PM2.5, haze and room size
A short, general guide to airborne particles, haze and room sizing. This page is for general information only and is not medical advice.
What is PM2.5?
PM2.5 refers to airborne particles 2.5 micrometres or smaller in diameter. The World Health Organization publishes air quality guidelines for PM2.5 concentrations; its 2021 guidelines set levels of 5 µg/m³ (annual mean) and 15 µg/m³ (24-hour mean).
Haze in Singapore
The National Environment Agency (NEA) publishes the Pollutant Standards Index (PSI) and PM2.5 readings for Singapore, along with official haze advisories. Check NEA's latest readings and follow its advisories during haze periods.
What CADR means
Clean air delivery rate (CADR) is a rated measure of how much filtered air a purifier delivers, in cubic metres per hour. The Clearday 270 has a rated CADR of 270 m³/h.
Air changes per hour (ACH)
ACH estimates how many times per hour a purifier could, in theory, pass a room's full volume of air through its filter. It is calculated as CADR ÷ (floor area × ceiling height). Real-world results vary with room layout, doors and windows, and purifier placement.
Room-size calculator
See the theoretical air changes per hour for the Clearday 270 in your room.
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Sources
- NEA Singapore: Haze (PSI and PM2.5 readings, advisories)
- NEA Singapore: Air quality
- WHO global air quality guidelines (2021)
- WHO fact sheet: Ambient (outdoor) air quality and health
HALE air purifiers are household appliances. They are not medical devices and are not intended to diagnose, treat or prevent any condition. If you have health concerns, please speak to a medical professional.