Global measurements of total ozone are necessary to evaluate ozone hole recovery above Antarctica. The Environmental Trace Gases Monitoring Instrument (EMI) onboard GaoFen 5, launched in May 2018, was developed to measure and monitor the global total ozone column (TOC) and distributions of other trace gases. In this study, some of the first global TOC results of the EMI using the differential optical absorption spectroscopy (DOAS) method and validation with ground-based TOC measurements and data derived from Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI) observations are presented. Results show that monthly average EMI TOC data had a similar spatial distribution and a high correlation coefficient (R ≥ 0.99) with both OMI and TROPOMI TOC. Comparisons with ground-based measurements from the World Ozone and Ultraviolet Radiation Data Centre also revealed strong correlations (R > 0.9). Continuous zenith sky measurements from zenith scattered light differential optical absorption spectroscopy instruments in Antarctica were also used for validation (R = 0.9). The EMI-derived observations were able to account for the rapid change in TOC associated with the sudden stratospheric warming event in October 2019; monthly average TOC in October 2019 was 45% higher compared to October 2018. These results indicate that EMI TOC derived using the DOAS method is reliable and has the potential to be used for global TOC monitoring.

A violent volcanic eruption attracting considerable attention occurred on 15 January 2022 near the South Pacific island nation of Tonga. To investigate its environmental impact, we retrieved the sulfur dioxide (SO₂) and bromine monoxide (BrO) vertical column densities of environmental trace gas monitoring instrument 2 (EMI-2) based on the differential optical absorption spectroscopy algorithm. The results showed westward and southeastward transport of principal parts of SO₂ and BrO plumes, respectively, from the Hunga Tonga–Hunga Ha’apai (HTHH) eruption. On 15 January, most of the released SO₂ entered the stratosphere (above 20 km) directly and spread rapidly westward (approximately 30 m/s). In contrast, the principal portion of the BrO spread southeastward slowly (approximately 10 m/s) within the 8–15 km altitude layer on 16 January. Our research results also suggest that during the HTHH eruption, BrO was released from the magmatic melt later than SO₂. The total SO₂ emissions from this eruption were approximately 0.24 Tg. The majority of SO₂ and BrO plumes were transported within the Southern Hemisphere. This study is an important extension to the empirical database of volcanological and magmatic degassing research.

The Environmental Trace Gases Monitoring Instrument 2 (EMI-2), a second-generation Chinese hyperspectral satellite-based spectrometer, was launched on 7 September 2021. The total ozone column (TOC) product, which is one of the most important elements of the EMI-2 mission, is required for monitoring the Antarctic ozone hole and regional tropospheric ozone pollution. The first EMI-2 TOC results using the differential optical absorption spectroscopy (DOAS) method are presented in this study. Significant improvements, such as the fitting interval, reference spectrum, and iterative air mass factor (AMF) calculation scheme, were implemented in the EMI-2 TOC retrieval in comparison with the EMI DOAS TOC algorithm, thus generating more accurate reads. The monthly average EMI-2 DOAS TOCs in November 2021 were compared with the TROPOspheric Monitoring Instrument (TROPOMI) TOCs, and the results showed a good correlation (R = 0.99). The EMI-2 TOCs showed similar global spatial distributions to those of TROPOMI, with an overall mean relative bias and mean standard deviation of 0.16% and 2.38%, respectively. However, large differences (up to 7%) appeared in some polar areas near the coastline, which were mainly caused by different surface albedo algorithms. Furthermore, ground-based measurements from 20 stations across different latitudes derived from the World Ozone and Ultraviolet Radiation Data Center dataset were used to assess the accuracy of the EMI-2 DOAS TOCs, and they had a mean relative bias and mean standard deviation of 0.70% and 3.65%, respectively. These results indicate that the EMI-2 DOAS TOC algorithm can yield reliable global TOCs and monitor daily Antarctic TOCs for assessing the healing of ozone holes.

We retrieved the absorbing aerosol index (AAI) based on the measured reflectance from the Environmental Trace Gases Monitoring Instrument (EMI) for the first time. EMI is a push-broom spectrometer onboard the Chinese GeoFen-5 satellite launched on 9 May 2018, which was initially developed to determine the global distribution of atmospheric composition. The EMI initial AAI results were corrected from physical stripes and yielded an offset of 5.92 as calibration errors from a background value based on the statistical method that count the EMI AAI over the Pacific Ocean under cloudless scenes. We also evaluated the consistency of the EMI AAI and data with the TROPOspheric Monitoring Instrument (TROPOMI) observations. A comparison between the monthly average EMI AAI data and TROPOMI AAI revealed regional consistencies between these instruments with a similar spatial distribution of AAI (correlation coefficient, r > 0.9). The daily-scale results demonstrated that EMI was also consistent with TROPOMI AAI (r = 0.9). The spatial distribution of EMI AAI is consistent with Aerosol Optical Depth (AOD) from TROPOMI. The daily variation of EMI AAI in an Australian wildfire event was consistent with TROPOMI (r = 0.92). Overall, we demonstrated that EMI AAI can be efficiently used to detect large aerosol events for reconstructing the spatial variability of Ultraviolet (UV) absorbing aerosols.

The Arctic stratospheric ozone depletion event in spring 2020 was the most severe compared with previous years. We retrieved the critical indicator ozone vertical column density (VCD) using zenith scattered light differential optical absorption spectroscopy (ZSL-DOAS) from March 2017 to September 2021 in Ny-Ålesund, Svalbard, Norway. The average ozone VCD over Ny-Ålesund between 18 March and 18 April 2020 was approximately 274.8 Dobson units (DU), which was only 64.7 ± 0.1% of that recorded in other years (2017, 2018, 2019, and 2021). The daily peak difference was 195.7 DU during this period. The retrieved daily averages of ozone VCDs were compared with satellite observations from the Global Ozone Monitoring Experiment-2 (GOME-2), a Brewer spectrophotometer, and a Système d’Analyze par Observation Zénithale (SAOZ) spectrometer at Ny-Ålesund. As determined using the empirical cumulative density function, ozone VCDs from the ZSL-DOAS dataset were strongly correlated with data from the GOME-2 and SAOZ at lower and higher values, and ozone VCDs from the Brewer instrument were overestimated. The resulting Pearson correlation coefficients were relatively high at 0.97, 0.87, and 0.91, respectively. In addition, the relative deviations were 2.3%, 3.1%, and 3.5%, respectively. Sounding and ERA5 data indicated that severe ozone depletion occurred between mid-March and mid-April 2020 in the 16–20 km altitude range over Ny-Ålesund, which was strongly associated with the overall persistently low temperatures in the winter of 2019/2020. Using ZSL-DOAS observations, we obtained ozone VCDs and provided evidence for the unprecedented ozone depletion during the Arctic spring of 2020. This is essential for the study of polar ozone changes and their effect on climate change and ecological conditions.