Physik | Technik
Dominique Wasescha, 2004 | Davos Platz, GR
In this paper the Particulate Matter (PM) was measured using the SDS011 sensors. This is a lowcost sensor with a laser based measuring method. Four such sensors had been distributed in different parts of Davos to show as much variety as possible. After the sensor have stayed there for a few months all the measurements from a fitting 100 day time span have been downloaded as CSV document. Then different averages from the data were created and compared to the professional measuring stations which use gravimetric measurements.
The question I dealt with was whether low-cost sensors could produce reliable results and what one could deduce from them. Part of my motivation was to further my theoretical understanding on the impact of particulate matter on the human body as well as to prove the quality of air in Davos. To do this, I analysed the concentration of PM 2.5 and PM 10 over a period of 100 days using the SDS011 sensor.
The sensor I used can measure particles from 0.3 micrometers up to 10 micrometers. I mainly used the sensor for measuring PM 2.5 and PM 10, which means particles with the size 2.5 respectively 10 micrometers. But 2 things were necessary for this sensor to work: a power connection and WiFi. This has to be provided since the data isn’t stored on the sensor directly but on a cloud. This device uses the laser scattering method. This means every 2-3 min particles are drawn into the sensing chamber, where they are illuminated by a laser. Depending on the size and density of a particle different waves hit the low noise amplifier. This light is then converted to different signals which are then visible on the website. Now the next step was to find locations that would give me an overview of the pollution in Davos. 3 of all sensors were placed in the centre, 2 of them along the main roads in Davos Platz and one in Davos Dorf. For more versatility I also placed one outside of the centre, in a calmer place, Davos Wiesen. The first one has the balcony adjacent to the road. Also, the grill is placed right next to the sensor. The second sensor was directly exposed to the road. During the time my measurements took place, there was a construction site at this turn. The third one in Davos Dorf again was placed on a balcony. This balcony however is wind still. The last sensor was placed in the green. No roads near, a very quiet place, and it showed. The descriptions for my locations were all criterias that influenced the data. My sensors stayed and measured for 100 days. After that period the data has been downloaded as a CSV document. In my charts, I wanted to show different graphs: the daily, weekly and overall average.
To check the accuracy my measurements I compared them to professional stations. Those stations both only measure PM 10. The measurements took place from 12.04 up until 19.07. In my charts the first thing to notice is that the trends almost match for the same size particle. Additionally Davos Wiesen has the lowest concentration of all. Thanks to this outcome and additional research I can confirm the assumptions, outside of the centre the air is healthier. All of my concentrations are below the legal limit, which also occurs for the professional stations. This again shows the quality of the air in Davos. A shock was the big deviation from the professional sensors. The sensor only shows half of the concentration it should. Following the discussion with my supervisor it came to light that such deviations are the norm with such low-cost sensors.
The question formulated at the beginning could be answered as presented, and interesting conclusions can be drawn from the results: The sensors were quite cheap, but the trend was surprisingly precise. The only part which deviates is the concentration. The strong deviations are normal with low-cost sensors and there are many factors that influence the trend like humidity for example. This brought the need to calibrate the measurements. The calibration process did not work out as accurately as hoped. There were only a few measuring errors, but since the sensor converts the data which is collected every few minutes into daily/weekly/monthly averages an overall correct visualisation of the pollution is portrayed.
All in all the project was successful and the goals set at the beginning were reached.
Würdigung durch den Experten
Dr. Stefan Horender
Für diese Arbeit hat die Schülerin mehrere Sensoren zur Messung der Partikelkonzentration in der Luft in Davos im Zeitraum April bis Juli 2021 betrieben. Zur Einordnung der erhaltenen Werte wurde eine Literaturrecherche durchgeführt und das breite Spektrum verschiedener Aspekte atmosphärischer Aerosole dargestellt und auch auf die Gesundheitsrelevanz eingegangen. Die erhaltenen Daten wurden mit den Messungen von amtlichen Luftüberwachungsstationen verglichen und die Effekte, die zu Abweichungen führten, diskutiert und korrigiert.
Schweizerische Alpine Mittelschule Davos, Davos-Platz
Lehrer: André van der Graaff