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 havebecome less common. In recent decades, smoke hasincreasingly darkenedthe 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 morenumerous and widespreadin February, March, and April. Fire activity typically peaks inMarchand fades by May as seasonal rains increase.
Research indicates that smoke frombiomass burningis one of thelargest contributorsto poorair qualityin northern Thailand during the dry season. Byone estimate, about 70 percent offine particulate matter in Chiang Mai in April comes from biomass burning. Smaller contributors to the region’s hazy skies includevehicles, power plants and industry, and charcoal burning for cooking and heating. Geography also plays a key role; the surrounding mountains block air flow and encouragetemperature inversionsthat 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 PM2.5air pollution throughout Chiang Mai and the region, according to data from theWorld Air Quality Index project. Prolonged exposure to high levels of air pollution can contribute to respiratory and cardiovascular diseases and other health problems.
News reportssuggest that the haze is affecting the tourism industry and has contributed to a decrease in the number of international travelers coming to Chiang Mai. After more than a month of persistent haze, the number of tourists arriving in the town of Pai, a popular destination for backpackers northwest of Chiang Mai, was down 90 percent, according to onelocal newspaper.
Unusually warm and dry conditions have gripped the region in recent weeks, according to meteorologists with theASEAN Specialised Meteorological Centre. On March 27, the group advised that there was a “high risk” of severe transboundary haze in the region and elevated itsalert level to three, the highest on the scale.
In late March, the group noted that dry conditions were forecast to persist over most parts of the Mekong sub-region, with prevailing winds expected to blow mostly from the south or southwest. “Under these conditions,” ASMC noted, “the hotspot and smoke haze situation could escalate further.”
NASA Earth Observatory image by Lauren Dauphin,using MODIS data from NASAEOSDIS LANCEandGIBS/Worldview. Story by Adam Voiland.
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ASMCRegional Haze Situation. Accessed April 22, 2026.
Bangkok PostPai tourism suffers as haze grips North. Accessed April 22, 2026.
NASA EarthdataStagnant Skies in Southeast Asia. Accessed April 22, 2026.
NASA Earth ObservatoryHazy Skies in a Growing City. Accessed April 22, 2026.
NASA Earth ObservatoryGrappling with Thailand’s Seasonal Haze. Accessed April 22, 2026.
The NationNorthern wildfire surge pushes Thailand hotspots to 2026 high. Accessed April 22, 2026.
Pani, S.,et al.Black carbon over an urban atmosphere in northern peninsular Southeast Asia: Characteristics, source apportionment, and associated health risks.Environmental Pollution,259, 113871.
Pirard, C. & Charoenpanwutikul, A.Comprehensive review of the annual haze episode in Northern Thailand.Earth ArXiv preprint.
OrionWhere There is Smoke. Accessed April 22, 2026.
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