AtmoChem

Kinetic & Photochemistry Data for Atmospheric Chemistry

by Dr. James B. Burkholder and Dr. Vassileios C. Papadimitriou

About AtmoChem

  • The kinetic and photochemical data included in this application focuses on atmospheric science.
  • The user is provided access to atmospherically relevant bimolecular and termolecular rate coefficient (k), equilibrium constant (Keq), and product yield recommendations for gas-phase reactions, and photochemical data.
  • Literature kinetic data is provided graphically and described in the attached notes.

  • The application includes interactive rate coefficient calculators.

  • Photochemical downloadable files are available.

Application Features

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Photochemistry

UV spectra for more than 300 molecules and multi-channel dissociation quantum yields are provided graphically and as downloadable excel files.

Atmospheric Kinetics

Recommended kinetic parameters for atmospherically relevant reactions are provided. Users can access OH, Cl, NO3, and O3 reaction rate coefficient recommendations and can use calculators to determine k(T,P) at input temperature and pressure conditions. Experimental rate coefficient data and recommendations are presented graphically. Atmospheric profiles of compound gas-phase kinetic losses are provided graphically along with notes and references.

Bimolecular Reactions

Reactions that proceed in a single step (one collision) are called bimolecular reactions.

Reaction Scheme: $$A+B \stackrel{k}{\rightarrow} C+D$$

Each reaction selection gives the user access to the reaction conditions (Temperature in K) to k(296 K) and the Arrhenius parameters, k(T) = A exp[-E/(RT)] parameters. Users can input temperature and Arrhenius parameters in a kinetic calculator. Default recommended values can be restored by pressing the “Recommendations” button. Information about the Arrhenius expression is accessible by pressing the info button .

Application Features

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Termolecular Reactions

Reactions that proceed via a relatively unstable intermediate adduct that can be thermally stabilized (via collisions) to products.

Reaction Scheme: $$A+B \underset{k_{-1}}{\stackrel{k_1}{\rightleftharpoons}}{[A B]^*}\underset{k_{2}}{\stackrel{M}{\rightarrow}} A B$$

Each reaction provides fall-off parameters.

Expression: $$k_f(T,[M])=\left\{\frac{k_{\infty }(T) k_0(T)[M]}{k_{\infty }(T)+k_0(T)[M]}\right\} {0.6^{\left\{1+\left[\log _{10}\left(\frac{k_0(T)[M]}{k_{\infty }(T)}\right)\right]^2\right\}^{-1}}}$$

$$k_0(T)=k_0^{298}\left(\frac{298}{T}\right)^n$$

$$k_{\infty}(T)=k_{\infty}^{298}\left(\frac{298}{T}\right)^m$$

Users can calculate rate coefficients with input temperature and pressure conditions. The user can also input fall-off parameters. Default recommended values can be restored by pressing the “Recommendations” button. Information about the fall-off expression can be accessed by pressing the info button, .

Chemical Activation Reactions

Reactions that proceed via a relatively unstable “activated” intermediate that include bimolecular and termolecular reaction pathways of the intermediate. The parallel channels are activated during the reaction process and the reaction scheme is called Chemical Activation Mechanism (CAM).

Reaction Scheme: $$A+B \underset{k_{-1}}{\stackrel{k_1}{\rightleftharpoons}}{[A B]^*}\underset{k_{2}}{\stackrel{M}{\rightarrow}} A B$$

$$[A B]^*{\stackrel{k_{3}}{\rightarrow}} products$$

Selections give the user the 296 K and 760 Torr rate coefficient value, k(296 K, 760 Torr), and the kinetic parameters.

Expression: $$k_f^{C A}(T,[M])=k_{\text {int }}(T)\left[1-\frac{k_f(T,[M])}{k_{\infty }(T)}\right]$$

$$k_{int}(T)=Aexp(-B/T)$$

$$k_f^{total}{(T,[M])}=k_f(T,[M])+k_f^{C A}(T,[M])$$

Users can input temperature and pressure conditions and calculate the rate coefficient, k(T, P), based on the recommended kinetic data. Kinetic parameters can be also input by the user.  Pressing the “Recommendations” button returns the default parameters. Information about the expression used in calculations can be accessed by pressing the info button, .

Application Features

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Equilibrium Reactions

Systems where the forward and backward reaction rates are equal have reached equilibrium.

Reaction Scheme: $$A+B \underset{k_{-1}}{\stackrel{k_1}{\rightleftharpoons}}C+D$$

Selections give the user the 296 K and 760 Torr equilibrium constant, K(296 K, 760 Torr) and the reverse reaction rate coefficient, k-1(T, P), when the forward reaction rate coefficient, k1(T, P), is known.

Users can input temperature and pressure parameters for the equilibrium constant of interest, in the calculator. Default recommended values can be restored by pressing the “Recommendations” button. Kinetic expression information can be accessed by pressing the info button, .

Kinetic Calculator

A user-friendly kinetic calculator for bimolecular, termolecular, chemical activation, and equilibrium reactions with user input parameters.

Team Members

James B. Burkholder

Dr. Burkholder is a research chemist in NOAA’s Earth System Research Laboratory in Boulder, Colorado, USA.

His primary research interest involves laboratory studies and instrument development to elucidate the role of chemical processes in Earth’s atmosphere and their impact on society.

Research studies involve a broad range of topics related to stratospheric ozone depletion, regional and global air quality, and climate change.

Vassileios C. Papadimitriou

Dr. Vassileios C. Papadimitriou leads the Laboratory of Photochemistry and Kinetics in the Department of Chemistry, University of Crete, Greece, where he is on the Lab Teaching Staff. He is also a research scientist (RSII) in the Chemical Processes and Instrument Development research group of NOAA, Boulder, Colorado, USA.

His research work focuses on Physical and Atmospheric Chemistry laboratory studies using state-of-the-art techniques and methods to further the understanding of the atmospheric processing of trace species and evaluate the impact of chemical processes on the environment, air-quality, ozone depletion, human health, and climate change.

CONTACT

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