SmogRank / Japan / Nagano / Saku
Saku, month by month
Saku has a measured daily mean on 892 days since 28 July 2023. Its worst month was July 2025, at 54 US AQI (10.7 µg/m³), 1,149th of 3,073 cities on that month's world ranking. Its cleanest was September 2026, at 16 US AQI (2.8 µg/m³). 2025 averaged 44 US AQI (7.9 µg/m³), against 39 US AQI (7.0 µg/m³) in 2024.
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
12 months
| Month | Why |
|---|---|
| Jan 2025 | 15 of 31 days measured; a month needs 22. The others: 16 with readings for part of the day (a day needs 18 hours). |
| Dec 2024 | 12 of 31 days measured; a month needs 22. The others: 19 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. |
| Mar 2024 | 14 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 16 with under 18 hours of readings or readings that failed our checks. |
| Feb 2024 | 9 of 29 days measured; a month needs 21. The others: 1 missing from OpenAQ's archive, 19 with under 18 hours of readings or readings that failed our checks. |
| Jan 2024 | 13 of 31 days measured; a month needs 22. The others: 18 with under 18 hours of readings or readings that failed our checks. |
| Dec 2023 | 8 of 31 days measured; a month needs 22. The others: 23 with under 18 hours of readings or readings that failed our checks. |
| Nov 2023 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Oct 2023 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Sep 2023 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Aug 2023 | 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.
Saku's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| July 2025 | 5410.7 µg/m³ | 1,149thof 3,073 | Japan and South Korea, June and July 2025 |
| August 2025 | 5310.3 µg/m³ | 1,218thof 3,095 | – |
| June 2024 | 529.6 µg/m³ | 752ndof 2,563 | – |
| July 2026 | 529.5 µg/m³ | 1,591stof 3,035 | – |
| March 2025 | 529.4 µg/m³ | 1,906thof 3,102 | Japan and South Korea, March 2025 |
| June 2025 | 519.1 µg/m³ | 1,748thof 3,112 | Japan and South Korea, June and July 2025 |
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.
Saku's worst days
| Day | US AQI | Episode |
|---|---|---|
| 26 Mar 2025 | 10135.7 µg/m³ | Japan and South Korea, March 2025 |
| 8 Jul 2025 | 8627.9 µg/m³ | Japan and South Korea, June and July 2025 |
| 21 May 2025 | 8226.0 µg/m³ | Japan, May 2025 |
| 25 Mar 2025 | 8225.5 µg/m³ | Japan and South Korea, March 2025 |
| 19 Apr 2025 | 7823.7 µg/m³ | – |
| 18 Apr 2025 | 7320.8 µg/m³ | – |
| 8 Sept 2024 | 7220.5 µg/m³ | – |
| 25 Aug 2025 | 7220.4 µg/m³ | – |
| 9 Jul 2025 | 7120.0 µg/m³ | Japan and South Korea, June and July 2025 |
| 26 Aug 2025 | 7119.8 µg/m³ | – |
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, Saku, Japan, 28 Jul 2023 – 13 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/saku/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.
Saku now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-13 21:07 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).