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| Titel |
Raman scattering investigations of the interaction of a COV with pure and acid doped ice particles |
| VerfasserIn |
S. Facq, A. Oancea, C. Focsa, B. Chazallon |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028445
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| Zusammenfassung |
| Ice present in polar stratosphere is as well a common component of the troposphere,
particularly in cirrus clouds widespread in tropopause and upper troposphere region. With
water droplets, ice constitutes the condensed matter that can interact with atmospheric trace
gases via many different trapping processes (co-deposition i.e; incorporation during growing
ice conditions, adsorption, freezing etc). The incorporation of trace gases in ice
surface/volume can both affect the atmospheric chemistry and the ice structure and reactivity.
This can therefore modify the nature and composition of the incorporated species in ice, or in
the gas phase.
Recently, field measurements have demonstrated the presence of nitric acid in ice
particles from cirrus clouds(1,2) (concentration between 0.63 wt% and 2.5 wt %). Moreover,
laboratory experiments have shown that the uptake of atmospheric trace gases can be
enhanced up to 1 or 2 orders of magnitude in these doped ice particles. Among trace
gases capable to interact with atmospheric condensed matter figure volatile organic
compounds such as aldehydes, ketones and alcohols (ex: ethanol and methanol).
They play an important role in the upper troposphere (3,4) and snowpack chemistry
(5) as they can be easily photolysed, producing free radicals and so influence the
oxidizing capacity and the ozone-budget of the atmosphere (3,4). The temperature range
at which these physico-chemical processes occur extents between ~ 190 K and
273K.
Interaction between ice and trace gases are therefore largely dependent on the
ice surface properties as well as on the phase formation dynamic (crystalline or
not).
This study aims to examine and characterize the incorporation of a COV (ex: ethanol), at
the surface or in the volume of ice formed by different growth mechanisms (vapour
deposition or droplets freezing). Vibrational spectra of water OH and ethanol CH-spectral
regions are analysed using confocal micro-Raman spectroscopy at different temperatures
(183 K to 273 K). Information at the molecular level on the surface structure can
be derived from accompanying changes observed in band shapes and vibrational
mode frequencies. The influence of the presence of nitric acid on the molecular
interactions with the trapped organic species in ice particles can be also spectroscopically
characterized.
(1) Gao et al., Science, 2004, 303, 516.
(2) Journet et al., J. Phys. Chem. B, 2005, 109, 14112.
(3)H. Singh, M. Kanakidou, P.J Crutzen & D.J Jacob, Nature, 1995, 378, 50.
(4)H. Singh, Y. Chen, A. Staudt, D. Jacob, D. Blake, B. Heikes & J. Snow, Nature, 2001,
410, 1078.
(5)F. Dominé & P.B Shepson, Science, 2002, 297, 1506 |
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