Is the air better up the mountain in Chiang Mai?

The mechanism has a name. Temperature inversion.

Cool air settles low in the valley overnight. Warm air sits on top of it like a lid. The particulates get trapped underneath. There is almost no wind in burning season, so nothing clears them out.

That is why you can see it. From high ground the haze reads as a flat brown blanket below you. You are not imagining that. You are looking at the top of the inversion layer.

A rough rule for elevation. Below 500m is the worst air, which covers the city and the lowlands. Between 500m and 900m it varies by the day. Between 900m and 1,200m it is usually much better. Above 1,200m it is often clean, unless regional smoke is heavy.

Here is what that looks like on a bad day. Say the city reads 200. On the valley floor at 300 to 400m you get 180 to 220. Mid Mae Rim, around 600 to 800m, drops to 120 to 170. High Mae Rim and Mon Jam, around 1,000 to 1,200m, drops to 60 to 130. On an exposed ridgeline with wind you sometimes see 40 to 80.

Those are typical readings rather than measurements I took myself. Treat them as a range, not a promise.

There are days when it barely helps. Regional smoke from Myanmar and Laos can swamp the whole north. If there is no wind anywhere, nothing moves. The inversion layer can also climb past 1,200m. Late March and early April are the worst weeks for this.

On those days the city at 200 becomes 140 to 180 up high. Better. Not an escape.

Trust your eyes over the apps up there. A brown blanket below you means you are above the inversion and the air is genuinely better. If you are still inside the haze, the lid is higher than you are. A clear horizon with wind is the best case.

Elevation is the only local lever that works consistently here. It is damage control rather than clean air. If you want actual clean air in March, it is the islands, the south, or leaving the region.