In three quarters of all Austrian classrooms, the average CO2 concentration exceeds the guideline value. Inadequate air quality impairs learning and increases the risk of infection and health issues.

Good indoor air quality is a basic prerequisite for human health and is crucial for the ability to concentrate at work, or while studying. A nationwide study by Graz University of Technology (TU Graz) has now shown that most Austrian schools do not comply with national and European guidelines on ventilation. In the past school year, the guideline value for the daily average CO₂ concentration of 1000 ppm was exceeded in 75 per cent of the classrooms examined. In winter, the rate even rose to 88 per cent. In individual cases, the average hourly CO₂ values exceeded 6900 ppm, almost seven times the guideline value. Worse still, A quarter of all classrooms did not even provide the absolute minimum level of ventilation (4 litres of air per second per person) that is required by current European and Austrian standards (10 litres per second per person is recommended under normal operating conditions). This means that many school children are getting less than 40 % of the recommended air flow rate per person.

Although carbon dioxide is not considered an air pollutant in itself, its concentration in indoor air has long been used as an indicator of air quality. Model calculations as part of the study have also shown that air quality correlates with the risk of respiratory infections. Regular ventilation can therefore not only reduce the CO₂ concentration but also the risk of airborne disease transmission.

Municipal schools performed better rural schools

For the study, a team led by Robert McLeod and Christina Hopfe from the Institute of Building Physics, Services and Construction at TU Graz was commissioned by the Federal Ministry of Education, Science and Research (BMBWF) to analyse the CO₂ concentrations, ventilation rates and environmental data in 1,200 classrooms in all Austrian federal states in the 2023/24 school year. This revealed considerable differences between school types and regions as well as the influence of the type of ventilation. Special schools scored particularly well because their classrooms have a relatively low occupancy rate. Surprisingly, schools in towns and cities usually had better CO₂ values than schools in rural areas.

Automatic mechanical ventilation offers advantages

The way in which classrooms are ventilated plays a very important role in the overall context: “In rooms with automatic, mechanical ventilation, the air quality is better on an annual average than in rooms that are ventilated manually by opening the windows,” says Robert McLeod. This benefit is particularly pronounced when outside air temperatures are below 16 °C. On such days, the average CO₂ concentration in mechanically ventilated schools is typically 450-600 ppm lower than in naturally ventilated schools.

Researchers recommend CO₂ sensors and ventilation training

Not every school can afford mechanical ventilation systems. However, during the study the relatively inexpensive CO₂ sensors proved to be an effective aid for manual ventilation. In half of the school classes studied, clearly visible sensors were installed that signalled when the guideline value was exceeded by using coloured lights. “Such sensors influence the ventilation behaviour in many classrooms and have significantly improved the air quality in manually ventilated rooms, especially in the winter months,” says Christina Hopfe. “Overall, our study provides important information and actionable advice on how to improve learning outcomes and the health and well-being of students and teachers.” Low cost CO₂ sensors and ventilation training (for staff and students) are important steps that all schools should consider investing in.

The final report of the ImpAQS (Improving Air Quality in Schools) project is available for download from the Institute of Building Physics, Services, and Construction website: https://www.tugraz.at/en/institute/ibpsc/report-form