Atmospheric Stability across the Lower Troposphere in Enugu City, Nigeria

Abstract

This study surveyed the atmospheric stability pattern in the lower troposphere over Enugu from 2010-2015. The widely and acceptably used Pasquill-Gifford stability scheme was utilized in evaluating the stability categories. Six-hourly synoptic data parameters for temperature, wind speed and cloud cover acquired from the Era-Interim platform at 1000 mbar pressure level were used in the analysis. The data were obtained at 0.125 degree resolution. Results showed that very stable stability classes D (neutral), E (stable), and F (very stable) conditions occurred during the night and early hours of dawn. Also, while class D dominated during the wet season, classes E and F portrayed a reverse trend during the dry season. During the Day, stability classes A (very unstable), B (moderately unstable) and C (slightly unstable) prevailed, however, (class C) prevailed throughout the year. While stability class A was dominant from December to January, with its least influence during the peak of the wet season at noontime, stability classes B and C prevailed during the wet season and was lowest at the peak of the dry season. The occurrence of stability class D at 6:00 pm local time indicates the beginning of transition periods, where increased wind speeds moderates the effects of heat fluxes from the earth’s surface. The surveyed atmospheric stability conditions in Enugu city indicates that emissions will be constrained at ground level during the night, where anthropogenic sources of emissions remain beneath the inversion layer. Nevertheless, where the sources are beyond the inversion layer, dispersion will take place upward away from ground level. Therefore, it is compelling that governments, agencies, and industries control emissions from industries within the city especially at night time to avoid ground level pollutant concentrations that will affect boundary layer dwellers. Also, potential emitters should be restrained from being sited at locations where pollutants could be concentrated with sensitive receptors.