Looking to find the worst AQI cities in Thailand? Smart Air analyzed 2025 air pollution data for dozens of Thailand cities to generate the ranking of the “10 Most Polluted Cities in Thailand”.

Scroll down for the full rundown of the most polluted cities in Thailand and their annual PM2.5 levels. and their annual PM2.5 levels. The annual average PM2.5 in micrograms (µg/m3) is also given. For reference, the WHO recommended annual limit is 5 micrograms.

Rankings: 10 Worst AQI Cities in Thailand

1. Samut Prakan (31.3 µg/m3)

2. Samut Sakhon (27.1 µg/m3)

3. Khon Kaen (26.5 µg/m3)

4. Phitsanulok (24.1 µg/m3)

5. Pak Kret (23.8 µg/m3)

6. Kanchanaburi (23.1 µg/m3)

7. Lampang (23 µg/m3)

8. Bangkok (22.7 µg/m3)

9. Nakhon Pathom (22.6 µg/m3)

10. Ubon Ratchathani (22.6 µg/m3)

Read More: The 10 Least Polluted Cities in Thailand?

Analysis: Most Polluted Cities in Thailand

This dataset shows PM2.5 levels ranging from 22.6 µg/m³ to 31.3 µg/m³, with Samut Prakan (31.3 µg/m³) recording the highest level among the cities listed. All cities fall well above the WHO annual guideline of 5 µg/m³, and even exceed the WHO interim target of 15 µg/m³. This indicates that air quality in these cities is consistently in the moderate-to-unhealthy range from a long-term health perspective.

A noticeable pattern is that several of the highest PM2.5 cities are located in or around the Bangkok metropolitan and central industrial corridor, including Samut Prakan, Samut Sakhon, Pak Kret (Nonthaburi), Bangkok, and Nakhon Pathom. These areas are heavily urbanized and industrialized, with dense traffic, logistics hubs, manufacturing activity, and port operations, all of which contribute to higher fine particulate concentrations.

Northern and northeastern cities such as Lampang, Khon Kaen, and Phitsanulok also appear in this higher-pollution list. In northern Thailand, seasonal agricultural burning and transboundary haze often elevate PM2.5 levels, while northeastern urban centers may experience a mix of traffic emissions and regional biomass burning impacts.

How Air Pollution Was Measured to Find the Most Polluted Cities in Thailand

The above rankings of the most polluted cities in Thailand were based on their average PM_2.5 pollution levels from 2025.

These small pollutants are under 2.5 micrograms in width and are considered to be one of the more dangerous pollutants due to their ability to enter deep into the lungs and bloodstream.