Area
Creates a shimmering dome that is selectively permeable to gases. It can either drive out specified gases, or draw them in. When the dome is created, the caster defines a target atmospheric composition; when the target level for each component gas is reached, the dome ceases acting on that gas until conditions inside the dome change. The composition selected
by the caster specifies both proportions and total pressure; this spell can thus be used either to change the composition of the air within the dome or its pressure relative to the surrounding area, or both. An Atmosphere Dome cannot create gas where none exists; if there is no oxygen in a planet’s atmosphere, a dome set to accumulate oxygen remains empty.

Duration: 6 hours.
Base cost: 4 to cast. Half that to maintain.
Prerequisites: Purify Air and Weather Dome.