The short answer
Indoors, PM2.5 under about 9 µg/m³ (the EPA's annual outdoor standard since 2024) is good; spikes from cooking or candles are normal and should clear within an hour with a range hood, ventilation or a purifier. Sustained high readings mean a source or outdoor smoke getting in.
What PM2.5 is
PM2.5 particles are small enough to reach deep into the lungs. Indoor sources include cooking (especially frying and searing), candles, fireplaces, smoking and outdoor smoke or pollution leaking in.
Reading the numbers
| Reading | Meaning | What to do |
|---|---|---|
| 0-9 | Good | Nothing |
| 9-35 | Moderate | Ventilate after cooking; run a purifier if it persists |
| 35-55 | Unhealthy for sensitive groups | Run purifiers on high; find the source |
| 55+ | Unhealthy | Close windows during smoke events; purifiers on high |
Short spikes are normal; what matters is how fast the reading comes back down.
Products mentioned
Questions readers ask
Why does my PM2.5 spike when I cook?
Frying, searing and toasting release fine particles; use the range hood and a purifier, and it should clear within an hour.
Are home PM2.5 monitors accurate?
Laser sensors track changes well; absolute values can read high in humid air.