Impact of secondary ice in a frozen NaCl freeze-concentrated solution on the extent of methylene blue aggregation

Lukáš Veselý and Radim Štůsek performed this study in cooperation with the A-ESEM microscopy group of the Czech Academy of Sciences. They were able to successfully connect microscopic images with spectroscopic data, which led to the first ever demonstration that the inner structure of the freeze-concentrated solution (as shown on the right) has a major influence on aggregation during freezing.

In this work the authors challaged a long standing theory, which assumed that the size of the ice crystals is the most important factor influencing the aggregation after freezing! This would not be possilble without close long-term collaboration of our research group with the ESEM group lead by Vilém Neděla.

Temperature and Concentration Affect Particle Size Upon Sublimation of Saline Ice: Implications for Sea Salt Aerosol Production in Polar Regions

The study was led by Dominik Heger in collaboration with the A-ESEM microscopy group of the Czech Academy of Sciences. The work focuses on the small (micrometre-sized) salt particles produced during ice sublimation. These particles are thought to facilitate photochemical reactions in polar regions.

In this paper, the authors show the surprising result that high-salinity ice requires temperatures of -30°C to produce particles small enough to form reactive aerosols. In contrast, in low-salinity ice, particles are produced at all sub-zero temperatures. This unique paper is the first to quantify the particle sizes produced by ice sublimation.

The importance of the article is immediately apparent as it has been chosen as the cover of the 8th issue of the 49th volume of Geophysical Research Letters.

Acidity and Phase Behavior of Frozen Hydrochloric Acid during Thawing

In a collaborative effort with Thomas Loerting’s group (University of Innsbruck), Radim Šťůsek, Lukáš Veselý, and Jan Zezula, led by Dominik Heger, explored how aqueous hydrochloric acid behaves during freezing and thawing. Using differential scanning calorimetry and UV–vis spectroscopy, the study revealed several nonequilibrium phase transitions — including glass transition and cold crystallization — and directly linked them to changes in acidity.

Notably, the results allowed the team to quantify the freeze concentration factor: dilute HCl solutions (down to 5 μM) concentrated by up to 250,000-fold upon freezing, while concentrated solutions showed minimal concentration (factor ~7). This work offers some of the first quantitative insights into freeze concentration and acidity changes in frozen hydrochloric acid — a system with important implications for atmospheric and planetary chemistry.

Spectroscopic characterization of phenol in frozen aqueous solution and on the ice surface

Marie Garncarzová, Lukáš Veselý, led by Dominik Heger, in collaboration with Korean researchers from KOPRI and UST, investigated the photophysical behavior of phenol in frozen aqueous environments and on ice surfaces. Using UV–vis, fluorescence, and Raman spectroscopy, they demonstrated that phenol can crystallize within freeze-concentrated solutions or form amorphous states, with each phase exhibiting distinct optical properties. Notably, crystallization and surface adsorption induced bathochromic shifts that allow absorption of solar UV photons — enabling photolysis pathways otherwise inaccessible in solution. This study highlights the unique microenvironments in ice and snow that may activate pollutant reactivity under polar and atmospheric conditions.