A: You've got access to a lot of solar power, on a completely predictable schedule. Especially convenient since in this particular case you don't need to convert it to electricity first. B: Anything you release as a gas flies harmlessly out into the universe, so your environmental restrictions are a great deal less. (Also, this is not "cheating regulations" or anything... this is
truly an environment with fewer restrictions. If you can vaporize it, it can be made to truly go away forever.) C: You've got zero G, and this sort of "massive mass spec" plan, while I question the numbers in general, is probably a great deal more practical in zero G than not zero G.
And it would all tie together; if the exhaust is in excess of escape velocity, which it probably is by an order of magnitude or two, you can just let anything you don't care to catch fly into space.
I'm not saying this is practical or necessarily a good idea, just pointing out that you do have some options in space that you don't have on Earth.