Sensitivity analysis of NO2 differential slant column density according to spatial resolution using GCAS data from the SIJAQ 2022 campaign

Abstract

The GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator (GCAS) instrument made observations over the South Korea during Satellite Integrated Joint Monitoring for Air Quality (SIJAQ) 2022 (July–August 2022) campaign aimed at collecting high-resolution remote sensing data. To investigate the impact of spatial resolution on nitrogen dioxide (NO2) retrieval from remote sensing data, the NO2 differential slant column density (dSCD) was examined using high-resolution GCAS data, which are suitable for upscaling, to identify differences related to spatial resolution. Through the GCAS NO2 dSCD, the structure at the original resolution (100 m × 200 m) was maintained even following a shift to a coarser resolution; however, it was difficult to distinguish boundary areas with large concentration differences at resolutions coarser than 1.5 km × 3 km. In the comparison of coadded NO2 dSCD and merged NO2 dSCD, the standard deviations from the merged data increased when NO2 dSCD was > 3 × 1016 molecules/cm2, such as in the high NO2 concentration cases. The slope of the scatter plot obtained using the top 25% of the data determined from the regression line tended to increase as the resolution became coarser. In addition, the average standard deviation within merged pixels at a resolution of 3 km × 6 km was twice that obtained at 400 m × 800 m resolution. Accordingly, the standard deviation of the information contained in the pixels increased when the spatial resolution became coarser.