Heterogeneous Chemistry of Gas-Phase Intermediates in the OH-oxidation of Dimethyl Sulfide

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

With support from the Environmental Chemical Sciences Program of the Division of Chemistry, Professor Timothy Bertram and his students at the University of Wisconsin, Madison are studying sulfur chemistry related to the atmosphere. Volatile organic compounds, emitted from the surface ocean, are oxidized in the earth atmosphere resulting in the formation of low volatility molecules that can nucleate new aerosol particles or condense onto existing aerosol particles. Dimethyl sulfide (DMS) is the most abundant source of reduced sulfur to the marine atmosphere and plays a central role in the formation and growth of aerosol particles in marine environments. Despite the importance of DMS in climate on earth, a comprehensive understanding of the intermediate products in the oxidation of DMS is limited, leading to large variability in estimates of sulfuric acid and methanesulfonic acid (MSA) yields; the key endpoints of DMS oxidation. This project will investigate the heterogeneous kinetics of key intermediates in the oxidation of DMS and how they regulate the production of sulfuric acid and MSA. This project will support the PhD thesis for one chemistry graduate student and multiple undergraduate thesis projects. The research team will continue to be involved the UW Madison chemistry recruitment program (CHOPS, CHemistry OPportunitieS) and the Bridge to the Chemistry Doctorate program designed to support underrepresented students in chemistry. Additionally, the research team will partner with local K-12 schools on the measurement and assessment of indoor air quality in public schools. This project will use laboratory measurements to: 1) quantify the rate of heterogeneous and multiphase reactions of key intermediates in the OH-oxidation of DMS and 2) determine the product yields and chemical mechanism for the condensed phase reaction of hydroperoxymethyl thioformate (HPMTF) in aerosol and cloud water. Specifically, using an entrained aerosol flow reactor coupled to a chemical ionization mass spectrometer, the team will determine the reactive uptake coefficient of dimethyl sulfoxide (DMSO), methanesulfinic acid (MSIA), MSA and HPMTF to representative marine aerosol mimics (e.g., sea spray, ammonium sulfate) as a function of relative humidity and particle acidity. Using a combination of online and offline sampling techniques, the product yields for the condensed phase reactions of HPMTF in cloud water and marine aerosol mimics will be determined. This is expected to permit a more accurate assessment of the fraction of DMS emitted that forms sulfate 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.