SmogRank / Episodes / Thailand

North-western Thailand and Laos, 30 March to 2 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 NakhonLamphunPhraeLampangNanBan HouakhouaChiang MaiPhayaoChiang 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/m³Mae Sai, 28 March: 499.0 µg/m³Mae Sai, 29 March: 323.0 µg/m³Mae Sai, 30 March: 282.0 µg/m³, 3.5× its usual 79.7Mae Sai, 31 March: 275.0 µg/m³, 3.5× its usual 77.9Mae Sai, 1 April: 316.0 µg/m³, 4.1× its usual 77.9Mae Sai, 2 April: 296.0 µg/m³, 3.8× its usual 78.6Mae Sai, 3 April: 172.0 µg/m³Mae Sai, 4 April: 198.0 µg/m³Mae Sai, 5 April: 229.0 µg/m³Ban HouakhouaBan Houakhoua, 27 March: 284.0 µg/m³Ban Houakhoua, 28 March: no readingBan Houakhoua, 29 March: 200.0 µg/m³Ban Houakhoua, 30 March: 240.0 µg/m³, 3.0× its usual 80.5Ban Houakhoua, 31 March: 227.0 µg/m³, 2.8× its usual 81.4Ban Houakhoua, 1 April: 240.0 µg/m³, 2.9× its usual 82.0Ban Houakhoua, 2 April: 197.0 µg/m³, 2.4× its usual 83.7Ban Houakhoua, 3 April: 144.0 µg/m³Ban Houakhoua, 4 April: 166.0 µg/m³Ban Houakhoua, 5 April: 182.0 µg/m³Chiang RaiChiang Rai, 27 March: 279.0 µg/m³Chiang Rai, 28 March: 348.0 µg/m³Chiang Rai, 29 March: 193.0 µg/m³Chiang Rai, 30 March: 238.0 µg/m³, 3.6× its usual 66.5Chiang Rai, 31 March: 256.0 µg/m³, 3.9× its usual 66.3Chiang Rai, 1 April: 261.0 µg/m³, 3.9× its usual 66.3Chiang Rai, 2 April: 202.0 µg/m³, 3.1× its usual 66.1Chiang Rai, 3 April: 124.0 µg/m³Chiang Rai, 4 April: 117.0 µg/m³Chiang Rai, 5 April: 118.0 µg/m³Chiang MaiChiang Mai, 27 March: 109.5 µg/m³Chiang Mai, 28 March: 95.9 µg/m³Chiang Mai, 29 March: 107.0 µg/m³Chiang Mai, 30 March: 149.0 µg/m³, 2.4× its usual 62.1Chiang Mai, 31 March: 154.0 µg/m³, 2.5× its usual 62.6Chiang Mai, 1 April: 195.0 µg/m³, 3.1× its usual 62.1Chiang Mai, 2 April: 180.0 µg/m³, 2.9× its usual 62.5Chiang Mai, 3 April: 97.4 µg/m³Chiang Mai, 4 April: 93.8 µg/m³Chiang Mai, 5 April: 128.5 µg/m³PhayaoPhayao, 27 March: 156.0 µg/m³Phayao, 28 March: 152.0 µg/m³Phayao, 29 March: no readingPhayao, 30 March: no readingPhayao, 31 March: no readingPhayao, 1 April: 205.0 µg/m³, 3.1× its usual 66.8Phayao, 2 April: 146.0 µg/m³, 2.1× its usual 70.7Phayao, 3 April: 99.0 µg/m³Phayao, 4 April: 112.0 µg/m³Phayao, 5 April: 145.0 µg/m³NanNan, 27 March: 197.0 µg/m³Nan, 28 March: 147.0 µg/m³Nan, 29 March: 108.0 µg/m³Nan, 30 March: 97.6 µg/m³Nan, 31 March: 127.0 µg/m³Nan, 1 April: 173.0 µg/m³, 2.3× its usual 74.8Nan, 2 April: 116.0 µg/m³Nan, 3 April: 90.3 µg/m³Nan, 4 April: 99.6 µg/m³Nan, 5 April: 139.0 µg/m³LampangLampang, 27 March: 108.0 µg/m³Lampang, 28 March: 108.0 µg/m³Lampang, 29 March: 112.0 µg/m³Lampang, 30 March: 96.7 µg/m³Lampang, 31 March: 119.0 µg/m³Lampang, 1 April: 154.0 µg/m³, 2.3× its usual 67.1Lampang, 2 April: 118.0 µg/m³Lampang, 3 April: 77.0 µg/m³Lampang, 4 April: 80.9 µg/m³Lampang, 5 April: 120.0 µg/m³LamphunLamphun, 27 March: 90.6 µg/m³Lamphun, 28 March: 95.6 µg/m³Lamphun, 29 March: 100.0 µg/m³Lamphun, 30 March: 97.8 µg/m³Lamphun, 31 March: 107.0 µg/m³Lamphun, 1 April: 135.0 µg/m³, 2.0× its usual 67.1Lamphun, 2 April: 130.0 µg/m³Lamphun, 3 April: 72.0 µg/m³Lamphun, 4 April: 69.4 µg/m³Lamphun, 5 April: 96.6 µg/m³PhraePhrae, 27 March: 124.0 µg/m³Phrae, 28 March: 98.6 µg/m³Phrae, 29 March: 60.6 µg/m³Phrae, 30 March: 55.7 µg/m³Phrae, 31 March: 72.4 µg/m³Phrae, 1 April: 118.0 µg/m³, 2.2× its usual 54.5Phrae, 2 April: 78.6 µg/m³Phrae, 3 April: 63.0 µg/m³Phrae, 4 April: 77.0 µg/m³Phrae, 5 April: 115.0 µg/m³27 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 316.01 April77.94.1×
Chiang RaiChiang Rai, Thailand4 261.01 April66.33.9×
PhayaoPhayao, Thailand2 205.01 April66.83.1×
Chiang MaiChiang Mai, Thailand4 195.01 April62.13.1×
Ban HouakhouaBokeo, Laos4 240.030 March80.53.0×
NanNan, Thailand1 173.01 April74.82.3×
LampangLampang, Thailand1 154.01 April67.12.3×
PhraePhrae, Thailand1 118.01 April54.52.2×
LamphunLamphun, Thailand1 135.01 April67.12.0×

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 20 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, 30 March to 2 April 2023: 9 cities with PM2.5 at twice their usual or more, 30 March to 2 April 2023, smogrank.com/episodes/2023-03-30-north-western-thailand-and-laos (accessed 4 October 2026).

Download top 10 (PNG)

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.