SmogRank / Japan / Chiba / Yokoshiba
Yokoshiba, month by month
Yokoshiba has a measured daily mean on 976 days since 28 July 2023. Its worst month was December 2023, at 56 US AQI (11.6 µg/m³), 466th of 2,247 cities on that month's world ranking. Its cleanest was February 2025, at 28 US AQI (5.1 µg/m³).
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
6 months
| Month | Why |
|---|---|
| Oct 2024 | 14 of 31 days measured; a month needs 22. The others: 17 with under 18 hours of readings or readings that failed our checks. |
| Sep 2024 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Aug 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Jul 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Jun 2024 | 14 of 30 days measured; a month needs 21. The others: 16 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.
Yokoshiba's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| December 2023 | 5611.6 µg/m³ | 466thof 2,247 | – |
| August 2025 | 5511.3 µg/m³ | 936thof 2,901 | – |
| July 2025 | 529.7 µg/m³ | 1,338thof 2,889 | Japan and South Korea, June and July 2025 |
| November 2023 | 529.6 µg/m³ | 717thof 2,243 | – |
| November 2025 | 529.5 µg/m³ | 1,141stof 2,715 | – |
| December 2025 | 529.5 µg/m³ | 1,458thof 3,006 | – |
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.
Yokoshiba's worst days
| Day | US AQI | Episode |
|---|---|---|
| 7 Jul 2025 | 10637.6 µg/m³ | Japan and South Korea, June and July 2025 |
| 6 Jul 2025 | 10637.5 µg/m³ | Japan and South Korea, June and July 2025 |
| 8 Jul 2025 | 9130.8 µg/m³ | Japan and South Korea, June and July 2025 |
| 18 Jan 2024 | 8426.9 µg/m³ | – |
| 26 Mar 2025 | 8426.9 µg/m³ | Japan and South Korea, March 2025 |
| 18 Apr 2024 | 8125.0 µg/m³ | Japan and South Korea, April 2024 |
| 10 Dec 2023 | 8024.8 µg/m³ | – |
| 30 Aug 2025 | 7823.7 µg/m³ | – |
| 3 Nov 2023 | 7823.6 µg/m³ | – |
| 5 Dec 2023 | 7723.2 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, Yokoshiba, 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/yokoshiba/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.
Yokoshiba now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 20:07 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).