Aerosol optical properties and composition retrieved from NASA PACE polarimetric measurements using FastMAPOL algorithm

NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, launched in February 2024, carries two multiangle polarimeters (MAPs): the UMBC Hyper-Angular Rainbow Polarimeter (HARP2) and SRON Spectropolarimeter for Planetary Exploration One (SPEXone). The two instruments provide complementary measurement capabilities, with HARP2 observing a wide swath at many viewing angles and four key wavelengths, while SPEXone collects hyperspectral data over a wider spectral range including UV wavelengths, but for a narrow swath at five key viewing geometries. Synergistic MAP measurements with rich information on aerosol microphysics provide unprecedented opportunities to advance aerosol studies and access their impacts on global climate.

The first part of this presentation will include overview of the operational aerosol retrievals over global ocean from PACE MAP measurements using FastMAPOL (Fast Multi-Angular Polarimetric Ocean color) joint retrieval algorithm highlighting several aspects of global aerosol distribution for the first two years of PACE launch. The second part will include the results from the research version of FastMAPOL with improved aerosol representation based on aerosol components called FastMAPOL/component. The representation includes Black Carbon, Brown carbon, non-absorbing insoluble and non-absorbing soluble in the fine mode and Sea Salt and non-spherical dust are in the coarse mode. The aerosol components with known size distribution and refractive index spectra are mixed externally with retrievable volume fraction of each component along with total aerosol loadings. The retrieval algorithm can be applied to measurements in several configurations of MAPs such as HARP2-only, SPEXone-only, and combined HARP2+SPEXone observations. Several validation and cross comparison results will be discussed:

• Retrieved aerosol optical properties validated against the measurements from several AERONET-OC stations across the globe.
• The qualitative verification of aerosol components retrieved in biomass burning, desert dust, and industrial aerosol dominated regions and their intercomparison with the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) assimilated aerosol components.
• Case studies including aerosol components retrieved in the vicinity of Los Angeles wildfire and volcano Gubbi in the Ethiopia's Afar region.
• Cross comparisons of the wind speed retrievals with MERRA-2 reanalysis data.

References:

• Gao, M., Franz, B. A., Zhai, P. W., Knobelspiesse, K., Sayer, A. M., Xu, X., ... & Werdell, P. J. (2023). Simultaneous retrieval of aerosol and ocean properties from PACE HARP2 with uncertainty assessment using cascading neural network radiative transfer models. Atmospheric Measurement Techniques, 16(23), 5863-5881.

• Aryal, K., Zhai, P. W., Gao, M., Franz, B. A., Knobelspiesse, K., & Hu, Y. (2024). Machine learning based aerosol and ocean color joint retrieval algorithm for multiangle polarimeters over coastal waters. Optics Express, 32(17), 29921-29942.