SmogRank / Spain / Basque Country / Zalla
Zalla, month by month
Zalla has a measured daily mean on 844 days since 14 February 2023. Its worst month was August 2025, at 54 US AQI (10.9 µg/m³), 1,027th of 2,901 cities on that month's world ranking. Its cleanest was November 2023, at 29 US AQI (5.3 µg/m³).
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
19 months
| Month | Why |
|---|---|
| Oct 2026 | 6 of 12 days measured; a month needs 9. The others: 1 with no readings from the monitor, 4 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. |
| Jul 2026 | 17 of 31 days measured; a month needs 22. The others: 14 with readings for part of the day (a day needs 18 hours). |
| Jun 2026 | 7 of 30 days measured; a month needs 21. The others: 23 with readings for part of the day (a day needs 18 hours). |
| May 2026 | 2 of 31 days measured; a month needs 22. The others: 10 with no readings from the monitor, 19 with readings for part of the day (a day needs 18 hours). |
| Apr 2026 | No day measured. The others: 25 with no readings from the monitor, 5 with readings for part of the day (a day needs 18 hours). |
| Mar 2026 | No day measured. The others: 31 with no readings from the monitor. |
| Feb 2026 | 3 of 28 days measured; a month needs 20. The others: 19 with no readings from the monitor, 6 with readings for part of the day (a day needs 18 hours). |
| Jan 2026 | 12 of 31 days measured; a month needs 22. The others: 19 with readings for part of the day (a day needs 18 hours). |
| Oct 2025 | 18 of 31 days measured; a month needs 22. The others: 13 with readings for part of the day (a day needs 18 hours). |
| Jun 2025 | 18 of 30 days measured; a month needs 21. The others: 12 with readings for part of the day (a day needs 18 hours). |
| Oct 2024 | 11 of 31 days measured; a month needs 22. The others: 20 with readings for part of the day (a day needs 18 hours). |
| Sep 2024 | No day measured. The others: 30 with readings for part of the day (a day needs 18 hours). |
| Aug 2024 | 7 of 31 days measured; a month needs 22. The others: 1 with no readings from the monitor, 23 with readings for part of the day (a day needs 18 hours). |
| Jul 2024 | 13 of 31 days measured; a month needs 22. The others: 18 with readings for part of the day (a day needs 18 hours). |
| Jun 2024 | 13 of 30 days measured; a month needs 21. The others: 17 with readings for part of the day (a day needs 18 hours). |
| Mar 2024 | 15 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). |
| Aug 2023 | 20 of 31 days measured; a month needs 22. The others: 3 with no readings from the monitor, 8 with readings for part of the day (a day needs 18 hours). |
| Mar 2023 | 11 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive. |
| Feb 2023 | 2 of 28 days measured; a month needs 20. The others: 13 missing from OpenAQ's archive. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Zalla's worst months
| Month | US AQI | World rank |
|---|---|---|
| August 2025 | 5410.9 µg/m³ | 1,027thof 2,901 |
| August 2026 | 5410.6 µg/m³ | 774thof 2,896 |
| January 2024 | 5410.5 µg/m³ | 831stof 2,385 |
| June 2023 | 5310.1 µg/m³ | 776thof 1,603 |
| December 2025 | 529.7 µg/m³ | 1,404thof 3,006 |
| September 2026 | 529.6 µg/m³ | 699thof 2,981 |
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.
Zalla's worst days
| Day | US AQI | Episode |
|---|---|---|
| 6 Feb 2024 | 8527.2 µg/m³ | Southern Europe, February 2024 |
| 8 Jul 2026 | 8527.1 µg/m³ | – |
| 31 May 2026 | 8225.6 µg/m³ | – |
| 10 Jun 2025 | 8125.0 µg/m³ | Basque Country and Castille and León, Spain, June 2025 |
| 23 Jun 2026 | 8024.7 µg/m³ | – |
| 1 Jul 2025 | 7924.2 µg/m³ | – |
| 25 Jun 2026 | 7723.1 µg/m³ | – |
| 10 Jul 2026 | 7522.2 µg/m³ | – |
| 24 Jun 2026 | 7421.3 µg/m³ | – |
| 20 Jun 2026 | 7421.2 µg/m³ | – |
Daily means, the highest since 14 Feb 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, Zalla, Spain, 14 Feb 2023 – 9 Oct 2026. Monitor data from EEA, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/es/zalla/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.
Zalla 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).