Air Purifier VOC Sensor Accuracy: MOS Sensors and Their Limitations

Volume I  ·  May 2026  ·  213 words

The VOC sensor in an air purifier — typically a metal oxide semiconductor (MOS) sensor — detects a broad range of volatile organic compounds but does not identify specific compounds or report concentrations in standard units (ppb or ug/m3). The sensor measures the change in electrical resistance of a heated metal oxide film when VOCs adsorb onto its surface — a non-specific measurement that responds differently to different VOCs and to humidity. The Levoit Core 600S and Coway Airmega series include MOS VOC sensors. The sensor output is typically displayed as a colored indicator (blue/green/yellow/red) or a relative scale (1-100) rather than as a concentration. This is useful for detecting relative changes — whether VOCs are increasing or decreasing — but cannot be compared to health-based exposure limits. MOS sensors drift over 1-2 years and most cannot be user-calibrated. For quantitative VOC measurement, a photoionization detector (PID) or gas chromatography is required — instruments costing $500-5,000 rather than the $5-10 sensor in a consumer air purifier.