SmogRank / Portugal / Azores / Horta

Horta, month by month

Horta has a measured daily mean on 563 days since 17 January 2023. Its worst month was April 2023, at 54 US AQI (10.6 µg/m³), 367th of 1,622 cities on that month's world ranking. Its cleanest was July 2023, at 16 US AQI (2.9 µg/m³).

Every month since 2023

2026too few days for a mean (a year needs 199)83 days measured
Jan1 dayFebnoneMar20 daysApr13 daysMay10 daysJun13 daysJul4 daysAug9 daysSep10 daysOct3 days
2025too few days for a mean (a year needs 256)97 days measured
Jan5 daysFeb9 daysMar9 daysApr9 daysMay11 daysJun4 daysJul13 daysAug17 daysSep1 dayOct6 daysNov4 daysDec9 days
2024too few days for a mean (a year needs 257)110 days measured
Jan49#1,039Feb52#744Mar15 daysApr12 daysMaynoneJunnoneJulnoneAugnoneSepnoneOct5 daysNov12 daysDec14 days
202335 for the year273 days measured1,152nd of 1,355 in the world
Jan10 daysFeb2 daysMar11 daysApr54#367May17#1,575Jun31#1,370Jul16#1,400Aug17#1,970Sep34#1,761Oct53#303Nov20#2,165Dec17#2,204
Each square is a month's mean PM2.5 in US AQI from Horta'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 Horta marked; each year, the year's.
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

35 months
MonthWhy
Oct 20263 of 11 days measured; a month needs 8. The others: 2 with no readings from the monitor, 5 with readings for part of the day (a day needs 18 hours), 1 with under 18 hours of readings or readings that failed our checks.
Sep 202610 of 30 days measured; a month needs 21. The others: 20 with readings for part of the day (a day needs 18 hours).
Aug 20269 of 31 days measured; a month needs 22. The others: 22 with readings for part of the day (a day needs 18 hours).
Jul 20264 of 31 days measured; a month needs 22. The others: 27 with readings for part of the day (a day needs 18 hours).
Jun 202613 of 30 days measured; a month needs 21. The others: 17 with readings for part of the day (a day needs 18 hours).
May 202610 of 31 days measured; a month needs 22. The others: 21 with readings for part of the day (a day needs 18 hours).
Apr 202613 of 30 days measured; a month needs 21. The others: 17 with readings for part of the day (a day needs 18 hours).
Mar 202620 of 31 days measured; a month needs 22. The others: 1 with no readings from the monitor, 10 with readings for part of the day (a day needs 18 hours).
Feb 2026No day measured. The others: 20 with no readings from the monitor, 8 with readings for part of the day (a day needs 18 hours).
Jan 20261 of 31 days measured; a month needs 22. The others: 19 with no readings from the monitor, 11 with readings for part of the day (a day needs 18 hours).
Dec 20259 of 31 days measured; a month needs 22. The others: 22 with readings for part of the day (a day needs 18 hours).
Nov 20254 of 30 days measured; a month needs 21. The others: 4 with no readings from the monitor, 22 with readings for part of the day (a day needs 18 hours).
Oct 20256 of 31 days measured; a month needs 22. The others: 25 with readings for part of the day (a day needs 18 hours).
Sep 20251 of 30 days measured; a month needs 21. The others: 29 with readings for part of the day (a day needs 18 hours).
Aug 202517 of 31 days measured; a month needs 22. The others: 14 with readings for part of the day (a day needs 18 hours).
Jul 202513 of 31 days measured; a month needs 22. The others: 18 with readings for part of the day (a day needs 18 hours).
Jun 20254 of 30 days measured; a month needs 21. The others: 26 with readings for part of the day (a day needs 18 hours).
May 202511 of 31 days measured; a month needs 22. The others: 1 with no readings from the monitor, 19 with readings for part of the day (a day needs 18 hours).
Apr 20259 of 30 days measured; a month needs 21. The others: 21 with readings for part of the day (a day needs 18 hours).
Mar 20259 of 31 days measured; a month needs 22. The others: 22 with readings for part of the day (a day needs 18 hours).
Feb 20259 of 28 days measured; a month needs 20. The others: 19 with readings for part of the day (a day needs 18 hours).
Jan 20255 of 31 days measured; a month needs 22. The others: 26 with readings for part of the day (a day needs 18 hours).
Dec 202414 of 31 days measured; a month needs 22. The others: 17 with readings for part of the day (a day needs 18 hours).
Nov 202412 of 30 days measured; a month needs 21. The others: 18 with readings for part of the day (a day needs 18 hours).
Oct 20245 of 31 days measured; a month needs 22. The others: 24 with readings for part of the day (a day needs 18 hours), 2 with readings left out by our checks.
Sep 2024No day measured. The others: 15 with no readings from the monitor, 15 with readings for part of the day (a day needs 18 hours).
Aug 2024No day measured. The others: 31 with no readings from the monitor.
Jul 2024No day measured. The others: 31 with no readings from the monitor.
Jun 2024No day measured. The others: 30 with no readings from the monitor.
May 2024No day measured. The others: 31 with no readings from the monitor.
Apr 202412 of 30 days measured; a month needs 21. The others: 14 with no readings from the monitor, 4 with readings for part of the day (a day needs 18 hours).
Mar 202415 of 31 days measured; a month needs 22. The others: 10 with no readings from the monitor, 6 with readings for part of the day (a day needs 18 hours).
Mar 202311 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive.
Feb 20232 of 28 days measured; a month needs 20. The others: 1 with readings for part of the day (a day needs 18 hours), 25 missing from OpenAQ's archive.
Jan 202310 of 31 days measured; a month needs 22. The others: 4 with readings for part of the day (a day needs 18 hours), 1 missing from OpenAQ's archive.

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

Horta's worst months

MonthUS AQIDays measuredWorld rank
April 2023 5410.6 µg/m³25 of 30367thof 1,622
October 2023 5310.4 µg/m³29 of 31303rdof 2,012
February 2024 529.5 µg/m³21 of 29744thof 2,486
January 2024 498.9 µg/m³31 of 311,039thof 2,385
September 2023 346.1 µg/m³30 of 301,761stof 2,176
June 2023 315.5 µg/m³30 of 301,370thof 1,603

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.

Horta's worst days

DayUS AQI
18 Jan 2023 11440.6 µg/m³
18 Feb 2024 9633.3 µg/m³
29 Jan 2023 9231.2 µg/m³
22 Jan 2024 9130.8 µg/m³
21 Jan 2023 9130.7 µg/m³
15 Oct 2023 9130.5 µg/m³
17 Jan 2023 9029.9 µg/m³
18 Jan 2024 8426.9 µg/m³
18 Oct 2023 7622.4 µg/m³
23 Jan 2023 7522.1 µg/m³

Daily means, the highest since 17 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, Horta, Portugal, 17 Jan 2023 – 11 Oct 2026. Monitor data from EEA, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/pt/horta/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.

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

Updated 2026-10-12 19:07 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).