Preview Environmental Chemistry, 5th Edition by Colin Baird, Michael Cann (2012)

Preview Environmental Chemistry, 5th Edition by Colin Baird, Michael Cann (2012) Preview Environmental Chemistry, 5th Edition by Colin Baird, Michael Cann (2012) Preview Environmental Chemistry, 5th Edition by Colin Baird, Michael Cann (2012) Preview Environmental Chemistry, 5th Edition by Colin Baird, Michael Cann (2012) Preview Environmental Chemistry, 5th Edition by Colin Baird, Michael Cann (2012)

ENVIRONMENTAL CHEMISTRY

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Preface xii

Introduction to Environmental Problems, Sustainability, and Green

Chemistry xix

PART I Atmospheric Chemistry and Air Pollution 1

Chapter 1 Stratospheric Chemistry: The Ozone Layer 3

Introduction 3

The Physics, Chemistry, and Biology of UV 6

Activity 11

Stratospheric Chemistry: The Ozone Layer 13

Catalytic Processes of Ozone Destruction 20

Box 1-1 The Rates of Free-Radical Reactions 22 Box 1-2 Calculating the Rates of Reaction Steps 24 Box 1-3 The Steady-State Analysis of Atmospheric Reactions 30

Review Questions 33

Additional Problems 34

Chapter 2 The Ozone Holes 37

Introduction 37

The Ozone Hole and Mid-Latitude Ozone Depletion 37

The Chemistry of Ozone Depletion 40

Polar Ozone Holes 49

Activity 49

Box 2-1 The Chemistry Behind Mid-Latitude Decreases in Stratospheric

Ozone 52

The Chemicals That Cause Ozone Destruction 54

Green Chemistry: The Replacement of CFC and Hydrocarbon Blowing

Agents with Carbon Dioxide in Producing Foam Polystyrene 57

Green Chemistry: Harpin Technology—Eliciting Nature’s Own Defenses

Box 3-1 The Interconversion of Gas Concentrations 71

Urban Ozone: The Photochemical Smog Process 76

Activity 81

Improving Air Quality: Photochemical Smog 87Green Chemistry: Strategies to Reduce VOCs Emanating from Organic Solvents 101

Green Chemistry: A Nonvolatile, Reactive Coalescent for the

Reduction of VOCs in Latex Paints 101

Green Chemistry: The Replacement of Organic Solvents with

Supercritical and Liquid Carbon Dioxide; Development of Surfactants for This Compound 103

Box 3-2 Supercritical Carbon Dioxide 104 Green Chemistry: Using Ionic Liquids to Replace Organic Solvents:

Cellulose, a Naturally Occurring Polymer Replacement for Petroleum-Derived Polymers 105

Improving Air Quality: Sulfur-Based Emissions 109Particulates in Air Pollution 118

Air Quality Indices and Size Characteristics for Particulate Matter 126

Box 3-3 The Distribution of Particle Sizes in an Urban Air Sample 129

Review Questions 161Additional Problems 162

PART II Energy and Climate Change 163

Chapter 5 The Greenhouse Effect 165

Introduction 165The Mechanism of the Greenhouse Effect 166Activity 169

Box 5-1 A Simple Model of the Greenhouse Effect 173

Molecular Vibrations: Energy Absorption by Greenhouse Gases 175The Major Greenhouse Gases 177

Other Greenhouse Gases 187

Box 5-2 Determining the Emissions of “Old Carbon” Sources

of Methane 190

The Climate-Modifying Effects of Aerosols 197

Box 5-3 Cooling over China from Haze 202

Global Warming to Date 202

Contents

Geoengineering Earth’s Climate to Combat Global Warming 210

Atmospheric Residence Time Analysis 216

Review Questions 219

Additional Problems 220

Chapter 6 Energy Use, Fossil Fuels, CO 2 Emissions,

and Global Climate Change 223

Box 6-3 The Deepwater Horizon Oil Spill Disaster 242

Green Chemistry: Polylactic Acid—The Production of Biodegradable

Polymers from Renewable Resources; Reducing the Need for Petroleum and the Impact on the Environment 249

The Storage of Carbon Dioxide 257

Activity 264

Other Schemes to Reduce Greenhouse Gases 264

Box 6-4 Removing CO2 from the Atmosphere: Direct Air Capture 265

Carbon Dioxide Emissions in the Future 267

Activity 268

The Extent and Potential Consequences of Future Global

Warming 276Review Questions 288

Green Chemistry Questions 289

Production of Chemicals and Liquid Fuels 311

Thermochemical Production of Fuels, Including Methanol 313

Hydrogen—Fuel of the Future? 320

Review Questions 334

Green Chemistry Questions 335

Additional Problems 336

Chapter 8 Renewable Energy Technologies: Hydroelectric, Wind, Solar, Geothermal, and Marine Energy and

Their Storage 337

Introduction 337Hydroelectric Power 338Wind Energy 340Marine Energy: Wave and Tidal Power 348Geothermal Energy 349

Direct Solar Energy 354The Storage of Renewable Energy—Electricity and Heat 369Activity 371

Review Questions 371Additional Problems 372

Chapter 9 Radioactivity, Radon, and Nuclear Energy 373

Introduction 373Radioactivity and Radon Gas 374

Box 9-1 Steady-State Analysis of the Radioactive Decay

Series 379

Nuclear Energy 383Environmental Problems of Uranium Fuel 390

Box 9-2 Radioactive Contamination by Plutonium Production 395

Accidents and the Future of Nuclear Power 398Nuclear Fusion 402

Review Questions 405Additional Problems 406

PART III Water Chemistry and Water Pollution 407

Chapter 10 The Chemistry of Natural Waters 409

Introduction 409Oxidation–Reduction Chemistry in Natural Waters 413

Green Chemistry: Enzymatic Preparation of Cotton Textiles 418

Acid–Base and Solubility Chemistry in Natural Waters:

The Carbonate System 430

Box 10-1 Derivation of the Equations for Species Diagram

Curves 432

The CO2–Carbonate System 432

Box 10-2 Solubility of CaCO3 in Buffered Solutions 437

Ion Concentrations in Natural Waters and Drinking Water 442Activity 445

Review Questions 451

Green Chemistry Questions 452

Additional Problems 452

The Accumulation of Organochlorines in Biological Systems 584Principles of Toxicology 589

Organophosphate and Carbamate Insecticides 597Activity 599

Activity 601Natural and Green Insecticides, and Integrated Pest Management 601

Green Chemistry: Insecticides That Target Only Certain Insects 603 Green Chemistry: A New Method for Controlling Termites 604 Green Chemistry: Spinetoram, an Improvement on a Green

Pesticide 605

Herbicides 607

Box 13-1 Genetically Engineered Plants 611

Final Thoughts on Pesticides 616

Box 13-2 The Environmental Distribution of Pollutants 617

Box 14-1 Deducing the Probable Chlorophenolic Origins of a Dioxin 628

PCBs 631

Box 14-2 Predicting the Furans That Will Form from a Given PCB 638

Other Sources of Dioxins and Furans 641

Green Chemistry: H2O2, an Environmentally Benign Bleaching Agent for the Production of Paper 643

The Health Effects of Dioxins, Furans, and PCBs 646Review Questions 659

Green Chemistry Questions 660

Additional Problems 660

Chapter 15 Other Toxic Organic Compounds

of Environmental Concern 663

Introduction 663Polynuclear Aromatic Hydrocarbons (PAHs) 664

Box 15-1 More on the Mechanism of PAH Carcinogenesis 670

Contents

PART V Environment and the Solid State 695

Chapter 16 Wastes, Soils, and Sediments 697

Introduction 697

Domestic and Commercial Garbage: Its Disposal and Minimization 698

The Recycling of Household and Commercial Waste 705

Green Chemistry: Development of Bio-based Toners 710

Activity 715

Green Chemistry: Development of Recyclable Carpeting 717

Soils and Sediments 719

Hazardous Wastes 742

Review Questions 750

Green Chemistry Questions 751

Additional Problems 752

PART VI Advanced Atmospheric Chemistry 753

Chapter 17 The Detailed Free-Radical Chemistry

Appendix Oxidation Numbers and Redox Equation

Balancing Reviewed AP-1 Answers to Selected Odd-Numbered Problems AN-1

Index I-1

To the Student

There are many definitions of environmental chemistry To some, it is solely the chemistry of Earth’s natural processes in air, water, and soil More com-monly, as in this book, it is concerned principally with the chemical aspects

of problems that humankind have created in the natural environment

Part  of this infringement on the natural chemistry of our planet has been a result of the activities of our everyday lives In addition, chemists, through the products that they create and the processes by which they make these products, have also had a significant impact on the chemistry of the environment

Chemistry has played a major role in the advancement of society and in making our lives longer, healthier, more comfortable, and more enjoyable

The effects of human-made chemicals are ubiquitous and in many instances quite positive Without chemistry there would be no pharmaceutical drugs,

no computers, no automobiles, no TVs, no DVDs, no lights, no synthetic fibers However, along with all the positive advances that result from chem-istry, copious amounts of toxic and corrosive chemicals have been produced and dispersed into the environment Historically, chemists as a whole have not always paid enough attention to the environmental consequences of their activities

But it is not just the chemical industry, or even industry as a whole, that has emitted substances into the air, water, and soil that are troublesome The fantastic increase in population and affluence since the Industrial Revolution has overloaded our atmosphere with carbon dioxide and toxic air pollutants, our waters with sewage, and our soil with garbage We are exceeding the planet’s natural capacity to cope with waste, and in many cases, we do not know the consequences of these actions As a character in Margaret

Atwood’s novel Oryx and Crake (McClelland and Stewart, 2003) stated,

“The whole world is now one vast uncontrolled experiment.”

During your journey through the chapters in this text, you will see that scientists do have a good handle on many environmental chemistry prob-lems and have suggested ways—although sometimes very expensive ones—

to keep us from inheriting the whirlwind of uncontrolled experiments on the planet Chemists have also become more aware of the contributions of their own profession and industry in creating pollution and have created the

concept of green chemistry to help minimize their environmental footprint in

the future

To illustrate these efforts, case studies of their initiatives have been cluded in the text However, as a prelude to these studies, the Introduction discusses something of the history of environmental regulations—especially

in-in the United States—and the prin-inciples, as well as an illustrative tion, of the green chemistry movement that has developed As concerns over

Preface

such issues as food, water, energy, climate change, and waste production

es-calate, the concept of sustainability is rapidly moving from the wings to center

stage on the world agenda Sustainability is introduced in the following

Introduction section and issues related to sustainability are blended throughout

the text

Although the science underlying environmental problems is often deningly complex, the central aspects of it can usually be understood and

mad-appreciated with only introductory chemistry as background preparation

However, students who have not had some introduction to organic

chemis-try are encouraged to work through the Background Organic Chemischemis-try

sec-tion in the online Appendix, particularly before tackling Chapters 13 to 15

Furthermore, the listing of general chemistry concepts that will be used in

each chapter should assist in identifying topics from the earlier course

mate-rial that would be worth reviewing

To the Instructor

Environmental Chemistry, Fifth Edition, has been revised, updated, and

ex-panded in line with comments and suggestions made by a variety of users

and reviewers of the fourth edition Since some instructors prefer to cover

chapters in an order different from ours, each chapter’s opening outline lists

previously introduced concepts that will be used again, which should

facili-tate reordering Furthermore, we have divided the material into smaller

subsections and numbered them The Detailed Chemistry of the Atmosphere

chapter has been repositioned to the end of the book since many instructors

do not teach from it, although in a course, it can readily follow Chapter 3

In addition, following discussions with our reviewers, in Chapter 13 we have

deleted some of the descriptive information about pesticides that are no

longer in use

We have expanded the coverage of topics related to climate change, especially the generation of sustainable, renewable energy—which is now

covered in two chapters, the first on biofuels and other alternative fuels, and

the second on solar energy As a consequence, this edition could be used as

the text for a number of types of courses in addition to Environmental

Chemistry For example, a one-semester Energy and the Environment course

might use Chapters 3 through 9 Instructors who do not cover policy

implica-tions of energy and climate change topics could skip the first and last parts

of Chapter 6

As in previous editions, the background required to solve both in-text and end-of-chapter problems is either developed in the text or would have

been covered previously in a general chemistry course—as listed for each

chapter at its beginning Where appropriate, hints are given to start students

on the solution The Solutions Manual to the text includes worked solutions

to most problems (other than Review Questions, which are designed to

direct students back to descriptive material within each chapter)

New to This Edition

Our philosophy in revising the textbook this time has been to make it more user-friendly (both for instructors and for students) as well as to bring it up-to-date Furthermore, we have expanded the coverage of energy production

ways to combat climate change

• Subsection numbering—to allow instructors to assign material to be covered

or skipped more easily and students to find particular topics more easily

• Breaking the text into smaller subsections and shorter paragraphs—to

promote student understanding and allow maximum instructor flexibility

• More schematic diagrams—to promote student comprehension of the

more complicated chemistry and appeal to a variety of learning styles

• An Activity has been inserted into many chapters—these Web- or

library-based miniprojects could be assigned to individual students or to a group to report on

• Marginal notes—to supplement the main text with additional interesting

material and to indicate which Review Questions are relevant to the material

at hand

• More hints and background—added to the more difficult in-text Problems

and Additional Problems

• Parts III and IV have been interchanged—so that water chemistry

appears earlier in the book, as preferred by many instructors

• Detailed mathematical material has been repositioned—toward the end

of the chapter in many cases, so instructors have flexibility in coverage

• Increased international coverage—to give all students a better perspective

on environmental problems and solutions around the world For example, there

and air quality standards in developed as well as developing countries

• An Appendix has been added—to review the balancing of redox equations

and assignment of oxidation numbers (states)

• Organic Chemistry Appendix has been moved—to the textbook’s Web site

at www.whfreeman.com/envchem5e

Preface

New Green Chemistry Cases

Latex Paints

Chemicals and Liquid Fuels

• Spinetoram, an Improvement on a Green Pesticide

New Material on Climate Change and CO2

Substantial sections on the following topics have been added:

Nuclear Fuel

Significant additions have also been made on many other topics, including:

Updates have been made throughout the book, especially concerning:

• Catalytic converters for diesel-powered vehicles

including in swimming pools

geographic scope

Supplements

The book companion Web site at www.whfreeman.com/envchem5e offers Case Studies that let students explore current environmental controversies and a Background Organic Chemistry section that provides a necessary in-troduction for those students who have not taken organic chemistry Here, instructors can also access PowerPoint slides of all art, tables, and graphs from the text

The Solutions Manual (1-4641-0646-0) includes worked solutions to almost

all problems (other than Review Questions, which are designed to direct dents back to the appropriate material within each chapter)

stu-To All Readers of the Text

The authors are happy to receive comments and suggestions about the tent of this book from instructors and students Please contact Colin Baird at ncolinbaird@gmail.com and Michael Cann at cannm1@scranton.edu

Preface

To W H Freeman Executive Editor for the third, fourth, and fifth tions, Jessica Fiorillo; Senior Project Editor Vivien Weiss; and Development

edi-Editor Brittany Murphy—for their encouragement, ideas, insightful

sugges-tions, patience, and organizational abilities To Margaret Comaskey for her

careful copyediting and suggestions again in this edition, to Cecilia Varas

for finding the photographs and for obtaining permissions for figures and

coordinat-ing production

Colin Baird wishes to express his thanks

To his colleagues at the University of Western Ontario and elsewhere who made valuable suggestions and supplied information and answered que-

ries on various subjects: Myra Gordon, Ron Martin, Martin Stillman, Garth

Kidd, Duncan Hunter, Roland Haines, Edgar Warnhoff, Marguerite Kane,

Currie Palmer, Rob Lipson, Dave Shoesmith, Felix Lee, Peter Guthrie, Geoff

Rayner-Canham, and Chris Willis

To his daughter, Jenny, and his granddaughters, Olivia and Sophie, for whom and for others of their generations this subject really matters

Mike Cann wishes to express his thanks

To his students (especially Marc Connelly and Tom Umile) and fellow faculty at the University of Scranton, who have made valuable suggestions

and contributions to his understanding of green chemistry and

environmen-tal chemistry

To Joe Breen, who was one of the pioneers of green chemistry and one

of the founders of the Green Chemistry Institute

To Paul Anastas and Tracy Williamson (both of the U.S tal Protection Agency), whose boundless energy and enthusiasm for green

Environmen-chemistry are contagious

To his loving wife, Cynthia, who has graciously and enthusiastically dured countless discussions of green chemistry and environmental chemistry

en-To his children, Holly and Geoffrey, and his grandchildren, McKenna, Alexia, Alan Joshua, Samantha, and Arik, who, along with future genera-

tions, will reap the rewards of sustainable chemistry

Both authors wish to express thanks to the reviewers of the fourth tion, as well as draft versions of sections of the fifth edition of the text, for

edi-their helpful comments and suggestions:

Samuel Melaku Abegaz, Columbus State University

John J Bang, North Carolina Central University

James Boulter, University of Wisconsin–Eau Claire

George P Cobb, Texas Tech University David B Ford, University of Tampa Chaoyang Jiang, University of South Dakota

Joseph P Kakareka, Florida Gulf Coast University

Michael E Ketterer, Northern Arizona University

Cielito DeRamos King, Bridgewater State University

Rachael A Kipp, Suffolk University

Min Li, California University of Pennsylvania

Kerry MacFarland, Averett University

Matthew G Marmorino, Indiana University–

South Bend

Robert Milofsky, Fort Lewis College

Jim Phillips, University of Wisconsin–Eau Claire Ramin Radfar, Wofford College

A Lynn Roberts, Johns Hopkins University Kathryn Rowberg, Purdue University–Hammond John Shapley, University of Illinois

Joshua Wang, Delaware State University Darcey Wayment, Nicholls State University Chunlong (“Carl”) Zhang, University of

Houston–Clear Lake

In this book you will study the chemistry of the air, water, and soil, as well as

the effects of anthropogenic activities on the chemistry of the Earth In

ad-dition, you will learn about sustainability and green chemistry, which aims to

design technologies that lessen the ecological footprint of our activities

Environmental chemistry deals with the reactions, fates, movements, and sources of chemicals in the air, water, and soil In the absence of humans,

the discussion would be limited to naturally occurring chemicals and

pro-cesses Today, with the burgeoning population of the Earth, coupled with

continually advancing technology, human activities have an ever-increasing

influence on the chemistry of the environment The earliest humans, and

even those living little more than a century ago, must have thought of the

Earth as so vast that human activity could scarcely have any more than local

effects on the soil, water, and air Today we realize that our activities can

have not only local and regional, but also global, consequences

The quotation from Einstein that begins this section was in reference to the dawn of the nuclear age and the concomitant threat of nuclear war

Today, Einstein’s words are just as appropriate from the perspective that the

effects upon the Earth of our current consumption of resources and

accompa-nying production of waste cannot be sustained The environmental impact (I)

of humans may be thought of as a function of population (P), affluence (A),

and technology (T).

The last 100 years have been witness to rapid growth in all of these areas, leading to the “perfect environmental storm.” It took until 1800 for the

human population of the Earth to reach 1 billion Since that time there has

been a seven-fold increase in population, with projections of 9 billion people

by 2050 By the end of today, there will be an additional 200,000 people on

this planet to feed, clothe, and shelter Although many people still live in

abject poverty, in terms of sheer numbers, never have so many lived so well

If mankind is to survive,

we shall require a substantially new manner of thinking.

Albert Einstein

Introduction to Environmental

Problems, Sustainability, and

Green Chemistry

China and India, the world’s two most populous countries with one-third of the world’s population, have recently had unprecedented economic growth,

as evidenced by their GDP growth rate of about 10% for several years This has lifted many of their people out of poverty and elevated their lifestyles

Unfortunately, their model for rising affluence is the same consumption/

waste paradigm common in the West The accompanying consumption of both renewable and nonrenewable resources and the production of pollution are simply not sustainable for so many across the globe

Fueled by human ingenuity and innovation, the last 100 years have also witnessed more technological advances than all of preceding human history

Remarkable discoveries include humans walking on the moon over 40 years ago, drugs and medical advances that have helped to increase our life expectancy in the United States from 47 years in 1900 to 79 years today, electronic devices that were not even imaginable a century ago, agricultural advances that allow us to feed 7 billion people, transportation that allows us to eat dinner in New York and breakfast the following morning in London, and the discovery of DNA and the human genome project that have unlocked many of the secrets of life However, most of these technological advances have been made with little attention to their local, regional, and even global environmental consequences This combi-nation of exponential population growth, dramatic rise in affluence, and unprec-edented technological advancement has left a legacy of toxic waste dumps, denuded landscapes, daunting climate change, spent natural resources, and ac-celerated extinction of species Never has a group of living organisms had such a far-reaching and significant impact on the environment of the Earth

There are now many indications that we have exceeded the carrying capacity of the Earth—that is, the ability of the planet to convert our wastes back into resources (often called nature’s interest) as fast as we consume its natural resources and produce waste Some say that we are living beyond the

“interest” that nature provides us and dipping into nature’s capital In short, many of our activities are not sustainable

As we write these introductory remarks, we are reminded of the mental consequences of human activities that impact the areas where we live and beyond Colin spends his summers on a small island just off the north Atlantic coast in Nova Scotia, while Mike spends a few weeks each winter on the west coast of southern Florida, a few kilometers from the Gulf of Mexico

environ-Although these locations are a great distance apart, if predictions are correct, both may be permanently submerged by the end of this century as a result of rising sea levels brought about by enhanced global warming (see Chapters 6 and 7) The public footbridge that links Colin’s island to the mainland is treated with creosote, and the local residents no longer harvest mussels from the beds below for fear they may be contaminated with PAHs (Chapter 15)

Colin’s well on this island was tested for arsenic, a common pollutant in that area of abandoned gold mines (Chapter 12) To the north, the once robust cod fishing industry of Newfoundland has collapsed due to overfishing

Mike lives in northeastern Pennsylvania on a lake where the wood in his dock is preserved with the heavy metals arsenic, chromium, and copper

Introduction to Environmental Problems, Sustainability, and Green Chemistry

(Chapter 12) Within a short distance are two landfills (Chapter 16), which

take in an excess of 8,000 tonnes of garbage per day (from municipalities as

far as 150 kilometers away), as well as two Superfund Sites (Chapter 16) and

a nuclear power plant that generates plutonium and other radioactive wastes

for which there is no working disposal plan in the United States (Chapter 9)

Furthermore, within the last couple of years, natural gas wells have sprung up

like weeds as drillers use a hydraulic fracturing process (fracking) ( Chapter 6)

that may leave a legacy of contaminated groundwater (Chapter 11) in many

states in the United States

Colin’s home in London, Ontario, is within an hour’s drive of Lake Erie, famous for nearly having “died” of phosphate pollution (Chapter 11), and

nuclear power plants on Lake Huron Nearby farmers grow corn to supply to

a new factory that produces ethanol for use as an alternative fuel (Chapter 7),

and in Ottawa, a Canadian company has built the first demonstration plant

to convert the cellulose from agricultural residue into ethanol (Chapter 7)

On sunny days we both apply extra sunscreen because of the thinning of the ozone layer (Chapters 1 and 2) and suffer the effects on our eyes and

lungs of ozone-polluted ground-level air each summer (Chapters 3 and 4)

Three of the best salmon rivers in North America in Nova Scotia must be

stocked each season because the salmon no longer migrate up the acidified

waters Many of the lakes and streams of the beautiful Adirondack region of

upstate New York are a deceptively beautifully crystal clear, only because they

are virtually devoid of plant and animal life, again because of acidified waters

(Chapter 4)

Environmental issues like these probably have parallels that exist where you live, and learning more about them may convince you that environmen-

tal chemistry is not just a topic of academic interest, but one that touches your

life every day in very practical ways Many of these environmental threats are

a consequence of anthropogenic activities over the last 50 to 100 years

In 1983 the United Nations charged a special commission with developing

a plan for long-term sustainable development In 1987 the report titled “Our

Common Future” was issued In this report (more commonly known as the The

Brundtland Report), the following definition of sustainable development is found:

Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs

Although there are many definitions of sustainable development (or

sustainabil-ity), this is the most widely used The three intersecting areas of sustainability are

focused on society, the economy, and the environment Together they are

known as the triple bottom line In all three areas, consumption (particularly of

natural resources) and the concomitant production of waste are central issues

The concept of an “ecological footprint” is an attempt to measure the amount of biologically productive space that is needed to support a particular

human lifestyle Currently there are about 4.5 acres of biologically productive

space for each person on the Earth This land provides us with the resources that

we need to support our lifestyles and to receive the waste that we generate and convert it back into resources If the entire population of 7 billion people lived like Colin and Mike, rather typical North Americans, the total ecological foot-print would require more than four planet Earths Obviously, everyone on the planet can’t live in as large and as inefficient a house, drive as many kilometers

in such an inefficient vehicle, consume as much food (in particular, meat) and energy, create as much waste, etc., as those living in developed countries

As developing countries such as China and India (with a combined total

of over 2 billion people and two of the fastest growing economies in the world) expand economically, they look to the lifestyles of the 1 billion peo-ple on the planet that live in developed countries Factor in the expected increase in global population to 9 billion by 2050 and clearly this is not sus-tainable development The people of the world (including and in particular those in developed countries) must strive to develop a lifestyle that is sus-tainable This does not necessarily mean a lower standard of living for those

in the developed world, but it does mean finding ways (more efficient nologies along with conservation) to reduce our consumption of natural re-sources and the concomitant production of waste

tech-There is now a widespread movement toward the growth and tation of sustainable, or green, technologies These technologies seek to re-duce energy and resource consumption, use and expand renewable resources, and reduce the production of waste In chemistry, these developments are

implemen-known as green chemistry, which we will describe later in this introduction and

will see as a theme throughout this text

Our ecological footprint in many cases is not limited to our backyard

As mentioned above, the consequences of our activities may be regional and even global As we will see in Chapter 4, the burning of coal to pro-duce electricity in the midwestern United States produces acid rain that falls in Ontario; in turn, emissions from Ontario are responsible for produc-ing much of the acid rain in northern New York State Rising global tem-peratures (Chapters 5 and 6), due in part to the burning of fossil fuels, have significant adverse impacts on those who use little, if any, fossil fuels

One of these groups is the Inuit, who inhabit the northern reaches of Canada, Russia, Greenland, and Alaska These people depend on hunting and fishing for sustenance Ironically, the northern latitudes of the planet have experienced some of the most significant temperature rises due to global warming—warming that has resulted in major changes in the surrounding flora and fauna and that has significantly altered the Inuits’ way of life The

atmosphere of our planet is a commons, or perhaps more appropriately scribed as an open resource We all use and benefit from this commons, but

de-no one is directly responsible for it Its use as a dumping ground for pollutants often affects more than those who are doing the dumping, a concept known

What we perceive as normal is primarily what we encounter in our day lives But of course, things change, sometimes in seconds or over millennia

To the untrained “eye,” most environmental changes are not that noticeable

But what we now think of as normal may not have been so 100 years ago or

even 50 years ago In the 1600s, English fishermen were quoted as saying the

cod off Newfoundland were “so thick by the shore that we hardly have been

able to row a boat through them.” In 1951 factory fishing began, and in a mere

50 years the cod industry off Newfoundland, the area’s main economic activity,

was dead, leading not only to environmental but to economic disaster To

to-day’s Newfoundland teenagers this is the norm, although to their parents and

grandparents this is far from what they grew up with This is an example of

shifting baselines, as well as another example of the tragedy of the commons

The melting ice sheets and loss of habitat for caribou that the Inuit are

experiencing is also an example of shifting baselines

The triple bottom line, ecological footprint, the tragedy of the mons, and shifting baselines are all examples of concepts that are commonly

com-used in discussing sustainability We will encounter these and other

sustain-ability concepts throughout this book We suggest that you make a list of

these concepts (Table 0-1) and as you read the text keep a record of where

and in what context these are encountered

Introduction to Environmental Problems, Sustainability, and Green Chemistry

Triple Bottom Line (TBL): Although corporations have traditionally been solely focused on the

economic (prosperity) bottom line, many (in this age of a greater corporate social responsibility) are adopting a wider corporate strategy that also includes the social (equality) and environmental

Tragedy of the Commons: In 1968, biologist Garrett Hardin put forth the argument that a common

(open) resource (e.g., water, air, land) used by rational individuals for their own good will result in decimation of that resource

Systems Thinking: Requires one to understand an entire system and how aspects of the system are

interconnected This understanding will allow one to realize that introducing change may have unintended consequences far beyond the original intent of the change This is particularly true of environmental systems and is a major theme of this book

Life-Cycle Assessment (LCA): Provides an inventory of materials and energy (inputs) that are

consumed and the waste and emissions produced during the entire life cycle of a product, from acquiring the materials (e.g., mining) needed to produce the product to disposing of the product;

i.e., from cradle to grave or better yet, cradle to cradle After identification of the inputs and releases

at each step of the LC, an analysis of the impact on the environment (in some cases, both social and economic impacts) can determine the steps that can be taken to minimize inputs and releases,and thus the impact on the environment

Cradle-to-Cradle: At the end of a product’s life cycle, rather than being disposed of (as in

cradle-to-grave), the spent product becomes the material to produce another product, thus mimicking the regenerative approach of nature

TABLE 0-1 Sustainability Concepts

(continued on p xxiv)

A Brief History of Environmental Regulation

In the United States, many environmental disasters came to a head in the 1960s and 1970s In 1962, the deleterious effects of the insecticide DDT were

brought to the forefront by Rachel Carson in her seminal book, Silent Spring

(Houghton Mifflin, 1962) In 1969, the Cuyahoga River, which runs through Cleveland, Ohio, was so polluted with industrial waste that it caught fire

The Love Canal neighborhood in Niagara Falls, New York, was built on the site of a chemical dump, and in the mid-1970s, during an especially rainy season, toxic waste began to ooze into the basements of area homes and drums of waste surfaced The U.S government purchased the land and cor-doned off the entire Love Canal neighborhood These distressing events were brought into the homes of Americans on the nightly news, and along with other environmental disasters they became rallying points for environ-mental reform

This era saw the creation of the U.S Environmental Protection Agency (EPA) in 1970, the celebration of the first Earth Day, also in 1970, and a mushrooming number of environmental laws Before 1960, there were ap-proximately 20 environmental laws in the United States; now there are over

120 Most of the earliest of these were focused on conservation or setting aside land from development The focus of environmental laws changed

Ecological Footprint: A measure of the biologically productive space (both land and water)

that is required to support a lifestyle You can test for your ecological footprint at http://

Carbon Footprint: A measure of the amount of greenhouse gases (in carbon dioxide equivalents)

that are produced from various activities such as transportation, manufacturing, food production, and

heating and cooling

Water Footprint: Also known as virtual water, an indication of the amount of water required

(both direct and indirect) to produce a particular product (e.g., a cup of coffee, an automobile,

a computer chip) For more information on how water footprint is assessed, visit http://www

Precautionary Principle: Even in the absence of scientific consensus, if an action or policy is likely to

cause harm to people or the environment, then the burden of proof that this action causes no harm

falls to the individuals taking the action

External Costs: Also known as externalities, these are costs (or benefits) that are not reflected in the

price of a good or service An example might be the environmental cost of emitting a pollutant into

the environment during the manufacture of a product This environmental cost is paid for, not by the

person using the product, but by all of the people who live in the commons where the pollutant was

released

TABLE 0-1 Sustainability Concepts (continued)

Introduction to Environmental Problems, Sustainability, and Green Chemistry

dramatically starting in the 1960s Some of the most familiar U.S

environ-mental legislation include the Clean Air Act (1970) and the Clean Water Act

(originally known as the Federal Water Pollution Control Act Amendments

of 1972) One of the major provisions of these acts was to set up

pollution-control programs In effect, these programs attempted to pollution-control the release

of toxic and other harmful chemicals into the environment The

Compre-hensive Environmental Response, Compensation and Liability Act (also

known as the Superfund Act) set up a procedure and provided funds for

clean-ing up toxic waste sites These acts thus focused on dealclean-ing with pollutants

after they were produced and are known as “end-of-the-pipe solutions” and

“command and control laws.”

The risk due to a hazardous substance is a function of the exposure to and the hazard of the substance:

The end-of-the-pipe laws attempt to control risk by preventing exposure to

these substances However, exposure controls inevitably fail, which points

out the weakness of these laws The Pollution Prevention Act of 1990 is the

only U.S environmental act that focuses on the paradigm of prevention of

pollution at the source: if hazardous substances are not used or produced,

then their risk is eliminated There is also no need to worry about controlling

exposure, controlling dispersion into the environment, or cleaning up

haz-ardous chemicals

Green Chemistry

The U.S Pollution Prevention Act of 1990 set the stage for green chemistry

Green chemistry became a formal focus of the U.S EPA in 1991, playing an

integral part in the EPA’s setting a new direction by which the agency

worked with and encouraged companies to voluntarily find ways to reduce

the environmental consequences of their activities Paul Anastas and John

Warner defined green chemistry as the design of chemical products and

pro-cesses that reduce or eliminate the use and generation of hazardous

sub-stances Moreover, green chemistry seeks to

• reduce waste (especially toxic waste),

• reduce the consumption of resources and ideally use renewable resources,

and

• reduce energy consumption

Anastas and Warner also formulated the Twelve Principles of Green

Chemistry These principles provide guidelines for chemists in assessing the

environmental impact of their work

The 12 Principles of Green Chemistry

1 It is better to prevent waste than to treat or clean up waste after it is

formed

2 Synthetic methods should be designed to maximize the incorporation

of all materials used in the process into the final product.

3 Wherever practicable, synthetic methodologies should be designed to

use and generate substances that possess little or no toxicity to human

health and the environment

4 Chemical products should be designed to preserve efficacy of function

while reducing toxicity.

5 The use of auxiliary substances (e.g., solvents, separation agents, etc.)

should be made unnecessary whenever possible and innocuous when used.

6 Energy requirements should be recognized for their environmental and economic impacts and should be minimized Synthetic methods

should be conducted at ambient temperature and pressure

7 A raw material feedstock should be renewable rather than depleting

whenever technically and economically practical

8 Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided

whenever possible

9 Catalytic reagents (as selective as possible) are superior to stoichiometric

reagents

10 Chemical products should be designed so that at the end of their

function they do not persist in the environment and instead break down

into innocuous degradation products

11 Analytical methodologies need to be further developed to allow for

real-time, in-process monitoring and control prior to the formation of

hazardous substances

12 Substances and the form of a substance used in a chemical process

should be chosen so as to minimize the potential for chemical accidents,

including releases, explosions, and fires

In most of the chapters in the text, real-world examples of green istry are discussed During these discussions, you should keep in mind the Twelve Principles of Green Chemistry and determine which of them are met

chem-by the particular example Although we won’t consider all of the principles

at this point, a brief discussion of some of them is beneficial

• Principle 1 is the heart of green chemistry and places the emphasis on the prevention of pollution at the source rather than cleaning up waste after it has been produced

Introduction to Environmental Problems, Sustainability, and Green Chemistry

• Principles 2–5, 7–10, and 12 focus on the materials that are used in the

production of chemicals and the products that are formed

º In a chemical synthesis, in addition to the desired product(s),

unwanted by-products are often formed and then usually discarded as waste Principle 2 encourages chemists to look for synthetic routes that maximize the production of the desired product(s) while at the same time minimizing the production of unwanted by-products (see the synthesis of ibuprofen discussed later)

º Principles 3 and 4 stress that the toxicity of materials and products

should be kept to a minimum As we will see in later discussions of green chemistry, Principle 4 is often met when new pesticides are designed with reduced toxicity to nontarget organisms

º During the course of a synthesis, chemists employ not only

compounds that are actually involved in the reaction (reactants) but also auxiliary substances such as solvents (to dissolve the reactants and to purify the products) and agents that are used to separate and dry the products These materials are usually used in much larger quantities than the reactants, and they contribute a great deal to the waste produced during a chemical synthesis When they are designing a synthesis, Principle 5 reminds chemists to consider ways to minimize the use of these auxiliary substances

º Many organic chemicals are produced from petroleum, which is a

nonrenewable resource Principle 7 urges chemists to consider ways to produce chemicals from renewable resources such as plant material (biomass)

º As we will see in Chapter 13, DDT is an effective pesticide However, a

major environmental problem is its stability in the natural environment

DDT degrades only slowly Although it has been banned in most developed countries since the 1970s (in the United States since 1972), it can still be found in the environment, particularly in the fatty tissues of animals Principle 10 stresses the need to consider the lifetime of chemicals in the environment and the need to focus on materials (such as pesticides) that degrade rapidly in the environment to harmless substances

• Many chemical reactions require heating or cooling and/or a pressure

higher or lower than atmospheric pressure Performing reactions at other

than ambient temperature and pressure requires energy; Principle 6 reminds

chemists of these considerations when designing a synthesis

Presidential Green Chemistry Challenge Awards

To recognize outstanding examples of green chemistry, the Presidential

Green Chemistry Challenge Awards were established in 1996 by the U.S

EPA Generally, five awards are given each year at a ceremony held at the

National Academy of Sciences in Washington, D.C The awards are given

in the following three Focus Areas

1 The use of alternative synthetic pathways for green chemistry, such as

• catalysis/biocatalysis,

• natural processes, such as photochemistry and biomimetic synthesis, and

• alternative feedstocks that are more innocuous and renewable (e.g., biomass)

2 The use of alternative reaction conditions for green chemistry, such as

• solvents that have a reduced impact on human health and the environment, and

• increased selectivity and reduced wastes and emissions

3 The design of safer chemicals that are, for example

• less toxic than current alternatives, and

• inherently safer with regard to accident potential

Real-World Examples of Green Chemistry

To introduce you to the important and exciting world of green chemistry, real-world cases of green chemistry are incorporated throughout this book

These examples are winners of Presidential Green Chemistry Challenge Awards As you explore these examples, it will become apparent that green chemistry is very important in lowering the ecological footprint of chemical products and processes in the air, water, and soil

We begin our journey into this important topic by briefly exploring how

green chemistry can be applied to the synthesis of ibuprofen, an important

everyday drug In this discussion, we will see how the redesign of a chemical synthesis can eliminate a great deal of waste and pollution and reduce the amount of resources required

Before discussing the synthesis of ibuprofen, we must first take a brief look

at the concept of atom economy, developed by Barry Trost of Stanford

Univer-sity, who won a Presidential Green Chemistry Challenge Award for it in 1998

Atom economy focuses our attention on Green Chemistry Principle 2 by asking

the question: How many of the atoms of the reactants are incorporated into the final

desired product and how many are wasted? As we will see in our discussion of the

synthesis of ibuprofen, when chemists synthesize a compound, not all the atoms

of the reactants are utilized in the desired product Many of these atoms may end up in unwanted products (by-products), which are in many instances con-sidered waste These waste by-products may be toxic and can cause considerable environmental damage if not disposed of properly In the past, waste products from chemical and other processes have been discarded with little thought, resulting in environmental disasters such as the Love Canal

Introduction to Environmental Problems, Sustainability, and Green Chemistry

Before we take on the synthesis of ibuprofen, let us look at a simple tration of the concept of atom economy using the production of the desired

illus-compound, 1-bromobutane (compound 4) from 1-butanol (compound 1)

H3C!CH2!CH2!CH2!OH⫹ Na!Br ⫹ H2SO4!:

1 2 3

4 5 6

If we inspect this reaction, we find that not only is the desired product

formed, but so are the unwanted by-products sodium hydrogen sulfate and

water (compounds 5 and 6) On the left side of this reaction, we have printed

in green all the atoms of the reactants that are utilized in the desired product;

the remaining atoms (which become part of our waste by-products) are

printed in black Adding up all of the green atoms on the left side of the

reaction, we get 4 C, 9 H, and 1 Br (reflecting the molecular formula of the

desired product, 1-bromobutane)

The molar mass of these atoms collectively is 137 g mol–1, the molar mass of

1-bromobutane Adding up all the atoms of the reactants gives 4 C, 12 H, 5 O,

1 Br, 1 Na, and 1 S, and the total molar mass of all these atoms is 275 g mol–1

If we take the molar mass of the atoms that are utilized, divide by the molar mass

of all the atoms, and multiply by 100, we obtain the % atom economy, here

50% Thus we see that half of the molar mass of all the atoms of the reactants

is wasted and only half is actually incorporated into the desired product

% atom economy ⫽ (molar mass of atoms utilized/

This is one method of accessing the efficiency of a reaction Armed with this information, a chemist may want to explore other methods of producing

1-bromobutane that have a greater % atom economy We will now see how the

concept of atom economy can be applied to the preparation of ibuprofen

Ibuprofen is a common analgesic and anti-inflammatory drug found in

such brand name products as Advil, Motrin, and Medipren The first

commer-cial synthesis of ibuprofen was by the Boots Company PLC of Nottingham,

England This synthesis, which has been used since the 1960s, is shown in

Figure 0-1 Although a detailed discussion of the chemistry of this synthesis is

beyond the scope of this book, we can calculate the atom economy of this

synthesis and obtain some idea of the waste produced In Figure 0-1, the atoms

printed in green are those that are incorporated into the final desired product,

ibuprofen, whereas those in black type end up in waste by-products

We can inspect the structures of each of the reactants and determine that the total of all the atoms in the reactants is 20 C, 42 H, 1 N, 10 O, 1 Cl,

and 1 Na The molar mass of all these atoms totals 514.5 g mol–1 We can

also determine that the number of atoms of the reactants utilized in the

ibu-profen (the atoms printed in green) is 13 C, 18 H, and 2 O (the molecular

formula of ibuprofen) These atoms have molar mass of 206.0 g mol–1 (the

molar mass of the ibuprofen) The ratio of the molar mass of the utilized

FIGURE 0-1 The Boots Company synthesis of ibuprofen [Source: M C Cann and M E Connolly,

Real-World Cases in Green Chemistry (Washington, D.C.: American Chemical Society, 2000).]

Cl 9999 COOC2H5

AlCl3

NaOC2H5

H s

s H

atoms to the molar mass of all the reactant atoms, multiplied by 100, gives

an atom economy of 40%:

% atom economy ⫽ (molar mass of atoms utilized/

molar mass of all reactants) ⫻ 100

⫽ (206.0/514.5) ⫻ 100 ⫽ 40%

Introduction to Environmental Problems, Sustainability, and Green Chemistry

Only 40% of the molar mass of all the atoms of the tants in this synthesis ends up in the ibuprofen; 60% is wasted

reac-Because more than 30 million pounds of ibuprofen are

pro-duced each year, if we propro-duced all the ibuprofen by this

synthesis, there would be over 35 million pounds of unwanted

waste produced just from the poor atom economy of this

synthesis

A new synthesis (Figure 0-2) of ibuprofen was oped by the BHC Company (a joint venture of the Boots

devel-Company PLC and Hoechst Celanese Corporation), which

won a Presidential Green Chemistry Challenge Award in

1997 This synthesis has only three steps as opposed to the

six-step Boots synthesis and is less wasteful in many ways

One of the most obvious improvements is the increased

atom economy The molar mass of all the atoms of the

reac-tants in this synthesis is 266.0 g mol–1 (13 C, 22 H, 4 O;

note that the HF, Raney nickel, and the Pd in this synthesis

are used in only catalytic amounts and thus do not

contrib-ute to the atom economy), whereas the utilized atoms

(printed in green) again weigh 206.0 g mol–1 This yields a

% atom economy of 77%

% atom economy ⫽ (molar mass of atoms utilized/

⫽ (206.0/266.0) ⫻ 100 ⫽ 77%

A by-product from the acetic anhydride (reactant 2) used in step 1 is acetic acid It is isolated and utilized, which

increases the atom economy of this synthesis to more than

99% Additional environmental advantages of the BHC

synthesis include the elimination of auxiliary materials

(Principle 5), such as solvents and the aluminum chloride

promoter (replaced with the catalyst HF, Principle 9),

and higher yields Thus the green chemistry of the BHC

Company synthesis lowers the environmental impact for

the synthesis of ibuprofen by lowering the consumption of

reactants and auxiliary substances while simultaneously

reducing the waste Other improved syntheses that are winners of

Presidential Green Chemistry Challenge Awards include the pesticide

Roundup, the antiviral agent Cytovene, and the active ingredient in the

antidepressant Zoloft.

Green chemistry provides a paradigm for reducing both the tion of resources and the production of waste, thus moving toward sustain-

consump-ability One of the primary considerations in the manufacture of chemicals

must be the environmental impact of the chemical and the process by

which it is produced Sustainable chemistry must become part of the psyche

CO Pd

O HF

FIGURE 0-2 The BHC Company synthesis of ibuprofen [Source: M C

Cann and M E Connolly,

Real-World Cases in Green Chemistry

(Washington, D.C.: American Chemical Society, 2000).]

of not only chemists and scientists, but also business leaders and makers With this in mind, real-world examples of green chemistry have been incorporated throughout this text to expose you (our future scientists, business leaders, and policymakers) to sustainable chemistry.

policy-Further Readings

1 Anastas, P T., and J C Warner, Green

Chemistry Theory and Practice (New York: Oxford

University Press, 1998)

2 Cann, M C., and M E Connelly, Real-World

Cases in Green Chemistry (Washington, D.C.:

American Chemical Society, 2000)

3 Cann, M C., and T P Umile, Real-World

Cases in Green Chemistry, vol 2 (Washington,

D.C.: American Chemical Society, 2007)

4 Cann, M C., “Bringing State of the Art,

Applied, Novel, Green Chemistry to the

Classroom, by Employing the Presidential Green

Chemistry Challenge Awards,” Journal of Chemical

Education 76 (1999): 1639–1641.

5 Cann, M C., “Greening the Chemistry

Curriculum at the University of Scranton,” Green

Chemistry 3 (2001): G23–G25

6 Ryan, M A., and M Tinnesand, eds.,

Introduction to Green Chemistry (Washington,

D.C.: American Chemical Society, 2002)

7 Kirchhoff, M., and M A Ryan, eds., Greener

Approaches to Undergraduate Chemistry Experiments

(Washington, D.C.: American Chemical Society, 2002)

8 World Commission on Environment and

Development, Our Common Future [The “Bruntland

Report”] (New York: Oxford University Press, 1987)

9 Wackernagel, M., and W Rees, Our Ecological

Footprint: Reducing Human Impact on the Earth

(Gabriola Island, BC: New Society Publishers, 1996)

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ATMOSPHERIC

CHEMISTRY AND

AIR POLLUTION

Contents of Part I

Chapter 1 Stratospheric Chemistry: The Ozone Layer

Chapter 2 The Ozone Holes

Chapter 3 The Chemistry of Ground-Level Air Pollution

Chapter 4 The Environmental and Health Consequences of

Polluted Air—Outdoors and Indoors

We begin this book by considering stratospheric

ozone depletion, chronologically the first truly

global environmental problem—one that

threat-ened life around the world and that required

inter-national agreements to solve We then turn to

ground-level air pollution, which by contrast is

primarily a local or regional environmental

namely, the climate change brought about by rising

concentrations of greenhouse gases, and the role of

energy production and use—problems with which

our global society currently is wrestling and which

will require a myriad of approaches to resolve In all

cases, we will concentrate our attention on

sustain-able solutions, and how a knowledge of

environ-mental chemistry is necessary to devise them

As you study the first two chapters, you will

be struck by the difficulty in living up to the

precautionary principle: that the burden of proof in

introducing a new product or process falls on the manufacturer to ensure that it causes no harm to the public or the environment Indeed, the replacement of the highly toxic gas sulfur dioxide

in refrigerators by CFCs (chlorofluorocarbons) in the 1930s was considered to be a boon to public safety Only decades later was the serious flaw of their role in the depletion of stratospheric ozone discovered As you shall see, knowledge of atmo-spheric chemistry has been uppermost in the development of CFC replacements

The production of smog and acid rain was an

unintended consequence of the combustion of

fos-sil fuels in power plants and vehicles In ters 3 and 4 we shall see how scientists have determined the reactions that produce air pollu-tion and invented devices such as catalytic con-verters that, at least in developed countries, have

Introduction

The ozone layer is a region of the

atmosphere that is called “Earth’s

nat-ural sunscreen” because it filters out

harmful ultraviolet (UV) rays from

sunlight before they can reach the

surface of our planet and cause

dam-age to humans and other life forms

Any substantial reduction in the

amount of this ozone would threaten

life as we know it Consequently, the

appearance in the mid-1980s of a large

“hole” in the ozone layer over

Antarc-tica represented a major

environmen-tal crisis Although steps have been

taken to prevent its expansion, the

hole will continue to appear each spring over the South Pole; indeed, one of

the largest holes in history occurred in 2006 Thus it is important that we

understand the natural chemistry of the ozone layer, the subject of this

chap-ter The specific processes at work in the ozone hole, and the history of the

evolution of the hole, are elaborated upon in Chapter 2

We begin by considering how the concentrations of atmospheric gases are reported and the region of the atmosphere where the ozone is concentrated

A young girl applies sunscreen to protect her skin against UV rays from the Sun [Source: Lowell George/CORBIS.]

1 Stratospheric Chemistry

The Ozone Layer

In this chapter, the following introductory chemistry

topics are used:

m Moles; concentration units including mole fraction

m Ideal gas law; partial pressures

m Thermochemistry: H, Hf; Hess’ law

m Kinetics: Rate laws; reaction mechanisms, activation energy,

catalysis

Introduction

1.1 Regions of the Atmosphere

The main components (ignoring the normally ever-present but variable

water vapor) of an unpolluted version of the Earth’s atmosphere are diatomic nitrogen, N2 (about 78% of the molecules); diatomic oxygen, O2 (about

0.04%)

This mixture of chemicals seems unreactive in the lower atmosphere even at temperatures or sunlight intensities well beyond those naturally encountered at the Earth’s surface

The lack of noticeable reactivity in the atmosphere is deceptive In fact, many environmentally important chemical processes occur in air, whether clean or polluted In this chapter and the next, these reactions will

be explored in detail In Chapters 3 and 4, reactions that occur in the

troposphere, the region of the sky that extends from ground level to about 15 kilometers altitude, and contains 85% of the atmosphere’s mass, are discussed In this chapter we will consider processes in the stratosphere, the portion of the atmosphere from approximately 15 to

50 kilometers altitude (i.e., 9 ⴚ30 miles) that lies just above the

tropo-sphere. The chemical reactions to be considered are vitally important to the continuing health of the ozone layer, which is found in the bottom half

of the stratosphere The ozone concentrations and the average tures at altitudes up to 50 kilometers in the Earth’s atmosphere are shown

tempera-in Figure 1-1

The names of chemicals

important to a chapter are

printed in bold, along with

their formulas, when they

are introduced The names

of chemicals less important

in the present context are

0

30 40 50 60

with altitude of (a) ozone

concentration (for

mid-latitude regions) and

(b) air temperature for

various regions of the

lower atmosphere.

Introduction 5

The stratosphere is defined as the region that lies between the tudes where the temperature trends display reversals: the bottom of the

alti-stratosphere occurs where the temperature first stops decreasing with

height and begins to increase, and the top of the stratosphere is the

alti-tude where the temperature stops increasing with height and begins to

decrease. The exact altitude at which the troposphere ends and the

strato-sphere begins varies with season and with latitude

1.2 Environmental Concentration Units

for Atmospheric Gases

Two types of concentration scales are commonly used for gases present in air

For absolute concentrations, the most common scale is the number of

molecules per cubic centimeter of air. The variation in the

concentra-tion of ozone with altitude on the molecules per cubic centimeter scale is

expressed in terms of the partial pressure of the gas, which is stated in

units of atmospheres or kiloPascals or bars According to the ideal gas law

concentra-tion n/V, and hence to the molecular concentraconcentra-tion per unit volume, when

different gases or components of a mixture are compared at the same Kelvin

temperature T The absolute concentration scale of moles per liter, familiar

to all chemists from its use for liquid solutions, is rarely used for gases because

they are so dilute

Relative concentrations are usually based on the chemists’ familiar mole fraction scale (called mixing ratios by physicists), which is also the

molecule fraction scale Because the concentrations for many constituents

are so small, atmospheric and environmental scientists often re-express the

mole fraction or molecule fraction as a parts per _ value Thus, a

concentration of 100 molecules of a gas such as carbon dioxide dispersed in

mil-lion, i.e., 100 ppm, rather than as a molecule or mole fraction of 0.0001

It is important to emphasize that for gases, these relative concentration units express the number of molecules of a pollutant (i.e., the “solute” in

chemists’ language) that are present in one million or billion or trillion

mol-ecules of air Since, according to the ideal gas law, the volume of a gas is

proportional to the number of molecules it contains, the “parts per” scales

also represent the volume a pollutant gas would occupy, compared to that of

the stated volume of air, if the pollutant were to be isolated and compressed

until its pressure equaled that of the air In order to emphasize that the

concentration scale is based upon molecules or volumes rather than upon

or 100 ppmv

The Physics, Chemistry, and Biology of UV

To understand the importance of atmospheric ozone, we must consider the ous types of light energy that emanate from the Sun and consider how UV light

vari-in particular is selectively filtered from sunlight by gases vari-in air This leads us to consider the effects on human health of UV, and quantitatively how energy from light can break apart molecules With that background, we then can inves-tigate the natural processes by which ozone is formed and destroyed in air

1.3 Absorption of Light by MoleculesThe chemistry of ozone depletion, and of many other processes in the stratosphere, is driven by energy associated with light from the Sun. For this reason, we begin by investigating the relationship between light absorp-tion by molecules and the resulting activation, or energizing, of the mole-cules that enables them to react chemically

An object that we perceive as black in color absorbs light at all wavelengths

of the visible spectrum, which runs from about 400 nm (violet light) to about