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


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Cleaning Up Pollution in the Atmosphere?

Both nitrogen and sulfur dioxides (NO2 and SO2) are pollutants present in the atmosphere; they are quite toxic for humans, as they can cause irritation to the eyes and the respiratory system. Furthermore, they are responsible for the phenomenon of acid rain. In fact, when in contact with atmospheric water vapor, they can form nitric and sulfuric acids (HNO3 and H2SO4) respectively.

Considering the reactivity of CH2OO with these oxides, it can be seen how this intermediate can act as a “cleaner” of the atmosphere for these two hazardous pollutants.

CH2OO Study: Meanings and Consequences

Criegee intermediate may favor the formation of clouds and aerosols. Phot by Soil Net Home

Dr. Carl Percival, one of the researchers who took part in the study, explained the importance of this research in an interview with Decoded Science:

These results were very interesting for us, as it was the first time we were able to study the reactivity and the kinetics of a Criegee radical. CH2OO reacts very fast with NO2 and SO2; now it has to be seen if other Criegee intermediates behave in the same way or not. If they do, the implications for these processes can be very important.

The reactions of Criegee intermediates with NO2 and SO2 (oxidation) can lead to the formation of aerosol, which in turn can act as cloud condensation nuclei (CCN); this is particularly true in the case of SO2. In other words, these intermediates may favor the formation of aerosols and clouds.

The presence of more aerosols and clouds in the atmosphere can cause a decrease in its temperature, or can partially off-set the increase observed in recent years. This may indicate that natural processes are in place to counterbalance the temperature increase.

In the last 100 years, the average Earth temperature increased by 0.8oC, although there is not a full agreement on the causes of such increase (natural Earth cycle or human actions). The possibility of reducing the Earth’s temperature with the use of Criegee radicals is likely to be the subject of much future study.


Welz O. et al. Direct Kinetic Measurements of Criegee Intermediate (CH2OO) Formed by Reaction of CH2I with O2. Science. 335, 204-207 (2012). Accessed on January 17, 2012.

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