What type of sensor is typically used to detect volatile organic compounds (VOCs) in landfill gas emissions?

The type of sensor typically used to detect volatile organic compounds (VOCs) in landfill gas emissions is a photoionization detector (PID). A PID works by using ultraviolet (UV) light to ionize VOC molecules in a gas sample. When a VOC molecule absorbs a UV photon with sufficient energy, it loses an electron, forming a positively charged ion. These ions are then detected by an electrode, generating an electrical current that is proportional to the concentration of VOCs in the gas sample. PIDs are commonly used because they are relatively sensitive, portable, and can detect a wide range of VOCs. However, PIDs are non-specific, meaning they detect the total concentration of ionizable compounds rather than identifying individual VOCs. For identifying specific VOCs and quantifying their concentrations, gas chromatography-mass spectrometry (GC-MS) is often used, but PIDs are better suited for continuous, real-time monitoring due to their portability and ease of use. A PID requires calibration to a known VOC to ensure accurate measurement.