Free Radicals - Michael Brooks [100]
Locking himself away in the laboratory he had built in the garden of his Wiltshire home, Lovelock set about building the most sensitive CFC sniffer the world had ever seen. He called it the electron capture gas chromatograph, and by the time he had finished it, it was sensitive enough to detect concentrations of atmospheric CFC equivalent to a single drop of water in a swimming pool. Ironically, it was so sensitive that he had to make his family stop using products that contained CFCs because they were interfering with his preliminary test results.
When the instrument was ready for service in the wider world, Lovelock booked a passage on the research vessel RRS Shackleton, which was making a return voyage to the Antarctic. All the way there and back, he took measurements of the concentrations of CFC in the atmosphere.
After his return, Lovelock attended a conference where he chatted over coffee with a scientist from DuPont, the principal manufacturer of CFCs. Together, the two men idly observed that Lovelock’s measurements of the total amount of CFC molecules in the atmosphere tallied almost exactly with the total worldwide production to date. They thought it an interesting coincidence, but nothing more than that. Eventually, though, a chemist called Sherwood Rowland came across this little nugget of information. And he thought it was astonishing.
The news that all the CFCs that had ever been manufactured were still in the atmosphere gave Rowland an idea for a research project. He knew that the CFC molecules would be stable in the lower atmosphere, but he also knew that they would eventually rise into higher layers of the atmosphere and become exposed to increasing levels of solar radiation. This, he reasoned, would break the molecules down into their constituent parts. But what would happen after that? Mario Molina, who was working as a postdoctoral researcher in Rowland’s lab, decided that he would be the person to find out. And by Christmas 1973, the full horror of the situation had become clear.
Molina found that the CFCs would take a few decades to reach the stratosphere, the atmospheric layer that sits between 10 and 30 miles above the Earth’s surface. Once they arrived there, solar radiation would break them apart, releasing free chlorine atoms. And these chlorine atoms would wreak havoc on the ozone layer.
Ozone is a molecule composed of three oxygen atoms (an ordinary molecule of oxygen contains two). There isn’t much of it in the atmosphere. What there is is all in the stratosphere, in extremely low concentrations. If you compressed it all together, the ozone would blanket the Earth’s surface in a layer no thicker than tissue paper.
Nevertheless, it does an important job. Ozone absorbs ultra-violet light, shielding the Earth’s surface from the harshest of the Sun’s rays. Thanks to the ozone layer, we are protected from radiation that induces skin cancer and blindness. According to the World Health Organization, if CFC production had carried on unchecked, the ensuing depletion of the Earth’s ozone layer would have caused an extra 500 million cases of skin cancer per year by 2050. Ten years on from that, the figures would have tripled. It is clear that destroying the Earth’s ozone would have serious effects on the human race. And it was clear to Molina in 1973 that CFCs would eventually cause such destruction.
The ozone molecule is unstable; oxygen is much more stable as a molecule when composed of the usual two atoms. Free chlorine atoms, released from CFCs by solar radiation, would easily knock that extra oxygen atom from an ozone molecule. Together they would form chlorine monoxide, one of the highly dangerous molecules that chemists know as free radicals. Free radicals have a spare, reactive electron in their chemical make-up, and that makes them hungry for something to react with. In the stratosphere, chlorine monoxide would greedily mop up any free oxygen atom, forming