1,2,2,3,1,1,4,5- 1Institute of Environmental Physics, Heidelberg University, Heidelberg, Germany (msindram@iup.uni-heidelberg.de)
- 2Kirchhoff-Institute for Physics, Heidelberg University, Heidelberg, Germany
- 3Max Planck Institute for Nuclear Physics, Heidelberg, Germany
- 4Heidelberg Center for the Environment (HCE), Heidelberg University, Heidelberg, Germany
- 5Interdisciplinary Center for Scientific Computing (IWR), Heidelberg University, Heidelberg, Germany
Urban areas globally are the major source regions of anthropogenic greenhouse gases [1]. To reduce city-scale uncertainties associated with bottom-up inventory-based emission estimates and to design and evaluate emission reduction measures, top-down emission estimates based on concentration measurements and transport modeling are necessary. Inferring these emissions from a number of in-situ concentration measurements comes with the challenge of limited measurement representativeness, uncertain knowledge of prior emissions, and uncertainties in transport modelling on very local scales. Path-integrated concentration measurements are representative of areas on the kilometer scale, and thus, they are less sensitive to very local processes and more representative of model grid scales. They therefore have the potential to improve measurement-based urban emission quantification in the future.
We measure path-integrated concentrations by sending light along kilometer-long air paths above the city of Heidelberg, Germany, to reflectors and spectroscopically analyze the returning signal. By fitting an absorption model to the spectra, we infer the CO2 concentrations along the respective paths. Our spectroscopic method of choice is Dual-Comb Spectroscopy (DCS) based on two interfering laser frequency combs. It allows measuring broadband spectra with high spectral resolution and signal-to-noise ratio.
We present the first nine months of concentration measurements of greenhouse gases along one path above the city of Heidelberg. We show first results from this deployment period and compare them to a co-deployed Fourier-transform spectrometer (FTIR) that has been continuously running since 2023 [2] and different in-situ sensors. We also report our current progress in expanding our setup into a network consisting of multiple light paths above the city, including modelling of expected concentration gradients, with the aim of inferring urban emissions.
References:
[1] Intergovernmental Panel on Climate Change (IPCC). (2021). Climate Change 2021: The Physical Science Basis. Working Group I Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, et al.]. Cambridge University Press. https://doi.org/10.1017/9781009157896
[2] Schmitt, T. D., et al. (2023). An open-path observatory for greenhouse gases based on near-infrared Fourier transform spectroscopy. Atmos. Meas. Tech., 16(24), 6097–6110. https://doi.org/10.5194/amt-16-6097-2023
How to cite: Sindram, M., Schmitt, T. D., Dubroeucq, R., Mukherjee, S., Pilz, L., Pfeifer, T., Oberthaler, M. K., and Butz, A.: Towards an Urban Network of Path Integrated Greenhouse Gas Measurements Using Dual-Comb Spectroscopy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9995, https://doi.org/10.5194/egusphere-egu26-9995, 2026.
