On-the-Fly Calibration of Direct Reading Photoionization Detectors

Photoionization detectors (PIDs) suffer from variable response to mixtures of airborne contaminants, such as partially evaporated hydrocarbon fuels or solvents. By using a charcoal tube attached to the outlet of a PID and by data-logging the measurements of the PID, two independent measurements can be made simultaneously. The measurements are related by calculating a response factor for the PID measurements, so the average corrected PID reading is equal to the average concentration found by the charcoal tube analysis. The information gained combines the advantages of both methods: an accurate time-weighted average concentration and knowledge of the chemical composition from the charcoal tube, and an immediate estimate of work site conditions with a correlation of exposure and activity from the PID. The method is simple to implement, needing no special equipment beyond the PID itself.