Good IAQ

The CO2 data recorded by the ImpAQS project indicates a widespread failure to comply with existing European and national ventilation guidelines in schools. The results showed that less than 25% of the schools are able to maintain an annual daily mean CO2 concentration below the existing 1000 ppm guideline threshold. Whilst for more than a quarter of the school year the recommended minimum outdoor airflow rate of 4 l/(s·person) (ÖNORM EN 16798-1:2024) is not met. During the winter season the situation is even worse with less than 12% of schools maintaining a daily mean CO2 concentration below the 1000 ppm threshold.

Notably, there is not a single school that performed consistently within the existing guidelines all-year around. In the worst cases hourly mean CO2 values were found to be nearly 7-times higher than the guideline threshold (exceeding 6900 ppm) over some teaching periods (with even higher values recorded over shorter time intervals).

Qualitative surveys, carried out alongside the quantitative monitoring, showed that ventilation practices are strongly influenced by two main factors: the room and external air temperature and external noise.

When the outside air temperatures are 10 °C or below, mechanically ventilated classrooms have on average 450–600 ppm lower daily mean CO2 concentrations than naturally ventilated schools. Whilst mechanically ventilated schools performed better overall, three naturally ventilated schools ranked amongst the top 10 best-performing schools. Their low CO2 readings can be traced back to the occupants’ diligent window opening behaviour, higher than average spatial densities in classrooms (more than 3.2 m2 per child) and well-designed window openings.

It should also be noted that in some cases, mechanical ventilation systems were permanently switched-off, due to high running costs, highlighting a major barrier to their use in financially constrained schools.

Four key outdoor air pollutants (PM2.5, PM10, NO2, O3) were assessed in proximity to the ImpAQS schools. The results show that the majority of measurement stations exceed the World Health OrganisaƟon (WHO) air quality guidelines reference levels for each pollutant, with some locations having mean values above thresholds which should not be breached more than 3 times per year. Despite these findings, teachers did not identify outdoor pollution to be a major hindrance to opening windows.

This situation suggests that the use of mechanical ventilation with appropriate particulate and/or activated carbon filters should be recommended to help safeguard the health of students and staff in the worst affected schools.

The use of visible CO2 monitors and ventilation guidance made a significant difference to the ventilation practices in naturally ventilated classrooms. In January, a quarter of naturally ventilated classes with visible CO2 monitors reported CO2 concentrations that were 500 ppm lower than the corresponding classrooms without visible monitors. Generally, the installation of CO2 monitors was perceived very positively by the majority of classroom teachers and school director. This led to an increase in the number of classroom CO2 champions (students alerting teachers to ventilate on a regular basis). It is anticipated that with appropriate training, the full benefit of students and teachers engaging in the ventilation process is likely to be much greater than demonstrated in the outcomes of this study.

To avoid further inequities in existing ventilation practices, the authors believe that responsibility for this transition cannot be delegated to individual schools but must be part of a nationally coordinated process.