Air quality
Air quality in Leiden today
Updated
Good (US AQI 34) Air quality is satisfactory and poses little or no risk; a good time for outdoor activity. Model estimate for Mon, Oct 26, 3:00 am (02:00 UTC).
Live AQI, PM2.5, PM10 and ozone for Leiden, South Holland, The Netherlands, with a 48-hour forecast and the best time to be outside.
- US AQI now
- 34 Good
- PM2.5
- 3.2 µg/m³ 0.2× WHO 24-h guideline
- PM10
- 13 µg/m³
- Ozone
- 70 µg/m³
- Dominant pollutant
- ozone sub-index 34
- Best hour today
- 8:00 pm AQI 24
- European AQI
- 25
Air quality in Leiden right now
Right now the modelled US Air Quality Index for Leiden, South Holland, The Netherlands is 34, which falls in the "Good" band (up to 50). Air quality is satisfactory and poses little or no risk; a good time for outdoor activity.
The index is driven mainly by ozone, whose own sub-index is 34. Ozone usually peaks in the afternoon on sunny days and falls back after sunset.
PM2.5 is 3.2 µg/m³, within the WHO 24-hour guideline of 15 µg/m³; PM10 is 13 µg/m³ against a guideline of 45; ozone is 70 µg/m³ (below the WHO 8-hour level of 100); nitrogen dioxide is 3.3 µg/m³ (below the 24-hour guideline of 25).
Also this hour: carbon monoxide 147 µg/m³.
NASA FIRMS shows 23 fire hotspots within 300 km in the last day (nearest about 34 km), but particle levels are not elevated enough to point to smoke right now.
Leiden AQI forecast: next 48 hours
Over the next 24 hours the AQI is forecast to range from 23 around Mon 10:00 pm to 34 around Mon 3:00 am, staying "Good" throughout.
The following day looks similar, averaging about 27.
| Local time (Europe/Amsterdam) | US AQI | Category | PM2.5 µg/m³ | PM10 µg/m³ | Ozone µg/m³ |
|---|---|---|---|---|---|
| Mon 3:00 am | 34 | Good | 3.2 | 13 | 70 |
| Mon 6:00 am | 34 | Good | 3.5 | 13 | 71 |
| Mon 9:00 am | 33 | Good | 3.8 | 14 | 66 |
| Mon 12:00 pm | 31 | Good | 5.5 | 13 | 54 |
| Mon 3:00 pm | 29 | Good | 5.7 | 12 | 54 |
| Mon 6:00 pm | 26 | Good | 4.3 | 8 | 49 |
| Mon 9:00 pm | 24 | Good | 4.4 | 7 | 46 |
| Tue 12:00 am | 23 | Good | 5.3 | 10 | 47 |
| Tue 3:00 am | 25 | Good | 5.1 | 8 | 40 |
| Tue 6:00 am | 26 | Good | 5.3 | 7 | 39 |
| Tue 9:00 am | 27 | Good | 5.8 | 7 | 40 |
| Tue 12:00 pm | 29 | Good | 5 | 6 | 45 |
| Tue 3:00 pm | 28 | Good | 4.4 | 7 | 53 |
| Tue 6:00 pm | 27 | Good | 4.4 | 12 | 55 |
| Tue 9:00 pm | 27 | Good | 3.5 | 13 | 59 |
| Wed 12:00 am | 26 | Good | 3.8 | 12 | 63 |
| Wed 3:00 am | 28 | Good | 3.8 | 13 | 64 |
Every third hour of the CAMS forecast via Open-Meteo. US AQI uses rolling averages (24 h for particles, 8 h for ozone), so it moves more slowly than the hourly concentrations.
Best time to be outside in Leiden today
Between 6 am and 9 pm local time, the cleanest air today is forecast around 8:00 pm (AQI 24, Good) and the worst around 6:00 am (AQI 34). That is a swing of 10 points, so a run or walk around 8:00 pm is noticeably better.
Leiden vs the rest of The Netherlands
Across 11 The Netherlands cities we track, the average US AQI right now is 32 (Good). Leiden at 34 is about average.
For context, the median across 3,556 cities worldwide is 58.
Air quality in cities near Leiden
| City | Distance | US AQI | Category | PM2.5 µg/m³ |
|---|---|---|---|---|
| Zoetermeer | 11 km | 31 | Good | 3.9 |
| The Hague | 16 km | 34 | Good | 3.8 |
| Rotterdam | 26 km | 31 | Good | 3.9 |
| Haarlem | 27 km | 33 | Good | 3.9 |
| Amsterdam | 36 km | 32 | Good | 3.7 |
| Zaandam | 39 km | 33 | Good | 3.9 |
| Zaanstad | 39 km | 33 | Good | 3.9 |
| Utrecht | 44 km | 31 | Good | 4.1 |
Model vs measured
The nearest measured PM2.5 reading is 2.5 µg/m³ from Sensor.Community (median of 174 sensors), centred about 6 km from the city centre. That is close to the model estimate of 3.2 µg/m³. Low-cost sensors can read high in humid air; reference monitors are more accurate but sparser.
Advice for sensitive groups
With the AQI at 34, there is no need for sensitive groups to change plans. People with asthma should still carry their reliever inhaler as usual.
What the US AQI numbers mean
| US AQI | Category | What it means |
|---|---|---|
| 0-50 | Good | Air quality is satisfactory and poses little or no risk; a good time for outdoor activity. |
| 51-100 | Moderate | Acceptable for most people. Unusually sensitive people should consider shortening long or heavy exertion outdoors. |
| 101-150 | Unhealthy for Sensitive Groups | People with heart or lung disease, older adults, children and teens should cut back on prolonged or heavy exertion outdoors. |
| 151-200 | Unhealthy | Everyone should reduce prolonged or heavy exertion outdoors; sensitive groups should avoid it and keep windows closed. |
| 201-300 | Very Unhealthy | Health alert: everyone should avoid prolonged or heavy exertion outdoors, and sensitive groups should stay indoors. |
| 301-500 | Hazardous | Emergency conditions: everyone should avoid all outdoor physical activity and stay indoors with filtered air if possible. The scale tops out at 500; heavier dust or smoke is shown as 500. |
Values on this page are modelled by CAMS (Copernicus) and served by Open-Meteo; they are estimates for the area around the city centre, not readings from an official monitor.
Nearby cities
More for Leiden
Air quality elsewhere
Data: Open-Meteo Air Quality API, Copernicus Atmosphere Monitoring Service (CAMS), Sensor.Community, NASA FIRMS.