SmogRank / Japan / Oita / Hiji

Hiji, month by month

Hiji has a measured daily mean on 224 days since 28 February 2026. Its worst month was March 2026, at 56 US AQI (11.8 µg/m³), 1,252nd of 2,971 cities on that month's world ranking. Its cleanest was September 2026, at 34 US AQI (6.1 µg/m³).

Every month since 2026

202649 so far224 days measured1,425th of 2,791 in the world
JanFeb1 dayMar56#1,252Apr53#931May52#860Jun38#1,514Jul55#1,114Aug40#1,998Sep34#1,709Oct43#1,250
Each square is a month's mean PM2.5 in US AQI from Hiji's measured days, with its place on that month's world ranking under it. A month has a mean once 70% of its days are measured, the rule the monthly rankings use; under that, the square gives the days measured. Each square opens that month's ranking with Hiji marked; each year, the year's. A dashed square is the running month, so far.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

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
MonthWhy
Feb 20261 of 28 days measured; a month needs 20.

A day counts once 18 hours of it are measured; a month needs 70% of its days.

Hiji's worst months

MonthUS AQIDays measuredWorld rankEpisode
March 2026 5611.8 µg/m³31 of 311,252ndof 2,971Japan and South Korea, March 2026
July 2026 5511.0 µg/m³31 of 311,114thof 2,784–
April 2026 5310.1 µg/m³27 of 30931stof 2,941–
May 2026 529.6 µg/m³31 of 31860thof 2,874–
August 2026 407.2 µg/m³31 of 311,998thof 2,896–
June 2026 386.9 µg/m³30 of 301,514thof 2,497–

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.

Hiji's worst days

DayUS AQIEpisode
29 Mar 2026 9633.1 µg/m³Japan and South Korea, March 2026
28 Mar 2026 8627.8 µg/m³Japan and South Korea, March 2026
21 Jul 2026 7924.3 µg/m³–
22 Jul 2026 7521.9 µg/m³–
18 Jul 2026 7421.5 µg/m³–
19 Jul 2026 7421.5 µg/m³–
30 Mar 2026 7019.3 µg/m³Japan and South Korea, March 2026
17 May 2026 6918.8 µg/m³–
22 Mar 2026 6918.7 µg/m³–
3 May 2026 6717.8 µg/m³–

Daily means, the highest since 28 Feb 2026; 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, Hiji, Japan, 28 Feb 2026 – 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/hiji/history (accessed 12 Oct 2026).

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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.

Hiji 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).