GEMS Ozone profile retrieval: impact of version 3.0 improvements and validations during ACCLIP and ASIA-AQ campaigns.

In the troposphere, ozone is a powerful greenhouse gas and air pollutant, harming human health and ecosystems. In the stratosphere, ozone is essential for protecting life on Earth by absorbing harmful ultraviolet (UV) radiation from the Sun. It also plays a key role in maintaining the Earth's radiative balance and stratospheric temperature structure. Monitoring both layers supports tracking pollutant transport, climate regulation, and environmental health.The Geostationary Environmental Monitoring Spectrometer (GEMS) onboard the GEO-KOMPSAT-2B satellite provides high temporal and spatial resolution data on ozone, its precursors (NO₂ and HCHO), SO2, and aerosols over East Asia. The two primary ozone products available from GEMS are total column ozone (O3T) and ozone profile (O3P). The total column ozone is derived using the historical TOMS look-up table algorithm, while the ozone profile product, offers detailed vertical information across 24 atmospheric layers, with an optimal estimation based inversion.

This study describes improvements in the GEMS ozone profile retrieval leading to version 3.0. Compared to 2.X versions, the key updates are as follows: (1) irradiance offset correction are implemented to address the solar diffuser-induced seasonal variation and optical degradation-induced long-term variation, (2) soft calibration is applied to correct residual radiometric biases in the normalized radiances, (3) wavelength shifts are corrected for both radiance and irradiance, and (4) the instrument response function is updated from pre-flight measurements to on-orbit simulations. This has brought the tropospheric O₃ closer to the observations from OMI and TROPOMI. Furthermore, the integrated total column O₃ demonstrates better agreement with ground-based Pandora observation compared to the GEMS O3T product. We also evaluate the information content of ozone profiles in summer during the 2022 ACCLIP campaign and in winter during the 2024 ASIA-AQ campaign. We will discuss how the GEMS ozone profile product adds value in understanding the meteorological modulation of summertime ozone in the troposphere and the dynamical processes affecting wintertime ozone in the upper troposphere and stratosphere.