Retrieval and Comparison of Multi−Satellite Atmospheric composition concentration Data from the EMI Series Instruments

The Environmental Trace Gases Monitoring Instruments (EMI) are the second generation of spectrometers on-aboard the Gaofen-5 (GF-5) and Daqi-1 (DQ-1) satellites in China, which can be used to analyze trace gases such as O₃ , NO₂ and BrO. EMI enables continuous daily global trace gas observations at a spatial resolution of 7×13 km². In this study, the differential optical absorption spectroscopy (DOAS) algorithm was used to invert EMI spectral data to obtain the total column concentrations of O₃ , NO₂ and BrO of the three satellite loads. Due to the different overpass times of different loads, the daily variation trend of trace gases is obtained through comparative analysis, and the overall quality and reliability of EMI series data sets are verified by cross-comparison. The daily EMI total ozone column (TOC) was compared with the vertical column density (VCD) collected by the TROPOspheric Monitoring Instrument (TROPOMI). The results showed that the spatial distribution of daily EMI series TOC and TROPOMI TOC from September to December 2023 had a good correlation (R≥0.95), and the relative differences were less than 5% when verified with data from ground-based stations. In addition, the EMI series TOC data fusion results were highly correlated with TROPOMI TOCs (R = 0.99), weighted fusion assigns weighting factors to each instrument by inverting RMS of different loads. The consistency of NO₂ between EMI loads was high (R ≥ 0.90), and the correlation between the total column concentration of NO₂ and TROPOMI was also high (R ≥ 0.80). Retrieval results of BrO products from March to May 2024 in Arctic region also revealed significant increases in BrO concentrations caused by bromine explosion events in the spring. The results of these products highlight the potential of EMI instruments for long-term continuous monitoring of global trace gas distribution and changes, helping to build high-quality atmospheric component concentration data sets.