Angewandte Chemie International Edition
Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2001, 40 (10), 1938-1941
Laughing Gas in a Vicious Circle
Italian researchers discover
another mechanism for the formation
of atmospheric N2O
Summer smog, the ozone hole, the greenhouse effect - the complex web of chemical reactions in the atmosphere, which leads to manifold environmental problems, is still not fully cleared up. In a tricky way, a single chemical compound is found at the center of the action: laughing gas (N2O). A group of Italian chemists working with Giulia de Petris at the University La Sapienza in Rome has now discovered an important mechanism by which laughing gas is formed in the atmosphere.
Laughing gas sounds like a nice, harmless substance. In humans, the slightly sweet-smelling gas is completely safe if properly handled. It is used as an anesthetic as well as for making whipped cream. Unfortunately it is also used as a party drug because it can cause convulsive laughter - hence the name - and a high when inhaled.
In our atmosphere, dinitrogen monoxide, as N2O is known to chemists, shows its unfriendly side; it acts as a greenhouse gas and is the main source of nitrogen oxides (NOx) in the upper layers of the atmosphere, the stratosphere. Nitrogen oxides also contribute to the greenhouse effect. On top of this, the reaction that converts laughing gas to nitrogen oxides destroys the ozone layer. The nitrogen oxides then also go on to contribute to the formation of the ozone hole. But how does laughing gas get into the atmosphere? The main route is through microbial decomposition of nitrogen-containing compounds in the soil, especially upon heavy fertilization with nitrogen-containing fertilizers. It is also a byproduct of combustion processes.
Additionally, De Petris and coworkers have discovered another important, completely different mechanism for the formation of laughing gas. They generated electrically charged ozone molecules and mixed them with nitrogen. This caused an adduct of the two compounds to form, which then decomposed to form N2O and dioxygen.
Charged ozone particles are formed in the atmosphere when ozone-enriched air is electrically charged. Sufficiently high voltages occur in the vicinity of power-lines and during thunderstorms. This thus closes the circle: Under summer smog conditions, nitrogen oxides from emissions form ozone. This ground-level ozone is then responsible for the formation of laughing gas, which then destroys the ozone layer in the stratosphere while making more nitrogen oxides.