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22/11/2014

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CSI: The Atmosphere

CSI: The Atmosphere

Crime committed

Holes have been punched in our Ozone layer; a layer of highly concentrated O3 in the Earth’s stratosphere.

Time of crime committed

Holes were first detected in 1974 and their size has been increasing ever since.

Names of those involved

Thomas Midgley Jr.: scientist and inventor of Chlorofluorocarbon (CFC) synthesis in the1920’s.

James Lovelock: first to detect CFCs in atmosphere in 1973 using electron capture. Concluded they were not harmful.

Prof Frank Rowland and his post-doctoral student Mario Molina: proved James Lovelock wrong in 1974; showed the long lifetime of CFCs caused devastating effect on the ozone layer. CFCs were shown to have a lifespan of more than 100 years.

Details of the scene

Since first detection, the level of CFCs in the upper atmosphere has been increasing. CFCs are dissociated by ultraviolet light, releasing chlorine atoms. These atoms break down the ozone, creating large holes. Recovery time can be decades due to longevity of CFCs.

Consequences

One of the principle jobs of the ozone layer is to absorb the harmful UVB rays that come from the Sun. When holes are formed, these rays can pass through, and it has been predicted that this could potentially increase the incidence numbers of skin cancer. This has not yet been proven, as the ozone depletion above populated areas has only been a few percent.

Principle Investigators

Atmospheric and forensic chemists

The above crime scene depicts the very basic principles going on behind the depletion of the ozone layer in our atmosphere caused by CFCs. But it is not just CFCs that have been rendered harmful.

Atmospheric chemists like Dr Johannes Laube are tracking down other potentially damaging molecules, and trying to work out how they affect our atmosphere, what problems they cause and how to reduce the adverse effects.

“We first have to separate the trace gases from the main components of the air using extraction techniques. We then have to separate them from each other and do that using gas chromatography. Finally we mainly use different variants of mass spectrometers to detect them.”

Many strong greenhouse gasses, much stronger than CO2, have been detected in this way. “They can be thousands of times more powerful than CO2 so you don't need much of them to cause the atmosphere to heat up quicker. In fact, more than 20 % of the man-made greenhouse effect is currently believed to be caused by halogenated greenhouse gases... , their decomposition in the atmosphere can produce compounds that are toxic to ecosystems such as trifluoroacetic acid… some of those compounds start to be toxic to humans at concentrations of a few parts in a million air parts. This can happen when their concentrations build up locally e.g. in confined spaces when somebody gets close to where plastics are heated or burned.”

Working out how to minimise the impact that they have on both the atmosphere and our health is difficult. “Predicting the future has always been a risky business… but knowledge of potential threats is a good start.”

Join Dr Laube, along with Dr Eva Krupp and Professor Roy Harrison on Wednesday September 5th at 10am in the Fraser Noble Building as they discuss the impact of airborne particular matter, and how it could affect our atmosphere and public health.

Join the debate...
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