Discovery of a new type of extremely reactive substance in the atmosphere

For the first time, an entirely new class of super-reactive chemical compounds has been discovered under atmospheric conditions. Researchers at the University of Copenhagen, in close collaboration with international colleagues, have documented the formation of so-called trioxides, a highly oxidizing chemical compound that likely affects both human health and our global climate.

Hydrogen peroxide is a commonly known chemical compound. All peroxides have two oxygen atoms attached to each other, which makes them highly reactive and often flammable and explosive. They are used for everything from whitening teeth and hair to cleaning wounds, and even as rocket fuel. But peroxides are also found in the atmosphere.

In recent years, there has been speculation as to whether trioxides – chemical compounds with three oxygen atoms bonded to each other, and therefore even more reactive than peroxides – are also found in the atmosphere. But so far this has never been unequivocally proven.

“That’s what we have now achieved,” says Professor Henrik Grum Kjærgaard, from the Department of Chemistry at the University of Copenhagen. Kjærgaard is the lead author of the study, which has just been published in Science. “The types of compounds we have discovered are unique in their structure. And, because they are extremely oxidative, they most likely bring about a multitude of effects that we have not yet discovered.”

Hydrotrioxides (ROOOH), as they are called, are an entirely new class of chemical compounds. Researchers from the University of Copenhagen (UCPH), along with colleagues from the Leibniz Institute for Tropospheric Research (TROPOS) and the California Institute of Technology (Caltech), have demonstrated that these compounds form under atmospheric conditions.

The researchers also showed that hydrotrioxides form during the atmospheric breakdown of several known and widely emitted substances, including isoprene and dimethyl sulfide.

“It is quite significant that we can now show, through direct observation, that these compounds actually form in the atmosphere, that they are surprisingly stable, and that they are formed from almost any chemical compound. speculation must now be put to rest,” says Jing Chen, who holds a Ph.D. student in the Department of Chemistry and second author of the study.

Hydrotrioxides are formed during a reaction between two types of radicals. Researchers expect almost all chemical compounds to form hydrotrioxides in the atmosphere and estimate their lifetimes to range from minutes to hours. This makes them stable enough to react with many other atmospheric compounds.

Likely absorbed in aerosols

The research team also believe the trioxides are able to penetrate tiny airborne particles, called aerosols, which pose a health risk and can lead to respiratory and cardiovascular disease.

“They will most likely enter aerosols, where they will form new compounds with new effects. It is easy to imagine that new substances are formed in aerosols that are harmful if inhaled. But further investigation is needed to address these potential health effects,” says Henrik Grum Kjærgaard.

Although aerosols also impact climate, they are one of the most difficult things to describe in climate models. And according to the researchers, there is a high probability that hydrotrioxides will have an impact on the number of aerosols produced.

“As sunlight is both reflected and absorbed by aerosols, this affects the Earth’s heat balance, that is, the ratio of sunlight that the Earth absorbs and reflects back into the space. When aerosols absorb substances, they expand and contribute to the formation of clouds, which affects the Earth’s climate as well,” says co-author and Ph.D. student, Eva R. Kjærgaard.

The effect of the compound needs further investigation

Researchers hope the discovery of hydrotrioxides will help us learn more about the effects of the chemicals we emit.

“Most human activities lead to the emission of chemicals into the atmosphere. Thus, knowledge of the reactions that determine atmospheric chemistry is important if we are to be able to predict how our actions will affect the atmosphere at future,” says the co-author. and postdoc, Kristan H. Møller.

However, neither he nor Henrik Grum Kjærgaard are worried about the new discovery: “These compounds have always existed, we just didn’t know about them. But the fact that we now have evidence that the compounds form and live for a period of time means that it is possible to study their effects in a more targeted way and to react if they turn out to be dangerous,” says Henrik Grum. Kjaergaard.

“The discovery suggests that there could be many other things in the air that we don’t yet know about. Indeed, the air around us is a huge tangle of complex chemical reactions. As researchers, we have to keep an open mind if we want to improve ourselves to find solutions,” concludes Jing Chen.