Remember aerosol hairspray? Along with blue eye shadow, it was a beauty regimen staple in the 1970s. Across the nation, women and girls were spraying with abandon to keep their feathered Farrah Fawcett flips in place. But it all came to a halt in 1978, when the United States government banned the use of chlorofluorocarbons (CFCs), the propellant that was used in aerosol cans. In an announcement that shocked the world, scientists told us that CFCs were causing the formation of a massive hole in the ozone layer.
“It’s still there,” says Anne Thompson, a Penn State professor of meteorology and director of the Center for Environmental Chemistry and Geochemistry. “Despite government intervention and industry cooperation, the size of the hole has not diminished since it was discovered,” she says, “but it hasn’t grown either and that’s key.”
Forming a thin layer in the stratosphere 10 miles above the Earth’s surface and ending roughly 50 miles above, ozone—a naturally-occurring form of oxygen—provides us crucial protection by filtering the Sun’s dangerous ultraviolet (UV) rays.
Notes Thompson, ozone (O3) is nothing more than an oxygen molecule (O2) that has gained an extra oxygen atom. When an oxygen molecule is shaken up by a powerful force—for instance, the electrical charge present in lightning or a waterfall, or the energy in UV light—its two atoms can be jolted apart. Desperate to reconnect, the best a lone oxygen atom can do is to latch onto any nearby intact oxygen molecule, creating the tri-part molecule we know as ozone.
But this bond is weak, and as soon as ozone passes near either a single oxygen atom or another ozone molecule, the extra atom jumps ship and recombines into a “normal” oxygen pair. What we know as “the ozone layer” is an upper-atmospheric region where billions of these back-and-forth chemical reactions are happening all the time.
CFCs—which were used not only as propellants in aerosol cans but also as refrigerants called Freon—destroy ozone molecules by “stealing” their oxygen atoms. More precisely, CFCs’ chlorine atoms bind with ozone’s oxygen atoms, effectively ripping the ozone molecules apart.
The widespread use of CFCs, then, weakened the ozone layer, creating a “hole” in our protection where the ozone is at its thinnest. (It’s not technically a hole, Thompson explains—but a region of depletion between 10 and 15 miles, in the lower stratosphere.) Each September, that hole reappears over Antarctica, where cold conditions and the return of Spring sunlight help chlorine atoms to bond with oxygen atoms. The annual seasonal depletion amounts to two-thirds of the ozone layer over the southernmost continent.
If CFC use had continued unabated, scientists say, today’s hole would be much larger than that. In 1987, however, following the United States’ lead, every country in the United Nations signed the Montreal Protocol, a pact to phase out CFCs over time. And in 2007, some 200 countries agreed to accelerate the elimination of CFCs entirely by 2020 (developing nations were given until 2030). The Protocol has worked as all nations took action. “The amount of CFCs peaked at the earth’s surface about 10 years ago but in the stratosphere they are declining more slowly,” states Thompson. As a result, models now predict that global ozone will return to 1950s levels by around 2070.
“The Montreal Protocol is one of the greatest success stories of international cooperation of all time,” says Thompson. “There was consensus science based on international assessments starting in the late 1970’s and there was acceptance of the science,” she adds. “We acted fast and we continue to assess the situation. Every 4 years a new assessment comes out and new data from ground stations, balloons and satellites are studied carefully. Models are updated with this information so we have confidence in the predictions of ozone hole ‘recovery.’ Now if only we can do the same for global warming…”
Sara LaJeunesse, Research Penn State