Inter-comparison of NO₂ column densities measured by Pandora and OMI over Seoul, Korea

Abstract

Total Vertical Column Density (VCD) of NO₂, a key component in air quality and tropospheric chemistry was measured using a ground-based instrument, Pandora, in Seoul from March 2012 to October 2013. The NO₂ measurements using Pandora were compared with those obtained by satellite remote sensing from Ozone Monitoring Instrument (OMI) where the intercomparison characteristics were analyzed as a function of measurement geometry, cloud amount and aerosol loading. The negative biases of the OMI NO₂ VCD were larger when cloud amount and Aerosol Optical Depth (AOD) were higher. The correlation coefficient between NO₂ VCDs from Pandora and OMI was 0.53 for the entire measurement period, whereas the correlation coefficient between the two was 0.74 when the cloud amount and AOD were low (cloud amount<3, AOD<0.4). The low bias of OMI data was associated with the shielding effect of the cloud and the aerosols.