SmogRank / Episodes / Thailand

North-western Thailand and Laos, April 2026

For 6 days, from 1 to 6 April 2026, 8 cities in Thailand and Laos had PM2.5 at least twice their usual for the time of year. The worst reading was Ban Houakhoua, Bokeo, Laos: 223.0 µg/m³ on 5 April, about 2.7× its usual 82.0.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached8in 2 countries
Days61 to 6 April 2026
Worst day5 April8 cities counted
Furthest above usual3.3×Pakxan

Day by day

5 April 8 cities at twice their usual or more
NanLoeiUttaraditLampangNong Bua LamphuUdon ThaniChiang MaiSukhothaiSakon NakhonLamphunPhraePhayaoChiang RaiBan HouakhouaMae SaiVientianePakxan
29 Mar30311 Apr23456789
Every measured city in the area, coloured by its PM2.5 that day; a dark ring marks a city at twice its usual or more. Bars: cities counted each day, coloured by their median level. Choose a day or press play; without JavaScript, the days link to that day's world ranking.

How it spread

PhayaoPhayao, 29 March: 156.0 µg/m³, 2.3× usualPhayao, 30 March: 151.0 µg/m³, 2.3× usualPhayao, 31 March: 139.0 µg/m³, 2.1× usualPhayao, 1 April: 143.0 µg/m³, 2.1× usualPhayao, 2 April: 168.0 µg/m³, 2.5× usualPhayao, 3 April: 144.0 µg/m³, 2.2× usualPhayao, 4 April: 136.0 µg/m³, 2.0× usualPhayao, 5 April: 148.0 µg/m³, 2.2× usualPhayao, 6 April: 134.0 µg/m³, 2.0× usualPhayao, 7 April: 115.0 µg/m³, 1.7× usualPhayao, 8 April: 94.5 µg/m³, 1.4× usualPhayao, 9 April: 81.2 µg/m³, 1.2× usualMae SaiMae Sai, 29 March: 139.0 µg/m³, 1.8× usualMae Sai, 30 March: 164.0 µg/m³, 2.1× usualMae Sai, 31 March: 209.0 µg/m³, 2.7× usualMae Sai, 1 April: 217.0 µg/m³, 2.8× usualMae Sai, 2 April: 217.0 µg/m³, 2.8× usualMae Sai, 3 April: 201.0 µg/m³, 2.6× usualMae Sai, 4 April: 210.0 µg/m³, 2.7× usualMae Sai, 5 April: 211.0 µg/m³, 2.7× usualMae Sai, 6 April: 141.0 µg/m³, 1.8× usualMae Sai, 7 April: 96.4 µg/m³, 1.2× usualMae Sai, 8 April: 80.8 µg/m³, 1.0× usualMae Sai, 9 April: 67.8 µg/m³, 0.9× usualBan HouakhouaBan Houakhoua, 29 March: 154.0 µg/m³, 1.9× usualBan Houakhoua, 30 March: 151.0 µg/m³, 1.8× usualBan Houakhoua, 31 March: 181.0 µg/m³, 2.2× usualBan Houakhoua, 1 April: 173.0 µg/m³, 2.1× usualBan Houakhoua, 2 April: 214.0 µg/m³, 2.6× usualBan Houakhoua, 3 April: 218.0 µg/m³, 2.7× usualBan Houakhoua, 4 April: 211.0 µg/m³, 2.6× usualBan Houakhoua, 5 April: 223.0 µg/m³, 2.7× usualBan Houakhoua, 6 April: 170.0 µg/m³, 2.1× usualBan Houakhoua, 7 April: 124.0 µg/m³, 1.5× usualBan Houakhoua, 8 April: 84.5 µg/m³, 1.0× usualBan Houakhoua, 9 April: 84.2 µg/m³, 1.0× usualVientianeVientiane, 29 March: 62.7 µg/m³, 1.2× usualVientiane, 30 March: 75.9 µg/m³, 1.4× usualVientiane, 31 March: 103.0 µg/m³, 1.9× usualVientiane, 1 April: 138.0 µg/m³, 2.6× usualVientiane, 2 April: 118.0 µg/m³, 2.2× usualVientiane, 3 April: 108.0 µg/m³, 2.0× usualVientiane, 4 April: 146.0 µg/m³, 2.8× usualVientiane, 5 April: 168.0 µg/m³, 3.2× usualVientiane, 6 April: 153.0 µg/m³, 2.9× usualVientiane, 7 April: 129.0 µg/m³, 2.4× usualVientiane, 8 April: 100.0 µg/m³, 1.9× usualVientiane, 9 April: 98.1 µg/m³, 1.9× usualPakxanPakxan, 29 March: 51.3 µg/m³, 1.2× usualPakxan, 30 March: 53.1 µg/m³, 1.2× usualPakxan, 31 March: 77.4 µg/m³, 1.8× usualPakxan, 1 April: 97.8 µg/m³, 2.3× usualPakxan, 2 April: 103.0 µg/m³, 2.4× usualPakxan, 3 April: 103.0 µg/m³, 2.4× usualPakxan, 4 April: 130.0 µg/m³, 3.0× usualPakxan, 5 April: 144.0 µg/m³, 3.3× usualPakxan, 6 April: 130.0 µg/m³, 3.0× usualPakxan, 7 April: 127.0 µg/m³, 2.9× usualPakxan, 8 April: 125.0 µg/m³, 2.9× usualPakxan, 9 April: 127.0 µg/m³, 2.9× usualChiang RaiChiang Rai, 29 March: 86.5 µg/m³, 1.3× usualChiang Rai, 30 March: 96.9 µg/m³, 1.5× usualChiang Rai, 31 March: 131.0 µg/m³, 2.0× usualChiang Rai, 1 April: 127.0 µg/m³, 1.9× usualChiang Rai, 2 April: 173.0 µg/m³, 2.6× usualChiang Rai, 3 April: 162.0 µg/m³, 2.4× usualChiang Rai, 4 April: 161.0 µg/m³, 2.4× usualChiang Rai, 5 April: 181.0 µg/m³, 2.7× usualChiang Rai, 6 April: 138.0 µg/m³, 2.1× usualChiang Rai, 7 April: 90.9 µg/m³, 1.4× usualChiang Rai, 8 April: 67.6 µg/m³, 1.0× usualChiang Rai, 9 April: 64.3 µg/m³, 1.0× usualPhraePhrae, 29 March: 96.6 µg/m³, 1.7× usualPhrae, 30 March: 87.9 µg/m³, 1.6× usualPhrae, 31 March: 79.4 µg/m³, 1.4× usualPhrae, 1 April: 105.0 µg/m³, 1.9× usualPhrae, 2 April: 120.0 µg/m³, 2.2× usualPhrae, 3 April: 116.0 µg/m³, 2.1× usualPhrae, 4 April: 114.0 µg/m³, 2.1× usualPhrae, 5 April: 116.0 µg/m³, 2.1× usualPhrae, 6 April: 97.6 µg/m³, 1.8× usualPhrae, 7 April: 82.7 µg/m³, 1.5× usualPhrae, 8 April: 86.6 µg/m³, 1.6× usualPhrae, 9 April: 78.0 µg/m³, 1.4× usualLamphunLamphun, 29 March: 114.0 µg/m³, 1.7× usualLamphun, 30 March: 87.9 µg/m³, 1.3× usualLamphun, 31 March: 92.7 µg/m³, 1.4× usualLamphun, 1 April: 108.0 µg/m³, 1.6× usualLamphun, 2 April: 129.0 µg/m³, 1.9× usualLamphun, 3 April: 138.0 µg/m³, 2.1× usualLamphun, 4 April: 146.0 µg/m³, 2.2× usualLamphun, 5 April: 141.0 µg/m³, 2.1× usualLamphun, 6 April: 113.0 µg/m³, 1.7× usualLamphun, 7 April: 112.0 µg/m³, 1.7× usualLamphun, 8 April: 96.2 µg/m³, 1.4× usualLamphun, 9 April: 85.8 µg/m³, 1.3× usual29 Mar311 Apr2468
Every counted city, in the order the episode reached them, 3 days before to 3 after. Each square is a day, coloured by that day's PM2.5; outlined: at twice the city's usual or more.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

Every city it reached

CityDaysHighestUsualAbove usual
PakxanBolikhamsai, Laos5 144.05 April43.23.3×
VientianeVientiane Prefecture, Laos5 168.05 April53.03.2×
Mae SaiChiang Rai, Thailand5 217.01 April77.22.8×
Chiang RaiChiang Rai, Thailand5 181.05 April66.42.7×
Ban HouakhouaBokeo, Laos6 223.05 April82.02.7×
PhayaoPhayao, Thailand4 168.02 April66.82.5×
LamphunLamphun, Thailand3 146.04 April67.12.2×
PhraePhrae, Thailand4 120.02 April55.42.2×

Daily means in µg/m³. Usual: the city's median for this time of year (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that.

Against other episodes in Thailand and Laos

Number 7 of 7 episodes in Thailand and Laos since our records began, by cities reached.

Bars: cities reached; colour: the level of the episode's highest daily reading.

Use this page

SmogRank, North-western Thailand and Laos, April 2026: 8 cities with PM2.5 at twice their usual or more, 1 to 6 April 2026, smogrank.com/episodes/2026-04-north-western-thailand-and-laos (accessed 2 October 2026).

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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms.

An episode is a run of days when many cities close to each other (four or more within 350 km on a day, 8 or more in all) each had a daily PM2.5 mean of at least 25 µg/m³ and at least 2 times their usual for that time of year. Found in our own measurements, not picked by hand. How we find episodes. Values are each city's daily mean of its own monitors; causes are the usual kinds for a pattern like this, not a confirmed source.