As of January 24, 2025, Bangkok was ranked as the fourth worst city in terms of air quality (Bangkok Post, 2025). There has been a rise in PM2.5 levels over the past week, as seen in Figure 1 [1]. The Bangkok Metropolitan Administration (BMA) declared 48 of Bangkok’s 50 districts as red zones–areas where the air quality is hazardous to health–with particulate matter less than or equal to 2.5 micrometers in diameter levels averaging 88.4 micrograms per cubic meter (µg/m³) (Bangkok Post, 2025).
Airborne particulate matter (PM) is not a single pollutant but a complex mixture of solids and aerosols that vary in shape, size, and chemical composition. Particles are defined by their diameter; those measuring 2.5 microns or less are called PM2.5. Compared to our human hair, these particles are much smaller, as seen in Figure 2. Long-term exposure to PM2.5 leads to premature death, especially among people with chronic heart or lung diseases, and can also reduce lung function growth in children (California Air Resources Board, 2025).
PM2.5 is caused by many sources such as vehicle emissions, including vehicle emissions, with diesel engines being a main contributor. Agricultural burning such as crop burning further worsens air quality. Other sources include landfill fires, power plant generation, windblown dust, and household activities (e.g. cooking and heating) (AQI, 2019).
According to the Air Quality Data Centre of Bangkok, the average PM2.5 levels measured from 5:00 am to 7:00 am have been summarized (Nation Thailand, 2025). Below is a list of the 12 districts with the highest PM2.5 levels; please note that this is not the full list:
Nong Chok: 82.7 µg/m³ Sai Mai: 73.9 µg/m³ Min Buri: 73.1 µg/m³ Bueng Kum: 72.8 µg/m³ Khlong Sam Wa: 72.2 µg/m³ Khan Na Yao: 71.0 µg/m³ Lak Si: 69.4 µg/m³ Lat Krabang: 67.5 µg/m³ Sathorn: 66.3 µg/m³ Bang Na: 65.3 µg/m³ Wang Thong Lang: 65.1 µg/m³ Phasi Charoen: 64.5 µg/m³
PM2.5 impacts citizens' health, especially in areas with red-level air quality. Breathing air that is in red zones is as harmful to one's health as smoking 2.2 cigarettes a day (AQI, 2019). Therefore, to minimize exposure, citizens are advised to avoid outdoor activities whenever possible (AQI, 2019). For necessary outdoor activities, wearing protective gear such as an N95 mask and limiting the duration of strenuous exercise is recommended; indoor measures including using air purifiers and car filters are also suggested (AQI, 2019).
People with pre-existing health conditions should stay informed about the severe air pollution levels, keep medications and equipment close, and follow medical advice precisely. Lastly, it is essential to watch for unusual symptoms (e.g. coughing, shortness of breath, eye irritation, etc.), and seek immediate medical attention if they occur (Nation Thailand, 2025).
The PM2.5 concentration around the world is 6.8 times the World Health Organization's annual PM2.5 guideline value (IQAir, 2025). Citizens should remain vigilant and aware of the air quality index (AQI) before traveling to a destination. Credible AQI sources include www.aqi.in and www.iqair.com/th-en/.