Millions of tons of a class of extremely reactive chemicals called hydrotrioxides can linger in the atmosphere for several hours, a new study suggests — which could have implications for human health and the global climate.
The chemicals interact with other compounds extremely quickly, and their presence means that chemists will have to rethink just how processes in Earth’s atmosphere occur.
It’s long been thought that hydrotrioxides — chemical compounds that contain a hydrogen atom and three oxygen atoms — were too unstable to last long under atmospheric conditions.
But the new research shows instead that hydrotrioxides are a regular product of many common chemical reactions, and that they can stay stable enough to react with other compounds in the atmosphere.
“We showed that the lifetime of one of them was at least 20 minutes,” Henrik Grum Kjærgaard, a chemist at the University of Copenhagen, told Live Science. “So that’s long enough for them to do stuff in the atmosphere.”
Kjærgaard is one of the authors of a new study on hydrotrioxide formation in the atmosphere published online May 26 in the journal Science.
The discovery doesn’t mean that something new is happening in the atmosphere; rather, it seems that hydrotrioxides have always formed there. But the new study is the first time that the existence of these ultra-reactive chemicals in the atmosphere has been verified.
“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 all chemical compounds,” University of Copenhagen doctoral student Jing Chen, the second author of the study, said in a statement. “All speculation must now be put to rest.”
Hydrotrioxides are a type of hydrogen polyoxide. Water is the simplest and most common hydrogen polyoxide, with two hydrogen atoms and one oxygen atom, or H2O.
Another hydrogen polyoxide is hydrogen peroxide, which has two oxygen atoms — H2O2 — and is commonly used as a bleach or disinfectant. The extra oxygen atom also makes many peroxides extremely flammable, and they are sometimes used as a component of rocket fuels.
Hydrotrioxides are a stage further, as they have three oxygen atoms attached to each other, which makes them even more reactive than peroxides. They’re written chemically as ROOOH, where R is any bonded group, such as a carbon group.
But while it’s known that peroxides can form from chemical reactions in the atmosphere, it wasn’t known before now that hydrotrioxides can also form there, albeit for a relatively short time before they decompose into less reactive chemicals.
In the new study, the researchers estimate that about 11 million tons (10 million metric tons) of hydrotrioxides form in the atmosphere each year as a product of one of the most common reactions: the oxidation of isoprene, a substance produced by many plants and animals and which is the main component of natural rubber.
The researchers estimate around 1% of isoprene released into the atmosphere forms hydrotrioxides, and that they are produced from these reactions in very low concentrations — about 10 million hydrotrioxide molecules in a cubic centimeter of the atmosphere, which is only a very faint trace.
“We are super-happy that we were able to show that [hydrotrioxides] are there and that they are living long enough to be — most likely — important in the atmosphere,” study lead author Torsten Berndt, an atmospheric chemist at the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig, Germany, told Live Science in an email.
The free-jet flow set-up at TROPOS allowed the study of oxidation reactions under atmospheric conditions, revealing the presence of highly-reactive hydrotrioxides.
Berndt led the research laboratory experiments at TROPOS to discover if hydrotrioxides were in fact produced by chemical reactions in the atmosphere, while the University of Copenhagen team studied the theoretical aspects of how hydrotrioxides form.
Berndt and his colleagues used very sensitive mass spectrometry to detect the ultra-reactive hydrotrioxides — a technique that can determine the molecular weight of chemicals to find out what atoms they consist of.
The reactions to make the hydrotrioxides took place in the TROPOS free-jet flow system which creates a flow of air unobstructed by solid boundaries.
And the study also used the results of experiments in an atmospheric chamber at the California Institute of Technology at Pasadena.
Now that their research has confirmed that hydrotrioxides are formed by common chemical reactions in the atmosphere, the scientists will next investigate how the compounds might affect human health and the environment during the minutes or hours of activity before the compounds decompose, Berndt said.
“From the knowledge of organic chemistry, we can expect that [hydrotrioxides] will act as an oxidant in the atmosphere,” he said. It’s also possible that hydrotrioxides could have an effect when our lungs breathe in air that contains them in very low concentrations, “but this is all very speculative at the moment.”
Berndt said hydrotrioxides could also penetrate atmospheric aerosols — very fine solid particles or liquid droplets suspended in the atmosphere, such as the ash from volcanic eruptions or the soot from large fires — and they might initiate chemical reactions there. But “experimental investigations on that are very challenging,” he said. “It’s a lot to do.”
Space, 3 June 2022