New type of extremely reactive substance in atmosphere

A well-known chemical compound is hydrogen peroxide. All peroxides have two oxygen atoms together, making 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 present in the air surrounding us.

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

“This is what we have now achieved,” said Professor Henrik Grum Kjærgaard from the University of Copenhagen’s Department of Chemistry. Kjærgaard is the senior author of the study, just published in the prestigious journal Science

He continues:

“The type of compounds we’ve discovered are unique in their structure. And because they’re extremely oxidizing, they’re very likely to bring a host of effects that we’ve yet to discover.”

Hydrotrioxides (ROOOH), as they are called, are a completely new class of chemical compounds. Researchers from the University of Copenhagen (UCPH), together with colleagues from the Leibniz Institute for Tropospheric Research (TROPOS) and the California Institute of Technology (Caltech), have shown that these compounds are formed under atmospheric conditions.

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

“It is very important that we can now show by direct observation that these compounds actually form in the atmosphere, that they are surprisingly stable and that they are formed from almost all chemical compounds. All speculation must now be stopped,” said Jing Chen, a PhD student in the Department of Chemistry and the study’s second author.

Hydrotrioxides are formed in a reaction between two types of radicals (see box of facts). The researchers expect that almost all chemical compounds will form hydrotrioxides in the atmosphere and estimate that their lifetimes range from minutes to hours. This makes them stable enough to react with many other atmospheric compounds.

Presumably contained in aerosol cans

The research team also strongly suspects that the trioxides can penetrate into small particles in the air, known as aerosols, which pose a health hazard and can lead to respiratory and cardiovascular diseases.

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

While aerosols also have an impact on climate, they are one of the most difficult things to describe in climate models. And according to the researchers, there is a good chance that hydrotrioxides influence the number of aerosols that are produced.

“Because sunlight is both reflected and absorbed by aerosols, it affects the Earth’s heat balance — that is, the ratio of sunlight Earth absorbs and returns to space. When aerosols take in substances, they grow and carry them.” contribute to cloud formation, which also affects the Earth’s climate,” said co-author and PhD student Eva R. Kjærgaard.

The effect of the compound needs further study

The researchers hope the discovery of hydrotrioxides will help us learn more about the effect of the chemicals we emit.

“Most human activity results in the emission of chemicals into the atmosphere. Knowledge of the reactions that determine atmospheric chemistry is therefore important if we want to be able to predict how our actions will affect the atmosphere in the future,” says co-author and postdoc, Kristan H. Møller.

However, neither he nor Henrik Grum Kjærgaard are concerned about the new discovery:

“These connections have always been there – we just didn’t know about them. But the fact that we now have evidence that the compounds are formed and live for a period of time means that it is possible to study their effect more specifically and react if they prove to be dangerous,” says Henrik Grum Kjærgaard.

“The discovery suggests there could be plenty of other things in the sky that we don’t know about yet. The air around us is indeed a huge tangle of complex chemical reactions. As researchers, we need to have an open mind if we want to get better at finding solutions,” concludes Jing Chen.


When chemical compounds in the atmosphere are oxidized, they often react with OH radicals, typically forming a new radical. When this radical reacts with oxygen, it forms a third radical called peroxide (ROO), which in turn can react with the OH radical, forming hydrotrioxides (ROOOH).

Response: ROO + OH → ROOOH


  • Isoprene is one of the most abundant organic compounds in the atmosphere. The research shows that about 1% of all released isoprene is converted into hydrotrioxides.
  • The researchers estimate that the concentrations of ROOOH in the atmosphere are about 10 million per cm . amounts3† In comparison, OH radicals, one of the major oxidants in the atmosphere, are found in about 1 million radicals per cm2.3


  • The discovery of hydrotrioxides is described in a research paper just published in the renowned journal Science.
  • While the theories behind the new research results were developed in Copenhagen, the experiments were conducted using mass spectrometry, partly at the Leibniz Institute for Tropospheric Research (TROPOS) in Germany, and partly at the California Institute of Technology (Caltech) in the United States. .
  • While many experiments have to use higher concentrations, these experiments are performed in an environment that is nearly identical to the atmosphere, making the results very reliable and comparable to the atmosphere. Measuring the hydrogen trioxides was made possible through the use of incredibly sensitive measuring instruments.
  • The study was conducted by: Torsten Berndt, Andreas Tilgner, Erik H. Hoffmann and Hartmut Hermann of the Leibniz Institute for Tropospheric Research (TROPOS); Jing Chen, Eva R. Kjærgaard, Kristian H. Møller and Henrik Grum Kjærgaard from the Department of Chemistry at the University of Copenhagen; and John D. Crounse and Paul O. Wennberg at Caltech.
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