SmogRank / Japan / Ibaraki / Shimo-tsuma
Shimo-tsuma, month by month
Shimo-tsuma has a measured daily mean on 1,053 days since 28 July 2023. Its worst month was December 2025, at 61 US AQI (14.5 µg/m³), 761st of 3,006 cities on that month's world ranking. Its cleanest was September 2026, at 38 US AQI (6.9 µg/m³). 2025 averaged 54 US AQI (10.8 µg/m³), against 52 US AQI (9.7 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
3 months
| Month | Why |
|---|---|
| Jan 2026 | 19 of 31 days measured; a month needs 22. The others: 12 with under 18 hours of readings or readings that failed our checks. |
| Feb 2025 | 17 of 28 days measured; a month needs 20. The others: 11 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.
Shimo-tsuma's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| December 2025 | 6114.5 µg/m³ | 761stof 3,006 | Japan, December 2025 |
| February 2026 | 6114.2 µg/m³ | 836thof 2,866 | Japan, 14 to 15 February 2026 |
| December 2023 | 6013.8 µg/m³ | 323rdof 2,247 | Japan, 9 to 10 December 2023 |
| November 2023 | 5913.6 µg/m³ | 197thof 2,243 | Japan, November 2023 |
| November 2025 | 5913.3 µg/m³ | 662ndof 2,715 | – |
| July 2024 | 5913.2 µg/m³ | 283rdof 2,566 | – |
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.
Shimo-tsuma's worst days
| Day | US AQI | Episode |
|---|---|---|
| 7 Jul 2025 | 12545.4 µg/m³ | Japan and South Korea, June and July 2025 |
| 9 Jul 2025 | 11541.3 µg/m³ | Japan and South Korea, June and July 2025 |
| 21 Dec 2025 | 11239.9 µg/m³ | Japan, December 2025 |
| 8 Jul 2025 | 10938.9 µg/m³ | Japan and South Korea, June and July 2025 |
| 20 Dec 2025 | 10236.1 µg/m³ | Japan, December 2025 |
| 4 Nov 2023 | 9834.4 µg/m³ | Japan, November 2023 |
| 15 Feb 2026 | 9733.9 µg/m³ | Japan, 14 to 15 February 2026 |
| 23 Nov 2023 | 9030.3 µg/m³ | – |
| 25 Nov 2025 | 9030.0 µg/m³ | – |
| 6 Jul 2025 | 9029.8 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, Shimo-tsuma, 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/shimo-tsuma/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.
Shimo-tsuma now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 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).