SmogRank / Episodes / Thailand

North-western Thailand and Laos, 26 to 28 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/m³Mae Sai, 26 March: 492.0 µg/m³, 6.0× its usual 82.3Mae Sai, 27 March: 554.0 µg/m³, 6.6× its usual 83.8Mae Sai, 28 March: 499.0 µg/m³, 6.2× its usual 80.8Mae Sai, 29 March: 323.0 µg/m³Mae Sai, 30 March: 282.0 µg/m³Mae Sai, 31 March: 275.0 µg/m³Ban HouakhouaBan Houakhoua, 23 March: no readingBan Houakhoua, 24 March: no readingBan Houakhoua, 25 March: 213.0 µg/m³Ban Houakhoua, 26 March: 228.0 µg/m³, 3.0× its usual 75.8Ban Houakhoua, 27 March: 284.0 µg/m³, 3.7× its usual 76.0Ban Houakhoua, 28 March: no readingBan Houakhoua, 29 March: 200.0 µg/m³Ban Houakhoua, 30 March: 240.0 µg/m³Ban Houakhoua, 31 March: 227.0 µg/m³Chiang RaiChiang Rai, 23 March: no readingChiang Rai, 24 March: no readingChiang Rai, 25 March: 148.0 µg/m³Chiang Rai, 26 March: 217.0 µg/m³, 3.3× its usual 66.3Chiang Rai, 27 March: 279.0 µg/m³, 4.2× its usual 66.4Chiang Rai, 28 March: 348.0 µg/m³, 5.2× its usual 66.6Chiang Rai, 29 March: 193.0 µg/m³Chiang Rai, 30 March: 238.0 µg/m³Chiang Rai, 31 March: 256.0 µg/m³PhayaoPhayao, 23 March: no readingPhayao, 24 March: no readingPhayao, 25 March: 127.0 µg/m³Phayao, 26 March: 175.0 µg/m³, 2.6× its usual 66.6Phayao, 27 March: 156.0 µg/m³, 2.4× its usual 65.3Phayao, 28 March: 152.0 µg/m³, 2.4× its usual 63.9Phayao, 29 March: no readingPhayao, 30 March: no readingPhayao, 31 March: no readingPakxanPakxan, 23 March: no readingPakxan, 24 March: no readingPakxan, 25 March: 144.0 µg/m³Pakxan, 26 March: 166.0 µg/m³, 3.8× its usual 43.3Pakxan, 27 March: 216.0 µg/m³, 5.0× its usual 43.4Pakxan, 28 March: 95.1 µg/m³, 2.2× its usual 42.8Pakxan, 29 March: 56.6 µg/m³Pakxan, 30 March: 38.4 µg/m³Pakxan, 31 March: 40.4 µg/m³NanNan, 23 March: no readingNan, 24 March: no readingNan, 25 March: 126.0 µg/m³Nan, 26 March: 165.0 µg/m³, 2.3× its usual 71.5Nan, 27 March: 197.0 µg/m³, 2.8× its usual 71.2Nan, 28 March: 147.0 µg/m³, 2.1× its usual 69.0Nan, 29 March: 108.0 µg/m³Nan, 30 March: 97.6 µg/m³Nan, 31 March: 127.0 µg/m³PhraePhrae, 23 March: no readingPhrae, 24 March: no readingPhrae, 25 March: 80.2 µg/m³Phrae, 26 March: 113.0 µg/m³, 2.0× its usual 56.0Phrae, 27 March: 124.0 µg/m³, 2.2× its usual 55.9Phrae, 28 March: 98.6 µg/m³Phrae, 29 March: 60.6 µg/m³Phrae, 30 March: 55.7 µg/m³Phrae, 31 March: 72.4 µg/m³LoeiLoei, 23 March: no readingLoei, 24 March: no readingLoei, 25 March: 68.9 µg/m³Loei, 26 March: 82.1 µg/m³Loei, 27 March: 96.5 µg/m³Loei, 28 March: 119.0 µg/m³, 2.4× its usual 49.5Loei, 29 March: 50.6 µg/m³Loei, 30 March: 45.0 µg/m³Loei, 31 March: 78.3 µg/m³23 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, 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 23 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, North-western Thailand and Laos, 26 to 28 March 2023: 8 cities with PM2.5 at twice their usual or more, 26 to 28 March 2023, smogrank.com/episodes/2023-03-26-north-western-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.