A portable air treatment device and system including a filter retaining mechanism for selectively retaining a replaceable filter assembly. The filter retaining mechanism includes a rigid, non-moveable body that reduces a size of an access opening to a filter chamber otherwise formed by the air treatment device housing, along with a bearing surface. The rigid body serves as a catch or latch, preventing unexpected dislodgement of a filter assembly from the chamber. The bearing surface is also rigid and non-moveable, and provides a means for easily inserting and removing a primarily non-permanently deflectable filter assembly about the rigid body.