Hanoi Air Quality: Which Months Are Worst, and Where Nomads Go Instead

When is Hanoi's air worst?

Officially, from about October to March. A ministry official quoted by VietnamNet described a season of worse air from September to March, with cold northeast monsoon air, inversions, and in January to March fog and drizzle that stop pollution from dispersing. A December 2025 Dan Tri report says the northern season lasts to April.

Our own history says something more awkward, and more useful if you are choosing a month. It comes from the CAMS air-quality model through Open-Meteo, for central Hanoi, averaged over 2023, 2024 and 2025. The strip also shows the three coastal bases and Bangkok for the same months, so you can compare as you read:

Read Hanoi's row first. The highest months are April, January and December, at 55, 53 and 52 µg/m³. The lowest is October at 39, with February, May and June at 40. That is a spread of 16 between the best and worst month, in a place where no month comes near the WHO daily guideline of 15 µg/m³.

Where to be next: your month-by-month route, $19

A route for your months with a leave-by date for each stop, a backup, and the seasonal traps on your path. Drafted from 11 years of weather data, every number checked against it, in your inbox within 48 hours. Not included: visas, insurance or bookings.

See a sample plan Get my plan, $19

Is there a clean month in Hanoi?

No, and this is the main thing to know before you plan around the "worst season" headlines. The cool-season peak is real in the official accounts and in our December and January figures, but the summer months are not clean either: July averaged 41 and August 47. Summer rain should help, but the city's traffic, construction and industry continue all year.

Year to year matters too. January averaged 58 in 2023, 31 in 2024 and 71 in 2025 in our model. One winter can be mild and the next heavy, so a three-year average is a guide, not a forecast.

The model also reads below ground stations on bad days (it averages an area about 45 km across and smooths peaks). Real streets in Hanoi on a bad morning will be worse than these numbers. Use the strip to compare months and cities with each other, not as the level outside your window.

What causes Hanoi's winter smog?

The sources we found agree on a mix:

• Traffic: motorbikes are the largest road source, followed by trucks and buses.
• Construction and industry: building sites, factories in and around the city, and coal for industry.
• Burning: household coal stoves, rubbish burning, and rice straw burning in districts outside the city after harvests.
• Weather in the cool season: temperature inversions and still air hold the city's emissions near the ground. From January to March, fog and drizzle add to it.

None of this is a surprise to residents, which is part of why the numbers do not change much with the calendar. The weather decides how bad, not whether.

Where is the air cleaner than Hanoi from December to February?

On the coast. The strip above shows it: Nha Trang is the cleanest at 9 µg/m³ in December, 13 in January and 12 in February, a third of Hanoi's level or less. Da Nang is next, and Ho Chi Minh City is higher but still well below the capital. Bangkok, at 31 in December, 54 in January and 50 in February, is not the escape from Hanoi in January.

The catch is weather. Da Nang is a winter trap for rain; see Da Nang in December and Vietnam in January for how the three regions compare. Hanoi itself is cool and grey in winter (all twelve months are in Hanoi weather by month), so the trade is a cool city with worse air against a warmer coast with cleaner air and, on the central coast in December, a lot of rain.

Where to go instead: three coastal bases

• Nha Trang

  26° high in Jan57 mm in Jan

  The cleanest of the group in our model, 9 to 13 µg/m³ from December to February, a third of Hanoi's level or less. Its wet season runs through December, so January and February suit it best.

  Suits: people who put air first and want a warm, dry coast from January

• Da Nang

  24° high in Jan100 mm in Jan

  Reads 17 in December, 20 in January and 17 in February. December is its wettest stretch: see Da Nang in December before you book.

  Suits: people who want a clean-air city and can take a cool, damp January

• Ho Chi Minh City

  32° high in Jan16 mm in Jan

  Higher than the coast, 29 in December, 31 in January and 21 in February, but well below the capital. Dry and hot all winter.

  Suits: people who want a big city, sun and every service, with better air than Hanoi

How should you plan a winter in Vietnam?

A few honest rules from the data:

1. If air is your priority, go south for December to February and visit Hanoi for a week, not a season. Ho Chi Minh City is the dry, warm option with air well below Hanoi's. Nha Trang has the cleanest air but is wet through December, so it suits January and February best. Da Nang is clean too, but December is its wettest month.
2. If you must be in Hanoi, no month beats the others by enough to justify moving your dates. Choose by weather, work and cost, then check live readings for your district and that day.
3. Check live readings before booking an apartment. IQAir and AQICN both list stations in Hanoi; check which one is nearest to where you will live, and when it last reported.
4. Compare with the other usual winter bases. For northern Thailand's season see Chiang Mai burning season, and for Bali's different problem, Bali air quality.

We give no health advice here. If you are sensitive to polluted air, speak to a doctor before choosing a long stay.