The elusive atmospheric molecule

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Sometimes, the simplest things are the hardest to find. Out there, up there, in the atmosphere, amongst the things that fly around, are things that collide with other things and make other things. Small things crash into each other and produce other small things. The layman’s way of saying chemical reactions happen. This one, the one we are concerned with is no more important than the rest, and it involves the degradation of atmospheric pollutants.

The story began over half a century ago when a German chemist, Rudolf Criegee, came up with a reaction. A reaction to which we are still trying to observe its smallest components. More than 50 years ago, he came up with a reaction that proposed that alkenes degrade by reacting with ozone to form a cyclic ozonide. Consequently, this ozonide falls apart and one product a carbonyl oxide called a Criegee intermediate.

Last year marked the first sighting of things that had — up until then — gone unseen. The simplest Criegge intermediate, CH2OO — carbon and two pairs of hydrogen and oxygen — tentatively attached to one another, destined to eventually fall apart and react with other things up there. This unique configuration of three different atoms were observed with the help of a cyclic particle accelerator — a synchrotron. Not your everyday piece of lab tech.

Criegee intermediates along with other important atmospheric elements are important as more and more we talk about climate change. And more and more we try and tease out the things up there that are relevant to our changing climate and environment. Whether the identification of the intermediate will lead to eventually finding a way to offset climate change is, at this point, speculation. The pollutants in the upper atmosphere — nitrogen dioxide and sulphur dioxide react extremely quickly with the Criegee intermediates. The story that gets bandied around is that Criegee intermediates have the potential to cool the planet by converting these pollutants into sulphate and nitrate compounds that will lead to aerosol and clouds (that to some extent will reflect solar radiation back into space and help reduce temperatures).

A recent study, published in Science, describes detection of the simplest Criegee intermediate in the gas phase using a technique much simpler and more accessible than previously. They detected the molecular fingerprint of their chemical structures. What was once unknown now left a detectable signal. Up until now not a lot was known due in part to the fact that it couldn’t be detected directly. The fact that this new method of detection uses a machine and instrumentation more widely available to researchers opens the doors up to more investigations on the Criegee intermediates exact nature.

The Criegee intermediates go back to the history of the ozone. One that has been formulating even long before Rudolf Criegee. And the story is far from over. The final numbers of the exact nature of the Criegee intermediates are still in the making. Now its reactivity with other compounds can be verified and tested — and perhaps provide more insight into its proposed “climate cooling” properties.

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