Accelerated Chemistry In Aerosol Droplets Relevant To The Atmosphere

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The Environmental Chemical Sciences Program of the Division of Chemistry supports Professor Murray Johnston of the University of Delaware to investigate chemical reactions in aerosol droplets that may contribute to formation of organic particulate matter in the atmosphere. The main health impacts of air pollution arise from ozone and particulate matter. This project studies how water in airborne particles can assist formation of organic particulate matter from volatile organic compounds in ways that are not readily predicted by studying chemical reactions in bulk aqueous solution. This project also contributes to the development of the scientific workforce through graduate student training in an environment that encourages multidisciplinary innovation and public outreach. An aerosol flow reactor is used to study chemical reactions on the surface of aqueous ammonium sulfate droplets that combine two volatile monomer reactants to give a nonvolatile dimer product. These reactions include aldehyde-aldehyde reactions to produce an aldol, aldehyde-alcohol reaction to produce a hemiacetal, and alcohol-acid reaction to produce an ester. The reactor system has the ability to precisely control initial droplet size and composition including water content, ionic strength and acidity. Systematic control of these variables provides insight into reaction mechanisms. Intermediates and products of the reactions are characterized and, where possible, quantified with a variety of online mass spectrometry methods. These methods include elemental analysis with the nano aerosol mass spectrometer, which gives a measure of droplet acidity based on the nitrogen-to-sulfur mole ratio, and molecular analysis with droplet assisted ionization and extractive electrospray ionization. Students supported by the project are broadly trained in environmental chemistry, analytical chemistry and nanoscience. They bring environmental topics to the attention of scientists and non-scientists alike through various outreach events.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.