Pressure is a part of the Force Aspect, which is made by combining Flow and Land.
This is an active fysa. Users can manipulate pressure-- from air, from steam, from liquids-- in an area up to 10 meters (11 yards). The larger the area, the smaller the pressure they can generate. Room sized is only enough to pop one's ears, but the size of an apple can make a small explosive force equivalent to a hammer blow. It is easier if the space they're applying pressure to is already enclosed (like a balloon) rather than an undefined space of air. This ability can be used to help regulate atmospheric pressure when travelling to heights or depths.
You must have already learned either Flow or Land in order to learn this ability.