SmogRank / Japan / Saitama / Niiza
Niiza, month by month
Niiza has a measured daily mean on 1,163 days since 28 July 2023. Its worst month was April 2024, at 60 US AQI (13.8 µg/m³), 504th of 2,520 cities on that month's world ranking. Its cleanest was January 2026, at 36 US AQI (6.5 µg/m³). 2025 averaged 53 US AQI (10.4 µg/m³), against 52 US AQI (9.4 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.
Niiza's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| April 2024 | 6013.8 µg/m³ | 504thof 2,520 | Japan and South Korea, April 2024 |
| August 2025 | 5913.2 µg/m³ | 542ndof 2,901 | Japan, 4 to 5 August 2025 |
| July 2025 | 5813.1 µg/m³ | 623rdof 2,889 | Japan and South Korea, June and July 2025 |
| July 2024 | 5712.4 µg/m³ | 377thof 2,566 | – |
| March 2025 | 5611.9 µg/m³ | 1,252ndof 2,862 | Japan and South Korea, March 2025 |
| November 2023 | 5611.6 µg/m³ | 347thof 2,243 | Japan, November 2023 |
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.
Niiza's worst days
| Day | US AQI | Episode |
|---|---|---|
| 7 Jul 2025 | 11440.8 µg/m³ | Japan and South Korea, June and July 2025 |
| 8 Jul 2025 | 11239.9 µg/m³ | Japan and South Korea, June and July 2025 |
| 9 Jul 2025 | 10637.7 µg/m³ | Japan and South Korea, June and July 2025 |
| 26 Mar 2025 | 9532.6 µg/m³ | Japan and South Korea, March 2025 |
| 4 Nov 2023 | 9331.4 µg/m³ | Japan, November 2023 |
| 18 Apr 2024 | 9130.5 µg/m³ | Japan and South Korea, April 2024 |
| 25 Mar 2025 | 8828.8 µg/m³ | Japan and South Korea, March 2025 |
| 19 Apr 2024 | 8828.7 µg/m³ | Japan and South Korea, April 2024 |
| 5 Aug 2025 | 8426.7 µg/m³ | Japan, 4 to 5 August 2025 |
| 20 Apr 2024 | 8226.0 µg/m³ | Japan and South Korea, April 2024 |
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, Niiza, 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/niiza/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.
Niiza 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).