The atmosphere type, along with the AtmospherePressure, define the nature of the world's atmosphere. Atmosphere classifications are deliberately broad, mostly because working out anything more detailed is far more complex, and would probably lead to less realistic results because of errors.
Many atmospheres require some level of protective clothing, which may range from a simple breathing mask, right up to a mini-tank. The general level of protection required can be described using the standard Imperium Ratings Code, as detailed below:
A rough measure of the quality of the world.
Can be lived on without any form of protection, ideal place where everyone wants to live. These will always be Gaian worlds.
Can be lived on without protection for the most part, but are unpleasant in some respects. They may be dry, cold, or have a polluted atmosphere.
Can be lived on with some protection. Atmosphere is probably very thin, or temperature might be very cold or Hot. The atmosphere is breathable however, and temperature survivable.
Cannot go onto the surface without protection. Vacuum worlds, or too cold to survive.
World is actively hostile, and requires far more than just a space suit. Dense atmosphere, extreme temperatures, acidic rain etc.