Mixed layer depth, Solar and flare stack radiations, Atmospheric boundary layer Abstract: Mixing of chemical species released from pollution sources occurs at certain heights in the atmospheric boundary layer of the troposphere. Within this height, mixing of materials occurs due to convective heat transport and mechanical (wind) actions. The mixed layer height can be estimated by analyzing measured meteorological parameters. In this study, the parameterization of meteorological variables based on established mathematical models were used to compute mixed layer height over Olorunsogo in Ogun State, Nigeria. The vertical extent through which pollutants mix occurs was described in a height-temperature profile for both the day time and nocturnal characteristics. The mixing depths were computed for two locations comprising one area with gas flaring operation present and another with no flare stack present. The findings of this study revealed that mixed layer depth for the location without flaring activities, day time ranged between 1200m and 1400m, and at night time as well as early morning ranged between 150m and 400m. In contrast with the location where gas flaring occurred, mixing height ranged between 9280m and 9310m for day time and between 9100m and 9180m for nocturnal period. In addition, it was observed that pollution trapped below the flare during the day, experience rapid vertical motion due to outgoing long wave radiation (OLR) from the surface. While above the flare a vertical motion coupled with dispersion occurs under lapse rate for pollutants, but remained trapped at the inversion layer. At night time, pollutants around the flare advect vertically and experience rapid vertical dispersed motion and after going through the flare are trapped at the inversion layer. Hence most submicron sized particulate matter hardly reaches ground level over areas where gas flaring operations occur except entrainments in wet depositions predominantly through rainfall.
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.
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.
The levels of emissions of gaseous pollutants from indoor fires within the conventional apartment types in Benin City have been studied. In Nigeria indoor smokes from domestic activities and mosquito coils occur in a significant number of houses. This study was conducted using carbon monoxide as a tracer gas within smoke in households over Benin City. Measurements were conducted using the most common residential building-type (flats) in the region. Sampling was done at 0.1m AGL, 1.0m AGL, 2.0m AGL and ceiling height to ascertain vertical distribution. The study indicated that huge levels of CO ranging between 25 and 40 ppm were observed in the self-contained or bachelor’s flat with windows closed during the night for guard against mosquitoes and crawling insects, while similar apartments with windows opened during the night equipped with protective mosquito nets showed CO concentrations with levels of between 28 and 42 ppm. The results of both house-types were significant when compared with values of the World Health Organization (WHO) and Federal ministry of environment (FMENV) acceptable limits for indoor CO concentrations.
In consideration to the numerous impacts of coal burning especially in domestic indoor fires, a coal-based composite solid fuel has been developed to immensely reduce gaseous emissions, while at the same time maintaining good heat generation rate. The fuel-type which was produced from a mixture of coal and clay solution yielded its optimum heating properties and minimum emission for a formulation of 2:1 of coal: clay solution (1:2.5 of clay: water) by mass fraction. The calorific value of the pure coal was higher than that of composite coal by a factor 1.2 for the same mass of sample used. The formulated composite solid fuel which was found to compete favourably with pure coal, was also efficient toward gaseous emission reduction when combusted at 400oC than at 800oC.
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