Chiang Mai, Thailand’s second-largest city, lies within a network of narrow valleys in the country’s northern highlands. Though the historic city is known for panoramic views of the surrounding mountains, clear skies have become less common. In recent decades, smoke has increasingly darkened the skies during the dry season, particularly in March and April.
A NASA satellite captured this smoky view of the city and the surrounding region on April 22, 2026, when haze partially obscured valleys and ridges typically visible under clearer conditions. Most of the smoke likely comes from small agricultural and forest fires lit to burn off crop debris or maintain forest ecosystems. In 2026, satellite sensors detected small numbers of fires throughout January, but fire detections became more numerous and widespread in February, March, and April. Fire activity typically peaks in March and fades by May as seasonal rains increase.
Research indicates that smoke from biomass burning is one of the largest contributors to poor air quality in northern Thailand during the dry season. By one estimate, about 70 percent of fine particulate matter (PM2.5) in Chiang Mai in April comes from biomass burning. Smaller contributors to the region’s hazy skies include vehicles, power plants and industry, and charcoal burning for cooking and heating. Geography also plays a key role; the surrounding mountains block air flow and encourage temperature inversions that trap both local pollution and haze from the broader region in the valleys.
On the same day the satellite image was captured, air quality sensors on the ground recorded “unhealthy” and “very unhealthy” levels of PM2.5 air pollution throughout Chiang Mai and the region, according to data from the World Air Quality Index project. Prolonged exposure to high levels of air pollution can contribute to respiratory and cardiovascular diseases and other health problems.
News reports suggest that the haze is …