Multicountry evaluation of indoor air in homes and schools: results from K-HEALTHinAIR project

Background

People spend 80 to 90% of their time indoors, making indoor air quality (IAQ) a major public health factor. Poor IAQ can increase the risk of respiratory issues, heart disease, cognitive impairments, and cancer. This study, within K-HEALTHinAIR project, aims to evaluate potential exposure risks in homes and schools, across four countries.

Methods

Data were collected using low-cost sensors to monitor CO₂, PM10, and PM₂.₅. Annual 24-hour average pollutant levels for 2025 were calculated, along with a risk analysis based on the frequency of exceedance of the guideline.

Results

CO₂ levels in homes generally stay below guidelines, with slight winter increases, particularly in wood-heated homes (up to 893 ppm), while schools showed exceedance during winter in Poland (954 ppm). Elevated PM2.5 concentration occurs in homes with district heating in the Netherlands (19.4 μg/m³), and air conditioning (34.8 μg/m3), smoking (93.9 μg/m³), and gas cooking (29.5 μg/m³) in Spain. In schools PM₂.₅ levels are higher in Polish schools (22.0 μg/m³) compared to those in Austria (9.5 μg/m³). Risk analysis indicates that CO₂ exceedance was 2 % (Spain), 8% (Austria), 11 % (the Netherlands), and 19 % (Poland), with wood-heated homes showing the highest frequencies. PM₂.₅ presents the highest exceedance rates: 36 % in Spanish smokers’ homes, 30 % in Dutch homes with passive smokers, 56 % in Austrian wood-heated homes, and 24 % in Polish homes heated by electricity. In schools, CO₂ exceedances reach 41 % in Austria and 34 % in Poland, while PM₂.₅ exceeds limits in 24 % of Polish schools compared to 10 % in Austria.

Conclusions

The findings highlight the important influence of indoor activities and household characteristics on IAQ and the potential health risks.

Acknowledgements: This study has been performed in the framework of the K-HEALTHinAIR project funded by the European Union (Grant agreement ID: 101057693).

Key messages

• Indoor activities and heating types strongly affect IAQ, with frequent PM2.5 guideline exceedances in smoking, wood-heated, and poorly ventilated homes.

• CO2 and PM levels often exceed guidelines in schools and homes, especially during winter, varying widely between countries and indicating potential health risks.