SmogRank / Japan / Ibaraki / Koga
Koga, month by month
Koga has a measured daily mean on 1,116 days since 28 July 2023. Its worst month was December 2025, at 52 US AQI (9.7 µg/m³), 1,404th of 3,006 cities on that month's world ranking. Its cleanest was September 2026, at 22 US AQI (4.0 µg/m³). 2025 averaged 39 US AQI (7.1 µg/m³), against 36 US AQI (6.5 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
2 months
| Month | Why |
|---|---|
| Jul 2024 | 19 of 31 days measured; a month needs 22. The others: 12 with under 18 hours of readings or readings that failed our checks. |
| Jul 2023 | 2 of 31 days measured; a month needs 22. The others: 2 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.
Koga's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| December 2025 | 529.7 µg/m³ | 1,404thof 3,006 | – |
| July 2025 | 509.0 µg/m³ | 1,519thof 2,889 | Japan and South Korea, June and July 2025 |
| August 2025 | 498.9 µg/m³ | 1,517thof 2,901 | – |
| February 2026 | 498.9 µg/m³ | 1,695thof 2,866 | Japan, 14 to 15 February 2026 |
| December 2023 | 488.7 µg/m³ | 1,044thof 2,247 | – |
| April 2024 | 478.4 µg/m³ | 1,248thof 2,520 | – |
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.
Koga's worst days
| Day | US AQI | Episode |
|---|---|---|
| 7 Jul 2025 | 9130.8 µg/m³ | Japan and South Korea, June and July 2025 |
| 15 Feb 2026 | 8728.5 µg/m³ | Japan, 14 to 15 February 2026 |
| 8 Jul 2025 | 8527.1 µg/m³ | Japan and South Korea, June and July 2025 |
| 9 Jul 2025 | 8326.2 µg/m³ | Japan and South Korea, June and July 2025 |
| 21 Dec 2025 | 7924.2 µg/m³ | – |
| 26 Mar 2025 | 7220.5 µg/m³ | – |
| 4 Nov 2023 | 7019.5 µg/m³ | – |
| 4 Feb 2024 | 6918.5 µg/m³ | – |
| 9 Jul 2024 | 6717.9 µg/m³ | – |
| 14 Feb 2026 | 6717.7 µg/m³ | Japan, 14 to 15 February 2026 |
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, Koga, 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/koga/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.
Koga 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).