SmogRank / Japan / Okayama / Sōja
Sōja, month by month
Sōja has a measured daily mean on 1,143 days since 28 July 2023. Its worst month was July 2025, at 62 US AQI (15.1 µg/m³), 398th of 2,889 cities on that month's world ranking. Its cleanest was September 2026, at 36 US AQI (6.5 µg/m³). 2025 averaged 55 US AQI (11.4 µg/m³), against 53 US AQI (10.1 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 |
|---|---|
| Jan 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 | 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.
Sōja's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| July 2025 | 6215.1 µg/m³ | 398thof 2,889 | Japan and South Korea, June and July 2025 |
| June 2025 | 6214.9 µg/m³ | 452ndof 2,508 | Japan and South Korea, June and July 2025 Japan, June 2025 |
| April 2024 | 6114.2 µg/m³ | 468thof 2,520 | Japan and South Korea, April 2024 |
| November 2023 | 6013.9 µg/m³ | 184thof 2,243 | Okayama, Fukuoka and Hiroshima, Japan, November 2023 Japan, November 2023 |
| March 2025 | 5913.5 µg/m³ | 1,069thof 2,862 | Japan and South Korea, March 2025 Japan, March 2025and 1 more |
| April 2025 | 5913.2 µg/m³ | 643rdof 2,951 | Japan and South Korea, April 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.
Sōja's worst days
| Day | US AQI | Episode |
|---|---|---|
| 4 Jul 2025 | 14854.4 µg/m³ | Japan and South Korea, June and July 2025 |
| 1 Mar 2025 | 12746.2 µg/m³ | Japan and South Korea, February and March 2025 |
| 18 Apr 2024 | 12344.5 µg/m³ | Japan and South Korea, April 2024 |
| 2 Mar 2025 | 12244.2 µg/m³ | Japan and South Korea, February and March 2025 |
| 3 Jul 2025 | 10738.1 µg/m³ | Japan and South Korea, June and July 2025 |
| 3 Nov 2023 | 10336.4 µg/m³ | Japan, November 2023 |
| 4 Nov 2023 | 10336.2 µg/m³ | Japan, November 2023 |
| 5 Jul 2025 | 10035.4 µg/m³ | Japan and South Korea, June and July 2025 |
| 2 Jul 2025 | 10035.2 µg/m³ | Japan and South Korea, June and July 2025 |
| 9 Jul 2025 | 9331.6 µg/m³ | Japan and South Korea, June and July 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, Sōja, 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/soja/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.
Sōja 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).