Antarctica's Ozone Hole Will Fill Itself Up ?

Ozone O3 is an allotrope (variety) of oxygen, much less stable than the generally found O2, and it is responsible for protecting living organisms by preventing damaging long-wavelength ultraviolet light from reaching the Earth's surface.

But not all ozone is good.

The beneficial one is situated in the upper layer of the atmosphere, the stratosphere, but there is another type, located in the troposphere, the atmosphere's lowest layer, that, in elevated levels, has harmful effects on the respiratory systems of all animals (humans obviously included), as well as on crops and forests.

Atmospheric ozone levels are regulated primarily by local chemical processes: in the stratosphere, ozone is produced following the breakdown of molecular oxygen (O2) by short-wavelength ultraviolet sunlight--the separate oxygen atoms then recombine with another molecule of oxygen gas to form ozone. The abundance of stratospheric ozone is maintained like liquid flowing into a leaky bucket.

Ozone is continuously produced and removed by natural processes, but industrial pollutants add "new leaks to the bucket," further reducing stratospheric ozone levels.

The ozone hole over Antarctica is well known and continuously monitored.

Responsible for the majority of observed stratospheric ozone depletion are Chlorofluorocarbons (CFCs). These gases had been used as refrigerants and solvents as well as propellants in aerosol cans. Although CFCs are non-reactive in the troposphere, they can be slowly transported to the stratosphere where they break down into molecules such as chlorine monoxide (ClO) which depletes ozone by transforming it back into oxygen gas.

There are also natural causes that contribute to the lack of ozone over the South Pole: every spring over Antarctica, extremely cold conditions enable chemical reactions that produce very high levels of ClO, resulting in rapid ozone removal

Ozone production in the troposphere is much less efficient than in the stratosphere because the intensity of ultraviolet sunlight is greatly reduced. Human activities such as fossil fuel combustion and biomass burning lead to elevated levels of tropospheric carbon monoxide, nitrogen oxides and hydrogen oxides. These gases participate in a series of chemical reactions that produce ozone.

But if there's so much ozone in the troposphere, why can't it fill up the holes in the upper layer?

In the troposphere, temperature decreases with increasing altitude, allowing convection - the rapid vertical mixing of air parcels - to occur. At its border with the stratosphere, temperature begins to rise and convection essentially stops.

The absence of convection means that lower ozone can't climb to the upper layer, and although there are some ozone exchanges between the layers, unfortunately, the transfer only occurs from up to down, leading to an increase in harmful ozone in the same time as the depletion of the "good" ozone.

The good news is that, if CFC pollution ends in the very near future, the stratospheric ozone layer is expected to fully recover over the next 50 to 100 years and to fill up the existing ozone hole over Antarctica. If...