New compound class found in atmosphere

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

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

The atmosphere’s lower layer is a massive chemical reactor. Hundreds of millions of metric tonnes of hydrocarbons are converted into CO2 and water in this band each 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 synthesised and used at around -80°C. So, finding these unstable compounds as a gas in the atmosphere at much higher temperatures is surprising.

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According to modelling, about 10 million metric tonnes per year of the ROOOHs are formed in the Earth’s atmosphere through isoprene – a common organic compound which 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 through the reaction of peroxy radicals (RO2 – two oxygen atoms attached to the “rest”) with hydroxyl radicals (OH – an oxygen and hydrogen atom). Radicals such as these have unpaired outer-shell electrons, making them highly reactive.

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

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

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

The significance of the compounds’ detection is yet to be fully determined. The researchers say that further investigation is required to outline 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 determine the role of hydrotrioxides for health and the environment,” says Dr. Torsten Berndt from TROPOS.

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