Air quality is a big issue in German cities, especially Stuttgart, home town of Mercedes and Porsche. One certain point of measurement is typically critical. Local, Federal and EU Governments are discussing the issue along with various courts. The whole automotive industry is turned upside down.

One might think that the basis of the discussion – the measurement – has been performed correctly.

Unfortunately, this is not the case, as Prof. Dr. Achim Dittler, professor at Karlsruhe Institute of Technology and specialist for exhaust gas treatment, writes in an excellent article (www.linkedin.com/pulse/stuttgarter-zeitung-verunsichert-bürger-mit-und-achim-dittler/, in German).

Here’s a summary with some comments from my side:

The yearly average value recommended by WHO for PM10 is 20 µg/m^3. The measurement published by the local newspaper Stuttgarter Zeitung was 28.9 µg/m^3. One might think: a very accurate measurement (one decimal place) and almost 50% higher than allowed.

The truth is, however, different: The sensor that was used is not fit for purpose. It is part of a project that adds more points of measurements to the official, precise air quality measurements using low cost sensors. It is a PM2.5 sensor that can also measure PM10 to a certain degree. The inaccuracy at a relative humidity between 25 and 50% is 10 µg/m^3, which is “critical value +/- 50%”. Under current conditions with a relative humidity of >>50% (aka. “fog”) the manufacturer does not recommend to use the sensor since it is even more inaccurate.

Why? Because the fog (water) droplets are counted as particles. I think you don’t need a degree in rocket science to understand that this results in a much higher value of “measured” air pollution.

Isn’t that crazy? They use a low cost sensor that is able to measure in a certain range of ambient conditions. And far above these values, the sensor is still in use and the values are published on the internet. I’d say that every Bachelor student would fail if he did so in his thesis due to violation of basic scientific principles.

And then a newspaper takes these values, publishes them without reflecting, people share it and at the end politicians and judges decide that the automotive industry is evil. Even if it was just foggy and someone wanted to save some money on a sensor.

I really appreciate living in a country that knows freedom of the press. However, I think that journalists have to accept their responsibility.

And wouldn’t it be a good idea if our government wouldn’t just pay our scientists but also listen to them?