Where Is the Air Cleanest for Nomads? 17 Places, Month by Month

Which nomad bases have the cleanest air in winter?

In December to March the cleanest places in our data are Oaxaca, Playa del Carmen and Mérida in Mexico, and the worst are Kathmandu, Bangkok and Hanoi. Next come the Malaysian and Thai coasts. The strip shows average PM2.5 (fine particles, in µg/m³) from the CAMS air-quality model through Open-Meteo, mean of 2023 to 2025, for the 17 places where we hold air history, cleanest winter first. The ring marks December to March:

The first group, Oaxaca, Playa del Carmen, Mérida and Langkawi, sits at 6 to 12 in all four months. The Thai coast (Krabi, Phuket, Koh Samui) and Nha Trang read 8 to 16, lowest in December, close to the WHO 24-hour guideline of 15. The bottom of the strip is a different world: Bangkok, Kuala Lumpur, Hanoi and Kathmandu all average above 30 in at least one of those months, and above 50 in some.

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Does the ranking hold in summer?

No, and this is the trap in most "cleanest city" lists, which use a yearly average. Read the same strip along June to September. The monsoon clears Thailand and Nepal, while the haze season hits Malaysia. Koh Samui, Krabi, Phuket and Bangkok all drop to 5 to 15, and Pokhara reads 9 to 10 in July to September. Kuala Lumpur goes the other way: 41 to 44 from June to September, in the months when the Thai coasts are clean. Hanoi stays between 40 and 47 through the summer. If you move around the year, the place to be for air is not the same place in January and July.

Which places are clean all year?

The three Mexican bases and Langkawi, in our data. Oaxaca peaks at 18 in May, Playa del Carmen at 13 in July, Mérida at 15 in July and Langkawi at 12 in March and July. That is a real advantage of these bases that most weather pages never mention. It does not make all of Mexico clean: Mexico City reads 20 to 28 in every month, and its other big problem, ozone, is not in a PM2.5 figure at all (see our Mexico City air guide).

Even the cleanest places are not under the WHO annual guideline of 5 µg/m³. The WHO's 2021 guidelines set 5 for a year and 15 for 24 hours (older pages still quote 25, the 2005 value), and a monthly average hides worse days. A "clean" month here means low compared with the alternatives.

Which months are worst, and why?

Each region has its own mechanism, and our deeper pages cover the causes:

• Hanoi: polluted most of the year, worst in the cool months. See Hanoi air quality by month.
• Bangkok: bad from about October to March, clean in the rains. See Bangkok air quality.
• Kathmandu: winter smog and spring fires. See Kathmandu air quality.
• Kuala Lumpur and Penang: haze from burning elsewhere, mostly July to October. See Malaysia air quality.
• Chiang Mai: a burning season of its own, roughly February to April and worst in March and early April. It is not in the strip above. See Chiang Mai burning season.
• Bali: no island-wide season, but local burning. See Bali air quality.

How should you use this to pick a base?

1. Start with the season you will be there, not the yearly average. A place that is clean in July can be among the worst in February.
2. Use the coasts as the escape. In Thailand, Vietnam, Malaysia and Mexico, the island or coast reads far lower than the capital in the dry season.
3. Combine with weather. Clean air on the Thai coasts comes with the rain: June to September is the wet season on Krabi and Phuket. Our where is warm in January page ranks places on warmth and dry days, not air, so check both.
4. Keep a margin. Years differ a lot, so a three-year average tells you when, not how bad one particular year will be.
5. Check a live reading before you book, and again on arrival. Our figures are history, not a forecast. Not sure what the numbers mean? See PM2.5 or AQI.

We give no health advice. If you are sensitive to polluted air, ask a doctor before planning a long stay.

About this data

Fine-particle PM2.5 is daily values averaged by month, for one point per place, from the CAMS global air-quality model through Open-Meteo (CC BY 4.0). It is a model on a grid of roughly 45 km, not a ground sensor, and it reads low on bad days. Compare places and months with each other, not with a live monitor.