The Effects of Aerosol on the Retrieval Accuracy of NO2 Slant Column Density

Abstract

We investigate the effects of aerosol optical depth (AOD), single scattering albedo (SSA), aerosol peak height (APH), measurement geometry (solar zenith angle (SZA) and viewing zenith angle (VZA)), relative azimuth angle, and surface reflectance on the accuracy of NO₂ slant column density using synthetic radiance. High AOD and APH are found to decrease NO₂ SCD retrieval accuracy. In moderately polluted (5 × 10¹⁵ molecules cm⁻² < NO₂ vertical column density (VCD) < 2 × 10¹⁶ molecules cm⁻²) and clean regions (NO₂ VCD < 5 × 10¹⁵ molecules cm⁻²), the correlation coefficient (R) between true NO₂ SCDs and those retrieved is 0.88 and 0.79, respectively, and AOD and APH are about 0.1 and is 0 km, respectively. However, when AOD and APH are about 1.0 and 4 km, respectively, the R decreases to 0.84 and 0.53 in moderately polluted and clean regions, respectively. On the other hand, in heavily polluted regions (NO₂ VCD > 2 × 10¹⁶ molecules cm⁻²), even high AOD and APH values are found to have a negligible effect on NO₂ SCD precision. In high AOD and APH conditions in clean NO₂ regions, the R between true NO₂ SCDs and those retrieved increases from 0.53 to 0.58 via co-adding four pixels spatially, showing the improvement in accuracy of NO₂ SCD retrieval. In addition, the high SZA and VZA are also found to decrease the accuracy of the NO₂ SCD retrieval.