Assessing Aerosol-Cloud Interactions Using Ground- and Space-Based Observations: Insights from Northern France

Aerosol-cloud interactions (ACI) remain a major source of uncertainty in anthropogenic radiative forcing, primarily due to the challenge of simultaneously observing aerosols acting as cloud condensation nuclei (CCN) and their impact on cloud microphysics. This study leverages the synergy between ground-based measurements at the ATOLL peri-urban site (Lille, Northern France) and satellite observations (CLAAS-3 SEVIRI) to quantify how variations in boundary-layer aerosol loading influence cloud droplet number concentration (n_d) and effective radius (r_e).

For the period between 2020 and 2024, collocated datasets of space- and ground-based instruments, in-situ and remote sensing, were analyzed under different conditions: filters have been applied to isolate CCN-relevant aerosols, low-level clouds, and stable atmospheric layers. Results reveal a relationship between aerosol scattering coefficient (σ_sp) related to aerosol concentration and cloud microphysical properties: n_d increases with σ_sp, while r_e decreases, in line with CCN impact on liquid clouds. The aerosol-cloud interaction indices related to n_d and r_e range from 0.11 to 0.36 and 0.07 to 0.13, respectively, depending on liquid water path (LWP) bins. These values align with previous field and satellite studies but are slightly lower, likely due to the coarse spatial resolution of SEVIRI and the predominance of winter conditions in the dataset.

This work highlights the measurable sensitivity of stratiform clouds to boundary-layer aerosol loadings in northern France and underscores the value of combining ground- and space-based observations. Future research will expand this methodology to sites with contrasting aerosol regimes and incorporate aerosol chemical composition data to further disentangle the influence of hygroscopicity and mixing state on cloud microphysical responses.