EN Correction for humidity

Language DE

Depending on both humidity and the particle composition, a certain amount of water condenses on the particulate matter. As a result, the particle's effective cross section increases as well as the likelihood of scattering of the laser in the detector. This can lead to the effect that particles which wouldn't have usually been detected during low humidity, might well be measured in high humidity conditions.

This effect cannot be universally represented with a simple formula, because its mainly determined by the composition of the particle which is usually unknown. The efforts to find a formula describing this effect empirically are ongoing, which is not linear and is especially noticeable above 70% humidity. This explains the fact that the data sheet of the SDS011 specifies the work environment for the sensor at max 70%.

This means that all measurements taken at a humidity level of more than 70% sometimes have very high readings ​​and, strictly speaking, should be discarded. One can try and attempt to partially neutralise this effect with a correction formula to make use of those readings which were gathered outside of the specifications valid work environment.

Following formulas were used so far:

• HackAir, Poland (sds011_nodemcu.ino)
  • gPM10 (h) = 1 + 0.816 ∙ h ^ 5.83
  • gPM2.5 (h) = 1 + 0.488 ∙ h ^ 8.60
• Norbert recommends Köhler formula, h normalized to 0 <h <1
  • gSoneja = 1 + α ∙ h² / (1-h)
  • gHänel = (1-h) -β
  • gKöhler = 1 + γ / (1 / h-1)
  • with α = 0.25, β = 0.47, γ = 0.22
• From Belgium
  • factorPM10 = 4.56 * (100 – PercRelHum)^-0.65
  • with DHT22 as Luftfeuchte-Sensor, source: RIVM

List of sensors located directly at official stations:

Bulgaria:
10001 10002 (42.669798,23.26841) Station Pavlovo
10003 10004 (42.655486,23.383278) Station Mladost

Austria
Linz:
11149, 11150 Luftprüfstation S341 Römerberg (http://www.land-oberoesterreich.gv.at/125879.htm)
17654, 17655 Luftprüfstation S341 Römerberg (http://www.land-oberoesterreich.gv.at/125879.htm)

Suisse
Zürich:
574, 575 Station Stampfenbachstr.
601, 602 Gerhardstrasse 1, keine Station???

Belgium
10975, 10976 Ukkel (Brüssel), Station 41R012 (http://www.irceline.be/de/luftqualitat/messungen/feinstaub/pro-messstation)