectrometer, a vacuum
ultraviolet hydrogen lamp emitting the wavelength of 121.6 nm and a microwave generator.
Our previous studies [2] were devoted to measurements of the absolute photodesorption
rate (loss of substance due to the escape of photoproducts into gas phase) from
thin water ice samples under temperatures typical for the upper part of the Earth’s
mesosphere. The results obtained show that the flow of photoproducts into the gas
phase was insignificant. Nearly all the photoproducts remain in the solid phase,
and the principal chemical reaction between them is the recombination reaction
H+OH->H2O.
This work is devoted to identify the formation of hydrogen peroxide and measure its
concentrations inside the VUV irradiated thin (20-100 nm) water ice samples in the
temperature range of 80-140K. H2O2 production was monitored via measuring its absorption
band near 2855-2860 cm-1. In particular, it was found that H2O2 could rich relative
concentrations up to 0.2%. The obtained estimates demonstrate that total absolute
concentrations of H2O2 accumulated in NLC particles can be essentially more than the
gas phase concentrations of this component at the relevant altitudes of the upper
mesosphere. Also, we discuss additional applications of the obtained results in
astrophysics.
The work was performed with support of the RFBR (projects 10-05-01112) and
DAAD.
1. M. Hervig, R.E. Thompson, M. McHugh, L.L. Gordley, J.M. Russell III, and M.E.
Summers, First confirmation that water ice is the primary component of polar mesospheric
clouds, Geophys. Res. Lett., 28, 971–974, 2001.
2. M. Yu. Kulikov, A. M. Feigin, S. K. Ignatov, P. G. Sennikov, Th. Bluszcz, and O. Schrems,
Technical Note: VUV photodesorption rates from water ice in the 120–150K temperature
range – Significance for Noctilucent Clouds, Atm. Chem. Phys. Discussions, 10,
22653–22668, 2010. |
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