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I read an article by popsci that talked about huge fans forcing methane over a catalyst.

Now that got me wondering, can't we produce hydroxyl radicals with powerfull uv lasers blasting the sky, creating more hydroxyl radicals to break down the methane.

Would this be effective enough to help create enough hydroxyl radicals to help break down methane or would it be a waste of energy against too small an offset?

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    $\begingroup$ It's kinda mean to insta-fry unsuspecting birds and bats. ;-) $\endgroup$ – Karl Aug 18 '19 at 13:29
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    $\begingroup$ Arising questions: a) How much methane is in the atmosphere, b) how effective is a hydroxyl radical in destroying methane, c) how effectively can we produce them, d) can we actually increase the local concentration, e) how long does the effect last, f) does it make sense to e.g. increase the concentration overnight? If you have all that info, it's easy to put the numbers together and make a business case for it. $\endgroup$ – Karl Aug 18 '19 at 15:09
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It would be a total waste of energy.

Remember that the Sun is sending orders of magnitude more energy than humanity can produce. A significant fraction of that is UV, so the Sun is already breaking up more Methane than humanity could do by adding laser diodes or whatnot.

We might be able to do more at the ground, where the Sun's UV is mostly filtered.
It would still be an enormous feat to merely reach the Sun's UV level.

However, there is a big reason NOT to do it at the ground: UV does not only break up methane, but also oxygen. Part of that will recombine to ozone, which is an irritant (in the medical sense, i.e. extended-time exposure will cause damage no matter what).
(I do not know whether the oxygen bonds are stronger or weaker than the methane bonds. If methane has the weaker bonds, one could use an UV wavelength below the oxygen energy. You'd still break up bonds of any atmospheric molecule that has weaker bonds than methane, such as pheromones and whatnot; it is entirely unclear what consequences that would have.)

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  • $\begingroup$ The ozone argument isnt really one: Hydroxyl radicals are made via singlett oxygen, which is also resonsible for ozone generation. As long as your artificial light source is less intense than the sun, it wont create unhealthy ozone levels. Of course it likely also wont make enough hydroxyls to make a difference. ;) $\endgroup$ – Karl Aug 19 '19 at 7:40
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Powerful ground lasers are surely inefficient. The radicals are created in close proximity, meaning they likely have a good chance to recombine. Also highpower lasers (or any strong light source) are generally not very efficient. A lot of small ones would be better.

I would mount simple UV LEDs on the underside of passenger planes, where they are switched on to illuminate clouds at night (there is no sense in doing it during daytime, obviously). If that's enough to lift the project over the "waste of time and energy" limit, I'm not so sure.

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  • $\begingroup$ So if you would take a couple of those superlong solar powered self flying planes and patch them up with uv leds you could have a sustainable solution? $\endgroup$ – Tschallacka Aug 18 '19 at 14:33
  • $\begingroup$ @Tschallacka No. You just make it mandatory for all planes landing in US or EU to have those and present a usage log. A kilowatt or two of electricity are basically free on a jet airplane. Much better scaleability. $\endgroup$ – Karl Aug 18 '19 at 14:56
  • $\begingroup$ At the risk of sounding too obvious, doesn't the sun already illuminate clouds with UV? $\endgroup$ – user253751 Aug 19 '19 at 3:34
  • $\begingroup$ @immibis Well, only during the day. But you're right. The underside of clouds is likely the only place where this might possibly make sense. $\endgroup$ – Karl Aug 19 '19 at 7:21

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