Eli5: how can earth ozone layers heal itself even with our high pollution level?
In: 5
Only because very intricate and specific chemicals called Chlorofluorocarbons are capable of doing that. Chlorofluorocarbons were introduced as aerosols and not using them just made a lot of convenience.Not really important but it will take the Ozone in antarctica until 2066 to heal.
A lot of air pollution has been reduced, but that varies country to country. US has cleaned up a ton of air pollution.
[source](https://gispub.epa.gov/air/trendsreport/2022/)
The ozone layer is a bit of a misnomer it is just a region of the atmosphere which has a slightly higher concentration of ozone than the rest of the atmosphere, ozone is being created and destroyed all the time in the atmosphere and at ground level it is itself a pollutant. https://youtu.be/CYVzcZbhxxs
Ozone is constantly generated in the upper atmosphere by the effects of radiation, mostly short-wave UV from the sun. This UV is higher energy than the UVA and UVB that reach the Earth’s surface (and, appropriately, is called UVC in this context). That range of energy happens to be just right for it to be absorbed by oxygen molecules (O2, the regular kind of oxygen we breathe here on the ground) in the upper atmosphere.
When O2 absorbs such a UV photon, it gains a bunch of energy, enough to “kick” the two oxygens apart. That produces two separate individual oxygen atoms. O2, the bound form of oxygen, is already pretty reactive, but pure atomic oxygen is a whole other matter and is ready to party with just about any molecule. And one of the options is…well, another O2 molecule. That produces ozone (O3).
Ozone absorbs longer-wave ultraviolet than oxygen does. Without ozone, oxygen would absorb UVC, but UVB and UVA would reach the surface almost totally unabsorbed. Ozone absorbs UVB as well, reducing the amount that reaches the ground; the remaining UVB is mostly what causes sunburns and skin cancer (since it’s high enough energy to easily damage biological molecules like DNA).
Ozone is unstable, though. The reaction 2 O3 -> 3 O2 is pretty favored from a pure energy perspective, although it’s kind of slow, in the same way that, say, a boulder going from the top of a mountain to the bottom releases a lot of energy but it takes a while to get there. (Chemistry and biology students will know what I’m talking about here as *thermodynamics* versus *kinetics*.) So even though the production of ozone is slow, the breakdown is also slow, and the combination of the two leads to a steady equilibrium of ozone in the upper atmosphere…
…or it did until some bozos called humans came along.
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During the 1900s, a class of chemicals called CFCs (chlorofluorocarbons, so-named because they have chlorine, fluorine, and carbon in their structures) became common. They have some convenient properties, and they’re relatively non-toxic, and they became common in uses like aerosol cans and refrigerators. They ended up being released in moderate amounts into the atmosphere.
Normally, you’d think this wouldn’t be a problem. In the scheme of things they were a pretty mild, relatively non-toxic pollutant.
But unfortunately, CFCs have two properties that make them bad news for ozone:
* First, CFCs *catalyze* the conversion of ozone back to O2. They don’t change the energies involved, but they speed up the reaction by a huge amount. That shifts the balance of ozone and O2 strongly in the direction of O2 if CFCs are present. Ozone is still produced by the same processes that always produced it, but it’s broken down more quickly so there’s less ozone around on average.
* And second, CFCs are extremely long-lived. They take decades to break down in the atmosphere, which is long enough for them to be mixed up into the layer where the ozone layer is, and stay there for a very long time.
After decades of CFC use, researchers noticed, hey, wasn’t there an ozone layer there a minute ago? A large “hole” of much lower ozone layers began appearing, particularly near the poles (for complicated reasons, CFCs do a better job damaging ozone in colder temperatures). Everyone freaked out, [one of the most successful environmental programs ever was launched](https://en.wikipedia.org/wiki/Montreal_Protocol), and we stopped using CFCs for most applications in 1989 (today we use their non-ozone-depleting cousins the fluorocarbons; it turns out the chlorine is the problem).
But because CFCs last a loooooooooong time, CFC levels in the upper atmosphere have only just come down. Now that CFCs aren’t naturally destroying ozone anymore, ozone – which was being naturally produced all along, but was quickly destroyed by CFCs – can start to stick around for longer, and levels of ozone in the ozone layer are starting to rise back towards their natural levels. They should return to close to their original values in another few decades.
So the answer to your question is: we don’t pollute the atmosphere with the specific chemicals that destroy the ozone layer anymore. (Or at least, we pollute it with far less of them.)
Because it’s only specific pollutants that caused most of the damage to the ozone layer. Greenhouse gases like CO2 have little to no effect on ozone. The majority of the damage caused to the ozone layer came from [CFC’s](https://en.m.wikipedia.org/wiki/Chlorofluorocarbon) or Chlorofluorocarbon. When CFC’s were first introduced they were widely used as a refrigerant and in aerosols because it is easy to compress and has a very low boiling point. Aerosol cans dump out all their refrigerant when used, and Freon in air conditioners and refrigerators can leak out slowly over time. Our atmosphere naturally produces some ozone from things like lightning, so switching to other chemicals for those uses can allow for ozone to be replenished. There’s a lot of benefit to having safer chemical with really low boiling points, heat pumps can heat a home even in winter because they use a refrigerant that boils well below the outside air temp.
Ozone layer is not damaged by all pollution, only by specific chemicals that reacts with ozone in a particular, a chain reaction-like way. Majority of those chemicals aren’t pollutants from industry, but industrial chemicals that have leaked into the atmosphere due to lack of regulations and accidental discharges. Car A/C refrigerants for example.
So as long as we stop leakage of those particular chemicals (bybiposing strict controls over handling, or replacing them with different ones), ozone layer helps over time.
It is the type of pollution that affects the ozone layer that is key for this topic. We realized back in the 70’s that fluorocarbons that we produced for use in things like air conditioners or the propellants used in deodorant sprays, were actually destroying the ozone layer. It took years to put into place and develop alternatives but a concerted effort was put into place to remove these substances from products. By the early 90’s we were developing refrigerants in air conditioners and refrigeration systems that did not cause these ozone-depleting issues. Fast forward a few decades and whoa, it’s working!
It’s a very specific kind of pollution that depletes atmospheric ozone – a few types of free chlorofluorocarbons.
These “CFCs” were used as consumer-grade refrigerants and propellants in a lot of different applications up through the 1990s or so, but have since been replaced with similar compounds that have acceptably close performance but do not react with ozone.
With the target pollution greatly mitigated, the natural ozone production rate in the upper atmosphere has been able to repair the damage.
This was possible because it was a relatively cheap and easy fix to coordinate globally.
Ozone is constantly being created in the upper atmosphere when ultraviolet light from the sun interacts with molecular oxygen. The ozone layer was being damaged because we were emitting ozone depleting chemicals faster than ozone was created naturally by this process. All we had to do was stop emitting ozone-depleting chemicals (which we did) and over time, new ozone forms naturally. It’s only those specific chemicals that damage the ozone layer, not all pollution in general. Now, the ozone layer is largely replenished from its low point in the 1980’s.
The degradation of the ozone layer was caused by a very specific set of gasses that were in use in spraycans and AC units. These CFC gases are no longer being released in the atmosphere.
CO2 and other pollutants don’t affect the ozone layer.
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