Detection and quantification of reactive atmospheric nitrogen species in remote ecosystems

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

Composition of size-resolved aged boreal fire aerosols: Brown carbon, biomass burning tracers, and reduced nitrogen

Aerosols that were size-resolved into 13 fractions between 10 nm and 18 μm were collected from an aged boreal forest wildfire plume in July 2013. Samples were extracted into water and analyzed for molecular-size-resolved brown carbon (BrC), biomass burning (BB) markers, reduced nitrogen compounds, and elemental composition. Absorption of BrC was primarily in fine-mode aerosols and dominated by high-molecular-weight compounds (>500 Da). The molecular size distribution of BrC was conserved across aerosol sizes, with a decrease in the importance of large molecules in smaller aerosols. The aerosol-size-resolved composition of BrC absorption was different than those of the two BB markers, non-sea-salt potassium and levoglucosan, suggesting that they may not be suitable for identifying BB BrC in aged plumes. Strong correlations were observed between BrC and the reduced nitrogen compounds ammonium, dimethylamine, and diethylamine. In aerosols with high BrC and reduced nitrogen, there was a strong cationic excess. These observations could be caused by (i) uptake of ammonium and alkylamines to form stable salts with organic acids or (ii) reactive uptake to form imines or enamines that were hydrolyzed during the BrC extraction process.Funding was provided by the Natural Sciences and Engineering Research Council of Canada through Discovery and Research, Tools, and Infrastructure Grants. T.C.V. acknowledges a Banting Postdoctoral Fellowship

Composition of Size-Resolved Aged Boreal Fire Aerosols: Brown Carbon, Biomass Burning Tracers, and Reduced Nitrogen

Aerosols that were size-resolved into 13 fractions between 10 nm and 18 μm were collected from an aged boreal forest wildfire plume in July 2013. Samples were extracted into water and analyzed for molecular-size-resolved brown carbon (BrC), biomass burning (BB) markers, reduced nitrogen compounds, and elemental composition. Absorption of BrC was primarily in fine-mode aerosols and dominated by high-molecular-weight compounds (>500 Da). The molecular size distribution of BrC was conserved across aerosol sizes, with a decrease in the importance of large molecules in smaller aerosols. The aerosol-size-resolved composition of BrC absorption was different than those of the two BB markers, non-sea-salt potassium and levoglucosan, suggesting that they may not be suitable for identifying BB BrC in aged plumes. Strong correlations were observed between BrC and the reduced nitrogen compounds ammonium, dimethylamine, and diethylamine. In aerosols with high BrC and reduced nitrogen, there was a strong cationic excess. These observations could be caused by (i) uptake of ammonium and alkylamines to form stable salts with organic acids or (ii) reactive uptake to form imines or enamines that were hydrolyzed during the BrC extraction process

A short history of evolutionary theory Uma breve história da teoria evolutiva

The history of the Theory of Evolution has been told a number of times by historians, philosophers, professors, writers, scientists and so on. However, many of these versions differ from or even contradict one another. In this article, the history of the Theory of Evolution is retold according to a dialectical-materialistic perspective. It analyzes the historical contradictions between Darwinian evolution theory and Mendel's model, the background that led to the synthetic theory of evolution, the debate carried out by classic schools and the result of synthesis, as well as the still current debate between Neutralism and Selectionism. Finally, it also discusses the interpretative model used ("an idiosyncratic dialectic materialism"), mainly in relation with Popper's and Kuhn's models.<br>A história da teoria evolutiva tem sito contada inúmeras vezes por historiadores, filósofos, professores, escritores, cientistas etc. Contudo, muitas destas versões diferem entre si ou mesmo se contradizem. Neste trabalho, a história da teoria evolutiva é recontada a partir de uma perspectiva materialista dialética. São analisadas as contradições históricas entre a teoria evolutiva darwiniana e o modelo mendeliano, o caminho para a teoria sintética da evolução, o debate entre as escolas clássica e do balanco que sucedeu a síntese, bem como o debate, ainda atual, entre neutralismo e selecionismo. Ao final, o modelo interpretativo utilizado ("um materialismo dialético idiossincrático") é discutido, principalmente, em relação aos modelos popperiano e kuhniano