An entirely new class of superreactive chemical compounds, trioxides, has been discovered under atmospheric conditions.
For the first time, a completely new class of superreactive chemical compounds has been found under atmospheric conditions. Scientists at the University of Copenhagen, in close collaboration with international colleagues, have documented the formation of so-called trioxides, an extremely oxidizing chemical compound that is likely to affect both human health and our global climate.
Hydrogen peroxide is a commonly known chemical compound. Because all peroxides have two oxygen atoms joined together, they are highly reactive and often combustible and explosive. They are used for everything from whitening teeth and hair, to cleaning wounds and even as rocket fuel. However, peroxides are also found in the air around us.
It has been speculated in recent years whether trioxides, chemical compounds with three oxygen atoms attached to each other and therefore even more reactive than peroxides, are also found in the atmosphere. But until now, it had never been unequivocally proven.
“This is what we have achieved now,” says Professor Henrik Grum Kjærgaard of the Department of Chemistry at the University of Copenhagen. Kjærgaard is the lead author of the study, published on May 26, 2022 in the prestigious journal Science.
Professor Henrik Grum Kjærgaard in the laboratory. Credit: University of Copenhagen
He continues:
“The type of compounds we discovered are unique in their structure. And because they are extremely oxidizing, they probably have a number of effects that we have yet to discover.”
Hydroxy oxides (ROOOH), as they are known, are a completely new class of chemical compounds. Researchers at the University of Copenhagen (UCPH), along with colleagues at the Leibniz Tropospheric Research Institute (TROPOS) and the California Institute of Technology (Caltech), have shown that these compounds form under atmospheric conditions.
Reaction: ROO + OH → ROOOH (red oxygen atoms). When chemical compounds oxidize in the atmosphere, they often react with OH radicals, usually 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 hydrotoxides (ROOOH). Credit: University of Copenhagen
Researchers have also shown that hydrotrioxides form during the atmospheric decomposition of several known and widely emitted substances, such as isoprene and dimethyl sulfide.
“It is quite significant that we can now show, by direct observation, that these compounds are actually formed in the atmosphere, that they are surprisingly stable, and that they are formed from almost all chemical compounds. to all speculations, ”says Jing Chen, a doctoral student in the Department of Chemistry and second author of the study.
Just how much
- Isoprene is one of the most frequently released organic compounds in the atmosphere. The study shows that approximately 1% of all isoprene released is converted to hydrotrioxides.
- Researchers estimate that ROOOH concentrations in the atmosphere are about 10 million cm3. In comparison, OH radicals, one of the most important oxidants in the atmosphere, are found in approximately 1 million radicals per cm3.
Hydrothyroxides are formed in a reaction between two types of radicals (see illustration below). Researchers expect that almost all chemical compounds form hydrotoxides in the atmosphere and estimate that their useful life ranges from minutes to hours. This makes them stable enough to react with many other atmospheric compounds.
It is presumably absorbed into aerosols
The research team also has trioxides under strong suspicion of being able to penetrate small particles in the air, known as aerosols, which pose a health hazard and can cause respiratory and cardiovascular disease.
“They will probably 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 more research is needed to address these possible health effects,” says Henrik Grum Kjærgaard .
While aerosols also have an impact on the climate, they are one of the hardest things to describe in climate models. And according to researchers, there is a high probability that hydrotrioxides will affect how many aerosols are produced.
Laboratory assembly of the free flow experiment at TROPOS in Leipzig, with this direct evidence for the first time that the formation of hydrotrioxides (ROOOH) also takes place under atmospheric conditions from the reaction of peroxy (RO2) radicals with radicals hydroxyl (OH). Credit: Tilo Arnhold, TROPOS
“Because sunlight is reflected and absorbed by aerosols, it affects the Earth’s thermal equilibrium, that is, the proportion of sunlight that the Earth absorbs and sends back into space. When aerosols absorb substances , they grow and contribute to the formation of clouds, which also affects the Earth ‘s climate, “says the co – author and PhD. student, Eva R. Kjærgaard.
The effect of the compound needs to be further studied
Researchers hope that the discovery of hydrotrioxides will help us learn more about the effect of the chemicals we emit.
“Most human activity leads to the emission of chemicals into the atmosphere. Therefore, knowledge of the reactions that determine atmospheric chemistry is important if we want to predict how our actions will affect the atmosphere in the future. says co-author and postdoctoral fellow Kristan H. Møller.
Until now, there was only speculation about hydrotryoxides (ROOOH), that these organic compounds would exist with the unusual group OOOH. In laboratory experiments at TROPOS in Leipzig, its formation during the oxidation of important hydrocarbons, such as isoprene and alpha-pinene, could now be clearly demonstrated. Credit: Tilo Arnhold, TROPOS
However, neither he nor Henrik Grum Kjærgaard are concerned about the new discovery:
“These compounds have always existed; we just didn’t know them. But the fact that we now have evidence that compounds form and live for a while means that it’s possible to study their effect more specifically and respond if they’re dangerous,” he says. Henrik Grum Kjærgaard.
“The discovery suggests that there may be many other things in the air that we don’t know yet. In fact, the air around us is a huge envelope of complex chemical reactions. As researchers, we need to keep an open mind if we want to improve when it comes to finding solutions, “concludes Jing Chen.
Reference: “Hydrotrioxide Formation (ROOOH) in the Atmosphere” by Torsten Berndt, Jing Chen, Eva R. Kjærgaard, Kristian H. Møller, Andreas Tilgner, Erik H. Hoffmann, Hartmut Herrmann, John D. Crounse, Paul O Wennberg and Henrik G. Kjaergaard, May 26, 2022, Science.DOI: 10.1126 / science.abn6012
About the study
- Although the theories behind the new research results were developed in Copenhagen, the experiments were carried out by mass spectrometry, partly at the Leibniz Institute for Tropospheric Research (TROPOS) in Germany, and partly in the California Institute of Technology (Caltech) in the United States. .
- Although higher concentrations must be used in many experiments, these experiments are performed in an environment almost identical to the atmosphere, which makes the results very reliable and comparable to the atmosphere. Hydrotoxide measurement was made possible by 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; and John D. Crounse and Paul O. Wennberg at Caltech.