Validation of GEMS tropospheric NO2 with the GEMS IUP-UB NO2 product, the TROPOMI NO2 product, and ground-based DOAS measurements

Nitrogen dioxide (NO2) is one of the most important air pollutants in the troposphere. NO2 can be retrieved by differential optical absorption spectroscopy measurements, which can be performed from various platforms. Measurements from low earth satellites in sun-synchronous orbits provide a global overview and have already contributed valuable insights into understanding NO2. The latest instrument, TROPOMI, with its high spatial resolution of 3.5 x 5.5 km2, has given new opportunities to disentangle and analyze NOx sources. However, instruments in low-earth orbits usually provide only one measurement per day at each location. To achieve diurnal cycles of trace gases, instruments on geostationary satellites are needed. The Korean instrument GEMS on GK2B, launched in February 2020, is the first instrument in geostationary orbit, delivering hourly daytime observations of NO2 with a spatial resolution of 3.5 x 8 km2 over a large part of Asia. In this study, one year of tropospheric NO2 vertical column densities (VCDs) of the operational GEMS product are compared to the scientific GEMS IUP-UB NO2 VCD product, the operational TROPOMI NO2 VCD product, and ground-based DOAS measurements in Korea. The diurnal variation of NO2 observed by GEMS is compared to the diurnal variation observed at several ground-based MAX-DOAS stations located in different pollution regimes in Korea. The large variety of observed diurnal cycles are interpreted regarding potential influencing factors. In this respect, the ERA5 10 m wind data provide valuable insights into the influence of transport effects on the tropospheric NO2 VCD depending on station location and seasonality.