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| Titel |
Uptake of ozone to mixed sodium bromide/ citric acid solutions |
| VerfasserIn |
Ming-Tao Lee, Emilie Steimle, Thorsten Bartels-Rausch, Shunsuke Kato, Markus Lampimäki, Matthew Brown, Jeroen van Bokhoven, Frithjof Nolting, Armin Kleibert, Andreas Türler, Markus Ammann |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076521
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| Zusammenfassung |
| Sea-salt solution – air interfaces play an important role in the chemistry of the marine
boundary layer. The reaction of ozone (O3) with bromide is of interest in the context of
formation of photolabile halogens (Br2, BrCl) in the marine boundary layer. Recent
experiments have suggested that the bromide oxidation rate is related to the surface
concentration of bromide [1] and inversely related to the gas phase concentration of O3, an
indication for a precursor mediated reaction at the surface [2]. So far, the effect of organics
(such as those occurring at the ocean surface or in marine aerosols) on the reaction of O3 with
bromide aerosols has not been studied yet. In our study we investigate the uptake kinetics of
O3 to a mixed solution of sodium bromide (NaBr) and citric acid (CA), which
represents highly oxidized organic compounds present in the environment, with a
well-established coated wall flow tube technique, which leads to exposure of the film to
O3 allowing the heterogeneous reactions to take place and the loss of O3 being
measured. The results indicate that the uptake of O3 to the films with the higher bromide
concentrations (0.34M and 4M) is independent of the gas phase concentration and
roughly consistent with uptake limited by reaction in the bulk. For the lower bromide
concentration (84mM), however, we observe a trend of the uptake coefficient to decrease
with increasing O3 concentration, indicating an increasing importance of a surface
reaction.
In an attempt to constrain the kinetic data, we employed X-ray photoelectron spectroscopy
(XPS) to get insight into the surface composition of the aqueous solution – air interface.
Previous XPS studies have shown that halide ion concentrations are enhanced at the aqueous
solution air interface [3-4], which likely promotes the surface reactions of bromide or iodide
with O3. A first XPS study of ternary solutions of KI with butanol indicated the
importance of specific interactions of the cation with the alcohol headgroup [5]. In
this study we would like to go one step further and look into the effect of a more
complex organic compound, CA. We used ambient pressure XPS on a vacuum liquid
microjet. The continuously refreshed free-flowing aqueous filament under vacuum
permits photoelectron spectroscopy measurements from volatile aqueous interfaces in
absence of beam damage [6]. Measurements were made at the SIM beam line of the
Swiss Light Source (SLS) at the Paul Scherrer Institute. The ability to tune the
photon energy (150-2000 eV) is crucial to get precise component ratios as a function
of photoelectron kinetic energy and thus probe depth, thus allowing to determine
relative concentrations of citric acid and bromide at the surface and in the bulk,
respectively.
REFERENCES
[1] Clifford and Donaldson, J. Phys. Chem. A, 111, 9809-9814, (2007).
[2] Oldridge and Abbatt, J. Phys. Chem. A, 115, 2590-2598, (2011).
[3] S. Ghosal et al., Science 307, 563 (2005).
[4] M.A. Brown et al., Phys. Chem. Chem. Phys. 10, 4778 (2008).
[5] M. Krisch et al., J. Phys. Chem. C 111, 13497 (2007).
[6] M.A. Brown et al., J. Phys. Chem. Lett. 3, 231 (2012). |
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