SmogRank / Episodes / Thailand

Northern 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/m³Pakxan, 11 April: 156.0 µg/m³Pakxan, 12 April: 142.0 µg/m³Pakxan, 13 April: 196.0 µg/m³, 4.6× its usual 42.9Pakxan, 14 April: 194.0 µg/m³, 4.6× its usual 42.6Pakxan, 15 April: 186.0 µg/m³, 4.6× its usual 40.7Pakxan, 16 April: 171.0 µg/m³Pakxan, 17 April: 211.0 µg/m³Pakxan, 18 April: no readingBan HouakhouaBan Houakhoua, 10 April: 102.0 µg/m³Ban Houakhoua, 11 April: 114.0 µg/m³Ban Houakhoua, 12 April: 121.0 µg/m³Ban Houakhoua, 13 April: 190.0 µg/m³, 2.1× its usual 90.4Ban Houakhoua, 14 April: 219.0 µg/m³, 2.4× its usual 92.8Ban Houakhoua, 15 April: 187.0 µg/m³, 2.0× its usual 93.4Ban Houakhoua, 16 April: 192.0 µg/m³Ban Houakhoua, 17 April: 179.0 µg/m³Ban Houakhoua, 18 April: 164.0 µg/m³VientianeVientiane, 10 April: 94.6 µg/m³Vientiane, 11 April: 91.0 µg/m³Vientiane, 12 April: 104.0 µg/m³Vientiane, 13 April: 157.0 µg/m³, 3.4× its usual 46.8Vientiane, 14 April: 141.0 µg/m³, 3.1× its usual 45.6Vientiane, 15 April: 123.0 µg/m³, 2.7× its usual 45.2Vientiane, 16 April: 145.0 µg/m³Vientiane, 17 April: 161.0 µg/m³Vientiane, 18 April: 82.7 µg/m³SukhothaiSukhothai, 10 April: 24.6 µg/m³Sukhothai, 11 April: 44.8 µg/m³Sukhothai, 12 April: 63.0 µg/m³Sukhothai, 13 April: 102.0 µg/m³, 2.1× its usual 48.1Sukhothai, 14 April: 105.0 µg/m³, 2.2× its usual 48.1Sukhothai, 15 April: 97.6 µg/m³, 2.0× its usual 48.1Sukhothai, 16 April: 70.0 µg/m³Sukhothai, 17 April: 95.6 µg/m³Sukhothai, 18 April: 118.0 µg/m³LoeiLoei, 10 April: 73.8 µg/m³Loei, 11 April: 61.6 µg/m³Loei, 12 April: 64.0 µg/m³Loei, 13 April: 101.0 µg/m³, 2.1× its usual 48.0Loei, 14 April: 102.0 µg/m³, 2.2× its usual 46.6Loei, 15 April: 81.9 µg/m³Loei, 16 April: 86.5 µg/m³Loei, 17 April: 104.0 µg/m³Loei, 18 April: 101.0 µg/m³Sakon NakhonSakon Nakhon, 10 April: 65.3 µg/m³Sakon Nakhon, 11 April: 66.0 µg/m³Sakon Nakhon, 12 April: 74.6 µg/m³Sakon Nakhon, 13 April: 78.1 µg/m³, 2.1× its usual 37.1Sakon Nakhon, 14 April: 68.6 µg/m³Sakon Nakhon, 15 April: 66.3 µg/m³Sakon Nakhon, 16 April: 54.5 µg/m³Sakon Nakhon, 17 April: 50.3 µg/m³Sakon Nakhon, 18 April: 36.1 µg/m³Mae SaiMae Sai, 10 April: 69.7 µg/m³Mae Sai, 11 April: no readingMae Sai, 12 April: no readingMae Sai, 13 April: 127.0 µg/m³Mae Sai, 14 April: 184.0 µg/m³, 2.3× its usual 78.6Mae Sai, 15 April: 187.0 µg/m³, 2.4× its usual 78.6Mae Sai, 16 April: 157.0 µg/m³Mae Sai, 17 April: 115.0 µg/m³Mae Sai, 18 April: 127.0 µg/m³Chiang RaiChiang Rai, 10 April: 80.6 µg/m³Chiang Rai, 11 April: 76.5 µg/m³Chiang Rai, 12 April: 84.8 µg/m³Chiang Rai, 13 April: 111.0 µg/m³Chiang Rai, 14 April: 147.0 µg/m³, 2.2× its usual 66.6Chiang Rai, 15 April: 153.0 µg/m³, 2.3× its usual 66.6Chiang Rai, 16 April: 126.0 µg/m³Chiang Rai, 17 April: 116.0 µg/m³Chiang Rai, 18 April: 130.0 µg/m³10 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 196.013 April42.94.6×
VientianeVientiane Prefecture, Laos3 157.013 April46.83.4×
Ban HouakhouaBokeo, Laos3 219.014 April92.82.4×
Mae SaiChiang Rai, Thailand2 187.015 April78.62.4×
Chiang RaiChiang Rai, Thailand2 153.015 April66.62.3×
SukhothaiSukhothai, Thailand3 105.014 April48.12.2×
LoeiLoei, Thailand2 102.014 April46.62.2×
Sakon NakhonSakon Nakhon, Thailand1 78.113 April37.12.1×

Daily means in µg/m³, over the days each city counted in this episode. Highest: its highest of those days. Usual: the city's median for the time of year of that day (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that, with a usual under 5 µg/m³ taken as 5.

Against other episodes in Thailand and Laos

Number 21 of 23 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. All 23.

Use this page

SmogRank, Northern 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-northern-thailand-and-laos (accessed 4 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.