Characterising dissolved nitrate in precipitation using stable nitrogen and oxygen isotopes

• Main Author: Lee, Vanessa Eileen
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2005
• Subjects: Major Point; Newfoundland
• Online Access: https://research.library.mun.ca/6529/; https://research.library.mun.ca/6529/1/VanessaEileenLee.pdf; https://research.library.mun.ca/6529/3/VanessaEileenLee.pdf

Single event precipitation samples were collected at two sites in Newfoundland for stable isotopic analysis of nitrogen and oxygen of dissolved nitrate. Nitrate, the second largest acidifying component of rain, is formed during the oxidation of NO and NO₂, collectively known as NOx, as well as other nitrogen species. Both natural and anthropogenic sources exist, however fossil fuel combustion in power plants and vehicles are the main contributors of NOx to the atmosphere. Nitrogen isotopes of nitrate may give insight into the source of the atmospheric oxinitrogen species, while oxygen isotopes may provide information about the type of oxidation the NOx emissions have undergone. The isotopic signatures, in combination with chemical and meteorological data, were used to characterise the main controls of the nitrate in the precipitation. -- The two sites chosen for this study represent different types of environments: St. John's is a marine/urban location, while McIvers is a marine/rural site with no major point sources in the area. St. John's precipitation samples generally displayed characteristics of oil combustion emissions from stationary sources (high V, Ni) with smaller inputs from the ocean. Samples collected at McIvers were not as strongly affected by inputs from fossil fuel combustion, and generally had stronger marine signatures along with wood combustion and vehicle emissions. However, several samples collected at this location did display characteristics of oil combustion as well as smelting processes, confirming that the site is affected by long range transport of pollutants from North America. -- Nitrogen isotopes appear to be controlled by the source of the nitrogen emissions. Fossil fuel combustion in stationary sources results in δ¹⁵N values close to 0‰, vehicle NOx emissions range from -2 to -13‰, while natural sources such as soil and oceanic emissions can result in NOx with values as low as -20‰. A seasonality in δ¹⁵N was observed at both sites, whereby samples collected during the warmer ...