Smokey Season

smokey season in chiang mai

Every year it’s the same story in Chiang Mai and Northern Thailand: as the cool season draws to an end around late February or early March, the air quality quickly takes 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.

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. It doesn’t usually become problematic, though, 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.

The air in Chiang Mai is good for about ten months of the year. The other two, however, can be quite bad.

what causes air pollution in Chiang mai

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. By the time February and March roll around, 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 as the dry season progresses.

The bordering areas of Myanmar and Laos face the same problem. They have similar terrain and similar human and natural causes that add to the total air pollution level in the region.

Although sugar cane is not extensively grown in the North, the practice of burning sugar cane fields in Central and Northeast Thailand and in Cambodia also contributes significantly to the region’s pollution woes.

The severity of the pollution problem can vary greatly from year-to-year and day-to-day within any single year. A large forest fire or crop-burning can spike the pollution level overnight, while a strong rainstorm or shift in wind currents can clear much of the dust from the air just as quickly.

The best way to monitor pollution levels is to install the AirVisual app on your phone. Their huge user base allows them to collect an incredible number of live Air Quality Index (AQI) readings from all over the globe.

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.

what does prem do to protect the community during smokey season?

One of the challenges that Term 3 (January-April) brings is the annual Smokey Season in Chiang Mai and the high AQI (Air Quality Index) levels. However, at Prem we are better prepared than ever to keep our community safe during these times. The Positive Pressure System (PPS), Air Purifiers and Smokey Season Protocols mean that we have a robust system in place to keep our learning spaces with clean and purified air, even when the AQI levels are high outside. We are proud to say that in terms of air quality within our learning spaces, we have the cleanest air out of all the international schools in Chiang Mai and among the best in Thailand.

Please see the Positive Pressure System Page for more details on how we protect the Prem Community for the effects of the Smokey Season

what can you do to protect yourself during smokey season?

There are three main things you can do to protect your health during times of bad air quality:

Limit outdoor activities
Wear a mask when outdoors
Purify 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. The Prem shop has a stock of 'Style Seal' pollution masks, which can also be found on Lazada or Shopee

Purifying 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. Additionally, you can purchase special filter material called Filtrete™ at the 3M Store to make your regular air conditioner units effective at filtering out some of the micro-particles. 3M’s Filtrete™ is also carried by HomePro. If both of these locations are out of stock, you can try checking Lazada to order some online.

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 HomePro. Small air purifiers start at around THB 5,000. A very popular model is the Xiaomi Mi 2S Air Purifier.

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