When I was digging Bennu I aimed to deliver oxygen like sealevel Earth. That's by number - so by moles. I aimed 1/3 oxygen and 2/3 inerts at 0.6 bar. In practice we don't get gas of any sort in a near-earth rock. Noble gasses are for Mars and Venus - only. We are stuck with nitrogen which we liberate from the rock, if we can.
So. Can we do density?
A mole of nitrogen gas (no isotopes) is 28 grams; oxygen gas 32g. By weight 1/3 × 32g + 2/3 × 28g = 10.66 + 18.66 = 30g per mole of the mix. A little more if we were counting isotopes.
Avogadro's 1/mol is 6.02214076×1023 but I don't care. I care now about ideal gas V = RT/P, = R 295K / 60000 Pa = 0.00492R [rounding up] = 0.04032 m3/mol.
Mole-by-mole that's a mix density 0.7441 kg/m3. Which seems low except - gas, not water (998.21 kg/m3); compare air on Earth 1.225.
On my asteroid oxygen is effectively infinite. So, 2/3 of those breathable moles are nitrogen. Note that I already did that - it came to 18.66g out of the 30g. This is 0.463 kg/m3.
On the top floor I want 30-foot ceilings and lots of space. The cubic dekameter is 10×10×10 so, 463 kg nitrogen / cube. On a modest parabolic trough I believe we can fill a 100m×100m×10m space for 46.3 "Mg" that is, tonnes of N2 (plus O2).
BACKDATED AGAIN 10/14
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