Why Bangkok air gets bad
Bangkok has three pollution sources stacked together: 11 million vehicles, dense industrial activity to the east, and seasonal agricultural burning that drifts in from northern Thailand and neighboring countries. PM2.5 is the main concern — particles small enough to enter the bloodstream. The cool, calm weather of December-February traps these pollutants close to the ground instead of dispersing them.
Most of the year (April through December) Bangkok AQI sits between 40-90 — comparable to a normal day in any large city. The problem window is short but real.
Burning season explained
From late January to mid-March, farmers across Southeast Asia burn rice stubble and sugarcane fields to clear land for the next planting. Northern Thailand, Myanmar, Laos, and Cambodia all burn at the same time, sending smoke south. Combined with Bangkok traffic and stagnant high-pressure weather, this drives AQI past 150 and occasionally over 200.
February is the worst month historically. By late March monsoon winds shift and rains begin clearing the air. April onwards is usually fine.
Apps to track AQI
Install IQAir AirVisual before you arrive — it pulls from multiple sensors and gives a Bangkok-specific reading. The official Air4Thai app and the WAQI website (waqi.info) are also reliable. Check before going out: under 100 is fine for everyone, 100-150 is fine for most but worth a mask if you are sensitive, 150+ means mask outdoors and limit time in traffic.
Masks that actually work
Surgical masks do nothing for PM2.5 — the particles pass right through. You need KN95, N95, or KF94 rated masks. They sell at every Boots, Watsons, and many 7-Elevens for 30-80 baht each. Pack one or two from home and buy more locally if needed. A proper fit (no gap around the nose) matters more than the brand.
When to stay indoors
Above AQI 150, shift outdoor sightseeing to indoor activities. Bangkok is excellent for this — air-conditioned malls (Iconsiam, EmSphere, Siam Paragon), the Bangkok Art and Culture Centre, the Jim Thompson House, the National Museum, and rooftop pools at sealed hotels are all comfortable. Movie theaters, cooking classes, and Muay Thai gyms with closed AC also work well.
Most modern hotels and condos run filtered AC. If air quality matters to you, search booking listings for "air purifier" — many Sukhumvit and Silom properties now advertise it.
Kids, elderly and asthma
Sensitive groups — under-5s, over-65s, asthmatics, and pregnant travelers — should be more cautious. On AQI 150+ days, keep outdoor time short, wear a properly fitted mask, and choose accommodation with air purifiers. Bring any inhalers or allergy medication you normally use; pharmacies stock generic versions but specific brands may not be available. Consider scheduling Bangkok visits for April-December if pollution sensitivity is significant.