Papers by Keyword: Tropospheric Ozone

Abstract: The rate of transformation of ozone in the troposphere over a temperature range of-100°C and +100°C has been established. Tropospheric ozone with the quality of a strong oxidizing agent, is secondary pollutant species associated with the initiation of numerous chemical reactions in the atmosphere. In this study, a theoretical approach utilized Gibb’s free energy of reaction and enthalpy of reaction in transition state theory model equations to generate chemical equilibrium data and consequently reaction kinetic parameters. The thermochemical properties were obtained using electronic structural methods of the quantum mechanics computational chemistries which approximates the Schrödinger equation. The model chemistry methods were evaluated using the GuassView for generating molecular structures of species and the Gaussian 03 (G03) package for energy computation. The study revealed that the most relevant of the reactions considered was that involving NO with a rate constant of 7.39 x 10¹¹ s^-1 and energy of activation (E_A/R) of-216.98 K while the least involved HS* with rate constant of 9.56 x 10⁶⁹ s^-1 and energy of activation (E_A/R) of-202.95 K.

Abstract: The thermochemical properties of varieties of species needed to assess the most prominent pathways of tropospheric ozone transformation have been established. In the troposphere, ozone which is a secondary pollution produced by photochemical induced transformation, acts as an oxidizing agent to numerous atmospheric reactions leading to the formation of particulate matter. Based on the climate related problems resulting from the precursor of particulate matter, it is adequate to establish the feasible routes of ozone formation. In this study, the electronic structure methods which approximate the Schrödinger equation to compute Gibbs free energies and enthalpies of formation of the various chemical species participating in the reactions were used. These thermodynamic properties were determined using four computational model chemistry methods integrated in the Gaussian 03 (G03) chemistry package. Five known reaction pathways for the formation of NO2 (the O3 precursor specie), as well as the dominant ozone formation route from NO2 were examined and their energies determined. Of all the computational methods, the complete basis set (CBS-4M) method produced energies for all species of the five reaction routes. Out of the five routes, only the reactions involving radical species were favoured to completion over a temperature range of -100 and +100oC. The most relevant reaction route for the formation of NO2 and subsequently O3 is that involving the peroxyl acetyl nitrate (PAN) and hydroxyl radicals. Chemical equilibrium analyses of the reaction routes also indicated that reduction in temperature encourages NO2 formation while increase in temperature favours O3 production.

Abstract: The thermochemical properties of varieties of species involved in the formation and consumption or destruction of tropospheric ozone during chemical reactions have been established. Ozone in the troposphere is produced during the day-time; hence it is a photochemically induced transformation process. This compound acts as precursor specie in many atmospheric transformations and constitutes a baseline component worth investigating. This study utilized electronic structure methods of computational model chemistries to evaluate for Gibbs free energies and enthalpies of formation and reactions of the various species. Ten prominent gas-phase and aqueous-phase reactions were analysed using five computational approaches consisting of four ab initio methods and one density functional theory (DFT) method. The computed energy values in comparison to those obtained through experimental approaches yielded an error of mean absolute deviation of 0.81%. The most relevant species that tend to enhance the production of ozone in the troposphere were O* and H2O2 for the gas-phase and aqueous-phase reactions respectively. Chemical equilibrium analysis indicated that the ozone formation and consumption reactions are more favourable in colder regions and at winter.