An atmospheric retention field (also called "atmospheric shielding" and "ARF") is an energy barrier that retains the pressure and volume of the relevant atmospheric gas.
Types
There are two types of field: static and passive.
Static fields display a visible barrier of energy and act as a definitive barrier between the desired and undesired atmospheres. Hangar bays of starships and space stations often utilize static fields to prevent atmospheric leakage into the vacuum of space while still allowing passage of solid objects. Low-energy static fields can allow passage of organic life forms, but mid- and high-energy fields require special suits for passage to prevent burns and electrocution.
Passive fields are nearly invisible. The boundary appears diffuse, and it allows minor passage of gases. The energy draws in outside air to maintain positive pressure, and also has the effect of cleaning the air that enters. Open-air structures situated at high altitudes, such as skyscraper rooftops and sky continents of Riesel and other heavily urbanized planets, often use passive fields to retain a comfortable pressure. It serves as a cheaper alternative to making the structure airtight.