Extended aerosol and surface characterization from S5P/TROPOMI with GRASP algorithm. Part I: Conditions, approaches, performance and new possibilities

Atmospheric aerosols have strong impact on climate, environment, and health. To account correctly for such impact, extended aerosol characterization, including spectral Aerosol Optical Depth (AOD), Angstrom Exponent (AE), spectral Single Scattering Albedo (SSA) etc., are required to be derived globally from space-borne observations. Together with the aerosol, the Earth's surfaces are an important component of climate system, reflecting and absorbing solar and atmospheric radiation and being sources of emission of different natural aerosol, for example, sea-salt, mineral dust or organic aerosol. Since the beginning of space-borne atmospheric observation it was recognized that the most comprehensive extended aerosol and surface characterization can be achieved from multi-angular polarimetric measurements. In this paper, we show that the extended aerosol characterization can be obtained even from single viewing radiance only satellite measurements when several crucial conditions are fulfilled both for the observations and retrieval algorithm: (i) wide spectral range (for example, covering UV, VIR, NIR and SWIR spectra) providing rich spectral information about aerosol and surface; (ii) wide swath of measurements ensuring frequent overpassing over the same ground pixel to account for the different temporal variability of aerosol and surface properties as well as for angular dependence of surface reflectance; (iii) applied algorithm should be able to treat multi-temporal and multi-spatial observation accounting for spatial and temporal dependencies of aerosol and surface characteristics. The new possibilities of retrieval of aerosol and surface properties are investigated by applying the advanced GRASP (Generalized Retrieval of Atmosphere and Surface Properties) algorithm to the space-borne S5P/TROPOMI observations. The most optimal for these purposes forward and inversion approaches are discussed, and the quality of retrieved aerosol and surface properties is evaluated. The possibilities of TROPOMI/GRASP approach for aerosol extended characterization are demonstrated on several aerosol events including dust storms, biomass burning and anthropogenic aerosol pollution outbreaks in worldwide locations.