SmogRank / Japan / Tochigi / Oyama
Oyama, month by month
Oyama has a measured daily mean on 1,153 days since 28 July 2023. Its worst month was July 2024, at 61 US AQI (14.6 µg/m³), 196th of 2,566 cities on that month's world ranking. Its cleanest was September 2026, at 30 US AQI (5.4 µg/m³). 2025 averaged 54 US AQI (10.7 µg/m³), against 53 US AQI (10.0 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
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.
Oyama's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| July 2024 | 6114.6 µg/m³ | 196thof 2,566 | – |
| July 2025 | 5913.6 µg/m³ | 542ndof 2,889 | Japan and South Korea, June and July 2025 |
| August 2025 | 5913.2 µg/m³ | 542ndof 2,901 | Japan, 4 to 5 August 2025 |
| December 2025 | 5812.8 µg/m³ | 881stof 3,006 | Japan, December 2025 |
| April 2024 | 5712.4 µg/m³ | 671stof 2,520 | Japan and South Korea, April 2024 |
| December 2023 | 5712.2 µg/m³ | 420thof 2,247 | – |
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.
Oyama's worst days
| Day | US AQI | Episode |
|---|---|---|
| 7 Jul 2025 | 12143.6 µg/m³ | Japan and South Korea, June and July 2025 |
| 9 Jul 2025 | 11340.4 µg/m³ | Japan and South Korea, June and July 2025 |
| 8 Jul 2025 | 10838.4 µg/m³ | Japan and South Korea, June and July 2025 |
| 21 Dec 2025 | 10135.7 µg/m³ | Japan, December 2025 |
| 5 Aug 2025 | 9331.9 µg/m³ | Japan, 4 to 5 August 2025 |
| 15 Feb 2026 | 9030.3 µg/m³ | Japan, 14 to 15 February 2026 |
| 18 Apr 2024 | 9030.0 µg/m³ | Japan and South Korea, April 2024 |
| 4 Nov 2023 | 9029.9 µg/m³ | Japan, November 2023 |
| 20 Dec 2025 | 8728.5 µg/m³ | Japan, December 2025 |
| 18 Jun 2025 | 8628.0 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, Oyama, 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/oyama/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.
Oyama 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).