SmogRank / Episodes / Thailand

North-western Thailand and Laos, March 2023

For 3 days, from 26 to 28 March 2023, 8 cities in Thailand and Laos had PM2.5 at least twice their usual for the time of year. The worst reading was Mae Sai, Chiang Rai, Thailand: 554.0 µg/m³ on 27 March, about 6.6× its usual 83.8.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached8in 2 countries
Days326 to 28 March 2023
Worst day26 March7 cities counted
Furthest above usual6.6×Mae Sai

Day by day

26 March 7 cities at twice their usual or more
VientianeTha BoUdon ThaniNong Bua LamphuUttaraditLampangSukhothaiLamphunChiang MaiSakon NakhonTakMukdahanMae SotHanoiPhraeLoeiPhayaoNanBan HouakhouaPakxanChiang RaiMae Sai
23 Mar2425262728293031
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

Mae SaiMae Sai, 23 March: no readingMae Sai, 24 March: no readingMae Sai, 25 March: 370.0 µg/m³, 4.4× usualMae Sai, 26 March: 492.0 µg/m³, 5.9× usualMae Sai, 27 March: 554.0 µg/m³, 6.6× usualMae Sai, 28 March: 499.0 µg/m³, 6.0× usualMae Sai, 29 March: 323.0 µg/m³, 3.9× usualMae Sai, 30 March: 282.0 µg/m³, 3.4× usualMae Sai, 31 March: 275.0 µg/m³, 3.3× usualBan HouakhouaBan Houakhoua, 23 March: no readingBan Houakhoua, 24 March: no readingBan Houakhoua, 25 March: 213.0 µg/m³, 2.8× usualBan Houakhoua, 26 March: 228.0 µg/m³, 3.0× usualBan Houakhoua, 27 March: 284.0 µg/m³, 3.7× usualBan Houakhoua, 28 March: no readingBan Houakhoua, 29 March: 200.0 µg/m³, 2.6× usualBan Houakhoua, 30 March: 240.0 µg/m³, 3.2× usualBan Houakhoua, 31 March: 227.0 µg/m³, 3.0× usualChiang RaiChiang Rai, 23 March: no readingChiang Rai, 24 March: no readingChiang Rai, 25 March: 148.0 µg/m³, 2.2× usualChiang Rai, 26 March: 217.0 µg/m³, 3.3× usualChiang Rai, 27 March: 279.0 µg/m³, 4.2× usualChiang Rai, 28 March: 348.0 µg/m³, 5.2× usualChiang Rai, 29 March: 193.0 µg/m³, 2.9× usualChiang Rai, 30 March: 238.0 µg/m³, 3.6× usualChiang Rai, 31 March: 256.0 µg/m³, 3.8× usualPakxanPakxan, 23 March: no readingPakxan, 24 March: no readingPakxan, 25 March: 144.0 µg/m³, 3.3× usualPakxan, 26 March: 166.0 µg/m³, 3.8× usualPakxan, 27 March: 216.0 µg/m³, 5.0× usualPakxan, 28 March: 95.1 µg/m³, 2.2× usualPakxan, 29 March: 56.6 µg/m³, 1.3× usualPakxan, 30 March: 38.4 µg/m³, 0.9× usualPakxan, 31 March: 40.4 µg/m³, 0.9× usualPhayaoPhayao, 23 March: no readingPhayao, 24 March: no readingPhayao, 25 March: 127.0 µg/m³, 1.9× usualPhayao, 26 March: 175.0 µg/m³, 2.6× usualPhayao, 27 March: 156.0 µg/m³, 2.3× usualPhayao, 28 March: 152.0 µg/m³, 2.3× usualPhayao, 29 March: no readingPhayao, 30 March: no readingPhayao, 31 March: no readingNanNan, 23 March: no readingNan, 24 March: no readingNan, 25 March: 126.0 µg/m³, 1.8× usualNan, 26 March: 165.0 µg/m³, 2.3× usualNan, 27 March: 197.0 µg/m³, 2.8× usualNan, 28 March: 147.0 µg/m³, 2.1× usualNan, 29 March: 108.0 µg/m³, 1.5× usualNan, 30 March: 97.6 µg/m³, 1.4× usualNan, 31 March: 127.0 µg/m³, 1.8× usualPhraePhrae, 23 March: no readingPhrae, 24 March: no readingPhrae, 25 March: 80.2 µg/m³, 1.4× usualPhrae, 26 March: 113.0 µg/m³, 2.0× usualPhrae, 27 March: 124.0 µg/m³, 2.2× usualPhrae, 28 March: 98.6 µg/m³, 1.8× usualPhrae, 29 March: 60.6 µg/m³, 1.1× usualPhrae, 30 March: 55.7 µg/m³, 1.0× usualPhrae, 31 March: 72.4 µg/m³, 1.3× usualLoeiLoei, 23 March: no readingLoei, 24 March: no readingLoei, 25 March: 68.9 µg/m³, 1.4× usualLoei, 26 March: 82.1 µg/m³, 1.7× usualLoei, 27 March: 96.5 µg/m³, 1.9× usualLoei, 28 March: 119.0 µg/m³, 2.4× usualLoei, 29 March: 50.6 µg/m³, 1.0× usualLoei, 30 March: 45.0 µg/m³, 0.9× usualLoei, 31 March: 78.3 µg/m³, 1.6× usual23 Mar2425262728293031
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
Mae SaiChiang Rai, Thailand3 554.027 March83.86.6×
Chiang RaiChiang Rai, Thailand3 348.028 March66.65.2×
PakxanBolikhamsai, Laos3 216.027 March43.45.0×
Ban HouakhouaBokeo, Laos2 284.027 March76.03.7×
NanNan, Thailand3 197.027 March71.22.8×
PhayaoPhayao, Thailand3 175.026 March66.62.6×
LoeiLoei, Thailand1 119.028 March49.52.4×
PhraePhrae, Thailand2 124.027 March55.92.2×

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 24 of 24 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 24.

Use this page

SmogRank, North-western Thailand and Laos, March 2023: 8 cities with PM2.5 at twice their usual or more, 26 to 28 March 2023, smogrank.com/episodes/2023-03-north-western-thailand-and-laos (accessed 3 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.