Air quality, and the months Hanoi is worth checking
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Nobody plans a trip around air quality, and for most visitors nobody needs to. The exception is specific enough to name. Hanoi between November and March: a still winter morning can put the city near the top of the world rankings for a few hours.
The rest of the country is mostly fine, and the pattern is seasonal rather than permanent.
Where is it actually bad?
Two cities, and one of them only in winter.
| Where | When | Typical winter AQI | Notes |
|---|---|---|---|
| Hanoi | November-March | Often 150-200+ on still mornings | Inversion traps traffic, industry and burning |
| Ho Chi Minh City | December-March | Usually 90-150 | Better ventilated, worse traffic |
| Central coast | All year | Mostly under 80 | Sea breeze does the work |
| Mountains, islands | All year | Under 50 typically | Except spring crop burning |
The mechanism is the one that gives northern European cities their bad winter days. Cool, still air sits under a lid of warmer air, and nothing disperses. Add traffic, construction and the burning of crop residue in the surrounding provinces, and a January morning can be genuinely unpleasant.
Summer clears it. The rain and wind of May to October scrub the city. That is inconvenient: the best time to visit points at exactly the months when northern air is worst.
How do you check it?
IQAir is the app most people use, and Google will show a city AQI if you search for it. Check on the morning rather than relying on a forecast. A clear day and a bad day sit next to each other in winter, and the difference is wind.
The numbers worth remembering: under 50 is clean and under 100 ordinary. Over 150 is unhealthy for everyone, and over 200 is a day to spend indoors.
What actually helps?
An N95 or KN95 mask, which filters fine particles. The cloth and surgical masks on every street corner do not: those are worn against sun, dust and exhaust. Bring a few or buy them at a pharmacy.
Timing the day helps too. Air is worst in the still hours after dawn in winter, the opposite of the morning advice that holds all year otherwise. On a bad week, move the outdoor part of the day to the afternoon when the air has stirred.
Hotels with decent air conditioning filter some of it, and a room with an air purifier is worth asking about for a long stay. The rainy day guide doubles as a bad-air-day guide: museums, cooking classes, coffee, tailors.
Does it change where you should go?
For a healthy adult on a two-week trip, no. Hanoi in January is a great city to visit. The air will not spoil it, even if a few mornings look like the photograph above.
Three cases are worth planning around: asthma or another lung condition, small children, and a stay of several weeks over the winter. The answer is not to skip the north but to weight the trip towards the coast and the mountains. The Ha Giang loop, Sapa, Phu Quoc and Con Dao are all clean.
What does it mean for a day of riding?
More than it means for a day of walking. A motorbike rider breathes hard at road level for hours, directly behind exhausts, which is the worst place to be on a bad day. So do the riders and pillions on every bike taxi in the city.
Exhaust at head height is why so many Vietnamese riders wear masks all year. Most of those masks are for sun and grit rather than particles, but the instinct is sound, and a proper mask under a helmet costs nothing and helps.
What about the countryside?
Cleaner, with one seasonal exception. Crop residue burning follows the harvests in the delta provinces around Hanoi and in the northwest. For a few weeks it puts smoke over places that are otherwise pristine.
Smoke like that is a nuisance for photographs more than for health, and it is short. The health guide covers what genuinely makes travellers ill here, and air quality sits well down that list. Food, sun and traffic all rank above it.
FAQ
Is air pollution a problem in Vietnam?
In Hanoi in winter, yes, and it regularly ranks among the worst capitals in the world during that stretch. Ho Chi Minh City is better, the coast is usually fine, and the mountains and islands are clean.
When is Hanoi's air at its worst?
Roughly November to March, and worst on still, cool mornings when a temperature inversion traps everything under the city. The summer is far better because rain and wind clear it, which is the opposite of the visiting season most people choose.
How do you check air quality in Vietnam?
IQAir and the AirVisual app read the same monitoring stations most people use, and Google shows an AQI figure for a city too. Check the morning of, not the forecast, since a bad day can follow a clear one.
What counts as bad?
An AQI over 150 is unhealthy for everyone and Hanoi passes that on many winter days; over 200 is where sensitive people should stay indoors. Under 100 is an ordinary day and under 50 is genuinely clean.
Does a mask help?
An N95 or KN95 does, and the cloth and surgical masks sold everywhere do not filter fine particles. Most Vietnamese masks are worn against sun, dust and exhaust rather than PM2.5, which is a different problem.
Should air quality change your plans?
Rarely for a healthy adult on a short trip. It is worth planning around for anyone with asthma or a lung condition, for small children, and for anyone spending several weeks in Hanoi over the winter.
Where is the air reliably clean?
Phu Quoc, Con Dao, the central coast outside the cities, and the northern mountains. Sapa, Ha Giang and Mu Cang Chai are clean apart from the smoke of agricultural burning in a few weeks of spring.