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ASSESSMENT OF CUMULATIVE IMPACTS ON AIR QUALITY: A CASE STUDY OF THE ABOADZE POWER ENCLAVE IN GHANA

초록/요약

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.

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목차

CHAPTER ONE: INTRODUCTION 1
1.1 Introductory Background 1
1.2 Problem Statement 2
1.3 Aim and Objectives of the Assessment Study 5
1.4 Significance of the Assessment Study 5
1.5 Organization of the thesis 6
1.6 Limitations of the Assessment Study 6
CHAPTER TWO: LITERATURE REVIEW 7
2.1 Aboadze Power Enclave in Brief 7
2.2 Description of Existing Power Plants 7
2.3 The Concept of Cumulative Impacts 9
2.4 Air Pollutants from Thermal Power Plant Operation and Effects 11
2.4.1 Air Pollutant Removal Mechanisms 12
2.5 Meteorological Basis for Atmospheric Pollution 12
2.5.1 Transport Phenomenon and Physical Dispersion of Air Pollutants 12
2.5.1.1 Wind Direction 13
2.5.1.2 Wind Velocity 13
2.5.1.3 Turbulence 13
2.6 Methods Used to Predict Air Quality 14
2.6.1 Emission Dispersion Models 15
2.6.2 The Need for Modelling 15
2.6.3 Errors and uncertainties involved in modelling 16
2.6.4 Gaussian Model 16
2.6.4.1 Gaussian Equation 17
2.6.5 AERMOD Software for Air Dispersion Modelling based on Gaussian Model 18
2.6.5.1 AERMOD Model for Pollutant Concentration Prediction 20
2.6.6 Performance Evaluation of Models 21
CHAPTER THREE: METHODOLOGY 22
3.1 Methodology Overview 22
3.2 Key Pollutants Considered 22
3.3 Dispersion Modelling Software Used 22
3.4 Meteorological Data 23
3.5 Modelling Assumptions 24
3.6 Scenarios Considered in the modelling 24
3.6.1 Existing Plants 24
3.6.2 Existing and proposed plants (cumulative) 24
3.7 Modelled Domain and Terrain 24
3.7.1 Domain 24
3.7.2 Terrain 25
3.8 National Ambient Air Quality Guideline and Background Pollutant Concentration Data 25
3.9 Emissions Data, Coordinates of Emission Stacks and Buildings used in the Existing Power Plants’ Modelling 27
3.10 Emissions Data, Coordinates of Emission Stacks and Buildings used in Proposed Power Plants’ Modelling 30
3.11 Criteria for Determining Degraded and Non-degraded Airshed and Impact Magnitude 33
CHAPTER FOUR: RESULTS, ANALYSIS AND DISCUSSION 35
4.1 Detailed Results from Model Simulations 35
4.2 Trend Analysis of Monitoring Station Data 35
4.3 Meteorological Data Processing 36
4.4 Analysis of Existing Power Plants’ Modelling Results 39
4.4.1 Scenario 1: When all plants are operating on light crude oil except Ameri plant which is designed to operate solely on natural gas. 39
4.4.1.1 Dispersion Contour Plots for scenario 1 40
4.4.2 Scenario 2: When all plants are operating on natural gas. 42
4.4.3 Evaluation of Model Results with Existing Monitoring Station Observations 43
4.5 Analysis of Results for Existing and Proposed Power Plants’ Modelling 46
4.5.1 Scenario 1: All plants are operating on natural gas. 46
4.5.1.1 Dispersion Contour Plots for Scenario 1 47
4.5.2 Scenario 2: All existing and proposed plants operate on light crude oil with the exception of plants designed to operate only on natural gas 48
4.5.2.1 Dispersion Contour Plots for Scenario 2 49
4.5.3 Scenario 3: All plants existing plants are operating on light crude oil and proposed plants are operating on natural gas 51
4.5.3.1 Dispersion Contour Plots for Scenario 3 52
4.6 Discussion of Results 53
4.6.1 Trend Analysis of Monitoring Station Observations 53
4.6.2 Meteorological Data Analysis 53
4.6.3 AERMOD Modelling for Existing Plants Operations 53
4.6.3.1 Evaluation of Model Results using Monitoring Station Observations 54
4.6.4 AERMOD Modelling for Existing and Proposed Plants’ Operations 55
4.6.4.1 Scenario 1- Existing and Proposed Plants Operating on Natural Gas 55
4.6.4.2 Scenario 2- Existing and Proposed Plants Operating on Light Crude Oil 56
4.6.4.3 Scenario 3 - Existing Plants Operating on Light Crude Oil and Proposed Plants Operating on Natural Gas 57
CHAPTER FIVE: CONCLUSION AND RECOMMENTATION 58
5.1 Conclusion 58
5.2 Recommendations 59
5.3 Suggestion for Further Assessment Study 60
REFERENCES 61
APPENDICES 65

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