Background: Indoor air quality (IAQ) in classrooms affects children's health and academic perfor-mance. The aim of this pilot study was to determine IAQ in elementary schools different in their inter-nal and external characteristics, in settings of COVID-19 epidemics.
Methods: IAQ parameters: fine particulate matter (PM2,5) mass concentration, CO2 concentration, tempera-ture and relative humidity were measured in parallel in four elementary schools/classrooms during October (non-heating season) and four months (including holiday in January) of heating season. IAQ parameters were measured in settings of anti-epidemic restrictions (≤13 students in classroom, frequent ventilation).
Results: During October, except in one school, PM2,5 concentrations were below the upper recommended value (25 μg/m³), but started rising in all schools in the heating season. The highest concentrations of PM2,5 were registered in two schools with closed or shortly opened windows. CO2 concentrations were mostly in the recommended range (up to 1000ppm) except in the school with constantly closed windows and in three schools in February when concentrations were higher. Except in one, the same school, and in January, both temperature and relative humidity were out of the recommended range (24,0-27,0°C in non-heating; 20,0-24,0°C in heating season; and 45-55%), with temperature mainly above and relative humidity mainly below it in three schools. The largest deviation in temperature and relative humidity were registered in urban schools. Registered differ-ences may be explained by different internal and external characteristics.
Conclusion: Despite anti-epidemic restrictions, most of the measured IAQ parameters were out of the recom-mended values in heating season. In addition, further deterioration of IAQ could be expected if all students had been presented in the classroom. Finally, to assure a healthy school environment in heating season, further optimisation of both indoor and outdoor conditions is needed in both pandemic and non-pandemic settings.