Nitrogen dioxide (NO₂) is a major air pollutant. Tropospheric NO₂ vertical column densities (VCDs) retrieved based on sun-synchronous satellite instruments have provided abundant NO₂ data for environmental studies, but such data are limited by insufficient temporal sampling (e.g., once a day). The Geostationary Environment Monitoring Spectrometer (GEMS) launched in February 2020 allows retrieval of NO­₂ at an unprecedented high temporal resolution. Here we present a research product for tropospheric NO₂ VCDs referred to as POMINO-GEMS. We develop a hybrid method combining GEMS and TROPOMI observations as well as GEOS-Chem simulations to generate hourly tropospheric NO₂ slant column densities (SCDs). We then derive tropospheric NO₂ air mass factors (AMFs) with explicit corrections for the anisotropy of surface reflectance and aerosol optical effects, through pixel-by-pixel radiative transfer calculations. Prerequisite cloud parameters are retrieved with O₂-O₂-based cloud algorithm by using ancillary parameters consistent with those used in NO₂ AMF calculations. Initial data of POMINO-GEMS tropospheric NO₂ VCDs for June–August 2021 exhibit strong hotspot signals over megacities and distinctive diurnal variations over polluted and clean areas. POMINO-GEMS NO₂ VCDs agree well with our POMINO-TROPOMI v1.2.2 product (R = 0.96, and NMB = 6.9%). Comparison with MAX-DOAS VCD data at five sites shows a small bias of POMINO-GEMS (NMB = –12.2%); yet the correlation for diurnal variation varies from -0.57 to 0.86, suggesting strong location-dependent performance. Surface NO₂ concentrations estimated from POMINO-GEMS VCDs are consistent with measurements from the Ministry of Ecology and Environment of China at 855 sites (NMB = – 5.6%, and R = 0.96 for diurnal correlation averaged over all sites). POMINO-GEMS will be made freely available for users to study the spatiotemporal variations, sources and impacts of NO₂.
 

satellite remote sensing,GEMS,tropospheric NO2 VCDs