SmogRank / United Kingdom / Northern Ireland / Belfast
Belfast, month by month
Belfast has a measured daily mean on 808 days since 1 January 2023. Its worst month was April 2025, at 53 US AQI (10.0 µg/m³), 1,174th of 2,951 cities on that month's world ranking. Its cleanest was September 2025, at 25 US AQI (4.5 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
22 months
| Month | Why |
|---|---|
| Sep 2026 | 1 of 30 days measured; a month needs 21. The others: 29 with under 18 hours of readings or readings that failed our checks. |
| Aug 2026 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Jul 2026 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Jun 2026 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| May 2026 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Apr 2026 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Nov 2025 | 12 of 30 days measured; a month needs 21. The others: 18 with under 18 hours of readings or readings that failed our checks. |
| Mar 2025 | 2 of 31 days measured; a month needs 22. The others: 29 with under 18 hours of readings or readings that failed our checks. |
| Feb 2025 | No day measured. The others: 28 with under 18 hours of readings or readings that failed our checks. |
| Jan 2025 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Dec 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Nov 2024 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Apr 2024 | 18 of 30 days measured; a month needs 21. The others: 12 with under 18 hours of readings or readings that failed our checks. |
| Mar 2024 | 19 of 31 days measured; a month needs 22. The others: 12 with under 18 hours of readings or readings that failed our checks. |
| Oct 2023 | 16 of 31 days measured; a month needs 22. The others: 15 with under 18 hours of readings or readings that failed our checks. |
| Aug 2023 | 15 of 31 days measured; a month needs 22. The others: 16 with under 18 hours of readings or readings that failed our checks. |
| Jul 2023 | 18 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 12 with under 18 hours of readings or readings that failed our checks. |
| Jun 2023 | 17 of 30 days measured; a month needs 21. The others: 13 with under 18 hours of readings or readings that failed our checks. |
| May 2023 | 18 of 31 days measured; a month needs 22. The others: 13 with under 18 hours of readings or readings that failed our checks. |
| Apr 2023 | 20 of 30 days measured; a month needs 21. The others: 2 missing from OpenAQ's archive, 8 with under 18 hours of readings or readings that failed our checks. |
| Mar 2023 | 9 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive, 2 with under 18 hours of readings or readings that failed our checks. |
| Feb 2023 | 3 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Belfast's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| April 2025 | 5310.0 µg/m³ | 1,174thof 2,951 | – |
| May 2024 | 529.4 µg/m³ | 877thof 2,684 | – |
| March 2026 | 488.6 µg/m³ | 1,980thof 2,971 | Europe, 18 to 25 March 2026 |
| January 2024 | 478.5 µg/m³ | 1,116thof 2,385 | – |
| September 2024 | 478.5 µg/m³ | 704thof 2,010 | – |
| December 2025 | 478.4 µg/m³ | 1,734thof 3,006 | – |
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.
Belfast's worst days
| Day | US AQI | Episode |
|---|---|---|
| 8 Jan 2024 | 10436.9 µg/m³ | – |
| 21 Mar 2026 | 8929.6 µg/m³ | Europe, 18 to 25 March 2026 |
| 8 Sept 2023 | 8326.4 µg/m³ | United Kingdom, Belgium and 2 more countries, September 2023 |
| 9 Jun 2025 | 7924.1 µg/m³ | – |
| 9 Sept 2023 | 7823.4 µg/m³ | United Kingdom, Belgium and 2 more countries, September 2023 |
| 14 Feb 2023 | 7723.0 µg/m³ | – |
| 31 Dec 2025 | 7522.1 µg/m³ | – |
| 29 Apr 2023 | 7321.0 µg/m³ | – |
| 2 Dec 2023 | 7320.8 µg/m³ | – |
| 24 Jul 2025 | 7320.8 µg/m³ | – |
Daily means, the highest since 1 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, Belfast, United Kingdom, 1 Jan 2023 – 11 Oct 2026. Monitor data from UK-AIR (Defra), read from the publisher; sources listed at smogrank.com/sources. smogrank.com/gb/belfast/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.
Belfast now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 20:07 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).