This project will characterize atmospheric aqueous-phase chemistry and formation of brown carbon, targeting two compounds: glycolaldehyde and hydroxyacetone. Other common atmospheric aldehydes such as acetaldehyde and formaldehyde, while not expected to form brown carbon, may still form large amounts of secondary organic aerosol (SOA) material via reactions with ammonium salts and amines. In the presence of alpha-dicarbonyls, these compounds can be incorporated into imidazole products, so their SOA-forming potential will be examined with and without alpha-dicarbonyls present. A suite of methods will be used. First, brown carbon formation will be studied by cavity attenuated phase-shift and ultraviolet-visible (UV-Vis) spectroscopy. Product structure will be characterized by proton nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization mass spectrometry. Hygroscopicity tandem differential mobility analysis and Raman microscopy will be used to measure water uptake and surface activity of reaction products. Reaction rates will be measured by NMR and UV-Vis spectroscopies. Aerosol will be generated by three different methods, as required for specific experiments. The aim of these studies will be to identify and characterize reaction products, measure reaction rates and gas/particle partitioning, and determine the atmospheric significance of these SOA and brown carbon formation pathways.
At least twenty diverse undergraduate students will be mentored in first research experiences as part of this project, widening the pipeline of students choosing careers in science by offering more student research opportunities, an enhanced research infrastructure, and an increased publication rate of articles with undergraduate co-authors. The addition of a postdoctoral teacher / researcher will allow more students to be mentored while providing excellent training for an early-career scientist. The field will benefit from the characterization of potentially significant sources of SOA and brown carbon, and from the training of a diverse group of young scientists. Finally, a connection between brown carbon formation and ammonia / amine emissions may suggest new avenues for mitigating aerosol formation to improve air quality and address global warming.