SmogRank / Thailand / Chiang Mai / Chiang Mai

Chiang Mai, month by month

Chiang Mai has a measured daily mean on 775 days since 1 January 2023. Its worst month was April 2024, at 168 US AQI (79.7 µg/m³), 6th of 2,520 cities on that month's world ranking. Its cleanest was September 2025, at 53 US AQI (10.1 µg/m³).

Every month since 2023

202678 so far255 days measured280th of 2,791 in the world
Jan70#474Feb75#485Mar99#193Apr160#26May61#445Jun55#540Jul3 daysAug58#507Sep58#463Oct59#295
2025too few days for a mean (a year needs 256)226 days measured
Jan6 daysFeb88#223Mar139#80Apr96#140May57#552Jun55#1,015JulnoneAug6 daysSep53#665Oct10 daysNov12 daysDec76#428
2024too few days for a mean (a year needs 257)205 days measured
Jan80#176Feb96#89Mar20 daysApr168#6May92#64Jun53#583Jul19 daysAug19 daysSep5 daysOct2 daysNov3 daysDec1 day
2023too few days for a mean (a year needs 256)89 days measured
Jan96#53Feb2 daysMar9 daysApr19 daysMay15 daysJun10 daysJul5 daysAug3 daysSep3 daysOctnoneNovnoneDecnone
Each square is a month's mean PM2.5 in US AQI from Chiang Mai'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 Chiang Mai 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

24 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 202512 of 30 days measured; a month needs 21. The others: 18 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.
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 20256 of 31 days measured; a month needs 22. The others: 25 with under 18 hours of readings or readings that failed our checks.
Dec 20241 of 31 days measured; a month needs 22. The others: 30 with under 18 hours of readings or readings that failed our checks.
Nov 20243 of 30 days measured; a month needs 21. The others: 27 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 202419 of 31 days measured; a month needs 22. The others: 12 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 20235 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 25 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 20239 of 31 days measured; a month needs 22. The others: 19 missing from OpenAQ's archive, 3 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.

Chiang Mai's worst months

MonthUS AQIDays measuredWorld rankEpisode
April 2024 16879.7 µg/m³29 of 306thof 2,520Thailand and Laos, April and May 2024
April 2026 16068.1 µg/m³30 of 3026thof 2,941–
March 2025 13951.0 µg/m³29 of 3180thof 2,862–
March 2026 9934.6 µg/m³31 of 31193rdof 2,971–
January 2023 9633.3 µg/m³23 of 3153rdof 1,261–
February 2024 9633.1 µg/m³24 of 2989thof 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.

Chiang Mai's worst days

DayUS AQIEpisode
7 Apr 2023 298223.0 µg/m³Northern Thailand and Laos around Bangkok, 5 to 8 April 2023
1 Apr 2023 270195.0 µg/m³Northern Thailand and Laos, March and April 2023
8 Apr 2023 263188.0 µg/m³Northern Thailand and Laos around Bangkok, 5 to 8 April 2023
2 Apr 2023 255180.0 µg/m³Northern Thailand and Laos, March and April 2023
31 Mar 2023 229154.0 µg/m³Northern Thailand and Laos, March and April 2023
7 Apr 2024 228153.0 µg/m³–
30 Mar 2023 224149.0 µg/m³Northern Thailand and Laos, March and April 2023
6 Apr 2024 215140.0 µg/m³–
12 Apr 2023 214139.0 µg/m³–
16 Apr 2023 212137.0 µg/m³–

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, Chiang Mai, Thailand, 1 Jan 2023 – 12 Oct 2026. Monitor data from Air4Thai via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/th/chiang-mai/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.

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

Updated 2026-10-12 19:07 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).