About the Seminar

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.

About the Speaker

Jennifer Murphy is a Professor in the Department of Chemistry at the University of Toronto, where she held a Canada Research Chair in Atmospheric and Environmental Chemistry from 2007 – 2016. She received a BSc in Chemistry from McGill University (2000), a PhD in Chemistry from the University of California at Berkeley (2005), and completed a postdoctoral fellowship at the University of East Anglia in 2006. She mentors a team of students and postdocs whose research focuses mainly on understanding the sources and sinks of reactive nitrogen in the atmosphere and on biosphere-atmosphere exchange. They deploy instruments at ground sites, on tall towers, stratospheric balloons, aircraft and ships to measure gases and particles in the atmosphere. Her group also analyzes long-term monitoring of atmospheric pollutants and weather to understand the ways that climate and chemistry influence trends in atmospheric composition.