SmogRank / Japan / Kumamoto / Aso
Aso, month by month
Aso has a measured daily mean on 996 days since 28 July 2023. Its worst month was January 2025, at 59 US AQI (13.2 µg/m³), 597th of 2,474 cities on that month's world ranking. Its cleanest was July 2024, at 21 US AQI (3.7 µg/m³).
Every month since 2023
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
7 months
| Month | Why |
|---|---|
| Nov 2024 | 20 of 30 days measured; a month needs 21. The others: 10 with under 18 hours of readings or readings that failed our checks. |
| Oct 2024 | 21 of 31 days measured; a month needs 22. The others: 10 with under 18 hours of readings or readings that failed our checks. |
| Apr 2024 | 5 of 30 days measured; a month needs 21. The others: 25 with under 18 hours of readings or readings that failed our checks. |
| Mar 2024 | No day measured. The others: 1 missing from OpenAQ's archive, 30 with under 18 hours of readings or readings that failed our checks. |
| Feb 2024 | No day measured. The others: 1 missing from OpenAQ's archive, 28 with under 18 hours of readings or readings that failed our checks. |
| Jan 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Jul 2023 | 4 of 31 days measured; a month needs 22. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Aso's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| January 2025 | 5913.2 µg/m³ | 597thof 2,474 | Japan and South Korea, 17 to 24 January 2025 |
| July 2025 | 5712.5 µg/m³ | 731stof 2,889 | Japan and South Korea, June and July 2025 |
| March 2026 | 5511.4 µg/m³ | 1,340thof 2,971 | Japan and South Korea, March 2026 |
| August 2025 | 5511.1 µg/m³ | 974thof 2,901 | – |
| March 2025 | 5511.0 µg/m³ | 1,407thof 2,862 | Japan and South Korea, February and March 2025 |
| April 2025 | 5410.5 µg/m³ | 1,054thof 2,951 | – |
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.
Aso's worst days
| Day | US AQI | Episode |
|---|---|---|
| 4 Jul 2025 | 13448.8 µg/m³ | Japan and South Korea, June and July 2025 |
| 2 Jul 2025 | 13147.5 µg/m³ | Japan and South Korea, June and July 2025 |
| 1 Jul 2025 | 12344.5 µg/m³ | Japan and South Korea, June and July 2025 |
| 3 Jul 2025 | 12043.4 µg/m³ | Japan and South Korea, June and July 2025 |
| 21 Jan 2025 | 9834.4 µg/m³ | Japan and South Korea, 17 to 24 January 2025 |
| 28 Mar 2026 | 9331.7 µg/m³ | Japan and South Korea, March 2026 |
| 27 Feb 2025 | 9231.0 µg/m³ | Japan and South Korea, February and March 2025 |
| 30 Jun 2025 | 9130.5 µg/m³ | Japan and South Korea, June and July 2025 |
| 8 Mar 2026 | 8627.8 µg/m³ | – |
| 24 Jan 2025 | 8426.7 µg/m³ | Japan and South Korea, 17 to 24 January 2025 |
Daily means, the highest since 28 Jul 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, Aso, Japan, 28 Jul 2023 – 12 Oct 2026. Monitor data from Ministry of the Environment Air Pollutant Wide Area Monitoring System via OpenAQ; sources listed at smogrank.com/sources. smogrank.com/jp/aso/history (accessed 12 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.
Aso now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 18:07 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).