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Highlights • We introduce the SPEXone instrument for the NASA PACE mission. • We demonstrate that SPEXone has high capability for aerosol retrieval. • Polarimetric accuracy is the most important factor determining capability for aerosol retrieval. • Having many spectral measurements, it is sufficient to measure at a small number (5) of viewing angles for aerosol retrieval. • On the PACE mission, retrieval capability will be further enhanced by combining with HARP-2 and OCI. Abstract SPEXone is a Multi-Angle Polarimeter instrument that is baselined to fly on the NASA Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission, to be launched in 2022. It will perform hyper-spectral measurements of radiance and polarization in the spectral range 385–770 nm at 5 viewing angles (± 57 o , ± 20 o , 0 o ) with high accuracy (0.003) on the Degree of Linear Polarization (DoLP). Based on linear error analysis and retrievals on synthetic data, we conclude that SPEXone has the capability to significantly advance the accuracy of retrievals of optical and microphysical aerosol properties compared to past, present, and planned satellite instruments, as required for better quantification of the effect of aerosols on climate. The products that SPEXone will provide are Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA), Aerosol Layer Height (ALH), effective radius, effective variance, complex refractive index, particle number column for both the fine and coarse mode as well as a shape parameter for the coarse mode. PACE will carry two other instrument: the Ocean Color Instrument (OCI) which is the main instrument and the Hyper-Angular Rainbow Polarimeter-2 (HARP-2). The synergistic use of SPEXone with these instruments will further increase retrieval accuracy, in particular for coarse mode parameters and absorption, and will provide unprecedented capability for aerosol above cloud retrievals. [ABSTRACT FROM AUTHOR]

• PCF suite is the first dedicated satellite sensor for PM 2.5 remote sensing. • The principle of PCF composed by DPC and POSP are described. • Retrievals of aerosols and PM 2.5 by PMRS model are investigated. • The errors propagation from aerosols to PM 2.5 retrievals are discussed. Focusing on satellite remote sensing of fine particulate matter PM 2.5 from space, the polarization crossfire (PCF) strategy has been developed, which includes the PCF satellite suite and the particulate matter remote sensing (PMRS) model. Expected to be the first dedicated satellite sensor for PM 2.5 remote sensing globally, the PCF suite is composed by the Particulate Observing Scanning Polarimeter (POSP) and the Directional Polarimetric Camera (DPC) together, and will be launched on board the Chinese GaoFen-5(02) satellite in 2021. Since the cross-track polarimetric measurements of POSP fully cover the multi-viewing swath of DPC, the sophisticated joint measurements could be obtained from the PCF suite in the range of 380–2250 nm including intensity and polarization, by the means of pixel matching and the cross calibration from POSP to DPC. Based on the optimal estimation inversion framework and synthetic data of PCF, the retrieval performances of key aerosol parameters are systematically investigated and assessed for the PM 2.5 estimation by the PMRS model. For the design of inversion strategy for PCF, we firstly test the retrievals of aerosol optical depth (AOD), fine mode fraction (FMF), aerosol layer height (H) and the fine-mode real part of complex refractive index (m r f) simultaneously with surface parameters from the synthetic PCF data, and then the columnar volume-to-extinction ratio of fine particulates (VE f), the aerosol effective density (ρ f) and the hygroscopic growth factor of fine-mode particles (f (RH)) are further obtained by the corresponding empirical relationship. The propagation errors from aerosol parameters to PM 2.5 retrieval are investigated with the key procedures of PMRS model. In addition, the influences of improving calibration accuracy of PCF on PM 2.5 retrievals are discussed, as well as the retrieval feasibility of PM 10 by PCF strategy. [ABSTRACT FROM AUTHOR]