SmogRank / Episodes / Thailand
Thailand, May 2023
For 1 day, on 26 May 2023, 18 cities in Thailand had PM2.5 at least twice their usual for the time of year. The worst reading was Khan Na Yao, Bangkok, Thailand: 34.3 µg/m³ on 26 May, about 2.0× its usual 16.9. Readings from most of its cities stopped after 26 May, so this episode may have run longer.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 18 in 1 country
Days 1 26 May 2023
Worst day 26 May 18 cities counted
Furthest above usual 3.1× Kamphaeng Phet
Day by day
Play 26 May 18 cities at twice their usual or more
Phichit Nakhon Sawan Tak Loei Chai Nat Chaiyaphum Nan Nong Bua Lamphu Lamphun Saraburi Tha Bo Udon Thani Vientiane Khlong Luang Sai Mai Lak Si Mueang Nonthaburi Khlong Sam Wa Nong Chok Nakhon Pathom Bueng Kum Saphan Sung Bangkok Si Maha Phot Nong Khaem Ban Khlong Prawet Lat Krabang Phra Pradaeng Bang Na Ban Samae Dam Samut Sakhon Bang Bo District Ratchaburi Buri Ram Roi Et Ban Houakhoua Chiang Khong Bueng Kan Laem Chabang Pakxan Aranyaprathet Yangon Si Sa Ket Khan Na Yao Suphan Buri Sing Buri Bang Kapi Nakhon Ratchasima Chiang Mai Lop Buri Mae Sot Samut Prakan Phra Nakhon Si Ayutthaya Uttaradit Lampang Phrae Phetchabun Chiang Rai Ban Thai Tan Sukhothai Kamphaeng Phet 23 May 24 25 26 27 28 29 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
Khan Na Yao Khan Na Yao, 23 May: no reading Khan Na Yao, 24 May: no reading Khan Na Yao, 25 May: 29.7 µg/m³ Khan Na Yao, 26 May: 34.3 µg/m³, 2.0× its usual 16.9 Khan Na Yao, 27 May: no reading Khan Na Yao, 28 May: no reading Khan Na Yao, 29 May: no reading Nakhon Ratchasima Nakhon Ratchasima, 23 May: no reading Nakhon Ratchasima, 24 May: no reading Nakhon Ratchasima, 25 May: no reading Nakhon Ratchasima, 26 May: 34.0 µg/m³, 2.1× its usual 16.1 Nakhon Ratchasima, 27 May: no reading Nakhon Ratchasima, 28 May: no reading Nakhon Ratchasima, 29 May: no reading Ban Thai Tan Ban Thai Tan, 23 May: no reading Ban Thai Tan, 24 May: no reading Ban Thai Tan, 25 May: no reading Ban Thai Tan, 26 May: 33.7 µg/m³, 2.9× its usual 11.7 Ban Thai Tan, 27 May: no reading Ban Thai Tan, 28 May: no reading Ban Thai Tan, 29 May: no reading Lampang Lampang, 23 May: no reading Lampang, 24 May: no reading Lampang, 25 May: no reading Lampang, 26 May: 33.2 µg/m³, 2.3× its usual 14.5 Lampang, 27 May: no reading Lampang, 28 May: no reading Lampang, 29 May: no reading Phrae Phrae, 23 May: no reading Phrae, 24 May: no reading Phrae, 25 May: no reading Phrae, 26 May: 31.2 µg/m³, 2.4× its usual 12.8 Phrae, 27 May: no reading Phrae, 28 May: no reading Phrae, 29 May: no reading Uttaradit Uttaradit, 23 May: no reading Uttaradit, 24 May: no reading Uttaradit, 25 May: no reading Uttaradit, 26 May: 31.2 µg/m³, 2.3× its usual 13.7 Uttaradit, 27 May: no reading Uttaradit, 28 May: no reading Uttaradit, 29 May: no reading Chiang Rai Chiang Rai, 23 May: no reading Chiang Rai, 24 May: no reading Chiang Rai, 25 May: no reading Chiang Rai, 26 May: 30.6 µg/m³, 2.9× its usual 10.5 Chiang Rai, 27 May: no reading Chiang Rai, 28 May: no reading Chiang Rai, 29 May: no reading Lop Buri Lop Buri, 23 May: no reading Lop Buri, 24 May: no reading Lop Buri, 25 May: no reading Lop Buri, 26 May: 29.4 µg/m³, 2.2× its usual 13.2 Lop Buri, 27 May: no reading Lop Buri, 28 May: no reading Lop Buri, 29 May: no reading Phetchabun Phetchabun, 23 May: no reading Phetchabun, 24 May: no reading Phetchabun, 25 May: no reading Phetchabun, 26 May: 29.3 µg/m³, 2.7× its usual 11.0 Phetchabun, 27 May: no reading Phetchabun, 28 May: no reading Phetchabun, 29 May: no reading Bang Kapi Bang Kapi, 23 May: 23.6 µg/m³ Bang Kapi, 24 May: 24.4 µg/m³ Bang Kapi, 25 May: 27.7 µg/m³ Bang Kapi, 26 May: 27.3 µg/m³, 2.1× its usual 12.9 Bang Kapi, 27 May: 25.5 µg/m³ Bang Kapi, 28 May: 19.1 µg/m³ Bang Kapi, 29 May: 19.4 µg/m³ Kamphaeng Phet Kamphaeng Phet, 23 May: no reading Kamphaeng Phet, 24 May: no reading Kamphaeng Phet, 25 May: no reading Kamphaeng Phet, 26 May: 27.2 µg/m³, 3.1× its usual 8.8 Kamphaeng Phet, 27 May: no reading Kamphaeng Phet, 28 May: no reading Kamphaeng Phet, 29 May: no reading Phra Nakhon Si Ayut… Phra Nakhon Si Ayutthaya, 23 May: no reading Phra Nakhon Si Ayutthaya, 24 May: no reading Phra Nakhon Si Ayutthaya, 25 May: no reading Phra Nakhon Si Ayutthaya, 26 May: 26.2 µg/m³, 2.3× its usual 11.3 Phra Nakhon Si Ayutthaya, 27 May: no reading Phra Nakhon Si Ayutthaya, 28 May: no reading Phra Nakhon Si Ayutthaya, 29 May: no reading Chiang Mai Chiang Mai, 23 May: no reading Chiang Mai, 24 May: no reading Chiang Mai, 25 May: no reading Chiang Mai, 26 May: 26.1 µg/m³, 2.2× its usual 12.1 Chiang Mai, 27 May: no reading Chiang Mai, 28 May: no reading Chiang Mai, 29 May: no reading Sing Buri Sing Buri, 23 May: no reading Sing Buri, 24 May: no reading Sing Buri, 25 May: no reading Sing Buri, 26 May: 26.1 µg/m³, 2.1× its usual 12.5 Sing Buri, 27 May: no reading Sing Buri, 28 May: no reading Sing Buri, 29 May: no reading Samut Prakan Samut Prakan, 23 May: 22.4 µg/m³ Samut Prakan, 24 May: 20.4 µg/m³ Samut Prakan, 25 May: no reading Samut Prakan, 26 May: 25.9 µg/m³, 2.3× its usual 11.4 Samut Prakan, 27 May: 26.5 µg/m³ Samut Prakan, 28 May: 19.6 µg/m³ Samut Prakan, 29 May: 14.9 µg/m³ Sukhothai Sukhothai, 23 May: no reading Sukhothai, 24 May: no reading Sukhothai, 25 May: no reading Sukhothai, 26 May: 25.5 µg/m³, 3.0× its usual 8.6 Sukhothai, 27 May: no reading Sukhothai, 28 May: no reading Sukhothai, 29 May: no reading Mae Sot Mae Sot, 23 May: no reading Mae Sot, 24 May: no reading Mae Sot, 25 May: no reading Mae Sot, 26 May: 25.3 µg/m³, 2.3× its usual 11.1 Mae Sot, 27 May: no reading Mae Sot, 28 May: no reading Mae Sot, 29 May: no reading Suphan Buri Suphan Buri, 23 May: no reading Suphan Buri, 24 May: no reading Suphan Buri, 25 May: no reading Suphan Buri, 26 May: 25.3 µg/m³, 2.1× its usual 12.2 Suphan Buri, 27 May: no reading Suphan Buri, 28 May: no reading Suphan Buri, 29 May: no reading 23 May 24 25 26 27 28 29 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
Kamphaeng Phet Kamphaeng Phet, Thailand 1 26 May 8.8 3.1× Sukhothai Sukhothai, Thailand 1 26 May 8.6 3.0× Ban Thai Tan Ang Thong, Thailand 1 26 May 11.7 2.9× Chiang Rai Chiang Rai, Thailand 1 26 May 10.5 2.9× Phetchabun Phetchabun, Thailand 1 26 May 11.0 2.7× Phrae Phrae, Thailand 1 26 May 12.8 2.4× Lampang Lampang, Thailand 1 26 May 14.5 2.3× Uttaradit Uttaradit, Thailand 1 26 May 13.7 2.3× Phra Nakhon Si Ayutthaya Phra Nakhon Si Ayutthaya, Thailand 1 26 May 11.3 2.3× Samut Prakan Samut Prakan, Thailand 1 26 May 11.4 2.3× Mae Sot Tak, Thailand 1 26 May 11.1 2.3× Lop Buri Lopburi, Thailand 1 26 May 13.2 2.2× Chiang Mai Chiang Mai, Thailand 1 26 May 12.1 2.2× Nakhon Ratchasima Nakhon Ratchasima, Thailand 1 26 May 16.1 2.1× Bang Kapi Bangkok, Thailand 1 26 May 12.9 2.1× Sing Buri Sing Buri, Thailand 1 26 May 12.5 2.1× Suphan Buri Suphan Buri, Thailand 1 26 May 12.2 2.1× Khan Na Yao Bangkok, Thailand 1 26 May 16.9 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
Number 13 of 24 episodes in Thailand 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 Thailand, May 2023 18 Bars: cities reached; colour: the level of the episode's highest daily reading. All 24 .
Use this page SmogRank, Thailand, May 2023: 18 cities with PM2.5 at twice their usual or more, 26 May 2023, smogrank.com/episodes/2023-05-thailand (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.
