DEVELOPING ENVIRONMENTAL INDICATORS FOR MINNESOTA
Atmosphere
The Environmental Indicators Initiative
State of MinnesotaFunded by the Minnesota Legislature
on recommendation of theLegislative Commission on Minnesota Resources
Sponsored byThe Environmental Quality Board
1998
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Citizens and decision makers useenvironmental indicators to helpeffectively manage and protectMinnesota�s air. Environmentalindicators answer four questions.
What is happening to ouratmosphere?Environmental condition can be assessedusing indicators based on characteris-tics of the atmosphere, includingconcentrations of various air-borne pollutants, the area andpercentage of forest land affected
by ground-level ozone pollution,the extent of thinning of theprotective ozone layer in theupper atmosphere, and the con-centration of carbon dioxide andother greenhouse gases that maycause global warming.
Why is it happening?Indicators of human activities thataffect the atmosphere include thenumber of permits issued forfacilities that pollute the air, thepercentage of electricity gener-
ated by burning coal or otherfossil fuels, the number of auto-mobiles on the road, and thepercentage of solid waste dis-posed of by incineration.
How does it affect us?Changes in air quality may diminishthe flow of benefits we derive from aclean atmosphere. Indicators of howwe are affected include the numberof new asthma cases, the numberof lakes having fish-consumptionadvisories based on airborne toxicchemicals, the amount of harmfulultraviolet radiation, and thenumber of people living in areaswhere pollution regularly exceedsair-quality standards.
What are we doing aboutit?Societal strategies to maintain or restoreair quality include pollution-controltechnologies (such as stack scrub-bers on coal-fired power plants andcatalytic converters on automobileengines), reductions in the use ofchemicals that cause thinning ofthe protective ozone layer, andreductions in emissions of carbondioxide.
In this chapter we outline the benefitsof a clean atmosphere, the keycharacteristics that determine thehealth of the atmosphere, thepressures affecting the atmospheretoday, and the most significant ofMinnesota�s policies and programsthat affect the atmosphere.
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troposphere
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stratosphere
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CH4
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NOx
CO2
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O3
CFCs
CO2
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HIGHLIGHTSBenefits of a HealthyAtmosphere� Livable temperatures� Protection from harmful
ultraviolet radiation� Lower rates of respiratory
ailments� Cycling of nutrients essential for
plant and animal growth� Pollination of crops and other
plant species� Precipitation� Wind energy
Important AtmosphericCharacteristics� Stratospheric ozone intercepts
ultraviolet radiation.� Uneven heating of the earth�s
surface generates weatherphenomena and climate patterns.
� Greenhouse gases maintain
livable temperatures.� The atmosphere is a major
reservoir for carbon, nitrogen,oxygen and water.
Pressures on AirResources� Release of carbon dioxide and
other greenhouse gases fromindustrial and agriculturalactivities, energy production, andautomobiles
� Heat islands in urban areas� Emission of persistent toxic
substances, particulate matter,and acid-forming compounds
� Depletion of stratospheric ozoneby chlorofluorocarbons
� Formation of ground-levelozone
Status and Trends� Approximately 70% of pollution
emitters are regulated by theMPCA
� Mercury deposition hasdecreased since 1970 in someareas of the state
Existing Policies andPrograms� Air-quality standards and
emission regulations that meetthe needs of the state
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HOW WE BENEFITFROM A HEALTHYATMOSPHEREThe atmosphere seems endless, but itis no more than a thin skin wrappedaround the earth�s surface. All livingthings depend on the atmosphere.Green plants and algae use sunlightto combine atmospheric carbon withwater to produce carbohydrates, thebasic fuel of life. As theyphotosynthesize, green plants andalgae release oxygen into theatmosphere, and it is this oxygen thatis critical to the survival of nearly allof earth�s organisms.
The atmosphere sustains conditionson earth that allow living organismsto survive. For example, naturallyoccurring greenhouse gases (carbondioxide and water vapor) allow solarenergy to enter the earth�satmosphere but slow its return tospace. The result is an averagesurface temperature of about 15oC.Without the greenhouse effect of theatmosphere, the earth�s averagetemperature would fall to -20oC,much too cold to support life as weknow it. Ozone high in thestratosphere protects livingorganisms by absorbing most of thesun�s harmful ultraviolet wavelengths,which cause skin cancer and eyedisease, and damage crops, otherplants, and immune systems. Thevast majority of meteorites movingtoward the earth�s surface burn upharmlessly in the atmosphere insteadof creating craters like thosecharacteristic of the moon.
A clean atmosphere is essential forhuman health. We inhale about sixliters of air every minute. Polluted aircan initiate asthma attacks, irritatethroats, eyes, and lungs, and causechronic lung disease and emphysema(MEQB 1988). In the worst cases,smog-prone cities issue pollutionalerts to warn their citizens to stayindoors when pollution levels arehigh. Children, the elderly, andpeople with heart disease are amongthose most susceptible to the illeffects of polluted air (MEQB1988).
The atmosphere plays a key role indistributing and cycling the elementsessential for life, such as carbon andnitrogen, and water. These nutrientscycle between the atmosphere andthe tissues of plants and animals.They are assimilated into soils asplant and animal remainsdecompose, and return to theatmosphere as gases.
Finally, our atmosphere is a physicalforce in every ecosystem. Erosion oflandscapes through the action ofwind and wind-induced waves hasshaped the earth throughout itshistory, creating places of beauty aswell as harsh, infertile landscapes.Winds transport pollen, seeds,bacteria, spores, and dust far fromtheir points of origin. Wheat, corn,rice, and many other crop plants andtrees depend on wind forpollination. The atmosphere receiveswater vapor from water bodies andtranspiring plants and redistributes itas rain and snow. The atmospherealso dilutes pollutants released frompoint sources.
In the following pages we describethe atmosphere and the pressures weexert on it, and give informationregarding the current state of ouratmosphere. This information iscritical to developing acomprehensive set of indicators formonitoring the atmosphere and thehuman, terrestrial, and aquaticsystems to which it is linked.
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CHARACTERISTICSOF THEATMOSPHEREEarth�s earliest atmosphere wasmostly nitrogen, methane, andcarbon dioxide, with little oxygen.The first living organisms, probablysimilar to today�s anaerobic bacteria,were adapted to this atmosphere.Evolution of the atmosphere weknow today began about 3.5 billionyears ago with the first additions offree oxygen from earlyphotosynthesis. Single-celled blue-green algae used carbon dioxide andemitted oxygen as a by-product,slowly increasing the free oxygen thatcould support more complex formsof life, and also allowing thedevelopment of a protective layer ofozone in the stratosphere. Over time,the action of living creaturesincreased oxygen and removed heat-trapping carbon dioxide from theatmosphere. With these changes, theearth�s environment becameincreasingly more like it is today.Although the composition of theatmosphere has changed continuallythrough the earth�s history, it hasremained fairly stable for the past10,000 years.
Today�s atmosphere is about 78percent nitrogen and 21 percentoxygen, with smaller amounts ofwater vapor (about 3 percent), argon(1 percent), and carbon dioxide(0.035 percent) (Miller 1991). Theatmosphere consists of several layersresulting from changes intemperature and in concentrations ofgases. About 80 percent of the massof the atmosphere lies within thetroposphere, the lowest layer of the
atmosphere. It is in this layer, 6 to 17km thick, that clouds, surface winds,water vapor, and many pollutantscirculate around the planet. Another19 percent of the mass of theatmosphere lies in the stratosphere,which extends to 50 km above theearth�s surface. Within this zoneozone absorbs ultraviolet radiation.The last two layers, the mesosphereand the thermosphere, are only 1percent of the atmosphere�s massbut reach out several hundredkilometers into space.
Uneven heating of the earth�s surfaceand the atmosphere creates windsand generates precipitation. Theequatorial regions receive moredirect sunlight and accumulate moreheat than do the polar regions.Warm, less dense air at the equatormoves upward and poleward,pushing cool, denser air from thepoles toward the equator. As warmair moves upward, the water it holdscondenses, forming clouds andeventually falling as precipitation. Theearth�s rotation bends some of thesemasses of rising and falling air intomajor air currents, such as the jetstream, which are more or lesspermanent features of the middleatmosphere.
Air movement is also affected bymountains and other major landfeatures, which divert air masseshorizontally and vertically. In NorthAmerica, for example, warm airmoving northward from the Gulf ofMexico often moves unobstructedinto Minnesota. On the other hand,air moving from the Pacific Ocean isusually diverted upward by the SierraNevada and the Rocky Mountains.As it rises, the air cools and the
moisture in it condenses to formrainfall on the west side of themountains. Only a small portion ofthis air and precipitation reachesMinnesota.
Around the world we see dramaticexamples of atmospheric forces,including the monsoons of India, thelarge desert regions of the world, thetorrential tropical rains of theAmazon, and the powerfulhurricanes in the southeast UnitedStates. These and other regionalclimate patterns help define theculture of an area. Clothing,architecture, agriculture, recreation,economic activities, and culturalactivities are all tightly linked toclimatic patterns determined bydynamic processes in ouratmosphere.
Humans have dramatically influencedatmospheric chemistry at both localand global scales, and we are onlybeginning to understand theimplications of those alterations.Pollutants are only a small percentageof the atmosphere but havedisproportionately large effects onhuman health and ecosystemfunction. While natural changes to theatmosphere have occurred since thebeginning of the earth�s history, theyhave occurred much more slowlythan those we are currentlyexperiencing. The unprecedentedrates of change present a unique andpressing challenge for humans.
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PRESSURES ON THEATMOSPHEREDuring the earth�s 4-billion-yearhistory, volcanoes spewed aerosolsand gases into the troposphere andstratosphere, changes in orbit andorientation altered weather andclimate patterns, and plant andanimals influenced concentrations ofcarbon dioxide and methane gas inthe air (Berger 1977; Houghton et al.1992). Such changes occurredgradually, over hundreds orthousands of years. Organisms andecosystems had time to adjust to thechanges. In the past 200 years,however, industrialization anddramatic human population growthhave put significant new pressures onthe atmosphere: large-scalealteration of natural ecosystems,construction and expansion ofurban environments, and pollution.
The atmosphere is a major reservoirof the carbon that is essential for life(Figure 1). Carbon dioxide gas helps
keep the earth at a temperaturehospitable to life. Plants removecarbon dioxide from the air viaphotosynthesis to build thecarbohydrates that support allorganisms. Proteins, carbohydrates,and the other chemicals that make upliving tissue are built aroundskeletons of carbon molecules.
Many human activities affect theamount of carbon stored in theatmosphere. Worldwide, about 700billion tons of carbon dioxide entersthe atmosphere each year fromnatural processes, and about 700billion tons are absorbed again byother natural processes. Over thepast several hundred years, however,increases in the amount of carbon inthe atmosphere have resulted fromhuman activity. We now add about24 billion additional tons of carbondioxide to the atmosphere annually(Morrisey and Justus 1998). Mininglimestone for construction andburning fossil fuels add largeamounts of carbon to theatmosphere. More recently, extensiveconversion of natural habitats toagriculture and urban lands also hasincreased the amount of carbon inthe atmosphere. As soils are plowed,peat is mined and burned, and treesare cut and burned, the carbon thatwas held in those reservoirs entersthe atmosphere. As agricultureexpands to feed burgeoning humanpopulations, paddy rice farming andcattle raising will add substantial
Figure 1
Global Carbon Cycle○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
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Figure 2
CO2 Production from Fossil Fuel
Combustion in Minnesota
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amounts of carbon (as methane) tothe atmosphere. The additionalcarbon dioxide and methane mayincrease the greenhouse effect of theatmosphere (Houghton et al. 1992,1995) and throw climate, weather,and other cycles out of balance.
In Minnesota, the primary source ofthe carbon dioxide released to theatmosphere is the combustion ofpetroleum, coal, and natural gas.Since 1960, transportation andelectric generation has accounted formost of the carbon dioxideemissions in the state (Figure 2).
The atmosphere is also a majorreservoir of the nitrogen that isessential for life (Figure 3). Most ofthis nitrogen is unavailable for use byliving organisms until bacteria thatlive symbiotically with plants(primarily legumes) and in soils and afew species of algae convert nitrogengas to chemical forms that can beused by other organisms. The
amount of nitrogen made availablein this way is a very small but vitalportion of the total nitrogen availableto living organisms. But largequantities of nitrogen in forms thatcan be used directly by plants arereleased to the atmosphere whenfossil fuels are burned. This excessnitrogen, distributed worldwide bythe atmosphere, may have seriousimpacts on many ecosystems becauseof the role that nitrogen limitationplays in organizing and maintainingliving systems. One anticipatedconsequence of increased nitrogenavailability due to depositionfrom the atmosphere is the loss ofbiological diversity, especially amongplants adapted to low-nitrogen soils(Vitousek et al. 1997).
UrbanizationOver 70 percent of the U.S.population lives in urban areas, and itis projected that by the year 2005urban centers will be home for morethan 50 percent of the world�s
population (Brown et al. 1996).Urbanization has significant effectson the atmosphere, especially onlocal heat balances. Asphalt andconcrete absorb large quantities ofsolar energy and reradiate it to thesurrounding air. Vehicles, apartments,and offices lose heat to theatmosphere. In addition, some of thepollutants common in urban areas(discussed in more detail later) areeffective at trapping heat. As aconsequence, urban areas becomeislands of heat compared to nearbyrural areas.
The elevation of temperatures inurban centers has importantimplications for air quality. Commonurban pollutants, such as nitrousoxides and volatile organiccompounds, combine in thepresence of elevated temperaturesand direct sunlight to form smogand ground-level ozone. When air isstagnant for several days and thesecompounds accumulate, the healthof people exposed to them can becompromised.
The intensity of the urban heat islandeffect depends on the extent ofurbanization, the local topography,the nature of the pollutants occurringin the area, and local weatherconditions (Government of Canada1991). For example, winds may carrypollutants away from the city,reducing their local impact butcontributing to regional pollutionproblems. Mountains or othertopographic barriers may prevent thedispersal of pollutants and allowpollutant concentrations to build totoxic levels.
Figure 3
Global Nitrogen Cycle
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The urban heat island phenomenoncan be moderated by many practices.Using light-colored concrete androofing materials that reflect morelight in place of asphalt and tar paperhelps keep the urban environmentcooler. Trees cool the city byabsorbing sunlight and providingshade (Chen 1997). These and similarmitigation strategies could save $10billion to $15 billion annually byreducing cooling costs and reducingsmog-related health problems(Stetson and Koedijk 1996).
PollutionMany human activities contribute topollution, including industrialactivities, the burning of fossil fuels,and mining and farming practicesthat introduce fine dust particles intothe atmosphere. Pollutants areemitted by mobile, industrial, andarea sources (MPCA 1997a; Table 1).Mobile pollution sources includevehicles and machines that burn fossilfuels, including cars and airplanes.Industrial sources, often called point
sources, are large stationary sourcessuch as factories, refineries, andpower plants. Area sources are small,widely distributed, stationary sourcessuch as home furnaces and restaurantkitchens. In the recent past, greaterattention was directed towardcontrolling point sources of pollution(e.g., factories, refineries) than othersources of pollution. Todaypollution-reduction regulationsalso control nonpoint and areasources.
GLOBALATMOSPHEREISSUESClimate changeClimate change is the cumulativechange in temperature and climatepatterns resulting from increases inthe atmospheric concentration ofgreenhouse gases from
anthropogenic and other sources(Figure 4). The earth retains heat dueto the presence of greenhouse gases(e.g., carbon dioxide, methane, watervapor) in the atmosphere, aphenomenon that is essential formaintaining conditions suitable forlife. However, some human activities,such as burning fossil fuels,deforestation, large-scale cattleraising, and paddy rice agriculture arerapidly increasing the concentrationof greenhouse gases in theatmosphere. This increase may causedramatic changes in climate over amuch shorter time than ever before.Rapid climate change on a globalscale would have massive effects onthe earth�s weather, agriculturalsystems, native ecosystems, andnatural preserves (Miller 1991).
Since the Industrial Revolution, theburning of fossil fuels has pumped
Table 1
Sources of ImportantPollutantsPollutant Mobile Industrial Area
source sources sourcesSmog-forming 45% 31% 24%chemicals
Particulates 15 60 25
Urban toxicsubstances 64 1 35(e.g., benzene)
Mercury 0 65 35
Acid rain-forming 5 91 4compounds
Ozone-depleting 18 5 77compoundsGreenhousegases 36 48 16
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Figure 4
The Greenhouse Effect
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massive amounts of carbon dioxideinto the atmosphere. Human activityadds about 24 billion tons of carbondioxide to the atmosphere annually(Morrisey and Justus 1998). Anaverage American automobile,driven about 10,000 miles per year,releases its own weight of carboninto the atmosphere (Miller 1991).
The increase in atmospheric carbondioxide accounts for 60 percent to70 percent of the observedgreenhouse effect (MPCA 1997a).One molecule of methane, however,is about 25 times more effective atretaining heat than is a molecule ofcarbon dioxide (Miller 1991), andsmall increases in methaneconcentrations may result in largechanges in heat retention. Rice paddyagriculture and large-scale cattleraising are significant sources ofmethane (Houghton et al. 1992,1995), and these sources mayincrease as the world populationincreases.
Global average temperatures have
risen 0.6o to 1.2oF since the late1800s (US EPA 1997), and climatescientists expect additional increasesof 2o to 5oF during the next centuryas carbon dioxide levels rise (Figure5; MPCA 1997a). Warmertemperatures may have profoundeffects on global weather patterns,creating violent storms anddisrupting rainfall patterns. The polarice caps may melt, raising sea levelsenough to flood island nations andlow-lying continental coasts. Globalwarming may also disruptecosystems and lead to the extinctionof species. The unprecedented speedof this human-caused change wouldhave serious implications for thesurvival of other species. Plants andanimals that once had thousands ofyears to migrate or adjust as climatechanged may now be caught in arapid warming trend for whichevolution has not prepared them(Halpin 1997). Natural preserves, setaside as refuges for wild species, maybecome unsuitable habitat as theclimate changes, for example,wetlands could turn to dry
meadows, and savannah ecosystemscould convert to deserts. Speciessurviving in park island ecosystemsmay find themselves with nowhereto go.
While global warming is not yetincontrovertibly confirmed, evidencecontinues to mount that the globalclimate is becoming warmer andmore violent. The effects of globalclimate change on any particularregion are hard to predict, thoughwe can make some educated guesses.Here in Minnesota, average rainfallin the state has increased over thepast century, rising as much as 20percent in the southern half of thestate. Average annual temperatures inMinneapolis have increased from43.9oF (average for 1888-1917) to44.9oF (average for 1963-1992; USEPA 1998). Some models predictthat if alteration of the globalatmosphere continues, Minnesota�saverage annual temperature couldrise by about 4oF by 2100, withhotter summers and, most likely,increased rainfall.
A warmer, wetter climate wouldaffect all of Minnesota�s ecosystemsand its citizens. Without severewinters, mosquitoes that carry yellowfever, dengue fever, eastern equineencephalitis, and LaCrosseencephalitis could survive in our state(they already breed as far north asChicago). Certain agricultural pestsmight also increase in a warmer,wetter climate. While warmer
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Figure 5
Average Temperature of the Earth Surface
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temperatures could expand the rangeof many crops northward, soils inthe northern part of the state are notwell suited to agriculture. Yields ofsoybeans and wheat in currentagricultural areas are likely to increaseunder expected temperature andprecipitation regimes, while yields ofcorn would likely decrease (Figure 6).
Trees and forests adapted to specificclimate conditions are likely tochange as climate changes. Underwarmer, wetter conditions, ournorthern forests might be replacedby a more southerly mix of oak andsouthern pines (Figure 7; US EPA1998). If the climate warms but alsobecomes drier, both hardwood andconifer forests could be replaced byprairie and savannah ecosystems.Wildlife species and economicactivities also would need toaccommodate the changedconditions.
Lakes, rivers, and wetlands would beaffected in several ways. Streamflows could peak sooner in thespring because of earlier snowmeltand ice breakup (US EPA 1998).This could mean reduced streamflows in summer, decreased waterquality, and reductions in fish habitat.Warmer lake temperatures mayaffect fish communities, favoringsome species and stressing others.
While a warmer climate would meana longer ice-free shipping season forthe Mississippi River and LakeSuperior, increased evaporation andlower water elevations could makeshorelines more susceptible todamage by wind and rain erosion. Awarmer climate could dry many ofthe state�s wetlands, including theprairie potholes that are thecontinent�s single most importantbreeding ground for waterfowl suchas mallards, pintails, and blue-wingedteal (US EPA 1998).
Best estimates suggest that stabilizingglobal temperatures would require a60 to 80 percent reduction inemissions of greenhouse gasesworldwide (MPCA 1997a).Industrial nations account for mostemissions of greenhouse gases,particularly carbon dioxide. TheUnited States, the largest singlecontributor, emitted 1.4 billion tonsof the 6.1 billion tons emittedworldwide in 1995 (Brown et al.1996) and also has the world�shighest per-capita emission rate, at
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Figure 6
Potential Climate Change Effects onAgriculture
Conifer forest Broadleaf forest
Grassland Savanna/Woodland
Current +10oF, +13% Precipitation
Figure 7
Changes in Forest Cover
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5.25 tons of carbon per person eachyear. It is difficult and expensive toremove the carbon dioxide fromexhaust gases and nearly impossibleto trap carbon dioxide from manyother sources. Strategies for reducingcarbon dioxide emissionsconcentrate on reducing the use offossil fuels through conservation,energy efficiency, and reliance onalternate energy sources, includingsolar and nuclear power. Since treesabsorb carbon dioxide and store thecarbon for long periods,reforestation and urban treeplanting can help offset increases inatmospheric carbon dioxide(Morrisey and Justus 1998).
Under the 1997 Kyoto Protocol, theUnited States has agreed to stabilizeits greenhouse gas emissions at 1990levels by the year 2000. However,emissions have not been stabilized,and it is unlikely that the UnitedStates will meet its treaty obligations(MPCA 1997a). Despite suchsetbacks, negotiations continue onother international agreements tolimit emissions of greenhouse gases.Reducing the threat of globalwarming will require internationalcooperation and coordination ofpolicies between industrial andindustrializing nations.
Ozone depletionAbout 90 percent of atmosphericozone is in the stratosphere, where itabsorbs 99 percent of high-energyultraviolet radiation from the sun(Miller 1991). The protectionafforded by ozone is vital to life onearth, as ultraviolet radiationdamages living tissue, causing skincancer, cataracts, and many otherdisorders. Since the early 1980s,scientists have noted a thinning of theozone layer, especially above theNorth and South Poles.
Ozone thinning is caused by long-lasting industrial chemicals that travelto the upper atmosphere andinterfere with ozone formation.These chemicals includechlorofluorocarbons, haloncompounds, and solvents such ascarbon tetrachloride.Chlorofluorocarbons and halons arenontoxic and unreactive at groundlevel but interrupt ozone formationwhen energized by high-altitudesunlight. Chlorofluorocarbons, orCFCs, are widely used as refrigerantsand aerosol propellants.
As much as 60 percent of thestratospheric ozone may disappear aswinter air currents trap CFCs abovethe poles (Steer et al. 1992; Brown etal. 1996). The annual spring breakupof the Antarctic air vortex sendsmasses of ozone-depleted air overAustralia and other populated areas.In these areas, levels of ultravioletradiation may increase by as much as20 percent (Miller 1991). A NASAstudy revealed that ozone declinedby 3 percent over the NorthernHemisphere between 1969 and 1988(Miller 1991). In parts of the middle
latitudes, ozone was reduced by 10percent during the spring of 1995(Brown et al. 1996).
As ozone thins, more ultravioletradiation reaches the earth. Each 1percent loss of ozone leads to anincrease of about 2 percent in theamount of ultraviolet radiation thatreaches the earth�s surface and anincrease of 5 to 7 percent in skincancer cases. The rate of damage tothe genetic material of humansand other organisms andincidences of skin cancer, eyecancer, cataracts, and immune-system disorders (Miller 1991) mayincrease. Amphibians, with their thinskins and jelly-coated eggs, may beparticularly vulnerable to damagefrom ultraviolet light (Blaustein1994). Many plants, includingimportant tree and crop species,suffer leaf damage and reducedgrowth as ultraviolet light increases.
Global efforts to reduce emissionsof ozone-depleting chemicalshave resulted in several internationalagreements. Under the 1987Montreal Protocol, 49 nations agreedto reduce production of the 8 mostwidely used CFCs. The 1989Helsinki Agreement requires 82countries to phase out use of the 5most damaging CFCs by the year2000, if substitutes are available bythen. However, putting theseprinciples into action has been slow,and worldwide commitment toozone layer protection has beenspotty. While consumption ofCFCs in industrial countriesdecreased by 74 percent from 1986to 1993, consumption in developingcountries increased by 40 percentduring the same period. As large
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ATMOSPHERE EII
nations such as China and India seekmore affluent lifestyles, use of CFCs(particularly as refrigerator coolant)may increase dramatically. In theUnited States the largest singlecontributor to CFC emissions isleakage from automobile airconditioners (Miller 1991). Thedamage these chemicals cause islong-term and expensive; one studyestimates that the CFCs releasedfrom one average aerosol can willcause $12,000 worth of damageover the life of the chemicals (Miller1991). CFC production peaked in1989 and has dropped to pre-1970levels (Figure 8; Brown et al. 1986),but because CFCs and other ozone-depleting chemicals can linger in theatmosphere for decades, even animmediate, total ban would notrestore the ozone to previousconditions for about 100 years(Miller 1991).
TRENDS IN AIRPOLLUTIONMinnesota has a strong andsuccessful regulatory process,credited for significantly reducingcertain pollutants in recent years.Levels of most major industrial airpollutants have decreased since 1971.Regulations have led to much bettercontrol of point-source pollutionand to reductions or leveling off inemissions of sulfur dioxide,ozone, volatile organiccompounds, lead, and carbonmonoxide. The following sectionsummarizes the status and trends ofsome of the most importantpollutants in Minnesota�satmosphere.
Smog-causing pollutantsSmog is a complex mixture ofpollutants. Burning fossil fuelsproduces nitrogen oxides, sulfurdioxide, and volatile hydrocarbon
compounds. When energized bysunlight, these chemicals react withother compounds in the atmosphereto form new, potentially harmfulcompounds (MPCA 1997a). Ozoneis one of the most destructive ofthese new compounds and is animportant component of smog. Thesame substance that absorbs harmfulultraviolet rays in our upperatmosphere is a corrosive pollutantthat damages crops and injures thelungs of humans and other animals atground level (MPCA 1997a).Nitrogen oxides also contribute toacid rain, forming corrosive nitricacid in reaction with water vapor(MEQB 1988).
Hydrocarbons are the combustiblecomponents of gasoline, oil, coal,wood, and natural gas. Whilecomplete combustion ofhydrocarbons produces only carbondioxide and water, combustion isseldom complete. The resultant mixof sooty chemicals contributes tourban smog, and some of thesechemicals, such as benzene, haveharmful effects on humans.Motorized vehicles produce 29percent of the hydrocarbons releasedin the state and 87 percent ofbenzene emissions in the Twin Citiesarea (Sigford and Eleff 1992).
Sulfur dioxide originates whensulfur-containing fuels, such as coaland oil, are burned. Sulfur dioxideirritates lungs and eyes andcontributes to smog. Asthma attacks,including tightening of the chest anddifficulty breathing, can be triggeredin sensitive people by low levels ofsulfur dioxide. An estimated 50,000to 150,000 asthma incidents aretriggered each year in Minnesota by
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Figure 8
Global CFC Production○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
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ATMOSPHERE EII
sulfur dioxide (MPCA 1997a). Sulfurdioxide also reacts with moisture toform sulfuric acid, an importantcontributor to acid precipitation(acid rain and acid snow). Acidprecipitation can significantly degradenatural systems by altering waterchemistry; it is corrosive to livingtissues and hastens the breakdown ofbuildings, statues, and other culturalstructures.
In Minnesota, emissions ofnitrogen oxides, sulfur dioxide,and volatile hydrocarbons haveremained fairly constant or haveincreased slightly since 1985 (Figure9) despite population and economicgrowth. Combustion of fossil fuelsaccounts for most emissions ofnitrous oxides and sulfur dioxide,and solvent use and fuelcombustion account for mostemissions of volatile hydrocarbons.As in the rest of the nation, controlof point sources (industrial facilities)has slowed the increase in emissionsof smog-causing pollutants inMinnesota. Factories and coal-firedpower plants have switched to low-sulfur coal and installed stackscrubbers to remove sulfur dioxidefrom smokestack gases. However,mobile and area sources continue tobe a problem. Future regulation mayinclude better control of nitrousoxides produced by automobilesand tighter standards for emissionsof these pollutants by area sources.
Minnesota�s air quality remains verygood by national standards.Minnesota is one of a very few statesentirely in compliance with thecurrent federal standard of 0.12 ppmfor ground-level ozone (MEQB1988; MPCA 1997a). Under a more
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Figure 9
Emissions of NOx, SO
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ATMOSPHERE EII
stringent standard that moreeffectively reduces potential injury tohumans and vegetation, the TwinCities might not be in compliancefor ground-level ozone (MPCA1997a). Appropriate ozone-reduction measures would then haveto be enacted.
Particulate matterParticulate matter includes particlesof dust, soot, smoke, or liquiddroplets that are emitted by factories,power plants, cars, and constructionactivities, and that enter theatmosphere via fire, naturalwindblown dust, and condensationfrom other atmospheric materials(US EPA 1995). Particulates less than10 microns in diameter areresponsible for the majority ofadverse health effects. These tinyparticles are able to penetrate deepinto lungs and cause irritation andtissue damage. For this reason, thesmallest particulates are closelyregulated by the U.S. EnvironmentalProtection Agency (US EPA).
Particulate pollution from factories,power plants, and automobiles hasbeen controlled through monitoringprograms and installation ofpollution control equipment. Inthe 1940s and 1950s, importantsources of particulate matterincluded transportation (railroadsand on-road vehicles), industrialprocesses, fuel combustion forheating, and wildfires. Today, fuelcombustion and metal processing arethe main sources of particulatepollution (Figure 10). Wind erosioncan contribute significant amounts ofdust and dirt to the atmosphere, butthis effect is highly variable. Duringthe drought of 1988, nationwide
contributions of wind-causedparticulate matter were estimatedat 18 million tons, compared to 2million tons during the flood year1993 (US EPA 1995).
In Minnesota, only a small portion ofSt. Paul fails to meet federal ambientair standards for particulates (MPCA1997a). Fine particles from chimneysand smokestacks are generally wellcontrolled by equipment such aselectrostatic particulate traps (MEQB1988). Particulates from excavationsites and agricultural fields are harderto control, but conservation tillagepractices and prompt revegetationon dig sites can help.
Current standards that regulateparticles smaller than 10 microns indiameter may not be stringentenough to protect human health.Particles smaller than 2.5 micronsappear to cause the greatestproblems for health, and provisionsnow under consideration may focusmore closely on this size class(MPCA 1997a).
Urban toxic pollutantsUrban toxic pollutants includehundreds of different pollutants,ranging from dust to cancer-causinghydrocarbons (MPCA 1997a). Someof these compounds, such asbenzene and formaldehyde, areknown to cause cancer or birthdefects in laboratory animals.However, at the low concentrationstypical in urban air, the impact ofmost urban toxic pollutants onhuman health is not welldocumented (MPCA 1997a).
Carbon monoxide is one of themost common urban toxic airpollutants. It is a colorless, odorlessgas that results from incompleteburning of wood or fossil fuels.Carbon monoxide can be poisonousbecause it replaces oxygen in ourbloodstream, binds tightly tohemoglobin, the blood protein thattransports oxygen, and prevents theblood from carrying enough oxygento our cells. Exposure to highconcentrations of carbon monoxide
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Figure 10
Particulate Matter Emission in Minnesota
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ATMOSPHERE EII
can be fatal; in smaller doses it causesheadaches, muscle aches, and othersymptoms of oxygen deprivation.Carbon monoxide from mobileoutdoor sources, particularlyautomobiles, may accumulate inareas where traffic is heavy and theair is stagnant. Motorized vehiclesproduce 69 percent of the carbonmonoxide in the Twin Cities area(Sigford and Eleff 1992).
Although emissions of carbonmonoxide have decreased inMinnesota in recent decades (Figure11) largely because of better controlson automobile emissions, excessivelevels still occur, particularly intraffic-congested cities. In addition tocarbon monoxide-reducingtechnologies required forautomobiles by the federalgovernment, Minnesota tests vehicleemissions in the metropolitan area.The program, initiated in 1991,requires vehicle owners to keepengines maintained for efficientcombustion and minimum carbonmonoxide production. Oxygenatedgasoline is also sold in some areas,reducing carbon monoxideproduction, especially in coldweather (MPCA 1997a). These twoprograms reduce emissions by anestimated 180,000 tons of carbonmonoxide each year (MPCA 1997a).Timed signal lights have also reducedcarbon monoxide build-up at busyurban intersections (MEQB 1988).
Indoor air pollutionBetween 80 and 90 percent of theurban population�s time is spentindoors (MEQB 1988). In recentyears, as buildings have been betterinsulated for energy efficiency,
concerns have arisen that certainchemicals may concentrate indoorsto irritating or toxic levels. Theseinclude cigarette smoke,formaldehyde (used in themanufacture of foam insulation andsynthetic carpet), and asbestos. TheMinnesota Clean Indoor Air actrecently banned smoking in all publicbuildings, and more and moreworkplaces are taking steps toremediate or eliminate other indoorair hazards.
Another concern for indoor airquality is radon, a radioactive gasthat can seep into homes andconcentrate to unhealthy levels.Long-term exposure to radon isassociated with an increasedlikelihood of lung cancer. Radon is anaturally occurring by-product fromthe decay of uranium in rocks, withsome rocks (e.g., granites) emittingmore than others (MEQB 1988). Noradon hot spots have been identifiedin Minnesota, but a survey by the
Minnesota Department of Healthfound that up to 40 percent ofMinnesota homes may have radonlevels above US EPA guidelines(MEQB 1988). Increased venting ofbasements and other areas nearground level where radon mayaccumulate usually is effective inreducing radon levels.
Persistent toxic pollutantsPersistent toxic pollutants includeindustrial chemicals such as dioxinsand polyaromatic hydrocarbons(PAHs) and heavy metals such asmercury and cadmium. All of theseare poisonous substances that are notreadily degraded and last a long timein the environment (MPCA 1997a).These substances can travel longdistances by air, raining out intowater and soil, and may accumulatein the tissues of plants and animals,causing various health problems.
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Figure 11
Emission of Carbon Monoxide from FuelCombustion in Minnesota
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Persistent toxic pollutants are ofspecial concern because low levels inthe environment quickly accumulateto high levels as they move up thefood chain. A fish or animal mayaccumulate the dioxins and mercuryit eats. If that fish or animal is eatenby another, the whole body burdenof these substances passes to theconsumer. Humans can be exposedto high levels of persistent toxicsubstances by eating game fish andturtles. At high levels, thesesubstances pose health risks. Dioxinshave been shown to cause cancer inlaboratory animals. PAHs, a broadclass of chemicals, also may causecancer and can decrease fertility inlab animals. Mercury causes kidneydamage and damage to orimpairment of the brain and nerves.Lead, another persistent toxicsubstance, can cause acute poisoningand brain damage.
Once emitted into the air, dioxins,mercury, and some other persistenttoxic pollutants are carried longdistances by wind. Measurableamounts persist in the atmospherebut also easily accumulate in aquaticsediments and in the tissues of fishand fish-eating animals. TheMinnesota Department of Healthprovides advisories on theconsumption of many species of fish(MDH 1996).
Mercury enters the atmosphere whenit volatilizes from spills, when coal isburned, and when mercury-containing consumer products, suchas batteries, thermometers, and somepaints, are incinerated. Once in theatmosphere, the mercury may betransported long distances before itis deposited onto forests, fields,
wetlands, lakes, and rivers. AlthoughMinnesota has strictly regulated in-state mercury emissions fromincinerators and has eliminated manypoint-sources (Sigford and Eleff1992), unsafe levels of mercury stillexist even in remote parts of the state(Swain et al. 1992). Regularconsumption of fish with even smalllevels of mercury may cause healthproblems in humans and otheranimals. Because mercury can causesevere birth defects, pregnantwomen should be especially carefulto limit consumption.
Globally, mercury deposition hasincreased steadily since the mid-1800s. In Minnesota, however,mercury deposition fromatmospheric sources may havedecreased since the 1970s. Regionaland global sources of atmosphericmercury appear to be moreimportant than local sources ascontributors to aquatic systems(Swain et al. 1992); although currentrates of deposition in Minnesota arelower than in 1970, lakes still showelevated mercury levels.
Lead, a heavy metal once added togasoline and used as a pigment inpaints, causes serious healthproblems. Acute (short-term)exposure to high levels of lead resultsin a syndrome of physicalimpairments called lead poisoning.Chronic (long-term) exposure causesneurological damage that interfereswith memory and learning. Childrenand developing fetuses are especiallyvulnerable; exposure to high levels oflead while brain tissue is forming cancause life-long impairment.
Lead pollution has been sharplyreduced in recent years through banson lead in gasoline and house paint.Airborne lead has been dramaticallyreduced since the mid-1970s byfederal policy requiring new cars toburn lead-free gasoline. Thereduction in emissions from 219,000tons in 1970 to 5,000 tons in 1994was due primarily to the shift tounleaded gasoline. Minnesota�sstringent standards for leademission from industrial sites alsohave helped cut airborne lead levels(MEQB 1988). However, emissionsof lead are on the rise again due toincreased industrial activity andincreased emission of lead byelectrical utilities (US EPA 1995).
Acid precipitation (acidrain, acid snow)Nitrogen oxides and sulfur dioxide,formed when fossil fuels are burned,react in the atmosphere to formnitric and sulfuric acids. These acidstravel widely through the atmosphereand eventually are incorporated intorain or snow. They fall to earth asacid precipitation, which corrodesbuildings and seriously damagesforests and aquatic ecosystems(Taylor et al. 1994). Acid rain injurestree leaves and needles, interfereswith soil nutrient cycles, and kills fishand amphibian eggs.
Acid rain is an issue that crossesregional boundaries. Because 90percent of the acid deposited inMinnesota is generated outside thestate, cooperation between variousstates and Canada (MEQB 1988) isnecessary for effective reductions inacid deposition.
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ATMOSPHERE EII
While acid precipitation is a seriousproblem in New England andcentral Europe, recent monitoringdata suggest that it is not a significantproblem in Minnesota. Many ofMinnesota�s lakes are buffered byalkaline, limestone-rich bedrock, andthe geologically more vulnerablenorthern lakes receive only moderateamounts of acid fallout due toprevailing wind patterns.Nevertheless, 8 million acres ofMinnesota lakes and forests may besusceptible to acid damage, including2,000 lakes in the state�s north andnortheast regions (MEQB 1988).
Existing Policies andProgramsThe federal Clean Air Act assigns thestate significant responsibility formaintaining air quality. In Minnesotathe Minnesota Pollution ControlAgency (MPCA) is the lead agency inmaintaining Minnesota�s air quality. Inconsultation with the US EPA,MPCA sets air quality standards,analyzes pollution levels, andmonitors compliance with airemission standards. Minnesota isone of only eight states that haveacted on the authority given in theClean Air Act to develop air qualitystandards for some pollutants thatare more stringent than the federalNAAQS (Sigford and Eleff 1992).
There are two levels of air qualitystandards: primary and secondary.These standards define the allowablehourly exposure to specificpollutants. Primary standards protecthuman health. If exposure to apollutant is kept below the primarystandard, even sensitive peopleshould experience no ill effects(MEQB 1988). Secondary standardsare intended to limit crop damage,injury to livestock, damage toproperty, annoyance, andtransportation hazards (MEQB1988). Although both primary andsecondary standards are establishedby the federal government, statesretain the right to set standards thatare more stringent. For example,Minnesota enforces a standard forshort duration (1-hour) exposure tosulfur dioxide that does not exist atthe federal level (MEQB 1988).
States may also modify standards tofit local needs. For instance, to
protect white pine and other acid-sensitive species in Minnesota�snorthern forests, the state has twostandards for sulfur dioxide. Themore stringent standard applies toareas north of St. Cloud (MEQB1988).
Of about 2,200 air emission facilitiesin the state, ranging from smallschool boilers and rural grainelevators to petroleum refineries andcoal-burning power plants,approximately 1,500 sites (nearly 70percent) are required to obtainMPCA air emission permits (MPCA1997a). The MPCA recognizes twoclasses of permitted facilities: thoseemitting between 25 and 100 tons ofpollutants per year, and thoseemitting more than 100 tons peryear. Facilities emitting less than 25tons per year are generally exemptfrom permits, although operationslikely to cause a local nuisance maybe reviewed on a case-by-case basis(MEQB 1988). Large facilities areissued one permit for total facilityemissions, streamlining an earlierprocess whereby permits weregranted for individual pieces ofequipment (MEQB 1988). Withtotal facility permits (TFPs) inplace, the MPCA can moreeffectively monitor pollution fromeach facility and makerecommendations for keepingemissions within standards.
Pollution reduction is the main goalof most air-quality control policies.Regulators seek to balance the needto protect the health of humans andthe environment by reducingpollution levels with society�sdemand for the goods and servicesthat produce air pollution. Broad
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ATMOSPHERE EII
measures to protect our air began in1967 with the passage of the federalAir Quality Act. This act providedthe authority to each state to set airpollution standards and plan controlstrategies to meet them. The act wasmodified into the Clean Air Act of1970, laying the foundation for mostof the regulatory efforts since thattime (Quarles and Lewis 1990).Additional revisions occurred in1974, 1977, and 1990. The 1990amendments set new deadlines formeeting target emissions, added newcontrol requirements, and requiredmore stringent regulations onautomobile emissions.
As part of the 1970 Clean Air Act,nationwide standards wereestablished for a set of criteriapollutants. These pollutants includecommon substances that are knownto impair human health: particulatematter, sulfur dioxide, carbonmonoxide, nitrogen oxides, ozone,and lead. The National Ambient AirQuality Standards (NAAQS) arebased on scientific determinations ofthe thresholds for air pollution abovewhich adverse effects areexperienced by humans or theenvironment (Quarles and Lewis1990). The standards aim to preventdeterioration of air quality and toencourage pollution reduction evenin areas with good air quality. Theyhave been criticized both for beingtoo stringent because they requirethat even the most vulnerable citizenssuffer no effects from each regulatedpollutant, and for being too weakbecause they do not consider theeffect of multiple pollutants on aperson�s health (Quarles and Lewis1990). Establishing acceptable limitson pollutants, revising those limits
when appropriate, and encouragingconservation and clean technologyare some of the goals of air-qualitycontrol regulators.
Monitoring is an importantcomponent of the MPCA�s activities.MPCA maintains a network of air-quality monitoring stations across thestate. Most of these stations arelocated near point sources ofpollution, such as factories and busyintersections. The MPCA alsorequires some factories to maintaintheir own air-quality monitoringstations (MPCA 1988). In recentyears, MPCA�s monitoring programshave emphasized pollutantsassociated with acid deposition,mercury deposition, and the criteriapollutants. As permitted under the1970 Clean Air Act, Minnesota alsorequires Continuous EmissionMonitors for several types offacilities, including electrical utilities,
paper mills, solid and hazardouswaste incinerators, petroleumrefineries, and wastewater treatmentplants (Sigford and Eleff 1992).
In addition, Minnesota hasimplemented an automobileemissions inspection program thattargets carbon monoxide, carbondioxide, and hydrocarbons (includingthe volatile organic compounds(VOCs) that are precursors to ozonesmog development). As the numberof vehicle miles driven inMinnesota increases (Figure 12),automobile emissions will be an evergreater threat to air quality inMinnesota. Finally, the MinnesotaEmergency Planning andCommunity Right-to-Know Act of1989 requires that companies reporton the storage and release ofhazardous chemicals and make thatinformation available to localcommunities.
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Figure 12
Vehicle Miles Traveled in Minnesota○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
19
ATMOSPHERE EII
EXAMPLEINDICATORSTable 2 lists potentially usefulindicators of air quality. Theindicators are organized within theEII framework, which helps illustraterelationships between humanactivities, environmental condition,the flow of benefits from the
environment, and strategies forsustaining a healthy environment.These indicators are examples thatillustrate how indicators may helpassess the condition of theatmosphere.
ENVIRONMENTALCONDITION
Nitrogen availability due todeposition
Temperatures in urban centersConcentrations of greenhouse
gases in the atmosphereGlobal average temperatureAverage rainfallAverage annual temperature in
MinnesotaStream flowsLake temperaturesAtmospheric ozone concentra-
tionRate of damage to genetic
materialAcid predipitationGround level ozoneWind-caused particulate matterIndoor air qualityMercury deposition from atmo-
spheric sources
HUMAN ACTIVITIES
Large scale alteration of naturalecosystems
Construction and expansion ofurban environments
Emissionsgreenhouse gasesozone depleting chemicalssulfur dioxide, ozone, volatileorganic compounds, lead, andcarbon monoxidenitrogen oxides, sulfur dioxide,and volatile hydrocarbons
Vehicle miles driven in Minne-sota
Production and consumption ofCFCs
Solvent useFuel combustion
SOCIETAL STRATEGIES
Pollution reduction regulationsReduction of fossil fuel useReforestationUrban tree plantingMonitoring programsInstallation of pollution control
equipmentAir quality standards and en-
forcementTotal Facility PermittingAutomobile emissions inspection
programs
Table 2
EXAMPLE INDICATORS
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
20
ATMOSPHERE EII
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