Changes in aerosol concentrations can modify cloud brightness, producing a strong but poorly constrained influence on Earth's energy balance. Because cloud reflectivity depends on the size distribution of cloud droplets, and aerosol size strongly governs activation into droplets, one might expect cloud properties to be sensitive to aerosol size distributions. Here we show, through a combination of cloud chamber experiments and high-resolution simulations, that cloud microphysical and optical properties are often insensitive to aerosol size. Detectable impacts on cloud optical properties occur only under weak convective forcing and high aerosol concentrations. These results indicate that, in most conditions, cloud reflectivity can be predicted from aerosol number alone without detailed knowledge of aerosol size distributions, providing new constraints on how aerosol perturbations affect climate.
@article{arxiv.2511.15832,
title = {Cloud droplet size distribution and optical properties only weakly linked to aerosol size},
author = {Kadja Flore Gali and Hamed Fahandezh Sadi and Jesse C. Anderson and Payton Beeler and Aaron Wang and David Richter and Raymond A Shaw and Fan Yang and Will Cantrell and Laura Fierce},
journal= {arXiv preprint arXiv:2511.15832},
year = {2025}
}