Development of a low-cost, real-time, telemetric, continuous residential indoor air quality monitoring system: progress and lessons learned

Abstract

Background: Short-term fluctuations in indoor air quality (IAQ) may be important for respiratory health; however, continuous IAQ monitoring is rarely assessed in residential settings. Barriers include cost and logistics. Aim: Development of a low-cost residential IAQ monitoring system with continuous, telemetric data transmission for 2 studies: Deep Green and Healthy Homes; National Children’s Study Remote Sensing Technology. Methods: A multidisciplinary team assembled IAQ monitors combining low-cost gas sensors with a wireless cellular radio. Calibration equations incorporating data from multiple sensors were developed for each system-gas combination. Additional data were used to assess accuracy. Monitors transmit data every 30 seconds; 62 systems were deployed for 1 year. An internet application (app) was developed to display real-time data. Results: The compact system measures temperature (T), relative humidity (RH), carbon dioxide (CO2), carbon monoxide (CO), nitrogen dioxide (NO2), total hydrocarbons (tVOC), and particulate matter (PM) (0.5-2.5 µm & 2.5-10 µm). T, RH and PM used manufacturer calibration. Individual gas sensors were highly variable. Calibration against gold standard instruments, using 70 environmental chamber test conditions, resulted in the following differences between measured and estimated values (N=16): CO2, ppm: 26.7 (robust standard error: 7.8); CO, ppm: 0.5 (0.2); NO2, ppb: 21.5 (3.5); tVOCs, ppb: 5.7 (5.6). For budgetary reasons, N=47 units were ‘tuned’ against portable field instruments. Differences for this method were: CO2, ppm: 7.44 (4.96); CO, ppm: -0.02 (0.01); tVOCs, ppb: 17.01 (6.39); however, only one test condition was used. The app facilitates real-time data visualization and equipment diagnostics. Quality assurance field testing data are currently being analyzed. Conclusions: This system is feasible and may be a valuable resource for IAQ assessment in future studies.