Assessment of the Baseline Meteorological and Air Quality Conditions over Uubvlei Oranjemund Namibia

Abstract

The 800 MW Kudu power project in south-west Namibia is a Combined Cycle Gas Turbine (CCGT) that will use natural gas from the Kudu gas field located in the Atlantic Ocean, 170 km off-shore. The Kudu Project aims to respond to the increased power demand in the southern African region and to limit Namibia's importation of energy from South Africa. The proposed site for the CCGT power plant is located at Uubvlei (25 km north of Oranjemund town and less than a kilometre from the coast). The proximity of the ocean to the proposed site means that ocean influence will play a significant role in the meteorological factors that affect pollution dispersion in the atmosphere. It is, therefore, necessary to study its effect by quantifying the occurrence of sea breeze circulation and fog in the region. It is also essential to study the formation and structure of the Thermal Internal Boundary Layer (TIBL) at this location, for it will affect the air quality in the region by creating fumigation conditions. An analysis of the meteorological and air-pollution climatology of the region is of importance in assessing the baseline conditions present over the region. The Air Dispersion Potential (ADP) of the study region was calculated based on an integral index that combines the parameters responsible for the dispersion of pollutants in the atmosphere. The meteorology and air-pollution climatology of the region are studied. These results are based on 20 years of meteorological data from the Alexander Bay weather station as well as on modelled data for a grid over the study region. The focus is predominantly on the parameters that have an influence on pollution dispersion. These include the wind speed and direction, stability conditions, mixing height, temperature, relative humidity, and precipitation. The ADP index, as proposed in the dissertation, gave an indication as to whether conditions were unfavourable, moderate or favourable for the dispersion of pollutants. It was found that, overall, the biggest contributor to favourable dispersion of air-pollution in the region is the Monin-Obukhov Length. Wind speed mostly contributes moderately to ADP, while mixing height is predominantly unfavourable. The occurrence of sea breeze circulation, foggy days, as well as the structure of the TIBL are discussed. Making use of the relevant meteorological data, it was found that sea breeze circulation occurs predominantly in the summer months. Fog conditions at the proposed site also occur mostly during the summer months, with the highest number of foggy hours being in the months of January, March and November. Fog is also expected to occur mostly between 21:00 and 09:00 at this site. All algorithms for the calculation of fog and breeze conditions, TIBL height, and ADP has been realized on MATLAB platform and can be used as a forecasting tool during the operation of the proposed CCGT power station. Taking into account the complicated coastal meteorology at the proposed site, the location is less than ideal and will present many challenges for pollutant dispersion and structural upkeep. The influence of mesoscale meteorological phenomena such as sea breezes and the TIBL, the frequent events of fog and the poor overall mixing heights in the region will all contribute unfavourably to the dispersal of pollutants emitted from the CCGT power station. Re-circulation and fumigation of pollutants will cause high ground-level pollutant concentrations in the region. A location further inland will experience better conditions for pollutant dispersion, less episodes of fog and will not experience the same corrosive effects as a coastal site. Placing the power station approximately 40 km inland could lessen or totally eliminate the effects of the unfavourable mesoscale meteorological phenomena (sea breezes and TIBL) and consequently also the processes of re-circulation and fumigation of pollutants.