Short answer
Chiang Mai's burning season runs from February to May, and in 2026 the worst smoke came in March. Thailand's National Environment Board has declared Chiang Mai a pollution control zone for those four months, and in 2026 the province banned open burning from 1 January to 31 May. On 3 March 2026 the Pollution Control Department counted 1,967 hotspots in one day. Thailand's 24-hour PM2.5 limit is 37.5 µg/m³, and readings in the north went well above it. Check Air4Thai each morning before you plan a day out.
The burning season runs from February to May
Chiang Mai, Chiang Rai, Lamphun and Mae Hong Son were declared a pollution control zone by the National Environment Board in 2025, to regulate and reduce pollution from February to May every year, according to Thairath. Chiang Mai province's own burning ban for 2026 was wider: the governor signed it on 2 January 2026 and it covered 1 January to 31 May, outside the designated fuel management zones.
Thairath names the sources as open burning, agricultural fires, community burning and vehicle emissions, and says PM2.5 has repeatedly exceeded the standard by multiples in recent years. A draft announcement of November 2025 added that farmers who burn would lose government support, and that anyone who thought burning unavoidable had to register first on the Fire-D app. The practical meaning for a visitor: smoke is a regular feature of February to May, not a freak event.
What the 2026 season looked like
The Pollution Control Department reported 1,967 hotspots across Thailand on 3 March 2026, 76 per cent of them in forest areas, according to The Nation. It listed Lampang, Phrae, Lamphun, Chiang Mai and Tak as the provinces with the most. PM2.5 exceeded the standard in 16 northern provinces, with readings between 18.4 and 112.7 µg/m³.
Late March was worse. GISTDA's satellite data for 27 March counted 2,302 hotspots in Thailand, against 8,804 in Myanmar and 4,189 in Laos, according to Thairath. The Pollution Control Department's Announcement No. 3/2026, dated 28 March, said many upper-northern areas were red, with Chiang Dao in Chiang Mai province under close watch, and that the wind in the upper North was blowing from the west and south-west into the country.
How to read a PM2.5 number
Thailand's 24-hour limit for PM2.5 is 37.5 µg/m³, tightened from 50 and in force since 1 June 2023, with an annual limit of 15 µg/m³, according to the Natural Resources and Environment Ministry's announcement in the Royal Gazette in July 2022. A reading above 37.5 over a day is above the national standard. The Pollution Control Department's Air4Thai website and app show the current readings.
Two cautions help. Hourly readings swing, so look at the 24-hour average too. And places differ: on 2 January 2026 Chiang Mai University's climate centre reported 74 µg/m³ at 10 am in Si Dong Yen subdistrict, classed orange, and 52 µg/m³ in the city centre at Mae Hia. The reading nearest your hotel and your destination is the one that matters.
Why March feels hot, dry and hazy
The weather adds to the problem. In the World Meteorological Organization's 1991 to 2020 normals for Chiang Mai, March has an average high of 35.4 degrees and April 36.7 degrees, with just 20.4 mm of rain in March and 54.3 mm in April. Relative humidity in March is 53.6 per cent, the lowest of the year. Rain returns in May with 167.5 mm.
Not every grey morning is smoke. The Thai Meteorological Department's winter outlook, issued in September 2024, expected thick fog or haze at many places on some days from December to January and again in early February. That is the start of the cool season, before the fires peak. The warning signs for smoke are the Air4Thai numbers, not the colour of the sky.
What to do on a smoke day
The advice from the Pollution Control Department is plain. In its announcement of 28 March 2026 it urged people in affected zones to avoid outdoor activities or use protective equipment, and said anyone with symptoms should consult a doctor. We are a tour company, not a health service, so we do not go beyond that: if you have a heart or lung condition, ask your doctor before you travel in February to May.
For a trip, the sensible approach is to treat air quality as you would a rain forecast. Look at Air4Thai the evening before and again in the morning. Keep the short, flexible plans for bad days, such as a museum, a temple visit or a cooking class, and move long hikes. Our guide to Chiang Mai in November and the best time to visit Chiang Mai show the months that avoid the problem.
Which days out are better in the smoke season
A half-day plan is easier to adjust than a full day. Our Thai cooking class is from $30 per person, about 6.5 hours, with a morning session (pickup about 8:00 to 8:30 am, back about 2:30 pm) and an evening session (pickup about 3:00 to 3:30 pm, back about 9:30 pm). The farm is in the countryside about 45 minutes from the Old City, near San Kamphaeng, and the day includes a walk through the herb garden, so it is not a day indoors.
The Doi Inthanon and elephant sanctuary day, from $40 per person, runs 10 to 12 hours and includes a forest hike, and Doi Inthanon is roughly 1.5 to 2 hours by road from the city. On a red day it is the one to move; ask us on WhatsApp about changing the date. Our cooking class price guide explains what the $30 covers.
Should you avoid Chiang Mai from February to May
Not necessarily, but choose with open eyes. If you have free dates, the cooler months from November to January avoid the burning season, and the rainy months from June to October avoid it too. If your dates are fixed in February to May, note that the Pollution Control Department said there had been no hotspots before February 2026, and that the normals show rain returning in May. The edges of the window carry less risk, but every year differs.
If you go in the peak, build a flexible plan: a few indoor options, a hotel booking you can change if possible, and no single must-do outdoor day. Check Chiang Mai in November for the alternative season, and the best time to visit Chiang Mai guide for every month side by side.
Practical checklist
- Install the Air4Thai app and check the 24-hour PM2.5 average for your district the evening before and again in the morning.
- Remember the national limit: 37.5 µg/m³ over 24 hours.
- Keep a flexible plan for February to May: one indoor option for each day.
- Ask your doctor before travelling if you have a heart or lung condition.
- Book the long outdoor day, such as Doi Inthanon, early in your stay so you can move it if the reading is red.
- Tell us your dates and your hotel on WhatsApp and ask what we can reschedule.
Questions and answers
When is the burning season in Chiang Mai?
February to May. The National Environment Board declared Chiang Mai a pollution control zone for those months in 2025, and the province's 2026 burning ban ran from 1 January to 31 May. In 2026 the worst readings came in March.
What is the PM2.5 limit in Thailand?
37.5 µg/m³ as a 24-hour average, tightened from 50 and in force since 1 June 2023, with an annual limit of 15 µg/m³. These were published in the Royal Gazette in July 2022.
How bad was the smoke in 2026?
On 3 March 2026 PM2.5 exceeded the standard in 16 northern provinces, with readings from 18.4 to 112.7 µg/m³. On 28 March the Pollution Control Department said many upper-northern areas were red.
Where can I check air quality?
On the Pollution Control Department's Air4Thai website and app, which the department says can be monitored around the clock. Readings differ between districts, so check the one nearest you.
Is the cooking class cancelled when the air is bad?
We do not have a published rule for that. Tell us your dates and we confirm what can be moved before you pay. The class includes a garden walk at a farm outside the city.
Is Chiang Mai fine from June to October?
Smoke is not a problem then, but it is the rainy season. The 1991 to 2020 normals show 118 to 223 mm of rain a month from June to September.