Chiang Mai smoke season: clean air at home
When the smoke comes, the numbers to know and what helps at home, including the 999 villas with an ERV system that filters PM2.5.
When is the smoke season?
In ten years of official measurements (Pollution Control Department, station 36T in Chiang Mai), the smoke came every year between February and April, from farm burning and forest fires in the north and the countries around. The rest of the year the air is usually much cleaner.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
smoke months usually much cleaner
It changes a lot from year to year: in 2022, with strict burning control, January to April averaged 29.5 µg/m³, against 54.2 in 2019.
How to read PM2.5
- What PM2.5 is
- Dust smaller than 2.5 micrometres, measured in micrograms per cubic metre (µg/m³).
- Thailand's standard
- 37.5 µg/m³ as a 24-hour average (since June 2023).
- The WHO guideline
- 15 µg/m³ as a 24-hour average.
- Check it live
- The Air4Thai app of the Pollution Control Department, or IQAir.
What helps at home
From the US Environmental Protection Agency's advice for smoky days.
Keep windows and doors closed on smoky days
Air the house when the reading is low, for example after rain.
An air purifier with a HEPA filter
Pick one made for the size of the room, and run it in the bedroom at night.
Air conditioning without outside air
Clean the filters more often in the smoke months.
One cleaner air room
Make one room the cleanest: closed, with a purifier. Good for children and older family members.
No smoke inside
No incense or candles indoors on smoky days.
A mask outside
An N95 or KN95 mask filters much more than a cloth or surgical mask.
999 villas with an ERV system that filters PM2.5
Every villa at 999@Pa Daet, the Gold villa at 999@World Club Land and the 999@Kad Farang villa come with an ERV system (energy recovery ventilation) that filters PM2.5.
999@Pa Daet
- ERV system, PM2.5 filterevery villa
999@World Club Land
- ERV system, PM2.5 filterthe Gold villa
999@Kad Farang
- ERV system, PM2.5 filterthis villa
Why an ERV and not a positive pressure system?
Stale air out, fresh air in
An ERV takes stale air out and brings filtered outside air in at the same time. A positive pressure system only blows air in and lets the old air leak out through gaps.
Easier on the air conditioning
The cool air going out takes heat from the warm air coming in. A system without energy recovery leaves the air conditioning to cool all the outside air.
Less humidity
An ERV also moves moisture, so less outdoor humidity comes in on hot, humid days.
Balanced air pressure
As much air goes out as comes in, so the house is not pushed to a high or low air pressure.
Like any filter system, its filters need cleaning or changing on time.
Questions people ask
When is the smoke season in Chiang Mai?
Usually February to April. It changes from year to year: rain and burning control make a big difference.
Is the air bad all year?
No. In ten years of official data the haze came between February and April. The rest of the year the air is usually much cleaner.
Which 999 villas have an ERV system that filters PM2.5?
Every villa at 999@Pa Daet, the Gold villa at 999@World Club Land and the 999@Kad Farang villa come with an ERV system (energy recovery ventilation) that filters PM2.5.
What is an ERV system?
A fresh air system that takes stale air out and brings filtered outside air in at the same time, through a heat exchanger. It recovers energy and moisture, so the air conditioning works less (US Department of Energy).
Does an air purifier help?
Yes, with the windows closed and a purifier made for the size of the room. Look for a HEPA filter and the room size on the box.
Book a viewing of a 999 pool villa
Or ask us anything. We reply within 1 working day, often sooner.
Opening hours: Monday to Saturday, 08:30 to 17:30
Thailand's PM2.5 standard: Pollution Control Department (37.5 µg/m³, 24 hours, since June 2023).
WHO global air quality guidelines (2021).
Smoke months and the 2019 and 2022 figures: Vijayan, Maneelok and Noosai, Thai Environmental Engineering Journal 39(2), 2025 (station 36T, 2015 to 2024).
Tips at home: the US EPA's Cleaner Air Room fact sheet.
ERV systems: US Department of Energy, Building America guide "Selecting Ventilation Systems for Existing Homes".
Updated October 2026 by the 999 Developments team