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| Titel |
The influence of physical state on shikimic acid ozonolysis: a case for in situ microspectroscopy |
| VerfasserIn |
S. S. Steimer, M. Lampimäki, E. Coz, G. Grzinic, M. Ammann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 19 ; Nr. 14, no. 19 (2014-10-13), S.10761-10772 |
| Datensatznummer |
250119096
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| Publikation (Nr.) |
 copernicus.org/acp-14-10761-2014.pdf |
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| Zusammenfassung |
| Atmospheric soluble organic aerosol material can become solid or
semi-solid. Due to increasing viscosity and decreasing diffusivity,
this can impact important processes such as gas uptake and
reactivity within aerosols containing such substances. This work
explores the dependence of shikimic acid ozonolysis on humidity and
thereby viscosity. Shikimic acid, a proxy for oxygenated reactive
organic material, reacts with O3 in a Criegee-type
reaction. We used an environmental microreactor embedded in
a scanning transmission X-ray microscope (STXM) to probe this
oxidation process. This technique facilitates in situ measurements
with single micron-sized particles and allows to obtain near-edge
X-ray absorption fine structure (NEXAFS) spectra with high spatial
resolution. Thus, the chemical evolution of the interior of the
particles can be followed under reaction conditions. The experiments
show that the overall degradation rate of shikimic acid is depending
on the relative humidity in a way that is controlled by the
decreasing diffusivity of ozone with decreasing humidity. This
decreasing diffusivity is most likely linked to the increasing
viscosity of the shikimic acid–water mixture. The degradation rate
was also depending on particle size, most congruent with
a reacto-diffusion limited kinetic case where the reaction
progresses only in a shallow layer within the bulk. No gradient in
the shikimic acid concentration was observed within the bulk
material at any humidity indicating that the diffusivity of shikimic
acid is still high enough to allow its equilibration throughout the
particles on the timescale of hours at higher humidity and that the
thickness of the oxidized layer under dry conditions, where the
particles are solid, is beyond the resolution of STXM. |
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