The influence of physical state on shikimic acid ozonolysis: a case for in situ microspectroscopy

Steimer, S. S.; Lampimäki, M.; Coz, E.; Grzinic, G.; Ammann, Markus (2014). The influence of physical state on shikimic acid ozonolysis: a case for in situ microspectroscopy. Atmospheric chemistry and physics, 14(19), pp. 10761-10772. European Geosciences Union 10.5194/acp-14-10761-2014

[img]
Preview
Text
acp-14-10761-2014.pdf - Published Version
Available under License Creative Commons: Attribution (CC-BY).

Download (1MB) | Preview

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.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Departement of Chemistry and Biochemistry

UniBE Contributor:

Ammann, Markus

Subjects:

500 Science > 570 Life sciences; biology
500 Science > 540 Chemistry

ISSN:

1680-7316

Publisher:

European Geosciences Union

Language:

English

Submitter:

Franziska Bornhauser-Rufer

Date Deposited:

17 Mar 2015 09:30

Last Modified:

17 Jun 2015 08:23

Publisher DOI:

10.5194/acp-14-10761-2014

BORIS DOI:

10.7892/boris.64722

URI:

https://boris.unibe.ch/id/eprint/64722

Actions (login required)

Edit item Edit item
Provide Feedback