Early results of HONO retrievals from the Geostationary Environment Monitoring Spectrometer (GEMS)

The Geostationary Environment Monitoring Spectrometer (GEMS), the world's first geostationary environment satellite launched in February 2020, performs hyperspectral observations in UV-visible wavelengths. In this study, the nitrous acid (HONO) column is retrieved from the GEMS measurements. The retrieval algorithm is based on the direct fitting method developed at the Smithsonian Astrophysical Observatory (SAO). To optimize the spectral fitting, we perform the sensitivity test of the slant column density (SCD) uncertainties, fitting residuals, and correlations between fitting parameters on the different fitting windows. The SCD, obtained from the optimized algorithm, is converted into vertical column density (VCD) using the geometric air mass factor (AMF). This retrieval provides the diurnal variation of HONO over Asia, which is obtained from the spaceborne spectrometer for the first time. Since HONO contributes to air pollution and tropospheric ozone generation, as a source of hydroxyl radicals (OH), so it is expected to improve the understanding of urban air pollution characteristics using these results. Besides, we describe the enhanced HONO column amounts from wildfire observed over the East Sea in South Korea in March 2022. These results can be utilized to investigate the nature of wildfire sources and vegetation types, especially through the comparison with NOX.