Research Team of Dominik Heger
Our Most Recent Publications
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.
Radim Štůsek and Lukáš Veselý performed a laboratory study of artificial seawater freezing. This was a topic of Radim’s bachelor thesis, and its results were finally published in impacted journal Science of the Total Environment. The authors discovered that the acidity of freeze-concentrated solution increases with decreasing temperature of the ice.
The samples of seawater were chosen to reflect natural conditions of seawater (3.5 % of salt weight and pH 8), frost flowers, and salty snow. The study focused on the investigation of acidity of the brine inside the ice vein (depicted in the abstract in the magnification on the right). The acidity was measured by the acid-base indicator present inside the ice veins. The study concluded that with decreasing temperature, the acidity of the brine increases above values that allow for efficient acid-base catalysis.
These results can explain the enhanced reactivity in the polar regions, both polluted by human-made chemicals and untouched pristine regions. The former was explained by scavenging of anthropogenic acids, however the latter remained as a mystery. This study finally cracked this mystery and proved that the sea ice can become acidic just by freezing by a completely natural mechanism. These results show that the anthropogenic acids are not necessary to facilitate the enhanced reactivity.
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.
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.
