Leading Edge / Winter 2008
Something in the Air

An international research team has found traces of phosgene in the atmosphere


There’s been a lot of discussion about man made gases in the atmosphere wreaking havoc on the Earth, but this one is a killer. Literally.

Allied and Central powers used phosgene as a chemical warfare agent in the First World War. But a University of Toronto project has found the deadly gas in our atmosphere as a result of human industry.

Phosgene is produced when chlorocarbons, a chemical relative of CFCs, break down in the upper atmosphere. On the ground, chlorocarbons are non-reactive strings of carbon and chlorine. They are used in the production of pharmaceuticals and insecticides and are even found in dry-cleaning fluid. But, when those chlorocarbons reach the stratosphere, ultraviolet light breaks them down into highly reactive smaller molecules. Not only do these molecules turn into nasty chemical gases, but they also contribute to the destruction of the ozone layer.

Dr. Kaley Walker, an assistant professor of physics at U of T, was part of an international team of researchers (from the University of Waterloo, the University of York in the UK, NASA’s Jet Propulsion Laboratory and the New Mexico Institute of Mining and Technology) that used the Canadian Atmospheric Chemistry Experiment satellite to measure worldwide concentrations of the gas for the first time. Their research, published recently in Geophysical Research Letters, shows that concentrations of phosgene are highest around the equator where the greatest amount of UV radiation hits.

The team also found that phosgene concentrations have steadily declined since the Montreal Protocol, which banned many varieties of CFCs, chlorocarbons and other ozone destroyers, was signed 20 years ago. (The researchers compared their worldwide measurements to isolated assessments from decades earlier, as well as the last few years.) International delegates met in Montreal on the 20th birthday of the Montreal Protocol this past September, and agreed to more stringent target dates for banning the final ozone-destroying compounds.

Although phosgene is harmful, the levels the researchers found in the atmosphere are at least 10,000 times less than what is considered an acceptable exposure for humans. The work was funded by the Canadian Space Agency and the Natural Sciences and Engineering Research Council of Canada.


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