[A-AS07] Atmospheric Chemistry

[AAS07-05] Geostationary Environment Monitoring Spectrometer GEMS: Ozone, NO₂, and HCHO version 1.0 data validation and updates

*Yugo Kanaya¹, Yongjoo Choi², Hisahiro Takashima³, Kihong Park⁴, Yoshiaki Endo¹, Limseok Chang⁵, Jae-Hwan Kim⁶, Hanlim Lee⁷, Rokjin Park⁸, Jhoon Kim⁹ (1.Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2.Hankuk University of Foreign Studies (HUFS), 3.Fukuoka University, 4.Gwangju Institute of Science and Technology, 5.National Institute of Environmental Research, 6.Pusan National University, 7.Pukyong National University, 8.Seoul National University, 9.Yonsei University)

Keywords:Atmospheric Chemistry, Geostationary Satellite, Air Quality, Validation

Korean geostationary environment monitoring spectrometer (GEMS) launched in February 2020 has started first-as-ever atmospheric environment monitoring from satellites with an hourly time resolution (Kim et al., 2020). After careful instrumental characterization and algorithm development, their official version 1.0 data from January 2021 became available for validation team members, including us who formed an official validation team GnGval. Here we present the validation results of the version 1.0 Level 2 (L2) products of total ozone, NO₂ and formaldehyde (HCHO) using data till August/September 2022, and the most recent status of the improved version 2 data (https://nesc.nier.go.kr/). Our validation was based on the MAX-DOAS network observations at Yokosuka, Fukue, Cape Hedo, Yongin, and Gwangju and a Pandora spectrometer at Yokosuka. The NO₂ and HCHO tropospheric vertical column densities derived from MAX-DOAS and Pandora strongly correlated (R > 0.89) and agreed to each other to within 22%. The total NO₂ column densities from GEMS at urban sites showed high correlations (R~0.8 at Yokosuka) with MAX-DOAS/Pandora but had positive intercepts (~10 x 10¹⁵ molecules cm^-2) to be unexplained by the stratospheric NO₂ amount. At Fukue and Cape Hedo, the correlations were poorer. This might be from unreasonable a priori profiles assumed for version 1.0 NO₂ retrievals; improvement may be expected with the version 2 products. The levels of HCHO from GEMS basically agreed with MAX-DOAS/Pandora at Yokosuka though with a weaker correlation (R~ 0.33-0.35). For total ozone, GEMS v1.0 showed high correlation(R²=0.94) against Pandora at Yokosuka but had a small negative bias (~6% or less), with the slope of the regression line of 0.91. A solar zenith angle dependence of the negative bias was found, commonly related to seasons and time of day; improvement with later versions would deserve attention.

Kim, J. et al. (2020). New Era of Air Quality Monitoring from Space: Geostationary Environment Monitoring Spectrometer (GEMS), Bull. Amer. Meteorol. Soc., 101(1), E1-E22, https://doi.org/10.1175/BAMS-D-18-0013.1