SmogRank / Episodes / Thailand
Northern Thailand and Laos, March and April 2023
For 9 days, from 25 March to 2 April 2023, 13 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. Ended 2 April.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 13 in 2 countries
Days 9 25 March to 2 April 2023
Worst day 1 April 10 cities counted
Furthest above usual 6.6× Mae Sai
Day by day
Play 1 April 10 cities at twice their usual or more
Vientiane Tha Bo Uttaradit Nong Bua Lamphu Udon Thani Sukhothai Tak Sakon Nakhon Mae Sot Mukdahan Lamphun Phrae Lampang Loei Nan Chiang Mai Phayao Ban Houakhoua Chiang Khong Pakxan Bueng Kan Chiang Rai Mae Sai 22 Mar 23 24 25 26 27 28 29 30 31 1 Apr 2 3 4 5 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 Sai Mae Sai, 22 March: no reading Mae Sai, 23 March: no reading Mae Sai, 24 March: no reading Mae Sai, 25 March: 370.0 µg/m³, 4.6× its usual 80.9 Mae Sai, 26 March: 492.0 µg/m³, 6.0× its usual 82.3 Mae Sai, 27 March: 554.0 µg/m³, 6.6× its usual 83.8 Mae Sai, 28 March: 499.0 µg/m³, 6.2× its usual 80.8 Mae Sai, 29 March: 323.0 µg/m³, 4.1× its usual 79.7 Mae Sai, 30 March: 282.0 µg/m³, 3.5× its usual 79.7 Mae Sai, 31 March: 275.0 µg/m³, 3.5× its usual 77.9 Mae Sai, 1 April: 316.0 µg/m³, 4.1× its usual 77.9 Mae Sai, 2 April: 296.0 µg/m³, 3.8× its usual 78.6 Mae Sai, 3 April: 172.0 µg/m³ Mae Sai, 4 April: 198.0 µg/m³ Mae Sai, 5 April: 229.0 µg/m³ Chiang Khong Chiang Khong, 22 March: 64.4 µg/m³ Chiang Khong, 23 March: no reading Chiang Khong, 24 March: no reading Chiang Khong, 25 March: 213.0 µg/m³, 2.8× its usual 75.4 Chiang Khong, 26 March: 228.0 µg/m³, 3.0× its usual 75.8 Chiang Khong, 27 March: 284.0 µg/m³, 3.7× its usual 76.0 Chiang Khong, 28 March: no reading Chiang Khong, 29 March: 200.0 µg/m³, 2.5× its usual 79.0 Chiang Khong, 30 March: 240.0 µg/m³, 3.0× its usual 80.5 Chiang Khong, 31 March: 227.0 µg/m³, 2.8× its usual 81.4 Chiang Khong, 1 April: 240.0 µg/m³, 2.9× its usual 82.0 Chiang Khong, 2 April: 197.0 µg/m³, 2.4× its usual 83.7 Chiang Khong, 3 April: 144.0 µg/m³ Chiang Khong, 4 April: 166.0 µg/m³ Chiang Khong, 5 April: 182.0 µg/m³ Ban Houakhoua Ban Houakhoua, 22 March: 64.4 µg/m³ Ban Houakhoua, 23 March: no reading Ban Houakhoua, 24 March: no reading Ban Houakhoua, 25 March: 213.0 µg/m³, 2.8× its usual 75.4 Ban Houakhoua, 26 March: 228.0 µg/m³, 3.0× its usual 75.8 Ban Houakhoua, 27 March: 284.0 µg/m³, 3.7× its usual 76.0 Ban Houakhoua, 28 March: no reading Ban Houakhoua, 29 March: 200.0 µg/m³, 2.5× its usual 79.0 Ban Houakhoua, 30 March: 240.0 µg/m³, 3.0× its usual 80.5 Ban Houakhoua, 31 March: 227.0 µg/m³, 2.8× its usual 81.4 Ban Houakhoua, 1 April: 240.0 µg/m³, 2.9× its usual 82.0 Ban Houakhoua, 2 April: 197.0 µg/m³, 2.4× its usual 83.7 Ban Houakhoua, 3 April: 144.0 µg/m³ Ban Houakhoua, 4 April: 166.0 µg/m³ Ban Houakhoua, 5 April: 182.0 µg/m³ Chiang Rai Chiang Rai, 22 March: 48.8 µg/m³ Chiang Rai, 23 March: no reading Chiang Rai, 24 March: no reading Chiang Rai, 25 March: 148.0 µg/m³, 2.3× its usual 65.2 Chiang Rai, 26 March: 217.0 µg/m³, 3.3× its usual 66.3 Chiang Rai, 27 March: 279.0 µg/m³, 4.2× its usual 66.4 Chiang Rai, 28 March: 348.0 µg/m³, 5.2× its usual 66.6 Chiang Rai, 29 March: 193.0 µg/m³, 2.9× its usual 66.7 Chiang Rai, 30 March: 238.0 µg/m³, 3.6× its usual 66.5 Chiang Rai, 31 March: 256.0 µg/m³, 3.9× its usual 66.3 Chiang Rai, 1 April: 261.0 µg/m³, 3.9× its usual 66.3 Chiang Rai, 2 April: 202.0 µg/m³, 3.1× its usual 66.1 Chiang Rai, 3 April: 124.0 µg/m³ Chiang Rai, 4 April: 117.0 µg/m³ Chiang Rai, 5 April: 118.0 µg/m³ Phayao Phayao, 22 March: 52.7 µg/m³ Phayao, 23 March: no reading Phayao, 24 March: no reading Phayao, 25 March: 127.0 µg/m³ Phayao, 26 March: 175.0 µg/m³, 2.6× its usual 66.6 Phayao, 27 March: 156.0 µg/m³, 2.4× its usual 65.3 Phayao, 28 March: 152.0 µg/m³, 2.4× its usual 63.9 Phayao, 29 March: no reading Phayao, 30 March: no reading Phayao, 31 March: no reading Phayao, 1 April: 205.0 µg/m³, 3.1× its usual 66.8 Phayao, 2 April: 146.0 µg/m³, 2.1× its usual 70.7 Phayao, 3 April: 99.0 µg/m³ Phayao, 4 April: 112.0 µg/m³ Phayao, 5 April: 145.0 µg/m³ Bueng Kan Bueng Kan, 22 March: 45.5 µg/m³ Bueng Kan, 23 March: no reading Bueng Kan, 24 March: no reading Bueng Kan, 25 March: 144.0 µg/m³ Bueng Kan, 26 March: 166.0 µg/m³, 3.8× its usual 43.3 Bueng Kan, 27 March: 216.0 µg/m³, 5.0× its usual 43.4 Bueng Kan, 28 March: 95.1 µg/m³, 2.2× its usual 42.8 Bueng Kan, 29 March: 56.6 µg/m³ Bueng Kan, 30 March: 38.4 µg/m³ Bueng Kan, 31 March: 40.4 µg/m³ Bueng Kan, 1 April: 37.0 µg/m³ Bueng Kan, 2 April: 49.7 µg/m³ Bueng Kan, 3 April: 33.3 µg/m³ Bueng Kan, 4 April: 46.7 µg/m³ Bueng Kan, 5 April: 101.0 µg/m³ Pakxan Pakxan, 22 March: 45.5 µg/m³ Pakxan, 23 March: no reading Pakxan, 24 March: no reading Pakxan, 25 March: 144.0 µg/m³ Pakxan, 26 March: 166.0 µg/m³, 3.8× its usual 43.3 Pakxan, 27 March: 216.0 µg/m³, 5.0× its usual 43.4 Pakxan, 28 March: 95.1 µg/m³, 2.2× its usual 42.8 Pakxan, 29 March: 56.6 µg/m³ Pakxan, 30 March: 38.4 µg/m³ Pakxan, 31 March: 40.4 µg/m³ Pakxan, 1 April: 37.0 µg/m³ Pakxan, 2 April: 49.7 µg/m³ Pakxan, 3 April: 33.3 µg/m³ Pakxan, 4 April: 46.7 µg/m³ Pakxan, 5 April: 101.0 µg/m³ Nan Nan, 22 March: 78.3 µg/m³ Nan, 23 March: no reading Nan, 24 March: no reading Nan, 25 March: 126.0 µg/m³ Nan, 26 March: 165.0 µg/m³, 2.3× its usual 71.5 Nan, 27 March: 197.0 µg/m³, 2.8× its usual 71.2 Nan, 28 March: 147.0 µg/m³, 2.1× its usual 69.0 Nan, 29 March: 108.0 µg/m³ Nan, 30 March: 97.6 µg/m³ Nan, 31 March: 127.0 µg/m³ Nan, 1 April: 173.0 µg/m³, 2.3× its usual 74.8 Nan, 2 April: 116.0 µg/m³ Nan, 3 April: 90.3 µg/m³ Nan, 4 April: 99.6 µg/m³ Nan, 5 April: 139.0 µg/m³ Phrae Phrae, 22 March: 55.4 µg/m³ Phrae, 23 March: no reading Phrae, 24 March: no reading Phrae, 25 March: 80.2 µg/m³ Phrae, 26 March: 113.0 µg/m³, 2.0× its usual 56.0 Phrae, 27 March: 124.0 µg/m³, 2.2× its usual 55.9 Phrae, 28 March: 98.6 µg/m³ Phrae, 29 March: 60.6 µg/m³ Phrae, 30 March: 55.7 µg/m³ Phrae, 31 March: 72.4 µg/m³ Phrae, 1 April: 118.0 µg/m³, 2.2× its usual 54.5 Phrae, 2 April: 78.6 µg/m³ Phrae, 3 April: 63.0 µg/m³ Phrae, 4 April: 77.0 µg/m³ Phrae, 5 April: 115.0 µg/m³ Loei Loei, 22 March: no reading Loei, 23 March: no reading Loei, 24 March: no reading Loei, 25 March: 68.9 µg/m³ Loei, 26 March: 82.1 µg/m³ Loei, 27 March: 96.5 µg/m³ Loei, 28 March: 119.0 µg/m³, 2.4× its usual 49.5 Loei, 29 March: 50.6 µg/m³ Loei, 30 March: 45.0 µg/m³ Loei, 31 March: 78.3 µg/m³ Loei, 1 April: 75.4 µg/m³ Loei, 2 April: 77.4 µg/m³ Loei, 3 April: 80.5 µg/m³ Loei, 4 April: 85.1 µg/m³ Loei, 5 April: 104.0 µg/m³ Chiang Mai Chiang Mai, 22 March: 62.7 µg/m³ Chiang Mai, 23 March: no reading Chiang Mai, 24 March: no reading Chiang Mai, 25 March: 80.5 µg/m³ Chiang Mai, 26 March: 111.0 µg/m³ Chiang Mai, 27 March: 109.5 µg/m³ Chiang Mai, 28 March: 95.9 µg/m³ Chiang Mai, 29 March: 107.0 µg/m³ Chiang Mai, 30 March: 149.0 µg/m³, 2.4× its usual 62.1 Chiang Mai, 31 March: 154.0 µg/m³, 2.5× its usual 62.6 Chiang Mai, 1 April: 195.0 µg/m³, 3.1× its usual 62.1 Chiang Mai, 2 April: 180.0 µg/m³, 2.9× its usual 62.5 Chiang Mai, 3 April: 97.4 µg/m³ Chiang Mai, 4 April: 93.8 µg/m³ Chiang Mai, 5 April: 128.5 µg/m³ Lampang Lampang, 22 March: 40.8 µg/m³ Lampang, 23 March: no reading Lampang, 24 March: no reading Lampang, 25 March: 103.0 µg/m³ Lampang, 26 March: 119.0 µg/m³ Lampang, 27 March: 108.0 µg/m³ Lampang, 28 March: 108.0 µg/m³ Lampang, 29 March: 112.0 µg/m³ Lampang, 30 March: 96.7 µg/m³ Lampang, 31 March: 119.0 µg/m³ Lampang, 1 April: 154.0 µg/m³, 2.3× its usual 67.1 Lampang, 2 April: 118.0 µg/m³ Lampang, 3 April: 77.0 µg/m³ Lampang, 4 April: 80.9 µg/m³ Lampang, 5 April: 120.0 µg/m³ Lamphun Lamphun, 22 March: 51.3 µg/m³ Lamphun, 23 March: no reading Lamphun, 24 March: no reading Lamphun, 25 March: 76.0 µg/m³ Lamphun, 26 March: 97.8 µg/m³ Lamphun, 27 March: 90.6 µg/m³ Lamphun, 28 March: 95.6 µg/m³ Lamphun, 29 March: 100.0 µg/m³ Lamphun, 30 March: 97.8 µg/m³ Lamphun, 31 March: 107.0 µg/m³ Lamphun, 1 April: 135.0 µg/m³, 2.0× its usual 67.1 Lamphun, 2 April: 130.0 µg/m³ Lamphun, 3 April: 72.0 µg/m³ Lamphun, 4 April: 69.4 µg/m³ Lamphun, 5 April: 96.6 µg/m³ 22 Mar 24 26 28 30 1 Apr 3 5 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. Good 0–50
Moderate 51–100
Sensitive groups 101–150
Unhealthy 151–200
Very unhealthy 201–300
Hazardous 301+
Every city it reached
City Days Highest Usual Above usual
Mae Sai Chiang Rai, Thailand 9 27 March 83.8 6.6× Chiang Rai Chiang Rai, Thailand 9 28 March 66.6 5.2× Bueng Kan Bueng Kan, Thailand 3 27 March 43.4 5.0× Pakxan Bolikhamsai, Laos 3 27 March 43.4 5.0× Chiang Khong Chiang Rai, Thailand 8 27 March 76.0 3.7× Ban Houakhoua Bokeo, Laos 8 27 March 76.0 3.7× Phayao Phayao, Thailand 5 1 April 66.8 3.1× Chiang Mai Chiang Mai, Thailand 4 1 April 62.1 3.1× Nan Nan, Thailand 4 27 March 71.2 2.8× Loei Loei, Thailand 1 28 March 49.5 2.4× Lampang Lampang, Thailand 1 1 April 67.1 2.3× Phrae Phrae, Thailand 3 27 March 55.9 2.2× Lamphun Lamphun, Thailand 1 1 April 67.1 2.0×
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 16 of 24 episodes in Thailand and Laos since our records began, by cities reached.
Thailand and Laos, March 2025 56 Thailand, February 2024 52 Northern Thailand, January 2025 51 Thailand and Laos, April and May 2024 47 Northern Thailand and Laos, 20 to 22 May 2023 44 Thailand, April 2023 36 Northern Thailand and Laos, January and February 2023 36 Northern Thailand and Laos, 16 to 18 May 2023 32 Northern Thailand and Laos around Bangkok, 5 to 8 April 2023 30 Thailand and Laos, October 2024 24 Thailand and Laos, November and December 2025 23 Thailand, 12 to 13 February 2025 18 Northern Thailand and Laos, March and April 2023 13 Bars: cities reached; colour: the level of the episode's highest daily reading. All 24 .
Use this page SmogRank, Northern Thailand and Laos, March and April 2023: 13 cities with PM2.5 at twice their usual or more, 25 March to 2 April 2023, smogrank.com/episodes/2023-03-northern-thailand-and-laos (accessed 5 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.
