Seminar

How Well Do We Really Understand Ultrafine Particle Growth?

Murray Johnston

Murray Johnston

University of Delaware

Wednesday, 2 February 2022
11:00 am Mountain Time
webinar only

Abstract

Tremendous advances have been made in the last decade to characterize gas-phase precursors to nanoparticle growth and to correlate formation of these precursors with particle growth rate and chemical composition. Nanoparticle growth is thought to be driven primarily by condensation of nonvolatile molecules produced in the gas phase by processes such as autooxidation monoterpenes. While this model works well, there are situations where predicted growth rates are slower than measured growth rates and particle composition does not match that expected from precursor molecule condensation, whether it be in the low nanometer size range or in larger ultrafine (sub 100 nm) particles. This begs the question: How well do we really understand particle growth? Ultrafine particles have relatively large surface area to volume ratios, so it is not unreasonable to expect that heterogeneous chemistry plays a role. In this presentation, I will first review some of our chemical composition measurements of ambient nanoparticles that point to an impact of heterogeneous chemistry. I will then discuss our current work to measure growth rates in a flow tube reactor where the seed (starting) particle characteristics are systematically varied. Our results show that growth is dependent on seed particle size, phase, and composition. Sorting out these dependencies should allow more accurate predictions of ultrafine particles across a wide range of atmospheric conditions.


Dr. Murray Johnston is a Professor in the Chemistry and Biochemistry Department at the University of Delaware. He received his PhD in Chemistry at the University of Wisconsin, and did his postdoctoral work at Northwestern University. In 1982, he became an assistant professor at the University of Colorado, Boulder, and in 1990, joined the faculty of the University of Delaware. During his tenure at Delaware, he has served as the Assistant Chair and Director of Graduate Studies and the Chemistry and Biochemistry department chair. He currently serves as the Associate Dean for Natural Sciences, and holds a joint professorship in the Oceanography Program. He has received numerous awards for his research, and has recently served as the Vice President of the American Association of Aerosol Research.

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