Hello, my name is Lemon. I am a maintainer at /tg/, and I have taken it on myself to document/update the atmos subsystem. I have been supported in this goal by Dunc and Aranclanos, the atmos maintainers who came before me.
I have stolen adapted this document from the work of Duncathan, an off and on maintainer who is responsible for the majority of the quality of the current atmos system. He pushed through several code cleanliness and sanity refactors to the system, and wrote the rundown of gas mixtures you'll find in this document. See the original for his draft.
Now then, onto the purpose of this document.