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Phase 1 Update: analysis

84% of monitored schools recorded poor indoor air quality

Launched in 2020 by Airscan in collaboration with Belfius, Clean Air for Schools measured CO₂, fine particles (PM2.5) and VOCs in classrooms over multi-month campaigns. The results show that many children are still learning in air that fails basic health guidance.

The project in brief

Phase 1 ran as a multi-year programme across Belgian schools, with monitoring campaigns designed to capture representative classroom conditions. Schools received structured diagnostics and practical recommendations, supported by ongoing feedback during the campaign.

72

schools equipped and monitored

6

months of measurements per school

5,670

children benefited from monitoring and improvements

What we measured and how

Phase 1 focused on three common indoor pollutants that affect health and learning: carbon dioxide (CO₂), fine particulate matter (PM2.5), and volatile organic compounds (VOCs). Sensors were installed in multiple classrooms per school, followed by an initial diagnosis and a final check after the improvement period.

  • Indoor sensors installed across classrooms

  • Initial diagnosis, then follow-up assessment after 6 months

Key findings

Indoor air quality is often poor across schools

Phase 1 focused on three common indoor pollutants that affect health and learning: carbon dioxide (CO₂), fine particulate matter (PM2.5), and volatile organic compounds (VOCs). Sensors were installed in multiple classrooms per school, followed by an initial diagnosis and a final check after the improvement period.

  • 84% of schools showed poor indoor air quality against reference recommendations

  • Fine particles (PM2.5) emerged as the biggest concern

See Results

Engagement and real-time support

Phase 1 wasn’t just data collection. Teachers and students were informed about the issue, and schools received participatory guidance on actions they could take immediately. When pollution peaks occurred, teachers were notified to respond in real time.

  • 13,737 alerts sent to teachers to flag pollution peaks

  • Practical tips shared on ventilation habits, room use, and everyday routines

What worked

Ventilation, plus targeted air purification

Ventilation remains the strongest structural lever, but it is not always sufficient—especially in older buildings, crowded classrooms, or where outdoor air brings particles indoors. Phase 1 therefore also tested air purification in targeted cases, with convincing results, particularly for reducing fine particles.

  • Ventilation improves outcomes, but has limits in real-world school buildings

  • Air purifiers can be an effective, budget-friendly option where needed

What's Next?

Large-scale improvement

Phase 1 produced a clear baseline, showed which actions improve conditions in practice, and confirmed that solutions exist. The next step is to move from diagnosis and pilots to implementation.

See Phase 2: Purify