Measured · 15050 point-daysWhen to go
Ten points on the circuit, four years of daily PM2.5. Ten months of the year the answer is yes.
3.0µg/m³ · Pai, July
Ten months of the year this is some of the cleanest air in Thailand
Pai measures 3.0 µg/m³ in July. The green months are the clean ones.
Every town, every month
Mean PM2.5 in µg/m³. Green is under the WHO-adjacent 9.0; the US 24-hour standard is 35.4.
Chiang Mai · worst Mar 37.8 · ×3.4 swing
Mae Malai · worst Apr 31.2 · ×4.9 swing
Pai · worst Apr 29.8 · ×9.9 swing
Soppong · worst Apr 29.6 · ×8.7 swing
Mae Hong Son · worst Apr 32.3 · ×9.0 swing
Khun Yuam · worst Apr 30.1 · ×10.8 swing
Mae La Noi · worst Apr 28.8 · ×11.5 swing
Mae Sariang · worst Mar 29.6 · ×12.9 swing
Mae Chaem · worst Apr 27.5 · ×9.8 swing
Hot · worst Mar 27.6 · ×12.5 swing
And the two months that are not
Late February to late April the hills burn, and it ends with the first rains.
Right now
| Station | PM2.5 | AQI | Reported |
|---|---|---|---|
| Yupparaj Wittayalai School Si Phum, Meuang, Chiang Mai | 7.8 | 13 | 2026-09-18 22:00 |
| Natural Resources and Environment Office, Mae Hongson Chong Kham, Meuang, Mae Hong Son | 7.7 | 13 | 2026-09-18 22:00 |
| City Hall, Chiangmai Chang Phueak, Meuang, Chiang Mai | 14.8 | 25 | 2026-09-18 22:00 |
| Meteorological Staions, Lamphun ฺBan Klang, Mueang, Lamphun | 9.3 | 16 | 2026-09-18 22:00 |
| Meteorological stations, Lampang Phra Bat, Meuang, Lampang | 7.5 | 13 | 2026-09-18 18:00 |
| Provincial Waterworks Authority Mae Moh Mae Mo, Mae Mo, Lampang | 7.3 | 12 | 2026-09-18 22:00 |
| Health Promotion Hospital Banthasri Ban Dong, Mae Mo, Lampang | 7.0 | 12 | 2026-09-18 18:00 |
| Phayao Provincial, Phayao Bantom, Meuang, Phayao | 7.8 | 13 | 2026-09-18 22:00 |
Fetched 2026-09-18 22:29 when this page was built — it does not update by itself. air4thai
The smoke
Two sources were fetched, and they are printed together because they disagree.
The long record is Copernicus CAMS through the Open-Meteo air quality service: hourly PM2.5 at ten points around the loop from 1 August 2022 to the day of the build. That is 15,050 point-days. Reduced to a daily mean and then to a month, the shape is not subtle. Take Pai: a July mean of 3.0 micrograms per cubic metre, a December mean of 9.9, a March mean of 26.1, an April mean of 29.8. Thirty of the thirty April days measured sat above 35.4 µg/m³, the figure the United States uses as its 24-hour standard. In July, across four years, not one day did.
The same shape repeats at every point on the circuit, and one thing about it is worth saying out loud: Chiang Mai is worse than the loop. Chiang Mai's March mean is 37.8 µg/m³ against Mae Hong Son's 29.1 and Pai's 26.1. The city you leave from is the dirtiest air on the route.
Where the long record fails. In 15,050 point-days the model never once produced a daily mean above 99.4 µg/m³. Ground stations in northern Thailand have recorded far higher. A model cell is tens of kilometres across; a Mae Hong Son valley on a windless March morning is not, and the averaging that makes a continental model tractable is exactly the averaging that removes the worst hour of the worst day. Inference — read the monthly shape from this data and do not read the ceiling from it.
The ground record, such as it is. Thailand's Pollution Control Department runs a national network and publishes the current hour. Its historical endpoint returned 404 on the fetch date, so what this site can show from it is now, not then. And there is a second problem, which is a finding in itself: Mae Hong Son province — 12,765 square kilometres, the largest by area in the north — has one station. It is 58t, in Mae Hong Son town. Pai has none. Soppong has none. Khun Yuam, Mae La Noi and Mae Sariang have none. Nobody official is measuring the air in the town most riders sleep in on night one.
Open-Meteo.com, from Copernicus Atmosphere Monitoring Service · 2022-08-01 → 2026-09-17