Wednesday, May 25, 2022

Chemistry in clouds: How ice particles promote the formation of radicals

Certain molecules with fluorine, chlorine or bromine, together with water, can release harmful substances into the atmosphere.

Chlorofluorocarbons (CFCs) are fully halogenated paraffin hydrocarbons that contain only carbon (С), chlorine (Cl), and fluorine (F), produced as a volatile derivative of methane, ethane, and propane. Because CFCs contribute to ozone depletion in the upper atmosphere, the manufacture of such compounds has been banned.

However, there are other substances that tear holes in the ozone layer in combination with ice particles, such as those found in clouds.

Scientists at the Ruhr-Universität Bochum, the University of Duisburg-Essen and Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have discovered a possible mechanism for this.

For the study, scientists produced tiny ice particles and analyzed how certain compounds containing chlorine or bromine interacted with them. They then condensed the ice particles onto copper.

Karina Morgenstern und Cord Bertram mit dem Versuchsaufbau (Bild: RUB, Marquard)
Karina Morgenstern und Cord Bertram mit dem Versuchsaufbau (Bild: RUB, Marquard)

Then by using microscopic and spectroscopic methods, they observed that the molecules especially connected themselves to abandons in the ice structure. The encompassing water atoms of the ice structure at that point reoriented themselves and hydrogenated the particles. This, thus, made it less demanding to ionize the atoms in the trial.

The researchers irradiated the ice crystals with the attached molecules using UV light, which excited electrons in the ice particles in the vicinity of the molecules. These excited electrons ionized the chlorine and bromobenzene molecules. Through ionization, the molecules disintegrated into organic residues and highly reactive chlorine and bromine radicals.

Dr. Cord Bertram, Professor Uwe Bovensiepen and Professor Michel Bckstedte said, “The mechanism could explain what happens when UV light hits mineral-contaminated ice. Our results could thus help to understand the fundamental processes behind phenomena such as ozone holes.”

The study is published in the journal Physical Review Letters.



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