Measurement: Sensors, Volume 17, October 2021,
Short-term exposures to indoor air contaminants can cause adverse health impacts and warrant a need for real-time measurements. The most common indoor pollutants are carbon dioxide (CO2), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), total volatile organic compounds (TVOCs), and particulate matter with a diameter of less than 2.5 μm (PM2.5). Several low-cost monitors for indoor air quality are commercially available; however, few of them are accurately tested. A stable, easy to use, and reproducible platform was developed in this paper. In these laboratory conditions, the comparison between the low-cost sensors and calculated concentration was shown to be linear (R2 of 0.980, 0.972, 0.990, 0.958, 0.987, and 0.816 and rs of 0.982, 0.985, 0.900, 0.924, 0.982, and 0.571 for PM2.5, CO2, CO, NO2, TVOC (ethylene), and O3 respectively). Laboratory conditions were used to test possible cross-interferences to the TVOC sensor; an increase of CO2, CO, and NO2 of 2500 ppm, 100 ppb, and 100 ppb respectively generated a change in the curve fit from linear to quadratic. A complete validation of a low-cost sensor was achieved by its application in a real indoor place. Good correlation between the reference methods and uHoo measurements of PM2.5, CO2, and O3 was achieved (rs = 0.765 to 0.894, 0.721 to 0.863, and 0.523 to 0.622 respectively).