Indoor air quality in Tyrolean classrooms – assessing different ventilation strategies with a citizen science approach in Austria

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 mechanical ventilation systems, installing CO2-monitoring signals, or raising awareness among teachers and students should be evaluated. This paper presents the results from the project ‘DIGIdat’ based on air quality measurements conducted 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, measurements were performed using multiple low-cost air sensors per classroom that were programmed and maintained by the students under scientific supervision. The citizen science approach helped 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, were installed in each of the ten participating schools. The sensors measured 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 the 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 utilising the Welch t-test and Mann-Whitney-U-test for differences between window airing and mechanical ventilation systems. Significantly higher CO2 and PM2.5 values were found with window airing compared to mechanical ventilation systems. Somewhat less significant, humidity was higher in classes with window airing 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 mechanical ventilation systems. The same analysis comparing inside and outside PM2.5 concentrations showed also the mechanically ventilated classrooms have, probably due to the use of 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.