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High ambient air concentrations of fine particulate matter are a problem in many European cities, especially in traffic loaded street canyons. Therefore, the introduction of traffic restricted or traffic reduced areas is discussed as a countermeasure in several towns. However, at that point it is not always clear, in what extent the restriction of traffic in presently overloaded streets causes the exceeding of limit values in other areas of the town after the redirection of the traffic. Presently this cannot be recorded appropriately, when the concentrations of fine particulate matter are monitored only at rarely distributed single points by the official measurement systems of the environmental state agencies.
On the other hand, meanwhile there are low cost and mid cost sensors for the measurement of fine particulate matter available, which enable the parallel monitoring with many measurement systems in an extended area of the town. By this way, the effect of traffic restrictions on the distribution of fine particulate matter in the city can potentially be observed. However, at this point the question arises, how reliable the results are, which are delivered by the low and mid cost sensors for fine particulate matter. For this reason different low cost and mid cost sensors have been evaluated for this study and intercompared with certified reference measurement systems for fine particulate matter. The study comprised the sensors SDS011 (Nova Fitness), which is in use already for several citizen science projects in Germany, SPS30 (Sensirion), OPC-R1 (Alphasense), OPC-N2 (Alphasense) and OPC-N3 (Alphasense).
This study was performed at urban sites in Düsseldorf (Germany) for several weeks and covered different traffic loads and different meteorological situations, in order to get representative results. As atmospheric humidity can influence the measurement results, the humidity was measured in parallel to the fine particulate matter. It could be shown that the validity of the measurement results of fine particulate matter could be improved, when the parallel readings of the humidity were taken into account.
It is well known from medical studies that fine particulate matter has adverse effects to human health. However, exceeding of limit values for fine particulate matter PM10 and PM2.5 is still a problem in major German cities. Therefore, fine particulate matter is monitored in Germany by environmental state agencies at fixed stations with certified instruments. These certified instruments are able to deliver reliable and high quality results. However, because of the costs of these certified instruments and the maintenance efforts, only few measurements stations are placed in the cities at places, which are regarded as representative for the air pollution. On the other hand, it is of interest to know the concentration of fine particulate matter in areas and at places, which are not covered by the fixed measurement stations of the environmental state agencies.
In this situation citizen science projects started in Germany using low cost sensors for fine particulate matter. In principle, with these low cost sensors citizens could measure fine particulate matter at places and in situations of their interests.
However, at that point the question of reliability of the low cost sensor data arises. Therefore the Duesseldorf University of Applied Sciences (HSD) in Germany started a project for the testing and evaluation of low-cost sensors. For this reason 20 low-cost sensor units have been built up based on the SDS 011 sensor of Nova Fitness Inc. within the Laboratory for Environmental Measurement Techniques at HSD. The sensor measurement data can be transferred into a network and can be visualized on a digital map.
This testing and evaluation at HSD of the low-cost sensors comprised:
• Short term and long term comparison studies within the laboratory and at different urban sites with a certifiedwide range aerosol measurement system (Grimm WRAS).
• Short term and long term comparison studies within the laboratory and at different urban sites with mid-cost sensors (Alphasense AN2).
• Intercomparison testing and evaluation of sensors of the same production charge.
• Intercomparison testing and evaluation of sensors of different production charges.
• Testing and evaluation of the sensors at different meteorological conditions.
The results of this testing and evaluation will be presented at the conference. Moreover, the potential of additional applications for low-cost sensors, e.g. for mobile measurements (multicopter UAS, bicycles, pedestrians) or for the validation of air pollution models, will be discussed