Measurements of CO2 Profiles in the Lower Troposphere with the new Raman Lidar Channel of ARTHUS

The variability of CO₂ in the atmosphere is still not well understood. Key to improve this understanding are continuous measurements of the CO₂ concentration over long periods of time as well as in different altitudes. At the “Land-Atmosphere Feedback Observatory” (LAFO) [1] of the University of Hohenheim, Stuttgart, Germany, we are operating the ground based Raman lidar system ARTHUS. ARTHUS stands for "Atmospheric Raman Temperature and HUmidity Sounder" [2]. This automatic system provides high resolution measurements up to the turbulent scale of temperature, water vapor mixing ratio as well as extinction and backscatter data continuously. But measuring CO₂concentrations with Raman lidar is quite challenging because of its comparatively low concentrationresulting in an overall weak backscatter signal and thus a low signal-to-noise ratio. To investigate the capabilities of our system for capturing CO₂ profiles, we developed and incorporated a new channel. For the measurements we utilize the 2ν₂ CO₂ Raman line, which is well separated from relevant Raman lines of other constituents of the atmosphere (e.g. O₂). At the conference we will present and discuss the first results of the first measurements at the LAFO site between August and October 2023. Comparison of the measured with expected profiles show good agreement. The latter where obtained by appropriately scaling profiles of the water vapor mixing ratio channel of the same system. In the near future, we will add a scanning unit to the system. This will enable us to calibrate and compare the CO₂ lidar data with in-situ instruments located at the ground. Furthermore, the identification and quantification of carbon sources and sinks along the surface will then be possible.

 

References:

[1] Späth, F., S. Morandage, A. Behrendt, T. Streck, and V. Wulfmeyer, 2021: The Land-Atmosphere Feedback Observatory (LAFO). EGU21-7693 (2021). DOI:10.5194/egusphere-egu21-7693

[2] Lange, D. et al.: Compact Operational Tropospheric Water Vapor and Temperature Raman Lidar with Turbulence Resolution. Geophys. Res. Lett. (2019). DOI:10.1029/2019GL085774