Chiang Mai Provincial Health Office: Air Quality Warning

PM2.5 levels across Chiang Mai are expected to remain at unhealthy levels the end of the month. PM2.5 refers to particles smaller than 2.5 micrometres, about thirty times thinner than a human hair. their tiny size, these particles can travel deep into the lungs and even enter the bloodstream.

Children, older people, pregnant women and people with heart or lung conditions are at risk. They should avoid outdoor exercise and stay indoors as much as possible.

When going outside, wear a properly fitted N95 mask. Ordinary cloth or surgical masks little protection against such small particles. Keep windows closed, and if possible use an air purifier in the room you sleep.

Seek medical advice immediately if you experience difficulty breathing, chest pain or a cough that does not . Updated readings are available every hour on the Air4Thai website and app.

Residents are reminded that outdoor burning of any kind is prohibited the dry season. Fines of up to 50,000 baht may apply.

Cars at the Gate: A Student Study of PM2.5 at School · by Mew Inthachai, Grade 12

Every dry season, Chiang Mai some of the worst air in the world. Most discussion focuses on crop burning and forest fires, which are the largest sources. However, I wanted to find out whether local sources, such as traffic, also a difference at my school.

I placed three low-cost sensors in a classroom, at the school gate and on the sports field. I recorded PM2.5 every fifteen minutes for two weeks. On alternate days, the school allowed cars to enter the gate area it did not.

The results were clear. On days when cars were allowed, PM2.5 at the gate rose sharply between 7:00 and 8:00, parents were dropping off their children. On car-free days, average levels at the gate were 38 per cent lower.

my study has limitations. Low-cost sensors are less accurate than official equipment, and two weeks is a short period. Weather also the results.

Still, the findings suggest a simple measure that the school can take immediately. The director has agreed to test a no-idling rule for one month. Traffic is not the main cause of Chiang Mai’s smoke, but it is one we can today. Large problems are often solved by many small changes, just one big one.

What Do the Colours Mean? · Air Quality Index (AQI) Guide for Schools

Blue (0–25): Very good. All outdoor activities are fine.

Green (26–50): Good. Outdoor activities are fine for everyone.

Yellow (51–100): Moderate. Students with asthma or allergies should take breaks during long outdoor activities.

Orange (101–200): Unhealthy for sensitive groups. Move PE lessons indoors. Shorten outdoor break times. Students with asthma should stay inside.

Red (above 200): Unhealthy for everyone. All activities must take place indoors. Schools should consider closing if classrooms do not have air purifiers.

Schools should check the AQI at 7:00 and again at 11:00, because levels can change quickly during the day.

Where Does the Smoke Come From?

Every year between February and April, northern Thailand faces some of the worst air pollution on Earth. On bad days, Chiang Mai’s air quality has ranked among the poorest of any major city in the world. Understanding the causes is the first step towards solving the problem, but the causes are more complicated than they first appear.

The largest single source is burning. Farmers in the region, and in neighbouring countries, burn crop waste after the harvest, especially from maize grown to feed animals. Burning is cheap and fast, while machines that remove crop waste are expensive. Forest fires, some started deliberately to clear land or to encourage the growth of mushrooms and young plants that can be sold, add even more smoke.

Geography makes the situation worse. Chiang Mai sits in a valley surrounded by mountains. In the dry season, a layer of warm air often lies above cooler air near the ground, trapping the smoke like a lid on a pot. Without wind or rain, the pollution has nowhere to go.

Local sources such as traffic and industry contribute less, but they are not unimportant, especially in the city centre.

Because smoke crosses borders, no single province or country can solve the problem alone. Some experts argue that the companies that buy maize from farmers should share responsibility, for example by refusing to buy crops from burned fields or by helping farmers afford alternatives. Others warn that punishing poor farmers without offering them real alternatives will simply move the burning somewhere else.

Letter: Don’t Blame the Farmers Alone

Every March, when the sky over Chiang Mai turns grey, the same story appears in newspapers and on social media: farmers are burning their fields, and they are poisoning the city. As a student who has interviewed farmers for a school project, I want to offer a more complete picture.

The farmers I met are not careless people. One of them, a maize grower in Mae Chaem, told me that his own grandchildren cough during the smoke season. He burns his fields because a machine to clear them would cost more than he earns in a year, and because the company that buys his maize pays for crops, not for clean air.

It is easy for city residents to point at farmers. It is harder to ask why so much maize is grown on steep hillsides in the first place, who profits from it, and why the cheapest choice for farmers is also the most harmful choice for everyone else.

I am not saying that burning is acceptable. It is not. But real solutions will require the companies that buy crops, the government and city residents to share the cost of change. Shared machines, fair prices for crops from unburned fields, and support for farmers who switch to other crops would all help.

Clean air is a right for everyone, including the farmers whose families breathe the same smoke.

Mew Inthachai, Chiang Mai