The collisional deactivation of metastable atoms and molecules in the upper atmosphere

1969 ◽  
Vol 47 (10) ◽  
pp. 1863-1870 ◽  
Author(s):  
E. C. Zipf
Keyword(s):  
Diffusion Coefficients ◽  
Reaction Rate ◽  
Vacuum Ultraviolet ◽  
Upper Atmosphere ◽  
Rate Coefficients ◽  
Atmospheric Measurements ◽  
Radiative Lifetimes ◽  
Atoms And Molecules ◽  
New Information ◽  
Excited Species

It is now possible to produce comparatively large concentrations of highly reactive metastable species in laboratory sources and to study metastable atoms and molecules with very long radiative lifetimes by photoionization mass spectroscopy, by vacuum ultraviolet absorption techniques, or by direct observation of the feeble radiation emitted by these excited species. These methods are being used widely to study the collisional deactivation of aeronomically important metastable species by quenching or by reaction. New information on radiative lifetimes, diffusion coefficients, and reaction rate coefficients is now available. These results are tabulated and reviewed in the light of atmospheric measurements and current theories of the terrestrial airglow and aurora.

scholarly journals Differential Diffusivity Effects in Reactive Convective Dissolution

Fluids ◽  
2018 ◽  
Vol 3 (4) ◽  
pp. 83 ◽  
Author(s):  
V. Loodts ◽  
H. Saghou ◽  
B. Knaepen ◽  
L. Rongy ◽  
A. De Wit
Keyword(s):  
Diffusion Coefficients ◽  
Reaction Rate ◽  
Chemical Species ◽  
Mixing Zone ◽  
Simultaneous Presence ◽  
Dynamic Effects ◽  
Density Profiles ◽  
Differential Diffusion ◽  
Different Types ◽  
Double Diffusive

When a solute A dissolves into a host fluid containing a reactant B, an A + B → C reaction can influence the convection developing because of unstable density gradients in the gravity field. When A increases density and all three chemical species A, B and C diffuse at the same rate, the reactive case can lead to two different types of density profiles, i.e., a monotonically decreasing one from the interface to the bulk and a non-monotonic profile with a minimum. We study numerically here the nonlinear reactive convective dissolution dynamics in the more general case where the three solutes can diffuse at different rates. We show that differential diffusion can add new dynamic effects like the simultaneous presence of two different convection zones in the host phase when a non-monotonic profile with both a minimum and a maximum develops. Double diffusive instabilities can moreover affect the morphology of the convective fingers. Analysis of the mixing zone, the reaction rate, the total amount of stored A and the dissolution flux further shows that varying the diffusion coefficients of the various species has a quantitative effect on convection.

Spreadsheet Method for Evaluation of Biochemical Reaction Rate Coefficients and Their Uncertainties by Weighted Nonlinear Least-Squares Analysis of the Integrated Monod Equation

1998 ◽  
Vol 64 (6) ◽  
pp. 2044-2050 ◽  
Author(s):  
Laurence H. Smith ◽  
Perry L. McCarty ◽  
Peter K. Kitanidis
Keyword(s):  
Least Squares ◽  
Mixed Culture ◽  
Substrate Concentration ◽  
Reaction Rate ◽  
Initial Rate ◽  
Weighted Least Squares ◽  
Nonlinear Least Squares ◽  
Rate Coefficients ◽  
Monod Equation ◽  
Best Fit

ABSTRACT A convenient method for evaluation of biochemical reaction rate coefficients and their uncertainties is described. The motivation for developing this method was the complexity of existing statistical methods for analysis of biochemical rate equations, as well as the shortcomings of linear approaches, such as Lineweaver-Burk plots. The nonlinear least-squares method provides accurate estimates of the rate coefficients and their uncertainties from experimental data. Linearized methods that involve inversion of data are unreliable since several important assumptions of linear regression are violated. Furthermore, when linearized methods are used, there is no basis for calculation of the uncertainties in the rate coefficients. Uncertainty estimates are crucial to studies involving comparisons of rates for different organisms or environmental conditions. The spreadsheet method uses weighted least-squares analysis to determine the best-fit values of the rate coefficients for the integrated Monod equation. Although the integrated Monod equation is an implicit expression of substrate concentration, weighted least-squares analysis can be employed to calculate approximate differences in substrate concentration between model predictions and data. An iterative search routine in a spreadsheet program is utilized to search for the best-fit values of the coefficients by minimizing the sum of squared weighted errors. The uncertainties in the best-fit values of the rate coefficients are calculated by an approximate method that can also be implemented in a spreadsheet. The uncertainty method can be used to calculate single-parameter (coefficient) confidence intervals, degrees of correlation between parameters, and joint confidence regions for two or more parameters. Example sets of calculations are presented for acetate utilization by a methanogenic mixed culture and trichloroethylene cometabolism by a methane-oxidizing mixed culture. An additional advantage of application of this method to the integrated Monod equation compared with application of linearized methods is the economy of obtaining rate coefficients from a single batch experiment or a few batch experiments rather than having to obtain large numbers of initial rate measurements. However, when initial rate measurements are used, this method can still be used with greater reliability than linearized approaches.

scholarly journals Temperature-dependent diffusion coefficient of H<sub>2</sub>SO<sub>4</sub> in air: laboratory measurements using laminar flow technique

2016 ◽  
Author(s):  
David Brus ◽  
Lenka Skrabalova ◽  
Erik Herrmann ◽  
Tinja Olenius ◽  
Tereza Travnickova ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Sulfuric Acid ◽  
Relative Humidity ◽  
Laminar Flow ◽  
Diffusion Coefficients ◽  
Loss Rate ◽  
Rate Coefficients ◽  
Flow Conditions ◽  
Flow Tube ◽  
Wall Loss

Abstract. We report measurements of the diffusion coefficient of sulfuric acid in humidified air at a range of relative humidities (from ~4 to 70 %), temperatures (278, 288 and 298 K) and initial H2SO4 concentration (from 1 × 10e6 to 1 × 10e8 molec. cm−3). The diffusion coefficients were estimated from the sulfuric acid wall loss rate coefficients under laminar flow conditions. The flow conditions were verified with additional fluid dynamics model CFD-FLUENT simulations which also reproduced the loss rate coefficients very well at all three temperatures with the maximum difference of 7 % between the measured and simulated values. The concentration of H2SO4 was measured continuously with chemical ionization mass spectrometer (CIMS) at seven different positions along the flow tube. The wall losses of H2SO4 were determined from the slopes of fits to measured H2SO4 concentrations as a function of the position along the flow tube. The observed wall loss rate coefficients, and hence the diffusion coefficients, were independent of different initial H2SO4 concentrations and different total flow rates. However, the determined diffusion coefficients decreased with increasing relative humidity, as also seen in previous experiments, and had a rather strong power dependence of the diffusion coefficient with respect to temperature, around ∝T5.4, which is in disagreement with the expected temperature dependency of ~T1.75 observed for other gases and not tested before for sulfuric acid. The effect of relative humidity on the diffusion coefficient is likely due to stronger hydration of H2SO4 molecules and likely also due to the presence of trace impurities such as amines, possibly brought to the system by humidification. Clustering kinetics simulations using quantum chemical data suggest that also the strong temperature dependence of the observed diffusion coefficient might be explained by increased diffusion volume of H2SO4 molecules due to stronger clustering with base-impurities like amines.

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