New composite class found in atmosphere

The Earth’s atmosphere is a gaseous soup made up of many different compounds. We know that almost 75% is nitrogen and about 20% is oxygen. But there are millions of tons of other organic and inorganic molecules. It is such a complex system, we are still finding completely new substances.

An international team has detected hydrotrioxides (ROOOH – a group of three oxygens and one hydrogen attached to a chemical “residue” labeled R) in the atmosphere for the first time. Until the discovery was made, the existence of these organic compounds with the strange OOOH group was only speculative. The team’s results were published in Science

The bottom layer of the atmosphere is a huge chemical reactor. Hundreds of millions of tons of hydrocarbons are converted into CO2 and water in this tire every year.

The hydrotrioxides are used in organic synthesis in oxidation processes. In chemical reactions, an oxidation process is when a molecule, atom or ion loses electrons. Under laboratory conditions, the ROOOHs can only be synthesized and used at about -80°C. So it is surprising to find these unstable compounds as gas in the atmosphere at much higher temperatures.

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According to models, about 10 million tons per year of the ROOOHs are formed in the Earth’s atmosphere through isoprene – a common organic compound that is the main component of natural rubber – oxidation. The estimated lifetime of the hydrotrioxides is minutes or hours.

The team was able to provide direct evidence that hydrotrioxides are formed under atmospheric conditions by the reaction of peroxy radicals (RO2 – two oxygen atoms on the “residue”) with hydroxyl radicals (OH – an oxygen and hydrogen atom). Radicals like these have unpaired electrons in their outer shell, making them highly reactive.

The newly discovered compounds were found at the Leibniz Institute for Tropospheric Research (TROPOS) in Germany using a free-jet flow tube and highly sensitive mass spectrometers.”

Information on the stability of the ROOOHs was obtained through experiments at Caltech in the US. Quantum chemical calculations performed at the University of Copenhagen, Denmark, helped describe the formation of the compounds and provided more information about their stability.

“It is really exciting to demonstrate the existence of a universal new class of compounds formed from atmospherically occurring precursors (RO2 and OH radicals),” said Henrik G. Kjærgaard, a professor at the University of Copenhagen.

“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,” explains Caltech professor Paul O. Wennberg out.

The significance of the detection of the compounds has yet to be fully determined. The researchers say further research is needed to map the environmental and health implications of the presence of ROOOHs in the atmosphere. “It is very surprising that these interesting molecules are so stable with such a high oxygen content. Further research is needed to establish the role of hydrotrioxides for health and the environment,” says Dr Torsten Berndt of TROPOS.

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