There are several different types of atmospheres to consider.
- Lunar atmosphere
- Earth's atmosphere
- Atmospheric pressure on Earth
- Cabin Pressurization
- Lunar Settlement Artificial Atmosphere
The most important for Lunar development is the pressure inside your space suit or habitat. Here is a listing of the relative pressures of other environments and the percentage oxygen in each.
|Earth at Sea Level||(21%)||101.3 kPa|
|Leadville Colorado, 10196 ft, or 3107 meters||(21%)||69.6 kPa|
|Denver Colorado, 5295 ft, 1613 m||(21%)||83.4 kPa|
|LaPaz, 3700 m||(21%)||62.0 kPa|
|Mercury Program||(100%)||34.5 kPa|
|Gemini Program||(100%)||34.5 kPa|
|Apollo Program||(100%)||34.5 kPa|
|Space Shuttle||(28.5%)||70.0 kPa|
In the extreme case of a severe leak in space, you have to consider what the Death Zone does to climbers on Everest . You should also consider "the bends," which results from nitrogen bubbles in the blood when depressurizing too fast.
Most desirable for long term habitats in the moon and in space is somewhere around 40kPa total with about 60% oxygen. In the event of an sudden depressurization this ratio means you do not have a hard transition to switch to your backup breathing systems. The rest is Nitrogen, water vapor and trace amounts of CO2 which can be isolated quite easily.