CO2 Measurements with Raman Lidar in the Lower Troposphere

Carbon dioxide is the most important greenhouse gas caused by emissions from human activities. Nevertheless, little is known about its distribution in the atmposphere. Thus, continuous CO₂ measurements not only on the ground but also in higher altitudes are key to improve our understanding of radiative forcing. Therefore, ground-based lidar systems with their ability of range-resolved CO₂ measurements are particularly interesting. In the recent two years, we have developed and incorporated a new channel to our ground-based Raman lidar system ARTHUS ("Atmospheric Raman Temperature and HUmidity Sounder") [1] and successfully collected more then 70 days of CO₂ profiles at the “Land-Atmosphere Feedback Observatory” (LAFO), in Stuttgart, Germany [2]. We utilize the 2ν₂ CO₂ Raman line, which is well separated from Raman lines of other atmosphere gases, especially O₂. With the current setup, we profile CO₂, temperature and humidity as well as particle extinction and particle backscatter coefficients in five receiver channels. The first CO₂measurements in 2023 with a preliminary calibration where already presented at the EGU24 [3]. Since then, the laser power has been doubled while still being an eye-safe system. With some other improvements in addition, the integration times needed at night and for a resolution of 300 m are for example 1.5 hours for an uncertainty of 1.5 ppm and 2 hours for an uncertainty of 2 ppm at altitudes of 500 m and 1 km, respectively.

We are currently (January 2025) adding a 2-mirror scanner to the system. With this, we will much better calibrate our CO₂ mixing ratio with low-level scans near our ground-based in-situ sensors located at the LAFO site. The scanning measuements of the CO₂ concentration will provide insights in its distribution around the surface sensors and enable us to identify and quantify local carbon sources and sinks. We will present the recent approaches and first scanning measurements at the EGU25.

References: 

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

[2] 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 

[3] Schumacher, M., D. Lange, A. Behrendt, V. Wulfmeyer, 2024: Measurements of CO₂Profiles in the Lower Troposphere with the new Raman Lidar Channel of ARTHUS. EGU24-9219 (2024). DOI: 10.5194/egusphere-egu24-9219