An air purification system including a housing defining a lumen, an inlet, an outlet, and a flow pathway between the inlet and the outlet and through the lumen; a filter assembly retained within the lumen and including a substrate defining an open three-dimensional volume, a photocatalytic material disposed on the substrate, and a photon source arranged to illuminate the photocatalytic material with optical radiation; and a flow control mechanism arranged along the flow pathway between the inlet and the outlet.