# Chiang Mai Burning Season & Air Quality | The Chiang Mai Brief > The definitive Chiang Mai burning-season guide — when it starts, why the air gets so bad, how to check AQI, protect yourself, and where to escape the smoke. URL: https://chiangmaibrief.com/air-quality-and-burning-season/ ![Chiang Mai under seasonal haze with Doi Suthep barely visible](/images/misc/chiang-mai-skyline-seen-through-thick-seasonal-haz.webp) Living in Chiang Mai # Chiang Mai's Burning Season & Air Quality, Explained Last updated: 7 September 2026 An authoritative, evergreen hub on Chiang Mai's seasonal air pollution — when the burning season runs, why the basin effect makes it so bad, how to monitor AQI and PM2.5, how to protect yourself indoors, and where to escape. Read the guides [#guides →](#guides) Subscribe to the Brief [/newsletter/ →](/newsletter/) In this section ## What's in our Air Quality coverage ### When it actually happens The realistic timeline — early signs, the peak weeks, and when the first rains usually clear it. ### Why Chiang Mai specifically The basin geography, the inversion layer and the regional agricultural burning that combine to trap smoke over the city. ### Monitoring that means something Reading AQI and raw PM2.5 numbers, which sources to trust, and what the thresholds mean for your day. ### Protecting yourself Purifier sizing, sealing a room, mask choice, and the habits that make March liveable. ## 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: | PM2.5 (µg/m³) | What it means in practice | | --- | --- | | Under 25 | Normal life, windows open | | 25–55 | Fine for most, sensitive people notice it | | 55–150 | Purifier on, limit outdoor exercise, mask outside | | 150+ | Stay indoors, seal the room, reconsider your March plans | **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. Guides ## Air Quality guides Every evergreen guide we've published on air quality & burning season in Chiang Mai. All guides [/guide/ →](/guide/) Comparison ### Best Air Purifiers for Chiang Mai (HEPA Buyer Guide) Choose an air purifier for Chiang Mai's smoke — HEPA H13/H14 and CADR explained, Xiaomi, Coway, Levoit and Blueair compared, and room sizing. 7 min read [Best Air Purifiers for Chiang Mai (HEPA Buyer Guide) →](/guide/best-air-purifiers-chiang-mai/) Step by step ### How to Check AQI & PM2.5 in Chiang Mai Monitor Chiang Mai air quality reliably — IQAir vs Air4Thai, reading PM2.5, what the numbers mean and setting alerts. 5 min read [How to Check AQI & PM2.5 in Chiang Mai →](/guide/how-to-check-aqi-pm25-chiang-mai/) Common concern ### Sealing Your Room & Staying Indoors Safely Practical steps to reduce indoor smoke exposure in Chiang Mai — sealing your room, positive-pressure setups, N95/KN95 masks and safe venues. 5 min read [Sealing Your Room & Staying Indoors Safely →](/guide/sealing-your-room-staying-indoors/) Decision guide ### Should You Leave Chiang Mai During Burning Season? An honest framing of the stay-or-go decision for Chiang Mai's burning season — health risk factors, the cost of leaving, and who should go. 5 min read [Should You Leave Chiang Mai During Burning Season? →](/guide/should-you-leave-during-burning-season/) How often ### When Is Chiang Mai's Burning Season? (Dates) When Chiang Mai's smoke season starts, peaks and ends — a month-by-month timeline, the historical AQI pattern and year-to-year variation. 6 min read [When Is Chiang Mai's Burning Season? (Dates) →](/guide/when-is-chiang-mai-burning-season/) Scenario ### Where to Escape the Smoke: Burning-Season Getaways Cleaner-air destinations to escape Chiang Mai's peak smoke — coastal and island options, higher-altitude escapes, timing and budget notes. 5 min read [Where to Escape the Smoke: Burning-Season Getaways →](/guide/where-to-escape-the-smoke/) Explainer ### Why Chiang Mai's Air Gets So Bad: The Basin Effect The causes of Chiang Mai's seasonal haze — agricultural burning, the Doi Suthep basin and inversion effect, and transboundary smoke. 5 min read [Why Chiang Mai's Air Gets So Bad: The Basin Effect →](/guide/why-chiang-mai-air-gets-bad-basin-effect/) Got questions? ## Air Quality: common questions When is Chiang Mai's burning season? The smoke season generally runs from February to April, with March almost always the worst month. Some years start earlier and some break earlier, so treat those dates as a pattern rather than a schedule. The first substantial rains, usually in late April or early May, clear the air quickly. How bad does the air actually get? In peak weeks Chiang Mai regularly appears at or near the top of global air-quality rankings, with PM2.5 readings many times World Health Organization guidance. Outside those weeks — for roughly nine months of the year — Chiang Mai's air is unremarkable and often good. Should I leave Chiang Mai during burning season? Many long-term residents do, for two to six weeks around the March peak. Whether you should depends on your health, your work flexibility and your tolerance. Our decision guide walks through the honest trade-offs and the alternatives if you're staying. What kind of air purifier do I need? A True HEPA (H13 or H14) filter with a CADR rating matched to your room size. Sizing matters more than brand — an underpowered purifier in a large room does very little. One good unit in the bedroom beats three weak ones spread around the flat. Do surgical masks help? Not meaningfully against PM2.5. You need an N95 or KN95 respirator with a proper seal around the nose and cheeks. A well-fitted KN95 makes a genuine difference on a bad day outdoors. Which app should I use to check air quality? IQAir is the most widely used among residents and shows both AQI and raw PM2.5. Air4Thai is the Thai government source. Cross-check the two, and pay attention to the sensor location — readings vary noticeably across the valley. Keep exploring ## Related sections ![The reception area of a private hospital in Chiang Mai](/images/misc/bright-modern-hospital-reception-area-in-chiang-ma.webp) Living in Chiang Mai ### Healthcare & Hospitals Hospitals, insurance and dental care for foreigners in Chiang Mai. [Healthcare & Hospitals →](/healthcare-and-hospitals/) ![Forested mountain ridges and mist in the valleys near Chiang Mai](/images/misc/forested-mountain-ridges-north-of-chiang-mai-with-.webp) Travel ### Day Trips & Nature Day trips beyond the city, nature and travel connections. [Day Trips & Nature →](/day-trips-and-nature/) ![Thai baht notes and a market receipt on a wooden table in Chiang Mai](/images/misc/thai-banknotes-and-coins-beside-a-market-receipt-a.webp) Living in Chiang Mai ### Cost of Living Realistic budgets and spending breakdowns for living in Chiang Mai. [Cost of Living →](/cost-of-living/) Newsletter ## Get the Brief in your inbox Twice a month: new openings, events, changes worth knowing about, and our latest guides. No filler. You're on the list Check your inbox: the next Brief goes out within a fortnight. ![Evening view across Chiang Mai rooftops toward Doi Suthep](/images/misc/evening-view-over-chiang-mai-rooftops-with-doi-sut.webp) The Chiang Mai Brief ## Keep up with Chiang Mai Twice a month we send the openings, changes and guides worth knowing about. It takes two minutes to read. Subscribe to the Brief [/newsletter/ →](/newsletter/) Explore the Guides [/guide/ →](/guide/)