Graduate School of International Studies Ajou University
AERMOD was used to assess the cumulative impact of additional proposed power plants at the Aboadze Power Enclave in Ghana on air quality by predicting the concentrations of air pollutants. The study was conducted to ascertain whether the enclave airshed could be sustained if the proposed power plants come on-stream. Pollutants assessed included: NOx, SO2, PM10, and CO. Emission data for the existing and proposed plants, together with meteorological and terrain data, were used in model simulations within a 25 km × 25 km domain for averaged periods of 1 hour, 24 hours, one month, and one year using different scenarios. Trend analysis was conducted using the results of the monitoring stations in the enclave. The analysis indicated that the airshed has not been degraded by the existing plants since the observed values were below the national ambient air quality guideline limits. The existing plants were modeled and the predicted results were evaluated against observed results from the monitoring stations in the enclave. The evaluation showed that AERMOD model results of PM10 agreed strongly with observations at the monitoring stations; data from the Aboadze Monitoring Station showed a correlation coefficient of 0.87. NOX and SO2 model results, however, agreed only moderately with observations.
The assessment demonstrated that, when the proposed and existing plants operate on light crude oil, the proposed plants would contribute more than 25% of the guideline limits for all pollutants except CO. The cumulative impact would, therefore, be high and the airshed would be degraded. The assessment has also demonstrated that if the existing and proposed plants operate on natural gas, the cumulative impact concentration would be below the national guideline limits for all the pollutants; the cumulative concentrations of pollutants would have a medium impact and the airshed would not be degraded. The proposed plants would, therefore, present a significant increase in the concentrations of pollutants and impact upon the air quality of the enclave. For the enclave to establish all of the six proposed plants used in the modeling, there is a need to operate them mainly on natural gas in order to sustain the airshed. The enclave would not, however, be able to support any more proposed plants apart from those used in the model. The study has highlighted the use of air dispersion modeling (AERMOD) to assess cumulative pollutant concentrations and hence cumulative impact. The findings of the study would help to streamline policies regarding permitting, monitoring, air quality management and airshed sustainability.