# Could ozone be used in a biodome on Mars?

How much ozone would it take to block solar radiation on Mars if chambered in double panned glass or material? Said $O_3$ would break down from the UV. Would applied electricity on $O$ and $O_2$ make $O_3$ again? Glass weighs to much and is not an option unless it is made on Mars. I propose gas because it doesn't brake down like UV film can.

Could a blimp house an entire colony on Mars?

Can air pressure be accumulated this way for a biodome or spacesuit?

• You can't block with anything resembling pure ozone, the UV would rapidly tear it up. You need a small amount of ozone mixed with lots of oxygen so when an ozone is split up the loose O attaches to another O2, not an O3. Apr 3 '18 at 1:14
• The frequencies that ozone blocks are, as @peterh has already said, easily blocked by window glass or many other things. The types of solar radiation that people designing Mars colonies are worried about are different, and Earth is protected from them by its magnetic field, not by ozone. Apr 3 '18 at 6:32
• @SteveLinton because there are other forms of radiation does not mean that "people designing Mars colonies" are not worried about UV. One does not necessarily exclude the other. The part about some kinds of glass or polymers, but not others is of course true. Not all glass will safely block UV. See Berlin’s renovated Tropenhaus botanical garden uses special UV-transmissible glass or just its plot: i.stack.imgur.com/J2yf2.jpg
– uhoh
Apr 3 '18 at 8:11
• @LorenPechtel I updated my question making your comment not applicable. Electricity can be used to make $O_3$
– Muze
Apr 7 '18 at 3:59

If we have $O_2$ lighted with UV, we have actually many reactions working together:

1. $O_2 + \gamma \rightarrow 2O$
2. $O_2 + O \rightarrow O_3$
3. $O_3 + \gamma \rightarrow O_2 + O$
4. $O + O_3 \rightarrow 2 O_2$
5. $O_3 + O_3 \rightarrow 3O_2$
6. $O + O \rightarrow O_2$

(1) produces nascent oxygen. This is slow, and its speed depends on the UV concentration.

(2) builds ozone from nascent oxygen. This is fast.

(3) means the decay of ozone to normal oxygen and nascent oxygen. This can be done very easily with UV light (it has a very big cross-section).

(4), (5) and (6) results the decay of ozone (or nascent oxygen) back to normal oxygen. All of them require that multiple $O$ or $O_3$ molecules need to meet. Thus, it can happen quickly only if there is a high partial ozone pressure.

The net result is that if you light $O_2$ with UV, you get an equilibrial concentration of $O$ and $O_3$ as well. If start with all of ozone, or without a single ozone molecula, the ozone concentration will decay because (4)-(6), or it will be built up because (1), until it reaches this equilibrial concentration. This equilibric concentration will depend on the UV intensity.

(2) and (3) doesn't affect.

Without it, the $O_3$ and $O + O_2$ states will only step into eachother, meanwhile they will eat up a lot of UV radiation. But it can work only if there is a lot of $O_2$ as well.

On the Earth, even in the ionosphere, the ozone concentration is very low: it is roughly 1:100000, and it is between roughly 20 and 30 km. (There are big differences here, for example there is far lesser ozone on the south pole.)

A quick calculation: the pressure of the air decreases to half with around every 5 km elevation. Thus, at 20km high, the pressure is around 1/16 atm. On 30km, it is around 1/64 atm. Calculating with a mean of 1/32, and 10km high, we can compress it to 1atm and 300m height. This calculation is un-exact, but there is no magnitudal differences.

Thus, we would need around a 300m high layer of pure oxygen to get the same UV defense as we have on the Earth.

Remark: a single glass window has a better UV defense as this ozone layer would have, this is why light-skinned people don't get tanned or burned behind them.

Thus, the best UV defense of this biodom would be if it would have simply glass walls. Beside that, there is no ozone layer needed.

• Thanks, light-skinned or light-complected are probably both fine. To me "light-skinned" reminds me of "thin-skinned", whereas complexion is a more specific and neutral word.
– uhoh
Apr 3 '18 at 5:57
• This is a super answer by the way! The chemistry of the ozone layer is complicated, kudos for taking it on an doing a great job!
– uhoh
Apr 3 '18 at 6:00
• Not all glass will safely block UV. See Berlin’s renovated Tropenhaus botanical garden uses special UV-transmissible glass or consider adding the image from that link: i.stack.imgur.com/J2yf2.jpg
– uhoh
Apr 3 '18 at 8:09
• uhoh - I don't think adding a link referring to a specialist glass made to explicitly not block UV is at all relevant here. Apr 3 '18 at 8:34
• It's a short comment, about glass, meant to be helpful, and can easily be ignored or remembered depending on level of interest. I've moved the comments to a chat
– uhoh
Apr 3 '18 at 11:18

The ozone layer of Earth is about 10 km high. A layer of ozone of some meters will not block UV light. Using high pressure ozone would require very heavy domes. A thin AND efficient filter for UV light is needed.

• What if the gas was electrified like a Faraday cage then would it block better?
– Muze
Apr 4 '18 at 17:35
• @Muze What means here "electrified"? Ionized? Faraday-cage mainly doesn't ionize gases. Apr 5 '18 at 13:24
• @peterh Sorry how would you say apply electricity like a neon bulb to the gas?
– Muze
Apr 5 '18 at 15:33
• @Muze It is not Faraday cage, there is an electric arc which ionises the gas (continuously gets away the electrons from the atoms). You get the light as the electrons find an ion and become atoms again (recombination). In such a light bulb, a part of the gas is plasma. Plasma reacts typically much better with any light, so it could be an UV shader, in theory. In practice, I think it is very likely that nothing can stand to compete with a 3mm thick, static glass wall. Apr 5 '18 at 16:49
• @peterh as stated before unless the special glass can be made on Mars using rubber to house the gas for a biodome would much weigh less. There is no such devise and the Faraday cage is the closest devise I could compare it to. Thanks for helping +++1
– Muze
Apr 5 '18 at 22:17