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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-2
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-2
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Feb 2019

Research article | 04 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Description of a formaldehyde retrieval algorithm for the Geostationary Environment Monitoring Spectrometer (GEMS)

Hyeong-Ahn Kwon1, Rokjin J. Park1, Gonzalo González Abad2, Kelly Chance2, Thomas P. Kurosu3, Jhoon Kim4, Isabelle De Smedt5, Michel Van Roozendael5, Enno Peters6,a, and John Burrows6 Hyeong-Ahn Kwon et al.
  • 1School of Earth and Environmental Science, Seoul National University, Seoul, Republic of Korea
  • 2Atomic and Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
  • 3Earth Science, Jet Propulsion Laboratory, Pasadena, California, USA
  • 4Department of Atmospheric Sciences, Yonsei University, Seoul, Republic of Korea
  • 5Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
  • 6Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • anow at: DLR – Institute for protection of maritime infrastructures, German Aerospace Center, Bremerhaven, Germany

Abstract. We describe a formaldehyde (HCHO) retrieval algorithm for the Geostationary Environment Monitoring Spectrometer (GEMS) that will be launched by the Korean Ministry of Environment in 2019. The algorithm comprises three steps: pre-processes, radiance fitting, and post-processes. The pre-processes include a wavelength calibration, and interpolation and convolution of absorption cross-sections; radiance fitting is conducted using a non-linear fitting method referred to as basic optical absorption spectroscopy (BOAS); and post-processes include air mass factor calculations and bias corrections for stripe patterns, background HCHO, and latitudinal biases. In this study, several sensitivity tests are conducted to examine the retrieval uncertainties using the GEMS HCHO algorithm. We evaluate the algorithm with the OMI Level 1B irradiance/radiance data by comparing our retrieved HCHO column densities with OMI HCHO products of the Smithsonian Astrophysical Observatory (OMHCHO) and the Belgian Institute for Space Aeronomy (OMI BIRA). Results show that OMI HCHO slant columns retrieved using the GEMS algorithm are in good agreement with OMHCHO, with correlation coefficients of 0.77–0.91 and regression slopes of 0.92–1.04 for March, June, September, and December 2005. Spatial distributions of HCHO slant columns from the GEMS algorithm are consistent with the OMI BIRA products, but have relatively poorer correlation coefficients of 0.52 to 0.76 compared to those against the OMHCHO products. Also, we compare the satellite results with ground-based MAX-DOAS observations. OMI GEMS HCHO vertical columns are by 0.8–30 % lower than those of MAX-DOAS at Haute-Provence Observatory (OHP) in France, Bremen in Germany, and Xianghe in China. We find that the OMI GEMS retrievals have less bias than the OMHCHO and OMI BIRA products for OHP and Bremen in comparison with MAX-DOAS.

Hyeong-Ahn Kwon et al.
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Hyeong-Ahn Kwon et al.
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Latest update: 21 Apr 2019
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Short summary
The Geostationary Environment Monitoring Spectrometer (GEMS) will be launched by South Korea in 2019, and it will measure radiances ranging from 300 to 500 nm every hour with a fine spatial resolution of 7 × 8 km2 over Seoul in South Korea to monitor column concentrations of air pollutants including O3, NO2, SO2, and HCHO, and aerosol optical properties. This paper describes a GEMS formaldehyde retrieval algorithm including a number of sensitivity tests for algorithm evaluation.
The Geostationary Environment Monitoring Spectrometer (GEMS) will be launched by South Korea in...
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