Meet Sarah Suda Petters, NSF Postdoctoral Fellow at the University of North Carolina at Chapel Hill.
B.S., Physics 2008
M.S., Atmospheric Science 2011
Ph.D., Atmospheric Science 2015
When Petters entered graduate school, the aerosol research group offered her a stipend for her work, which led her to her current field of study. For over eight years, Petters has been studying atmospheric aerosol particles, which are suspensions of nano-scale particles with diameters of roughly 10 to 1000 nanometers. These ubiquitous particles can exceed concentrations of 10,000 particles per cubic centimeter and impact air quality, visibility of remote landmarks, regional climate systems and human health.
The effect of aerosols on large-scale phenomena depends in part on the physical properties of the particles themselves including solubility in water, their volatility, or the time it takes for them to equilibrate under environmental changes.
Petters’ work specifically addresses the question of aerosol volatility.
“I am generating particles by feeding an aqueous solution of dissolved organic compounds (via tubing and fittings from Component Supply Company) through a 20-micrometer orifice. A jet forms as the liquid is ejected at about 0.2 mL/min through the orifice, and the surface tension around the liquid jet pinches off droplets at a uniform rate. As these droplets evaporate, the organic compound remains in the condensed phase.”
However, Petters’ dissolved samples are slightly volatile and will evaporate with the water. Residual particle size shows how volatile the sample is. Petters hopes to link the volatility and hygroscopic character of aerosol particles to some of the chemical pathways that result in particle formation in the atmosphere. But, as with any research, it is challenging to control the conditions of the experiment.
“Aerosol measurements are made using suspended particles that must be either generated in the lab or captured from the environment and measured in an airstream without impacting them on anything. Thus, conditioning the airstream during all stages of the measurement is critically important. It is also challenging to verify the chemical reaction pathways for even the simplest of reactions. For example, if you oxidize a common atmospheric gas, pinene (it evaporates from pine needles), using ozone, you will end up with over 1000 products. There are a handful of different schools of thought on how to understand the complexity of atmospheric chemical reactions. Some people simplify these into categories of reactions. Others view this process only through the formed chemicals and bypass the complexity of the entire reaction, others study simple systems and make inferences extending to more complex systems.”