Detection and quantification of reactive atmospheric nitrogen species in remote ecosystems

Place, Bryan K. (2017) Detection and quantification of reactive atmospheric nitrogen species in remote ecosystems. Masters thesis, Memorial University of Newfoundland.

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Abstract

Anthropogenic inputs of nitrogen to the environment have increased by over 150 % in the last 150 years causing concern for vital biophysical processes on Earth. Thus being able to measure these increased inputs in terrestrial, aquatic and atmospheric environments is essential to understanding how the global nitrogen cycle has been impacted since the industrial revolution. With respect to the atmosphere, emissions of reduced and oxidized forms of nitrogen have increased largely due to the anthropogenic activities of agriculture and combustion, respectively. Emissions of these nitrogenous species not only impact regions adjacent to their point sources, but also have the ability to influence ecosystems hundreds of kilometers away due to the long-range transport of some of these compounds. This can impact sensitive remote ecosystems positively or negatively by either stimulating growth or causing acidification, eutrophication and biodiversity shifts. Therefore developing analytical techniques that are capable of measuring oxidized and reduced atmospheric inputs to remote ecosystems is of great importance. In part I of this work a method employing custom-built physisorption-based passive samplers coupled with ion chromatography analysis was developed to sample atmospheric nitric acid (HNO₃(g)) in remote ecosystems. The developed HNO₃(g) sampling method was able to detect HNO₃(g) mixing ratios as low as 2 parts per trillion by volume (pptv) over a monthly sampling period, following a rigorous quality assurance and quality control procedure. The passive samplers were installed across the Newfoundland and Labrador – Boreal Ecosystem Latitudinal Transect (NL-BELT) in the summer of 2015, and average mixing ratios of HNO₃(g) at the NL-BELT field sites from 2015-16 were determined to be in the tens of parts per trillion by volume (pptv) range. The dry deposition flux of HNO₃(g) as nitrogen (N) to the field sites ranged from 3 – 16 mg N yr-1. Through an air mass back trajectory analysis, coupled with a steady-state chemical box model approximation, it was determined that the HNO₃(g) quantities observed at a single NL-BELT site likely originated from local production and regional transport from central and eastern Newfoundland, with an additional contribution from the down welling of peroxyacetyl nitrates from the upper troposphere, possibly occurring during the spring and early summer. In part II of this work, an ion chromatography method was developed to speciate and quantify alkylamines (NR₃(g)). NR₃(g) have been shown to influence Earth’s climate and may be an important source of new nitrogen to remote ecosystems. The developed method was shown to be sensitive, accurate, and robust in separating and quantifying 11 atmospheric alkylamines, including 3 sets of alkylamine isomers, from 5 common atmospheric inorganic cations. The method was able to detect NR₃(g) at a picogram per injection level, and the method performed robustly in the presence of a complex biomassburning matrix containing amounts of inorganic cations up to 3 orders of magnitude larger than the NR₃(g) quantified in the samples. Thus the ion chromatography method can be applied to the remote atmosphere where alkylamine concentrations are often detected in quantities 1000 times less than other atmospheric cations. In the biomass-burning particle samples tested using the ion chromatography method unprecedented quantities of dimethylamine and diethylamine were observed, with the summed molar quantity exceeding that of ammonium in the 100 – 560 nm particle diameter fraction. The applicability of these atmospheric measurement techniques to measure and quantify HNO₃(g) and NR₃(g) has been demonstrated for remote ecosystems and will hopefully allow for a greater understanding of these two species roles’ in remote environments.

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