Metrology for low-cost CO<sub>2</sub> sensors applications: the case of a steady-state through-flow (SS-TF) chamber for CO<sub>2</sub> fluxes observations

Abstract

Abstract. Soil CO2 emissions are one of the largest contributions to the global carbon cycle, and a full understanding of processes generating them and how climate change may modify them is needed and still uncertain. Thus, a dense spatial and temporal network of CO2 flux measurements from soil could help reduce uncertainty in the global carbon budgets. In the present study, the design, assembly, and calibration of low-cost air enquirer kits, including CO2 and environmental parameters sensors, is presented. Different types of calibrations for the CO2 sensors and their associated errors are calculated. In addition, for the first time, this type of sensor has been applied to design, develop, and test a new steady-state through-flow (SS-TF) chamber for simultaneous measurements of CO2 fluxes in soil and CO2 concentrations in air. The sensors' responses were corrected for temperature, relative humidity, and pressure conditions in order to reduce the uncertainty in the measured CO2 values and of the following calculated CO2 fluxes based on SS-TF. CO2 soil fluxes measured by the proposed SS-TF and by a standard closed non-steady-state non-through-flow (NSS-NTF) chamber were briefly compared to ensure the reliability of the results. The use of a multiparametric fitting reduced the total uncertainty of the CO2 concentration measurements by 62 %, compared with the uncertainty that occurred when a simple CO2 calibration was applied, and by 90 %, when compared to the uncertainty declared by the manufacturer. The new SS-TF system allows the continuous measurement of CO2 fluxes and CO2 ambient air with low cost (EUR ∼1200), low energy demand (<5 W), and low maintenance (twice per year due to sensor calibration requirements).

Validation and field application of a low-cost device to measure CO2 and ET fluxes

“…The same tends to be true for obtained GPP parameters, which were highly comparable for LI-850 (⍺: -0.048; were not obtained. Our findings are further supported by studies that compared the accuracy of K-series sensors against commercial sensor counterparts and its accuracy for field CO2 flux measurements (Curcoll et al, 2022). They integrated a K30…”

“…Although low-cost NDIR CO2 sensors are commonly used in air quality monitoring studies (Araujo et al, 2020;Wastine et al, 2022), these sensors have also been applied in environmental research (Bastviken et al, 2015;Brown et al, 2020). For example, multiple studies have demonstrated the applicability of using low-cost NDIR CO2 sensors for reliable measurements of soil CO2 efflux (Brändle and Kunert, 2019;Curcoll et al, 2022;Harmon et al, 2015) and water crop use determination (Capri et al, 2021). However, in case of RH sensors, the inversely increased measurement uncertainty of total water vapor concentration with decreasing RH (e.g.…”