Comparison of the performance of two atmospheric dispersion models (AERMOD and ADMS) for open pit mining sources of air pollution By Martha Nyambali Neshuku Submitted as partial fulfilment of the requirements For Masters of Science in Applied Science: Environmental Technology In the Department of Chemical Engineering Faculty of Engineering, Built Environment and Information Technology University of Pretoria 2012 © University of Pretoria Comparison of the performance of two atmospheric dispersion models (AERMOD and ADMS) for open pit mining sources of air pollution Martha Nyambali Neshuku Supervisor: Dr. Gerrit Kornelius Department: Chemical engineering Faculty: Engineering, Built Environment and Information Technology Degree: Masters of Science in Applied Science: Environmental Technology Synopsis The performance of the AERMOD and ADMS dispersion models was tested using PM10 (thoracic dust) emissions from Rössing Uranium Mine open pit in Namibia. The performance of the two models was evaluated against the observations and also against each other using various statistical measures. The models were tested under different case scenarios (cases explained in chapter 4) with the aim of evaluating their performances as well as their inter model variability. The study was undertaken from the 13 July 2009 – 14 August 2009. The results from the study showed that the performance of ADMS was superior to that of AERMOD. In general, the performance of AERMOD was very poor and simulated extremely high concentration values. AERMOD performed even more poorly during calm conditions. ADMS performance was superior to AERMOD as was evident from the values of various performance statistical measures and a conclusion reached was that ADMS is likely to be a better model to use in cases where prolonged calm conditions are experienced. Keywords: air dispersion modeling, fugitive emissions, open cast mining, particulate matters i Acknowledgements First and foremost, I would like to thank and praise the Almighty God for giving me the knowledge and energy to complete this study. Next, I thank Rössing Uranium Limited for funding my studies. My sincere gratitude goes to the Department of Chemical Engineering at the University of Pretoria for partly funding my research. I wish to extend my heartfelt gratitude to my supervisor, Dr. Gerrit Kornelius for his scholarly guidance and support. I am indebted to Neel Breitenbach and Reneé von Gruenewaldt of Airshed Planning Professionals (Pty) Ltd for their assistance in the preparation of the topographical and meteorological files. I also would like to thank Coleen De Villiers of the South African Weather Services for providing me with the meteorological data. I am grateful to the Rössing Uranium Limited employees for the support they rendered to me during the time of my study. Some of them include Aina Kadhila Amoomo, Pedru Shamba, Rabanus Shoopala, Besser Rowhan and Jacklyn Mwenze. I also would like to thank Prof Jairos Kangira for his editorial work. Last but not least, I want to thank my family and friends for their patience and moral support from the beginning of my study to the end. Thank you all. I would not have completed this study without your support. ii Dedication This thesis is dedicated to my late mother, Mrs Diina Neshuku. Despite her physical absence, she continues to be my inspiration in every respect. iii Table of Contents Synopsis ....................................................................................................................................i Acknowledgements.................................................................................................................ii Dedication............................................................................................................................... iii Table of Contents...................................................................................................................iv LIST OF FIGURES.................................................................................................................vi LIST OF TABLES..................................................................................................................vii Abbreviations and Acronyms............................................................................................. viii NOMENCLATURE.................................................................................................................xi Chapter 1: Introduction...........................................................................................................1 1.1 Background ...................................................................................................................1 1.2 Objectives of the study ................................................................................................3 1.3 The outline of the dissertation ....................................................................................4 Chapter 2: Literature Survey .................................................................................................6 2.1 Background information on Rössing Uranium Mine ...............................................6 2.1.1 Location and topography .....................................................................................7 2.1.2 Climate....................................................................................................................8 2.1.3. Mining operations.................................................................................................9 2.1.4 Other sources of dust at Rössing Mine: Processing plant and tailings ......12 2.2 Dust theory ..................................................................................................................13 2.2.1 Dust classification ...............................................................................................14 2.2.2 Impacts of dust ........................................................................................................15 Impacts on human health.............................................................................................15 Impacts on environment...............................................................................................16 Impacts on safety and productivity.............................................................................16 Impacts on operational cost.........................................................................................17 2. 3. Regulations and air quality standards for PM10 ...................................................17 2. 3.1 Ambient Air quality standards for PM10...........................................................17 2. 3.2 Occupational exposure limits for PM10 ...........................................................19 2. 4. Air dispersion modelling theory..............................................................................20 2.4. 1. Mechanisms of pollutants dispersion in the atmosphere...........................21 2.4.2. Types of models .................................................................................................23 2.4.3. Factors affecting dispersion of pollutants in the atmosphere......................27 2.5 Review of models used in the study: AERMOD and ADMS................................31 2.5.1 AERMOD..............................................................................................................31 2.5.2 ADMS....................................................................................................................33 2.6.1 AERMOD studies ................................................................................................35 2.6.2 ADMS studies ......................................................................................................36 2.7. Emission estimation ..................................................................................................39 2.7.1. Drilling and Blasting (EPA, 1998) ....................................................................40 2.7.2. Aggregate handling............................................................................................42 2.7.3. Unpaved road .....................................................................................................43 2.7.4. Wind erosion from active stockpiles................................................................46 Chapter 3: Methodology.......................................................................................................49 3.1 Data collection.............................................................................................................49 3.1.1 Monitoring.............................................................................................................49 3.1.2 Data processing...................................................................................................50 iv 3.2. Modelling methodology.............................................................................................51 3.2.1 Meteorological data.............................................................................................51 3.2.2. Topographical data ............................................................................................52 3.2.3 Source parameters and geometry....................................................................54 3.2.4. Source geometry and location .........................................................................58 3.2.4. Modelling grids and receptor locations...........................................................61