Short answer. Check the Pollution Control Department's Air4Thai site, which shows the air quality index (AQI) at each monitoring station 2. Thailand's AQI has five levels, from "excellent" (0-25, blue) to "very unhealthy" (over 200, red); 100 equals the general air quality standard, and above it air starts to affect health 1. On orange and red days, the PCD advises PM2.5 masks outdoors 1.
Where can I check air quality right now?
On Air4Thai, run by the Pollution Control Department (PCD), which shows the index for each monitoring station 2. One index value stands for the concentrations of six pollutants: PM2.5, PM10, ozone, carbon monoxide, nitrogen dioxide and sulphur dioxide; the pollutant with the highest sub-index sets the AQI 1.
What do the index levels mean?
The official PCD scale 1:
| AQI | Level | Colour | Official advice 1 |
|---|---|---|---|
| 0-25 | Excellent | Blue | Everyone can live their life normally |
| 26-50 | Satisfactory | Green | General public: outdoor activities as normal. People needing special health care: watch for symptoms such as frequent coughing, difficulty breathing, wheezing, chest tightness, palpitations or dizziness |
| 51-100 | Moderate | Yellow | General public: reduce time spent on strenuous outdoor activity or exercise. People needing special health care: wear a PM2.5 mask every time you go out, reduce strenuous outdoor activity, see a doctor at once if symptoms appear |
| 101-200 | Unhealthy | Orange | General public: wear a PM2.5 mask outdoors, limit strenuous outdoor activity, watch for cough, breathing difficulty or eye irritation. People needing special health care: wear a mask, avoid strenuous outdoor activity, follow your doctor's advice |
| Over 200 | Very unhealthy | Red | Everyone: avoid outdoor activities, wear a PM2.5 mask outdoors, see a doctor if you have symptoms. People with chronic disease: stay in an area safe from air pollution, keep medicines and equipment ready |
For fine particles, an AQI of 100 matches a 24-hour PM2.5 average of 37.5 µg/m³, and the "very unhealthy" level starts above 75 µg/m³ 1. See Air quality index explained.
How polluted is the air on average?
The population-weighted median of Thai cities shows about 28 µg/m³ of PM2.5 (annual mean 2021-2023) 3, more than five times the WHO guideline of 5 µg/m³ 5. Nitrogen dioxide is about 18.5 µg/m³ 4, nearly twice the WHO guideline of 10 µg/m³ 5. That NO2 figure is a regional background over roughly 80 km: a busy street will be higher.
What should I do on a bad air day, or with smoke or dust?
- Yellow (51-100): if someone at home is sensitive, they should wear a PM2.5 mask outdoors and cut strenuous effort 1. See Sensitive people and polluted air and Children and polluted air.
- Orange (101-200): everyone should wear a PM2.5 mask outdoors and limit strenuous effort 1. See Masks for smoke.
- Red (over 200): everyone should avoid outdoor activities; people with chronic disease should stay somewhere safe from air pollution with their medicines ready 1. See A clean-air room at home.
- Smoke from fires: Phaenyx found no separate national page on wildfire smoke; follow the AQI advice above. See Wildfire smoke and Pollution episodes.
How official warnings reach you is on our Thailand alerts page. A household plan can note who at home is sensitive to polluted air and where to stay on bad days.
Frequently asked questions
What AQI is unhealthy in Thailand?
Above 100 the air begins to affect public health; 101-200 is "unhealthy" (orange) and over 200 is "very unhealthy" (red) 1.
How is Thailand's AQI scaled?
In five levels, from 0 to over 200, each with a colour; 100 corresponds to a 24-hour PM2.5 average of 37.5 µg/m³ 1.
When should I wear a PM2.5 mask?
The PCD advises it for sensitive people from the yellow level and for everyone from the orange level 1.
Which pollutants are in the index?
PM2.5, PM10, ozone, carbon monoxide, nitrogen dioxide and sulphur dioxide 1.
Sources
- Pollution Control Department (PCD, กรมควบคุมมลพิษ) — Air4Thai — About air quality index (AQI information) — https://air4thai.pcd.go.th/webV3/#/AQIInfo (accessed 2026-10-27)
- Pollution Control Department (PCD, กรมควบคุมมลพิษ) — Air4Thai (station map) — https://air4thai.pcd.go.th/webV3/ (accessed 2026-10-27)
- Atmospheric Composition Analysis Group (ACAG), Washington University in St. Louis — Surface PM2.5, V6.GL.02.04 (annual mean 2021-2023) — https://sites.wustl.edu/acag/datasets/surface-pm2-5/ (accessed 2026-10-27)
- Copernicus Atmosphere Monitoring Service (CAMS) — CAMS global reanalysis (EAC4) — https://ads.atmosphere.copernicus.eu/ (accessed 2026-10-27)
- World Health Organization (WHO) — WHO global air quality guidelines (2021) — https://www.who.int/publications/i/item/9789240034228 (accessed 2026-10-27)
Turn this into action
Your plan for Thailand, worked out for your household.
- Water, food and equipment counted for each person and pet
- The nuclear plants and zones around your home
- Phaenyx Safe: one tap to tell your people you are safe
Sources
- Pollution Control Department (PCD, กรมควบคุมมลพิษ) · Air4Thai — About air quality index (AQI information) checked 2026-10-27
- Pollution Control Department (PCD, กรมควบคุมมลพิษ) · Air4Thai (station map) checked 2026-10-27
- Atmospheric Composition Analysis Group (ACAG), Washington University in St. Louis · Surface PM2.5, V6.GL.02.04 (annual mean 2021-2023) checked 2026-10-27
- Copernicus Atmosphere Monitoring Service (CAMS) · CAMS global reanalysis (EAC4) checked 2026-10-27
- World Health Organization (WHO) · WHO global air quality guidelines (2021) checked 2026-10-27