Models and measurements of surface properties of single microdroplets are essential for accurate predictions of the surface-based processes aerosol particles undergo in the atmosphere, such as CCN and IN activation, heterogeneous chemical reactions, and condensational growth. Despite their extensive impacts on climate and weather, their overall uncertainty remains large, partially due to a lack of supporting data of surface properties of multi-component aqueous solutions containing mixtures of organics and inorganics. With single particle techniques, we observe how aqueous chemical mixtures change their surface tensions and compositions as a function of relative humidity and temperature. While data is limited in general, they are much more commonly provided at lab temperatures, i.e. without temperature control. Therefore, temperature-controlled measurements at atmospherically accurate cold temperatures are a necessary step towards producing relevant data to inform global aerosol models.  In this research, individual microdroplet surficial properties and processes are explored using a dual balance quadrupole electrodynamic balance with temperature control. Results will be presented such as measurements of the hygroscopicity of aqueous microdroplets containing mixtures of inorganics and organics to mimic the chemical complexity of real atmospheric aerosols. Atmospheric aerosols commonly exhibit liquid-liquid phase separation, resulting in an organic surface layer that can impede diffusion of water and other vapor chemical species. Hygroscopicity of homogeneous and phase-separated organic aerosol will be presented. Surface tension is a proxy for the particle surface’s chemical composition, and it influences particle activation to clouds. A thermodynamic model using adsorption isotherms and statistical mechanics at the interface to accurately model multi-component aqueous solutions will be presented. This builds on our recent models which were successful in predicting surface tensions of mixtures using the binary parameters, based on prior work that reduced the parameters of the binary models down to zero. Therefore, the mixture surface tension model uses zero empirical parameters, but instead relies on molecular properties that trend well with the model parameters. Predictions at cold temperatures will be presented for binary and multi-component solutions. The thermodynamic model predictions are supported by single particle measurements.

Exploring surfaces of multi-component aqueous microdroplets in a double-balance electrodynamic balance

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.