SmogRank / Portugal / Santarém / Riachos

Riachos, month by month

Riachos has a measured daily mean on 273 days since 6 May 2023. Its worst month was February 2024, at 42 US AQI (7.6 µg/m³), 1,259th of 2,486 cities on that month's world ranking. Its cleanest was September 2023, at 14 US AQI (2.5 µg/m³).

Every month since 2023

2026too few days for a mean (a year needs 199)9 days measured
Jan4 daysFeb1 dayMarnoneAprnoneMaynoneJunnoneJulnoneAugnoneSep4 daysOctnone
2025too few days for a mean (a year needs 256)1 day measured
JannoneFebnoneMarnoneAprnoneMaynoneJunnoneJulnoneAug1 daySepnoneOctnoneNovnoneDecnone
2024too few days for a mean (a year needs 257)65 days measured
Jan29#2,003Feb42#1,259Mar5 daysApr2 daysMay1 dayJun1 dayJulnoneAugnoneSepnoneOctnoneNovnoneDecnone
2023too few days for a mean (a year needs 256)198 days measured
JanFebMarAprMay28#1,430Jun31#1,370Jul20#1,364Aug21 daysSep14#2,167Oct29#1,721Nov21#2,154Dec31#1,936
Each square is a month's mean PM2.5 in US AQI from Riachos'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 Riachos 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

33 months
MonthWhy
Oct 2026No day measured. The others: 8 with no readings from the monitor, 2 with readings left out by our checks, 1 with under 18 hours of readings or readings that failed our checks.
Sep 20264 of 30 days measured; a month needs 21. The others: 26 with readings left out by our checks.
Aug 2026No day measured. The others: 3 with readings for part of the day (a day needs 18 hours), 28 with readings left out by our checks.
Jul 2026No day measured. The others: 3 with readings for part of the day (a day needs 18 hours), 28 with readings left out by our checks.
Jun 2026No day measured. The others: 7 with readings for part of the day (a day needs 18 hours), 23 with readings left out by our checks.
May 2026No day measured. The others: 1 with readings for part of the day (a day needs 18 hours), 30 with readings left out by our checks.
Apr 2026No day measured. The others: 30 with readings left out by our checks.
Mar 2026No day measured. The others: 31 with readings left out by our checks.
Feb 20261 of 28 days measured; a month needs 20. The others: 3 with readings for part of the day (a day needs 18 hours), 24 with readings left out by our checks.
Jan 20264 of 31 days measured; a month needs 22. The others: 8 with readings for part of the day (a day needs 18 hours), 19 with readings left out by our checks.
Dec 2025No day measured. The others: 2 with readings for part of the day (a day needs 18 hours), 29 with readings left out by our checks.
Nov 2025No day measured. The others: 1 with no readings from the monitor, 5 with readings for part of the day (a day needs 18 hours), 24 with readings left out by our checks.
Oct 2025No day measured. The others: 10 with readings for part of the day (a day needs 18 hours), 21 with readings left out by our checks.
Sep 2025No day measured. The others: 2 with readings for part of the day (a day needs 18 hours), 28 with readings left out by our checks.
Aug 20251 of 31 days measured; a month needs 22. The others: 30 with readings left out by our checks.
Jul 2025No day measured. The others: 31 with readings left out by our checks.
Jun 2025No day measured. The others: 9 with readings for part of the day (a day needs 18 hours), 21 with readings left out by our checks.
May 2025No day measured. The others: 1 with no readings from the monitor, 8 with readings for part of the day (a day needs 18 hours), 22 with readings left out by our checks.
Apr 2025No day measured. The others: 1 with no readings from the monitor, 6 with readings for part of the day (a day needs 18 hours), 23 with readings left out by our checks.
Mar 2025No day measured. The others: 7 with readings for part of the day (a day needs 18 hours), 24 with readings left out by our checks.
Feb 2025No day measured. The others: 5 with readings for part of the day (a day needs 18 hours), 23 with readings left out by our checks.
Jan 2025No day measured. The others: 2 with readings for part of the day (a day needs 18 hours), 29 with readings left out by our checks.
Dec 2024No day measured. The others: 4 with readings for part of the day (a day needs 18 hours), 27 with readings left out by our checks.
Nov 2024No day measured. The others: 3 with readings for part of the day (a day needs 18 hours), 27 with readings left out by our checks.
Oct 2024No day measured. The others: 16 with readings for part of the day (a day needs 18 hours), 15 with readings left out by our checks.
Sep 2024No day measured. The others: 30 with readings for part of the day (a day needs 18 hours).
Aug 2024No day measured. The others: 3 with no readings from the monitor, 13 with readings for part of the day (a day needs 18 hours), 15 with readings left out by our checks.
Jul 2024No day measured. The others: 1 with readings for part of the day (a day needs 18 hours), 30 with readings left out by our checks.
Jun 20241 of 30 days measured; a month needs 21. The others: 1 with readings for part of the day (a day needs 18 hours), 28 with readings left out by our checks.
May 20241 of 31 days measured; a month needs 22. The others: 1 with readings for part of the day (a day needs 18 hours), 29 with readings left out by our checks.
Apr 20242 of 30 days measured; a month needs 21. The others: 2 with readings for part of the day (a day needs 18 hours), 26 with readings left out by our checks.
Mar 20245 of 31 days measured; a month needs 22. The others: 15 with no readings from the monitor, 6 with readings for part of the day (a day needs 18 hours), 5 with readings left out by our checks.
Aug 202321 of 31 days measured; a month needs 22. The others: 1 with no readings from the monitor, 9 with readings for part of the day (a day needs 18 hours).

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

Riachos's worst months

MonthUS AQIDays measuredWorld rank
February 2024 427.6 µg/m³25 of 291,259thof 2,486
June 2023 315.5 µg/m³22 of 301,370thof 1,603
December 2023 315.5 µg/m³31 of 311,936thof 2,247
January 2024 295.3 µg/m³31 of 312,003rdof 2,385
October 2023 295.2 µg/m³25 of 311,721stof 2,012
May 2023 285.0 µg/m³23 of 311,430thof 1,600

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.

Riachos's worst days

DayUS AQI
6 Aug 2023 7521.8 µg/m³
24 Aug 2023 7421.5 µg/m³
6 Feb 2024 7321.0 µg/m³
5 Feb 2024 7119.9 µg/m³
6 Aug 2025 7119.9 µg/m³
2 Feb 2024 6818.2 µg/m³
19 May 2023 6818.1 µg/m³
30 Dec 2023 6617.2 µg/m³
4 Feb 2024 6315.8 µg/m³
25 Nov 2023 6214.8 µg/m³

Daily means, the highest since 6 May 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, Riachos, Portugal, 6 May 2023 – 25 Sep 2026. Monitor data from EEA, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/pt/riachos/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.

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

Updated 2026-10-12 21:07 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).