Review Sheet for ATMO 569A at UA
Review Sheet for ATMO 569A at UA
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EE ZT EN quot quot FDF F 5 3 llliq 3 2 quot Equot E quotquot 139 39 wp quotquotI BIO IRAQ hEmilm5ca venbicraclcom Arctic Air Pollution Origins and Impacts Kathy S Law et al Science 315 1537 2007 DOI 101126science1137695 Science The following resources related to this article are available online at wwwsciencemagorg this information is current as of March 27 2007 Updated information and services including highresolution gures can be found in the online version of this article at httpwwwsciencemagorgcgicontentfull31558181537 A list of selected additional articles on the Science Web sites related to this article can be found at httpwwwsciencemagorgcgicontentfull31558181537reated content This article cites 4 articles 3 of which can be accessed for free httpwwwsciencemagorgcgicontentfull31558181537otherarticles This article appears in the following subject collections Oceanography httpwwwsciencemagorgcgicollectionoceans Information about obtaining reprints of this article or about obtaining permission to reproduce this article in whole or in part can be found at httpwwwsciencemagorgaboutpermissionsdtl Science print ISSN 00368075 online ISSN 10959203 is published weekly except the last week in December by the American Association for the Advancement of Science 1200 New York Avenue NW Washington DC 20005 Copyright c 2007 by the American Association for the Advancement of Science all rights reserved The title SCIENCE is a registered trademark of AAAS Downloaded from wwwsciencemagorg on March 27 2007 REV EW Arctic Air Pollution Origins and Impacts Kalhy 5 Law and Andreas smhlZ Nmable warming frends have been observed in fhe Arcric Alfhough increased humansinduced emissions oi lungslived greenhouse gases are cenainlyfhe main driving iacror air pollufanfs such as aerosols and alone are also impuriam Air pollufanfs are fransponed in ihe Arcric primarily irom Eurasia leading in high concenfrafions in winfer and spring Arclic haze local ship emissions and summenime boreal ioresf iires may also be imponanf pollufion sources Aerosols and ozone could be penurbing fhe radiafiye budgei oi fhe Arcric fhrough processes speciiic in fhe region Absorpfion oi solar radiafion by aerosols is enhanced by highly reilecriye snow and ice suriaces depusi un oi lighisabsurbing aerosols on snow or ice can decrease suriace albedo and irupuspheric ozoneiorcing may also be confribufing in warming in ihis region Fuiure increases in pollufanf emissions locally or in midslaiiiudes could iunher accelerafe global warming in fhe Arcric noiiced armospheric haze and dirty de posits on he snow 1 he remoie Arc ic atmosphere was long believed io be ex remely clean However pilois ying over he Nonh American Arc ic in he 1950s observed wide spread haze 2 ha could be seen every win er and early spring 1i ook uniil he 1970s for scieniisis io realize hai he haze was air polluiion ransponed from he middle laximdes 3 Arc ic haze coniinues o be an air qual39nty problem and he acidic compounds mainly sulfaie associaied wi h ii can be washed oui wi h precipitation or deposned at he surface leading io increased acid iiy in naurral ecosys ems 4 Long range rans pon of polluiion o he Arc ic also carries oxic subs ances such as mercury or persis eni organic polluian s hai can have adverse e eax on eco sys ems and human heal h Over he pasi 20 years here has been much research on he climaiic consequences of his polluiion which is also preseni in summer albeii at lower concen rations Climare change is pro ceeding fasiesi at he high laiiiudes of he Arctic Surface air emperacures have increased more han he global average over he pasi few decades and are predicied io warm by about 5 C over a large part of he Arc ic by he end of he 21si cenorry he most rapid of any region on Ear h 5 Models also predici hai summer sea ice may completely disappear by 2040 6 These changes are caused by global increases in long lived greenhouse gases GHGs whose effecis are enhanced in he Arciic hrough feedback mechanisms such as he sea ice albedo feed back However air polluiion also affecis Arciic Even hough early Arc ic explorers had 1Senice d39 Aermomie NR5 IPSUUillleime Pierre er Marie Curie Boil Tuz a Plate lursieu Paiix Cedex us 75252 Frame Email kalhylawaemillxsiellii ZNorwegian ln ilule iDr Air Rexeaith NILU Imamaim 18 2027 HELL Norway E mail rdniluno wwwsciencemagcrg SCIENCE VOL 315 climaie panicularly hrougr changes in surface radiaiive forcing Arctic Haze Arc ic haze is amixorre of sulfaxe and paniculare organic mauer and o a lesser ex eni ammoni um ni raie black carbon BC 7 and dusi aero sols 8 1i also coniains relatively high levels of ozone precursors such as ni rogen oxides NOX and volarile organic compounds VOCs 9 Aerosol haze panicles are well aged very edicieni ax scauering solar radiau39on and also weakly absorbing The haze has a distinci seasonal cycle wi h a maximum in late win er and early spring 3 when he removal pro cessesindredryandstableArcticat mosphere are very slow For example Fig 1 shows he seasonal cycleinBc measured at Alert 623 W 325 N 210 m above sea level ASL 10 Near he surface he haze s ans dis appearing inApril bri layers athigher altitudes may persisi in o May Trerds in race constiuems and aerosols are complex in he Arco39c region Al hough sulfareaerosolligh scat ering and absorption exhibii significani downward rcnds at most Arctic sra tions 8 because of emission reduc tions in he haze s source regions ni rare conceroarions have been in creasing ovedrepastivodecades 4 Eat Hgm A 103 102 10 Air Pnllutim Transmrl inlnlhe Arctic 0 practically all polluiion in he high Arc ic originates from more sou h erly ladordes Local pollution sources are crummy small and limi ed o near he Arctic Circle These include vol SPECIALSECTION canic emissions in Alaska and Kamchatka an hropogenic emissions from conurbations like Murmanslc indus n39al emissions mosi norably in he nonhern pans of Russia and emissions from he oil indus ry and shipping 4 Surfaces of consani poieno39al emperacure 11 form a dome above he cold Arc ic lower roposphere forcing airparcelsaaveling nonhwardio ascend 12 13 This isolaxes he Arctic lower roposphere from he resi of he atmosphere by a ranspon barrier he Arctic froni On iime scales ofa few days io weeks he Arciic lower roposphere is accessi ble only io polluiion originaiing from very cold source regions 14 15 The polar dome is noi zonally symmem39c and can exiend io aboui 40 N over Eurasia in January hus making nonhern Eurasia he maior source region for he Arctic haze Air masses leaving densely populated areas on he easi coasts ofAsia and Nonh America are ioo warm and moisi o direcily penetrate he polar dome bui hey can ascend io he Arctic middle or upper roposphere However Greenland because of its high iopography is exposed o pollution from sou heast Asia and Nonh America more s rongly han is he resi of he Arctic 16 The polar dome also makes it difficuli for s rarospheric air masses o reach he Arctic lower roposphere A receni model s udy sugges ed a s rong vertical gradieni in he influence of s raro sphenc air masses 16 For a ranspon iime scale Fig 1 Longderm lrends A and seasonal varialion B oi rhuurly eguivalenf ac concenrrarions ai Alerl Reproduced modiiied irom 10 by permission uHhe American Geophysical Union Copyrighr 2006 American Geaphysilal Union 16 MARCH 2007 Downloaded from www50iencemagorg on March 27 2007 1537 nitrogen containing constituents most notably PAN 31 is poorly known Another process iden ti ed relatively recettly is the production ofNox and HONO from photolysis of nitrate in the snowpack in the presetce of sunligtt 32 Al though very high levels of Nox gt600 parts per trillion have beet obseved at South Pole eleva tion of 2340 m because of the existence ofpro longed peiods with avery stable shallow boundary layer 33 much lower ethancenents have so far been reported in the Arctic 34 making it unlikely that these emissions are important on regional scales at northern high latitudes Climatic Effects oi LighlsAbsmbing Aerosols Measurements at Barrow 1566 W 713 N ll m ASL have shown that the single scattering albedo of haze aerosols in the Arctic can be as low as 09 in winter 35 indicating that these aerosols contain large amounts oflight absorbing material In the Arctic the e 39iciency of sunlight absorption in aerosol layers is greater than the e 39lciency at lower latitudes because of the high albedo of snow and ice and multiple reflection and scattering of light between the surface and the aerosol layers BC which is responsible for most of the aerosol light absorption is a minor but important component ofthe Arctic haze 10 and causes heating in the haze layers a In addi as ml m Fig 3 A Moderate Resolution imaging Spectroradiometer MODlS satellite image irom 5 luly 2004 showing the intrusion oi thick smoke trom boreal torest tires red dots into the Canadian Maritime Arctic image courtesy oi MODlS Rapid Response Project at NASA Goddard Space Flight Center View trom the Zeppelin station near Ny Alesund on Svalbard Norway under clear conditions B on 26 April 2006 and C on 2 May 2006 when smoke trom agricultural tires burning in Eastern Europe was transported to the station 43 image courtesy oi AxC Engvall Stockholm University wwwsciencemagcrg SCIENCE VOL 315 tion deposition ofBC onto snow and ice results in a reduction of the surface albedo 36 37 It has been suggested that the climate forcing due to this albedo effect is relevant when compared with the effect ofGHGs 38 Its e 39lcacy measured as the etiectiv39cy in increasing the surface air tem perature per unit of forcing is twice as large as that of carbon dioxide and it may be even more effective in melting snow and ice BC concettrations aiehigtest duringthe Arctic haze season and lowest in summer 10 As aresult of emission reductions BC concettrations have declined by 54 at Alert and 27 at Barrow from 1989 to 2003 but with some indication ofarecett tretd reversal Fig 1 In winter BC originates mostly from anthropogenic activities but the re gional distribition of sources is debated In a cli mate model study it was argued that alter recent strong emission increases in southeast Asia and decreases elsewhere southeast Asia is now the largest BC source for the Arctic 39 However this result also has been questioned 16 because the large temperature difference betweet southeast Asia and the Arctic lower troposphere does not allow for direct transport betweet the two regions Observations linked with trajectory calculations suggested Russian sources have the strongest in tluetce on BC levels at Alet and Barrow 10 More BC measurements in the Arctic especially at SPECIALSECTION higher altitudes are required to clarify the relative importance of different BC sources During summer atmospheric BC concettra tions are much lower than in late winter and early spring 10 bit still are important for the Arctic radiation budget because of the abundance of solar radiation A recett model study suggests that in summer boreal irest res are the dominant source r BC in the Arctic because many ofthe res burn at higt latitudes 16 Chemical sigtatures of bio mass burning emissions have beet preserved in Arctic snow and ice records 40 and biomass burning plumes have beet observed in the Arctic 41 42 For example large pan Arctic ethance ments of atmospheric BC concentrations occurred as aresult of strong buming inthe boreal forests of North America in summer 2004 Fig 3A which also lead to a decrease in the snow albedo at Sum mit Greetland during one episode 43 In spring 2006 smoke om agricultural res in eastern Europe was transported into the European Arctic and led to the highest concettrations of many pollutants ever measured at the Zeppelin station 119 E 789 N 478 m ASL on Svalbard Nor way as well as a dramatic reduction in visibility Fig 3 B and C 44 Atmospheric BC concen tralions reached record levels and also led to a visible discoloration ofdri ing snow on a glacier All this points toward a strong influence of biomass burning on Arctic BC levels snow ice albedo and radiation trans mission in the Arctic atmosphere PymsClmvedinn It has been known for some time that rest res can inject emissions into the upper troposphere but it was dis covered only recettly that injections deep into the stratosphere also occur and are in fact quite common 45 47 The highest altitude where smoke from boreal forest res was obse ved in situ is 17 km several kilometers above the tropopause and at potential temper atures greaterthan 380 K 46 Remote sensing observations indicate that even deeper injections into the stratospheric overworld are possible 47 The life time of aerosols and also many trace gases at these altitudes can be months thus prolonging their possible radiative effects It has been suggested that a cold bias in the high latitude lower stratosphere that exists in many climate models could be removed by including high altitudeBC injections from boreal res 48 However nothing is known about the impact of pyro convection on stratospheric chemistry l Indirect Aerosol Effects Aerosols also influence irradiances in the Arctic indirectly via changes inthe 16 MARCH 2007 Downloaded from www50iencemagorg on March 27 2007 1539 Polar Science microphysical properties of clouds Enhanced particle concentrations increase the number con centration and decrease the size of cloud droplets 49 which increases the cloud albedo They can also reduce rain formation and increase cloud lifetime The Arctic is particularly susceptible to aerosol indirect effects because the low aerosol number concentrations result in a large fraction of particles being activated during cloud formation 8 It has also been suggested that aerosols can increase the longwave emissivity of Arctic liquid phase clouds 50 Most liquid phase clouds con tain enough water to be considered blackbodies with unit emissivity at thermal wavelengths in which case aerosol effects can be ignored How ever Arctic clouds are often so thin that their emissivity increases with increasing cloud drop let number concentrations This enhances the downwelling thermal radiation uxes an effect opposed to the indirect effects on the solar radiation The effect is most important in winter and early spring when Arctic haze aerosols are abundant thin clouds exist and the radiation balance is tied toward thermal uxes because of the absence or small magnitude of solar radiation It may trigger more rapid warming of the Arctic in spring and thus an earlier snowrnelt However a quantitative understanding of aerosol indirect effects including those involving mixed phase and ice clouds remains elusive Future Changes The disappearance of summertime sea ice could have a huge impact on trace gas and aerosol dis tributions in the Arctic For example increased areas of open ocean could lead to increases in natural dimethyl sul de emissions and production of sulfate aerosols 51 whereas emissions of halogens and NOc from the ice and snow could be reduced There is evidence that ship tra ic is already affecting the summertime Arctic atrno sphere with strong signatures seen in marine aerosols 52 Increased deposition of soot from increased shipping after the reduction of summer time sea ice could further accelerate sea ice melting Increases in surface ozone by a factor of 2 to 3 to levels currently observed at Northern Hemisphere mid latitudes as a result of increasing ship NOc emissions have been predicted 53 Similar effects might also be expected from an increase in Arctic oil drilling As northern high latitudes warm because of climate change boreal forest fires are becoming more frequent 54 thus increasing pollution transport into the Arctic This may also trigger a feedback cycle where forest re emissions lead to earlier melting of Arctic snow and ice and thus further warming Furthermore the polar dome which currently presents a barrier to pollution transport into the Arctic may weaken in the future as the Arctic continues to warm relatively faster than the lower latitudes thus allowing more ef cient pollution into the Arctic This could be 1 540 facilitated by for instance an upward trend in the North Atlantic Oscillation which correlates with the transth of pollutants into the Arctic 55 56 Future Directions Clearly many uncertainties still exist in our knowledge of processes governing the buildup of air pollution in the Arctic and its role in climate change Within the framework of the Internation al Polar Year D Y the scienti c community is mobilizing to tackle these issues through a series of coordinated eld measurement programs and analysis using climate models that also include trace gases and aerosols Most of the ongoing and predicted rapid changes in the Arctic climate are a direct conse quence of the increasing levels of long lived green house gases and positive feedbacks speci c to the Arctic 5 In order to combat these changes re ductions in the emissions of long lived greenhouse gases particularly carbon dioxide are urgently needed However the Arctic may also bene t more than other regions from reductions in the emissions of short lived climate agents In partic ular reducing BC emissions could slow atrno spheric warming and the melting of snow and ice and reducing tropospheric ozone concentrations could slow the increase in Arctic surface air temperatures Increases in emissions of BC and ozone precursors in the Arctic itself should be strictly avoided References and Notes 1 A E Nordenskio39ld Science ns 2732 1883 2 illi Niitchell Atmos Terr Phys special suppl 195 1957 3 L A BarrieAtmos Environ 20 643 1986 4 Acidifying pollutants Arctic haze and acidification in the Arcticquot Arctic Monitoring and Assessment Programme ANiAP Oslo Norway 2006 5 intergovernmental Panel on Climate Change iPCC Climate Change 2001 The Scientific Basis T Houghton Ed Cambridge Univ Press New Vork 2001 6 Ni Ni Holland C Ni Blitz B Trembley Geophys Res Lett 33 1010292006GL028024 2006 7 We use the term black carbon BC here although it is poorly defined Often light absorption is measured and convened to equivalent BC 8 P K Quinn et al Tellus 59B 99 2007 9 S Solberg C Dye N Schmidbauer Atmos Chem 25 33 1996 10 S Sharma E Andrews L A Barrie A Ogren D Lavoue Geophys Res 111 101029 2005D0065812006 11 Potential temperature 8 is almost a conserved quantity in the atmosphere Radiational cooling decreases 8 by about 1 Kday in the free troposphere whereas condensation of watervapor increases a 12 A Klonecki etal Geophys Res 108 101029 2002D002199 2003 13 The ascent of moist airparcels is even strongerbecause of the extra heat released by the condensation of water vapor 14 T N CarlsonAtmos Environ 15 1473 1981 15 T iversen Geophys Res Lett 11 457 1984 16 A Stohl Geophys Res 111 1010292005D006888 2006 17 S Oltmans et al Atmos Environ 40 101016 jatmosenv200601029 2006 8 D Shindell etal Geophys Res 111 101029 2005D006348 2006 H 19 D W Tarasick V E Eioletov D i Wardle B Kerr Davies Geophys Res 110 101029 2004D004643 2005 20 E V Browell et al Geophys Res 108 101029 2001D001390 2003 21 C Stroud etalAtmos Environ 37 101016S1352 23100300353 4 2003 22 L K Emmons et al Geophys Res 108 101029 2002D002665 2003 23 S A Penkett K A Brice Nature 319 655 1986 24 S Sjostedt etalAtmos Environ 41 101016 jatmosenv200608058 2007 25 S S Brown et al Science 311 67 2006 26 L A Barrie W Bottenheim W Schnell P Crutzen R A Rasmussen Nature 334 138 1988 27 P A Ariya et al Tellus BS6 397 2004 28 A Ni Rankin E W Wolff S Martin Geophys Res 107 4683 2002 29 W R Simpson et al Atmos Chem Phys Discuss 6 11051 2006 30 r Zeng etal Geophys Res 111 101029 2005D006706 2006 31 E Real et al Geophys Res 1010292006D007576 in press 2007 32 E Domine E P B Shepson Science 297 1506 2002 33 D Davis etalAtmos Environ 38 5375 2004 34 R E Honrath etalAtmos Environ 36 2629 2002 35 P K Quinn etal Geophys Res 107 101029 2001D001248 2002 36 S G Warren W Wiscombe Atmos Sci 37 2734 1980 37 A D Clarke K Noone Atmos Environ 19 2045 1985 38 Hansen L Nazarenko Proc Natl Acad Sci USA 101 423 2004 39 D Koch Hansen Geophys Res 110 101029 2004D005296 2005 40 S Whitlow P Niayewski Dibb G Holdsworth Ni Twickler Tellus 46B 234 1994 41 N C Hsu etal Geophys Res Lett 26 1165 1999 42 Ni G iziomon U Lohmann P K Quinn Geophys Res 111 1010292005D006223 2006 43 A Stohl et al Geophys Res 111 101029 2006D007216 2006 44 A Stohl etalAtmos Chem Phys 7 511 2007 45 Ni Eromm et al Geophys Res Lett 27 1407 2000 46 H ost etal Geophys Res Lett 31 101029 2003GL019253 2004 47 Ni Eromm etal Geophys Res
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