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This study surveyed the levels of boundary layer surface turbulence across a West African climate region. Five years (2011-2015) temperature and wind speed data at synoptic hours 0000 Hr, 0600 Hr, 1200 Hr and 1800 Hr within 0.125° grid resolution was sourced from Era-Interim Reanalysis platform at 1000 mbar pressure level. Using the Richardson (Ri) number technique, results showed that mechanical turbulence of Ri range 0.04 - 0.57 dominates across the surface layer for study locations of Port Harcourt, Enugu, Jos, Kano and Maiduguri than thermal turbulence. However, the least turbulent area was the coastal zone of surveyed region. Results also indicated that the vertical height (L) at which thermal turbulence replaces mechanical turbulence across study locations ranged from 20 - 250 m with lowest replacement levels (20 - 50 m) occurring mainly in the coastal area of Port Harcourt during periods of dawn. The most turbulent periods in the southern coastal location of study region were during key rainy periods from June-August while that for the rest far northern inland areas occur during the dry season/early rainy periods i.e. November-May. The implication of the lower surface turbulence/replacement level within coastal domains most especially during periods of dawn is that emission releases near surface layer will be dispersed after initial rise due to buoyancy at horizontal levels thereby increasing ground level pollutants concentration across sensitive receptors that are close to emission source. At heights of thermal turbulence replacement, emission releases will be transported vertically and then dispersed further away from emission sources, thus impacting sensitive receptors at farther distances. This is the atmospheric boundary layer dynamics that makes ground level pollution worse in the coastal city of Port Harcourt in recent times during periods of dawn. Efforts must be made by concerned Stakeholders towards ensuring that emissions are reduced during the periods of dawn within and around coastal environments.

Understanding the spatial distribution of temperature, especially the relationship between temperature and altitude, is essential for understanding both climatological and hydrological processes and their variabilities. This is because those processes are sensitive to air temperature, especially in sub humid tropical regions, where air temperature influences the movements of pollutants and controls exchanges of energy and water fluxes between land and atmosphere particularly within the lower troposphere. This study examined the trend of lower tropospheric lapse rate in the coastal area of Port Harcourt, Nigeria. Six years’ data (2010-2015) for temperature between 1000 mbar and 850 mbar pressure levels was retrieved from era-interim re-analysis platform for the analysis. The data was acquired at 6-hourly synoptic hours: 0000H, 0600H, 1200H and 1800H at 0.125° grid resolution. Findings from the computed environmental lapse rate (ELR) show that conditional instability with an annual lapse rate of 5.5°C/km persists at the area from January to December. It was revealed that the months of December and January constituted the highest ELR trends of 6.5°C/km and 5.9°C/km respectively. This indicates that the month of December assumes a normal tropospheric lapse rate trend. The average range of lapse rate trend in the area which is close to the moist adiabatic lapse rate (MALR) of 5.0°C/km than the dry adiabatic lapse rate (DALR) shows that the study atmospheric environment is rich in water vapour. The 6-hourly synoptic analysis of the ELR pattern shows that lapse rate range between 1°C/km - 6.4°C/km and 6.5°C/km - 10°C/km dominates throughout the year at 0000 - 0600 Hrs and 1200 - 1800 Hrs respectively. This demonstrates a higher and lower lapse rate trend during the day and night periods respectively. Relating study findings to the potential of air to disperse emissions in the area suggests that air emissions will be conveyed through far and near distances across the boundary layers due to the moderate dispersive potential of air regarding the closeness of the average ELR to the MALR. Policies that will ensure that pollutants are dispersed aloft especially emission stacks above 50 m is advocated in the city of Port Harcourt.