The ZiCOS-M CO<sub>2</sub> sensor network: measurement performance and CO<sub>2</sub> variability across Zurich
<p>As a component of the ICOS Cities project, a “mid-cost” NDIR (nondispersive infrared) <span class="inline-formula">CO<sub>2</sub></span> sensor network was deployed across the city of Zurich (Switzerland), known as ZiCOS-M. The network was operational betwe...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/2781/2025/acp-25-2781-2025.pdf |
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| Summary: | <p>As a component of the ICOS Cities project, a “mid-cost” NDIR (nondispersive infrared) <span class="inline-formula">CO<sub>2</sub></span> sensor network was deployed across the city of Zurich (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 the city of Zurich, with 5 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 <span class="inline-formula">ppm</span> (range of 0.46 and 1.5 <span class="inline-formula">ppm</span>) and the mean bias ranged between <span class="inline-formula">−</span>0.72 and 0.66 <span class="inline-formula">ppm</span> when undergoing parallel measurements with a high-precision reference gas analyser for a period of 2 weeks or more. <span class="inline-formula">CO<sub>2</sub></span> concentrations (technically, dry-air mole fractions) were highly variable with site means in Zurich ranging from 434 to 460 <span class="inline-formula">ppm</span>, and Zurich's mean urban <span class="inline-formula">CO<sub>2</sub></span> dome was 15.4 <span class="inline-formula">ppm</span> above the regional background. Some of the highest <span class="inline-formula">CO<sub>2</sub></span> levels were found at two sites exposed to strong plant respiration in a very confined nocturnal boundary layer. High-<span class="inline-formula">CO<sub>2</sub></span> episodes were detected outside Zurich's urban area, demonstrating that processes acting on a variety of scales drove <span class="inline-formula">CO<sub>2</sub></span> levels. The ZiCOS-M network offered significant insights at a cost an order of magnitude lower compared to reference instruments, and the observations generated by ZiCOS-M will be used in additional ICOS Cities activities to conduct <span class="inline-formula">CO<sub>2</sub></span> emission inventory validation with inversion modelling systems.</p> |
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| ISSN: | 1680-7316 1680-7324 |