Evaluating nitrogen oxide sources and oxidation pathways impacting aerosol production on the Southern Ute Indian Reservation and Navajo Nation using geochemical isotopic analysis
Increased emissions of nitrogen oxides (NOx = NO + NO 2) as a result of the development of oil, gas and coal resources in the Four Corners region of the United States have caused concern for area American Indian tribes that levels of ozone, acid rain, and aerosols or particulate matter (PM) may increase on reservation lands. NOx in the atmosphere plays an important role in the formation of these pollutants and high levels are indicators of poor air quality and exposure to them has been linked to a host of human health effects and environmental problems facing today's society. Nitrogen oxides are eventually oxidized in the atmosphere to form nitrate and nitric acid which falls to earth's surface by way of dry or wet deposition. In the end, it is the removal of NOx from the atmosphere by chemical conversion to nitrate that halts this production of oxidants, acids, and aerosols. Despite the importance of understanding atmospheric nitrate (NO3- = HNO3-(g), NO3-(aq), NO3-(s)) production there remains major deficiencies in estimating the significant key reactions that transform NOx into atmospheric nitrate. Stable isotope techniques have shown that variations in oxygen (16O, 17O, 18O) and nitrogen (14N, 15N) isotope abundances in atmospheric nitrate provide significant insight to the sources and oxidation pathways that transform NOx. Therefore, this project applied this resolution using high pressure liquid chromatography and isotope ratio mass spectrometry to determine the chemical and isotopic composition of particulate nitrate (PM2.5 and PM10), collected on the Southern Ute Indian Reservation and Navajo Nation. It was determined that the observed particulate nitrate concentrations on tribal lands were likely linked to seasonal changes in boundary layer height (BLH), local sources, meteorology, photochemistry and increases in windblown crustal material. The Southern Ute Indian Reservation indicated higher δ15N values in comparison to the Navajo Nation study site. The offset accounted for a 9.7 / mean difference and was likely associated with higher NO x inputs from anthropogenic sources. It was determined both sources and NOx chemistry attribute to δ15N seasonal variations in coarse particulate nitrate (PM10). The observed δ18O values and δ17O values measured in PM10 nitrate on both tribal lands exhibited a seasonal trend similar to observed values in particulate nitrate collected at mid-latitudes (Michalski et al., 2003). Elevated values were observed during winter compared to summer, reflecting changes in NOx oxidation pathways. This thesis project provides insight into the sources of NOx and the oxidation pathways that convert NOx into nitrate on these tribal lands.
Michalski, Purdue University.
Atmospheric Chemistry|Atmospheric sciences|Native American studies
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