Advances in reconstructing past atmospheric oxidation chemistry using the oxygen isotope composition of nitrate and sulfate in ice cores

Atmospheric oxidants determine the lifetimes of reduced trace gases that act as greenhouse gases and pollutants. There has thus been great interest in deducing past variability in oxidant concentrations from ice cores. Ice core measurements of Delta17O of nitrate and sulfate (Delta 17O(NO3-) and Delta17O(SO 42-)(Delta17O ≈ delta 17O - 0.52x (delta18O)) provide a means of reconstructing past changes in the oxidation chemistry of nitrate and sulfate production. This dissertation describes improvements to methods for Delta 17O(NO3-) and Delta17O(SO 42-) analysis and contributes new snow and ice core records of Delta17O(NO3-) and Delta17O(SO42-) in Greenland and Antarctica, respectively. Measurements of sulfur isotopes of sulfate (delta 34S, Delta33S, Delta36S) provide complementary information on sources of atmospheric sulfate.;Methods are presented for automated, simultaneous analysis of Delta 17O(NO3-) and Delta17O(SO 42-) at micromole levels and for Delta 17O(NO3-) analysis at submicromole levels. The automation of simultaneous Delta17O(NO3 -) and Delta17O(SO4 2-) analysis will expand environmental applications of these complementary isotopic measurements. Reduced sample size requirements will improve the temporal resolution of ice core analysis.;We present measurements of seasonal changes in Delta17O(NO 3-) from a snowpit at Summit, Greenland, and compare them with calculations from an atmospheric chemical box model. The box model underestimates summer Delta17O(NO3 -), suggesting several important influences on nitrate isotopic composition that are not accounted for in our box model: Non-zero Delta 17O of OH over polar regions, stratospheric influence on surface O 3 at Summit, participation of BrO in nitrate production, and tropospheric transport of nitrate. A box model sensitivity study shows that annual mean Delta 17O(NO3-) at Summit is most sensitive to changes in the ratio of [O3]/([HO2]+[RO2]) in summer.;Ice core measurements of Delta17O, delta34 S, Delta33S, and Delta36S of sulfate over the past 230 years from the West Antarctic Ice Sheet (WAIS) Divide are also presented. Sulfur isotope measurements suggest stronger influence of volcanogenic and/or stratospheric sulfate in West relative to East Antarctica. The lack of change in Delta17O of non-sea salt sulfate from the mid-1800s to early 2000s (2.4--2.6+/-0.2‰) is consistent with atmospheric chemistry model estimates indicating preindustrial to industrial increases in O3 as high as 50% and decreases in OH of 20% in the southern polar troposphere, as long as H2O2 concentrations also increase by over 50%.