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  • 70
  • 71Credit: Morgue File
  • 72The Earth’s atmosphere is a collec-tion of gases, vapor, and particu-lates that together form a blanketof “air” that surrounds the planet. Theatmosphere extends over 560 km (348miles) from the surface of the Earth outtoward space, and can be roughly dividedinto five major layers or sections (Figure3.4). The primary components of the at-mosphere are three gases: nitrogen (N2, 78per cent), oxygen (O2, 21 per cent), andargon (Ar, 1 per cent). Other components,present in smaller amounts, include watervapor (H2O, 0-7 per cent), ozone (O3, 0-0.01 per cent), and carbon dioxide (CO2,0.01-0.1 per cent) (Phillips 1995).The Earth’s atmosphere plays manyvital roles essential to sustaining life onthe planet. The air we breathe circulatesthrough its lowest level. The chemical ele-ments carbon, nitrogen, oxygen, and hy-drogen, which are constituents of all livingthings, are cycled and recycled in the atmo-sphere. Organisms convert these elementsinto carbohydrates, proteins, and otherchemical compounds. The atmospherealso shields life on the planet’s surfacefrom harmful solar radiation, and—for themost part—from the threat of meteorites,which typically burn up as they go throughthe atmosphere (UNEP 1999a).Human activities impact the Earth’satmosphere in many ways. Some activitiesproduce a quite direct effect, such as gen-erating and releasing pollutants that foulthe air, and adding carbon dioxide andother greenhouse gases to the atmospherethat induce global warming and climatechange. Other human impacts, such aswater pollution, land degradation, andhuman-induced loss of biodiversity, canindirectly affect the atmosphere, as well asthe water and land.In this section, four major issues that in-volve human impacts on the atmosphere—ozone depletion, global warming, climatechange, and air pollution—are addressed.Ozone DepletionOzone is a relatively unstable molecule,made up of three oxygen atoms (O3). Inthe atmosphere, ozone is formed naturallyin the stratosphere. It is concentratedthere as an “ozone layer” that acts as aprotective shield against harmful ultravio-let (UV) radiation coming from the Sun.The loss of stratospheric ozone allowsmore UV radiation to reach the Earth’ssurface, where it can cause skin cancer andcataracts in people and negatively affectother living things as well.Ozone is also found in the troposphere,the layer of the Earth’s atmosphere that isclosest to the planet’s surface. Ozone can3.1 AtmosphereFigure 3.4: The Earth’s atmosphere Credit: Used with permission from Centre for Atmospheric Science, University of Cam-bridge, UK. Source: km400 km altitude50 km40 km10 kmCredit: Image Analysis Laboratory, NASA Johnson Space Center
  • 73be formed naturally in the troposphere—for example, by lightning. However,tropospheric ozone is also a byproduct ofcertain human activities. Vehicle exhaustcontributes large quantities of ozone to thetroposphere each year.Depending on where ozone resides,it can protect or harm life on the Earth(Figure 3.5). In the stratosphere, ozoneis “good” as it shields life on the surfacefrom harmful solar radiation. In the tropo-sphere, ozone can be “bad” as it becomesa type of air pollution. Changes in theamount of ozone in either the stratosphereor the troposphere can have seriousconsequences for life on the Earth. Forseveral decades, “bad” tropospheric ozonehas been increasing in the air we breathe,while “good” stratospheric ozone has beendecreasing, gradually eroding the Earth’sprotective ozone shield (Thompson 1996).Since the late 1970s, scientists havedetected a slow but steady decline in theamount of ozone in the stratosphericozone layer. This ozone destruction re-sults from the presence of certain typesof chemicals in the atmosphere, espe-cially chlorofluorocarbons (CFCs) andother chlorine- and bromine-containingcompounds, coupled with fluctuations instratospheric temperature.In polar regions, particularly the areaof the atmosphere that overlies Antarctica,ozone depletion is so great that an “ozonehole” forms in the stratosphere there everyOzone in the Earth’s AtmosphereStratosphere:Troposphere: EarthMesosphereIn this region,ozone is“bad.”It can damagelung tissure and plants.In this region,ozoneis “good.”It protectsus from the sun’sharmful ultravioletradiation.Figure 3.5: Ozone in the stratosphere forms the protective ozone layer that shields the Earth’s sur-face from harmful solar radiation. Ozone in the troposphere, the lowest part of the atmosphere,can be a form of air pollution. Source: Image Analysis Laboratory, NASA Johnson Space Center
  • 74austral spring (late August through earlyOctober). In the past few years, the Ant-arctic ozone hole has been about the sizeof North America. In 2000, the Antarcticozone hole was the largest on record,covering 29.6 million km2 (11.4 millionsquare miles). In the austral spring of2003, it was almost as large, covering 28.9million km2 (11.1 million square miles)(Figure 3.6).Seasonal ozone depletion is alsonoticeable around the North Pole. Morethan 60 per cent of stratospheric ozonenorth of the ArcticCircle waslost during the winter and early spring of1999-2000 (Shah 2002).Some ozone-depleting chemicals, suchas CFCs, also contribute to global warm-ing. Like carbon dioxide and methane,CFCs are powerful greenhouse gasesthat trap heat radiating from the Earth’ssurface and prevent it from immediatelyescaping into space. This causes the partof the atmosphere nearest the Earth’s sur-face to warm, resulting in global warming.This warming in the troposphere, how-ever, leads to colder-than-normal tempera-tures in the stratosphere. This, in turn,enhances the formation of certain types ofstratospheric clouds that foster ozone-de-stroying chemical reactions in the strato-sphere (Shanklin n.d.).Fortunately, bans against the produc-tion and use of CFCs and other strato-spheric ozone-destroying chemicals ap-pear to be working to reverse the damagethat has been done to the ozone layer. Inthe past few years, the Antarctic ozonehole has not increased significantly in sizeFigure 3.7: Growth of the Antarctic ozonehole over 20 years, as observed by the satel-lite-borne Total Ozone Mapping Spectrometer(TOMS). Darkest blue areas represent regionsof maximum ozone depletion. Atmosphericozone concentration is measured in DobsonUnits. A “normal” stratospheric ozone mea-surement is approximately 300 Dobson Units.Measurements of 220 Dobson Units and belowrepresent significant ozone depletion. Source: Sep 200306 Sep 2000Ozone • Total Ozone Mapping Spectrometer (TOMS)Figure 3.6: Every austral spring, an area of severe stratospheric ozone depletion— an “ozonehole”—forms in the atmosphere over Antarctica. The ozone holes that formed in 2000 and 2003were the largest and second largest on record, respectively. Source: and 2004a)
  • 7519901992199419971999or intensity. Some researchers predict thatif atmospheric concentrations of ozone-de-stroying chemicals drop to pre-ozone-holelevels, the Antarctic ozone hole should dis-appear in approximately 50 years (Figure3.7) (WMO-UNEP 2002).Global WarmingAtmospheric temperature and chemistryare strongly influenced by the amountand types of trace gases present in theatmosphere. Examples of human-madetrace gases are chlorofluorocarbons, suchas CFC-11, CFC-12, and halons. Carbondioxide, nitrous oxide, and methane (CH4)are naturally formed trace gases producedby the burning of fossil fuels,released by living anddead biomass,and resulting from various metabolicprocesses of microorganisms in the soil,wetlands, and oceans. There is increasingevidence that the percentages of environ-mentally significant trace gases (green-house gases) are changing due to bothnatural and human factors, and contribut-ing to global warming.Global warming is recognized as one ofthe greatest environmental threats facingthe world today. Global warming is thegradual rise of the Earth’s average surfacetemperature caused by an enhancing of theplanet’s natural greenhouse effect. Radi-ant energy leaving the planet is naturallyretained in the atmosphere thanks to thepresence of certain gases such as watervapor and carbon dioxide. This heat-trap-ping effect is, in fact, what makes life on theEarth possible.Global warming, by contrast, is anintensification of the Earth’s greenhouseeffect. The Earth’s average surface tem-perature, which has been relatively stablefor more than 1 000 years, has risen byabout 0.5 degrees Celsius in the past 100years (Figure 3.8). The nine warmestyears in the 20th century have all occurredsince 1980; the 1990s were probably thewarmest decade of the second millennium(IPCC 2001).Global warming has occurred in the dis-tant past as the result of natural influences.However, since the industrial era, the termis most often used to refer to the currentwarming predicted as a result of increasesin the atmospheric concentrations of cer-tain heat-trapping greenhouse gases gener-ated by human activities (Figure 3.9).Most scientistsCredit: NOAA Photo Library
  • 76Figure 3.8: Satellite data of Arctic regions showwarming is taking place there at an accelerat-ing rate. These two maps show temperatureanomalies in the Arctic in 1981 and in 2003.The anomalies range from 7ºC (12.6ºF) belownormal to 7ºC (12.6ºF) above normal. Shadesof orange and red show areas of warming;shades of blue shows areas of cooling; whiterepresents little or no change (map adaptedfrom Comiso). The data reveal that some re-gions are warming faster than 2.5ºC (4.5ºF) perdecade (NASA 2003b).Source:
  • 77believe that much of this global tempera-ture increase is due to increased use offossil fuels, which when burned, releasecarbon dioxide into the atmosphere whereit absorbs infrared radiation that normallywould pass through the atmosphere andtravel out into space (Brehm 2003).The planet is not as warm as it was ap-proximately 1 000 years ago (Figure 3.10).Nevertheless, CO2 currently accounts forthe greatest proportion of greenhouse gasemissions. Much of the CO2 added to theatmosphere comes from the burning offossil fuels in vehicles, for heating,and for the production of electricity(Figure 3.11).In addition to carbon dioxide, ris-ing levels of methane in the atmosphereare also of concern. The relative rate ofincrease of methane has greatly exceededthat of carbon dioxide in the last severaldecades. Methane is released into theatmosphere in many ways: as a result of ag-riculture and ranching activities; throughthe decay of organic matter, includingwaste dumps; through deforestation; andas a by-product of the hydrocarbon econo-my. None of these sources are anticipatedto decrease in the future. On the contrary,methane emissions are expected to in-crease, as each year an additional 100 mil-lion people require food and fuel as worldpopulation expands (Figure 3.12).Most scientists believe that recentglobal warming is mainly due to humanactivities and related increases in concen-trations of greenhouse gases (Figure 3.13),primarily CO2, CH4, nitrous oxide (N2O),hydrofluorocarbons (HFCs), perfluoro-carbons (PFCs), and sulfur hexafluoride(SF6). These changes are driven by world-wide population and economic growth,and the underlying production andconsumption of fossil fuels, as well as bythe intensification of agricultural activityand changes in land use and land cover.Energy production and use, the largestsole source of CO2 emissions and a largecontributor of CH4 and N2O emissions, ac-counted for 81.7 per cent of emissions inindustrialised countries in 1998(UNFCCC 2000).From far out in space, instrumentscarried aboard satellites, such as NASA’sFigure 3.9: Human activities directly influence the abundance of greenhouse gases and aerosols inthe atmosphere. Carbon dioxide, nitrous oxide, methane, and sulfur aerosols have all increasedsignificantly in the past 50 years. Source: Intergovernmental Panel on Climate Change, IPCC (2001)Figure 3.10: Variations in the Earth’s temperature for the past 140 years (global) and for the past1 000 years (Northern Hemisphere). Source: IPCC (2001)
  • 78Moderate Resolution Imaging Spectrora-diometre (MODIS) sensor, are taking thetemperature of the Earth’s surface. Satel-lite data confirm that the Earth’s averagesurface temperature has been slowly risingfor the past few decades (Figure 3.14).Satellite records are more detailed andcomprehensive than previously availableground measurements, and are essentialfor improving climate analyses and com-puter modeling.One of the more predictable effects ofglobal warming will be a rise in sea levels(Figure 3.15). It is already under way ata pace of about a millimetre a year—aconsequence of both melting land ice andthe thermal expansion of the oceans (Har-rison and Pearce 2001). Predictions as tohow much global sea levels may rise overthe next century range from half a metre(1.5 feet) (Houghton et al. 2001) to be-tween 1 and 2 m (3 to 6 feet) (Nicholls etal. 1999). Such an increase would drownmany coastal areas and atoll islands. Un-less countries take action to address risingsea levels, the resulting flooding is ex-pected to impact some 200 million peopleworldwide by the 2080s. In addition,around 25 per cent of the world’s coastalwetlands could be lost by this time due tosea-level rise (DETR 1997).Global warming may have some posi-tive impacts. It could, for example, openFigure 3.13: The role of different gases and aerosols in global warming. Source: IPCC (2001)Figure 3.14: Global warming is an increase inthe Earth’s average surface temperature. Thesegraphs illustrate how a shift in the mean temper-ature and its variance can affect weather. Source:IPCC (2001)Figure 3.12: Methane is the second largest contributor to global warming and its atmosphericconcentration has increased significantly over the last two decades. Methane emissions fromhuman-related activities now represent about 70 per cent of total emissions, as opposed to lessthan 10 per cent 200 years ago. Source: IPCC (2001)Figure 3.11: Between 1971 and 1998, energy use and carbon dioxide emissions both increasedsignificantly, contributing to the likelihood of global warming. Source: IPCC (2001)
  • 79new lands for agriculture and forestry inthe far north. During the past 30 years inIceland, old farmlands have been exposed,and are being used, as the Breidamerkur-jökull Glacier has receded. All told,however, the negative impacts of un-checked global warming outweigh anypositive benefits.Climate ChangeClimate is the statistical description interms of the mean and variability of rel-evant measures of the atmosphere-oceansystem over periods of time ranging fromweeks to thousands or millions of years.Climate change is defined as a statisticallysignificant variation in either the meanstate of the climate or in its variability,persisting for an extended period (typicallydecades or longer). Climate change may bedue to natural internal processes or to ex-ternal forcing (Figure 3.16). Volcanic gasesand dust, changes in ocean circulation,fluctuations in solar output, and increasedconcentrations of greenhouse gases in theFigure 3.15: Reasons for sea level change Source: IPCC (2001)European Heat Wave, July 2003 Credit: NASA—Satellite Thermometers Show Earth Has a Fever (2004)Case Study: European Heat WaveJuly 2003This image shows the differencesin daytime land surface temperatures(temperature anomalies) collected overEurope between July 2001 and July 2003by the Moderate Resolution ImagingSpectroradiometer (MODIS) on NASA’sTerra satellite. A blanket of deep red acrosssouthern and eastern France (left of im-age center) reveals that temperatures inthis region were 10ºC (18ºF) hotter dur-ing 2003 than in 2001. Temperatures weresimilar in white areas and cooler in blueareas. Although models predict an overallincrease in global average temperatures,regional differences may be pronounced,and some areas, such as mid-continentalzones in North America and Asia, mayactualy experience some degree of cooling(NASA 2003c).79
  • 80atmosphere can all cause climate changes(USCCSP 2003).Global warming, whatever its underly-ing causes, is expected to have adverse,possibly irreversible effects on the Earth’sclimate, including changes in regional tem-perature and rainfall patterns and morefrequent extreme weather events. Climatechange will affect the ecology of the planetby impacting biodiversity, causing speciesextinctions, altering migratory patterns,and disturbing ecosystems in countlessways. Climate change will impact humansocieties by affecting agriculture, watersupplies, water quality, settlement patterns,and health.Overall, climate change is likely to in-tensify the already increasing pressures onvarious sectors. Although the impact of cli-mate change may, in some cases, be smallerthan other stresses on the environment,even relatively small changes can have seri-ous adverse effects, especially where theremay be critical thresholds, wheredevelopment is already marginal, or wherea region is less able to implement adapta-tion measures (DETR 1997).For example, climate change is likelyto exacerbate already increasing pressurebeing put on water resources by a growingglobal population, particularly in Africa,Central America, the Indian subcontinent,and southern Europe. By the 2050s, mod-els indicate that there may be an additional100 million people living in countries withextreme water stress due to climate changealone (DETR 1997).Figure 3.16: Climate change is the result of complex interactions among many factors. Source: IPCC (2001)Credit: Topfoto
  • 81Carbon dioxide, the gas largely blamedfor global warming, has reached record-high levels in the atmosphere (Hanley2004). Carbon dioxide levels have risenby 30 per cent in the last 200 years as aresult of industrial emissions, automobiles,and rapid forest burning, especially in thetropics. Much of this increase has occurredsince 1960. This increase in CO2 is thoughtto enhance the Earth’s natural greenhouseeffect and thus increase global tempera-tures (Figure 3.17).The Intergovernmental Panel on Cli-mate Change projects that, if unchecked,atmospheric carbon dioxide concentra-tions will range from 650 to 970 ppm by2100. As a result, the panel estimates, aver-age global temperature may rise by 1.4ºC(2.5ºF) to 5.8ºC (10.4ºF) between 1990 and2100 (Hanley 2004).Interestingly, increased levels of atmo-spheric CO2 may stimulate the growth ofsome kinds of plants. Researchers in theAmazon have noted increased growth ratesin several species of trees (Laurance et al.2004). The forests are also becoming moredynamic, with existing trees dying and be-ing replaced by new trees at a more rapidpace. In addition, the species compositionof the forest is changing. Rising atmospher-ic CO2 concentrations may explain thesechanges, although the effects of this andother large-scale environmental alterationsremain uncertain.Air PollutionAir pollution is the presence of contami-nants or pollutant substances in the air thatinterfere with human health or welfareor produce other harmful environmentaleffects (EEA 2004). The term “smog”—firstcoined in London, England, to describea combination of smoke and fog—is nowused in reference to a specific combinationof airborne particles, gases, and chemicalsthat together affect peoples’ health andtheir natural environment (HealthCanada 2003).Aerosols are tiny particles suspendedin the air. Some occur naturally, originat-ing from volcanoes, dust storms, forestand grassland fires, living vegetation, andsea spray. Human activities, such as theburning of fossil fuels and the alteration ofnatural land cover, also generate aerosols.Averaged over the globe, human-gener-ated aerosols currently account for aboutten per cent of total atmospheric aerosols.Most of those aerosols are concentratedin the Northern Hemisphere, especiallydownwind of industrial sites, slash-and-burn agricultural regions, and overgrazedgrasslands (Figure 3.18).As the composition of Earth’s atmo-sphere changes, so does its ability to ab-sorb, reflect and retain solar energy. Green-house gases, including water vapor, trapheat in the atmosphere. Airborne aerosolsfrom human and natural sources absorb orreflect solar energy based on colour, shape,size, and substance. The impact of aerosols,tropospheric ozone, and upper tropospher-ic water vapor on Earth’s climate remainslargely unquantified (NASA 1989).About 25 per cent of the world’s popu-lation is exposed to potentially harmfulamounts of SO2, O3, and particulate matterin smog (Schwela 1995). Globally, some 50per cent of cases of chronic respiratory ill-ness are now thought to be associated withair pollution (UNEP 1999b).Some pollutants travel long distanceson the wind, causing acid deposition inthe surrounding countryside and even inneighboring countries. In the 1980s, “acidrain” was identified as a major internation-al environmental problem, moving fromFigure 3.17: For more than 40 years, researchers at Mauna Loa Observatory, Hawaii, have tracked the steadyincrease of atmospheric carbon dioxide (concentration expressed in parts per million, or ppm). Source: SIO(2004) and SeaWiFS: NASA Carbon Cycle Initiative, NASA/Goddard Space Flight Center Scientific Visualization Studio (2004).Source: NASA (2004b)Figure 3.18: Aerosol particles larger than 1 mi-crometre are composed primarily of windblown dustand sea salt from sea spray. Aerosols smaller than1 micrometre are mostly formed by condensationprocesses, such as the conversion of SO2gas releasedby volcanic eruptions to sulfate particles and by for-mation of soot and smoke during burning processes.After aerosols form, they are mixed and transportedthroughout the atmosphere by wind and weather; theyare removed from the atmosphere primarily throughcloud formation and precipitation. Source: (NASA 2004c)
  • 82heavily industrialized areas of both Europeand North America into prime agriculturalareas that lay downwind. Mountain regionssuffered the most because their higherrainfall increased the volume of acid depo-sition and their often thin soils could notneutralize the acid. Lakes and streams inpristine parts of Scandinavia and Scotlandbecame acidified, and fish populationswere decimated in some areas. The mostintense acid rain fallout occurred in theso-called Black Triangle region borderedby Germany, Czech Republic, and Poland(Harrison and Pearce 2001) (Figure 3.19).Acid precipitation decreased through-out the 1980s and 1990s across large por-tions of North America and Europe. Manyrecent studies have attributed observedreversals in surface-water acidification atnational and regional scales to this de-cline (Stoddard et al. 1999; Larssen 2004).Decreases in acid precipitation have beenachieved largely through improved flue gastreatments, fuel switching, use of low-sulfurfuels in power stations, and use of catalyticconverters in automobiles. Since 1985,international treaties and heavy investmentin desulphurization equipment by powerstation operators have cut sulfur pollutionin Europe and North America by as muchas 80 per cent (Harrison and Pearce 2001).Although significant progress has beenmade in controlling acid-forming emissionsin some countries, the global threat fromacid precipitation still remains. In fact, theproblem is growing rapidly in Asia, where1990s-level SO2 emissions could triple by2010 if current trends continue. Curtailingthe already substantial acid precipitationdamage in Asia, and avoiding much moresevere damage in the future, will requireinvestments in pollution control similiar tothose made in Europe and North Americaover the past 20 years (Downing 1997;WRI 1998).Nitrogen dioxide is the orange gas thatis the most visible component of most airpollution. In many cities, NO2 and otherpollutants are suspended in the air to forma brownish haze commonly called smog.Nitrogen dioxide is formed when oxygenin the air combines with nitric oxide.Nitric oxide comes from automobiles,aerosols, and industrial emissions, andcontributes to the formation of acid rain.In addition, this pollutant can cause a widerange of environmental damage, includingeutrophication of water bodies—explosivealgae growth that can deplete oxygen andkill aquatic organisms.Fig.3.19: Aerosols affect climate both directly by reflecting and absorbing sunlight and indirectly by modifying clouds. The Total Ozone Mapping Spectrometer(TOMS) aerosol index is an indicator of smoke and dust absorption. This figure shows aerosols—the hazy green, yellow, and red patches—crossing the Atlantic andPacific Oceans. Dust from the Sahara Desert is carried westward toward the Americas and provides nutrients for Amazon forests. Asian dust and pollution travel tothe Pacific Northwest. Source: NASA ( (NASA 2004a)
  • 83Case Study: Emissions in Paris1999-2003Paris, France, lies on a relatively flat plain.Most of the time, Paris benefits from a wetand windswept oceanic climate that en-courages the dispersal of air pollution andthus cleans the air. However, under certainmeteorological conditions (anticyclonesand a lack of wind), pollutants can remaintrapped in the atmosphere above the city,where they become concentrated, resultingin significantly higher levels of pollution.Thus, for equivalent pollutant emissions interms of location and intensity, the levels ofpollutants recorded in the atmosphere canvary by a factor of 20 according to meteoro-logical conditions.This explains why peaks in secondarypollutants often affect wider areas thanpeaks in primary pollutants. For example,when the wind blows from the city in acertain direction, the rural area surround-ing the Paris region is also subject to ozonepollution. Indeed, ozone levels registeredin these areas are often much higher thanthose in the centre of Paris itself.In 1994, according to the CentreInterprofessionnel Technique d’Etudede la Pollution Atmosphérique (CITEPA,Inter-professional Technical Centre forResearch into Air Pollution) SO2 emissionsin the Paris region corresponded to eightper cent of national emissions (mainlandFrance and overseas territories), oxidesof nitrogen (NOx) emissions to 10per cent, Volatile Organic Compound(non-methane) (VOCNM) emissions to 12per cent, carbon monoxide (CO) emis-sions to 15 per cent, and CO2 emissions to14 per cent. Given that 19 per cent of thepopulation lives in the Paris region, emis-sions per inhabitant in this area are lessthan the national average for all substances(CITEPA 1994).Existing air-quality-monitoring toolsin the greater region of Paris provide aconstant indication of air pollution levelsat specific background and roadside loca-tions. In addition to standard monitoring,specific modeling applications give ex-tensive descriptions of air-quality patternsfor several significant pollutants. Despitethe involvement of the transport sector inmonitoring local atmospheric emissions,there is no direct and constant trafficdata feed. Recently, a project known asHEAVEN (Healthier Environment throughthe Abatement of Vehicle Emissions andNoise) was implemented in Paris. Its mainobjective was to integrate real-time trafficinformation with the air quality monitoringtools. HEAVEN helped develop and dem-onstrate new concepts and tools to allowcities to estimate emissions from traffic innear-real time. This enhanced the identifi-cation and evaluation of the best strategiesfor transport demand management.Souce: http://heaven.rec.orgConcentrations of SO2, NOx, CO, and VOC over Paris. Source: SO2 emmissions in the Paris region Annual NOx emmissions in the Paris regionAnnual CO emmissions in the Paris region Annual VOC emmissions in the Paris regionAir quality dynamics over the region of Paris, France, from 1999 to 2003. Source: averages of SO2 in Ile-de-France from1999 to 2003Regional cartography of the annual level ofbenzene evaluated within the framework of theEuropean project LIFE “RESOLUTION”83
  • 84Northern Hemisphere seasonal variation in atmospheric carbon monoxide and its global distribution. Source: (NASA 2004d)Case Study: Pollution from Wild Fires2003–2004Whether started by people or naturalevents, fires add large quantities of pollut-ants to the atmosphere every year, primar-ily in the form of CO and aerosols. Satellitesensors can help researchers distinguishbetween wildfires and urban or industrialfires. Some can also distinguish differenttypes of fire-generated pollutants. Forinstance, two sensors aboard NASA’s Terrasatellite—the Measurements of Pollutionin the Troposphere (MOPITT) instru-ment and the Moderate Resolution Imag-ing Spectroradiometer (MODIS) instru-ment—gather data on CO and aerosols,respectively.Carbon monoxide is one of the moreeasily mapped air pollutants. In theMOPITT-generated series of maps shownbelow, global seasonal variations in COconcentration are clearly visible (high-est concentrations of CO appear as red).Major concentrations of CO during dif-ferent seasons can be easily identified andtracked over time on such images, leadingto better understanding of sources of COpollution and its transcontinental trans-port (NASA 2004d). For example, in thesummer image of this series, a very highconcentration of CO appears over westcentral Africa, largely due to forest fires.Wildfires in southern Africa are a ma-jor source of carbon monoxide pollution.Every August in southern Africa, thou-sands of people equipped with lighters ortorches travel out onto the savanna andintentionally set the dry grasslands ablaze.Burned grasses send up tender new growththat is ideal for cattle consumption. Thefires typically scorch an area the size ofMontana, Wyoming, Idaho, and the Dako-tas combined. Long plumes of smoke riselike hundreds of billowing smokestacks,and herds of animals are sent scurryingacross open grassland.During this fire season, a thick pall ofsmoke clouds the sky for many weeks. Thesmoke is laced with a number of pollut-ants, including nitrogen oxides, carbonmonoxide, and hydrocarbons. Some ofthese substances react with the intenseheat and sunlight to form ozone. Ground-level ozone contributes to respiratorydiseases and can seriously damage crops.At higher levels in the troposphere, ozonemolecules trap thermal radiation emanat-ing from the Earth’s surface in the sameway as carbon dioxide and other green-house gases do. In fact, up to 20 per centof the global warming experienced by theEarth over the past 150 years is thought tobe from ozone.In the spring of 2003, the MODIS andMOPITT instruments were used to moni-tor fires and fire-produced air pollutantsin Siberia, especially in the Baikal region.These fires produced large amounts of finecarbon aerosols that spread out over thePacific Ocean and remained suspendedin the atmosphere for a few days. Carbonmonoxide was also produced by the fires,84
  • 85but unlike the aerosols, remained airbornefor a much longer period of time, allowingit to cross the Pacific Ocean and reduce airquality over North America before continu-ing on around the globe.Gas and particle emissions producedas a result of fires in forests and othervegetation impact the composition of theatmosphere (WHO 2000). These gases andparticles interact with those generated byfossil-fuel combustion or other technologi-cal processes, and are major causes of ur-ban air pollution. They also create ambientpollution in rural areas. When biomass fuelis burned, the process of combustion is notcomplete and pollutants released includeparticulate matter, carbon monoxide, ox-ides of nitrogen, sulfur dioxide and organiccompounds. Once emitted, the pollut-ants may undergo physical and chemicalchanges. Thus, vegetation fires are majorcontributors of toxic gaseous and particleair pollutants into the atmosphere. Thesefires are also sources of “greenhouse” andreactive gases. Particulate pollution affectsmore people globally on a continuingbasis than any other type of air pollu-tion. In 1997/98, forest fires in SoutheastAsia affected at least 70 million people inBrunei Darussalam, Indonesia, Malaysia,the Philippines, Singapore, and Thailand.Thousands of people fled the fires andsmoke and the increase in the number ofemergency visits to hospitals demonstratedthe severity of the fires and pollution theycaused (WHO 2000).Case Study: African Fires2002Wildfires—from forest fires and brush firesto grass fires and slash-and-burn agricul-ture—can be sweeping and destructiveconflagrations, especially in wilderness orrural areas. As biomass burns, particulates,black carbon, and gases including CO2,CO, NOx, CH4, and CH3Cl are producedin great quantities. All of these pollutantscan be lofted relatively high in the atmo-sphere due to the convective heating of araging fire (Graedel and Crutzen 1993).The image at right shows fire activity inAfrica from 1 January 2002 to 31 Decem-ber 2002. The fires are shown as tiny dotswith each dot depicting the geographic re-gion in which fire was detected. The colorof a dot represents the number of dayssince a sizable amount of fire was detectedin that region, with red-orange represent-ing less than 20 days, orange representing20 to 40 days, yellow representing 40 to 60days, and gray to black representing morethan 60 days. These data were gatheredby the MODIS instrument on the Terrasatellite. MODIS detects fires by measuringthe brightness temperature of a region inseveral frequency bands and looking forhot spots where this temperature is greaterthan the surrounding region.Global statistics on the amount of landburned worldwide every year vary consid-erably. It has been estimated that from7.5 million to 8.2 million km2 (4.6 millionto 5.1 million square miles) are burnedand between 1 800 million and 10 000million metric tonnes of dry biomass areconsumed in fires annually. Global changescenarios predict an increase in total areaburned, with an increase in very large andintense fires.Pollution outflow from spring 2003 fires in Siberia can be seen in the top and middle image.These fires produced large amounts of fine carbon aerosol detected by MODIS instrument(bright colours) on the Terra satellite, which spread over the Pacific Ocean but lasted only a fewdays. They also produced carbon monoxide, which was detected by the MOPITT instrument onthe Terra satellite (bottom image). This gas can last over a month, which allowed it to cross thePacific Ocean and reduce air quality over North America before continuing on around the globe.Credit: David Edwards, The National Center for Atmospheric Research (NCAR) (NASA 2004e)African Fires during 2002 Credit: (NASA 2004f)85
  • 86Case Study: Pollution in China2001 and 2004During February 2004, a considerable out-flow of pollution stemmed from China andSoutheast Asia. The image at right showsatmospheric concentrations of carbonmonoxide at an altitude of roughly 3 km(1.9 miles) over this region that were mov-ing across the Pacific Ocean and at somepoints reaching the western coast of theUnited States.Carbon monoxide is a good indicatorof air pollution since it is produced duringcombustion processes, such as the burningof fossil fuels in urban and industrial areas,as well as by wildfires and biomass burn-ing in more rural areas. Industrial emis-sions were mainlyresponsible for thehigh levels of car-bon monoxide overChina in this image,whereas emissions inSoutheast Asia weredue primarily to agri-cultural fires.Natural pro-cesses and events canalso be a source oftranscontinental air pollution. In 2001, alarge dust storm developed over China (seebelow). Prevailing winds swept particulatesfrom this storm all the way to the easterncoast of North America.6 April 2001 normal aerosol levels are apparent on the first day of the dust storm. 7 April 2001 - Blue represents just slightly higher-than-normal aerosols and red repre-sents the highest concentration of aerosols.10 April 2001 - The aerosol impact from the dust storm can clearly be seen overChina, Mongolia, Russia, Korea, Japan, and the Pacific Ocean.13 April 2001 - The aerosol impact from the dust storm can clearly be seen overJapan, the Pacific Ocean, Alaska, and the United States.14 April 2001 - The aerosol impact from the dust storm can clearly be seen in thePacific Ocean, and the United States.17 April 2001 - High levels of aerosols are visible over the East Coast of the UnitedStates, especially Maine.A large dust storm developed over China on 6-7 April 2001. This series of images shows air-borne dust from the storm moving over China, Russia, Japan,the Pacific Ocean, Canada, and ultimately over the United States on 17 April 2001 (NASA 2004g). Visualization Credit: NASA/Goddard Space Flight Center ScientificVisualization Studio Source: image was developed from a composite of car-bon monoxide data collected over China and South-east Asia from 1-25 February 2004, by the Measure-ments of Pollution in the Troposphere (MOPITT)instrument aboard NASA’s Terra satellite. The colorsrepresent the mixing ratios of carbon monoxide inthe air, given in parts per billion by volume. Thegrey areas show where no data were collected due topersistent cloud cover. Source: (NASA 2004g)86
  • 87Credit: Morgue File