Scientists have detected a new type of extremely reactive substance in the Earth’s atmosphere that could pose a threat to human health, as well as the global climate.
Researchers from the University of Copenhagen have demonstrated that trioxides – chemical compounds with three oxygen atoms attached to each other – are formed under atmospheric conditions.
Trioxides are even more reactive than peroxides – which have two oxygen atoms attached to each other, making them highly reactive and often flammable and explosive.
Peroxides are known to exist in the air surrounding us, and it was predicted that trioxides were probably in the atmosphere as well, but until now it has never been unequivocally proven.
‘This is what we have now accomplished,’ says Professor Henrik Grum Kjærgaard, at the University of Copenhagen’s Department of Chemistry.
‘The type of compounds we discovered are unique in their structure. And, because they are extremely oxidising, they most likely bring a host of effects that we have yet to uncover.’
Scientists have detected a new type of extremely reactive substance in the Earth’s atmosphere that could pose a threat to human health, as well as the global climate
When chemical compounds are oxidised in the atmosphere, 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, thereby forming hydrotrioxides (ROOOH). Reaction: ROO + OH → ROOOH
How hydrotrioxides are formed
When chemical compounds are oxidised in the atmosphere, 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, thereby forming hydrotrioxides (ROOOH).
Reaction: ROO + OH → ROOOH
The specific trioxides they have detected – called hydrotrioxides (ROOOH) – are a completely new class of chemical compounds.
Hydrotrioxides are formed in a reaction between two types of radicals (molecules that contain at least one unpaired electron).
In laboratory experiments – using a free-jet flow tube at room temperature and a pressure of 1 bar air, combined with very sensitive mass spectrometers – the researchers demonstrated that hydrotrioxides are formed during the atmospheric decomposition of several known and widely emitted substances, including isoprene and dimethyl sulfide.
Isoprene is one of the most frequently emitted organic compounds into the atmosphere. It is produced by many plants and animals and its polymers are the main component of natural rubber.
The study shows that approximately one per cent of all isoprene released turns into hydrotrioxides.
However, the researchers expect that almost all chemical compounds will form hydrotrioxides in the atmosphere, and estimate that their lifespans range from minutes to hours.
This makes them stable enough to react with many other atmospheric compounds.
The researchers estimate that the concentrations of hydrotrioxides in the atmosphere are approximately 10 million per cubic centimetre.
In comparison, OH radicals (one of the most important oxidants in the atmosphere) are found at concentrations of about one million per cubic centimetre.
‘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,’ said Jing Chen, a PhD student at the Department of Chemistry and second author of the study.
‘All speculation must now be put to rest.’
Laboratory set-up of the free-jet flow experiment, which provided the first direct evidence that the formation of hydrotrioxides (ROOOH) also takes place under atmospheric conditions.
The research team claims that the hydrotrioxides are likely to be able to penetrate into tiny airborne particles, known as aerosols, which pose a health hazard and can lead to respiratory and cardiovascular diseases.
‘They will most likely enter aerosols, where they will form new compounds with new effects,’ said Prof Kjærgaard.
‘It is easy to imagine that new substances are formed in the aerosols that are harmful if inhaled. But further investigation is required to address these potential health effects.’
There is also a high probability that hydrotrioxides impact how many aerosols are produced, according to the researchers, which in turn has an impact on climate.
‘As sunlight is both reflected and absorbed by aerosols, this affects the Earth’s heat balance – that is, the ratio of sunlight that Earth absorbs and sends back into space,’ explained co-author and PhD. student Eva R. Kjærgaard.
‘When aerosols absorb substances, they grow and contribute to cloud formation, which affects Earth’s climate as well.’
The researchers hope that the discovery of hydrotrioxides will help scientists learn more about the effect of the chemicals we emit.
‘Most human activity leads to emission of chemical substances into the atmosphere,’ said co-author and postdoc, Kristan H. Møller.
‘So, 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 in the future.’
Prof Kjærgaard added: ‘These compounds have always been around – we just didn’t know about them.
‘But the fact that we now have evidence that the compounds are formed and live for a certain amount of time means that it is possible to study their effect more targeted and respond if they turn out to be dangerous.’
The study was published in the journal Science.
Moon may have been siphoning water from Earth’s atmosphere for billions of years
The moon may have been siphoning water from Earth’s atmosphere for billions of years, storing it up as ice deep inside craters, a new study has found.
Research by the University of Alaska Fairbanks suggests that ions making up water are pulled in by the moon as it passes through part of Earth’s magnetosphere.
This adds to other suspected methods, including bombardment from asteroids 3.5 billion years ago, and solar wind delivering oxygen and hydrogen ions.
The team estimate there are up to 840 cubic miles of surface permafrost or subsurface liquid water on the moon that escaped from Earth’s atmosphere – enough to fill North America’s Lake Huron – the eighth largest lake on the planet.
The work, by lead author, professor Gunther Kletetschka, adds to a growing body of research about water at the moon’s north and south poles, prime targets for a base.