Will the Ozone Layer Recover? Can We Make More Ozone?
The answers are: yes, assuming full compliance with the Montreal Protocol, and no. It makes sense to explore the questions in reverse order, but understanding either answer requires some basic facts about how ozone levels remain relatively constant and what ozone depletion means. In this discussion, we are mainly concerned with global ozone depletion, as opposed to what happens during the annual Antarctic ozone hole .
Ozone molecules are constantly being produced and destroyed by different types of ultraviolet light from the sun. Normally, the production and destruction balances, so the amount of ozone at any given time is pretty stable. Think of the amount of ozone as the water level in a bucket with a small hole in the bottom and a hose adding water at the top. When you turn on the water, you'll find a balance point where the amount of water in the bucket stays constant, even though the hose is adding water and the hole is removing it. The addition and removal are happening at the same rate, so the water level stays the same. Note that the hole in the bucket is not analogous to the Antarctic ozone hole; the ozone hole is an area of severe depletion, but it is not a physical hole that drains away ozone.
Now pour in a glass of water. You'll see that the water just drains faster for a little while until the level returns to the previous depth. The balance is stable. That's because with more water in the sink, there's more pressure at the bottom, and the water drains faster. In the same way, if you dump more ozone into the ozone layer, the destruction process will speed up a little bit until the amount of ozone returns to the stable point.
The other difficulty with simply manufacturing ozone is that the sun provides huge amounts of energy for the ozone production process. In fact, to produce the amount of ozone normally in the ozone layer, you'd have to use about double the total annual U.S. electricity production. There's simply no way we could create ozone fast enough, in large enough quantities, to replace the natural ozone production process.
The issue with ozone-depleting substances is that they add chlorine and bromine to the ozone layer, which effectively widens the hole. Thus, the stable point is lower than it used to be; this lowering of the stable point represents ozone depletion. Since we can't make more ozone, the solution is to reduce the hole in the bucket back to its natural size. The only way to do that is to remove the excess chlorine and bromine from the stratosphere. And the only way to do that is to stop making CFCs and several other chemicals. Although several other measures have been proposed to accelerate the removal of chlorine and bromine from the stratosphere, none has proven to be practical, and most could produce unwanted side effects that are not understood very well.
Over time, stratospheric chlorine and bromine will combine with other chemicals and eventually fall back to Earth. That's the point of ending production of these chemicals under the Montreal Protocol and the Clean Air Act. The good news is that the stability works both ways. In our bucket, narrowing the hole allows the water inside to rise to a higher stable point. Similarly, by ending production of ozone depleters, we allow natural processes to remove excess chlorine and bromine, which slows the ozone destruction reactions to normal speeds, and the production process will have the chance to restore the ozone layer to normal levels. Scientists expect that with full compliance with the Montreal Protocol, the ozone layer will heal by about 2050.