Retrieval of aerosol components directly from satellite and ground-based measurements

Abstract

Abstract. This study presents a novel methodology for the remote monitoring of aerosol components over large spatial and temporal domains. The concept is realized within the GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm to directly infer aerosol components from the measured radiances. The observed aerosols are assumed to be mixtures of hydrated soluble particles embedded with black carbon, brown carbon, iron oxide, and other (non-absorbing) insoluble inclusions. The complex refractive indices of the dry components are fixed a priori (although the refractive index of the soluble host is allowed to vary with hydration), and the complex refractive indices of the mixture are computed using mixing rules. The volume fractions of these components are derived along with the size distribution and the fraction of spherical particles, as well as the spectral surface reflectance in cases when the satellite data are inverted. The retrieval is implemented as a statistically optimized fit in a continuous space of solutions. This contrasts with most conventional approaches in which the type of aerosol is either associated with a pre-assumed aerosol model that is included in a set of look-up tables, or determined from the analysis of the retrieved aerosol optical parameters (e.g., single scattering albedo, refractive index, among others, provided by the AERONET retrieval algorithm); here, we retrieve the aerosol components explicitly. The approach also bridges directly to the quantities used in global chemical transport models. We first tested the approach with synthetic data to estimate the uncertainty, and then applied it to real ground-based AERONET and spaceborne POLDER/PARASOL observations; thus, the study presents a first attempt to derive aerosol components from satellite observations specifically tied to global chemical transport model quantities. Our results indicate aerosol optical characteristics that are highly consistent with standard products (e.g., R of ∼0.9 for aerosol optical thickness) and demonstrate an ability to separate intrinsic optical properties of fine- and coarse-sized aerosols. We applied our method to POLDER/PARASOL radiances on the global scale and obtained spatial and temporal patterns of the aerosol components that agree well with existing knowledge on aerosol sources and transport features. Finally, we discuss limitations and perspectives of this new technique.

Climatology of Fine and Coarse Mode Aerosol Optical Thickness Over East and South Asia Derived From POLDER/PARASOL Satellite

“…The GRASP/Component version of the GRASP algorithm was applied to POLDER/PARASOL over the ESA region aiming climatological analysis of fine and coarse mode AOT and fine mode aerosol fraction. The component retrieval approach was used because it is expected to improve separating characterization of fine and coarse size modes and optimizing retrieval stability (Li et al, 2019). This is in addition to the original goal of this development—retrieval of aerosol component fractions.…”

“…A full description of the “forward model” and “numerical inversion” modules can be found in Dubovik et al (2011). Here we only provide a general description of the GRASP/Component approach, which is developed to retrieve aerosol optical properties and aerosol component fractions assumed in fine and coarse modes, and the detailed description is provided in Li et al (2019).…”

Constraining global aerosol emissions using POLDER/PARASOL satellite remote sensing observations

“…The assumption of external mixing of spherical particles is adopted in our inversion, as it is commonly done in most CTMs. It should be noted, however, that the particle morphologies and mixing states could have strong affects on scattering and absorption properties, thus affecting mass to optical conversion (Liu and Mishchenko, 2018). For example, the "lensing effect" of less absorbing components coated on BC could amplify total aerosol absorption (Lesins et al, 2002).…”

Retrieval of aerosol properties from Airborne Hyper-Angular Rainbow Polarimeter (AirHARP) observations during ACEPOL 2017

“…In order to achieve seamless global coverage, we need to rely on satellite remote sensing to characterize the global aerosol system, including particle properties. Most aerosol products retrieved from satellite instrument data are limited to AOD or qualitative aerosol type (Diner et al, 2008;Kahn et al, 2009;Lenoble et al, 2010;Levy et al, 2013;Limbacher and Kahn, 2019;Martonchik et al, 2002), whereas a multi-angle polarimeter (MAP) has enough information content to retrieve particle properties with a greater degree of accuracy (Dubovik et al, 2011;Hasekamp and Landgraf, 2007;Knobelspiesse et al, 2012;Mischenko et al, 2002;Mishchenko and Travis, 1997). A MAP instrument looks at Earth scenes at different viewing angles and measures the angular scattering and polarization of reflected light after interacting with Earth's surface, atmospheric molecules, clouds, and aerosols.…”