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.

Hyperspectral observations are used to retrieve high-resolution horizontal distribution and vertical profiles of trace gases (O₃, NO₂, HCHO, and SO₂), thereby playing a vital role in monitoring the spatio-temporal distribution and transportation of atmospheric pollutants. These observations reflect air quality changes on global and regional scales, including China, thereby elucidating the impacts of anthropogenic and natural emissions on atmospheric composition and global climate change. The DaQi 02 (DQ02) satellite carries the Environmental Trace Gases Monitoring Instrument with Nadir and Limb modes (EMI-NL) onboard, which will simultaneously perform nadir and limb measurements of high-resolution ultraviolet and visible solar scattered light in the nadir and limb directions. Combined with the absorption of different trace gases in this wavelength band, this information can provide high-resolution horizontal and vertical distributions of trace gases. We examined the spectral measuring ability and instrument characteristics of both modules of EMI-NL by measuring different light sources and concentrations of the NO₂ sample gas. In the nadir module test, when the NO₂ sample gas concentration was 198 ppm and 513 ppm with scattered sunlight as the light source, the average relative errors of spatial pixels were 4.02% and 3.64%, respectively. At the NO₂ sample gas concentration of 198 ppm with the integrating sphere as the light source, the average relative error of spatial pixels was −2.26%. In the limb module test, when the NO₂ sample gas concentration was 198 ppm and 1000 ppm with the tungsten halogen lamp as the light source, the average relative errors of spatial pixels were −3.07% and 8.32%, respectively. When the NO₂ sample gas concentration was 198 ppm and 1000 ppm with the integrating sphere as the light source, the spatial pixel average errors were −3.5% and 8.06%, respectively. The retrieved NO₂ slant column density between different spatial pixels exhibited notable inconsistency in both modules, which could be used to estimate the stripe of spatial dimension. These results confirm the ability of EMI-NL to provide accurate spaceborne monitoring of NO₂ globally.

Calibrating the top-of-atmospheric reflectance measurements of spaceborne hyperspectral atmospheric composition monitoring instruments is necessary to ensure the accuracy during cloud and aerosol retrieval. Here, we present a method for calibrating full-pixel reflectance data collected by the Environmental Trace Gases Monitoring Instrument (EMI). This method compares EMI reflectance data with simulation using a radiative transfer model (RTM). To simplify the radiative transfer calculations, a clear observation situation without clouds or aerosols was chosen. Correction coefficients for each spatial dimensional pixel were obtained by comparing the EMI Earth reflectance with the simulated reflectance under clear sky conditions. The corrected reflectance data were cross-compared with Tropospheric Monitoring Instrument (TROPOMI) reflectance data, highlighting that there were relative errors of >20% at 345, 388, 425, and 440 nm before correction. After correction, however, the errors of all selected wavelength bands were < 5%, demonstrating that the developed method can help in calibrating EMI in-flight reflectance measurements.

The Environmental Trace Gases Monitoring Instrument 2(EMI-02) payload, embarked on a hyperspectral observation satellite, was launched on September 7, 2021. The satellite's transit time is 10:30 local time. This study, drawing on data from EMI-02, introduces a methodology for measuring the tropical tropospheric ozone column (TOC) using the convectivecloud-differential (CCD) method. We successfully applied this method to derive TOC in tropical regions from the EMI-02 data. The results indicate a general consistency between the EMI-02 TOC and TROPOspheric Monitoring Instrument (TROPOMI) TOC. However, owing to the difference in transit times, the TOC observed by TROPOMI at 13:30 is higher than that observed by EMI-02 at 10:30. Comparisons with ozonesonde data revealed discrepancies attributed to varying observation times, but nonetheless presented a high degree of consistency. These findings affirm the efficacy of our algorithm in providing reliable and precise TOC data. This capability is instrumental in understanding the diurnal variations of tropical TOC, where concentrations are higher in the afternoon than in the morning. The characteristics of tropical TOC varied by month. From June to October, the tropical TOC predominantly accumulated over the South Atlantic region, whereas, it tended to disperse and distribute near the 20°N latitude from November to May.