Complex Acid-Base Chemistry in Minimal Solvation Environments - The Case of Atmospheric New Particle Formation

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In this project, which is jointly funded by the Chemical Structure, Dynamics, and Mechanisms-A program of the Chemistry Division and the Atmospheric Chemistry Program of the Division of Atmospheric and Geospace Science, Professor Christopher Johnson of Stony Brook University is developing a quantitative description of the fundamental molecular interactions involved in the formation of aerosol particles directly from atmospheric gases. This process accounts for a significant fraction of aerosol particles in the atmosphere. The underlying mechanisms governing aerosol particle formation are not well understood, leading to uncertainty about their impact on climate change. Due to the sub-nanometer size of newly formed particles, it is difficult to study them using conventional measurements. New techniques to create these particles are combined with recently developed laser spectroscopy methods to investigate the chemistry driving the formation of these particles. The results aid the refinement of models of new particle formation that can be used to improve weather and climate models. In the course of performing this work, young researchers from high school through graduate school are involved in the design, construction, and modification of sophisticated instrumentation and analysis tools.This project focuses on the development of a new understanding of acid-base chemistry with minimal or no solvent. Though acid-base chemistry in solvents is well understood, new particle formation occurs largely via acid-base chemistry in air, and the role of water vapor in particle formation has not been well established. Clusters of a few acid and base molecules, chosen from those expected to play a role in new particle formation, are generated in a mass spectrometer and studied one specific composition at a time. In ion traps, clusters are exposed to atmospheric trace vapors and their growth is determined by mass spectrometry. Each cluster composition is characterized structurally using vibrational spectroscopy and energetically using temperature-controlled ion traps. These results reveal the energetic factors driving growth, how molecules arrange in the particle, the role of proton transfer between the acids and bases, and whether atmospheric vapors integrate into the acid-base salt structure or bind to its surface. The results aid the refinement of models of new particle formation that can be used to improve weather and climate models.