A Survivor’s Guide to Chiang Mai’s Burning Season

Ryan Zander
6th March 2018

March is here, and right on cue the air quality in Chiang Mai and Northern Thailand has taken a turn for the worse. Yes, the “smoky season”—otherwise known as Chiang Mai’s “burning season”—is back again.

If you’re a new arrival to the city, you might have many questions: “What causes the smoke?”, “How bad does it get?”, “How long does it last?”, “Should I go somewhere else?”, etc.

As someone who has lived through many a smoky season—going back to 2002—I feel qualified to weigh in on this topic and give some advice. So let’s get right to it…

When is the smoky season in Chiang Mai?

The smoky season in Northern Thailand and the surrounding parts of Southeast Asia generally occurs during the months of February, March, and April.

The exact timing and severity of the haze is different every year because it is dependent on human activity and the weather.

The rainy season in this region is typically over by November, and so the air can start to get more hazy as early as December, though it doesn’t usually become problematic until late February or early March.

On the tail end, the haze doesn’t fully clear until the burning stops and rains come to wash the pollution out of the sky.

The real start of the rainy season isn’t until June, but there is usually enough rain in May to clear things up considerably. Hot season flash-storms in March and April can also help provide temporary relief for a couple days.

The smoky season consistently reaches it’s peak in the second half of March, and the air is usually much improved after the mid-April Songkran holiday. But there have been years where the hazy air has lingered on well into May.

What is the cause of the air pollution?

There are three main causes of the yearly northern haze:

  • Naturally occurring forest fires
  • Intentionally set forest fires
  • Burning crop fields

Smoky season coincides with the tail end of the yearly dry season, when there hasn’t been any significant rainfall in the region for several months. The forests of Northern Thailand are covered with dry leaves, and wildfires can spread quickly once there is a naturally occurring or accidental spark.

There are also many man-made forest fires at this time of year. Some are set to clear land for planting corn and other cash crops on mountain slopes. Some are set to clear underbrush in order to encourage the growth of rare, prized mushrooms. Others are set to trap wild boar and other game animals.

Down in the valleys, farmers burn the rice straw and corn stalks leftover from the previous harvests in preparation for the next planting.


The mountainous terrain of Northern Thailand causes the smoky air to stay trapped in the valleys and gradually increase in pollution levels.

How bad is the air during Chiang Mai’s burning season?

You can check real-time Air Quality Index (AQI) readings for Chiang Mai at or

During the month of March, AQI levels in Chiang Mai regularly fall in the 150-200 “Unhealthy” range in which “Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects”.

At “Unhealthy” levels, AQICN recommends “Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion”.

When the AQI spikes to 300+ the recommendation changes to “Everyone should avoid all outdoor exertion”.

Air quality tends to be worse in the mornings. Fires are often set in forests at night under the cover of darkness, and overnight cool temperatures make the polluted air heavier and sink down into the valleys. In the afternoons, the midday sun can heat up the air to “burn off” some of the smog for a slight improvement.

Is the burning season in Chiang Mai really that bad?


You may encounter a few strongly-opinionated members of the expat community on social media who claim to be completely unaffected by the smog and belittle anyone who believes it to be a serious health hazard.

For your own benefit, don’t listen to these stubborn folk and take the necessary steps to protect your short-term and long-term health.

The smoke is especially dangerous for young children, the elderly, and anyone who has ever suffered from asthma symptoms.

Hospital visits spike at this time every year, as people complain of sore throats, itchy eyes, coughing, sneezing, chest pain, and shortness of breath.

Longterm, there is some evidence that yearly exposure to seasonal smog doubles the lung cancer risk among Chiang Mai’s residents.

The smoke has been thick enough in the past to cause cancellation of flights scheduled to arrive at Chiang Mai International Airport and other regional airports due to a lack of visibility.

If the smog gets thick enough to hide runways and entire mountains from view, just think about what that’s doing to the inside of your body.

Should you leave town during the smoky season?

I always do—at least for the worst few weeks of it.

Once I can no longer see the mountain clearly from the center of town, I take it as a signal to head down south.


Obviously, not everyone is in a position to leave Chiang Mai for an extended period of time. If you’re involved in location-independent work, however, I think it makes little sense to stay in town and “tough it out” when you could be breathing fresh air elsewhere.

Where are the best places in Thailand to go during burning season?

Don’t make the mistake of thinking that just getting out of the city will lead to cleaner air. Much of the countryside in the northern region actually has higher air pollution levels than Chiang Mai. This is because most of the forest fires burn in the mountains.

For cleaner air, you need to head down south to the coastal regions, but not all are created equally.

The coastal areas on the Eastern Seaboard such as Pattaya and Rayong can still be affected by pollution blowing down from nearby industrial and agricultural regions.

The cleanest air at this time of year will be found on the southern peninsula and nearby islands.

Some popular locations to escape the smog include Phuket, Krabi, Koh Lanta, Koh Samui, and Koh Phangan. The only real downside is that you’ll be paying tourist prices for food and accommodation at all of these beach destinations.

How can you protect your health if you stay in Chiang Mai?

If you decide to stay in Chiang Mai during the burning season, there are three main things you can do to protect your health:

  1. Limit outdoor activities
  2. Wear a mask when outdoors
  3. Filter the air within your home

First, regarding outdoor activities, it is rather foolish to engage in jogging, cycling, and other strenuous physical activity outdoors during the smoky season.

In particular, outdoor sports should be avoided on the days when the AQI is over 150.

Aside from sporting activities, it’s a good idea to limit the amount of time you spend outdoors in general. When indoors, keep the windows shut and run the air conditioning instead.

Pollution masks

You will see many local people wearing standard surgical masks during the smoky season. These are, however, mostly useless for filtering out the small pollution particles of 2.5 microns in diameter that can lodge deep inside the lungs and cause the most health problems.

You need to get masks labeled “N95”, which are able to filter out 95% of the airborne particles measuring 0.3 microns and up.


Most of the pharmacies in town don’t sell these higher quality masks. One place that I’ve always been able to find them is at the large branch of Pharma Choice on Suthep Road located across the street from Suan Dok Hospital.

There is also a 3M Store located on Wulai Road (Saturday walking street) where these masks are available.


Filtering the air within your home

To keep the air within your home free of smog particles, the first thing you should do is keep the windows and doors shut on smoggy days. Run the air conditioner instead, even if it’s not that hot outside.

Make sure to clean the filters in your air conditioner. Not only will it help to keep the air clean, but you should already be doing this regularly to help the air conditioner run efficiently.

The next step that you can take is to purchase a home air purifier. These are available at large electric appliance stores such as Siam TV and home improvement stores such as Home Pro. Small air purifiers start at around THB 5,000.

Additionally, you can purchase special filter material at the 3M Store to make your regular air conditioner units effective at filtering out micro-particles.

You should also check your windows and doors for cracks that let smoky air get inside. I found that stuffing a rolled-up towel in the small gap at the bottom of my condo door really helped to prevent polluted air from getting in.

But I heard there won’t be any smoke this year because of a burning ban?

If you believe this, then I’ve got a lovely seaside resort in Chiang Rai I’d love to sell to you.

In all seriousness though, I’m always hopeful that the situation will improve. Every year there is a lot of talk, but I’ve seen no indication in the past 15+ years of any real change to the human behavior that causes the smoke pollution.

While it’s good to be optimistic, it’s even better to be realistic and make plans to deal with the pollution here or escape for several weeks.