24 Jan 2023
24 Jan 2023
Status: this preprint is currently under review for the journal ACP.

Photo-Induced Shrinking of Aqueous Glycine Aerosol Droplets

Shinnosuke Ishizuka1,2,3,, Oliver Reich1,, Grégory David1, and Ruth Signorell1 Shinnosuke Ishizuka et al.
  • 1Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093, Zurich, Switzerland
  • 2Institute of Advanced Research, Nagoya University, Nagoya 046-8601, Japan
  • 3Institute of Space-Earth Environmental Research, Nagoya University, Nagoya 046-8601, Japan
  • These authors contributed equally to this work.

Abstract. Due to their small size, micrometer and submicron sized solution droplets can respond differently to physical and chemical processes compared with extended bulk material. Using optically trapped micrometer sized aqueous glycine droplets, we demonstrate photo-induced degradation of glycine upon irradiation with visible light, even though molecular glycine does not absorb light in the near UV/vis range to any significant extent. This reaction is observed as photo-induced shrinking of the droplet, which we characterize by analyzing the elastic light scat-tering and the Raman spectrum of the droplet over the course of the reaction. We find the volume to shrink with a constant rate over the major part of the shrinking process. This indicates the presence of a rate limiting photo-catalyst, which we attribute to mesoscopic glycine clusters in the droplet solution. Our findings relate to previous reports of visible light absorption by photosensitizers. However, to the best of our knowledge, this is the first experimental evidence of a photochemical pathway facilitated by mesoscopic clusters. Light interaction with such mesoscopic photoactive molecular aggregates might be more important for aerosol photochemistry than previously anticipated.

Shinnosuke Ishizuka et al.

Status: open (until 07 Mar 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Shinnosuke Ishizuka et al.

Shinnosuke Ishizuka et al.


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Short summary
Photosensitizers play an important role in the photochemistry of atmospheric aerosols. Our study provides evidence that mesoscopic glycine clusters forming in aqueous droplets act as unconventional photosensitizers in the visible light spectrum. We observed the influence of these photoactive molecular aggregates in single optically-trapped aqueous droplets. Such mesoscopic photosensitizers might be more important for aerosol photochemistry than previously anticipated.