# How to Check AQI & PM2.5 in Chiang Mai (IQAir, Air4Thai) > Monitor Chiang Mai air quality reliably — IQAir vs Air4Thai, reading PM2.5, what the numbers mean and setting alerts. URL: https://chiangmaibrief.com/guide/how-to-check-aqi-pm25-chiang-mai/ Last-Modified: 2026-09-07 Author: The Chiang Mai Brief ## Two numbers, not one Most air quality apps lead with AQI, a scaled index designed for easy comparison. It’s useful, but it hides the underlying measurement and different countries calculate it differently. The number that actually matters for your lungs is **PM2.5 in µg/m³** — the raw concentration of fine particulate matter. Learn to read that directly and the readings stop being abstract. This guide sits under our burning season hub [/air-quality-and-burning-season/ →](/air-quality-and-burning-season/) , which covers the causes and the mitigation. ![A small air-quality monitor on a windowsill](/images/content/small-desktop-air-quality-monitor-device-sitting-o.webp) ## The sources residents use **IQAir** is the default for most people here. It aggregates official monitoring stations and a large network of private sensors, shows a map, and displays both AQI and raw PM2.5. The sensor density around Chiang Mai is good enough to see genuine variation across the valley. **Air4Thai** is the Thai Pollution Control Department’s official source. Fewer stations, government-calibrated equipment, and the authoritative reference when numbers are disputed. **Personal monitors.** A desktop PM2.5 monitor costs a few thousand baht and tells you what’s happening in your actual room rather than at a station two kilometres away. If you’re running purifiers, this is how you find out whether they’re working. Use a public app for the outdoor picture and a personal monitor for the indoor one. They answer different questions. ## Reading the numbers Working bands most Chiang Mai residents settle on: | PM2.5 (µg/m³) | Practical meaning | | --- | --- | | 0–12 | Excellent. Windows open, exercise outside | | 12–25 | Good. Normal life | | 25–55 | Moderate. Sensitive people notice it. Purifier on at night | | 55–100 | Unhealthy. Mask outside, limit outdoor exercise, purifiers running | | 100–150 | Very unhealthy. Stay indoors, seal the room | | 150+ | Hazardous. Minimise all outdoor exposure | These are practical thresholds, not medical advice. If you have a respiratory condition, your personal thresholds should be lower. ![A map of air quality sensor readings across Chiang Mai](/images/content/laptop-screen-showing-a-map-of-air-quality-sensor-.webp) ## Location matters Chiang Mai is not a single air quality reading. On a given morning you can see meaningfully different numbers between the Old City, Nimman, Hang Dong, Mae Rim and the higher ground. When you check, look at the sensor nearest to where you actually are, then a couple of others nearby to sanity-check. A single sensor can drift, sit next to a construction site, or simply be indoors by mistake. ## Setting up alerts Two settings worth configuring once and forgetting: 1. **A threshold alert** at whatever number changes your behaviour — commonly 55 µg/m³. The app tells you when to close windows rather than you remembering to look. 2. **A morning summary**, because the daily peak often comes early and the decision about whether to run or cycle is made before breakfast. ## Building a routine During the season, a workable habit is: - **Check at wake-up.** Decides windows, exercise and mask. - **Check before going out** in the afternoon. - **Watch the trend, not the spot value.** A rising number over three hours matters more than a single high reading. - **Cross-check indoors** with a personal monitor to confirm your purifiers are actually keeping up. Once your indoor numbers are consistently low, the outdoor readings become a planning tool rather than a source of anxiety. Our guide to sealing your room and staying indoors safely [/guide/sealing-your-room-staying-indoors/ →](/guide/sealing-your-room-staying-indoors/) covers how to get there. Got questions? ## Common questions What's the best air quality app for Chiang Mai? IQAir is the most widely used among residents, showing both AQI and raw PM2.5 with a map of nearby sensors. Air4Thai is the official Thai government source and useful as a cross-check. Most people run one as their default and glance at the other when readings look surprising. What PM2.5 level is unhealthy? World Health Organization guidance sets a very low annual threshold, but for daily decisions most residents use rough bands: under 25 µg/m³ is normal life, 25–55 is noticeable for sensitive people, 55–150 means purifiers on and masks outside, and above 150 means staying indoors and reconsidering your plans. Why do different apps show different numbers? Because they read different sensors in different places. Air quality varies substantially across the Chiang Mai valley — a reading from Hang Dong can differ from one in the Old City on the same morning. Check the sensor location, not just the number, and look at two or three nearby readings. More in this area ## Related guides 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/) 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/)