Effects of spatiotemporal O-4 column densities and temperature-dependent O-4 absorption cross-section on an aerosol effective height retrieval algorithm using the O-4 air mass factor from the ozone monitoring instrument

Abstract

In this present study, an aerosol effective height (AEH) retrieval algorithm has been developed using the O-4 air mass factor (AMF) at 477 nm from the hyperspectral Ozone Monitoring Instrument (OMI). We investigated the magnitude of change in topographical and seasonal O-4 vertical column density (VCD) in Northeast Asia and evaluated its effect on AEH retrieval accuracy using our AEH retrieval algorithm. In addition, the effect of a temperature-dependent cross-section for O-4 (TDCS) on Look Up Table (LUT)-based AEH retrieval accuracy was quantified. A comparison between the retrieved AEH and those from the NIES lidar network for the period from January 2005 to June 2009, applying both the TDCS and the seasonal and topographical O-4 VCDs, resulted in a root mean square error (RMSE) of 0.44 km for both smoke and dust aerosols. However, when both a TDCS (an O-4 absorption cross-section at a single temperature of 293 K; SCS) and a single O-4 VCD value were applied to the LUT, the RMSE for both aerosol types was calculated to be 0.52 km (0.51 km), which implies that TDCS contributes most to AEH retrieval accuracy when accurate O-4 VCDs are applied to the LUT. For smoke aerosols only, both TDCS and multiple O-4 VCD (SCS and single O-4 VCD) applications had RMSE values of 0.46 km (0.66 km). The retrieved AEHs were additionally compared with satellite-based lidar measurements. We also investigated the effects of uncertainties in our algorithm input data (e.g., O-4 VCD, TDCS, AOD, and surface reflectance) on AEH retrieval error using synthetic radiances. Large errors can be caused by uncertainties in O-4 VCD and AOD. In particular (0.4 <= AOD < 1.0), O-4 VCD uncertainty led to AEH errors 0.96 km. However, the effect of uncertainty of TDCS on AEH retrieval is much smaller than that of O-4 VCD, which agrees with a small contribution of TDCS to an improvement of AEH retrieval accuracy found in the comparison between the lidar data and the retrieved AEH with the TDCS LUT.