# Retrieval and Comparison of Multi-Satellite Polar Ozone Data from the EMI Series Instruments
## 5 Conclusions and Future Work  
In this study, the daily and monthly retrieval results of the EMI series TOCs were obtained through the DOAS method and compared with the TROPOMI TOCs on both global and regional scales. The DOAS TOCs of the EMI-GF5 (01A), EMI-GF5 (02), and EMI-DQ01 datasets show good agreement with the TROPOMI TOCs, with high correlation coefficients (R) of 0.97, 0.96, and 0.97, respectively. The EMI-GF5 (01A) results were consistent with the EMI-DQ01 datasets (R = 0.98), illustrating the stability and consistency between the EMI instruments' observations. In addition, the November 2023 global maps of monthly TOCs exhibited a spatial distribution similar to that of the TROPOMI TOCs, with the EMI-DQ01 dataset showing the highest consistency. Moreover, we compared the daily mean EMI series DOAS TOCs with the corresponding ground-based TOCs. The relative variations in the EMI series TOCs agreed well with the corresponding ground-based TOC results. In the mid-latitude regions, the errors between the TOCs of the ground-based stations and those of the EMI-GF5 (01A), EMI-GF5 (02), and EMI-DQ01 datasets were within 5%, indicating that the target accuracy of \(\pm\)5% had been reached. In the polar regions examined in this study, the errors were relatively large. The high-latitude areas of the northern and southern hemispheres exhibited a significant negative difference of up to \(-\)5% and a positive difference of up to 6%, respectively. The average standard deviations between the selected polar ground-based stations' data and the EMI-GF5 (01A), EMI-GF5 (02), and EMI-DQ01 datasets were 5.96-7.34%, 5.04-7.45%, and 5.13-6.32%, respectively, which were primarily caused by weak light absorption. Furthermore, we analyzed the diurnal variations in the TOCs by combining the EMI-GF5(01A) and EMI-DQ01 observations (morning overpass) with the EMI-GF5(02) (afternoon overpass) observations. The combined satellite observations systematically reflected the trend of low TOC results in the morning and afternoon in different latitude regions and demonstrated the capability of the EMI instruments to monitor the diurnal ozone variations in the global area. In addition, through the observation of the total ozone column by the long-term stable EMI series, the seasonal changes and long-term trends of ozone can be tracked, helping to study the impact of climate change on ozone distribution. Finally, the TOC values resulting from the EMI series data fusion are significant for accurate and continuous polar ozone research. Through the weighted fusion of the EMI TOC values, the accuracy of the data was improved (the R value increased to 0.99), which provides a basis for more refined polar ozone monitoring. Compared to a single sensor, the result has differences within 3 DU, which is smaller than from each individual EMI instrument. The experimental results show that this fusion method can effectively fuse multi-satellite TOC results and improve the spatial resolution and coverage of the EMI series instruments. In future work, the following directions will be pursued: (1) further elimination of the spatial differences and random error between the other trace gases so that they can be compared and analyzed according to the same spatial framework and (2) exploring machine learning to integrate the TOC values from EMI series datasets, aiming to facilitate weight adjustment and address diverse uncertainties. Conceptualization, K.W., F.S., and Y.L. ; methodology, K.W. and Q.L. ; software, K.W., Z.X. and K.Y. ; validation, K.W. and F.S. ; formal analysis, K.W. and Y.L. ; investigation, K.W. ; resources, K.W., F.S., and Y.L. ; writing--original draft preparation, K.W. ; writing--review and editing, Y.L. and F.S. ; visualization, K.W. ; supervision, Y.L. and F.S. ; project administration, F.S. ; funding acquisition, F.S. All authors have read and agreed to the published version of the manuscript. This study was financially supported by National Key R&D Program (2022 YFC3700102), the Youth Innovation Promotion Association of CAS (Grant No.