Estimating Top-of-Atmosphere (TOA) flux and radiance is essential for understanding Earth's radiation budget and climate dynamics. This study utilized polar nephelometer measurements of aerosol scattering coefficients at 17 angles (9-170 degrees), enabling the experimental determination of aerosol phase functions and the calculation of Legendre moments. These moments were then used to estimate TOA flux and radiance. Conducted at a tropical coastal site in India, the study observed significant seasonal and diurnal variations in angular scattering patterns, with the highest scattering during winter and the lowest during the monsoon. Notably, a prominent secondary scattering mode, with varying magnitude across different seasons, was observed in the 20-30 degrees angular range, highlighting the influence of different air masses and aerosol sources. Chemical analysis of size-segregated aerosols revealed that fine-mode aerosols were dominated by anthropogenic species, such as sulfate, nitrate, and ammonium, throughout all seasons. In contrast, coarse-mode aerosols showed a clear presence of sea-salt aerosols during the monsoon and mineral dust during the pre-monsoon periods. The presence of very large coarse-mode non-spherical aerosols caused increased oscillations in the phase function beyond 60 degrees during the pre-monsoon and monsoon seasons. This also led to a weak association between the phase function derived from angular scattering measurements and those predicted by the Henyey-Greenstein approximation. As a result, TOA fluxes and radiances derived using the Henyey-Greenstein approximation (with the asymmetry parameter as input in the radiative transfer model) showed a significant difference- up to 24% in seasons with substantial coarse-mode aerosol presence- compared to those derived using the Legendre moments of the phase function. Therefore, TOA flux and radiance estimates using Legendre moments are generally more accurate in the presence of complex aerosol scattering characteristics, particularly for non-spherical or coarse-mode aerosols, while the Henyey-Greenstein phase function may yield less accurate results due to its simplified representation of scattering behavior.

Purpose of ReviewCalculating atmospheric aerosol radiative forcing is a crucial aspect of climate change research. The aerosol scattering phase function stands out as a vital parameter for radiative forcing computations and holds significant importance in the remote sensing retrievals of aerosols. Despite its significance, research on aerosol scattering phase function measurements has been limited over the years. This review article provides a comprehensive summary of relevant studies on the measurements of aerosol scattering phase functions.Recent FindingsIn recent times, the application of imaging detection techniques in the measurement of aerosol scattering phase functions has emerged, highlighting advantages such as portability and high temporal-angular resolution. In addition, the development of aerosol retrieval algorithms facilitates a broader application of the results obtained from aerosol scattering phase function measurements in estimating aerosol physical properties and satellite retrievals.SummaryThis review introduces the measurement techniques, instruments, and retrieval algorithms associated with aerosol scattering phase functions, encompassing laboratory experiments, in situ field measurements, and remote sensing retrieval. The measurement results and related research on aerosol morphological effects and physical property retrievals have been summarized. Finally, it outlines future research prospects, suggesting improvements in instruments, experimental expansion, and enhanced data analysis and application, providing feasible suggestions for further studies.