On 13 May 2014 we had Hans Berkhout of RIVM as a guest of the Smart Citizen project in Amsterdam. A very informative evening it was, about measuring air quality, the measuring results and comparing those results - with at the end a sobering message about the gas sensor used in the Smart Citizen Kit.
Hans Berkhout validates the official measuring air quality results from the national grid in The Netherlands, called Landelijk Meetnet Luchtkwaliteit. During his presentation, he talked about the history of the network, the regulation (EU and national) and gave some remarkable examples from his practice.
Of course, most of the audience was very keen to hear about the significance of the measuring results from the Smart Citizen Kit (SCK). Berkhout made it quite clear that the industrial type of gas sensor used to measure CO/NO2 in the SCK is not very suitable for this task, as the average levels of these gasses in the city will normally stay under the measuring range of the sensor. It could probably very well be used in chimneys or exhausts, but not to monitor the air quality outside.
It is also important to notice that the sensor in the kit produces a resistance value, expressed in kΩ. This value can not easily be converted to ppm or µg/m3. And: the value for CO is inversely proportional (a lower value means more CO in the air), while that of NO2 is not, so a higher value here represents more NO2 and both can be considered as indicative values only.