SmogRank / Thailand / Bangkok / Lak Si

Lak Si, month by month

Lak Si has a measured daily mean on 812 days since 1 January 2023. Its worst month was January 2025, at 135 US AQI (49.5 µg/m³), 35th of 2,474 cities on that month's world ranking. Its cleanest was September 2025, at 55 US AQI (11.4 µg/m³).

Every month since 2023

202675 so far257 days measured321st of 2,793 in the world
Jan103#115Feb91#252Mar80#448Apr79#321May69#317Jun57#462Jul3 daysAug60#434Sep64#350Oct78#65
2025too few days for a mean (a year needs 256)246 days measured
Jan135#35Feb110#111Mar21 daysApr73#309May58#508Jun56#810JulnoneAug6 daysSep55#514Oct10 daysNov12 daysDec88#325
2024too few days for a mean (a year needs 257)220 days measured
Jan126#42Feb12 daysMarnoneApr12 daysMay73#134Jun59#269Jul3 daysAugnoneSep15 daysOct68#158Nov81#101Dec101#57
2023too few days for a mean (a year needs 256)89 days measured
Jan101#42Feb2 daysMar9 daysApr19 daysMay16 daysJun8 daysJul6 daysAug3 daysSep3 daysOctnoneNovnoneDecnone
Each square is a month's mean PM2.5 in US AQI from Lak Si'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 Lak Si 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

23 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.
Mar 202521 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks.
Sep 202415 of 30 days measured; a month needs 21. The others: 15 with under 18 hours of readings or readings that failed our checks.
Aug 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Jul 20243 of 31 days measured; a month needs 22. The others: 28 with under 18 hours of readings or readings that failed our checks.
Apr 202412 of 30 days measured; a month needs 21. The others: 18 with under 18 hours of readings or readings that failed our checks.
Mar 2024No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks.
Feb 202412 of 29 days measured; a month needs 21. The others: 1 missing from OpenAQ's archive, 16 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 20236 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 24 with under 18 hours of readings or readings that failed our checks.
Jun 20238 of 30 days measured; a month needs 21. The others: 22 with under 18 hours of readings or readings that failed our checks.
May 202316 of 31 days measured; a month needs 22. The others: 15 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.

Lak Si's worst months

MonthUS AQIDays measuredWorld rankEpisode
January 2025 13549.5 µg/m³31 of 3135thof 2,474Northern Thailand, January 2025
January 2024 12645.8 µg/m³25 of 3142ndof 2,385–
February 2025 11039.0 µg/m³28 of 28111thof 2,633–
January 2026 10336.3 µg/m³31 of 31115thof 2,617–
December 2024 10135.6 µg/m³31 of 3157thof 2,616–
January 2023 10135.5 µg/m³23 of 3142ndof 1,261Northern Thailand and Laos, January and February 2023

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.

Lak Si's worst days

DayUS AQIEpisode
24 Jan 2025 17792.4 µg/m³Northern Thailand, January 2025
1 Feb 2023 16676.7 µg/m³Northern Thailand and Laos, January and February 2023
25 Jan 2025 16575.9 µg/m³Northern Thailand, January 2025
23 Jan 2025 16271.1 µg/m³Northern Thailand, January 2025
13 Feb 2024 16170.4 µg/m³Thailand, February 2024
15 Feb 2024 15967.2 µg/m³Thailand, February 2024
8 Jan 2025 15966.3 µg/m³–
21 Jan 2025 15763.5 µg/m³–
15 Jan 2025 15662.4 µg/m³–
31 Jan 2024 15662.3 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, Lak Si, Thailand, 1 Jan 2023 – 12 Oct 2026. Monitor data from Air4Thai via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/th/lak-si/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.

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

Updated 2026-10-12 22:07 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).