Standards & Resources
Authoritative guideline values, classroom ventilation targets, and material you can hand to teachers, parents, and administrators.
Guideline values
| Pollutant | WHO 2021 | U.S. EPA | Classroom target |
|---|---|---|---|
| PM2.5 | 5 µg/m³ (annual) | 9 µg/m³ (annual NAAQS) | Keep below 12 µg/m³ |
| PM10 | 15 µg/m³ (annual) | — | Keep below 40 µg/m³ |
| NO₂ | 10 µg/m³ (annual) | 53 ppb (annual) | Lower is better; ventilate during traffic peaks |
| CO₂ | — | — | Below 1,000 ppm during occupied hours |
| TVOC | — | No federal limit | Below 500 µg/m³ |
Classroom ventilation rule of thumb
- Aim for at least 6 air changes per hour during occupied periods.
- Use CO₂ as your low-cost ventilation proxy — if it climbs past 1,000 ppm, open windows or boost mechanical ventilation.
- Combine ventilation with portable HEPA filters in classrooms next to busy roads.
Authoritative documents
WHO Global Air Quality Guidelines (2021)
The reference values used worldwide. Tightened in 2021 — most current school targets sit between the old and new WHO levels.
Open document →EPA IAQ Tools for Schools
Step-by-step assessment, action plans, and ventilation guidance produced by the U.S. EPA. Free, widely cited, applicable beyond the U.S.
Open document →SINPHONIE Guidelines
European Commission guidance based on a 25-country, 114-school survey. The most relevant baseline for European school IAQ programmes.
Open document →ASHRAE 62.1
Industry standard for ventilation rates in commercial buildings, including schools. The basis for most building-code ventilation requirements.
Open document →Fact sheets & downloads
For Teachers
A one-page guide on what to do when classroom CO₂ or PM2.5 reads high. Coming soon — get notified by joining our newsletter.
Notify me →For Parents
How to ask your school about indoor air quality, what data to request, and what good looks like. Coming soon.
Notify me →For Administrators
Procurement guidance, monitoring placement, action thresholds, and a sample annual reporting template. Coming soon.
Notify me →