Atmospheric aerosols have an outsized influence on Earth’s climate through their interactions with light and clouds. These nanometer-scale particles scatter and absorb incoming sunlight as well as outgoing terrestrial radiation. The relative contributions of these optical processes underpin aerosols’ direct impacts on the radiative balance of our atmosphere – the ratio of solar energy absorbed to energy emitted that, when tipped, drives the climate out of equilibrium. Aerosols also nucleate cloud droplets, influencing local droplet densities, size distributions, and lifetimes which cause cascading indirect effects on climate and weather. Aerosol-light and aerosol-cloud interactions remain the largest sources of uncertainty in our best models of Earth’s radiative balance. Our current knowledge of these intricate systems is not sufficient to quantitatively capture their role in the climate crisis.
In order to improve climate predictions, we must clarify precisely how aerosols of different size and composition scatter and absorb light and nucleate cloud droplets. We must additionally determine how aging, wetting, and chemical processing of particles changes their behavior over time. Our lab is performing laboratory spectroscopy to interrogate detailed atmospheric aerosol microphysics. To correlate aerosol size and composition with optical behavior, we perform spectroscopy on a well-defined sample: the isolated single particle. We are harnessing broadband cavity-enhanced spectroscopy for measurements of the optical properties, droplet nucleation dynamics, and chemical aging of electrodynamically-trapped atmospherically-relevant aerosols.
We are also collaborating with Prof. Luc Deike’s group in the Princeton Department of Mechanical and Aerospace Engineering to develop a new rapid expansion cloud chamber to study wetting, icing, aggregation, and aging of aerosol ensembles under atmospheric conditions.
Current Project Members
Dr. Cole Sagan
Arden Floyd
Recent Publications
- C. R. Sagan, G. F. Pokrifka, S. M. Koblensky, M. A. Erinin, I. Ahmed, N. Jeevanjee, L. Deike, and M. L. Weichman. Tracking water vapor homogeneous nucleation and droplet growth with spectroscopy and holography in a free expansion cloud chamber. arXiv 2605.21509 (2026).
- M. A. Erinin, C. R. Sagan, I. Ahmed, G. F. Pokrifka, N. Jeevanjee, M. L. Weichman, and L. Deike. Droplet heterogeneous nucleation in a rapid expansion aerosol chamber. Rev. Sci. Instrum. 96, 055104 (2025).