A Photoionization Detector (PID) is primarily used to measure which of the following?

• A. Particulate matter
• B. Oxygen concentration
• C. Carbon dioxide
• D. Total organic compounds (aromatic hydrocarbons)

Answer: (D)

Photoionization detectors use UV light to ionize organic molecules in the air, and the resulting ions produce a signal that is proportional to the amount of volatile organic compounds present. Because many VOCs, especially aromatic hydrocarbons, have low ionization potentials, a PID responds strongly to a broad range of organics, making it a convenient tool for screening total VOC levels in workplace air. It won’t reliably measure oxygen concentration, carbon dioxide, or particulate matter, which require other types of sensors or instruments. So the PID is best described as measuring total organic compounds, with aromatic hydrocarbons being a representative class that it detects well.