Synergistic Use of CO2 and NO2 for Emission Characterization: A Study Using TANGO Mission Simulations and ENMAP Data

The Twin Anthropogenic Greenhouse Gas Observers (TANGO) mission is an ESA Scout initiative scheduled for launch in 2028, designed to monitor anthropogenic and natural greenhouse gas emissions from point sources at high spatial resolution. The mission consists of two 16U CubeSat platforms flying in tandem with a temporal separation of less than one minute, each carrying a pushbroom imaging spectrometer.  The first satellite is dedicated to the measurement of atmospheric CO₂ and CH₄ in the 1.6 μm spectral region, while the second satellite is optimized for the detection of NO₂ in the visible spectral range. Both instruments provide observations over a 30 × 30 km² swath with a ground spatial sampling of 300 × 300 m². TANGO is designed to survey more than 10,000 emission sources per year with a nominal revisit time of four days, focusing on emissions from sources with annual fluxes ≥ 2.5 Mt CO₂ and ≥ 5 kt CH₄.

In this study, we investigate the synergistic exploitation of collocated CO₂ and NO₂ observations to achieve an improved characterization of atmospheric emissions. The primary objective is to quantify the source emission ratio CO₂/NO₂ and to derive diagnostic parameters that elucidate an effective reaction rate associated with the transformation NO + O₃ → NO₂ + O₂. The tandem configuration of TANGO facilitates quasi-simultaneous measurements of both trace gases, thereby minimizing temporal variability in ambient atmospheric conditions between individual observations.

We evaluate the proposed methodology using dedicated microHH large-eddy simulations that incorporate realistic operational scenarios, including variable source strengths, temporal offsets between the two satellite overpasses, and heterogeneous spatial discretizations for CO₂ and NO₂. These simulations enable a quantitative assessment of the feasibility and accuracy of retrieving emission ratios and chemical parameters under conditions representative of actual measurement configurations. Subsequently, we validate the approach by applying it to ENMAP (Environmental Mapping and Analysis Program) satellite observations, thereby demonstrating its practical suitability for prospective TANGO measurements. The results underscore the potential of synergistically exploiting multispecies trace gas measurements to enhance emission quantification and to advance the characterization of atmospheric chemical processes.

The TANGO mission is a small satellite mission to be launched in 2028, under the ESA Scout Programme tapping into NewSpace to quickly deliver affordable and innovative science, as part of ESA’s FutureEO Programme, within a budget of 35M€ and a schedule of three years from mission kick-off to launch.