Retrieval of UV–visible aerosol absorption using AERONET and OMI–MODIS synergy: spatial and temporal variability across major aerosol environments

Abstract

Measuring spectral aerosol absorption remains a challenging task in aerosol studies, especially in the UV region, where ground and airborne measurements are sparse. In this paper, we introduce an algorithm that synergizes ground measurements with satellite observations for the derivation of spectral single scattering albedo (SSA, ωo) of aerosols in the UV-to-visible wavelength range (340–670 nm). The approach consists in explaining satellite-measured near-UV radiances (340, 354, 388 nm) by the Ozone Monitoring Instrument (OMI) and visible radiances (466, 646 nm) by the Moderate Resolution Imaging Spectroradiometer (MODIS), given the collocated ground-based Aerosol Robotic Network (AERONET) measurements of total column extinction aerosol optical depth (AOD, τ), in terms of retrieved total column wavelength-dependent SSA using radiative transfer calculations. Required information on aerosol particle size distribution is adopted from AERONET-based aerosol type-dependent seasonal climatologies specifically developed for this project. The inversion procedure is applied to about 110 AERONET sites distributed worldwide, for which continuous, long-term AERONET measurements are available. Using the derived data set, we present seasonal and regional climatology of ωo(λ) for carbonaceous, dust, and urban/industrial aerosols. The resulting UV–visible spectral dependence of ωo obtained for these three major aerosol types is found to be both qualitatively and quantitatively consistent with independent measurements reported in the literature. A comparison to standard AERONET SSA product at 440 nm shows absolute differences within 0.03 (0.05) for 40 % (65 %) of the compared observations. The derived aerosol ωo(λ) data set provides a valuable addition to the existing aerosol absorption record from AERONET by extending it to the near-UV region. Furthermore, SSA retrievals from our method at visible wavelengths and around satellite overpass time also complement the equivalent inversion available during early morning/late afternoon from AERONET. In addition to improving our understanding of spectral aerosol absorption properties, the combined UV–visible data set also offers wavelength-dependent dynamic aerosol absorption models for use in the satellite-based aerosol retrieval algorithms.