SmogRank / Episodes / Thailand

North-western Thailand, May 2023

For 2 days, from 6 to 7 May 2023, 9 cities in Thailand and Laos had PM2.5 at least twice their usual for the time of year. The worst reading was Phayao, Phayao, Thailand: 78.5 µg/m³ on 6 May, about 3.3× its usual 24.0.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached9in 2 countries
Days26 to 7 May 2023
Worst day7 May9 cities counted
Furthest above usual3.3×Phayao

Day by day

7 May 9 cities at twice their usual or more
NanVientianeTha BoUttaraditLampangSukhothaiPhichitBan HouakhouaKhon KaenLamphunChaiyaphumKamphaeng PhetTakMae SaiKalasinSakon NakhonMae SotRoi EtMukdahanUdon ThaniPhraeNong Bua LamphuPhetchabunChiang MaiChiang RaiLoeiPakxanPhayao
3 May45678910
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

PhayaoPhayao, 3 May: 39.3 µg/m³, 1.6× usualPhayao, 4 May: 31.1 µg/m³, 1.3× usualPhayao, 5 May: 49.8 µg/m³, 2.1× usualPhayao, 6 May: 78.5 µg/m³, 3.3× usualPhayao, 7 May: 51.8 µg/m³, 2.2× usualPhayao, 8 May: no readingPhayao, 9 May: no readingPhayao, 10 May: no readingPhraePhrae, 3 May: 34.5 µg/m³, 1.4× usualPhrae, 4 May: 38.5 µg/m³, 1.5× usualPhrae, 5 May: 47.3 µg/m³, 1.9× usualPhrae, 6 May: 53.3 µg/m³, 2.1× usualPhrae, 7 May: 51.4 µg/m³, 2.0× usualPhrae, 8 May: no readingPhrae, 9 May: no readingPhrae, 10 May: no readingChiang MaiChiang Mai, 3 May: 25.3 µg/m³, 1.1× usualChiang Mai, 4 May: 26.6 µg/m³, 1.2× usualChiang Mai, 5 May: 36.9 µg/m³, 1.6× usualChiang Mai, 6 May: 48.9 µg/m³, 2.2× usualChiang Mai, 7 May: 52.1 µg/m³, 2.3× usualChiang Mai, 8 May: no readingChiang Mai, 9 May: no readingChiang Mai, 10 May: no readingLoeiLoei, 3 May: 29.9 µg/m³, 1.6× usualLoei, 4 May: 27.0 µg/m³, 1.4× usualLoei, 5 May: 40.7 µg/m³, 2.2× usualLoei, 6 May: 42.8 µg/m³, 2.3× usualLoei, 7 May: 46.6 µg/m³, 2.5× usualLoei, 8 May: no readingLoei, 9 May: no readingLoei, 10 May: no readingPakxanPakxan, 3 May: 36.2 µg/m³, 1.9× usualPakxan, 4 May: 34.0 µg/m³, 1.8× usualPakxan, 5 May: 36.4 µg/m³, 1.9× usualPakxan, 6 May: 39.0 µg/m³, 2.1× usualPakxan, 7 May: 54.6 µg/m³, 2.9× usualPakxan, 8 May: no readingPakxan, 9 May: no readingPakxan, 10 May: no readingPhetchabunPhetchabun, 3 May: 26.4 µg/m³, 1.5× usualPhetchabun, 4 May: 36.2 µg/m³, 2.0× usualPhetchabun, 5 May: 34.6 µg/m³, 1.9× usualPhetchabun, 6 May: 38.2 µg/m³, 2.1× usualPhetchabun, 7 May: 40.9 µg/m³, 2.3× usualPhetchabun, 8 May: no readingPhetchabun, 9 May: no readingPhetchabun, 10 May: no readingChiang RaiChiang Rai, 3 May: 27.7 µg/m³, 1.3× usualChiang Rai, 4 May: 21.9 µg/m³, 1.1× usualChiang Rai, 5 May: 25.6 µg/m³, 1.2× usualChiang Rai, 6 May: 36.3 µg/m³, 1.7× usualChiang Rai, 7 May: 50.3 µg/m³, 2.4× usualChiang Rai, 8 May: no readingChiang Rai, 9 May: no readingChiang Rai, 10 May: no readingUdon ThaniUdon Thani, 3 May: 32.1 µg/m³, 1.7× usualUdon Thani, 4 May: 28.2 µg/m³, 1.5× usualUdon Thani, 5 May: 32.3 µg/m³, 1.7× usualUdon Thani, 6 May: 35.3 µg/m³, 1.8× usualUdon Thani, 7 May: 40.5 µg/m³, 2.1× usualUdon Thani, 8 May: no readingUdon Thani, 9 May: no readingUdon Thani, 10 May: no readingNong Bua LamphuNong Bua Lamphu, 3 May: 26.8 µg/m³, 1.6× usualNong Bua Lamphu, 4 May: 25.3 µg/m³, 1.5× usualNong Bua Lamphu, 5 May: 29.7 µg/m³, 1.8× usualNong Bua Lamphu, 6 May: 30.2 µg/m³, 1.8× usualNong Bua Lamphu, 7 May: 37.2 µg/m³, 2.2× usualNong Bua Lamphu, 8 May: no readingNong Bua Lamphu, 9 May: no readingNong Bua Lamphu, 10 May: no reading3 May45678910
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
PhayaoPhayao, Thailand2 78.56 May24.03.3×
PakxanBolikhamsai, Laos2 54.67 May18.92.9×
LoeiLoei, Thailand2 46.67 May18.72.5×
Chiang RaiChiang Rai, Thailand1 50.37 May20.82.4×
Chiang MaiChiang Mai, Thailand2 52.17 May22.52.3×
PhetchabunPhetchabun, Thailand2 40.97 May18.12.3×
Nong Bua LamphuNong Bua Lamphu, Thailand1 37.27 May16.92.2×
PhraePhrae, Thailand2 53.36 May25.52.1×
Udon ThaniUdon Thani, Thailand1 40.57 May19.42.1×

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 19 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, May 2023: 9 cities with PM2.5 at twice their usual or more, 6 to 7 May 2023, smogrank.com/episodes/2023-05-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.