| Summary: | This collaborative study between South Dakota State University and University of California, San Diego will investigate mechanisms of atmospheric oxidation chemistry using sulfur dioxide from volcanic eruptions. The Principal Investigators will: 1) obtain several shallow ice cores from central Greenland; 2) extract sulfate from a number of known large volcanic eruptions in the last 600 years; 3) measure the mass independent fractionation (MIF) of sulfur and oxygen isotopes in the volcanic sulfate; 4) test hypotheses of sulfur dioxide oxidation by active oxidation intermediates and by photochemistry; and 5) investigate the quantitative impact of atmospheric variables on ice core volcanic signals. The goals are to: 1) better understand the chemical processes of atmospheric oxidation and the effect of atmospheric dynamics on ice core volcanic signals, and 2) to establish a new mechanism to track the sensitivity of the atmosphere to environmental disturbance and hence, is of importance to anthropogenic impact models. Intellectual Merit: Oxidation is one of the basic chemical transformation processes in the atmosphere. It plays a critically important role in global biogeochemical cycles and in the removal of many pollutant chemicals from the atmosphere. Introduction of large amounts of chemical substances, from either natural or anthropogenic sources, can alter the atmosphere's oxidative abilities and affect the quality and functions of the atmospheric environment. Very limited knowledge of the mechanisms of atmospheric oxidation, particularly in the stratosphere, hampers the efforts to construct robust models to predict anthropogenic impact on the atmospheric environment. The Principal Investigators recently discovered that MIF isotopic signatures of volcanic sulfate extracted from Antarctica ice cores contain new and valuable information on atmospheric oxidation that is unavailable by other means. Limited data have attracted attention from atmospheric modelers with proposals of alternative photochemical and/or oxidation processes. More isotopic MIF data are needed both to test and to encourage new hypotheses spurred by preliminary results. In an on-going project, they added to the MIF dataset with measurements on volcanic sulfate from South Pole ice cores. This project will produce first volcanic sulfate MIF data from Northern Hemisphere ice cores. They will use the bi-polar volcanic sulfate MIF dataset to: 1) determine the global homogeneity of stratospheric oxidation chemistry, 2) test the hypothesis of stratospheric SO3 photolysis, 3) determine the stratospheric or tropospheric nature and degree of two climatologically important large volcanic eruptions; and 4) establish and verify a quantitative MIF-mass loading relationship that can be used to estimate aerosol impact of past volcanic eruptions from their ice core sulfate signals. Broader Impacts: Achieving the goals of the research will help advance the frontiers of environmental science, particularly in the areas of climate change and human impact. By providing educational and research opportunities to SDSU and UCSD students, the project will promote the integration of research with education and contribute to human resource development in science and engineering. The project will contribute to a current REU chemistry site program at SDSU.
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