Criegee Intermediates: Newly Detected Molecules Having Beneficial Effects on the Atmosphere

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Criegee intermediates may have a beneficial effect on the atmosphere. Photo by Jason Dunn

Could we actually lower the temperature of our atmosphere with a Criegee radical?

The detection of a Criegee radical (CH2OO) was reported in a paper published in Science in January 2012. The molecule shows a very high reactivity towards atmospheric pollutants such as sulfur and nitrogen dioxides. The reactions between CH2OO and these oxides could help to lower the temperature of Earth’s atmosphere.

Criegee Intermediates: What Are They?

Criegee intermediates are a chemical species formed during the reaction of unsaturated hydrocarbons with ozone (O3). These hydrocarbons can come from various sources, the main one being bio-organisms, such as plants. The intermediates can have different formulas, depending on the reactions they were formed from; all of them have the characteristic carbonyl group C=O.

Criegee intermediates are radicals (i.e. they have one or more unpaired electrons). This makes them very unstable; therefore, they tend to react and/or transform into more stable molecules as soon as they are formed.

Although there was much indirect evidence of their existence, it was impossible to isolate them and measure them directly, due to their instability and very short existence time.

Criegee Intermediates: Recent Experiments

A study on the detection and the reactivity of Criegee intermediates was performed recently as a joint project by the School of Earth, Atmospheric and Environmental Sciences (University of Manchester, UK), the School of Chemistry  (University of Bristol, UK) and the Combustion Research Facility (Sandia National Laboratories, US).

The researchers involved in this work were able to detect directly a Criegee intermediate; more exactly, they measured CH2OO, the intermediate from the reaction between iodo-methyl-radical CH2I with molecular oxygen O2.

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