Chemically Resolving the Growth of Gas Phase Clusters into Nanoparticles

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The Environmental Chemical Sciences Program of the Chemistry Division funds this research by Professor James Smith of the Chemistry Department at the University of California, Irvine. Professor Smith and his students study the growth and change in chemical composition of small molecular clusters in the atmosphere. These clusters can grow to become nanometer-sized particles. The goal of this project is to directly observe, for the first time, compositional changes that occur in atmospheric nanoclusters (ANs) and to understand, at a molecular level, the interactions that control these processes. This fundamental understanding makes it possible predict how particles form and evolve in a number of atmospheric environments that are natural or influenced by human activities. Understanding the evolution of clusters is necessary for creating models of AN growth rates and survival probabilities and in turn, correlates to nanoparticle impacts on air quality and climate. This project includes a peer mentorship program that pairs graduate and undergraduate students. This partnership helps prepare undergraduate students for future careers in STEM. The formation and evolution of atmospheric nanoparticles (AN) are studied using a combination of laboratory experiments and computational chemistry simulations. Laboratory experiments explore AN formation and evolution from reactions of ammonia and organic bases with sulfuric acid. Experiments focus on reactions between organic compounds such as benzoic acid and glyoxal and clusters of known composition. Experimental observations are performed in concert with computational chemistry calculations that elucidate cluster and AN growth mechanisms. These simulations explore specific processes such as proton transfer reactions and the role of trace water in clusters of various sizes, up to several nanometers, as well as for different initial cluster compositions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.