Preprints
https://doi.org/10.5194/egusphere-2024-2925
https://doi.org/10.5194/egusphere-2024-2925
21 Oct 2024
 | 21 Oct 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

The ZiCOS-M CO2 sensor network: measurement performance and CO2 variability across Zürich

Stuart K. Grange, Pascal Rubli, Andrea Fischer, Dominik Brunner, Christoph Hueglin, and Lukas Emmenegger

Abstract. As a component of the ICOS Cities project, a "mid-cost'' NDIR (nondispersive infrared) CO2 sensor network was deployed across Zürich city (Switzerland), known as ZiCOS-M. The network was operational between July 2022 and July 2024 and consisted of 26 monitoring sites, 21 of which were located in or around Zürich city with five sites outside the urban area. Daily calibrations using two reference gas cylinders and corrections of the sensors' spectroscopic response to water vapour were performed to reach a high level of measurement accuracy. The hourly mean root mean squared error (RMSE) was 0.98 ppm (range of 0.46 and 1.5 ppm) while the mean bias was -0.09 ppm (range of -0.72 and 0.66 ppm) when undergoing parallel measurements with a high-precision reference gas analyser. CO2 concentrations (technically, dry air mole fractions), were highly variable with site means in Zürich ranging from 434 to 460 ppm and Zürich's mean urban CO2 dome was 15.4 ppm above the regional background. Some of the highest CO2 levels were found at two sites exposed to a combination of strong plant respiration and very confined nocturnal boundary layers. High CO2 episodes were detected outside Zürich's urban area demonstrating that processes acting on a variety of scales drove CO2 levels. The ZiCOS-M network offered significant insights at an order of magnitude lower cost compared to reference instruments and the observations generated by ZiCOS-M will be used in additional ICOS Cities activities to conduct CO2 emission inventory validation with inversion modelling systems.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Stuart K. Grange, Pascal Rubli, Andrea Fischer, Dominik Brunner, Christoph Hueglin, and Lukas Emmenegger

Status: open (until 02 Dec 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2925', Anonymous Referee #1, 29 Oct 2024 reply
  • RC2: 'Comment on egusphere-2024-2925', Anonymous Referee #2, 10 Nov 2024 reply
Stuart K. Grange, Pascal Rubli, Andrea Fischer, Dominik Brunner, Christoph Hueglin, and Lukas Emmenegger
Stuart K. Grange, Pascal Rubli, Andrea Fischer, Dominik Brunner, Christoph Hueglin, and Lukas Emmenegger

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Short summary
Carbon dioxide (CO2) is a very important atmospheric pollutant and to better understand the gas's source and sink dynamics, a mid-cost sensor network hosting 26 sites was deployed in and around Zürich, Switzerland. The sensors' measurement performance was quantified and natural and anthropogenic CO2 emission sources were explored with a focus on what drives high CO2 levels. The observations will be used further by others to validate what is thought to be known about CO2 emissions in the region.