MS Thesis Defense : Danielle Chambers

Advisor: 

Dr. Chris Hennigan

Brown carbon (BrC), a light-absorbing organic aerosol, plays a significant role in Earth's radiative forcing and atmospheric chemistry, yet its optical behavior in aqueous environments remains poorly constrained. This study investigates how pH and ionic strength (IS) affect the light-absorption properties of water-soluble BrC in authentic fog-water samples from southeastern China. Using long-path UV-visible spectroscopy, systematic pH-cycling and salinity-adjustment experiments, revealed that absorbance at 365 nm (Abs₃₆₅) and mass absorption coefficients (MAC₃₆₅) increase linearly with pH, driven by chromophore deprotonation and enhanced conjugation. In contrast, elevated IS suppresses absorption through ionic association and aggregation. Control experiments using Suwannee River Natural Organic Matter verified that IS effects occur independent of pH. These findings show that fog and cloud water chemistry, specifically, pH and IS exert strong control on BrC optical behavior, challenging current models that assume composition-invariant absorption.

9:45 am EST - Meeting room opens and welcome

10:00 am EST - Presentation followed by questions from the audience. 

After the questions from the public, the meeting will be closed for the committee discussion.