The most important factor of a planet's atmosphere is simply having one. Specifically, having air pressure similar to Earth's 100,000 pascals (Pa) at sea level. From orbit, your planet's atmospheric pressure will affect the visibility of the air above the surface: too thin and it will be invisible, too thick and it will be opaque.
Changing Pressure also affects accumulation of Temperature. "Atmosphere Thinning" causes loss of heat, while "Atmosphere Thickening" causes increase of heat. Increasing Pressure will create the status of Temperature that is "Retained by Atmosphere". That is the greenhouse effect. The Temperature increases by 0.046 mK for every pascal.
The state of Water is affected by Pressure. At less than 600 Pa, all water is held as vapor or ice even though the temperature is not at the full ice or vapor point. When 600 Pa is breached (and the temperature is within the liquid range (between 200,500 and 399,500 mK)), a percentage of the vapor/ice will turn into liquid water instantly, which can destroy every outpost and city that happens to be below the sealevel.
Habitability for plants and microbes to grow on a planets surface requires an atmospheric pressure of 10,000 to 190,000 Pa. Habitability for animals and humans outside of a Habitation building is a narrower range between the 50,000 and 150,000 Pa.
|Pressure (Pa)||Effect on world|
|>0||Clouds start forming, but cannot be seen|
until Pressure is higher.
|>42,000||The atmosphere outline can be seen.|
|>110,000||Clouds start to turn opaque and expand.|
|150,000||The atmosphere outline is at it's thickest|
- Above that point, it fades.
|>190,000||The atmosphere outline cannot be seen.|
|>200,000||The surface is hidden by the clouds.|
|Biofixture Lab||-Pressure, +Biomass (Biomass only), +Oxygen (Biospheres only)|
|Hydrogen Processor||-Pressure, +Temperature, +Water|
|AtmoGen Suite||+Pressure, +Oxygen|
|Pocket Mine||+Pressure, +Oxygen, +Credits|
|Carbon Fixer||-Oxygen, +Pressure|
|Kelp Farm||+Oxygen, -Pressure|
|Ice Launcher||-Water, -Pressure|
|Aquifer Network||+Water, +Pressure|
|Spaceport||+Population, +Pressure, +Credits|