Assessing the performance of the Copernicus Atmosphere Monitoring Service reanalysis: a comprehensive analysis of...

This study presents a comprehensive performance evaluation of the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis total aerosol optical depth (AOD) over India. We first use AOD observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) for the period 2003 to 2020 to evaluate the spatial and temporal patterns of AOD simulated by CAMS. Owing to the lack of aerosol speciation in MODIS, we complement it with the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2), which provides individual aerosol species such as dust, black carbon, organic carbon, sulfate, and sea salt. The results demonstrate that CAMS exhibit high AOD, similar to MODIS, particularly over the Indo-Gangetic Plain, despite some underestimations in total AOD. Temporal trend analysis indicates that CAMS exhibited rising AOD trends similar to MODIS across Indian regions, though discrepancies arise in western India during pre-monsoon and monsoon seasons. Spatial differences in different aerosol species between CAMS and MERRA-2 suggest potential differences in model parameterizations. Principal component analysis (PCA) further reveals that the first mode of AOD (PCA-1) in both CAMS and MERRA-2 shows a strong correlation (> 0.7) with MODIS during all seasons except pre-monsoon. This enhances our understanding of aerosol distribution and its implications for regional climate and air quality. Consequently, this study provides valuable insights into the performance of CAMS, supporting advancements in climate modeling, air quality management, and environmental policy-making in densely populated and rapidly developing regions.