# Persistence time of ozone

Ozone is formed in the upper atmosphere by ultraviolet light, and broken down by ultraviolet, spontaneous reactions and artificial pollutants among other things.

Suppose there were no artificial pollutants, and the sun was magically replaced with a giant heat lamp that put out no ultraviolet but kept the current temperature, how long would it take for the ozone to decay of its own accord or by reacting with natural pollutants?

The accepted answer for the other question is three days. That's wildly inconsistent with everything else I've heard said about ozone depletion taking years to recover. Maybe that's because the other question asks about ozone released near sea level, and I'm asking about ozone in the stratosphere?

• The answer differs widely between troposphere and stratosphere. Which one are you interested in? – gerrit Apr 18 '17 at 13:49
• @gerrit Stratosphere. – rwallace Apr 19 '17 at 15:50
• Possible duplicate of Ozone gas (O₃) endurance in the atmosphere – Harish Oct 9 '17 at 12:07
• This is not a duplicate - the other question asks about the real world, wheras this one is interested in a fantasy. It's arguable whether or not it's on-topic here, but it's not a dupe :-) – Semidiurnal Simon Oct 9 '17 at 12:48
• Some comments to 'natural' and 'artificial' pollutants. Maybe you can edit your question. Human-made pollutants are commonly denoted as 'anthropogenic pollutants -- which you probably mean with 'artificial pollutants'. Most pollutants are of anthropogenic origin (exceptions are emissions from forest fires and from volcano eruptions; and heavy metals in water). I would even more guess, that all pollutants reaching the ozone layer and depleting it are of anthropogenic origin. But I am not 100% sure. – daniel.heydebreck Oct 9 '17 at 17:01

Let's first consider the scenario in the absence of free radicals that can act as catalysts of $O_3$ destruction. In such scenario, added to the absence of UV radiation, the photolysis of ozone ($O_3 + UV → O_2 + O$) would not be possible. Therefore, the only way to destroy ozone would be by the reaction

$O_3 + O· → 2 O_2$

But the lack of UV radiation would also stop the production of atomic oxygen by photolysis, therefore only the preexisting atomic oxygen would be available for that reaction. Then, for simplicity we can consider two extreme scenarios:

1. All the atomic Oxygen forms $O_2$ and the Ozone level remains constant at the same level it has prior to the shut down of UV radiation.
2. All the atomic Oxygen is used to destroy Ozone

In the second scenario the final concentration of $O_3$ will depend on the initial concentration of it and atomic oxygen. But as seen in the following image, the stratospheric concentration of atomic oxygen is much lower than the one of $O_3$, therefore the ozone levels would never fall to zero.

(Figure taken from here)

Let's now consider the more realistic case, on which there are other "polutants" that can break down ozone. The moste common ones are hydroxyl radical (OH·), nitric oxide radical (NO·), chlorine radical (Cl·) and bromine radical (Br·) (source), and the first two are the only ones naturally occurring. Therefore, the ozone remaining from our first scenario would be reduced to zero by reactions like:

$OH + O_3 → {HO}_2 + O_2$

or

${NO}_2 + O_3 → {NO}_3 + O_2$

Among others.

The exact time that will take will depend on the elevation, as the abundance of ozone as well as the radicals can vary orders of magnitude trough the stratosphere. It will also depend on the exact spectrum of your "sustitute Sun", as some of those reactions are also mediated by light and might not happen in the absence of light of the right wavelength.

I know this answer might be disappointing, as it seem that a model would need to be run to really say how long it would take to destroy all stratospheric ozone. But still I thought would be an informative answer after 11 month without one. I hope, it motivate a better answer or the improvement of this one.

• Solid answer and I think with the uncertainties, a better answer might be impossible. I'd add that there is some mixing as well. The stratosphere is mostly still, but there's still some atmospheric mixing between stratosphere and troposphere, and once in the troposphere, Ozone would deplete fairly quickly. Mixing might deplete the Ozone faster than stratospheric chemical processes (not counting catalysts, of-course). – userLTK Mar 23 '18 at 4:29