Methodology
Transparency matters to us: this is how the numbers on this site are produced.
Data source
All readings come from Sensor.Community (formerly luftdaten.info), a worldwide network of self-built measuring stations. We use its freely accessible interface for current readings and its public data archive for the history. The data is licensed under the Open Database License (ODbL).
City and district boundaries come from OpenStreetMap. Only stations inside the city limits are included; indoor sensors are excluded. Fresh readings are fetched whenever someone opens the site (at most once per minute). Any gaps are filled automatically once a day from the archive.
Measured values
| Value | Sensors in Wuppertal | Note |
|---|---|---|
| Particulate matter PM10 & PM2.5 | SDS011 (laser scattering) | Particles smaller than 10 or 2.5 µm |
| Temperature, humidity | DHT22, BME280 | The DHT22 is cheaper but less accurate |
| Air pressure | BME280 | Station pressure, converted by us to sea level if not supplied |
| Dew point | calculated | Magnus formula from temperature and humidity |
If further sensor types appear in Wuppertal – such as noise (DNMS), PM1/PM4 (SPS30) or CO₂ – they are detected and displayed automatically.
Calculation
Median instead of mean
Citizen sensors hang on balconies, in gardens and on house walls. Individual devices can deviate strongly because of direct sunlight, a barbecue or a defect. We therefore first average per station and then combine all stations using the median. In the history chart the shaded area shows the range covering the middle 50 % of stations (interquartile range).
“Current”
The current value is the mean of the last 20 minutes per station. Stations that have not reported for more than 30 minutes are considered offline.
Air quality index
We follow the European Air Quality Index of the EEA. The worse of the two classes for PM2.5 and PM10 determines the result. Ozone and nitrogen dioxide, which are also part of the official index, are not measured by citizen sensors.
Guideline and limit values
WHO 2021 guidelines for the 24-hour mean: PM2.5 15 µg/m³, PM10 45 µg/m³. EU limit for PM10: 50 µg/m³ as a daily mean, exceeded on no more than 35 days per year.
Limitations
- Humidity: laser particle sensors such as the SDS011 read considerably too high above roughly 80 % relative humidity, because particles absorb water and fog droplets are counted as dust. We show a notice in that case.
- Not official data: the sensors are not calibrated and are not comparable with official monitoring stations. Official data for Wuppertal is published by LANUV NRW.
- Temperature: sensors in full sun or on house walls often read too high; the median dampens this.
- Locations are usually rounded to about 100 m by Sensor.Community.