SmogRank / Episodes / Thailand

North-western Thailand, March and April 2023

For 4 days, from 30 March to 2 April 2023, 9 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: 316.0 µg/m³ on 1 April, about 4.1× its usual 77.9.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached9in 2 countries
Days430 March to 2 April 2023
Worst day1 April9 cities counted
Furthest above usual4.1×Mae Sai

Day by day

1 April 9 cities at twice their usual or more
UttaraditSukhothaiTakLoeiVientianeTha BoNong Bua LamphuUdon ThaniPakxanSakon NakhonLamphunPhraeNanLampangBan HouakhouaPhayaoChiang MaiChiang RaiMae Sai
27 Mar282930311 Apr2345
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, 27 March: 554.0 µg/m³, 7.1× usualMae Sai, 28 March: 499.0 µg/m³, 6.4× usualMae Sai, 29 March: 323.0 µg/m³, 4.1× usualMae Sai, 30 March: 282.0 µg/m³, 3.6× usualMae Sai, 31 March: 275.0 µg/m³, 3.5× usualMae Sai, 1 April: 316.0 µg/m³, 4.1× usualMae Sai, 2 April: 296.0 µg/m³, 3.8× usualMae Sai, 3 April: 172.0 µg/m³, 2.2× usualMae Sai, 4 April: 198.0 µg/m³, 2.5× usualMae Sai, 5 April: 229.0 µg/m³, 2.9× usualBan HouakhouaBan Houakhoua, 27 March: 284.0 µg/m³, 3.5× usualBan Houakhoua, 28 March: no readingBan Houakhoua, 29 March: 200.0 µg/m³, 2.5× usualBan Houakhoua, 30 March: 240.0 µg/m³, 3.0× usualBan Houakhoua, 31 March: 227.0 µg/m³, 2.8× usualBan Houakhoua, 1 April: 240.0 µg/m³, 3.0× usualBan Houakhoua, 2 April: 197.0 µg/m³, 2.4× usualBan Houakhoua, 3 April: 144.0 µg/m³, 1.8× usualBan Houakhoua, 4 April: 166.0 µg/m³, 2.1× usualBan Houakhoua, 5 April: 182.0 µg/m³, 2.3× usualChiang RaiChiang 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, 3.9× usualChiang Rai, 1 April: 261.0 µg/m³, 3.9× usualChiang Rai, 2 April: 202.0 µg/m³, 3.0× usualChiang Rai, 3 April: 124.0 µg/m³, 1.9× usualChiang Rai, 4 April: 117.0 µg/m³, 1.8× usualChiang Rai, 5 April: 118.0 µg/m³, 1.8× usualNanNan, 27 March: 197.0 µg/m³, 2.6× usualNan, 28 March: 147.0 µg/m³, 2.0× usualNan, 29 March: 108.0 µg/m³, 1.4× usualNan, 30 March: 97.6 µg/m³, 1.3× usualNan, 31 March: 127.0 µg/m³, 1.7× usualNan, 1 April: 173.0 µg/m³, 2.3× usualNan, 2 April: 116.0 µg/m³, 1.6× usualNan, 3 April: 90.3 µg/m³, 1.2× usualNan, 4 April: 99.6 µg/m³, 1.3× usualNan, 5 April: 139.0 µg/m³, 1.9× usualPhayaoPhayao, 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 readingPhayao, 1 April: 205.0 µg/m³, 3.1× usualPhayao, 2 April: 146.0 µg/m³, 2.2× usualPhayao, 3 April: 99.0 µg/m³, 1.5× usualPhayao, 4 April: 112.0 µg/m³, 1.7× usualPhayao, 5 April: 145.0 µg/m³, 2.2× usualPhraePhrae, 27 March: 124.0 µg/m³, 2.3× 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× usualPhrae, 1 April: 118.0 µg/m³, 2.2× usualPhrae, 2 April: 78.6 µg/m³, 1.4× usualPhrae, 3 April: 63.0 µg/m³, 1.2× usualPhrae, 4 April: 77.0 µg/m³, 1.4× usualPhrae, 5 April: 115.0 µg/m³, 2.1× usualChiang MaiChiang Mai, 27 March: 109.5 µg/m³, 1.8× usualChiang Mai, 28 March: 95.9 µg/m³, 1.5× usualChiang Mai, 29 March: 107.0 µg/m³, 1.7× usualChiang Mai, 30 March: 149.0 µg/m³, 2.4× usualChiang Mai, 31 March: 154.0 µg/m³, 2.5× usualChiang Mai, 1 April: 195.0 µg/m³, 3.1× usualChiang Mai, 2 April: 180.0 µg/m³, 2.9× usualChiang Mai, 3 April: 97.4 µg/m³, 1.6× usualChiang Mai, 4 April: 93.8 µg/m³, 1.5× usualChiang Mai, 5 April: 128.5 µg/m³, 2.1× usualLampangLampang, 27 March: 108.0 µg/m³, 1.6× usualLampang, 28 March: 108.0 µg/m³, 1.6× usualLampang, 29 March: 112.0 µg/m³, 1.7× usualLampang, 30 March: 96.7 µg/m³, 1.4× usualLampang, 31 March: 119.0 µg/m³, 1.8× usualLampang, 1 April: 154.0 µg/m³, 2.3× usualLampang, 2 April: 118.0 µg/m³, 1.8× usualLampang, 3 April: 77.0 µg/m³, 1.1× usualLampang, 4 April: 80.9 µg/m³, 1.2× usualLampang, 5 April: 120.0 µg/m³, 1.8× usualLamphunLamphun, 27 March: 90.6 µg/m³, 1.4× usualLamphun, 28 March: 95.6 µg/m³, 1.4× usualLamphun, 29 March: 100.0 µg/m³, 1.5× usualLamphun, 30 March: 97.8 µg/m³, 1.5× usualLamphun, 31 March: 107.0 µg/m³, 1.6× usualLamphun, 1 April: 135.0 µg/m³, 2.0× usualLamphun, 2 April: 130.0 µg/m³, 1.9× usualLamphun, 3 April: 72.0 µg/m³, 1.1× usualLamphun, 4 April: 69.4 µg/m³, 1.0× usualLamphun, 5 April: 96.6 µg/m³, 1.4× usual27 Mar282930311 Apr2345
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, Thailand4 554.027 March77.97.1×
Chiang RaiChiang Rai, Thailand4 348.028 March66.35.2×
Ban HouakhouaBokeo, Laos4 284.027 March80.53.5×
Chiang MaiChiang Mai, Thailand4 195.01 April62.13.1×
PhayaoPhayao, Thailand2 205.01 April66.83.1×
NanNan, Thailand1 197.027 March74.82.6×
LampangLampang, Thailand1 154.01 April67.12.3×
PhraePhrae, Thailand1 124.027 March54.52.3×
LamphunLamphun, Thailand1 135.01 April67.12.0×

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 20 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, March and April 2023: 9 cities with PM2.5 at twice their usual or more, 30 March to 2 April 2023, smogrank.com/episodes/2023-03-north-western-thailand (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.