El Nino Watch
Tiny particles smaller than 2.5 micrometres (about 1/30 of a hair) that go deep into the lungs. Thailand's 24-hour standard is 37.5 µg/m³ since June 2023.
Koh Samui watch
PM2.5 comes from smoke (forest fires, crop burning), traffic and industry. Because the particles are so small, they reach deep into the lungs and the blood. It is measured in micrograms per cubic metre of air (µg/m³), usually as a 24-hour average.
Thailand tightened its standard on 1 June 2023: the 24-hour limit went from 50 to 37.5 µg/m³, and the red band now starts at 75.1 µg/m³.
| PM2.5, 24 h (µg/m³) | Thai PCD band |
|---|---|
| 0 to 15.0 | Very good |
| 15.1 to 25.0 | Good |
| 25.1 to 37.5 | Moderate |
| 37.6 to 75.0 | Starting to affect health |
| 75.1 or more | Affects health |
Bands as used by the risk engine (Thai PCD, revised 2023).