An aircraft pressurized air system and method is disclosed. The system includes a compressor that receives and compresses outside air, and an air cycle machine that receives compressed air from the compressor and directs conditioned air to an aircraft pressurized zone. The system also includes a contaminant sensor disposed along an air flow path between the compressor and the aircraft pressurized zone, comprising an optical guide, a metal organic framework on an exterior surface of the optical guide in operative fluid communication with air from the air flow path, a light source in communication with the optical guide at a first end of the optical guide, and a light detector in communication with the optical guide at a second end of the optical guide.