SmogRank / The Netherlands / Limburg / Heerlen
Heerlen, month by month
Heerlen has a measured daily mean on 1,133 days since 1 January 2023. Its worst month was February 2025, at 62 US AQI (15.0 µg/m³), 863rd of 2,633 cities on that month's world ranking. Its cleanest was September 2025, at 19 US AQI (3.5 µg/m³). 2025 averaged 40 US AQI (7.2 µg/m³), against 39 US AQI (7.0 µg/m³) in 2024.
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
8 months
| Month | Why |
|---|---|
| Dec 2023 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Nov 2023 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Oct 2023 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Sep 2023 | 4 of 30 days measured; a month needs 21. The others: 26 with under 18 hours of readings or readings that failed our checks. |
| Aug 2023 | 5 of 31 days measured; a month needs 22. The others: 26 with under 18 hours of readings or readings that failed our checks. |
| Jul 2023 | 7 of 31 days measured; a month needs 22. The others: 24 with under 18 hours of readings or readings that failed our checks. |
| Jun 2023 | 18 of 30 days measured; a month needs 21. The others: 12 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. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Heerlen's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| February 2025 | 6215.0 µg/m³ | 863rdof 2,633 | Europe, 14 February to 1 March 2025 Europe, 1 to 14 February 2025 |
| February 2023 | 5812.7 µg/m³ | 498thof 1,129 | Europe, 28 February to 4 March 2023 Europe, 6 to 25 February 2023 |
| March 2025 | 5712.5 µg/m³ | 1,156thof 2,862 | Europe, March 2025 Europe, 14 February to 1 March 2025 |
| January 2026 | 5611.8 µg/m³ | 937thof 2,617 | Europe, January and February 2026 |
| March 2026 | 5511.1 µg/m³ | 1,401stof 2,971 | Europe, 18 to 25 March 2026 Europe, 1 to 12 March 2026 |
| January 2024 | 5310.4 µg/m³ | 839thof 2,385 | Europe, 8 to 27 January 2024 |
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.
Heerlen's worst days
| Day | US AQI | Episode |
|---|---|---|
| 26 Jan 2026 | 11942.7 µg/m³ | Europe, January and February 2026 |
| 10 Feb 2025 | 11541.2 µg/m³ | Europe, 1 to 14 February 2025 |
| 3 Mar 2023 | 11541.1 µg/m³ | Europe, 28 February to 4 March 2023 |
| 13 Feb 2025 | 11340.5 µg/m³ | Europe, 1 to 14 February 2025 |
| 14 Feb 2025 | 10637.5 µg/m³ | Europe, 14 February to 1 March 2025 Europe, 1 to 14 February 2025 |
| 25 Mar 2025 | 10537.1 µg/m³ | Europe, March 2025 |
| 25 Jan 2026 | 10436.7 µg/m³ | Europe, January and February 2026 |
| 11 Jan 2024 | 9733.9 µg/m³ | Europe, 8 to 27 January 2024 |
| 12 Feb 2023 | 9231.0 µg/m³ | Europe, 6 to 25 February 2023 |
| 8 Mar 2026 | 9231.0 µg/m³ | Europe, 1 to 12 March 2026 |
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, Heerlen, The Netherlands, 1 Jan 2023 – 11 Oct 2026. Monitor data from RIVM Luchtmeetnet and EEA, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/nl/heerlen/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.
Heerlen 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).