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Yann Büchau :nixos:

My first scientific paper has been published! 📰 🎉

Büchau (2022): An Autarkic Wireless Sensor Network to Monitor Atmospheric CO2 Concentrations

doi.org/10.1127/metz/2022/1125

In my PhD I am building a wireless CO2 sensor network with mostly components. This paper describes it.

Code and hardware designs are available here: gitlab.com/tue-umphy/co2mofett

An Autarkic Wireless Sensor Network to Monitor Atmospheric CO2 Concentrations Abstract In this study an autarkic low-cost wireless network infrastructure suitable for areas spanning a couple of hectares is introduced. Open source hard- and software components make up the infrastructure’s core, rendering it very scalable in terms of cost and deployment density. The network is designed to operate continuously throughout the year in a wide range of weather conditions.Four different embedded, low-cost Sensirion SCD30 non-dispersive infrared (NDIR) CO 2 sensors are evaluated under laboratory conditions and tested for cross-sensitivity on water vapour and linear characteristics, of which the Sensirion SCD30 sensor exhibits the best overall performance. An in-field comparison of eleven Sensirion sensors with an eddy-covariance station verifies its outdoor applicability. The network’s suitability to monitor natural CO 2 emissions was tested at a site in the upper Neckar Valley in southwestern Germany. A station with a single Sensirion sensor observed a strong diurnal cycle of the near-surface CO 2 concentration over the course of several months. While only slightly elevated CO 2 levels above 400 ppm prevailed during the day, concentrations reached the sensor’s output limit of 40 000 ppm during the night when wind speeds are low.
Figure 1: Aerial view of the Starzach site taken in summer 2019 by Martin Schön and map of Germany with part of the Neckar valley region as orientation. Visible focused CO 2 exhalation spots are marked as yellow dots, their size loosely indicating the apparent intensity. Fields of diffuse degassing are indicated as purple areas. Degassing spots appear in SW-NE direction across the site and are discussed by Lübben and Leven (2018) to be associated with a geological fault line. Map data ' OpenStreetMap contributors (2021).
Figure 3: Network infrastructure schematic. An on-site single-board computer acts as a central station and establishes a Wireless Local Area Network (WLAN) to which all stations connect. Stations store their sensor data locally and transmit it wirelessly to the central station, where data is logged to a database. The central station maintains an internet connection to an off-site server to enable remote maintenance and live data monitoring. This server mirrors the on-site network traffic and relays a selection of the measurements to the openSenseMap platform for data display and live monitoring.
Figure 4: General design of a sensor station. (a) An ESP8266 microcontroller mounted on a custom circuit board in a weatherproof box is powered externally via a 12 V two-wire cable. (b) A custom circuit board capable of holding up to eight Sensirion SCD30 CO 2 sensors mounted below a simple radiation shield is connected to the microcontroller via a patch cable with RJ45 connector. (c) Radiation shield holding a custom multi-sensor circuit board with Sensirion SCD30 CO2 sensor, Bosch BME280 environmental sensor (atmospheric pressure, temperature, relative humidity), CUBIC CM1106 CO 2 sensor and theben CO 2 Sensor Module.
#raspberrypi#esp8266#mqtt
Aug 29, 2022, 12:41 PM·Public
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Yann Büchau :nixos:

I compared the preformance of four low-cost sensors quantitatively and concluded that the Sensirion SCD30 sensor works best for this use case.

Table 2: Specifications of four miniature, low-cost NDIR CO 2 sensor models evaluated for application in our project.
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Yann Büchau :nixos:

At the site I am investigating (openstreetmap.org/node/7554014) there are the naturally occurring exhalation spots called ”mofettes”. Nearly pure of presumably magmatic origin is being degassed there. One of the mofettes outputs in the range of several 100kg per day!

Figure 2: Selection of CO 2 exhalation spots at the Starzach site: (a) time-lapse of diffuse exhalation visible as a stream of ascending gas bubbles during spring 2020 when the site was flooded, (b) the site’s largest mofette during winter 2019 with a line of icing indicating the exiting gas’ path and (c) time-lapse of the focused degassing of the mofette with the largest pressure and exhalation velocity. This mofette developed several months after the installation of a ground-water monitoring well. Pictures in (c) taken in summer 2019 by Martin Schön.
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Yann Büchau :nixos:

For the network I am using:

- @kicad for PCB design
- for 3D design
- for flashing the ESP8266 sensor station µControllers
- for data analysis, data management, device interaction, etc...
- mosquitto broker as data transmission protocol
- a as central station
- etc...

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