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17 Atmospheric Science and Air Pollution Chapter Objectives This chapter will help students: Describe the composition, structure, and function of Earth’s atmosphere Outline the scope of outdoor air pollution and assess potential solutions Explain stratospheric ozone depletion and identify steps taken to address it Define acidic deposition and illustrate its consequences Characterize the scope of indoor air pollution and assess potential solutions Lecture Outline I. Central Case: Charging toward Cleaner Air in London A. Thick and blinding smog first settled over the city on December 5, 1952, when many residents stoked their coal stoves because of unusually cold temperatures. B. A wind finally relieved Londoners of the smog on Tuesday, December 9, but by that time thousands of people had died from lung ailments. C. Many similar events have taken place in Pennsylvania, New York, Mexico, and Malaysia. D. We have improved, however, as declines in air pollution represent some of the biggest successes of environmental policy. E. Much remains to be done because there are hundreds of people who die prematurely each year due to vehicle emissions. II. The Atmosphere A. The atmosphere is a thin layer of gases that surrounds Earth. B. The atmosphere consists of several layers. 1. The bottommost layer is the troposphere, where temperature decreases with altitude. IG-247 C. D. E. F. 2. The stratosphere extends from 11 km to 50 km above sea level, with its temperature rising gradually with altitude. 3. A portion of the stratosphere between 17 and 30 km above sea level contains most of the atmosphere’s ozone and is called the ozone layer; this layer greatly reduces the amount of UV radiation that reaches Earth’s surface. The protection of the ozone layer is vital for life on Earth. 4. Above the stratosphere lies the mesosphere, which extends from 50 to 90 km above sea level. 5. From the outer mesosphere, the thermosphere extends upward to an altitude of 500 km, where solar rays produce temperatures over 1,700 degrees Celsius. Atmospheric properties include temperature, pressure, and humidity. 1. Atmospheric pressure measures the weight per unit area produced by a column of air and decreases with altitude. 2. Relative humidity is the amount of water vapor a given volume of air holds relative to the maximum amount it could contain for a given temperature. 3. The temperature of air varies with location and time, and these temperature differences affect air circulation. Solar energy heats the atmosphere, helps create seasons, and causes air to circulate. 1. Energy from the sun plays a major role in our atmosphere by driving most of its air movements. 2. The spatial relationship between Earth and the sun determines the amount of solar radiation that strikes each point of Earth’s surface. 3. Because Earth is tilted on its axis by about 23.5 degrees, the Northern and Southern Hemispheres each face the sun for onehalf of the year. 4. Land and surface waters absorb solar energy, reradiating some heat and causing some water to evaporate. 5. The difference in air temperatures at different altitudes sets into motion convective circulation, as warm air rises, cools, and expands, and then descends past other warm air that is rising. The atmosphere drives weather and climate. 1. Weather consists of the local physical properties over short time periods in relatively small geographic areas. 2. Climate describes the pattern of atmospheric conditions found across a relatively large geographic region over a long period. Weather is produced by interacting air masses. 1. The boundary between two air masses that differ in temperature and density is called a front. a. A mass of warmer, moister air replacing a mass of colder, drier air is a warm front. b. A mass of colder, drier air displacing a warmer, moister air mass is a cold front. 2. Opposing air masses may also differ in atmospheric pressure. a. Air moving outward away from a center of high pressure as it descends is a high-pressure system. IG-248 b. Air moving toward a low atmosphere pressure at the center of a rising system is a low-pressure system. 3. One type of weather event has implications for environmental health. a. If a layer of cool air occurs beneath a layer of warmer air, this is known as a temperature inversion, or thermal inversion. b. The band of air in which temperature rises with altitude is called an inversion layer. G. Global climate patterns result from large-scale circulation systems. 1. Sunlight near the equator produces pairs of convection cells called Hadley cells. 2. Two pairs of similar but less intense convective cells, Ferrel cells and polar cells, lift air and create precipitation around 60 degrees latitude north and south and cause air to descend at around 30 degrees latitude and in the polar regions. 3. These three pairs of cells account for the latitudinal distribution of moisture across Earth’s surface. 4. As Earth rotates on its axis, north–south air currents of convective cells appear to be deflected from a straight path; this is called the Coriolis effect. III. Outdoor Air Pollution A. Air pollutants are gases and particulate material added to the atmosphere that can affect climate and/or harm organisms, including ourselves. B. Natural sources can pollute. 1. Winds sweeping over arid terrain can send huge amounts of dust aloft. 2. Volcanic eruptions release large quantities of particulate matter, as well as sulfur dioxide and other gases, into the troposphere and can even cause global cooling by a fraction of a degree. 3. Sulfur dioxide reacts with water and oxygen and condenses into fine particles called aerosols. 4. The burning of vegetation pollutes the atmosphere with smoke and soot. C. We create various types of outdoor air pollution. 1. Since the onset of industrialization, outdoor air pollution from human activity can originate from stationary or mobile sources. 2. Once in the air, a pollutant may do harm directly or may induce chemical reactions that produce harmful compounds. a. Primary pollutants, such as soot and carbon monoxide, are pollutants emitted into the troposphere in a form that can be directly harmful or that can react to form harmful substances. b. Secondary pollutants are harmful substances produced when primary pollutants interact or react with constituents of the atmosphere. D. Clean Air Acts legislation has addressed pollution in the United States. 1. Congress has passed a number of laws dealing with pollution. IG-249 E. F. G. H. I. J. a. The Clean Air Act of 1970 set strict standards for air quality, imposed limits on emissions, provided funds for research, and allowed citizens to sue parties violating the standards. b. The Clean Air Act of 1990 sought to strengthen regulations pertaining to air quality standards, auto emissions, toxic air pollution, acidic deposition, and ozone depletion, while introducing market-based incentives. c. In 1995, businesses and industry were allocated permits to release sulfur dioxide that they could buy, sell, or trade among one another. This market-based incentive program reduced sulfur dioxide levels. The EPA sets standards for “criteria pollutants.” 1. The EPA gives special attention to several pollutants judged to pose especially great threats to human health and welfare. 2. For six criteria pollutants, the EPA has established maximum allowable concentrations. a. Carbon monoxide is a colorless, odorless gas produced primarily by the incomplete combustion of fuels. b. Sulfur dioxide is a colorless gas with a pungent odor that is released when coal is burned and contributes to acid rain. c. Nitrogen dioxide is a highly reactive, foul-smelling reddish gas that contributes to smog and acid rain. d. Tropospheric ozone results from the interaction of sunlight, heat, nitrogen oxides, and volatile organic compounds. e. Particulate matter is any solid or liquid particle small enough to be carried aloft; it may cause damage to respiratory tissues when inhaled. f. Lead is a metal that enters the atmosphere as a particulate pollutant released by industrial processes and fuel combustion. Agencies monitor pollutants that affect air quality. 1. Volatile organic compounds (VOCs) are a large group of potentially harmful organic chemicals emitted by vehicle engines and used in solvents and industrial processes such as dry cleaning, household chemicals, and manufacturing. 2. Human activity accounts for about half of U.S. VOC emissions, but many tons of VOCs are released from natural sources (plants and animals) each year. Air pollution has decreased markedly since 1970. 1. Reduction in air pollutants have occurred despite population increases. 2. New technologies such as catalytic converters, electrostatic precipitators, and scrubbers helped to reduce pollutants. Toxic substances also pollute. 1. Other chemicals known to cause serious health or environmental problems are classified as toxic air pollutants. Recent policy proposals have been contentious. 1. The George Bush administration has vigorously advocated proposals that would overturn key provisions of the Clean Air Act. Burning fossil fuels produces industrial smog. IG-250 K. Photochemical smog is produced by a complex series of atmospheric reactions. L. Air quality is a rural issue too. 1. Pesticide drift contributes to poor air quality in rural areas. 2. Huge confined animal feeding operations with their associated manure add methane, sulfur dioxide, hydrogen sulfide, and ammonia to rural areas. These pollutants have harmful effects on humans and animals. M. Industrializing nations are suffering increasing air pollution. 1. Chinese cities suffer the worst air pollution as they industrialize rapidly. N. Synthetic chemicals deplete stratospheric ozone. 1. Ozone molecules are considered a pollutant at low altitudes, but at altitudes of 25 km (15 mi) they are highly effective at absorbing incoming ultraviolet radiation from the sun, thus protecting life on Earth’s surface. 2. Starting in the 1960s, atmospheric scientists began wondering why their measurements of ozone were lower than theoretical models predicted. 3. In 1974, Sherwood Rowland and Mario Molina broke the news that chlorofluorocarbons (CFCs) depleted stratospheric ozone by splitting ozone molecules and creating O2 molecules from them. 4. In 1985, scientists from the British Antarctic Survey announced that stratospheric ozone levels over Antarctica had declined 40 to 60% in the previous decade, leaving behind a thinned ozone concentration that was soon dubbed the “ozone hole.” O. The Montreal Protocol addressed ozone depletion. 1. The world community came together in 1987 to design the Montreal Protocol, which has been signed by 180 nations. 2. The production and use of ozone-depleting compounds has fallen 95% since the late 1980s. 3. Environmental scientists have attributed the success of the Montreal Protocol to two factors. a. Policymakers engaged industry in helping to solve the problem. b. The process after 1987 successfully followed an adaptive management approach, which allows for altering strategies midstream in response to new scientific data, technological advances, or economic figures. 4. Due to the lag time between policy implementation and desired effect, scientists often advocate a proactive approach, following the precautionary principle. P. Acidic deposition represents another transboundary pollution problem. 1. Acidic deposition refers to the deposition of acidic or acidforming pollutants from the atmosphere onto Earth’s surface. 2. Acidic deposition is one type of atmospheric deposition, which is the wet or dry deposition on land of a wide variety of pollutants. 3. Because the pollutants leading to acid rain may travel long distances, their effects can be felt far from their point sources. IG-251 4. Acid deposition can also mobilize toxic metal ions from the soil and convert them from insoluble to soluble molecules where they hinder nutrient uptake by plants. 5. Acid water running off the land is toxic to many aquatic life forms and has led to the death of ecosystems. Q. Acid deposition has not been reduced as much as scientists had hoped. IV. Indoor Air Pollution A. Indoor air pollution in the developing world arises from fuelwood burning. B. Tobacco and radon gas are the two most dangerous indoor air pollutants in the developed world. 1. Secondhand smoke has been found to cause many of the same problems as directly inhaled cigarette smoke. 2. After cigarette smoke, radon gas is the second-leading cause of lung cancer for Americans. C. Many VOCs pollute indoor air. 1. Products that emit VOCs surround us; VOCs are emitted in very small amounts. 2. The implications for human health of chronic exposure to VOCs are far from clear. There are so many, at such low levels, that it is difficult to study their effects. D. Living organisms can pollute indoor air. 1. Dust mites, animal dander, fungi, mold, mildew, and bacteria can all cause health problems. 2. These organisms may be the most widespread source of indoor air pollution in the developed world. 3. Microbes that induce allergic responses are thought to be one frequent cause of building-related illness. E. We can reduce indoor air pollution. 1. The 1970 U.S. Clean Air Act did not even mention indoor air pollution; rather, indoor spaces were assumed to be safe havens from outdoor pollution. 2. Today we know far less about indoor air pollution than we do about outdoor air pollution. V. Conclusion A. Indoor air pollution is a potentially serious health threat but one that we can do a great deal to minimize for ourselves and our families. B. Outdoor air pollution has been addressed more effectively by government legislation and regulation. C. Much room for improvement remains, particularly in reducing acidic deposition and photochemical smog. Key Terms acidic deposition aerosols air pollutant air pollution atmospheric deposition atmospheric pressure carbon monoxide chlorofluorocarbons (CFCs) Clean Air Act of 1970 Clean Air Act of 1990 IG-252 climate cold front convective circulation Coriolis effect criteria pollutant Ferrel cell Hadley cell high-pressure system industrial smog inversion layer lead low-pressure system Montreal Protocol nitrogen dioxide ozone layer particulate matter photochemical smog polar cell primary pollutant radon relative humidity secondary pollutant stratosphere sulfur dioxide temperature inversion thermal inversion toxic air pollutant troposphere tropospheric ozone volatile organic compounds (VOCs) warm front weather Teaching Tips 1. Use the AirData website made available by the U.S. Environmental Protection Agency (www.epa.gov/air/data/index.html). This website provides air pollution data for the entire United States and produces reports and maps using criteria that you specify. Air data are acquired from two EPA databases, Air Quality System (AQS) and National Emission Inventory (NEI). Present students with air data from your geographic area or ask them to retrieve data themselves. The database will generate tables showing the facilities within a state or a county that emit various particulates, in the order of total amount of emission. 2. Assign students to read papers about air pollution and environmental justice at the University of Michigan’s website (www.umich.edu/~snre492/cases.html). You can have groups of students each choose a paper from the website that relates to air pollution. Have them read the paper and then do follow-up research to find out the current status of the problem. You can have the groups write reports, do poster projects, or do PowerPoint presentations to the class or an invited assembly. Ask students to begin by considering the following questions: What was the initial discovery? What was the source of the problem? What lawsuits have been filed? What were the outcomes? What health effects have been documented? What do you think can be done to prevent similar problems? IG-253 3. As a classroom demonstration or student assignment, go to Smog City at www.smogcity.com, developed by the Sacramento Metropolitan Air Quality Management District. Smog City is an interactive air pollution simulator that shows how population, environmental factors, and land use contribute to air pollution. Smog City allows the user to adjust these factors to see the effect on ground-level ozone formation. Ask students to consider the following questions: Does one factor seem to affect smog formation more than others? How do weather variables affect smog formation? How does population affect smog formation? What can you do as an individual to reduce smog? 4. To find out about pollution in your community, go to Scorecard: The Pollution Information Site (www.scorecard.org/). Have students enter their ZIP codes to learn about toxic chemicals released into the air by local sources. 5. A poster project can be an exercise in learning good communication skills. Students must summarize a great deal of information, use principles of color and design, and have both graphic impact and a presentation style that draws and holds interest. A short presentation to use in class, or to have students access on their own, can be found at dv.pima.edu/~jduek. Click on “Education Power Points” and from that page choose “Poster Projects.” It includes an outline for students to follow and for instructors to use in grading projects: 20% content: written material and visual material 20% accuracy: content, grammar, and spelling 20% neatness: lettering, visuals, and use of color/design/layout 20% layout: tips are given about colors, lettering, placement, shape, and decoration 20% creativity: written, visual, layout, humor, and other creative directions 6. Provide white or light-colored cotton squares to students for an outdoor activity that will answer the question: “Is there particulate matter in the atmosphere around campus that I am unable to see?” Be sure that all swatches are the same size. Ask students if they can predict where there might be higher levels of air quality impact. If in urban areas, regions near the ground that are subject to diesel fumes provide interesting collecting sites. If possible, leave the swatches outdoors secured to trees, posts, or even the building. Retrieve the material after 24 hours and examine the swatches against a control swatch kept inside the classroom in an airtight container. Ask students if any of their predictions match the visual results. Additional Resources IG-254 Websites 1. AIRNow, U.S. Environmental Protection Agency (airnow.gov) This interagency and international website provides air quality forecasts, information, and reports on air quality to the general public. 2. Air and Radiation: Where You Live, U.S. Environmental Protection Agency (www.epa.gov/air/where.html) This resource has general information about air quality and regulation, including criteria on air pollutants, air quality trends, and toxic air pollution. 3. Encyclopedia of the Atmospheric Environment, Manchester Metropolitan University (www.ace.mmu.ac.uk/eae/english.html) Published by the Atmosphere, Climate, and Environment Information Programme, this website is supported by the United Kingdom Department for Environment, Food, and Rural Affairs. It is a source of information on air quality, ozone depletion, acid rain, and global warming. 4. The Great Smog of 1952, Met Office Education Service, United Kingdom, (www.met-office.gov.uk/education/secondary/students/smog.html) This website has a detailed summary of London’s Killer Smog of 1952. 5. The Hubbard Brook Ecosystem Study, Hubbard Brook Research Station (www.hubbardbrook.org) The home page of the Hubbard Brook Ecosystem Study (HBES) provides access to its three main resources: Research and Data, Hubbard Brook Research Foundation, and Educational Resources. Audiovisual Materials 1. Ozone: Cancer of the Sky, 1994, produced by Television New Zealand Natural History, distributed by The Video Project (www.videoproject.com) This video presents general information about the ozone layer. The program follows scientists as they convene in Antarctica to study the ozone hole that forms there each spring. 2. Assault on the Ozone Layer, distributed by Films for the Humanities and Sciences (www.films.com) This program shows how the ozone layer is depleted and how its depletion is stunting, mutating, and destroying life. 3. What’s Up with the Weather? NOVA video, distributed by WGBH (shop.wgbh.org) This program examines today’s extreme weather patterns, such as flooding, hurricanes, and high temperatures. It addresses the question as to whether these are natural phenomena or whether they are indicators of global warming. IG-255 4. The Air We Breathe, 1997, produced by Hamm Productions and the National Film Board of Canada, distributed by Bullfrog Films (www.bullfrogfilms.com) In two videos, this program shows the connection between suburban sprawl, air pollution, and increases in asthma and other respiratory diseases. 5. What’s in Our Air, 1999, produced and distributed by Rainbow Video and Film Productions (www.rainbowvideoandfilm.com) This 25-minute video documents community members in Oregon, Washington, and California using low-tech bucket monitors to sample the air for 43 hazardous air pollutants. Weighing the Issues: Facts to Consider Your County’s Air Quality Facts to consider: In order to determine local air quality, the instructor could suggest websites for county departments of environmental quality or some equivalent state agency that monitors air quality. For national comparisons, the instructor may recommend the first website in the Additional Resources, AIRNow (www.airnow.gov), as a source of comparative information. The Internet has numerous websites that have ideas for air pollution reduction, from international to local and personal perspectives. Ideas and opinions about the causes of local air pollution and solutions for reducing air pollution will vary, depending on the social, economic, and industrial context of the county being investigated and the experience, knowledge, and priorities of the student. International Cooperation to Solve Global Problems Facts to consider: Substantive action on issues such as organic pollutants, climate change, and biodiversity loss will require definitive proof of direct harm to human health. The human health consequences of the Antarctic ozone hole were straightforward, and governments and industry had no choice but to act accordingly. Negative environmental effects, and even more specifically negative human health effects, are not as straightforward in many other situations. A relatively easy fix, such as CFCs in the case of ozone depletion, is more palatable to politicians than complex lifestyle changes. Organic pollutants are plentiful, and global climate change and biodiversity crises appear to have multiple causes. Developing sufficient viable alternatives to the significant causal agents would be enormously difficult. IG-256 Fortunately, there have been some other large-scale environmental success stories. Most lead sources have been eliminated in the United States. Urban air quality has improved significantly in the United States and Britain due to the results of clean air legislation. Exposure to tobacco smoke, an indoor pollutant, has decreased in the United States and some other nations. Growing awareness of naturally emitted radon has resulted in over a million homes being built with radon-resistant features. In the future, the use of low-toxicity building materials and good ventilation hold promise for reducing indoor air pollution. Indoor air pollution in developing countries can also be reduced in the near term by drying wood before burning and using less-polluting fuels and cleaner-burning stoves. How Safe Is Your Indoor Environment? Facts to consider: This question requires an individual response, but responses should consider a wide range of potential sources of air pollution, as designated by the EPA, including asbestos; biological pollutants such as mold, mildew, or pollen; carbon monoxide from gas appliances or woodstoves; formaldehyde used in building materials; organic chemicals used in cleaning products, dry cleaning, or hobbies; lead from old paint; nitrogen dioxide from gas or kerosene heaters; pesticides to control indoor insects or microorganisms; naturally occurring radon gas; combustion products from fireplaces or woodstoves; and secondhand smoke. Generally applicable ways to make indoor spaces safer from pollution include limiting use of plastics and treated wood where possible, increasing ventilation, having the space tested for radon gas, and storing cleansers and other household products in a garage or shed. The Science behind the Stories: Thinking Like a Scientist How Scientists Identified CFCs as the Main Cause of Ozone Depletion Observation: By the 1970s, industrial chemicals known as chlorofluorocarbons (CFCs) were being produced in vast quantities. However, in 1974, F. Sherwood Rowland and Mario Molina published a paper whose main point was that the inertness of CFCs could have disastrous consequences for the ozone layer. Hypothesis: CFCs were causing significant decreases in global stratospheric ozone. Rowland and Molina hypothesized that CFCs would not be broken down in the lower atmosphere and would reach the stratosphere undamaged. Intense ultraviolet light would break down CFCs into chlorine and carbon atoms. The chlorine atoms would catalyze the destruction of ozone molecules. IG-257 Experiment: Several experiments had to be conducted to provide data to support this hypothesis. Richard Stolarski and Ralph Cicerone showed that chlorine atoms acted as catalysts for ozone molecule destruction. James Lovelock devised an instrument to measure extremely low concentrations of atmospheric gases. James Farman and his colleagues reported that Antarctic atmospheric ozone levels had been dramatically falling since the 1970s. Paul Crutzen showed that the Antarctic ozone hole was the result of a combination of Antarctic weather conditions and the presence of CFCs in the stratosphere. Results: By the mid-1980s, scientists had conclusive evidence that global ozone levels were declining, particularly over Antarctica, and that those declines were due primarily to CFCs and other human-made chemicals. Acid Rain at Hubbard Brook Research Forest Observation: Long-term studies of water flow and nutrient cycling are important to understanding the interplay between abiotic and biotic portions of any ecosystem. Study: The 7,800 acre Hubbard Research Forest was established in New Hampshire in 1955 as a long-term hydrological study and was augmented in 1963 by Dartmouth University researchers to include the study of nutrient cycling. Precipitation was collected in clean plastic bottles from funnels with a 30-cm opening. These bottles were retrieved each week and measured for acidity and electrical conductivity. Concentrations of specific compounds were also measured by other labs. Results: In the 1960s, Gene Likens, F. Herbert Bormann, and others found that the pH of the Hubbard Brook precipitation was several hundred times more acidic than natural rainwater. Other studies in the 1970s supported this finding, eventually showing that the precipitation from Pennsylvania to Maine was averaging a pH of 4.0, with some precipitation measured as low as 2.1. The result of this study was the implementation of the National Atmospheric Deposition Program to measure precipitation and dry deposition across the United States. This program developed a nationwide pH map that showed that the northeast United States had the worst acid deposition problem. It was hypothesized that the fossil-fuel burning plants of the Midwest provided the compounds that increased the acidity of the soil in the northeast United States. The Clean Air Act of 1970 was amended in 1990 to restrict acidic compounds from these Midwest factories and power plants. In 1996, researchers also found that acidic deposition was leaching calcium and magnesium out of the soil while increasing the amount of aluminum in the soil. These nutrient deficiencies and surpluses weakened trees and slowed forest growth, making trees more vulnerable to drought and insect damage. Causes and Consequences IG-258 The following answers for the Causes and Consequences features are examples, and are not intended to represent a comprehensive list. In addition, the sequence of items is not meant to connote relative importance. Issue: Indoor Air Pollution Causes: radon seepage into homes the need to burn fuelwood in developing nations cigarette smoking volatilization from manufactured products bacteria, viruses, mildew, etc. poor ventilation Consequences: lung cancer: 20,000 deaths per year in the United States various other illnesses and health impacts deaths from chronic or acute exposure Solutions: measure radon with a test kit; increase ventilation replace indoor wood fires with stoves keep ducts clean quit smoking minimize chemicals in one's house Unintended consequences: Increasing ventilation increases energy expenditure for heating and cooling a home. Buying stoves is more expensive for poor families—and they are the ones who need them. …and New solutions: Ventilate at times of day when temperature is moderate; improve insulation and other energy-saving features of home. Government can assist in purchases, or can enact other measures to attempt to relieve poverty. InvestigateIt Case Studies and Videos Case Studies Something (and Lots of It) Is in the Air Critics Say Clean-Air Plan May Be a Setback for Parks Trucks Soil Mont Blanc's Sparkling Slopes Indonesia's Yearly Smoke Location Topic Connecticut Air Pollution Tennessee Air Pollution France Malaysia Air Pollution Air Pollution IG-259 Region Cloud Reaches Malaysia and Thailand Parents and Health Experts Unite in Effort to Ease Pollution in Northern Italy Bangkok Journal: Breathing Easier as the Battle for Blue Skies Pays Off As China Roars, Pollution Reaches Deadly Extremes Fitness: For Athletes, An Invisible Traffic Hazard Milan, Italy Air Pollution Italy Bangkok, Thailand Air Pollution Thailand China Air Pollution China California Toxicology California Answers to End-of-Chapter Questions Testing Your Comprehension 1. The Earth’s atmosphere is about 500 km (300 mi) thick, consisting of four layers: the bottommost layer, the troposphere, is only 11 km (7 mi) thick but contains three-quarters of the atmosphere’s mass; the stratosphere extends from 11–50 km (7–31 mi) above sea level and contains most of the atmosphere’s UV-absorbing ozone; the mesosphere is a zone of declining temperatures and extremely low pressures, extending 50–90 km (31–56 mi) above sea level; finally, the thermosphere is the outermost layer of the atmosphere, extending from 90–500 km (56–300 mi) above sea level. In this layer, infrequent molecular collisions allow the atmosphere to become chemically stratified, with lighter hydrogen and helium rising to the top of the layer, and the heavier oxygen and nitrogen sinking toward the bottom. 2. The ozone layer is concentrated 17–30 km (10–19 mi) above sea level in the stratosphere. Stratospheric ozone absorbs UV radiation, which is harmful to life. Tropospheric ozone can contact living organisms, and react chemically with their tissues, causing harmful oxidation to occur. This oxidation can chemically alter a cell’s DNA, leading to mutations and the possibilities of cell death or cancer. 3. Solar energy heats air, causing pressure gradients that drive Earth’s atmospheric circulation. This circulation distributes heat and moisture over Earth’s surface (i.e., determines the main factors of climate). Hadley, Ferrel, and polar cells are convection patterns in the atmosphere, driven by the sun’s energy, that produce predictable bands of precipitation and wind direction over the globe. These factors in turn control the distribution of Earth’s biomes. 4. The London smog event of 1952 was caused by the exhaust of coal-burning power plants and of home fireplaces/furnaces being trapped in a layer of colder, denser air near the surface—a so-called thermal inversion. 5. Natural sources of outdoor pollution include plant metabolism, dust storms, volcanoes, and forest fires. Anthropogenic sources include industrial combustion processes, home fireplaces, and automobile exhaust, among other sources. 6. A primary pollutant, such as soot, is emitted into the atmosphere in a form that is directly harmful. A secondary pollutant is produced in the atmosphere by IG-260 7. 8. 9. 10. means of a chemical reaction occurring there. For example, the nitric acid in acid rain is produced by reaction of the primary pollutant NO2 and water vapor in the air. The term “smog” was coined from the combination of “smoke” and “fog,” and today refers to unhealthy mixes of air pollutants that often occur over urban areas, especially when the air pollutants are trapped there by a temperature inversion. Photochemical smog is caused by secondary pollutants and other chemicals, often including ozone and NO2. Industrial smog is caused by the by-products of industrial combustion, especially soot, CO, CO2, SO2, and NO2, resulting in a characteristically gray, acidic mixture. CFCs split O3 to produce O2. Because CFCs persist in the atmosphere for years, are mixed all over the world regardless of their source, and destroy UVprotective stratospheric ozone, they are considered a long-term international problem. Many nations of the world came together to create the Montreal Protocol, which limited the production of CFCs and similar chemicals internationally. Acidic deposition, an example of a secondary pollutant, can occur far from the source of its precursor pollutants because of the long-range atmospheric transport that occurs while the atmospheric chemical reactions are occurring. Acidic deposition can change soil chemistry, kill trees, acidify lakes, harm aquatic organisms, eat away at buildings, and cause other impacts. Common indoor air pollution sources include tobacco smoke, radon gas, volatile organic compounds, living organisms from mites to bacteria, and smoke from indoor fires. Exposure can be reduced for each (in the order of the factors just mentioned) by not smoking indoors, ventilating confined spaces in basements, choosing alternative products for floor coverings or cleaning compounds, minimizing sources of standing water in the building’s HVAC system, and limiting wood fires to the outdoors, or at least proving a working chimney and adequate ventilation. Interpreting Graphs and Data 1. Relative to 1970, GDP is up 203%, vehicle miles traveled is up 177%, energy consumption is up 49%, population is up 46%, and aggregate emissions are down 54%. GDP per capita is up 105%, vehicle miles traveled per capita is up 94%, energy consumption per capita is up 5%, and aggregate emissions per capita are down 67%. 2. Relative to 1970, aggregate emissions per unit of energy consumed is down 69% for 2006. 3. Technological advances will continue to be made, but to date, those advances have accounted for virtually all of the decreased emissions. Note that the change in aggregate emissions per capita and the change in aggregate emissions per unit of energy consumed are nearly identical. Significant decreases could be made if we changed our behavior and drove our modern, efficient cars only as many miles per person as we did in 1970. Calculating Ecological Footprints IG-261 You Your Class Your State United States Total NOx emissions (lb) NOx emissions due to light-duty vehicles (lb) 146.4 Answers will vary Answers will vary 42,204,000,000 24.9 Answers will vary Answers will vary 7,166,000,000 1. The U.S. population increase from 2002 to 2010 is projected to be 7.1%. NOx emissions have decreased slightly during the past decade, even as the population has grown, largely the result of improved technology. Unless unexpected technological breakthroughs occur, or unless fuel demand surges, we may expect these trends to continue. 2. By reducing your vehicle miles traveled by one-half, 12.45 pounds of NOx emissions could be avoided, which would be an 8.5% reduction in your total NOx emissions. 3. Answers will vary. Anything that would reduce your combustion of fossil fuels would also reduce your amount of NOx emissions (e.g., setting your thermostat lower in the winter and higher in the summer; using only those lights necessary; taking cooler, shorter showers). Reducing the per capita share of vehicle miles traveled is as easy as carpooling, combining several errands into one trip, or walking/biking when possible. IG-262