SmogRank / Japan / Yamaguchi / Hōfu
Hōfu, month by month
Hōfu has a measured daily mean on 1,150 days since 28 July 2023. Its worst month was April 2024, at 57 US AQI (12.5 µg/m³), 653rd of 2,520 cities on that month's world ranking. Its cleanest was October 2025, at 34 US AQI (6.2 µg/m³). 2025 averaged 52 US AQI (9.8 µg/m³), against 48 US AQI (8.6 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
1 month
| Month | Why |
|---|---|
| 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.
Hōfu's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| April 2024 | 5712.5 µg/m³ | 653rdof 2,520 | Japan and South Korea, April 2024 |
| March 2025 | 5712.5 µg/m³ | 1,156thof 2,862 | Japan and South Korea, March 2025 Japan and South Korea, February and March 2025 |
| July 2025 | 5712.3 µg/m³ | 768thof 2,889 | Japan and South Korea, June and July 2025 |
| April 2025 | 5612.0 µg/m³ | 763rdof 2,951 | – |
| June 2025 | 5611.6 µg/m³ | 875thof 2,508 | Japan and South Korea, June and July 2025 |
| January 2025 | 5410.7 µg/m³ | 884thof 2,474 | Japan and South Korea, 17 to 24 January 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.
Hōfu's worst days
| Day | US AQI | Episode |
|---|---|---|
| 3 Jul 2025 | 9934.8 µg/m³ | Japan and South Korea, June and July 2025 |
| 10 Jul 2025 | 9733.9 µg/m³ | Japan and South Korea, June and July 2025 |
| 18 Apr 2024 | 9231.2 µg/m³ | Japan and South Korea, April 2024 |
| 2 Jul 2025 | 9130.8 µg/m³ | Japan and South Korea, June and July 2025 |
| 19 Apr 2024 | 9030.0 µg/m³ | Japan and South Korea, April 2024 |
| 4 Jul 2025 | 8829.1 µg/m³ | Japan and South Korea, June and July 2025 |
| 26 Mar 2025 | 8627.9 µg/m³ | Japan and South Korea, March 2025 |
| 9 Jul 2025 | 8427.0 µg/m³ | Japan and South Korea, June and July 2025 |
| 21 Jul 2026 | 8426.7 µg/m³ | Japan and South Korea, July 2026 |
| 23 Jan 2025 | 8426.6 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, Hōfu, 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/hofu/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.
Hōfu 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).