Chiang Mai's Burning Season & Air Quality, Explained

The honest picture

Chiang Mai’s air quality is the single biggest quality-of-life issue for people living here, and it is also the topic most often either exaggerated or brushed aside. Both distortions are unhelpful.

The accurate version: for roughly nine months of the year, Chiang Mai’s air is fine — often genuinely good, especially in the cool season. For roughly two months, typically late February through early April, it is bad, sometimes among the worst in the world. Understanding that shape is what lets you plan around it rather than being blindsided by it.

This hub is our most detailed evergreen coverage, because it’s the thing readers most need us to get right.

Why it happens here

Three factors stack up.

First, transboundary haze: agricultural burning across northern Thailand, Myanmar and Laos releases enormous quantities of PM2.5 particulate matter in the dry season, when clearing land before planting is cheapest and fastest.

Second, geography. Chiang Mai sits in a valley ringed by hills, with Doi Suthep on the western edge. The basin / inversion effect means that on still, cool mornings a layer of warmer air sits above the valley and caps it, trapping smoke at ground level instead of letting it disperse.

Third, timing. The same weeks that bring the burning also bring the least wind and no rain. The smoke arrives and then simply stays.

Monitoring that’s actually useful

Learn to read two numbers rather than one. AQI (Air Quality Index) is a scaled composite that’s easy to compare; raw PM2.5 in µg/m³ is what your lungs actually experience. Residents typically watch PM2.5 directly.

Rough working thresholds most people here settle on:

IQAir and Air4Thai are the two sources residents rely on. Check the sensor location — the readings in Hang Dong, the Old City and Mae Rim can differ substantially on the same morning.

What actually works

Four things, in order of impact:

1. One well-sized purifier in the room where you sleep. A True HEPA (H13/H14) unit with a CADR matched to the room does more than anything else you can buy.
2. Seal that room. Draught-proofing around doors and windows makes a modest purifier behave like a much better one.
3. A properly fitted N95 / KN95 respirator for the times you have to be outside.
4. A plan for the peak weeks. Whether that’s leaving the city, working from a cleaner room, or simply cancelling outdoor plans, deciding in January beats improvising in March.

Our guides cover each of these in detail, including where to go if you decide to escape and what a realistic budget for that looks like.