Atmospheric aerosol particles play a large role in climate and air quality. Sea spray aerosol (SSA), transferred to the atmosphere via bubble bursting at the ocean surface, represent a large fraction of naturally-occurring aerosol particles. Thus, understanding the physico-chemical properties of SSA is therefore of extreme relevance towards understanding atmospheric and climate processes. SSA is known to have a large organic fraction in addition to the inorganic components of ocean water. The organic fraction can include biologically-derived saccharides, among other compounds. In controlled laboratory studies, compounds found in SSA can take on a wide range of physical states, including glassy and gelatinous. For example, aqueous monosaccharide aerosols are known to exist as ultra-viscous or glassy particles, dependent on the RH. However, a comprehensive understanding of the rheological properties (such as viscosity) of mixed organic-inorganic aerosol particles remains lacking. In particular, the role of gel formation is poorly understood because the solute concentration in aerosol micro-environments can greatly exceed what is possible in a bulk solution. New micro-analytical techniques are thus necessary to fully explore the rheological properties of aerosol particles under atmospheric conditions.<br/> <br/>Here, we present a new experimental technique to probe the micro-rheological properties of levitated aerosol particles and explore gel formation in aerosols. In order to experimentally characterize the viscosity and gel structure of various organic-inorganic mixtures in aerosol form, electrostatically induced collisions of levitated droplets composed of known saccharide-salt composition were performed using a dual-balance quadrupole electrodynamic balance. Charged aerosol droplets were radially confined within the quadrupole trap where counterbalance electrodes then vertically levitated the droplets in a contactless environment. With the inclusion of two counterbalance electrodes, droplets of opposite polarity were trapped and equilibrated under a given RH and then subsequently merged. The viscosity and/or phase of the droplet was then determined by various optical imaging techniques. We demonstrate that aerosols that contain both organic and certain inorganic salt components can exist in a gelatinous phase. The technical details of our newly developed micro-analytical technique will be discussed along with the micro-rheological results. <br/>

Probing the rheology of model sea spray aerosol particles using a dual-balance linear quadrupole trap as a micro-analytical tool

2019 Fall National Meeting

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