Validation and diurnal variation evaluation of MERRA-2 multiple aerosol properties on a global scale

The Modern-Era Retrospective analysis for Research and Applications (MERRA-2) provides a spatiotemporal seamless simulation of global aerosol properties. This study focused on evaluating its diurnal AOD accuracy and variation and the performance of multi-aerosol properties (including Ångström exponent (AE), fine mode fraction (FMF), and single scattering albedo (SSA)) using AERONET measurements. The spatial distribution patterns of MERRA-2 AOD are compared with the MODIS (daytime) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO, nighttime) satellite products, respectively. The results show that MERRA-2 AOD exhibits good agreement with AERONET AOD during daytime and nighttime, with a Pearson correlation coefficient (R) exceeding 0.785, and the fraction of meeting the expected error (EE) exceeding 0.705. The accuracy of daytime AOD is comparable to that of the MODIS AOD product. Furthermore, MERRA-2 AE and FMF have a higher accuracy than MODIS products, with an R > 0.840 and an RMSE of 0.313 for AE and 0.150 for FMF. And it effectively captures the diurnal variation of aerosol properties, with an R of 0.911, 0.392, and 0.72 for AOD, AE, and FMF at different times of day compared to AERONET. Additionally, MERRA-2's ability to characterize the spatial patterns of daytime and nighttime is comparable to those of satellite products. Overall, this study provides the usage references for MERRA-2 aerosol product, highlighting its high accuracy and ability to capture diurnal variation and spatial patterns.