SmogRank / United States / Hawaii / Hilo

Hilo, month by month

Hilo has a measured daily mean on 1,312 days since 3 January 2023. Its worst month was February 2026, at 25 US AQI (4.5 µg/m³), 2,658th of 2,866 cities on that month's world ranking. Its cleanest was December 2023, at 14 US AQI (2.5 µg/m³). 2025 averaged 19 US AQI (3.5 µg/m³), against 17 US AQI (3.1 µg/m³) in 2024.

Every month since 2023

202620 so far272 days measured2,768th of 2,791 in the world

Jan22#2,493 Feb25#2,658 Mar20#2,860 Apr22#2,738 May19#2,760 Jun16#2,438 Jul17#2,752 Aug19#2,872 Sep19#2,867 Oct22#2,509

202519 for the year348 days measured2,664th of 2,681 in the world

Jan22#2,382 Feb18#2,588 Mar17#2,788 Apr19#2,874 May19#2,692 Jun18#2,472 Jul17#2,849 Aug21#2,824 Sep20#3,000 Oct18#2,541 Nov21#2,603 Dec23#2,831

202417 for the year352 days measured2,086th of 2,097 in the world

Jan22#2,254 Feb18#2,410 Mar19#1,560 Apr20#2,313 May18#2,555 Jun19#2,442 Jul16#2,533 Aug16#2,004 Sep16#1,991 Oct15#2,004 Nov14#2,590 Dec16#2,566

202318 for the year340 days measured1,346th of 1,355 in the world

Jan19#1,213 Feb15#1,121 Mar22#859Apr19 daysMay19#1,558 Jun18#1,546 Jul17#1,396 Aug22#1,917 Sep20#2,124 Oct15#1,992 Nov18#2,186 Dec14#2,225

Each square is a month's mean PM2.5 in US AQI from Hilo'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 Hilo 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

Month	Why
Apr 2023	19 of 30 days measured; a month needs 21. The others: 11 with under 18 hours of readings or readings that failed our checks.

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

Hilo's worst months

Month	US AQI	Days measured	World rank
February 2026	254.5 µg/m³	28 of 28	2,658thof 2,866
December 2025	234.2 µg/m³	31 of 31	2,831stof 3,006
August 2023	224.0 µg/m³	31 of 31	1,917thof 1,980
January 2026	224.0 µg/m³	27 of 31	2,493rdof 2,617
March 2023	223.9 µg/m³	27 of 31	859thof 911
January 2024	223.9 µg/m³	29 of 31	2,254thof 2,385

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.

Hilo's worst days

Day	US AQI
9 Nov 2025	5611.7 µg/m³
8 Aug 2023	5310.1 µg/m³
8 Oct 2026	529.5 µg/m³
2 Feb 2026	519.3 µg/m³
12 Dec 2025	519.2 µg/m³
5 Jan 2025	509.0 µg/m³
13 Dec 2025	509.0 µg/m³
5 Feb 2026	509.0 µg/m³
7 Aug 2023	498.9 µg/m³
3 Feb 2026	498.9 µg/m³

Daily means, the highest since 3 Jan 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, Hilo, United States, 3 Jan 2023 – 10 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/hilo/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.

Hilo now: the last 24 hours, its ranks today and the last 12 months day by day.

Updated 2026-10-12 17:07 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).