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We propose a novel, to the best of our knowledge, active–passive collaborative retrieval method for measuring XCO2 (APCRM-CO2). This method simultaneously uses observations from spectrometers and integrated path differential absorption laser detection and ranging (IPDA LIDAR), thus making its products have both the coverage advantages of passive detection and the high information content of active detection. The results of simulation experiments show that APCRM-CO2 can reduce the retrieval error by 15% to 70%. The minimum SNR for achieving 1 ppm is 24.7 dB. All these results are obtained without considering the LIDAR measured aerosol profile as input. Therefore, greater performance improvements on XCO2 retrievals are expected in the future for real data processing. The first satellite mission, DQ-2, carrying both a spectrometer and an IPDA LIDAR is planned to be launched by 2025. With the help of APCRM-CO2, its XCO2 products would better assist us with understanding the carbon cycle.

Quantum chemical calculations have been performed to study the interplay between halogen bond and lithium bond in the ternary systems FX-C6H5CN-LiF, FLi-C6H5CN-XF, and FLi-C6H5X-NH3 (X = Cl, Br, and I) involving aromatic compounds. This effect was studied in terms of interaction energy, electron density, charge transfer, and orbital interaction. The results showed that both FX-C6H5CN-LiF and FLi-C6H5CN-XF exhibit diminutive effects with the weakening of halogen bond and lithium bond, while FLi-C6H5X-NH3 displays synergistic effects with the strengthening of halogen bond and lithium bond. The nature of halogen bond and lithium bond in the corresponding binary complexes has been unveiled by the quantum theory of atoms in molecules methodology and energy decomposition analysis.