SmogRank / Episodes / Thailand

North-western Thailand and Laos, April 2026

For 3 days, from 13 to 15 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: 219.0 µg/m³ on 14 April, about 2.4× its usual 92.8.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached8in 2 countries
Days313 to 15 April 2026
Worst day14 April7 cities counted
Furthest above usual4.6×Pakxan

Day by day

14 April 7 cities at twice their usual or more
NanUdon ThaniNong Bua LamphuPhraePhayaoUttaraditKhon KaenPhetchabunLampangKalasinPhichitLamphunChiang MaiKamphaeng PhetMukdahanMae SotSakon NakhonLoeiSukhothaiChiang RaiMae SaiBan HouakhouaVientianePakxan
10 Apr1112131415161718
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

PakxanPakxan, 10 April: 131.0 µg/m³, 3.1× usualPakxan, 11 April: 156.0 µg/m³, 3.6× usualPakxan, 12 April: 142.0 µg/m³, 3.3× usualPakxan, 13 April: 196.0 µg/m³, 4.6× usualPakxan, 14 April: 194.0 µg/m³, 4.5× usualPakxan, 15 April: 186.0 µg/m³, 4.3× usualPakxan, 16 April: 171.0 µg/m³, 4.0× usualPakxan, 17 April: 211.0 µg/m³, 4.9× usualPakxan, 18 April: no readingVientianeVientiane, 10 April: 94.6 µg/m³, 2.0× usualVientiane, 11 April: 91.0 µg/m³, 1.9× usualVientiane, 12 April: 104.0 µg/m³, 2.2× usualVientiane, 13 April: 157.0 µg/m³, 3.4× usualVientiane, 14 April: 141.0 µg/m³, 3.0× usualVientiane, 15 April: 123.0 µg/m³, 2.6× usualVientiane, 16 April: 145.0 µg/m³, 3.1× usualVientiane, 17 April: 161.0 µg/m³, 3.4× usualVientiane, 18 April: 82.7 µg/m³, 1.8× usualSakon NakhonSakon Nakhon, 10 April: 65.3 µg/m³, 1.8× usualSakon Nakhon, 11 April: 66.0 µg/m³, 1.8× usualSakon Nakhon, 12 April: 74.6 µg/m³, 2.0× usualSakon Nakhon, 13 April: 78.1 µg/m³, 2.1× usualSakon Nakhon, 14 April: 68.6 µg/m³, 1.8× usualSakon Nakhon, 15 April: 66.3 µg/m³, 1.8× usualSakon Nakhon, 16 April: 54.5 µg/m³, 1.5× usualSakon Nakhon, 17 April: 50.3 µg/m³, 1.4× usualSakon Nakhon, 18 April: 36.1 µg/m³, 1.0× usualBan HouakhouaBan Houakhoua, 10 April: 102.0 µg/m³, 1.1× usualBan Houakhoua, 11 April: 114.0 µg/m³, 1.2× usualBan Houakhoua, 12 April: 121.0 µg/m³, 1.3× usualBan Houakhoua, 13 April: 190.0 µg/m³, 2.0× usualBan Houakhoua, 14 April: 219.0 µg/m³, 2.4× usualBan Houakhoua, 15 April: 187.0 µg/m³, 2.0× usualBan Houakhoua, 16 April: 192.0 µg/m³, 2.1× usualBan Houakhoua, 17 April: 179.0 µg/m³, 1.9× usualBan Houakhoua, 18 April: 164.0 µg/m³, 1.8× usualSukhothaiSukhothai, 10 April: 24.6 µg/m³, 0.5× usualSukhothai, 11 April: 44.8 µg/m³, 0.9× usualSukhothai, 12 April: 63.0 µg/m³, 1.3× usualSukhothai, 13 April: 102.0 µg/m³, 2.1× usualSukhothai, 14 April: 105.0 µg/m³, 2.2× usualSukhothai, 15 April: 97.6 µg/m³, 2.0× usualSukhothai, 16 April: 70.0 µg/m³, 1.5× usualSukhothai, 17 April: 95.6 µg/m³, 2.0× usualSukhothai, 18 April: 118.0 µg/m³, 2.5× usualLoeiLoei, 10 April: 73.8 µg/m³, 1.6× usualLoei, 11 April: 61.6 µg/m³, 1.3× usualLoei, 12 April: 64.0 µg/m³, 1.4× usualLoei, 13 April: 101.0 µg/m³, 2.2× usualLoei, 14 April: 102.0 µg/m³, 2.2× usualLoei, 15 April: 81.9 µg/m³, 1.8× usualLoei, 16 April: 86.5 µg/m³, 1.9× usualLoei, 17 April: 104.0 µg/m³, 2.2× usualLoei, 18 April: 101.0 µg/m³, 2.2× usualMae SaiMae Sai, 10 April: 69.7 µg/m³, 0.9× usualMae Sai, 11 April: no readingMae Sai, 12 April: no readingMae Sai, 13 April: 127.0 µg/m³, 1.6× usualMae Sai, 14 April: 184.0 µg/m³, 2.3× usualMae Sai, 15 April: 187.0 µg/m³, 2.4× usualMae Sai, 16 April: 157.0 µg/m³, 2.0× usualMae Sai, 17 April: 115.0 µg/m³, 1.5× usualMae Sai, 18 April: 127.0 µg/m³, 1.6× usualChiang RaiChiang Rai, 10 April: 80.6 µg/m³, 1.2× usualChiang Rai, 11 April: 76.5 µg/m³, 1.1× usualChiang Rai, 12 April: 84.8 µg/m³, 1.3× usualChiang Rai, 13 April: 111.0 µg/m³, 1.7× usualChiang Rai, 14 April: 147.0 µg/m³, 2.2× usualChiang Rai, 15 April: 153.0 µg/m³, 2.3× usualChiang Rai, 16 April: 126.0 µg/m³, 1.9× usualChiang Rai, 17 April: 116.0 µg/m³, 1.7× usualChiang Rai, 18 April: 130.0 µg/m³, 2.0× usual10 Apr1112131415161718
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, Laos3 211.017 April42.94.9×
VientianeVientiane Prefecture, Laos3 161.017 April46.83.4×
SukhothaiSukhothai, Thailand3 118.018 April48.12.5×
Mae SaiChiang Rai, Thailand2 187.015 April78.62.4×
Ban HouakhouaBokeo, Laos3 219.014 April92.82.4×
Chiang RaiChiang Rai, Thailand2 153.015 April66.62.3×
LoeiLoei, Thailand2 104.017 April46.62.2×
Sakon NakhonSakon Nakhon, Thailand1 78.113 April37.12.1×

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 6 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, 13 to 15 April 2026, smogrank.com/episodes/2026-04-north-western-thailand-and-laos-2 (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.