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DTSTART;TZID="Pacific Time (US & Canada)":20260928T161000
DTEND;TZID="Pacific Time (US & Canada)":20260928T170000
SUMMARY:Department of Chemistry Seminar – Dr. Kristen Johnson
LOCATION:Fulmer Hall
DESCRIPTION:The Role of Self-Assembly in the Atmospheric Processing of Model Cooking Emission Films\n\nDr. Kristen Johnson, Assistant Professor\n\nDepartment of Chemistry, Tennessee Tech University\n\nE-mail: knjohnson@tntech.edu\n\nCooking emissions are a major source of organic aerosol particles in urban environments and have been associated with increased organic material on the surfaces of atmospheric particulate matter. Evidence suggests that molecules within cooking-derived aerosols can self-assemble into densely packed domains that reduce oxidation rates, leading to longer atmospheric lifetimes than predicted from measurements of single-component particles. In this work, we use thin films containing an equimolar mixture of oleic acid and sodium oleate as a model system to investigate how nanoscale film structure influences heterogeneous and multiphase reaction kinetics. Under ambient conditions, this mixture forms lipid bilayer-like structures, making it a useful proxy for studying the behavior of complex organic aerosol surfaces. We examine the effects of reactions with common atmospheric oxidants, including ozone (O₃), as well as indoor cleaning-related oxidants such as hypochlorous acid (HOCl), on film composition and microstructure. Model films were exposed to controlled flows of reactive gases in an attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy system to quantify heterogeneous reaction kinetics. Following oxidation, the films were characterized using atomic force microscopy (AFM) to identify changes in morphology and the formation of highly viscous or polymerized domains. Both ozonolysis and HOCl reaction rates for the mixed oleic acid/sodium oleate films were slower than the ozonolysis rate measured for pure oleic acid films. AFM imaging revealed a transition from initially smooth films to morphologies dominated by aggregated particle-like structures following oxidation. These results demonstrate that molecular organization within organic films can significantly influence heterogeneous oxidation kinetics and chemical aging processes. More broadly, this work provides new insights into the transformation of organic aerosol coatings, with implications for understanding the evolution of atmospheric particles and improving predictions of air quality in both indoor and outdoor environments.
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