SmogRank / Thailand / Chiang Rai / Mae Sai

Mae Sai, month by month

Mae Sai has a measured daily mean on 745 days since 1 January 2023. Its worst month was April 2026, at 191 US AQI (112.6 µg/m³), 2nd of 2,941 cities on that month's world ranking. Its cleanest was August 2026, at 56 US AQI (11.7 µg/m³).

Every month since 2023

2026103 so far251 days measured108th of 2,791 in the world
Jan90#176Feb96#215Mar160#34Apr191#2May75#254Jun63#335Jul3 daysAug56#599Sep62#362Oct68#134
2025too few days for a mean (a year needs 256)207 days measured
Jan5 daysFeb112#98Mar164#21Apr149#25May67#329Jun63#397JulnoneAug6 daysSep14 daysOct10 daysNov11 daysDec90#311
2024too few days for a mean (a year needs 257)200 days measured
Jan91#112Feb122#46Mar20 daysApr175#4May115#42Jun61#215Jul18 daysAug19 daysSep5 daysOct2 daysNov4 daysDecnone
2023too few days for a mean (a year needs 256)87 days measured
Jan98#49Feb2 daysMar8 daysApr19 daysMay15 daysJun10 daysJul4 daysAug3 daysSep3 daysOctnoneNovnoneDecnone
Each square is a month's mean PM2.5 in US AQI from Mae Sai's measured days, with its place on that month's world ranking under it. A month has a mean once 70% of its days are measured, the rule the monthly rankings use; under that, the square gives the days measured. Each square opens that month's ranking with Mae Sai marked; each year, the year's. A dashed square is the running month, so far.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales

Months without a mean, and why

25 months
MonthWhy
Jul 20263 of 31 days measured; a month needs 22. The others: 28 with under 18 hours of readings or readings that failed our checks.
Nov 202511 of 30 days measured; a month needs 21. The others: 19 with under 18 hours of readings or readings that failed our checks.
Oct 202510 of 31 days measured; a month needs 22. The others: 21 with under 18 hours of readings or readings that failed our checks.
Sep 202514 of 30 days measured; a month needs 21. The others: 16 with under 18 hours of readings or readings that failed our checks.
Aug 20256 of 31 days measured; a month needs 22. The others: 25 with under 18 hours of readings or readings that failed our checks.
Jul 2025No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Jan 20255 of 31 days measured; a month needs 22. The others: 26 with under 18 hours of readings or readings that failed our checks.
Dec 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Nov 20244 of 30 days measured; a month needs 21. The others: 26 with under 18 hours of readings or readings that failed our checks.
Oct 20242 of 31 days measured; a month needs 22. The others: 29 with under 18 hours of readings or readings that failed our checks.
Sep 20245 of 30 days measured; a month needs 21. The others: 25 with under 18 hours of readings or readings that failed our checks.
Aug 202419 of 31 days measured; a month needs 22. The others: 12 with under 18 hours of readings or readings that failed our checks.
Jul 202418 of 31 days measured; a month needs 22. The others: 13 with under 18 hours of readings or readings that failed our checks.
Mar 202420 of 31 days measured; a month needs 22. The others: 11 with under 18 hours of readings or readings that failed our checks.
Dec 2023No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Nov 2023No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks.
Oct 2023No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Sep 20233 of 30 days measured; a month needs 21. The others: 27 with under 18 hours of readings or readings that failed our checks.
Aug 20233 of 31 days measured; a month needs 22. The others: 28 with under 18 hours of readings or readings that failed our checks.
Jul 20234 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 26 with under 18 hours of readings or readings that failed our checks.
Jun 202310 of 30 days measured; a month needs 21. The others: 20 with under 18 hours of readings or readings that failed our checks.
May 202315 of 31 days measured; a month needs 22. The others: 16 with under 18 hours of readings or readings that failed our checks.
Apr 202319 of 30 days measured; a month needs 21. The others: 2 missing from OpenAQ's archive, 9 with under 18 hours of readings or readings that failed our checks.
Mar 20238 of 31 days measured; a month needs 22. The others: 19 missing from OpenAQ's archive, 4 with under 18 hours of readings or readings that failed our checks.
Feb 20232 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive, 1 with under 18 hours of readings or readings that failed our checks.

A day counts once 18 hours of it are measured; a month needs 70% of its days.

Mae Sai's worst months

MonthUS AQIDays measuredWorld rankEpisode
April 2026 191112.6 µg/m³27 of 302ndof 2,941Northern Thailand and Laos, April 2026
Northern Thailand and Laos, March and April 2026
April 2024 17589.8 µg/m³29 of 304thof 2,520Thailand and Laos, April and May 2024
March 2025 16474.5 µg/m³27 of 3121stof 2,862–
March 2026 16068.2 µg/m³30 of 3134thof 2,971Northern Thailand and Laos, March and April 2026
April 2025 14955.1 µg/m³23 of 3025thof 2,951–
February 2024 12244.0 µg/m³23 of 2946thof 2,486–

Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.

Mae Sai's worst days

DayUS AQIEpisode
27 Mar 2023 500+554.0 µg/m³Northern Thailand and Laos, March and April 2023
28 Mar 2023 500+499.0 µg/m³Northern Thailand and Laos, March and April 2023
26 Mar 2023 500+492.0 µg/m³Northern Thailand and Laos, March and April 2023
25 Mar 2023 500+370.0 µg/m³Northern Thailand and Laos, March and April 2023
7 Apr 2023 500+345.0 µg/m³Northern Thailand and Laos around Bangkok, 5 to 8 April 2023
8 Apr 2023 500+326.0 µg/m³Northern Thailand and Laos around Bangkok, 5 to 8 April 2023
29 Mar 2023 495323.0 µg/m³Northern Thailand and Laos, March and April 2023
1 Apr 2023 481316.0 µg/m³Northern Thailand and Laos, March and April 2023
2 Apr 2023 441296.0 µg/m³Northern Thailand and Laos, March and April 2023
30 Mar 2023 414282.0 µg/m³Northern Thailand and Laos, March and April 2023

Daily means, the highest since 1 Jan 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.

Use this history

SmogRank, PM2.5 monthly and daily means, Mae Sai, Thailand, 1 Jan 2023 – 12 Oct 2026. Monitor data from Air4Thai via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/th/mae-sai/history (accessed 12 Oct 2026).

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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.

Mae Sai now: the last 24 hours, its ranks today and the last 12 months day by day.

Updated 2026-10-12 20:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).