Cloud condensation nuclei concentrations derived from GRASP synergetic aerosol products for Sentinel-3/OLCI and Sentinel-5P/TROPOMI

Cloud condensation nuclei (CCN) concentrations indicate the ability of aerosols to activate into cloud droplets and therefore play an important role in aerosol–cloud interactions and their associated radiative forcings. Reliable observational constraints on CCN are essential for improving the representation of aerosol–cloud processes in climate models, yet remain challenging to obtain at adequate spatial and temporal scales.

The GRASP synergetic retrieval framework is designed to integrate complementary information from multiple satellite sensors, i.e., Sentinel-3/OLCI and Sentinel-5P/TROPOMI, enabling the retrieval of aerosol microphysical properties with enhanced spatial resolution and temporal coverage. In this study, we derived total CCN, as well as the CCN of each aerosol species, from the GRASP retrieved aerosol microphysical properties by defining CCN as the number of dry aerosol particles with radii exceeding 0.12 µm.  

Using data over 2022, we focus on Europe – the Mediterranean – Western Asia – Northern Africa as a testbed region characterized by diverse CCN distributions over both land and ocean. The obtained CCN values are evaluated against a CAMS reanalysis-derived CCN dataset (Block et al., 2024), and compared to the MODIS cloud droplet number concentration for a consistency check. The results show a robust agreement in both spatial patterns and magnitudes, particularly for biomass-burning and sulfate-dominated CCN over oceanic regions, which are especially relevant for aerosol–cloud interaction studies.

Our generated CCN dataset has been realistically applied to a case study of marine cloud perturbations associated with the 2018 Kīlauea volcanic eruption. The analysis demonstrates the capability of the dataset to capture coherent variability among sulfate aerosols, CCN, and low-level marine clouds in response to volcanic degassing, highlighting its potential for applications such as Marine Cloud Brightening research and broader evaluation and constraint of aerosol–cloud interactions in regional and global atmospheric models.