Aerosols influence cloud properties through multiple pathways, yet their overall impact remains one of the largest uncertainties in climate science. Aerosols can modify cloud microphysics directly by acting as cloud condensation nuclei (CCN), and indirectly through radiative and thermodynamic feedbacks. The net effect depends on aerosol type, concentration, and the surrounding meteorological conditions.

Our investigations using satellite observations and ground-based measurements highlight the strong regional and environmental dependence of aerosol–cloud interactions. In polluted continental regions such as northern India and eastern China, increased aerosol loading often stabilizes the lower atmosphere, enhancing cloud droplet collision–coalescence processes and leading to larger cloud droplets with more aerosols — a manifestation of the anti-Twomey effect. In contrast, over clean maritime regions, higher aerosol concentrations typically reduce cloud droplet size, consistent with the Twomey effect, and do so without substantially altering atmospheric thermodynamics. Furthermore, our results provide clear evidence that radiative effects of absorbing aerosols can feed back on cloud development by modifying temperature and stability profiles. This radiative pathway can, under certain conditions, reverse the conventional Twomey effect and produce a positive correlation between aerosols and droplet size. Together, these findings emphasize that aerosol–cloud interactions cannot be characterized by a single global relationship. Instead, they must be understood within the context of aerosol composition, background thermodynamics, and radiative forcing. These insights are essential for improving the representation of aerosol–cloud interactions in climate models and for reducing uncertainties in climate projections.