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Dr. Jennifer Murphy
University of Toronto
Quantifying the pH of atmospheric aerosol
Wednesday, January 29, 2025
C9000 @ 3:30 p.m.
Host: Dr. George Agnes
Abstract
The acidity of atmospheric particles is important for the phase partitioning of semi-volatiles, the solubility of metals, and the rates of heterogeneous reactions, but is challenging to measure directly. Even with extremely accurate measurements of the dominant contributors to the ion balance in particles, one can rarely deduce the activity of H+ with sufficient precision to estimate pH. In the seminar, I will share examples from our ambient measurements demonstrating how simultaneous knowledge of the gas phase ammonia concentration alongside particle phase composition can provide the necessary constraint to reliably calculate pH values. As the dominant atmospheric base, ammonia serves as the key multiphase buffer through much of the atmosphere. As traditional inorganic acid precursor emissions drop, we are seeing evidence that organic acids may be increasingly important to the ion balance of aqueous aerosol, with implications for the robustness of traditional sampling strategies.