About the air purifer study
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This page contains information on the air purifier study and the implementation of the study.
Background and purpose
The pilot study showed that air purifiers with high-efficiency particulate air (HEPA) filters in classrooms reduce airborne particles. However, there is little evidence whether installing air purifiers in classrooms reduces absence among students and teachers. The main study aims to:
- Investigate whether air purifiers in classrooms reduce absence among students.
- Investigate whether air purifiers in classrooms reduce self-reported absence and cases of respiratory illness among teachers.
- Investigate teachers’ perceptions of classroom air quality.
Implementation and data collection
We aim to recruit approximately 30 primary schools with more than 10 students in 7th grade to take part in the study during each of the winter seasons 2025/2026 and 2026/2027. Participating schools will be allocated at random, by drawing lots, to either intervention or control groups.
In the intervention group, we will install two portable air purifiers with HEPA filters in each main classroom in 7th grade (or, alternatively, 5th- or 6th grade). The air purifiers in this group will operate at the highest fan setting that meets classroom noise requirements. In the control group, we will install two modified air purifiers with HEPA filters in each main classroom in 7th grade (or, alternatively, 5th – or 6th grade). The air purifiers will operate at the lowest possible fan setting. Air quality monitors will be installed in all classrooms.
The study will be conducted over a three-month period in each winter season. We will compare absence and the spread of infection among students and teachers at schools in the two groups. Student absence data will be collected directly from the municipality or relevant registers, at class level, on a weekly basis. These data will be anonymous. Teacher absence data will be collected through short weekly questionnaires completed by teachers who have consented to take part. Completing these questionnaires will be voluntary, and a school may participate in the study even if a teacher does not wish to complete them.
Potential benefits and disadvantages of air cleaners
Air purifiers may improve classroom air quality by removing particles such as pollen, mould and even viruses. This could potentially reduce problems related to asthma and allergic reactions. Some studies also suggest that cleaner air may help children perform better in academic tests and improve their general well-being. We do not know yet whether air purifiers can reduce the risk of viral infection, which is why we wish to conduct this study.
Air purifiers may produce some noise, and incorrect positioning may cause draughts. We will try to position the air purifiers so that they do not cause draughts, and they will be set to comply with applicable classroom noise requirements. The pilot study showed that neither students nor teachers reported any adverse events or disadvantages associated with having air cleaners in the classroom.