Nanoscale Visualization and Understanding of Atmospheric Aerosol Dissolution Kinetics in Aqueous Organic Droplets

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The Environmental Chemical Sciences Program of the NSF Division of Chemistry funds this research led by Professors Akua Asa-Awuku and Taylor Woehl. The project studies the interactions between organic vapors in the atmosphere and atmospheric particles (also known as aerosols). Of particular interest is the ability of these aerosols to affect cloud formation, which in turn is important for the Earth's climate. Atmospheric particles are complex mixtures of water-soluble and insoluble compounds. Chemists want to determine the ability of aerosols to act as effective cloud condensation nuclei (CCN), but chemical and physical diversity results in complicated interactions between aerosols and clouds. Models often assume that water-insoluble organic aerosols cannot act as CCN. The processes by which aerosols take up water and form droplets are not fully known. It is assumed that partially soluble particles must first dissolve and enter the water phase before readily adding more water. However, this phenomenon has not been directly seen. The project directly visualizes the processes that occur during CCN activation of water-insoluble aerosols on the nanometer scale. From these observations, the team derives a new mechanistic understanding of CCN behavior of this important class of aerosols. The project provides opportunities for engaging a diverse STEM workforce. Both Professor Asa-Awuku and Professor Wohl mentor K-12 students and engage with existing STEM outreach programs at the University of Maryland College Park.This project focuses on the impact of organic vapors on the CCN activity of water-insoluble aerosols and the nanoscale dynamic processes that occur during droplet condensation. The project directly visualizes nanoscale dynamic processes that occur during CCN activation. These observations are used to derive new mechanistic understanding of the CCN behavior of this important class of aerosols. The team utilizes a novel single particle technique, liquid cell transmission electron microscopy, to visualize particle dissolution kinetics and droplet growth kinetics in real time with nanometer scale spatial resolution. The electron microscopy data are directly correlated with quantitative measurements of CCN activation using controlled aerosol characterization techniques. Together these data are expected to reveal the series of chemical and physical processes occurring during CCN activation of water insoluble aerosols. These insights will contribute to a broader theoretical framework for cloud-aerosol interactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.