For the first time, hydrotrioxides (ROOOH) have been detected under atmospheric conditions by an international research team.

Until today, the existence of these chemical molecules with the unusual OOOH group was simply a hypothesis. In the lab, it has been shown that they are made when important hydrocarbons like isoprene and alpha-pinene are broken down by oxygen.

Quantum chemical simulations and model calculations have yielded vital information about this new family of compounds. Through the oxidation of isoprene, about 10 million metric tonnes of them are made every year in the Earth’s atmosphere.

ROOOHs are thought to have a lifespan of minutes to hours. In the current issue of the prestigious scientific journal SCIENCE, researchers led by the Leibniz Institute for Tropospheric Research (TROPOS) write that hydrotrioxides represent a previously unnoticed class of substances in the atmosphere whose effects on health and the environment need to be investigated.

The bottom layer of our planet’s atmosphere acts as a vast chemical reactor, converting several hundred million metric tonnes of hydrocarbons each year, eventually resulting in the formation of carbon dioxide and water.

Forests or anthropogenic sources emit these hydrocarbons. There are many different types of oxidation processes, but only a few of them are thoroughly known. Hydrotrioxides (ROOOH) have become a focus of research on the atmosphere in recent years.

These are gaseous compounds containing a group of three successive oxygen atoms “O” and a hydrogen atom “H” bonded to an organic rest (R). Hydroperoxides (ROOH) containing two oxygen atoms have been recognized and proved for a long time.

It has been suggested in the literature that there may be compounds in the atmosphere that contain not only two but also three oxygen atoms. Hydrotrioxides are employed in chemical synthesis to create specific oxidation products in the reaction with alkenes.

However, at very low temperatures around -80°C, these reactive and thermally unstable hydrotrioxides are formed in organic solvents and further react. Until now, it was unknown whether this chemical class occurs as a gas in the atmosphere at much higher temperatures.

Researchers from the Leibniz Institute for Tropospheric Research (TROPOS), the University of Copenhagen, and the California Institute of Technology (Caltech) have now provided direct evidence for the first time that hydrotrioxides are formed under atmospheric conditions when peroxy radicals (RO2) react with hydroxyl radicals (OH).

The experiments were mostly carried out at TROPOS in Leipzig in a free-jet flow tube at room temperature and 1 bar air pressure, with the use of highly sensitive mass spectrometers. Caltech’s investigations offered further experimental data, particularly on the stability of the hydrotrioxides.

The University of Copenhagen used quantum chemical simulations to describe the reaction processes as well as the temperature and photostability of hydrotrioxides.

Global simulations using the chemistry-climate model ECHAM-HAMMOZ allowed for a preliminary assessment of the effects on the Earth’s atmosphere.

Prof. Henrik G. Kjaergaard of the University of Copenhagen says, “It is really exciting to show the existence of a universal new class of compounds formed from atmospherically prevalent precursors (RO2 and OH radicals).”

“It is very surprising that these interesting molecules are so stable with such a high oxygen content. Further research is needed to determine the role of hydrotrioxides for health and the environment,” TROPOS’ Dr. Torsten Berndt emphasizes this.

“Our study has shown that direct observation of hydrotrioxides using mass spectrometry is feasible. This means that it is now possible to further investigate these compounds in different systems including, perhaps, the quantification of their abundance in the environment,” Prof. Paul O. Wennberg of Caltech adds.

Only in the coming years will the importance of the first successful identification of this new material class, “hydrotrioxides,” become obvious.

The research study by Berndt et al., on the other hand, has created the first footing with the experimental demonstration and current knowledge, which should pique the curiosity of other research organizations.

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