SmogRank / Taiwan / Taiwan / Chiayi City
Chiayi City, month by month
Chiayi City has a measured daily mean on 831 days since 28 February 2024. Its worst month was February 2026, at 83 US AQI (26.2 µg/m³), 337th of 2,866 cities on that month's world ranking. Its cleanest was June 2025, at 31 US AQI (5.5 µg/m³).
Every month since 2024
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
5 months
| Month | Why |
|---|---|
| Nov 2025 | 12 of 30 days measured; a month needs 21. The others: 18 with under 18 hours of readings or readings that failed our checks. |
| Oct 2025 | 10 of 31 days measured; a month needs 22. The others: 21 with under 18 hours of readings or readings that failed our checks. |
| Aug 2025 | 6 of 31 days measured; a month needs 22. The others: 25 with under 18 hours of readings or readings that failed our checks. |
| Jul 2025 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Feb 2024 | 2 of 29 days measured; a month needs 21. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Chiayi City's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| February 2026 | 8326.2 µg/m³ | 337thof 2,866 | – |
| January 2025 | 8125.2 µg/m³ | 162ndof 2,474 | Taiwan, 21 to 22 January 2025 |
| February 2025 | 8024.8 µg/m³ | 293rdof 2,633 | Taiwan, 17 February 2025 |
| March 2024 | 7924.3 µg/m³ | 90thof 1,698 | – |
| January 2026 | 7823.5 µg/m³ | 288thof 2,617 | – |
| March 2026 | 7622.6 µg/m³ | 511thof 2,971 | – |
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.
Chiayi City's worst days
| Day | US AQI | Episode |
|---|---|---|
| 11 Mar 2025 | 14854.7 µg/m³ | Taiwan, March 2025 |
| 22 Jan 2025 | 13549.4 µg/m³ | Taiwan, 21 to 22 January 2025 |
| 15 Nov 2024 | 12846.3 µg/m³ | Taiwan, November 2024 |
| 17 Feb 2025 | 12645.7 µg/m³ | Taiwan, 17 February 2025 |
| 23 Jan 2025 | 12645.6 µg/m³ | – |
| 26 Feb 2025 | 12244.2 µg/m³ | – |
| 27 Feb 2025 | 11942.8 µg/m³ | – |
| 16 Mar 2024 | 11641.6 µg/m³ | – |
| 6 Feb 2025 | 11541.2 µg/m³ | – |
| 1 Jan 2025 | 11541.1 µg/m³ | – |
Daily means, the highest since 28 Feb 2024; 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, Chiayi City, Taiwan, 28 Feb 2024 – 12 Oct 2026. Monitor data from Taiwan's Ministry of Environment via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/tw/chiayi-city/history (accessed 13 Oct 2026).
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.
Chiayi City now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-13 02:07 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).