Ozone Holes and Good Intentions
As football fills weekend afternoons, players and watchers both receive reminders that yesterday's hero easily becomes today's goat. Last week's game was saved by the kicker who today misses an easy twenty-yard field goal; the quarterback whose multimillion-dollar contract seemed fair in the preseason can be the one with the most interceptions by midseason.
It can happen to scientists as much as to football players. As evidence, I offer the sad case of Thomas Midgley.
Midgley was an American chemist given an important problem in 1930 by Charles Kettering, then the chief of research for General Motors. The problem was to devise a better refrigerant for GM's Frigidaire division. Until Thomas Midgley started work, gases such as sulfur dioxide and ammonia had been used for the purpose. These gases performed adequately in heat exchangers such as refrigerators, but had major drawbacks. They were poisonous and flammable. Kettering wanted a safer substance.
It took the clever Midgley only three days to come up with Freon, the grandaddy of the chlorofluorocarbon refrigerants. He proved its safety by inhaling the stuff, then exhaling it to blow out a candle. Modern coolers, freezers, air conditioners, and refrigerators are very much the offspring of Midgley's quick work and dramatic demonstration.
Sadly for history's view of Thomas Midgley's gift to human safety and comfort, the ozone hole above the southern polar zone might also be an offspring of his discovery. Or, properly, ozone holes; the Arctic too shows a seasonal depletion, though one not yet severe enough to qualify as a hole. So far, the north polar area seems to have been protected by its pattern of atmospheric circulation, which is quite different from the pattern above Antarctica.
Chlorofluorocarbons (CFCs) are the chemicals usually blamed for depleting ozone high above Earth. The processes going on because of CFCs in the stratosphere seem to be fairly well understood, and fairly inescapable. Energy provided by ultraviolet light at those altitudes breaks a chlorine atom loose from the chlorofluorocarbon molecule. The chlorine atom grabs one oxygen atom from the three held in an ozone molecule, leaving molecular two--atom oxygen--the good old breathable stuff that doesn't block ultraviolet light. If the new one-oxygen, one-chlorine molecule encounters another lone oxygen atom, the two oxygen atoms bind, leaving the naked chlorine free to break up another ozone triad. Which it will go on doing, through decades of activity and tens of thousands of ozone molecules.
Less ozone up high means more ultraviolet light down low--right to the surface and even penetrating into the sea. That, many scientists fear, could mean trouble for everything from blue whales to penguins in the Southern Ocean. The sea life depends ultimately on phytoplankton as the basis for the food chain, and--so to speak--phytoplankton is susceptible to sunburn. (The good news is that this alarming if eventually likely effect hasn't shown up yet.)
Early on in the fuss over CFCs, some scientists found it unlikely that these useful chemicals could be causing the antarctic ozone hole. Sounding a bit like realtors, they said what matters is location, location, and location. It was hard to believe that industrial activities in the distant Northern Hemisphere, where almost all CFC manufacture and the bulk of its use takes place, could be reaching the stratosphere over Antarctica.
Yet it's fairly well understood that the planet-wide atmospheric circulation can in time bring northern surface-produced gases to the southern polar stratosphere. There is even some hard evidence that Northern Hemisphere pollution products make their way to Antarctica. An especially clear clue is the abrupt appearance of lead in the south polar snowpack after leaded gas became the fuel of choice in Europe and North America.
That happened quickly after the 1925 discovery that adding tetraethyl lead to gasoline reduced engine knocking. The chemist who made that discovery earned a secure place in the annals of science--until people realized what a huge environmental hazard leaded gas really was. The chemist was Thomas Midgley.
