CO2 Sensor Technology in Air Quality Monitors: NDIR Principles and Accuracy

Volume I  ·  May 2026  ·  217 words

Carbon dioxide sensors in consumer air quality monitors use non-dispersive infrared (NDIR) technology: an infrared LED emits light at the CO2 absorption wavelength (4.26 microns), and a detector measures the attenuation of the beam after it passes through the air sample. The attenuation is proportional to the CO2 concentration per the Beer-Lambert law. NDIR sensors have an accuracy of +/-50 ppm +3% of reading, which means a true 1,000 ppm CO2 reading is reported as 950-1,050 ppm — adequate for ventilation assessment. The Airthings View Plus and Aranet4 use NDIR CO2 sensors. Sensor drift: NDIR sensors drift by approximately 20-50 ppm per year due to optical component aging and require automatic baseline correction (ABC), which assumes the lowest CO2 reading over a 7-14 day period represents fresh outdoor air (approximately 420 ppm) and adjusts the calibration accordingly. ABC requires the monitor to be exposed to fresh air periodically; a monitor in a continuously occupied, poorly ventilated room may never see 420 ppm and will gradually over-read CO2 concentration.