Gueymard, CA; Yang, DZ (2020). Worldwide validation of CAMS and MERRA-2 reanalysis aerosol optical depth products using 15 years of AERONET observations. ATMOSPHERIC ENVIRONMENT, 225, 117216.

This contribution compares 3-hourly estimates of aerosol optical depth at 550 nm (AOD550) and Angstrom exponent (AE) from two similar reanalysis models, ECMWF's CAMS and NASA's MERRA-2, to reference remotesensed observations from the worldwide AERONET network during the period 2003-2017. All data points are first subjected to a thorough quality assessment analysis. All valid AOD550 reanalysis estimates are also corrected to account for the difference in elevation between the nominal grid cell size (0.5. 0.625.) and the reference AERONET ground station. Comparative results are obtained both on a continental basis and on climate disaggregation basis using the Koppen-Geiger (KG) classification. Based on 793 AERONET stations and.1.8 million valid 3-h data points, it is found that CAMS and MERRA-2 behave relatively similarly, with however some regional differences, depending on continent or KG class. AOD550's root-mean-square error (RMSE) varies in the range 0.031-0.268 for CAMS and 0.017-0.232 for MERRA-2, depending on continent. Globally, MERRA-2 performs better than CAMS, achieving an RMSE of 0.126, as compared to 0.144 for CAMS. In contrast, the two reanalyses have very similar overall RMSEs for AE, i.e., 0.382 for CAMS and 0.378 for MERRA-2. For local or regional studies, these results allow users to select the best possible source of data. For global studies, both aerosol products are found appropriate, albeit with different statistical properties.