Cat urine can soak into porous materials (carpet, upholstery, mattress, wood, cracks) and release odors again when exposed to warmth and moisture. Often the source is small or hidden (under furniture, at the baseboard, at the edge of the carpet), but the smell spreads throughout the room – making it seem as if it's "coming from the air".
AnoKath advantage: AnoKath helps you especially with hard, wipeable surfaces and environmental management, so that the odor does not become more trapped via contact zones.