A large-scale longitudinal indoor air quality study: is low-cost sensor deployment a viable approach?

To date, the vast majority of indoor air quality studies have relied on repeated visits to dwellings to obtain data derived from short-term monitoring exercises, a time-consuming process that places considerable constraints on personnel, equipment and costs. These studies have focussed on the use of research-grade instrumentation; however, recent developments in the field of consumer-grade indoor air quality sensor technology offers new opportunities. Several studies have reported that these devices provide sufficient accuracy to be utilised in longitudinal studies and collect data via remote transmission. This new development means that it is now possible to collect longer-term data and larger sample sizes than was previously possible. However, additional factors need to be considered that did not represent issues when short-term sampling methodologies were employed. Factors that influence occupant engagement and data transmission need to be considered. With reference to three customer-grade sensors, this current study focusses on reviewing a set of parameters that should be considered for longitudinal studies. 

One customer-grade sensor device was selected for demonstrative purposes and its capability to remotely transmit  data was assessed. To date, the device has recorded data for 86 consecutive days from March to June 2019. In addition to compiling summary statistics, it was possible to download all the raw data and analyse indoor environmental quality parameters which exceeded baseline scenarios. The results showed that while the average temperature was 20.4 ^oC; the average hourly temperatures exceeded 24 ^oC for a cumulative time of 1512 hours and exceeded 26 ^oC for a cumulative time of 509 hours over the period. Similarly for CO2, the average concentration was 546 ppm; however, the hourly average of the CO2 concentrations exceeded 1000 ppm for 100 hours over the period.  

While several factors need to be considered when selecting a device, and it is possible that a single device will not fit all scenarios, preliminary results indicate that customer-grade instruments have the potential for applications in conducting longitudinal based indoor air quality studies. Further work is planned to evaluate the effectiveness of larger-scale deployment within  indoor environments for extended periods.