Environmental Health Science: Air Pollution

In collaboration with the Ethiopia Public Health Training Initiative, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education

August 2006

Funded under USAID Cooperative Agreement No. 663-A-00-00-0358-00. Produced in collaboration with the Ethiopia Public Health Training Initiative, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education.

Important Guidelines for Printing and Photocopying Limited permission is granted free of charge to print or photocopy all pages of this publication for educational, not-for-profit use by health care workers, students or faculty. All copies must retain all author credits and copyright notices included in the original document. Under no circumstances is it permissible to sell or distribute on a commercial basis, or to claim authorship of, copies of material reproduced from this publication.

©2005 by Mengesha Admassu, Mamo Wubeshet
All rights reserved. Except as expressly provided above, no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission of the author or authors.

This material is intended for educational use only by practicing health care workers or students and faculty in a health care field.

PREFACE
Shortage of appropriate textbooks that could meet the need for training professionals on the nature and the magnitude of ambient and indoor air pollutions and their effects have been one of the outstanding problems in the existing higher health learning institutions in Ethiopia. Therefore, a well-developed teaching material to produce the required qualified health professionals, who are considered to shoulder the responsibility of preventing and controlling of air pollutions by creating awareness and entertaining some interventional measures among the communities, is obvious. The present lecture note on “Air pollution” is therefore, prepared to be used as a teaching material to train mainly environmental health and other students of health category in Ethiopia. It is believed this teaching material plays a significant role to solve the critical shortage of reference books and text on the subject.

The lecture note is designed to make the training somehow a practical application to the actual indoor and out door air pollutions in the country. It contains five chapters in which the major current out/ in-door air pollution problems with their suggested solutions are discussed. Each chapter is presented in simple language and is provided with learning objectives, body introduction, exercises, and suggested reading as appropriate. Text books, journals, internet sources and other lecture manuscript are used to develop this lecture material. We have also incorporated the useful ideas of different instructors of the course to standardize it to its present status, which the authors hope to further improve the draft through the consultations, pretest and revisions. It is also hoped that this lecture note will be of particular use not only for students of health category in colleges and universities, but to those graduates working in health care service institutions and environmental protection agencies.

ACKNOWLEDGEMENTS
We would like to express our thanks to The Carter Center, Atlanta Georgia, for financial supports to the subsequent workshops conducted to develop the lecture note. The Carter Center would also be acknowledged for providing useful guidelines, technical and moral support during the development of the lecture note. All the instructors, who teach the courses in the existing higher teaching-learning institutions, who critically reviewed the manuscript on subsequent mini-workshops, are acknowledged. Finally, we thank all the individuals who have in some ways contributed to this lecture note, either in conversations with us or through reviewing the draft.

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Table Contents
Preface ……………………………………………………………… Acknowledgements ……………………………………………… Table of content ………………………………………………….. List of Tables ………………………………………………………. List of figures/boxes …………………………………………….. Abbreviation ……………………………………………………….. CHAPTER ONE: Introduction ……………………………….. 1.1. Learning Objective …………………………………… 1.2. Introduction to the course …………………………. 1.3. Historical Overview ………………………………….. 1.4. Definition of terms and scale conversion…….. 1.5. Energy Transfer ………………………………………. 1.6. Public Health importance of Air Pollution ……. 1.7. Exercise question ……………………………………. CHAPTER TWO: Meteorology and Air Pollution ……… 2.1. Learning Objective …………………………………… 2.2. Introduction to the chapter ………………………… 2.3. Temperature Lapse rate and stability
…………. 2.4. Wind velocity and turbulence ……………………. 2.5. Plume behavior ……………………………………….. 2.6. The Gaussian Plume Model ……………………… 2.7. Estimation of Plume rise ………………………….. i iii iv viii ix x 1 1 1 8 10 14 15 17 18 18 18 21 32 34 37 42

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CHAPTER THREE: Sources, Types of Air Pollutants and Their Effects……………………………………………. 3.1 Learning Objective ……………………………………. 3.2 Introduction to the Chapter ………………………… may contribute…………………………………………. 3.4 Types of Air Pollutants………………………………. 3.4.1. Conventional Air Pollutants ……………… 3.4.2. Non Conventional Air Pollutants ……….. 3.5. Magnitude and source of ambient air pollution 3.6. Exercise question ……………………………………. CHAPTER FOUR: Industrial Air Pollution ……………… 4.1 Learning Objective ……………………………………. 4.2 Introduction to the Chapter ………………………… 4.3 Types of Industrial Air Pollutants ……………….. 4.4 Air Pollution from Industrial Accidents ………… 4.5 Air Pollution in the Workplace ……………………. 4.6. Exercise question ……………………………………. CHAPTER FIVE: Global Environmental Problems Due to Air Pollution ………………………………… 5.1. Learning Objective …………………………………… 5.2. Introduction to the Chapter ……………………….. 5.3. Global warming (Green house effect) ……….. 5.4. Ozone depletion …………………………………….. 5.5. Acid Rain ………………………………………………. 93 93 93 94 97 100 46 46 46 47 49 49 62 78 83 84 84 84 85 87 90 92

3.3 Common condition to which air pollution exposure

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5.6. Exercise question ……………………………………. CHAPTER SIX: Indoor Air Pollution ……………………… 6.1. Learning Objective …………………………………… 6.2. Introduction to the Chapter ……………………….. 6.3. Environmental tobacco smoke ………………….. 6.4. Radon gas ……………………………………………… 6.5. Formaldehyde ……………………………………….. 6.6. Asbestos ………………………………………………… 6.7. Lead ………………………………………………………. 6.8. Carbon Monoxide ……………………………………. 6.9. Biological Contaminants ………………………….. 6.10. Building materials, furniture’s and chemical products ………………………………………………… 6.11. Sick Building Syndrome (SBS) ………………… 6.12. Indoor air pollution in relation to developing countries ……………………………………………….. 6.13. Exercise questions ………………………………… CHAPTER SEVEN: Risk Assessment…………………… 7.1 Learning Objective ……………………………………. 7.2 Introduction to the Chapter ………………………… 7.3 The health risk assessment and risk management framework …………………………. 7.4. Epidemiological methods………………………….. 7.5. Hazard identification in the field …………………

106 107 107 107 109 110 113 114 114 115 119 120 120 124 135 136 136 136 137 139 153

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7.6. The relationship between dose and health outcome ……………………………………………….. 7.7. Human exposure assessment ………………….. 7.8. Health risk characterization ……………………… 7.10. Exercise question ………………………………….. CHAPTER EIGHT: Sampling and
Analysis ………….. 8.1 Learning Objective ……………………………………. 8.2 Introduction to the Chapter ………………………… 8.3 Ambient Air Quality Standards and Guidelines 8.4 Exercise question …………………………………….. CHAPTER NINE: Air Pollution Prevention and Control 9.1. Learning Objective …………………………………… 9.2. Introduction to the Chapter ……………………….. 9.3. Control of Ambient Air Pollution ……………….. 9.4. Exercise question ……………………………………. REFERENCES ……………………………………………………. APPENDIX …………………………………………………………. 1. Weather- man wind measuring reports system 2. Some questions worth asking about fuel, cooking and ventilation 3. Indoor air sampling procedure 4. Composition of clean dry Atmospheric air 155 157 171 176 177 177 177 178 184 185 185 185 187 195 196 199

7.9. Health in environmental impact assessment (EIA) 172

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List of Tables
1. Examples of common conditions to which air exposure may contribute ………………………………………………………… 48 2. 3. 4. Potential Human effects of Nitrogen Dioxide ……………….. 55 Major types of occupational pulmonary disease ………….. 81 Common air pollutants, their sources and pathological effects on man ……………………………………………………….. 82 5. Types of air pollution by chemical characteristics and source ………………………………………………………………….. 86 6. Predicted carboxyl hemoglobin levels for subjects engaged in Different types of work …………………………….. 116 7. Human Health effects associated with Low-Level carbon monoxide exposure: Lowest-observedadverse-effect level …………………………………………………. 118 8. 9. Sources
of pollutant Emissions in the United States 1959 122 Relative contribution of different emissions and respective pollutants in Sao Paulo. Brazil …………………………………… 179 10. Air quality standards, United States, 1989 …………………… 181 11. WHO Air quality guidelines for Europe, Revised 1994 ….. 182

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List of Figures/boxes
Figures
1. Deaths in London Administration country and the outer ring by weeks ………………………………………. 2. Range of particles diameters from Airborne Dusts and fumes. …………………………………………………… 3. Deposition of dust particles by size …………………. 60 70 53

Boxes
1. London Fog …………………………………………………. 2. Bhopal – A case study of an International disaster 3. Motor vehicle Air pollution: Health effects and control strategies …………………………………………………….. 197 51 89

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ABBREVIATIONS
CNS – COHbDALYS – EPA – EPHTI GCMHS – IRLOAEL – M.P.H. – PM – TSM – TSP – UOGUVVOCCentral Nerve System Carboxihemoglobine. Disability Adjusted Life Years Environmental Protection Agency Ethiopian Public Health Training Initiative Gondar College of Medical and Health Sciences Infrared Radiation Lowest –Observed – Adverse –Effect – Level Miles Per Hour Particulate Matter Total Suspended Matter Total Suspended Particulates University of Gondar Ultra-Violet rays Volatile Organic Compounds

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CHAPTER ONE INTRODUCTION
1.1. Learning Objective
After the completion of this chapter, the student will be able to: 1. Describe the importance of Air as the basic health requirement of human life 2. Define what air pollution means and other related terms 3. Enumerate different types of air pollutants 4. List physical forms of pollutants

1.2. Introduction to the course
Air is essential for life it self; without it we could survive only a few minutes. It constitutes immediate physical environment of living organisms. It is a mixture of various gases like nitrogen, oxygen and carbon dioxide, and others in traces; along with water vapor perceptible as humidity and suspended solids in particulate form. The atmosphere is layered in to four distinct zones of contrasting temperature due to differential absorption of solar energy. The four atmospheric layers are: Troposphere, stratosphere, mesosphere, and thermosphere. Understanding

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how these layers differ and what creates them helps us understand atmospheric function.

TROPOSPHERE
The layer of air immediately adjacent to the earth’s surface is called the troposphere. Ranging in depth from about 16 km (10 mile) over the equator to about 8 km over the poles, this zone is where most weather events occur .Due to the force of gravity and the compressibility of gases, the troposphere contains about 80% of the total mass of the atmosphere .Air temperature drops rapidly with increasing altitude in this layer, reaching about -600C at the top of the troposphere .A sudden reversal of this temperature gradient creates a sharp boundary, the tropopause, that limits mixing between the troposphere and the upper zones. Other characteristics of troposphere • • • • All life activities occur in this zone Contains water vapor, gases and dust The residence time of particle in the troposphere is short due to rain (ppt), gravity, air movement Mixing time is rapid due to
wind or turbulence

STRATOSPHERE
The stratosphere extends from the tropopause up to about 50 km. Air temperature in this zone is stable or even increases with higher altitude. Although 2 more dilute than the

troposphere, the stratosphere has a very similar composition except two important components: water and ozone. The fractional volume of water vapor is about one hundred times lower, and ozone is nearly one thousand times higher than in the troposphere. Ozone is produced by lighting and irradiation of oxygen molecules and would not be present if photosynthetic organisms were not releasing oxygen. Ozone protects life on the earth surface by absorbing most incoming solar ultra violet radiation. Recently discovered decreases in stratospheric ozone over the Antarctica (and to a lesser extent over the whole planet) are of a serious concern if these trends continue, we would be exposed to increasing amount of dangerous UV rays, resulting in: • • • • • Higher rate of skin cancer Problem with eyes (Cataract, conjunctivitis etc.) Genetic mutations Crop failures & Disruption of important living organisms

Other characteristics of stratosphere • • Contain no water vapor and dust Amount of ozone vary depending on location and season of the year. Ozone concentration are lowest above the equator, increasing towards the poles, they also increased markedly between autumn and spring 3

• •

Mixing time is lower Pollution entering in this region tends to remain long time due to low mixing

MESOSPHERE
Above the stratosphere, the temperature diminishes again creating the mesosphere, or the middle layer. The minimum temperature in this region is about -80°C.

THERMOSPHERE
At an altitude of 80 km, another abrupt temperature change occurs. This is the beginning of the thermosphere, a region of highly ionized gases, extending to about 1600 km. Temperatures are very high in the thermosphere because molecules there are constantly bombarded by high energy solar & cosmic radiation The lower part of the thermosphere is called the ionosphere; this is where the aurora borealis (northern lights) appears when showers of solar or cosmic energy causes ionized gases to emit visible light. There is no sharp boundary that marks the end of the atmosphere. Pressure and density decreases gradually as one travels away from the earth until they become indistinguishable from the near vacuum of interstellar space. The composition of the thermosphere also gradually merges with that of interstellar space, being made up mostly of He & H2.

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The immediate concern of human beings is that the nature of air they breathe for oxygen and respiratory should always be access to human body. The thermal comfort experienced and the smell and hearing sense activated through the medium of air are of other area of health concern. What is air Pollution? Air pollution may be defined as any atmospheric condition in which certain substances are present in such concentrations that they can produce undesirable effects on man and his environment. These substances include gases (SOx, NOx, CO, HCs, etc) particulate matter (smoke, dust, fumes, aerosols) radioactive materials and many others. Most of these substances are naturally present in the atmosphere in low (background) concentrations and are usually considered to be harmless. The background concentrations of various components of dry air near sea level and their estimated residence times are given in Annex-1 Thus, a particular substance can be considered as an air pollutant only when its concentration is relatively high compared with the back ground value and causes adverse effects. Air pollution is a problem of obvious importance in most of the world that affects human, plant and animal health. For example, there is good evidence that the health of 900 million urban people suffers daily
because of high levels of ambient air sulfur dioxide concentrations. Air pollution is one of the

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most serious environmental problems in societies at all level of economic development. Air pollution can also affect the properties of materials (such as rubber), visibility, and the quality of life in general. Industrial development has been associated with emission to air of large quantities of gaseous and particulate emissions from both industrial production and from burning fossil fuels for energy and transportation. When technology was introduced to control air pollution by reducing emissions of particles, it was found that the gaseous emissions continued and caused problems of their own. Currently efforts to control both particulate and gaseous emissions have been partially successful in much of the developed world, but there is recent evidence that air pollution is a health risk even under these relatively favorable conditions. In societies that are rapidly developing sufficient resources may not be invested in air pollution control because of other economic and social priorities. The rapid expansion of the industry in these countries has occurred at the same time as increasing traffic from automobiles and trucks, increasing demands for power for the home, and concentration of the population in large urban areas called mega cities. The result has been some of the worst air pollution problem in the world. In many traditional societies, and societies where crude household energy sources are widely available, air pollution 6

is a serious problem because of inefficient and smoky fuels used to heat buildings and cook. This causes air pollution both out door and indoors. The result can be lung disease, eye problems, and increased risk of cancer. The quality of air indoors is a problem also in many developed countries because buildings were built to be airtight and energy efficient. Chemicals produced by heating and cooling systems, smoking and evaporation from buildings materials accumulate indoors and create a pollution problem. In Ethiopia, like many traditional societies, the problem of indoors air pollutions resulted from in efficient and smoky fuels used to heat buildings and cook.
In the rural households of Ethiopia, most of the children and women are staying in overcrowded condition of a one roomed /thatched roof /Tukul/ house that exposed them for the indoor air pollution. It is also known that mothers and children are spending more than 75% percent of their day time at home. Identification of the problems of both at out doors and indoors air pollutions in the societies one has to make interventions to alleviate the health related problems and promote safe ventilation of air in the living and working areas. First, however, some basic science is needed to understand air pollution.

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1.3. Historical overview
Human have undoubtedly been coping with a certain amount of polluted air ever since primitive Homo sapiens sat crouched by the warmth of a smoky fire in his Paleolithic cave. An inevitable consequence of fuel combustion, air pollution mounted as a source of human discomfort as soon as man begins to live in towns and cities. It has become an extremely serious problem on the world wide basis during the past century for two primarily reasons: 1. There has been an enormous increase in world population, particularly in urban areas, and 2. The rapid growth of energy intensive industries and rising level of affluence in the developed countries has led to record levels of fossil fuel combustion Prior to the 20 th Century problems related to air pollution were primarily associated, in public mind at least, with city of London. As early as 18 th

Century small amount of coal from

Newcastle were being shipped in London for fuel. As the population and the manufacturing enterprises grew, wood supplies diminished and coal burning increased, in spite of the protestation of a long serious of both monarchs and private citizens who objected to the odor of coal smoke. One petitioner to king Charles II in 1661 complained that due to the greed of manufacturers, inhabitants of London were forced to “breath nothing but an impure and thick mist, accompanied by 8

a fuliginous (sooty) and filthy vapor, which render them obnoxious to a thousand in conveniences, corrupting the lungs, disordering the entire habit of their bodies. In spite of such railings, English coal combustion increased even faster than the rate of population growth and by the 19th Century London’s thick,” pear soup” fogs had become a notorious trade mark of the city, numerous well meaning attempts at smoke abatement were largely ignored during the hay day of laissez-faire capitalism, epitomized by the industrialists slogan “where there is muck there is money “ The same condition, which had made London air pollution capital of the world, began to prevail in the United States as well during the 19th and early 20th Century. St. Louis. Plagued by smoke condition. Passed an ordinance as early as 1867 mandating that smoke stacks be at least 20 ft higher than adjacent buildings The Chicago City council in 1881 passed the notion first smoke ordinance. Pittsburgh, once one of the smokiest cities in the US was the site of pioneer work at the Mellon In the harmful impact of smoke both on property and human health .In spite of gradually increasing public awareness of the problem, levels of air pollution and the geographical extent of the areas affected continued to increase. Although by the late 1950’s and 1960’s large scale fuel switching from coal to natural gas oil had significantly reduced smoke condition in many American cities, other 9

newer pollutants products of the new ubiquitous automobile had assumed worrisome level. Today foul air has become a problem of global proportions; no longer does one have to travel to London or Pittsburg or Los Angeles to experience the respiratory irritation or the aesthetic distress. The contaminated atmosphere can provoke in the 1990’s virtually every metropolitan area in the world New York, Rome Athens, Bombay, Tokyo, Mexico City capitalist and communities industrialized and developing nation alike are grappling with the problem of how to halt further deterioration air quality with out impending

1.4. Definition of terms and scale conversion
1.4.1. Air pollution: – concentration of foreign matter in air in excessive quantity which is harmful to the health of man. 1.4.2. Indoor air
pollutions: – Pollutions from the housing made materials and living and working activities of the house, such as: natural radiation-radon, domestic combustion-coal gas, and human habitstobacco smoking. 1.4.3. Out door air pollution: – Pollutions from out door services and environmental mixings, such as: 10

transportation-automobiles, atomic energy activities-cleaning of streets.

industries-refineries, and community

plant-nuclear,

1.4.4. Acute effects: – with in twenty four hours of sudden exposure to polluted air illness would occur. 1.4.5. Delayed effect: – The cause and effect relationship of air pollution and chronic effects on health is in a way difficult to prove due to long time contact and accumulation effect. 1.4.6. Aerosols: Small solid or liquid particles (fine

drops or droplets) that are suspended in air. 1.4.7. Dust: – aerosols consist of particles in the solid phase. 1.4.8. Smoke: – aerosols consist of particles in the solidand sometimes also liquid-phase and the associated gases that result from combustion. 1.4.9. Ash: – aerosols of the solid phase of smoke, particularly after it settles into a fine dust. 1.4.10. Particulates: – Small particles, that travel in air and settles or lands on something. 1.4.11. Fumes: – are polydispersed fine aerosols consisting of solid particles that often aggregate together, so that many little particulates may form one big particle. 11

1.4.12. Inhalable fraction: – Particles less than 100 μm that can be inhaled into the respiratory throat (trachea). 1.4.13. Thoracic fraction: – Those particles below 20 μm, that can penetrate into the lungs. 1.4.14. Respirable range: – the greatest penetration and retention of particles is in the range 10.0 to 0.1 μm. 1.4.15. Mist: – A cloud or dense collection of droplets suspended in air. 1.4.16. Vapour: – The evaporated compound in the gas phase. 1.4.17. Troposphere: – The first and lowest of the atmospheric layers
is called the “troposphere”. 1.4.18. Stratosphere: – The second layer of air is called the “stratosphere”. 1.4.19. Ionosphere: – Above the stratosphere is the “ionosphere” the top of which is the border line space. 1.4.20. Thermosphere:- This is a region of highly ionized gases, extending to about 1600 km. 1.4.21. Mesosphere: – Above the stratosphere, or the middle layer. 1.4.22. Wind: – Is simply air in motion

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Unit of measurement
Concentrations of air pollutants are commonly expressed as the mass of pollutant per Unit volume of air mixture, as mg/m3, μg/m3, ng /m3 Concentration of gaseous pollutants may also be expressed as volume of pollutant per million volumes of the air plus pollutant mixture (ppm) where 1ppm= 0.0001 % by volume. It is sometimes necessary to convert from volumetric units to mass per unit volume and vice versa. The relation ship between ppm and mg/m3 depends on the gas density, which in turn depends on: Temperature Pressure Molecular weight of the pollutant The following expression can be uses to convert of between ppm and mg/m3 at any temperature or pressure. mg/m3 = 273 X PPM X molecular wt. X pressure 22.4 X temperature Simply multiply the calculated value obtain μg/m3 The constant 22.4 is the volume in liter occupied by 1 mole of an ideal gas at standard concentration (0 0c and 1 atm.). One of mg/m3 by 1000 to

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mole of any substance is a quantity of that substance whose mass in grams numerically equals its molecular weight

1.5. Energy transfer in the atmosphere
The physical &chemical characteristics of the atmosphere and the critical heat balance of the earth are determined by energy and mass transfer processes in the atmosphere. Incoming solar energy is largely in the visible region of the spectrum (400-700nm). The shorter wavelength blue solar light is scattered relatively more strongly by molecules and particles in the
upper atmosphere, which is why the sky is blue as it is viewed by scattered light. Similarly, light that has been transmitted through scattering atmospheres appears red, particularly around the sun set and sun rise, and under circumstances in which the atmosphere contains a high level of particles. Radiation from the sun arrives just out side the earth’s atmosphere with average annual intensity; called the solar constant (isolation) S, currently equal about 1370 W/m2. If all this energy reached the earth’s surface and was retained, the planet would have vaporized log ago

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Some of the incoming solar energy that hits the earth is reflected back in to the space; such reflected energy is not absorbed by the earth or its atmosphere and does not contribute their heating. The fraction of incoming solar radiation that is a reflected is called albedo, and for the earth, the global annual mean value is now estimated to be about 31 percent.

1.6. Public Health importance of Air
1.6.1 Air pollution is a very complicated physical and chemical system. It can be thought of as a variety of constituents that are dissolved or suspended in air, many of which interact with one another and many of which acts together to produce their effects. 1.6.2 The constituents of air pollution change with the season, with industrial activity, with changes in traffic, and with the prevailing winds, to name just a few relevant factors. The composition of air pollution is, therefore, not constant from day to day or even week to week on an average, but trends to cycle. Average levels go up and down fairly consistently depending on the time of year but the actual levels are highly variable from one year to the next.

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1.6.3 One of the most dangerous modes of transmission of health related problems is, air serves as a vehicle. Therefore poor ventilation of air and overcrowding favorable pollutants. 1.6.4 In Ethiopia rural household conditions, where there are more family members, without having enough
number of doors and windows and staying at home significant proportion of the day time are highly victims for indoor air pollutions. conditions to are the creating more of situation transmission

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1.7. Exercise question
Table 1.1: Exercise on the basic requirements for a healthy environment Please make a rank according to their degree of importance to health Using => ++++ Highly important +++ Moderately important ++ Important + Less important – No important Parameter Air Water Degree of importance Degree of accessibility Magnitude of health problem Risk of pollution at the Global level Risk of pollution at the National level Manageability level: -Globally – National – Households Preventive and control measures: – At policy – At community – At households Other parameters that need to be consider

Food

Settlement

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CHAPTER TWO METEOROLOGY AND AIR POLLUTION
2.1. Learning objective
After the completion of this chapter, the student will be able to: 1. Describe the importance of metrology regarding to air pollution 2. Identify the importance of environmental and adiabatic laps rate 3. State the role of inversion on the concentration of air pollutants 4. Analyze plumes behavior in different environmental conditions

2.2. Introduction to the chapter
Meteorology specifies what happen to puff or plume of pollutants from the time it is emitted to the time it is detected at some other location. The motion of the air causes a dilution of air pollutant concentration and we would like to calculate how much dilution occurs as a function of the
meteorology or atmospheric condition.

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Air pollutants emitted from anthropogenic sources must first be transported and diluted in the atmosphere before these under go various physical and photochemical transformation and ultimately reach their receptors. Otherwise, the pollutant concentrations reach dangerous level near the source of emission. Hence, it is important that we understand the natural processes that are responsible for their dispersion. The degree of stability of the atmosphere in turn depends on the rate of change of ambient temperature with altitude.

I. VERTICAL DISPERSION OF POLLUTANTS
As a parcel of air in the atmosphere rises, it experience s decreasing pressure and thus expands. This expansion lowers the temperature of the air parcel, and there fore the air cools as it rises. The rate at which dry air cools as it rises is called the dry adiabatic lapse rate and is independent of the ambient air temperature. The term adiabatic means that there is no heat exchange between the rising parcel of air under consideration and the surrounding air. The dry adiabatic lapse rate can be calculated from the first law of thermodynamics (1°C per 100m) As the air parcel expands, it does work on the surroundings. Since the process is usually rapid, there is no heat transfer between the air parcel and the surrounding air.

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Saturated adiabatic lapse rate, (Γs)
Unlike the dry adiabatic lapse rate, saturated adiabatic lapse rate is not a constant, since the amount of moisture that the air can hold before condensation begins is a function of temperature. A reasonable average value of the moist adiabatic lapse rate in the troposphere is about 6°C/Km. Example An air craft flying at an altitude of 9 km draws in fresh air at 40°C for cabin ventilation. If that fresh air is compressed to the pressure at sea level, would the air need to be heated or cooled if it is to be
delivered to the cabin at 20°C. Solution As the air is compressed, it warms up it is even easier for the air to hold whatever moisture it may have, had .so there is no condensation to worry about and the dry adiabatic lapse rate can be used, At 10°C per km, compression will raise the air temperature by 10×9=90°C making it -40+90°c=50°C It needs to be the air conditioned The air in motion is called wind, air which is rushing from an area of high pressure towards an area of low pressure. When the weather-man reports the wind to us he uses a measuring system worked out in 1805 by Adoniral Beaufort. For 20

example, a “moderate breeze” is a wind of 13 to 18 miles an hour (see annex 2). Obviously air quality at a given site varies tremendously from day to day, even though the emissions remain relatively constant. The determining factors have to do the weather: how strong the winds are, what direction they are blowing , the temperature profile , how much sun light available to power photochemical reactions, and how long it has been since the last strong winds or precipitation were able to clear the air. Air quality is dependent on the dynamics of the atmosphere, the study of which is called meteorology

2.3. Temperature lapse rate and stability
The ease with which pollutants can disperse vertically into the atmosphere is largely determined by the rate of change of air temperature with altitude. For some temperature profiles the air is stable, that is, air at a given altitude has physical forces acting on it that make it want to remain at that elevation. Stable air discourages the dispersion and dilution of pollutants. For other temperature profiles, the air is unstable. In this case rapid vertical mixing takes place that encourages pollutant dispersal and increase air quality. Obviously, vertical stability of the atmosphere is an important factor that helps

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determine the ability of the atmosphere to dilute emissions; hence, it is crucial to air quality. Let us investigate the relationship between atmospheric stability and temperature. It is useful to imagine a “parcel” of
air being made up of a number of air molecules with an imaginary boundary around them. If this parcel of air moves upward in the atmosphere, it will experience less pressure, causing it to expand and cool. On the other hand, if it moves dawn ward, more pressure will compress the air and its temperature will increase. As a starting point, we need a relationship that expires an air parcel’s change of temperature as it moves up or down in the atmosphere. As it moves, we can imagine its temperature, pressure and volume changing, and we might imagine its surrounding adding or subtracting energy from the parcel. If we make small changes in these quantities, and apply both the ideal gas law and the first law of thermodynamics, it is relatively straightforward to drive the following expression. dQ=CpdT –VdP…………………….. (2.1)

Where: dQ = heat added to the parcel per unit mass (J/kg)
Cp = Specific heat at a constant pressure (1005J/Kg-oC) dT= Incremental temperature change(oC) V = volume per unit mass (m3/kg) dP = Incremental pressure change in the parcel(Pa)

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Let us make the quite accurate assumption that as the parcel moves, there is no heat transferred across its boundary, that is, that this process is adiabatic This means that dQ = 0; so we can rearrange (2.1) as

dT V = − − − − − − − − − − − − − − − − − −(2.2) dP Cp The above equation gives us an indication of how atmospheric temperature would change with air pressure, but what are really interested in is how it changes with altitude .To do that we need to know how pressure and altitude are related. Consider a static column of air with a cross section A, as shown in figure 2.1 .A horizontal slice of air in that column of thickness dZ and density ρ will have mass ρAdZ. If the pressure at the top of the slice due to the weight of air above it is P(Z+dZ), then the pressure at the bottom of the slice ,P(Z) will be P(z+dz)plus the added weight per unit area of the slice it self:

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P ( z ) = P( z + dz ) +

gρAdz − − − − − − − − − − − − − − − − − − − (2.3) A

Where: g is the gravitational constant. We can write the
incremental pressure dP for incremental change in elevation, dz as

dP= p(z+dz) –p(z) = -gρdz……………………(2.4) Expressing the rate of change in temperature with altitude as a product, and substituting in (2.2) and (2.3), gives

dT dT dP V = × = (− gρ ) − − − − − − − − − − − − − − − − − −(2.5) dZ dP dZ Cp However, since V is volume per unit mass and ρ is mass per unit volume, the product Vρ=1 , and the expression simplifies to

dT − g = − − − − − − − − − − − − − − − − − − − − − − − − − (2.6) dZ Cp

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The negative sign indicates that temperature decreases with increasing altitude. Substituting the constant g =9.806m/s2, and the constant –volume specific heat of dry air at room temperature, Cp 1005J/kg. 0C in (2.6) yields 1J dT − 9.806m / s 2 = x = −0.009760 c / m ….…(2.7) 2 2 dZ 1005J / kg − oC Kg − m / s

Γ=−

dT = 9.760 C / km ≈ 100 C ……………………. (2.8) dZ

ATMOSPHERIC STABILITY
The ability of the atmosphere to disperse the pollutants emitted in to it depends to a large extent on the degree of stability. A comparison of the adiabatic lapse rate with the environmental lapse rate gives an idea of stability of the atmosphere. When the environmental lapse rate and the dry
adiabatic lapse rate are exactly the same, a raising parcel of air will have the same pressure and temperature and the density of the surroundings and would experience no buoyant force. Such atmosphere is said to be neutrally stable where a displaced mass of air neither tends to return to its original position nor tends to continue its displacement

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When the environmental lapse rate (-dT/dz.)Env is greater than the dry adiabatic lapse rate,Γ the atmosphere is said to be super adiabatic. Hence a raising parcel of air, cooling at the adiabatic rate, will be warmer and less dense than the surrounding environment. As a result, it becomes more buoyant and tends to continue it’s up ward motion. Since vertical motion is enhanced by buoyancy, such an atmosphere is called unstable. In the unstable atmosphere the air from different altitudes mixes thoroughly. This is very desirable from the point of view of preventing pollution, since the effluents will be rapidly dispersed through out atmosphere. On the other hand, when the environmental lapse rate is less than the dry adiabatic lapse rate, a rising air parcel becomes cooler and denser than its surroundings and tends to fall back to its original position. Such an atmospheric condition is called stable and the lapse rate is said to be sub adiabatic. Under stable condition their is very little vertical mixing and pollutants

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can only disperse very slowly. As result, their levels can build up very rapidly in the environment. When the ambient lapse rate and the dry adiabatic lapse rate are exactly the same, the atmosphere has neutral stability. Super adiabatic condition prevails when the air temperature drops more than 1°C /100m; sub adiabatic condition prevail when the air temperature drops at the rate less than 1°c/100m

Inversion
Atmospheric inversion influences the dispersion of pollutants by restricting vertical mixing. There are several ways by which inversion layers can be
formed .One of the most common types is the elevated subsidence inversion, This is usually associated with the sub tropical anti cyclone where the air is warmed by compression as it descends in a high pressure system and achieves temperature higher than that of the air under neath. If the temperature increase is sufficient, an inversion will result • • • It lasts for months on end Occur at higher elevation More common in summer than winter

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Altitude Inversion layer

The subsidence is caused by air flowing down to replace air, which has flowed out of the high-pressure region

Radiation Inversion
The surface of the earth cools down at night by radiating energy toward space. On cloudy night, the earth’s radiation tends to be absorbed by water vapor, which in turn reradiates some of that energy back to the ground. On the clear night, however, the surface more readily radiate energy to space, and thus ground cooling occurs much more rapidly. As the ground cools, the temperature of the air in contact with the ground also drops. As is often the case on clear winter nights, the temperature of this air just above the ground becomes colder than the air above it, creating an inversion. Radiation inversions begins to form at dusk .As the evening progresses, the inversion extends to a higher and higher elevation, reaching perhaps a few hundred meters before the morning sun warms the ground again, breaking up the inversion. 28

Radiation inversion occurs close to the ground, mostly during the winter, and last for only a matter of hours. They often begin at about the time traffic builds up in the early evening, which traps auto exhaust at ground level and causes elevated concentration of pollution for commuters. With out sunlight, photochemical reactions can not takes place, so the biggest problem is usually accumulation of carbon monoxide (CO). In the morning, as the sun warms the ground and the inversion begins to the break up,
pollutants that have been trapped in the stable air mass are suddenly brought back to earth in a process known as fumigation. Fumigation can cause shortlived high concentrations of pollution at ground level. Radiation inversions are important in another context besides air pollution. Fruit growers in places like California have long known that their crops are in greatest danger of frost damage on winter nights when the skies are clear and a radiation inversion sets in. Since the air even a few meters up is warmer than the air at crop level, one way to help protect sensitive crops on such nights is simply to mix the air with large motor driven fans.

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Subsidence inversion

Radiation inversion

Temperature The third type of inversion, know as advective inversion is formed when warm air moves over a cold surface or cold air. The inversion can be a ground based in the former case, or elevated in the latter case. An example of an elevated advective inversion occurs when a hill range forces a warm land breeze to follow at high levels and cool sea breathes flows at low level in the opposite direction.

TOPOGRAPHICAL EFFECTS
In large bodies of water the thermal inertia of the water causes a slower temperature change than the near by land. For example, along an ocean coastline and during periods of high solar input, the daytime air temperature over the ocean is lower than over the land. The relative warm air over the land 30

rises and replaced by cooler ocean air. The system is usually limited to altitudes of several hundred meters, which of course, is where pollutants are emitted. The breeze develops during the day and strongest in mid after noon. At night the opposite may occur, although, usually not with such large velocities. At night the ocean is relatively warm and the breeze is from the
cooler land the warmer ocean. The on shore breeze is most likely in the summer months, while the off-shore land breeze more likely occur in winter months. A second common wind system caused by topographical effect is the mountain – valley wind. In this case the air tends to flow down the valley at night Valleys are cooler at higher elevation and the driving force for the airflow result from the differential cooling. Similarly, cool air drains off the mountain at night and flows in to the valley. During the day light hours an opposite flow may occur as the heated air adjacent to the sun warmed ground begins to rise and flow both up the valley and up the mountain slopes. However, thermal turbulence may mask the daytime up- slope flow so that it is not as strong as the nighttime down – slope flow. Both the sea breeze and the mountain valley wind are important in meteorology of air pollution. Large power stations are often located on ocean costs or adjacent to large lakes. In this case the stack effluent will tend to drift over the land during the day and may be subjected to fumigation.

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2.4. Wind velocity and turbulence
The wind velocity profile is influenced by the surface roughness and time of the day. During the day, solar heating causes thermal turbulence or eddies set up convective currents so that turbulent mixing is increased. This results in a more flat velocity profile in the day than that at night. The second type of turbulence is the mechanical turbulence, which is produced by shearing stress generated by air movement over the earth’s surface. The greater the surface roughness, the greater the turbulence. The mean wind speed variation with altitude is the planetary boundary layer can be represented by a simple empirical power.

U ⎡Z⎤ = α − − − − − − − −( 211) . U 1 ⎢ Z1⎥ ⎣ ⎦ Where: U is the wind at altitude Z U1 is the wind speed at altitude Z1

α

The exponent varies between 0.14 and 0.5 depending on the roughness of the
ground surface as well as on the temperature stability of the atm.

α = 0.25 for unstable atmosphere
= 0.5 for stable condition

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In practice, because of the appreciable change in wind speed with altitude, a wind speed value must be quoted with respect to the elevation at which it is measured. This reference height for surface wind measurement is usually 10 meters Table 2.1: Wind velocity in different topography Surface configuration Smooth open country Stability Unstable Neutral Moderate stability Large stability Flat open country Sub-urns Urban area

α
0.11 0.14 0.20 0.33 0.16 0.28 0.40

Atmospheric turbulence is characterized by different sizes of eddies. These eddies are primarily responsible for diluting and transporting the pollutants injected in to the atmosphere. If the size of the eddies is larger then the size of the plume or a puff then the plume or the puff will be transported down wind by the eddy with little dilution. Molecular diffusion will ultimately dissipate the plume or the puff. If the eddy is smaller than the plume or the puff, the plume or the puff will be disperse uniformly as the eddy entrains fresh air at its boundary.

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2.5. Plume behavior
The behavior of a plume emitted from an elevated source such as a tall stack depends on the degree of instability of the atmosphere and the prevailing wind turbulence.

Classification of plume behavior
1. Looping: it occurs under super adiabatic conditions with light to moderate
wind speeds on a hot summer after noon when large scale thermal eddies are present. The eddies carry portion of a plume to the ground level for short time periods, causing momentary high surface concentration of pollutants near the stack. Thus the plume moves about vertically in a spastic fashion and the exhaust gases disperse rapidly 2. Conning: It occurs under cloudy skies both during day and night, when the lapse rate is essentially neutral. The plume shape is vertically symmetrical about the plume line and the major part of the pollutant concentration is carried down -wind fairly far before reaching the ground level. 3. Fanning: occurs when the plume is dispersed in the presence of very light winds as a result of strong atmospheric inversions. The stable lapse rate suppresses the vertical mixing, but not the horizontal mixing entirely. For high stacks, fanning is considered a favorable 34

meteorological condition because the plume does not contribute to ground pollution. 4. Fumigation: here a stable layer of air lies a short distance above the release point of the plume and the unstable air layer lies below the plume .This unstable layer of air causes the pollutant to mix down -wind toward the ground in large lumps, but fortunately this condition is usually of short duration lasting for about 30 minutes Fumigation is favored by clear skies and light winds, and it is more common in the summer seasons. 5. Lofting : The condition for lofting plume are the inverse of those for fumigation , when the pollutants are emitted above the inverse layer , they are dispersed vigorously on the up ward direction since the top of the inversion layer acts as a barrier to the movement of the pollutants towards the ground . 6. Trapping: occurs when the plume effluent is caught between two inversion layers. The diffusion of the effluent is severely restricted to the unstable layer between the two unstable layers.

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PLUME DISPERSION
Dispersion is the process by which contaminants move through the air and a
plume spreads over a large area, thus reducing the concentration of pollutants it contains. The plume spreads both horizontally and vertically. If it is gaseous, the motion of the molecules follows the low of gaseous diffusion The most commonly used model for the dispersion of gaseous air pollutants is the Gaussian, developed by Pasquill, in which gases dispersed in the atmosphere are assumed to exhibit idea gas behavior

2.6. The Gaussian plume model
The present tendency is to interpret dispersion data in terms of the Gaussian model. The standard deviations are related to the eddy diffusivities

Plume dispersion coordinate sysem, showing Gaussian distributions in the horizontal and vertical directions (Turner, 1970)