Indoor air quality in Austrian classrooms – Assessing different ventilation strategies with a citizen science approach

With many existing Austrian school buildings to be renovated in the coming years, there are debates between stakeholders, about which ventilation strategy to pursue in existing schools. Therefore, different intervention strategies such as retrofitting ventilation systems, installing CO₂-monitoring signals, or raising awareness among teachers and students should be evaluated. This paper presents the preliminary results of the project “DIGIdat” on air quality measurements in the first quarter of 2023. The “as-is” indoor air quality situation in 36 classrooms in western Austria is assessed by comparing results between different classrooms and ventilation types. To gather information on indoor air quality, data is collected using multiple low-cost air sensors per classroom that are programmed and maintained by the students under scientific supervision. The citizen science approach helps to overcome the spatial barrier between the scientists and the measurement sites, with students being “responsible” for the continuous operation of their sensor kit. Altogether 15 sensor kits, distributed over three to four classrooms, are installed in each of the ten participating schools. The sensors measure CO₂-, fine particulate matter (PM), and volatile organic compounds (VOC) concentration as well as temperature and humidity. The sensor kits were positioned and started recording after finishing programming workshops, i.e., in January and February 2023 for most schools. Statistical analysis of the measured data (with varying sample size of approx. 10 to 20 thousand five-minute averages per category) was carried out utilizing the Welch t-Test and Mann-Whitney-U-Test for differences between window airing and ventilation systems. Significantly higher CO₂ and PM2.5 values were found with window airing compared to ventilation systems. Somewhat less significantly, humidity was also higher in classes with natural ventilation than with mechanical ventilation. In addition to that, a correlation analysis showed a dependency between average CO₂-levels in window-ventilated classrooms and average outside temperature, whereas this was not the case with classrooms equipped with ventilation systems. The same analysis comparing inside and outside PM2.5 concentrations showed also the mechanically ventilated classrooms have, probably due to fine particulate filters, lower ratios of fine particulate matter between inside and outside. Boxplots and correlation regression lines confirm graphically the data analysis results and highlight the conclusions.