Influences of season, ventilation, SARS-CoV-2 pandemic protective measures, and energy-shortage on VOC levels in Western Switzerland’s primary schools

Indoor air pollution is a major threat to human health, contributing to both acute and chronic diseases in exposed individuals. School environments are particularly at risk, as they host vulnerable populations which spend a considerable amount of time indoors. Among the myriad pollutants found in indoor settings, volatile organic compounds (VOCs) are especially common and some of them have been associated with health effects from irritation to cancer following prolonged exposure. In this study, we assessed the presence of VOCs in 24 primary schools in the canton of Fribourg, Switzerland. VOCs were passively sampled at each school in three locations (twice indoors and once outdoors) for four one-week campaigns conducted across different seasons. These campaigns also captured variations due to SARS-CoV-2 protective measures and energy-saving restrictions. Overall, indoor air quality was found to be good in most of the monitored classrooms. However, elevated levels of alcohol (ethanol and isopropanol), reaching up to 40,000 µg/m³, were observed in classrooms during the enforcement of pandemic-related protective measures. Mechanical ventilation systems were associated with a general reduction in VOC exposure. Regarding indoor air reference values, most of the regulated compounds were in line with Switzerland’s or neighboring countries’ guidelines. This study demonstrates that although VOC concentrations generally remain low and within recommended limits, their consistent presence indicates numerous potential sources of exposure for both children and teachers, who spend extended periods in these environments.