First Global Twice-Daily Ozone Profiles from Chinese Uv-Vis Satellites Via Synergistic Spectral Calibration and Retrieval

Abstract

Global ozone profiles at different diurnal overpass times from synergistic satellite retrievals offer unprecedented insights into the signatures of ozone photochemical mechanisms and atmospheric oxidation capacity. However, due to differences in instrument performance and retrieval algorithms, cross-satellite biases existed among different ozone retrievals, complicating the derivation of ozone diurnal variations. Here, we first present global twice-daily ozone profiles and ozone diurnal variations derived through synergistic calibration and retrievals from twin Chinese Environmental Trace Gases Monitoring Instruments (EMIs) with varying overpass times, onboard Gaofen-5B (GF-5B) and Daqi-1 (DQ-1) satellites. By correcting systematic reflectance biases and instrument degradation errors while estimating the measurement errors in GF-5B and DQ-1 EMI observations, we successfully enhanced the synergistic retrievals of GF-5B and DQ-1 EMI and addressed their cross-satellite biases. With correction for instrument degradation, the average biases of both GF-5B and DQ-1 EMI profiles were reduced from 14.2% and 39.5% at 16 km to less than 10% with similar altitude patterns, facilitating reliable diurnal variations in ozone profiles. The synergistic retrievals of GF-5B and DQ-1 EMI have unveiled the spatiotemporal characteristics of the diurnal variations in global ozone profiles. These variations were significant below 100 hPa, exhibiting seasonal and latitudinal dependencies and geographical patterns. We have also identified more accurate ozone formation sensitivities using ozone diurnal variations and the formaldehyde-to-nitrogen dioxide ratio (HCHO/NO2, FNR), compared to relying on daily single-temporal ozone concentrations. This synergistic method provides ideas for future multi-satellite joint monitoring of atmospheric environments, which can contribute to the understanding of diurnal variations in atmospheric chemistry and further refinement of pollution control.

Keywords: Ozone profile, Diurnal variation, remote sensing, Synergistic Retrieval, EMI