scholarly journals Theoretical calculation of oxygen equilibrium isotope fractionation factors involving various NO molecules, OH, and H2O and its implications for isotope variations in atmospheric nitrate

2016 ◽  
Vol 191 ◽  
pp. 89-101 ◽  
Author(s):  
Wendell W. Walters ◽  
Greg Michalski
Keyword(s):  
Theoretical Calculation ◽  
Isotope Fractionation ◽  
Oxygen Equilibrium ◽  
Atmospheric Nitrate ◽  
Fractionation Factors

scholarly journals i<sub>N</sub>RACM: Incorporating <sup>15</sup>N into the Regional Atmospheric Chemistry Mechanism (RACM) for assessing the role photochemistry plays in controlling the isotopic composition of NO<sub>x</sub>, NO<sub>y</sub>, and atmospheric nitrate.

2020 ◽  
Author(s):  
Greg Michalski ◽  
Huan Fang ◽  
Wendell W. Walters ◽  
David Mase
Keyword(s):  
Atmospheric Chemistry ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
Trace Gases ◽  
Organic Aerosols ◽  
Organic Nitrates ◽  
Tropospheric Photochemistry ◽  
Atmospheric Nitrate ◽  
N Compounds ◽  
Fractionation Factors

Abstract. Nitrogen oxides, classified as NOx (nitric oxide (NO) + nitrogen dioxide (NO2)) and NOy (NOx + NO3, N2O5 HNO3, + HNO4 + HONO + Peroxyacetyl nitrate (PAN) + organic nitrates + any oxidized N compound), are important trace gases in the troposphere, which play an important role in the formation of ozone, particulate matter (PM), and secondary organic aerosols (SOA). Among many uncertainties in movement of atmospheric N compounds, nowadays understanding of NOy cycling is limited by NOx emission budget, unresolved issues within the heterogeneous uptake coefficients of N2O5, the formation of organic nitrates in urban forests, etc. A photochemical mechanism used to simulate tropospheric photochemistry was altered to include 15N compounds and reactions as a means to simulate δ15N values in NOy compounds. The 16 N compounds and 96 reactions involving N used in Regional Atmospheric Chemistry Mechanism (RACM) were replicated using 15N in a new mechanism called iNRACM. The 192 N reactions in iNRACM were tested to see if isotope effects were relevant with respect to significantly changing the δ15N values (±1 ‰) of NOx, HONO, and/or HNO3. The isotope fractionation factors (α) for relevant reactions were assigned based on recent experimental or calculated values. Each relevant reaction in the iNRACM mechanism was tested individually and in concert in order to assess the controlling reactions. The final mechanism was tested by running simulations under different conditions that are typical of pristine, rural, urban, and highly polluted environments. The results of these simulations predicted several interesting δ15N variations.

scholarly journals i<sub>N</sub>RACM: incorporating <sup>15</sup>N into the Regional Atmospheric Chemistry Mechanism (RACM) for assessing the role photochemistry plays in controlling the isotopic composition of NO<sub><i>x</i></sub>, NO<sub><i>y</i></sub>, and atmospheric nitrate

2021 ◽  
Vol 14 (8) ◽  
pp. 5001-5022
Author(s):  
Huan Fang ◽  
Wendell W. Walters ◽  
David Mase ◽  
Greg Michalski
Keyword(s):  
Particulate Matter ◽  
Atmospheric Chemistry ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
Nox Emission ◽  
Organic Nitrates ◽  
Atmospheric Nitrate ◽  
N Isotopes ◽  
N Compounds ◽  
Fractionation Factors

Abstract. Nitrogen oxides, classified as NOx (nitric oxide (NO) + nitrogen dioxide (NO2)) and NOy (NOx+ NO3, N2O5 HNO3, + HNO4+ HONO + Peroxyacetyl nitrate (PAN) + organic nitrates + any oxidized N compound), are important trace gases in the troposphere, which play an important role in the formation of ozone, particulate matter (PM), and secondary organic aerosols (SOA). There remain many uncertainties in the origin and fate of atmospheric N compounds including the understanding of NOy cycling, NOx emission budgets, unresolved issues within the heterogeneous uptake coefficients of N2O5, and the formation of organic nitrates in urban forests, to name a few. A potential tool to resolve some of these uncertainties are using natural abundance N isotopes in NOy compounds. Here we have developed a photochemical mechanism used to simulate tropospheric photochemistry to include 15N compounds and reactions as a means to simulate δ15N values in NOy compounds. The 16 N compounds and 96 reactions involving N used in the Regional Atmospheric Chemistry Mechanism (RACM) were replicated using 15N in a new mechanism called iNRACM. The 192 N reactions in iNRACM were tested to see if isotope effects were relevant with respect to significantly changing the δ15N values (±1 ‰) of NOx, HONO, and/or HNO3. The isotope fractionation factors (α) for relevant reactions were assigned based on recent experimental or calculated values. Each relevant reaction in the iNRACM mechanism was tested individually and in concert in order to assess the controlling reactions. The controlling reactions and their diurnal importance are discussed. A comparison between iNRACM predictions and observed δ15N NO3- in particulate matter from Tucson, Arizona, suggests the model, and isotope fractionation factors incorporated into it, are accurately capturing the isotope effects occurring during the photochemistry of NOy. The implication is that measurements of δ15N in NOy compounds may be a new way of tracing in situ N chemistry and a means of assessing NOx emission budgets.

scholarly journals Measurement on Diffusion Coefficients and Isotope Fractionation Factors by a Through-Diffusion Experiment

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 208
Author(s):  
Takuma Hasegawa ◽  
Kotaro Nakata ◽  
Rhys Gwynne
Keyword(s):  
Groundwater Flow ◽  
Diffusion Coefficients ◽  
Isotope Fractionation ◽  
Free Water ◽  
Effective Porosity ◽  
Diffusion Experiment ◽  
Fractionation Factor ◽  
Through Diffusion ◽  
Geological Formations ◽  
Fractionation Factors

For radioactive waste disposal, it is important that local groundwater flow is slow as groundwater flow is the main transport medium for radioactive nuclides in geological formations. When the groundwater flow is very slow, diffusion is the dominant transport mechanism (diffusion-dominant domain). Key pieces of evidence indicating a diffusion-dominant domain are the separation of components and the fractionation of isotopes by diffusion. To prove this, it is necessary to investigate the different diffusion coefficients for each component and the related stable isotope fractionation factors. Thus, in this study, through-diffusion and effective-porosity experiments were conducted on selected artificial materials and natural rocks. We also undertook measurements relating to the isotope fractionation factors of Cl and Br isotopes for natural samples. For natural rock samples, the diffusion coefficients of water isotopes (HDO and H218O) were three to four times higher than those of monovalent anions (Cl−, Br- and NO3−), and the isotope fractionation factor of 37Cl (1.0017–1.0021) was slightly higher than that of free water. It was experimentally confirmed that the isotope fractionation factor of 81Br was approximately 1.0007–1.0010, which is equivalent to that of free water. The enrichment factor of 81Br was almost half that of 37Cl. The effective porosity ratios of HDO and Cl were slightly different, but the difference was not significant compared to the ratio of their diffusion coefficients. As a result, component separation was dominated by diffusion. For artificial samples, the diffusion coefficients and effective porosities of HDO and Cl were almost the same; it was thus difficult to assess the component separation by diffusion. However, isotope fractionation of Cl and Br was confirmed using a through-diffusion experiment. The results show that HDO and Cl separation and isotope fractionation of Cl and Br can be expected in diffusion-dominant domains in geological formations.

scholarly journals Empirical and Experimental Constraints on Fe-Ti Oxide-Melt Titanium Isotope Fractionation Factors

2021 ◽  
Author(s):  
Liam Hoare ◽  
Martijn Klaver ◽  
Stephan Klemme ◽  
Duncan Muir ◽  
Jane Barling ◽  
...  
Keyword(s):  
Isotope Fractionation ◽  
Oxide Melt ◽  
Fractionation Factors

scholarly journals Oxygen and silicon β-factors of zircon estimated from first principles

2019 ◽  
Vol 27 (4) ◽  
pp. 420-430
Author(s):  
D. P. Krylov
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Isotope Fractionation ◽  
Isotopic Equilibrium ◽  
Functional Theory ◽  
Empirical Calibration ◽  
The Density Functional Theory ◽  
Cubic Polynomials ◽  
Semi Empirical ◽  
Fractionation Factors

Zircon β-factors have been calibrated against temperature for isotopic substitutions of 18O/16O and 30Si/28Si. Calculations were performed using the density functional theory (DFT) with the “frozen phonon” approach. The deduced geometric parameters of the zircon unit cell, and the phonon frequencies calculated, agree well with the experimental data. The results are expressed by the cubic polynomials on x = 106/T(K)2: 1000lnβzrn(18O/16O) = 9.83055x – 0.19499x2 + 0.00388x3;  1000lnβzrn(30Si/28Si) = 7.89907x – 0.17978x2 + 0.00377x3. The expressions deduced can be utilized to construct geothermometers if combined with β-factors of coexisting phases. New calibrations of quartz-zircon are given. The new values of 1000lnβzrn and the estimated isotope fractionation factors between quartz and zircon (1000lnβqtz–1000lnβzrn) deviate considerably from previously used experimental, empirical, and semi-empirical calibration of the isotopic equilibrium.

Calibrating equilibrium Fe isotope fractionation factors between magnetite, garnet, amphibole, and biotite

2020 ◽  
Vol 271 ◽  
pp. 78-95 ◽  
Author(s):  
Hui Ye ◽  
Changzhi Wu ◽  
Matthew J. Brzozowski ◽  
Tao Yang ◽  
Xiangping Zha ◽  
...  
Keyword(s):  
Isotope Fractionation ◽  
Fractionation Factors
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