Investigations of the oxidation capacities of polar atmospheres with multiple oxygen isotopes

This study provides new perspectives on the atmospheric chemistry in Polar Regions using multiple oxygen isotopes of nitrate and sulfate. Despite their remote locations, these unique environments play an important role in the present state of global climate and contain invaluable clues to observing past relationships between earth's atmosphere and surface temperature. With current temperatures and greenhouse gas concentrations rising rapidly as a result of human activities, continued investigation of the effects on polar environments will elucidate their relationship to the global climate system. Three studies are presented here to constrain the oxidation pathways of nitrogen and sulfur compounds in polar atmospheres. These findings provide a new means to observe current and past oxidation conditions of tropospheric and stratospheric polar atmospheres. Currently, two uncertain aspects of climate are the projected changes in tropospheric and stratospheric oxidation chemistry and the role of aerosols in cloud formation and the global radiation budget. Because the levels of oxidants in the atmosphere directly influence greenhouse gas concentrations and aerosol distribution, the following work presents results implicit to improving knowledge of the climate system.; The results presented in this dissertation include measurements of oxygen isotopes (delta17O, delta18O, and Delta 17O) in nitrate and sulfate from South Pole, Antarctica and Alert, Canada, respectively. In addition, a photochemistry experiment was conducted to measure the effects of ultraviolet (UV) irradiation on oxygen isotopes of nitrate in water and ice. Chapter 2 compares oxygen isotopes in sulfate aerosol collected at Alert, Canada over the course of one year (July 1999--June 2000) to a chemical transport model describing sulfate formation. Chapter 3 presents the results from the nitrate photochemistry experiments conducted at California Institute of Technology in Pasadena, California. Chapter 4 contains results and interpretations of nitrate oxygen isotopes from South Pole, Antarctica measured in aerosol and surface snow during 2004 and a 6-meter snow pit that provides a record 1977 to 2003. The isotope measurements from South Pole are compared to instrumental measurements of October-November-December column ozone, October-November-December UV, annual surface ozone, the quasi-biennial oscillation, and solar variability. A summary of related work on the oxygen and sulfur isotopic composition of volcanic sulfate from the Masaya volcano in Nicaragua is presented in the appendix along with measurements of ion chemistry used to establish a chronology in the South Pole snow pit.; The nitrogen cycle has been drastically altered by human influence; however the sources of nitrogen to the Antarctic are expected to be relatively unaffected by human activity and may provide a means of establishing natural variability of nitrogen sources. Unfortunately, two significant problems exist. One, the sources to Antarctica are quite uncertain, and two, the records are difficult to interpret as a result of post-depositional effects in the ice. Through the use of multiple oxygen isotopes, the present work provides new insights into Antarctic nitrate records. The results suggest that greater knowledge of the influence of post-depositional effects (volatilization, photochemistry and diffusion) emerges from multiple oxygen isotope measurements in aerosol, surface snow and firn nitrate. The seasonal variation in winter stratospheric and summer tropospheric values of oxygen isotopes in Antarctic nitrate aerosol is preserved in surface snow. Evidence of stratospheric nitrate in snow at the South Pole suggests the potential for a proxy of ozone hole variability and solar variability; however, the location and meteorology of the South Pole create a site best suited for understanding boundary layer oxidation conditions across the Antarctic plateau. Changes in these conditions are driven by vari...