Bradley Parsons

Bradley Parsons, Ph.D.


Bradley Parsons, Ph.D.
Assistant Professor
Physical Chemistry

Hixson-Lied Science Building 264

Bradley Parsons

In our laboratory we are interested in the processing of atmospheric aerosol. Atmospheric processing continually alters the aerosol's chemical and physical properties. These composition changes complicate the accurate prediction of the aerosol contribution to climate change. We are specifically interested in aerosol consisting of both an aqueous component and an organic component. Such aerosol is common in both marine and terrestrial environments. The aqueous and organic components separate to form an inverse micelle having an aqueous core with the organic fraction located on the surface.

Single aerosol is confined using optical tweezers. The confined aerosol is then exposed to atmospheric gases such as H2O or to the OH radical. The atmospheric gases adsorb to the aerosol and may undergo subsequent reaction either heterogeneously at the aerosol surface or homogeneously after diffusion of the gas into the bulk aerosol. In our experiment, we record Raman scattered light from the aerosol. The Raman spectrum is a useful tool to determine the aerosol composition. For instance in a water uptake experiment, we can use the OH or OD stretching modes to determine the amount of H2O that has been adsorbed by an initially isotopically pure D2O droplet. Furthermore, by recording the Raman spectrum as a function of time we can obtain kinetic information on the gas uptake mechanism.

In conjunction with our experimental studies, we use molecular dynamics simulations (AMBER 9) to assist in the interpretation of experimental data. Molecular dynamics simulations provide adsorption free energies for organic species onto a water surface. By combining the adsorption free energy with uptake kinetics, we can determine mass accommodation for the organic species onto the aerosol.

Currently, we have trapped 8 mm and 16 mm polystyrene spheres using the optical tweezers. The video (below) shows a 16 mm polystyrene sphere that is initially confined in the optical trap. The motion of the sphere results from blocking and unblocking the confinement laser. Currently, we are working on molecular dynamics simulations for small alcohols on water surfaces to compare our free energies with those from the literature. In addition, we have recently begun to construct an OH radical source and detection system for planned experiments to explore reactivity with the organic component of the aerosol.


Ph.D. (2001) The University of Chicago
M.S. (1997) The University of Chicago
B.A. (1996) Blackburn College