Kinetics and Mechanisms of Atmospheric Gas-Phase Reactions

Kinetics and mechanisms of atmospheric gas-phase reactions underpin the transformation and removal of trace gases, pollutants and greenhouse substances from the troposphere to the stratosphere. The predominant pathways involve radical-mediated processes, notably those initiated by the hydroxyl radical, alongside ozone, nitrate and chlorine species. Reaction rate coefficients and branching mechanisms dictate the production of secondary pollutants such as ozone and secondary organic aerosol, and they determine atmospheric lifetimes that in turn influence air quality and climate forcing. Advances in experimental kinetics, high-level quantum chemical methods and automated mechanism generation now enable detailed mapping of complex reaction networks and accurate prediction of temperature and pressure dependencies of key reactions.

Research from Nature Portfolio

Recent investigations have applied high-level quantum chemistry and transition-state theory to predict rate coefficients and reaction pathways for small oxygenated organic molecules in the gas phase. For instance, ab initio studies of 2-methoxyethanol have elucidated the energetically preferred unimolecular decomposition channels and associated Arrhenius parameters across a wide temperature range, revealing the prominence of 1,3-hydrogen transfer processes. Complementary work on the reaction of methyl radicals with 2-methoxyethanol employs density functional theory to derive site-specific hydrogen-abstraction barriers and branching ratios, offering a template for the automated construction of reaction mechanisms in atmospheric models.

Kinetics and Mechanisms of Atmospheric Gas-Phase Reactions publication trend

The graph below shows the total number of articles in kinetics and mechanisms of atmospheric gas-phase reactions across all publications each year (not limited to Nature Index journals).

Technical terms

Rate coefficient: A numerical measure of the speed at which a chemical reaction proceeds, expressed per unit concentration and time.

Transition-state theory: A theoretical framework that relates reaction rates to the energy barrier and molecular partition functions at the transition state.

Branching ratio: The fraction of reactant consumption that follows a particular reaction pathway among several competing channels.

Structure–activity relationship: An empirical or semi-empirical model linking molecular structural features to kinetic parameters such as rate coefficients.

Photolysis: The decomposition of a chemical species upon absorption of photons, often initiated by solar radiation in the atmosphere.

Hydroxyl radical: A highly reactive •OH species that serves as the primary oxidant in the atmosphere, initiating the removal of many trace gases.

References

1. Database for the kinetics of the gas-phase atmospheric reactions of organic compounds. Earth System Science Data (2020).
2. Estimation of rate coefficients and branching ratios for gas-phase reactions of OH with aliphatic organic compounds for use in automated mechanism construction. Atmospheric Chemistry and Physics (2018).
3. Evaluated kinetic and photochemical data for atmospheric chemistry: volume VIII – gas-phase reactions of organic species with four, or more, carbon atoms (≥ C4). Atmospheric Chemistry and Physics (2021).
4. Thermochemistry and Kinetics of the Thermal Degradation of 2-Methoxyethanol as Possible Biofuel Additives. Scientific Reports (2019).
5. Computational Studies on the Thermodynamic and Kinetic Parameters of Oxidation of 2-Methoxyethanol Biofuel via H-Atom Abstraction by Methyl Radical. Scientific Reports (2019).