How much does the Chiang Mai burning season really matter?
Chiang Mai is one of the highest-rated cities in our entire dataset — 4.5 overall on $1,000 a month, which almost nothing else matches. It also carries an air quality rating of 2.6 out of 5, one of the lowest we record anywhere.
Both of those are true at once, and the reason they are both true is that Chiang Mai is a different city for roughly nine months of the year than it is for the other three. This page is about how much that actually matters and what the numbers behind it are.
What the burning season is
Every year, agricultural land across northern Thailand, Myanmar and Laos is cleared by burning ahead of the new planting cycle. Chiang Mai sits in a valley ringed by mountains, and in the late dry season the air above the valley stagnates. Smoke from hundreds of thousands of individual fires accumulates in it and does not clear for weeks. NASA's Earth Observatory has documented the resulting smoke layers over northern Thailand from orbit (satellite imagery and background).
It is not urban pollution. It is not traffic. Chiang Mai's air outside the burning months is unremarkable for a city of its size. The problem is seasonal, regional and almost entirely agricultural in origin, which is why it responds to the farming calendar rather than to anything the city itself does.
The actual numbers
IQAir's historical record for Chiang Mai gives an annual mean PM2.5 of 32.3 µg/m³ for 2019, up from 24.5 in 2018 and 22.7 in 2017. Within that year the monthly figures diverge sharply: February averaged 47.2 µg/m³, March 98.7 µg/m³, and April 74.1 µg/m³ (IQAir, Chiang Mai). The World Health Organization's annual guideline value is 5 µg/m³.
| Month | PM2.5 mean (µg/m³), 2019 | Multiple of WHO annual guideline |
|---|---|---|
| February | 47.2 | ≈9× |
| March | 98.7 | ≈20× |
| April | 74.1 | ≈15× |
| Annual mean | 32.3 | ≈6× |
Chiang Mai PM2.5 by month, 2019. Source: IQAir historical data.
March is the month that does the damage. A monthly mean near 100 µg/m³ is not a bad day with good days around it — it is a sustained condition, and on the worst days the hourly readings go multiples higher again. This is the part that gets lost when the season is described as “a bit smoky”.
So does it break the recommendation?
It breaks the year-round recommendation and leaves the rest intact. That distinction is worth being precise about, because both the “Chiang Mai is a scam” and the “it's overblown” positions are answering the wrong question.
From roughly May to January, Chiang Mai is what its reputation says: cheap, well set up for remote work, with a coworking and cafe density that very few cities at that price point can match. Our overall rating of 4.5 is earned in those months. From late February to April it is a city where outdoor exercise is inadvisable, where a lot of long-stay residents leave, and where anyone with asthma or a young child should not be. Those are both accurate descriptions of the same place.
The practical answer for a nomad is therefore not “avoid Chiang Mai” but “do not sign a twelve-month lease”. A stay from November to mid-February gets the best months — cool, dry, clear — and leaves before the air turns. It also lines up with when a northern hemisphere winter escape is most wanted.
Where people actually go for those three months
The usual move is south or east, to somewhere outside the smoke basin. Our air quality ratings for the common destinations, with the caveat that these are annual ratings and subject to the same seasonal limitation described on our page about annual ratings:
| City | Country | Air quality (0–5) | Cost/month | Overall |
|---|---|---|---|---|
| Ko Pha Ngan | Thailand | 4.3 | $1,200 | 4.0 |
| Langkawi | Malaysia | 4.3 | $1,200 | 3.7 |
| Kota Kinabalu | Malaysia | 4.0 | $1,100 | 3.8 |
| Phuket | Thailand | 3.8 | $1,500 | 4.1 |
| Da Nang | Vietnam | 3.7 | $1,000 | 4.4 |
| George Town | Malaysia | 3.6 | $1,100 | 4.3 |
| Kuala Lumpur | Malaysia | 3.3 | $1,300 | 4.4 |
Common burning-season alternatives, by our air quality rating.
Note that Bangkok is not on that list. Bangkok rates 2.8 for air quality, barely better than Chiang Mai's annual figure, and it has its own late-winter haze problem. Moving from Chiang Mai to Bangkok in March is not the escape it looks like on a map.
The island and coastal options — Phuket on the Andaman side, Ko Pha Ngan on the Gulf side, Langkawi and Penang across the Malaysian border — are all outside the affected region. Note that the two Thai coasts are on opposite monsoon cycles, which matters if you are also choosing for rain; that is covered in the northeast monsoon page.
What we do not claim
We do not publish our own air measurements and we are not a health authority. The PM2.5 figures on this page come from IQAir's historical record and are attributed as such; the WHO guideline is theirs. Our own 0–5 air quality rating is a relative rating across the 500 cities we track and an annual one, so it compresses exactly the seasonal variation this page is about. If you have a respiratory condition, the numbers here are background for a conversation with a doctor, not a substitute for one.
Common follow-up questions
When is the Chiang Mai burning season?
Roughly the second half of February through April, ending when the rains arrive. March is consistently the worst month. In IQAir's 2019 record February averaged 47.2 µg/m³ of PM2.5, March 98.7 and April 74.1, against an annual mean of 32.3.
Is Chiang Mai still worth basing in?
For roughly May to January, yes — that is where its high rating comes from, and very few cities match it at $1,000 a month. The sensible pattern is a stay that ends before late February rather than a twelve-month lease.
Is Bangkok a good escape from the burning season?
Not really. Bangkok rates 2.8 out of 5 for air quality in our data against Chiang Mai's 2.6, and it has its own late-winter haze. The Thai islands, Malaysia and central Vietnam are outside the affected region; Bangkok is only partly so.
What causes the smoke?
Agricultural land clearance by burning across northern Thailand, Myanmar and Laos in the late dry season, trapped in the Chiang Mai valley by surrounding mountains and stagnant air. It is regional and agricultural rather than urban or industrial.