CAREER: Molecular-level Multiphase Reactivity of Biogenic Sulfur from Bulk Water to Atmospheric Droplets

With support from the Environmental Chemical Sciences Program, Dr. Megan Willis and her students at Colorado State University (CSU) are studying multiphase chemistry—molecular-scale chemistry across gas and condensed phases in Earth’s atmosphere. Natural aerosol particles set the background conditions in Earth's atmosphere; therefore, an understanding of the processes that determine the background is important. Marine sulfur compounds are a large source of natural aerosol to Earth's atmosphere. They undergo a cascade of atmospheric reactions that lead to either formation of new particles or growth of existing particles through competing gas and multiphase reaction pathways. Despite its importance, a complete understanding of this marine multiphase chemistry is lacking. This project will investigate controls on multiphase sulfur chemistry and provide chemical parameters that can be incorporated into large-scale atmospheric models. The project, in partnership with the CSU Education and Outreach Center, will create inquiry-driven STEM experiment kits that engage middle and high-school students in the scientific process through studying multiphase atmospheric chemistry. This project will use laboratory experiments and kinetic models to provide quantitative descriptions of the fate of multiphase biogenic sulfur fate in atmospheric particles and droplets. Using a combination of direct, relative-rate, and aerosol kinetics experiments, this project will: (1) quantify solvent environment effects on ozone reactivity with biogenic sulfur compounds, and (2) predict the timescale and location of multiphase ozone reactivity with oxidized biogenic sulfur. Solvent environment effects on the kinetics of aqueous-phase ozone reactions with dimethyl sulfide and methanethiol, and their oxidation products, will be quantified. Bulk rate constants and laboratory aerosol kinetics will be combined in a multiphase kinetic model to describe the fate of oxidized biogenic sulfur in aerosol. Outcomes of this project are expected to improve estimates of the fraction of marine biogenic sulfur that leads to either new particle formation or growth of existing aerosol. 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.