©ThiscopyofthethesishasbeensuppliedonconditionthatanyonewhoconsultsitisunderstoodtorecognisethatitscopyrightrestswiththeauthorandthatuseofanyinformationderivedtherefrommustbeinaccordancewithcurrentUKCopyrightLaw.Inaddition,anyquotationorextractmustincludefullattribution.
NewapplicationsofcontinuousatmosphericO2measurements:
meridionaltransectsacrosstheAtlanticOcean,andimproved
quantificationoffossilfuel‐derivedCO2
By
PENELOPEPICKERS
Athesissubmittedtothe
SchoolofEnvironmentalSciencesofthe
UniversityofEastAngliainpartial
fulfilmentoftherequirementsforthe
degreeofDoctorofPhilosophy
SchoolofEnvironmentalSciences
UNIVERSITYOFEASTANGLIA
2016
Chapter5
QuantifyingfossilfuelCO2usingAPO:anovelapproach
1925.1Introduction
Anthropogenicgreenhousegasemissionsfromfossilfuelburningarethedominant
driverofcurrentclimatechange.Inordertomitigateadverseconsequencesofanthropogenic
climatechange,emissionsofanthropogenicCO2andnon‐CO2long‐livedgreenhousegases,
suchasmethane(CH4)andnitrousoxide(N2O),requiresignificantreduction,whichhasledto
widespreadnationalandinternationalregulationofsomeanthropogenicgreenhousegas
emissionsinrecentyears(WeissandPrinn,2011).Althoughonaglobalscale,annual
anthropogenicgreenhousegasemissionsarerelativelywellknown,thereissignificant
uncertaintyassociatedwithregionalandcountry‐scaleannualemissions,aswellastheintra‐
annualvariabilityofemissions(Peylinetal.,2011).
Thesourceofuncertaintyinanthropogenicgreenhousegasemissionslargelystems
fromtheso‐called‘bottom‐up’methodologiesemployed;typically,greenhousegasemissions
arecalculatedusingabook‐keepingorinventoryapproach,wherebyemissionfactorsare
appliedtoparticulareconomicactivities,whicharethenscaled‐uptoregionalandcountry‐
levelspatialscalesusingland‐useandeconomicdatabases,withuncertaintiesthatareoften
eitherstatedas‘unknown’orarequotedtounrealisticallyhighprecision(NisbetandWeiss,
2010;WeissandPrinn,2011).Suchbottom‐upmethodsarevulnerabletolargeuncertainties
andbiasesbecausetheyarebasedonemissionfactorsassociatedwiththerawmaterialsused
forvariouseconomicactivities,ratherthantheactualemissionsthataregeneratedbysuch
economicactivities,whichcanbeveryvariable,dependingontheefficiencyofindividual
processesandonthequalityofthefuel,forexample.Asstatedby(NisbetandWeiss,2010),
relyingonbottom‐upmethodologiesforquantifyingandsubsequentlymitigating
anthropogenicgreenhousegasemissionsisanalogousto“dietingwithoutweighingoneself”,or
inotherwords,relyingoncaloriecountingalone.
Accurateandprecisequantificationofanthropogenicgreenhousegasemissionsmay
benecessaryinordertofacilitatealegallybindinginternationalagreementonclimatechange,
withtrulyeffectiveemissionsreductions.Inaddition,well‐knownanthropogenicgreenhouse
gasemissionsarerequiredinordertoprovidestabilitytothecarbonemissionstrading
markets,whicharecurrentlyworthaboutUS$350billionperyearglobally(Kossoyetal.,
2015).Thereisalsoastrongneedfromthescientificcommunityforaccurateanthropogenic
greenhousegasquantification,owingtothefactthatmanygreenhousegases(suchasCO2and
CH4)haveanthropogenicandnaturalsources.Inversemodellingstudiesaimingtoquantify
naturalgreenhousegassourcesandsinksoftenassumethatanthropogenicgreenhousegas
emissionsareaccurateandprecise,whichcanleadtosignificantbiasesinnaturalgreenhouse
193gasfluxes,particularlyasthespatialandtemporalresolutionofatmospherictransportmodels
increases(Gurneyetal.,2005;Peylinetal.,2011).
Usingatmosphericmeasurementsandinversemodellingtoverifyanthropogenic
greenhousegasemissions,knownasa‘top‐down’approach,canprovideanindependent
methodforverifyinganthropogenicgreenhousegasemissions.Recentimprovementsin
atmosphericgreenhousegasmeasurementtechnologies,theexpansionofmeasurement
networks,anddevelopmentsininversemodellingtechniquesnowenablecountry‐scaletop‐
downverificationofsomeanthropogenicgreenhousegasemissionsindevelopedregions,such
asNorthAmericaandEurope(e.g.Bergamaschietal.,2005;Levinetal.,2011),with
uncertaintiesthatareatleastcomparabletorealisticbottomupinventoryestimates(Nisbet
andWeiss,2010;WeissandPrinn,2011).
QuantifyingfossilfuelCO2emissionsusingatmosphericmeasurementsrequiresthe
separationofnatural(mainlybiospheric)andanthropogenic(mainlyfossilfuel)influenceson
atmosphericCO2molefractions,inordertoisolatethefossilfuelcomponentofatmospheric
CO2(ffCO2).InversemodellingcanthenbeperformedusingatmosphericffCO2data(inppm)to
verifyfossilfuelCO2emissions.Thistop‐downseparationofbiosphericandfossilfuelderived
CO2andsubsequentquantificationofffCO2isnottrivial.Thecurrentmethodologyfor
quantifyingffCO2fromatmosphericCO2measurementsistousediscretemeasurementsof
radiocarbon(14C)contentinCO2(14CO2):14Chasahalf‐lifeofabout5730years,andtherefore
fossilfuelderivedCO2containsno14C(Manningetal.,1990;Turnbulletal.,2009;Zondervan
andMeijer,1996).Measurementsof14CO2are,expensive,however,andcannotbemade
continuously;hence,most14CO2timeseriesconsistofasinglemeasurementapproximately
onceortwiceeverytwoweeks.ffCO2iscalculatedfrom14CO2measurementsasfollows(Levin
etal.,2003;Turnbulletal.,2009):
∆ ∆
∆ ∆ (Eq.5.1)
whereCO2obsdenotestheatmosphericCO2molefraction,andΔobs,ΔbgandΔffdenotethe14C
contentofCO2(inpermilunits)oftheobservations,well‐mixedatmosphericbackground,and
fossilfuels(‐1000‰,whichisthevalueforzero14Ccontent),respectively.Inadditiontothe
termsshowninEquation5.1,asmallcorrectionisalsoappliedtoffCO2whichaccountsfor
otherminorsourcesof14C,includingheterotrophicrespirationandnuclearindustrysources
(Turnbulletal.,2009).
194 InordertoobtainhighertemporalresolutionffCO2quantification(i.e.dailyorhourly,
asopposedtoweeklyorfortnightly),continuousatmosphericmeasurementsofcarbon
monoxide(CO)canbeusedaccordingtoEquation5.2,becauseCOisco‐emittedwithCO2
whenfossilfuelsarecombusted(Gamnitzeretal.,2006;Turnbulletal.,2006;vanderLaanet
al.,2010).
:
(Eq.5.2)
whereCOobsandCObgaretheCOmolefractionsoftheobservationsandofthewell‐mixed
atmosphericbackgroundrespectively,andRCO:CO2istheCO:CO2combustionratioforfossilfuel
emissions,whichvariesbothtemporallyandspatiallyaccordingtochangesinfueltype.
AlthoughitisalotcheapertomakecontinuousCOmeasurementsthandiscrete14CO2
measurements,itisnotpossibletouseCOaloneasareliabletracerforffCO2,owingtothelarge
uncertaintyandspatialandtemporalvariabilityassociatedwithRCO:CO2(Gamnitzeretal.,2006;
Vogeletal.,2010).Inaddition,thereislargeuncertaintyassociatedwithnon‐fossilfuelrelated
COsources(e.g.biomassburning,soils,andatmosphericmethaneoxidation)andsinks(e.g.
fromhydroxylradicalreactions,anduptakebysoils)(Gamnitzeretal.,2006).ffCO2from
continuousCOmeasurementscan,however,becalibratedbyco‐located14CO2measurements,
whichcanbeusedtodetermineaccurateRCO:CO2values(Vogeletal.,2010).Therefore,
continuousCOmeasurementscombinedwithdiscrete14CO2measurementscanbeusedto
quantifyffCO2withhightemporalresolution,butthismethodstillassumesthatanynatural
influencesonCOarenegligible.
Thereareseveralkeylimitationstousing14CO2andCOmeasurementsinorderto
quantifyffCO2.Firstly,RCO:CO2ishighlyvariable,andisknowntovaryondiurnalandsub‐
diurnaltimescales.Thus,using14CO2tocalibrateffCO2fromCOmeasurementsonceperweek
oronceperfortnightwillonlyguaranteeaccurateffCO2atthetimeofthe14CO2measurements.
Secondly,itisnotpossibletodistinguishbetweenfossilfuelsourcesandbioenergysources
usingatmosphericCOdata;hence,calculatingffCO2usingCOmayresultinerroneously
allocatingbioenergy‐derivedCO2asffCO2.Althoughbioenergycurrentlyaccountsforasmall
proportionoftotalanthropogenicfuelsources(approximately10%ofglobalprimaryenergy
supply;IEA,2012b),itispredictedtobecomemuchmoreprevalentinthecomingdecades,
whichmayrenderCOmeasurementsredundantasamethodforquantifyingffCO2inthe
future.Thirdly,itisnotpossibletoaccuratelyquantifyffCO2from14CO2measurementsinsome
195regions,owingtointerferencefromcertainnuclearpowerplant14Cemissions(Gravenand
Gruber,2011;Vogeletal.,2013).ThisisparticularlyaproblemintheUK,wheretheprevailing
south‐westerlywindsoftenpreventaccurateffCO2from14CO2quantification,owingtothe
abundanceofgas‐coolednuclearpowerplantsinsouthernEngland.Thus,intheUK,theonly
top‐downmethodforCO2emissionsverificationthatiscurrentlyavailableinvolves
performingatmosphericinversionsusingwinter‐timeonlytotalCO2atmospheric
measurements(AlistairManning,personalcommunication,2015),whichareverylikelytobe
significantlyinfluencedbywinter‐timebiosphericrespiration.ForParis,thecurrentapproach
istoquantifyffCO2fromdown‐windgradientsinCO2data,incombinationwithbiogenicCO2
fluxesfromlandsurfacemodels,althoughthismethodresultsinverydrasticdataflaggingand
posteriorfluxestimatesthatareheavilyreliantonthepriorinventoryestimates(Breonetal.,
2015;Stauferetal.,2016).
Inadditiontothenuclearpowerplantemissionsissue,(Graven,2015)suggeststhat
thesensitivityof14CO2tofossilfuelderivedCO2iscurrentlydecreasing,owingtotheglobal
increaseinanthropogenicCO2intheatmosphere,andthat14CO2measurementprecisionwill
needtoimprovebyafactorof2overthenextfewdecades,inordertomaintaintoday’s
detectioncapabilityof14CO2toffCO2.ThedevelopmentofanewtracertoquantifyffCO2,which
ismorepreciseandmoreaccuratethanCO,andwhichcanalsobeusedindependentlyfrom
14CO2measurements,wouldthereforebeahighlyvaluedtoolforatmosphericverificationof
fossilfuelCO2inventoryestimates;suchatoolwouldbeextremelyusefultoday,inregionsthat
areseverelyaffectedbygas‐coolednuclearpowerplant14Cinfluences,andalsointhecoming
decades,asthesensitivityof14CO2measurementstoffCO2declines.
5.1.1Outlineofthischapter
InSection5.2,IpresentatmosphericO2,CO2andAPOdatameasuredfromtheroofof
theEnvironmentalSciencesbuildingattheUniversityofEastAnglia(UEA),duringthesummer
of2014.Ithencomparetheshorttermvariabilityinthesedatatotwoothermeasurement
sitesinNorfolk,UK:theTacolnestontalltower(TAC)andWeybourneAtmospheric
Observatory(WAO).InSection5.3,IpresentanewmethodologyforcalculatingffCO2from
APOdata,andcomparetheresultstoffCO2calculatedusingCOand14CO2measurementsand
tomodelledffCO2usingbottomupinventorydata.Lastly,inSection5.4,Isummarisethe
resultsfromthischapter,andoutlineanewpotentialforurbanatmosphericO2andCO2
measurements.
1965.2AtmosphericO2andCO2measuredfromtheEnvironmentalSciences
building,UniversityofEastAnglia
PriortofinaldeploymentonboardtheCapSanLorenzocontainership,the
atmosphericO2andCO2measurementsystemwastestedintheCRAMLaboratoryatUEA
(52.62°N,1.24°E;seeFigure5.1),andairwassampledfromtheroofoftheEnvironmental
Sciencesbuilding(~25mabovetheground)usingaspiratedairinlets,from09Jul‐03Sep2014.
Theaspiratedairinletsweremountedatthehighestpointoftheenvironmentalsciences
building,andthereforewerenotobstructedbyanyotherbuildings,andwerenotclosetoany
ofthebuildingvents.FortechnicaldetailsrelatingtotheatmosphericO2andCO2
measurementsystem,seeChapter2.
Figure5.1.MapshowingthelocationoftheUniversityofEastAnglia(UEA),andalsotheTacolnestontalltower(TAC)andWeybourneAtmosphericObservatory(WAO).
Figure5.2presentstheUEAatmosphericO2,CO2,andAPOdata,aswellasmodel‐
derivedmeteorologicaldata(atmospherictemperature,relativehumidity,atmospheric
pressure,winddirection,andwindspeed),whicharefromtheUSANationalOceanicand
197AtmosphericAdministration(NOAA)GlobalDataAssimilationSystem(GDAS)database.APO
iscalculatedfromtheUEAatmosphericO2andCO2datausingEquation5.3:
.
. 350 (Eq.5.3)
whereO2andCO2aretheatmosphericO2andCO2measurementsinpermegandppmunits,
respectively,‐1.1istheO2:CO2ratioofglobalterrestrialbiosphere‐atmosphereexchange,
0.2095isthemolefractionofO2moleculesindryair,and350isanarbitraryreference.
MultiplyingCO2by‐1.1anddividingby0.2095convertstheCO2datafromppmtopermeg
units.
LargegapsintheatmosphericO2,CO2andAPOdataareduetoperiodsofexperimental
testingofthemeasurementsystem(forexample,whencheckingthemeasurementsystemfor
leaks),whichmeantthatitwasnotpossibletosampleoutsideair.Shortgaps(1‐3hours)are
mostlycausedbyWSS,ZT,andTTcalibrationroutinesbeingcarriedout(seeChapter2,
Section2.3fordetails).AsshowninFigure5.2,theCO2andO2dataarestronglyanti‐correlated,
owingtothedominanceofterrestrialprocessesonthedata.Strongdiurnalvariabilityis
apparentinbothspecies,withhigherCO2andlowerO2generallyoccurringatnight‐time.This
diurnalvariabilityislikelytobestronglyinfluencedbythediurnalrectifiereffect,whereby
atmosphericCO2andO2isdilutedduringtheday,owingtoawell‐mixedboundarylayer,and
relativelyhighboundarylayerheight,andbothspeciesareconcentratedatnight,whenthe
boundarylayerisstableandtheboundarylayerheightisrelativelylow.Inaddition,owingto
thetimeofyearandrelativelyrurallocation,photosynthesiswilllikelybedominatingthe
atmosphericCO2andO2signalsduringtheday,causingadrawdownofCO2andreleaseofO2,
whereasatnight,respirationwillbethedominantbiosphericprocess,resultingintherelease
ofCO2anduptakeofO2.
Thus,inthesummer,diurnalvariabilityinatmosphericCO2andO2iscausedbytwo
reinforcingeffects:diurnalvariabilityinatmosphericmixing,anddiurnalvariabilityin
biosphericO2andCO2fluxes.IncontrastwiththeatmosphericO2andCO2datafromUEA,the
APOdatashowverylittlevariability,andingeneral,donotexhibitastrongdiurnalpattern.
ThisisbecauseAPOisinvarianttolandbiosphericinfluences,andlargelyreflectsonlyfossil
fuelinfluencesonshort‐timescales,andoceaninfluencesonseasonalandlong‐termtime
scales.
198
Figure5.2.Hourly‐averagedatmosphericCO2(toppanel),δ(O2/N2)(2ndpanel)andAPO(3rdpanel)measuredfromtheroofoftheEnvironmentalSciencesbuildingatUEA.Notethatthey‐axesforδ(O2/N2)andAPOhavebeenscaledtobevisuallycomparabletotheCO2y‐axisonamolepermolebasis,and‘bad’datacausedbytechnicalproblemshavebeenexcludedpriortoaveraging.Alsoshownare3‐hourlymodel‐derivedGDASmeteorologicaldata(NOAA):atmospherictemperature(4thpanel:darkredsolidline),relativehumidity(4thpanel:cyanshort‐dashedline),atmosphericpressure(4thpanel:pinkdottedline),winddirection(bottompanel:darknavylong‐dashedline),andwindspeed(bottompanel:greydashed/dottedline).
199
Figure5.3.O2:CO2ratioofhourly‐averageddatameasuredatUEAduringthesummerof2014.δ(O2/N2)isgiveninppmequivalentunitstobecomparabletoCO2onamolepermolebasis.Thesolidredlineindicatesthemajoraxisregressionline,whichisweightedaccordingtothedifferenceinmeasurementprecision(andthereforeuncertainty)associatedwiththeδ(O2/N2)andCO2data,andhasaslopeof‐1.10.ThenegativevalueoftheO2:CO2ratioindicatesthatthetwospeciesareanti‐correlated.
Asmentionedabove,theUEACO2andO2variabilityshowninFig.5.2isdominatedby
terrestrialprocesses,ratherthanfossilfuelburning.ThisisalsodemonstratedinFigure5.3,
whichshowsthatthemeanO2:CO2molarratioforthedatasetis‐1.10;avaluethatisindicative
ofterrestrialbiosphereO2andCO2exchange(Severinghaus,1995).Thereisasmallamountof
scatteraroundthemajoraxisregressionlineshowninFig.5.3,whichsuggeststhatthereis
sometemporalvariabilityintheO2:CO2ratioduringthisperiod.
200
Figure5.4.Hourly‐averagedCO2(toppanel)andδ(O2/N2)(bottompanel)withselecteddiurnaleventscolouredaccordingtotheO2:CO2ratio(seelegendinfigure).They‐axeshavebeenscaledsothattheδ(O2/N2)andCO2panelsarevisuallycomparableonamolepermolebasis.
InordertoinvestigatethisO2:CO2temporalvariability,IcalculatedtheO2:CO2ratiofor
someofthelargest(inmagnitude)individualdiurnalO2andCO2events,andthencategorised
theseeventsintothreegroups,accordingtotheO2:CO2ratiovalues.Figure5.4showsthat
thereisnocorrelationbetweenthemagnitudeandtheO2:CO2ratioofthediurnalevents,
whichindicatesthatthelargesteventsarenotcausedbyacommonsource,andsuggeststhat
atmospherictransporteffectsmayhaveasignificantimpactonthemagnitudeofthediurnal
variabilityatUEA.TherangeofO2:CO2ratiosforthediurnaleventsis‐1.03to‐1.14,which
suggeststhatmanyoftheeventswithmorenegativeO2:CO2ratiosarecausedbya
combinationofbiosphericandfossilfuelCO2.Sincetheterrestrialbiosphereisdominatingthe
O2andCO2variabilitysostrongly,itisdifficulttoidentifywhicheventsarelikelytobe
influencedbyfossilfuelprocesses,andwhicharenot.Thisdifficultyisinpartcausedby
uncertaintyintheO2:CO2ratioofthelocalterrestrialbiosphere.Althoughonaglobalscale,
terrestrialprocesseshaveanoxidativeratioofapproximately‐1.1,onalocalscale,thisvalue
canbeeitherlowerorhigher,dependingonthelocaltypesofvegetationandsoil.Thedata
showninFig.5.4seemtoindicatethatinNorfolk,theO2:CO2ratioofthelocalterrestrial
201biospheremaybeslightlyhigher(lessnegative)than‐1.1,althoughanexactvaluecannotbe
determinedfromtheatmosphericO2andCO2dataalonewithoutalsohavingindependent
quantitativeknowledgeoftheimpactoffossilfuelcombustionontheatmosphericCO2data,or
conductinganelementalanalysisoftheO2:CO2ratioofvarioussoilsandvegetation
representativeoftheNorfolkregion.
Figure5.5.Apolarplotofthevariabilityin2‐minuteO2:CO2ratioswithwindspeed(ms‐1)andwinddirection.MeteorologicaldataarefromtheNOAAGDASproduct.ThepolarplotwascreatedinRusingthe‘polarPlot’functionfromthe‘Openair’package(CarslawandRopkins,2012).
Byusingthehigh‐resolution,2‐minuteO2andCO2datatocalculate2‐minuteO2:CO2
ratios,itispossibletocreateapolarplot,asshowninFigure5.5,toexaminetheoriginof
oxidativeratiosthatareindicativeoffossilfuelinfluences,andthosethatareindicativeof
biosphericinfluences.Thelowest(mostnegative)O2:CO2ratios(i.e.thosethatareindicativeof
fossilfuelcombustion)originatefromtheeast,whichindicatesthatthereisastrongfossilfuel
influencefromNorwich.Thereisalsoanoticeablefossilfueloxidativeratiosignalfromthe
south‐west,whichissuggestiveoffossilfuelinfluencesfromLondon,andpossiblyalsofrom
thenearbyA47andA11majorroadstothesouth‐west.TheUEAcampusisover1.2km2in
area,andischaracterisedbywoodland,marshland,andopengreenareas.Thecampusis
202surroundedbyfieldsandfarmland,withafewsmallvillagestothenorth,southandwest,and
thesuburbsofNorwichcitytotheeast.TheabundanceofvegetationontheUEAcampusand
inthesurroundingarealikelyexplainswhytheO2:CO2ratiosareclosetotheexpectedvaluefor
terrestrialbiosphereprocesseswhenthewindspeedislow(<5ms‐1),withtheexceptionof
windsthatoriginatefromthenorth‐east,forwhichtheO2:CO2ratiosaremorenegative.There
isalsoasmallamountofdatathatdisplaysquitehigh(lessnegative)O2:CO2ratios,which
occurswhenthewindspeedishigh(>15ms‐1)andthewinddirectionisfromthenorth‐west.
Thisdatamayberepresentativeofoceanicinfluence,whichcancauseO2:CO2ratiostobeclose
toorlessnegativethan‐1.0,long‐rangetransportofairfromahigherlatitude,oran
undiagnosedtechnicalproblemwiththemeasurementsystem.
ItisusefultocomparetheatmosphericO2andCO2datafromUEAtoothernearby
atmosphericmeasurementsofeachspecies,inordertogaingreaterunderstandingofthe
spatialvariabilityofatmosphericO2andCO2.TheTacolnestontalltower(TAC)issituated
about12kmsouth‐westofUEA(seeFig.5.1),andisfundedbytheUKGovernment
DepartmentofEnergyandClimateChange(DECC)tomeasurearangeofatmosphericspecies,
includingCO2(fromthreeheights:54m,100m,and185m)andCO(fromasingleheight:100
m).WeybourneAtmosphericObservatory(WAO)issituatedabout35kmnorthofUEAonthe
northNorfolkcoast(seeFig.5.1).WAOismanagedbytheUniversityofEastAngliaandisalso
supportedbyNCAS(NationalCentreforAtmosphericScience),tomakemeasurementsof
atmosphericgreenhousegasesandrelatedspecies,includingatmosphericO2,CO2,andCO(all
from~15mheight).
Figure5.6comparesatmosphericCO2atUEAandTAC,andatmosphericCO2andO2at
UEAandWAO.Ingeneral,thethreemeasurementlocationsexhibitverysimilardiurnal
variabilityinCO2(andO2forUEAandWAO),withonlyafewrareexceptions,suchasthe
differencesinO2andCO2betweenWAOandUEAon26‐27August.Althoughthediurnal
patternintheatmosphericCO2andO2isverysimilarbetweenthemeasurementsites,the
magnitudeofthevariabilitydifferssignificantly.CO2measuredatUEAisalmostalwayshigher
atnight‐timethanCO2measuredatTACandWAO.Similarly,night‐timeO2atUEAisalmost
alwayslowerthanO2measuredatWAO.Themostlikelyreasonforthesedifferencesin
magnitudebetweenUEAandTACisthatthemeasurementheightatUEA(~25m)ismuch
lowerthanallthreeofthemeasurementheightsatTAC(lowestheightof54m).CO2
measurementsthataremadeclosertothegroundareusuallyhigherinCO2molefractionthan
thosethataremeasuredfurtherupintheatmosphere,partlybecauseCO2sourcesaremainly
atgroundlevel,andpartlybecausetheentrainmentof‘backgroundair’(lowerCO2mole
fractions)fromabovetheboundarylayerwillaffectCO2measurementsmadehigherupmore
203thanthosemadeclosetotheground.Thus,CO2measurementsmadefrom~25mheightabove
thegroundwilllargelyreflectlocalinfluencesonCO2,whereasCO2measurementsmadeat
185mabovethegroundwillreflectCO2influencesfromanentireregion,coveringatleast
severalhundredsquarekilometres.
Figure5.6.ComparisonofatmosphericCO2atUEAandTAC(toppanel),andcomparisonofatmosphericCO2andδ(O2/N2)atUEAandWAO(middlepanelandbottompanel).Y‐axeshavebeenscaledsothattheδ(O2/N2)andCO2panelsarevisuallycomparableonamolepermolebasis.
Somewhatcontradictorytothisexplanation,isthefactthatUEAconsistentlyexhibits
higherCO2thanWAOatnight,whenthemeasurementsatWAOaremade~10mclosertothe
groundthanthoseatUEA.ThereasonwhyO2andCO2variabilityatWAOisattenuatedin
magnitudecomparedtoO2andCO2variabilityatUEA,isthatWAOissituatedonthecoast,and
soanyterrestrialsourcesorsinksofO2andCO2willbedilutedwithcoastalandopenoceanair,
whichwillusuallyexhibitO2andCO2molefractionsclosetothoseofwell‐mixed‘background
204air’.Thisalsoexplainswhy,duringtheday‐time,atmosphericCO2molefractionsareoften
loweratUEAthanatWAO,andatmosphericO2molefractionsareoftenhigheratUEAthan
WAO(e.g.26July),whereastheatmosphericCO2molefractionatTACdoesnoteverdrop
significantlybelowtheatmosphericCO2molefractionatUEA.Duringthesummer,the
biosphericphotosynthesisduringthedaytimewilltakeupCO2andproduceO2;thisbiospheric
signalwillmanifestmuchmorestronglyatarural,in‐landmeasurementlocation,suchasUEA,
thanatacoastalmeasurementsite,suchasWAO.
Therearealsosomesignificantdifferencesintheanthropogenicsignalsinatmospheric
speciesbetweenTAC,UEAandWAO.Figure5.7comparesshort‐termvariabilityinAPOfrom
UEAandCOfromTAC(100mheight),aswellasAPOandCOfromWAO.Itisclearthatthereis
oftensignificantanti‐correlationintheAPOandCOshort‐termvariability,whichislikely
attributabletothefactthatbothspeciesarepredominantlyaffectedbyanthropogenicsources.
AlthoughtheUEAAPOandTACCOdataarenotco‐located,itisassumedthattheyaresituated
closeenoughthatthepatternsofvariabilityseenateachlocationwilllargelybesimilar.Hence,
periodswhentheAPOandCOdatadonotdisplayanti‐correlatedsignalsmaybeduetothefact
thatthemeasurementsarenotco‐locatedandaresampledfromdifferentheightsabovethe
ground,butalsomaybecausedbythesignificantnaturalsourcesandsinksthatexistforCO,
suchassoilsandtroposphericphotochemicalreactions(Bergamaschietal.,2000;Moxleyand
Cape,1997),whereasthemainnaturalinfluenceonAPOisfromtheoceans,whichisnot
expectedtohaveasignificanteffectonAPOonshorttimescales(seeChapter4,Section4.2for
details).
ThemiddlepanelofFig.5.7showsco‐locatedAPOandCOmeasuredatWAO,fromthe
samesamplingheight.AswiththeUEAandTACdata,thereissubstantialanti‐correlation
betweenthetwospecies,aswellassomeperiodswherethevariabilityisnotanti‐correlated.
BasedonvisuallyinspectionofFig.5.7alone,thereisasimilaramountofanti‐correlation
betweentheWAOCOandAPOdataasthereisbetweentheUEAAPOandTACCOdata,where
thetwospeciesarenotco‐located.Thisfindingsuggeststhatperiodsofdatathatdonotshow
anti‐correlationbetweenAPOandCOmaybedominatedbydifferencesintheCOandAPO
sourcesandsinks,andnotbywhetherthemeasurementsareco‐locatedornot.Thebottom
panelofFig.5.7,showingwinddirectionmeasuredatWAO,showsthattheperiodsof
strongestanti‐correlationbetweenWAOCOandAPOmostlycoincidewithsouth‐westerly
winddirections(i.e.fromtheland),andperiodsshowinglittleornoanti‐correlationbetween
COandAPOoftencoincidewithnortherlyandeasterlywinddirections(i.e.fromthesea),
althoughthelinkbetweenCOandAPOcorrelation/anti‐correlationandwinddirectionat
WAOdoesnotalwaysholdtrue.
205
Figure5.7.Comparisonofhourly‐averagedTACCOandUEAAPOdata(toppanel)andhourly‐averagedWAOCOandAPOdata(middlepanel),illustratingthatalotoftheshort‐termvariabilityinCOandAPOisanti‐correlated.AlsoshowniswinddirectionmeasuredatWAO(bottompanel).TheCOmeasurementsatTACaresampledfromthe100mtowerinlet.ItshouldbenotedthattheTACCOdatashownabovearenotthefinalised,qualitycontrolleddata,duetoanon‐goingcalibrationissuethatisaffectingtheaccuracyofthehighCOvalues.
5.3FossilfuelCO2quantificationusingAPOfromsitesinNorfolk,UK
5.3.1.Using‘fixed’fossilfuelemissionratios
Inthissection,IpresentanewmethodologyforquantifyingffCO2usingAPOdatafrom
UEAandWAO.Asmentionedpreviously,thereareseverallimitationsassociatedwithusingCO
asatracerforquantifyingffCO2,includinglargeuncertaintyinthenaturalsourcesandsinks,
206largeuncertaintyintheCO:CO2emissionratiosforfossilfuels,andtheCOtracermethodis
unabletodistinguishbetweenCO2producedbyrenewablebioenergysourcesandffCO2.In
contrast,theonlysignificantnaturalsource/sinkaffectingAPOistheocean,whichisnot
expectedtohaveanimpactonshorttimescales.Inaddition,anyshort‐termoceanicinfluences
onAPOshouldbeeasytoidentify,becauseoceanicairmassesarecharacterisedbyinvariant
CO2(owingtothelong‐equilibrationtimeofair‐seaCO2fluxescomparedtotherateof
atmosphericmixing).APOisalsoassociatedwithamuchsmallerrangeofpossibleO2:CO2
emissionratiosforfossilfuels(from~‐1.2to~‐1.95,buttypicallyintherangeof‐1.3to‐1.4)
comparedtoCO:CO2emissionratios(from<5to>100,buttypicallyintherangeof5to25),
whichtranslatesintoloweruncertaintyinthedenominatorofEquation5.4(seebelow)
comparedtothedenominatorofEq.5.2.
Finally,althoughAPOcannotdistinguishbetweenbiodieselandbiogasemissionsand
theirfossilfuelcounterparts,owingtothefactthattheoxidativeratiosforbiodieselandbiogas
areverysimilartothoseforliquidandgaseousfossilfuels,APOisabletodistinguishbetween
biomassburningemissions,whichhaveanoxidativeratioofapproximately‐1.1,andfossilfuel
emissions,whichhaveoxidativeratiosintherangeof~‐1.2to~‐1.95.Thispotentiallyenables
APOtobeusedasatracerofffCO2incitiesindevelopingcountries,suchasIndia,whichstill
heavilyrelyonbiomassburningasamajorsourceofenergyindomesticsettings,andalsoin
citiesindevelopedcountriesthatarefrequentlyaffectedbylocalforestfires,suchasinVictoria,
Australia,andCalifornia,USA.
ffCO2canbecalculatedfromAPOdatausingEquation5.4,whichisanalogous
toEq.5.2forcalculatingffCO2fromCO:
: (Eq.5.4)
whereAPOistheatmosphericvaluecalculatedfromhigh‐precisionatmosphericO2andCO2
data,APObgistheAPObackground,orbaselinevalue,whichisdeterminedusingastatistical
baselinefittingmethod,andRAPO:CO2istheAPO:CO2combustionratioforfossilfuelemissions.
IhaveusedEq.5.4tocalculateffCO2fromAPOdataatUEAandWAO,andhave
comparedtheresultstoffCO2fromCOdataatTACandWAO,calculatedusingEq.5.2(see
Figure5.8).NotethatasmallamountofAPOdatawasexcludedfromtheffCO2calculationasit
wasnotdeemedtoberelatedtofossilfuelvariability(owingtolittleornovariabilityinCO2),
andismostlikelycausedbytechnicalproblems.Therearetwoimportantunknown
207parametersthatmustbedeterminedinEq.5.2and5.4:theCOandAPObaselines,andthe
CO:CO2andAPO:CO2emissionratios.Fornow,Ihaveusedtime‐invariantvaluesof5ppbppm‐
1fortheCO:CO2emissionratioatTACandWAO(atypicalvaluefortrafficemissions),and‐0.3
molmol‐1fortheAPO:CO2emissionratioatUEAandWAO(atypicalvalueforliquidfossilfuel
emissions,giventhatAPO:CO2ratio=O2:CO2ratio+1.1).Amoresophisticatedmethodfor
calculatingtime‐varyingCO:CO2andAPO:CO2emissionratioswillbediscussedandpresented
laterinthissection.ItshouldbenotedthattheequationforcalculatingAPOfromO2andCO2
measurementsthatIhaveusedthroughoutthisthesisisactuallyasimplificationofthefullAPO
equationgivenin(Stephensetal.,1998),whichalsotakesintoaccounttheeffectsofCH4and
COoxidationonO2,althoughtheseeffectsarenegligibleformostapplications.Ihavenotused
thefullAPOequationinthischapterbecauseCH4andCOemissionsinNorfolkarerelatively
low,andIcalculatedthattheywouldnotsignificantlyaffectAPO.ForurbanAPO
measurements,however,itmaybeadvisabletousethefullAPOequationthatisconservative
withrespecttoCH4andCOoxidationinadditiontoterrestrialbiosphereprocesses,because
CH4andCOfluxesaremuchlargerinurbanenvironments.
Fig.5.8showsffCO2calculatedusingCOand14CO2fromTACandAPOfromUEA(top
panel),aswellasffCO2calculatedusingCOandAPOfromWAO(bottompanel).Althoughthe
COandAPOdataatTACandUEAarenotco‐located,theffCO2calculatedusingthetwotracers
appearsverysimilar,withthemaindifferencespresentingasdifferencesinthemagnitudeof
theffCO2peaks(e.g.14‐15Aug),ratherthandifferencesinthepatternsofffCO2variability(e.g.
3Aug).TheffCO2from14CO2dataatTACwereprovidedbyAngelinaWenger,Universityof
Bristol.Approximately40%oftheffCO2from14CO2dataatTACcollectedfromJul‐Sep2014
weredeemedtobeunreliable,eitherowingtonegativeffCO2values,whicharecausedby
strongnuclearpowerplantemissionscancellingoutanyffCO2signalin14CO2,orbecause
NAMEmodelbacktrajectoriesindicatedtheairmassesarrivingatTAChadoriginatedfrom
thesouth‐west,andffCO2from14CO2wasthereforelikelytobebiasedbynuclearpowerplant
influences,eventhoughthevalueswerenotnegative.Ingeneral,theffCO2from14CO2agrees
wellwiththeffCO2calculatedfromtheCOandAPOdata,although,owingtodatagaps,there
areonlytwo14CO2datapointsthatcoincidewithperiodsofAPOdata.Allofthe14CO2data
pointsalsohappentocoincidewithperiodsofrelativelylowffCO2,becausethe14CO2flask
Figure5.8.ffCO2fromCOatTACandAPOatUEA(toppanel)andffCO2fromCOandAPOatWAO(bottompanel).AlsoshownisffCO2from14CO2atTAC(toppanel,blackdots).
209
samplesaredeliberatelycollectedduring‘cleanair’conditions,totryandavoidnuclearpower
plantinfluences.WhenadifferenceinffCO2betweenthe14CO2methodandtheothertwo
methodsdoesoccur,andtheffCO2from14CO2valueislowerthantheffCO2fromCOorAPO
(e.g.29Aug),itisdifficulttoascertainwhichffCO2valueiscorrect,becausenuclearpowerplant
influenceswillcausetheffCO2from14CO2tobebiasedlow,anditisthereforedifficulttohave
confidenceintheaccuracyofthe14CO2datainsuchinstances.
AtWAO,theffCO2agreementbetweentheAPOandCOtracersissimilartothatatUEA
andTAC,withperiodswhentheffCO2fromthetwotracersagreewell(e.g.7‐11Aug),andother
timeswhentheffCO2patternofvariabilityisverysimilar,butthemagnitudesoftheffCO2
signalsdiffer(e.g.31Jul‐2Aug).Overall,theffCO2observedatWAOislessthanthatobservedat
UEAandTAC,whichisexpected,giventhedilutionofterrestrialsignalsthatoccuratWAO,due
toitscoastallocation,aswellasthefactthatWAOislocatedfurtherfromthemainlocalffCO2
hotspots,suchasNorwich,andtheA11andA47mainroads.
TheCOandAPObaselineshavebeencalculatedusingthe‘rfbaseline’functionfromthe
‘IDPmisc’packageinR.‘rfbaseline’isastatisticalmethodforcalculatingabaselinefrom
atmosphericdatabasedonrobustlocalregression,andemploysasymmetricalweightingto
theresidualsofthefit,inordertopreventthebaselinefrombeingbiasedbyuni‐directional
pollutionevents,whichisacommoncharacteristicofmanyatmosphericspecies(Ruckstuhlet
al.,2012).ThisasymmetricalweightingisimportantinthebaselinefittingofbothAPOandCO,
becauseallofthefossilfuelrelatedvariabilityinAPOpresentsasnegativeexcursions(because
O2isconsumedduringfossilfuelcombustion),whilethefossilfuelrelatedvariabilityinCO
presentsaspositiveexcursions(becauseCOisproducedduringfossilfuelcombustion),as
illustratedinFig.5.7.
5.3.2.Baselineandmeasurementuncertaintyanalysis
InordertodeterminetheuncertaintyoftheffCO2calculatedusingAPOorCO,onemust
determinetheuncertaintyassociatedwiththethreecomponentsofEqs.5.2and5.4:theAPO
orCOmeasurementuncertainty,theuncertaintyassociatedwiththebaselinefitting,andthe
uncertaintyassociatedwiththefossilfuelemissionratios(RCO:CO2orRAPO:CO2).Thebaseline
uncertaintycanbequantifiedbyassessingthevariabilityintheffCO2whendifferentbaselines
areused.InFig.5.8,IusedAPOandCObaselinesofmoderateflexibilitytocalculateffCO2.In
Figure5.9,IpresentffCO2forbothAPOandCOatUEAandTACusingthebaselinesemployed
forFig.5.8,aswellasveryflexiblebaselines,wherealotmoreoftheshort‐termvariabilityin
Figure5.9.ffCO2calculatedfromCoatTAC(toppanel)andAPOatUEA(bottompanel)usingthemoderatelyflexiblebaselinefitsusedinFig.5.8,aswellasinflexiblebaselinefits(dashedpinkandorangelines)andflexiblebaselinefits(dotted‐dasheddarkpurpleanddarkredlines).
211
APOandCOisassignedas‘backgroundair’variability,andalsoveryinflexiblebaselines,which
hardlyvaryatall,thusalmostalloftheshort‐termvariabilityinAPOandCOisexcludedfrom
thebaseline.
Fig.5.9demonstratesthatattimes,thereissignificantuncertaintyassociatedwiththe
statisticalbaselinefittingprocedurefortheCOandAPOmethods,asthemagnitudeofffCO2is
oftendependentonthechoiceofbaselinefit.ItshouldbenotedthatthevariabilityinffCO2is
notdependentonthechoiceofbaselinefit.Figure5.10demonstratesthedifferencesinthe
baselinefitsusedtocalculatetheffCO2fromCOandAPOthatisshowninFig.5.9.Sincethe
numeratortermsinEqs.5.2and5.4aredeterminedfromthedifferencebetweenthe
measurementsandthebaselineforeachspecies,theflexiblebaselinefitstendtoproduce
smallerffCO2values,andtheinflexiblebaselinefitstendtoproducelargerffCO2values,with
themoderatelyflexiblebaselinefitsproducingintermediateffCO2values.
Figure5.10.Moderatelyflexible,inflexible,andflexiblebaselinefitstoCOfromTAC(toppanel)andAPOfromUEA(bottompanel).
ThemeanuncertaintyinffCO2associatedwiththechoiceofbaselinefitiscalculatedto
be±17.5%and±27.5%fortheCOdataandAPOdatarespectively(basedontheffCO2
differencesusingdifferentbaselineflexibilities),withnosignificantdifferencesinthebaseline
uncertaintiesateachmeasurementsite.Theseuncertaintyestimatesarebasedonthefactthat
theflexiblebaselinefitsareprobablynotfitforpurpose,giventhattheygenerallycauseffCO2
212tobeunderestimated,andthatthemostappropriatebaselinefitliesbetweenthestandardfit
andtheinflexiblefit:thus,theflexiblebaselinefithasnotbeenaccountedforinthebaseline
uncertaintyestimates.Inreality,theinflexiblefitislikelytobethemostappropriatebaselinefit,
assumingthatffCO2‘events’maybepresentinatmospherictimeseriesdataforperiodsof
severaldaysuptoaboutaweek,ratherthanforperiodsofonlyseveralhoursuptoadayorso;
hence,theuncertaintyestimatesstatedaboveareconservative.
TheuncertaintyassociatedwiththeCOandAPOdataisquantifiedfromthe±1σ
standarddeviationofthehourly‐averagedatmosphericmeasurementsduringaperiodwhen
theatmosphericvariabilityineachspeciesislow,andthusincludesboththeuncertaintyofthe
measurementtechnique,andtheuncertaintyassociatedwithsomenaturalatmospheric
variability.ForCO,themeasurementuncertaintyis±5.54ppbatTACand±1.58ppbatWAO.
ThelargermeasurementuncertaintyatTACisprimarilyduetogreaterimprecisioninthe
measurementtechniqueemployedatTACcomparedtothatusedatWAO,butisalsopartly
duetotheslightlygreaterCOvariabilityobservedatTACcomparedtoWAO.
ForAPO,themeasurementuncertaintyisdeterminedfromthe±1σstandarddeviation
inboththehourlyCO2andO2measurements,sinceAPO=O2+(‐1.1×CO2),where‐1.1isthe
oxidativeratiooftheglobalterrestrialbiosphere.Sincetheoxidativeratiooftheterrestrial
biospherecanvaryregionally,anuncertaintyof±0.05isassigned,whichisthensummedin
quadraturewiththeuncertaintiesoftheO2andCO2measurementstoobtainanoverall
uncertaintyestimatefortheAPOdata,whichis±13.80permegatUEAand±12.35permegat
WAO.TheO2andCO2measurementuncertaintiesatUEAareactuallysmallerthanthoseat
WAO;however,theAPOuncertaintyatUEAislargerthanthatatWAOowingtothelargerAPO
variabilityobservedatUEAcomparedtoWAO.Aspercentages,themeasurement
uncertaintiesare±4.29%forCOatTACand±1.28%forCOatWAO,and±4.63%forAPOat
UEAand±4.14%forAPOatWAO;thus,allofthemeasurementuncertaintiesaresignificantly
smallerthantheuncertaintiesassociatedwiththechoiceofCOandAPObaselinefits.
5.3.3.Using‘time‐varying’fossilfuelemissionratios
InFig.5.8,IpresentedffCO2fromCOandAPOdatausingfixedvaluesforthefossilfuel
emissionratios.Inreality,thefossilfuelemissionratiosobservedatameasurementsitecan
varysignificantly,owingtochangesintheemissionratiosthemselvespriortotransportation
tothemeasurementsite,aswellaschangesintheatmosphericfootprintofthemeasurement
site.Hence,amuchmoreappropriatewaytocalculatedffCO2fromCOandAPOdataistouse
time‐varyingfossilfuelemissionratios,whichcanbedeterminedbycombiningfossilfuel
213
emissionratiosfromgriddeddatabaseswithatmospherictransportmodelfootprints,as
showninEquation5.5:
∑ (Eq.5.5)
whereRtisthetime‐varyingfossilfuelemissionratioatthemeasurementsitefromtimest1to
tn,b1tobnrepresenttheindividualgridboxesoftheatmospherictransportmodelfootprint,E
isthefossilfuelemissionratioforeachgridboxoftheatmospherictransportmodel,Pisthe
numberofatmospherictransportmodelparticlesinthegridbox,andTPisthetotalnumberof
particlesinthewholeatmosphericfootprint.
InordertocalculateRtinEq.5.5,IusedtheUKMetOfficeNAME(Numerical
Atmospheric‐dispersionModellingEnvironment)model(Jonesetal.,2007)toproduce2‐day,
backwardsrunatmosphericfootprintsevery3hours,consistingof10,000inertparticles,that
weremonitoredfrom0‐200mabovetheground.TheNAMErunsweredrivenbytheMet
OfficeUnifiedModelmeteorology,whichhasaspatialresolutionof17kmby17km.ForE,the
fossilfuelemissionratios,IusedgriddedO2:CO2ratiosfromtheCOFFEE(CO2releaseand
OxygenuptakefromFossilFuelEmissionsEstimate)database(Steinbachetal.,2011)forthe
APOmethod,whichwereconvertedtoAPO:CO2ratiosbysubtractingtheO2:CO2ratioofglobal
terrestrialbiosphere‐atmosphereexchange(‐1.1)fromallthevalues,andgriddedCO:CO2
ratiosfromtheEDGAR(EmissionsDatabaseforGlobalAtmosphericResearch)databasefor
theCOmethod.
TheEDGARCO:CO2ratiosareonlyavailablewithannualtimeresolution(andarealso
onlyavailableupto2010,not2014),andthereforethetime‐varyingCO:CO2ratioscalculatedat
TACandWAOonlyincludevariabilityfromthechangingNAMEfootprints(i.e.spatial
variability).TheCOFFEE‐derivedAPO:CO2ratiosareavailableonhourlytimeresolution,and
wereconvertedinto3‐hourlyaveragesinordertomatchthetimeintervaloftheNAME
footprints.Originally,theCOFFEEdatabasewasonlyavailableupto2010,however,COFFEE
hasrecentlybeenupdatedto2014byChristophGerbig(MaxPlanckInstituteof
Biogeochemistry,Jena,Germany),andnowincludesanupdatedsetofO2:CO2ratiosfor
differentfueltypes(includingbetterdifferentiationoflightoilversusheavyoilratios,and
differentratiosfordifferenttypesofbioenergy),whichIcalculated.Boththetime‐varying
CO:CO2andAPO:CO2emissionratioswerecalculatedon3‐hourlytimeintervalstobe
compatiblewiththeNAMEfootprints,whichweretheninterpolatedtohourlytimeresolution
tobecompatiblewiththehourly‐averagedAPOandCOatmosphericdata.
214 Theuncertaintyofthetime‐varyingemissionratiosisdifficulttocalculate,sinceneither
theEDGARorCOFFEEdatabasesassignuncertaintiestothefossilfuelemissionsestimates.
Therefore,aproxyfortheuncertaintyofthetime‐varyingemissionratioswasdeterminedby
dividingRtbythe±1σstandarddeviationofalloftheemissionratiosinthefootprint.Themean
uncertaintiesofthetime‐varyingCO:CO2emissionratiosatTACandWAOare±78.3%and
±72.9%,respectively,andthemeanuncertaintiesofthetime‐varyingAPO:CO2emissionratios
atUEAandWAOareboth±21.8%.ThelargedifferencebetweentheCOandAPOfossilfuel
emissionratiouncertaintiesreflectsthemuchlargerspatialvariabilityintheCO:CO2ratio
values(sincethereisnotemporalvariabilityavailableintheEDGARgriddeddatabases),
comparedtoboththespatialandtemporalvariabilityoftheAPO:CO2ratiovaluesfromthe
COFFEEdatabase.
5.3.4.ComparisonofCOandAPOfossilfuelquantificationmethods
ThetotalffCO2uncertaintyforboththeCOandAPOmethodscanbecalculatedby
summinginquadraturethemeasurement,baseline,andemissionratiouncertainties.This
producesmeantotalffCO2(CO)uncertaintiesof±87.5%atTACand±78.4%atWAO,andmean
ffCO2(APO)uncertaintiesof±35.8%atUEAand±35.6%atWAO.Atbothlocations,themean
ffCO2(CO)uncertaintyismuchlargerthanthemeanffCO2(APO)uncertainty(bymorethana
factorof2).ThisispredominantlyduetothemuchlargeruncertaintyintheCO:CO2emission
ratioscomparedtotheAPO:CO2emissionratios.TheffCO2uncertaintiesatWAOarelower
thanthoseatTACandUEAforboththeCOandAPOmethods,owingtothesmallerffCO2
signalsthatareobservedatWAOinbothspecies.Table5.1summarisesthedifferencesin
uncertaintybetweenffCO2(CO)andffCO2(APO)ateachmeasurementsite.
Table5.1.ComponentandtotaluncertaintiesfortheCOandAPOffCO2quantificationmethodsatTAC,WAOandUEA,givento2significantfiguresforeasiercomparison.
ffCO2(CO) ffCO2(APO)
TAC WAO UEA WAO
Baselineuncertainty ±18% ±18% ±28% ±28%
Measurementuncertainty ±4.3% ±1.3% ±4.6% ±4.1%
Emissionratiouncertainty ±78% ±73% ±22% ±22%
Totaluncertainty ±88% ±78% ±36% ±36%
215
AsshowninTable5.1,fortheCOmethod,thetotalffCO2uncertaintyatbothlocations
isdominatedbytheCO:CO2emissionratiouncertainty,withtheCObaselineuncertainty
contributingfarless,andtheCOmeasurementuncertaintycontributingtheleast.Incontrast,
theAPOmethodtotalffCO2uncertaintyismoststronglyinfluencedbytheAPObaseline
uncertainty,closelyfollowedbytheAPO:CO2emissionratiouncertainty,withtheAPO
measurementuncertaintycontributingtheleast.ItisclearthattheCOmethodisfarless
precisethantheAPOmethod,owingtothelargeuncertaintyassociatedwiththeCO:CO2
emissionratios.ItshouldbenotedthatthetotalffCO2(CO)uncertaintiesdonotincludethe
uncertaintyassociatedwithpotentialnaturalCOsourcesandsinks,whichwouldbevery
difficulttoquantify.Additionally,neitherthetotalffCO2(CO)northetotalffCO2(APO)
uncertaintiesincludetheuncertaintyassociatedwithpotentialbioenergyinfluences,which
wouldalsobedifficulttoquantify,andwillhaveagreaterinfluenceontheCOmethodthanthe
APOmethod,becausetheAPOmethodisconservativewithrespecttosolidbioenergyand
biomassburning.
ffCO2(CO)fromTACandWAOandffCO2(APO)fromUEAandWAOcalculatedusing
time‐varyingfossilfuelemissionratios(usingEquation5.4)arepresentedinFigure5.11.In
contrasttoFig.5.8,theffCO2datainFig.5.11havebeencalculatedusinginflexiblebaselines,
ratherthanmoderatelyflexiblebaselines,asthelattercanleadtounderestimationoftheffCO2
variability,particularlyforffCO2eventslastingseveraldays,asshowninFig.5.10and
describedpreviously.TheffCO2uncertaintiesarerepresentedbytheshadedregions,andwere
calculatedbysummingthemeasurement,baselineandemissionratiouncertaintiesin
quadrature.AlsoshownistheffCO2calculatedfromdiscrete14CO2measurementsmadeat
TAC.Overall,theffCO2calculatedfromCOandAPOappeartoagreemorecloselyinFig.5.11
thanpreviously,inFig.5.8.Therearestillsomeperiodswherethetwocontinuousmethodsdo
notagreewithintheuncertaintiesofeachother,suchas31JulyatWAO,forexample.TheffCO2
from14CO2atTACisnormallyalsoinagreementwiththeffCO2fromCOandAPO,althoughas
before,theffCO2(14CO2)valuestendtobelowerthantheffCO2(APO)andffCO2(CO)values.Fig.
5.11illustratesthedifferenceinuncertaintybetweentheCOandAPOmethodsthatIhave
numericallypresentedinTable5.1,andshowsthattheAPOmethodissignificantlymore
precisethantheCOmethod.AnanalysisoftheairmasshistoryusingNAMEfootprintsreveals
thatmostoftheffCO2duringthesummer2014periodIhaveanalysedisfromthesouthofthe
UKandLondon,withsomefromthenorthoftheUK,andveryoccasionalffCO2fromFrance,
theNetherlandsandtheNorthSea(presumablyfromoilplatforms).Thereisnoapparent
connectionbetweentheagreementoftheCOandAPOffCO2quantificationmethodsandthe
Figure5.11.ffCO2(CO)andffCO2(APO)atTACandUEA,respectively(toppanel),andffCO2(CO)andffCO2(APO)atWAO(bottompanel),calculatedusingtime‐varyingemissionratiosandinflexiblebaselines.ShadedareasdenotetherespectiveuncertaintiesofthecalculatedffCO2.ffCO2from14CO2measurementsatTACaredenotedbytheblackcircles,ofwhichthesizerepresentstheuncertaintyoftheffCO2(14CO2)values.
217
originsoftheNAMEfootprints.Itisthereforelikelythatmostofthedisagreementbetweenthe
twomethodscanbeattributedtothefactthattheTACandUEAmeasurementsarenotco‐
located,aswellasundiagnosedtechnicalissuesanddifferencesinpotentialCOandAPO
influencesthatcannoteasilybequantified,suchasbiomassburning(forCO).
IncontrasttoFig.5.7,wheretheanti‐correlationinAPOandCOwassimilaratWAO
andatUEAandTAC,Fig.5.11indicatesthatffCO2agreementisactuallycloseratWAOthanat
UEAandTAC.Thisismostlikelyduetotheco‐locationoftheCOandAPOmeasurementsat
WAO,andaddsconfidencetobothffCO2quantificationmethods.Indeed,sinceffCO2hasbeen
calculatedusingtwoentirelyindependenttracers,periodsofstrongagreementinffCO2
betweenthetwomethodsareassociatedwithextremelyhighconfidenceintheffCO2accuracy
(e.g.21‐28Aug2014atWAO).
ItisalsoclearfromFig.5.11thattheCOmethodproducessignificantlyhigherffCO2
valuesthantheAPOmethod.ThisislargelyduetotheCO:CO2emissionratiosfromtheEDGAR
database,whicharelowerthanexpected,andcausethemagnitudeoftheffCO2fromCOtobe
high.Table5.2showstypicalffCO2valuesfromtheliterature,mostofwhichalsousetheCO
method,alongsidetheffCO2rangefromtheCOandAPOmethodsshownabove,and
demonstratesthattheffCO2fromCOatTACandWAOismuchhigherthanexpected,whenthe
valuesarecomparedtotypicalffCO2observedinurbanareas,suchasParis.Infact,itisnot
possibleforsomeofthelargestffCO2(CO)peaksatTACandWAOtobeaccurate,sincetheffCO2
valuesarelargerthantheCO2enhancementabovethebaseline,showninFig.5.6.This
suggeststhattheEDGARCOinventorydataareincorrect(toolow),sincetheCOFFEEAPO:CO2
ratiosarederivedfromEDGARCO2data(seeSteinbachetal.,2011fordetails),andthe
ffCO2(APO)valuesarewithintheexpectedrangeforarelativelyruralarea.Itshouldalsobe
notedthattheTACCOdataareknowntohaveanon‐goingcalibrationissuethatisaffectingthe
accuracyofthehighCOvalues.Itispossiblethatoncecorrected,thehighestffCO2(CO)valuesat
TACmayreducebyasmuchas30%(GrantForster,personalcommunication,2016),although
thiscorrectionwillnotaffectthepatternofvariability,northefactthattheCOmethodstill
produceshigherffCO2valuesoverallthantheAPOmethod,andunrealisticallyhighvaluesat
WAO,wheretheCOdatahavebeenqualitycontrolledandaredeemedaccurate.
218
Table5.2.TypicalffCO2rangesfromtheliterature,shownalongsidetheffCO2rangesforTAC,UEAandWAOpresentedinthiswork,calculatedusingCO,APOand14CO2atmosphericdata.Publication Location Speciesused TypicalffCO2
range
ffCO2uncertainty
vanderLaan
etal.(2010)
Lutjewad,The
Netherlands
14CO2andCO 0–30ppm ±2.5ppm
Lopezetal.
(2013)
Paris,France 14CO2,CO,NOx
and13CO2
0–40ppm Notgivenformost
species.±1.0ppm
for14CO2
Gravenetal.
(2009)
California,U.S.A. 14CO2andCO 0–10ppm ±1.6–2.9ppm
Turnbullet
al.(2006)
NewEngland
andColorado,
U.S.A.
14CO2,COand
SF6
0–15ppm ±2–4ppm
Thiswork Norfolk,U.K. CO(TAC)
CO(WAO)
APO(UEA)
APO(WAO)
14CO2(TAC)
0–70ppm
0–40ppm
0–20ppm
0–15ppm
1.2–2.5ppm
±5.8ppm
±4.5ppm
±1.2ppm
±1.1ppm
±1.6ppm
Fig.5.11suggeststhatusinginventorydatacombinedwithanatmospherictransport
modeltoestimatetheemissionratiosmayleadtoinaccurateffCO2,mainlyduetoinaccuracies
withtheinventorydata,butalsoduetopotentialatmospherictransportmodelinaccuracies.
Therefore,itisimportanttoconsiderothermethodsofdeterminingthefossilfuelemission
ratiosfortheCOandAPOmethods.Figure5.12showsffCO2fromUEAandTACcalculated
usingthetime‐varyingemissionratios(asshownFig.5.11,withuncertaintiesomittedfor
visualclarity),aswellasffCO2usingthepreviousfixedemissionratiosof0.3molmol‐1for
APO:CO2and5ppbppm‐1forCO:CO2(verysimilartoffCO2showninFig.5.8,onlyusingan
inflexiblebaseline).AlsoshownisffCO2calculatedusingemissionratiosthathavebeen
‘calibrated’bytheTAC14CO2data,andfortheAPOmethodonly,ffCO2calculatedusingthe
meanAPO:CO2ratiooftheatmosphericmeasurementsatUEAduringthesummer2014
period.ffCO2(CO)wascalculatedusingthemeanCO:CO2ratiooftheatmospheric
measurementsaswell,butthevaluesproducedwereextremelyhigh(upto350ppm)andnot
realistic;hence,thesedataarenotshowninFig.5.12.Thereasonwhythemeanmeasured
CO:CO2ratioistoolow,causingffCO2tobebiasedtoohigh,isduetolargenon‐fossilfuelrelated
219
CO2signalsfromtheterrestrialbiospherecoincidingwithfossilfuelrelatedCOsignals.In
contrast,themeanAPO:CO2ratioduringthisperiodisnotsoseverelyaffectedbytheactivityof
theterrestrialbiosphere.
Figure5.12.ffCO2fromAPOatUEA(toppanel)andCOatTAC(bottompanel)calculatedusingavarietyofemissionratios(seetextaboveandfigurelegends).TheffCO2fromtime‐varyingratiosisthesameastheffCO2showninFig.5.11(toppanel),onlywithouttheuncertaintyshading,toaidvisualcomparisonwiththeffCO2calculatedusingtheotheremissionratios.AlsoshownisffCO2fromTAC14CO2data(blacksymbols).
Fig.5.12demonstratesthattheffCO2(APO)values(toppanel)areallquitesimilarto
eachother,despiteusingdifferentfossilfuelemissionratiosources.Theonlyexceptionisthe
ffCO2(APO)calculatedfromtheemissionratiosthatwerecalibratedusingtheTAC14CO2data,
whichislowerthanthatcalculatedusingtheotherthreetypesofemissionratios.The14CO2
calibratedAPO:CO2emissionratiohadtobeadjustedtothehighestpossiblevalueforfossilfuel
emissions(0.9molmol‐1)inordertobeabletocalculateffCO2thatwaslowenoughtomatch
theffCO2fromthe14CO2data.Infact,insomecases,itwasnotpossibletomatchthe
ffCO2(14CO2)valuewithoutusinganAPO:CO2emissionratiothatishigherthanthemaximum
possiblefossilfuelemissionratiovalue,whichsuggeststhateventhoughtheffCO2(14CO2)was
correctedfornuclearinfluences,thevaluesarestillaffectedandarebiasedlow.Thisis
supportedbytheffCO2(CO)calculatedusingthe14CO2calibratedemissionratios,whereitwas
alsooftennecessarytouseextremelyhighemissionratios(upto100ppbppm‐1)inorderto
producealowenoughffCO2valuethatwouldmatchtheffCO2(14CO2)value.
220
UnlikeAPO,theffCO2(CO)showninFig.5.12ishighlydependentupontheemission
ratiosused,withthetime‐varyingratios,fixedratios,14CO2calibratedratios,andmean
measuredratios(notshown)producingverydifferentffCO2values.Asmentionedbefore,the
meanmeasuredratiosandtime‐varyingratiosfromtheEDGARdatabaseproduceffCO2from
COthatistoohighforarelativelyrurallocationsuchasTACorWAO,andthe14CO2calibrated
ratiosproduceffCO2valuesthatarebiasedlowbynuclearpowerplantemissions,giventhat
sometimesveryhighCO:CO2emissionratiosarerequiredtoreproducetheffCO2(14CO2)values.
ThefixedemissionratiosproducetheffCO2valuesthatmostcloselymatchthosecalculated
usingtheAPOmethod(fromdifferenttypesofemissionratios)atUEA,andarealsointhe
expectedrange,consideringthelocationofTAC.Thus,Fig.5.12suggeststhataswellastheAPO
methodbeingmoreprecisethantheCOmethodforquantifyingffCO2,itisalsoverylikelythat
theAPOmethodisalsomoreaccuratethantheCOmethod,giventhatthemagnitudeofffCO2
calculatedfromCOissovariable,dependingonthechoiceofemissionratiosused.
5.4Summaryandfuturework
InthischapterIhavepresentedanewmethodforquantifyingffCO2usingAPOdata,
whichIhavecomparedtoffCO2calculatedfromCOand14CO2data.Overall,IfoundtheAPO
methodtobesignificantlymoreprecisethantheCOmethod,whichislargelyowingtothe
reduceduncertaintyintheAPO:CO2fossilfuelemissionratioscomparedtotheuncertaintyin
theCO:CO2fossilfuelemissionratios.ThelargestsourceofuncertaintyintheAPOmethodis
currentlythebaselinefittingprocedure.Futuretechnicalimprovementsinmakinghigh‐
precisionO2measurementswillhelptoreducetheAPObaselineuncertainty.Iwouldalso
expectthatshort‐termdeviationsfromtheAPObaselinewillbecomeeasiertodetermineina
moreurbansetting,wherethemagnitudeofthesignalsarelarger,andthatthiswillalsohelpto
221
reducetherelativeuncertaintyintheAPObaseline.Incontrasttothetwocontinuousmethods,
Ifoundthatrelyingonthe14CO2dataaloneledtosignificantunderestimationofffCO2in
Norfolk,partlyduetonuclearpowerplantinfluencesthathavenotbeenadequatelycorrected
for,andalsopartlyduetocleanairsampling(AngelinaWenger,personalcommunication,
2016).
WhencomparingtheCOandAPOmethods,IfoundthattheAPOmethodwasvery
likelytobemoreaccuratethantheCOmethod.Thisconclusionislargelybasedonasensitivity
analysisoffourdifferentemissionratiosources.FortheAPOmethod,Ifoundthattherangein
ffCO2valuesassociatedwiththefouremissionratiosourceswasmuchsmallerthantheffCO2
rangefortheCOmethod.IwasalsoabletodeterminethatsomeofthelargestffCO2peaksfrom
theCOmethodcouldnotpossiblybereal,sincetheywerelargerthanthemeasuredCO2
enhancementabovethebackgroundCO2molefraction.Ideally,Iwouldhavedeterminedthe
accuracyoftheAPOandCOmethodsbycomparingtoffCO2from14CO2atalocationthatisnot
affectedbygas‐coolednuclearpowerplantinfluences,becauseffCO2from14CO2isgenerally
expectedtobethemostaccuratewayofdeterminingffCO2.AsfarasIamaware,however,
thereisnoexistingdatasetofconcurrent,high‐precisionAPO,COand14CO2dataatalocation
thatalsoexperiencespollutedair,andisnotaffectedbynuclearpowerplantinfluences.
Despitethislimitation,theresultsIhavepresentedhereindicatethatitisverylikelythatthe
APOmethodismoreaccuratethantheCOmethod.Mostencouragingly,Ihavefoundthatat
WAOinparticular(wherethemeasurementsareco‐located),theffCO2variabilitybetweenthe
twomethodsisoftenverysimilar,andperiodswheretheffCO2magnitudeisalsoinagreement
affordsmeextremelyhighconfidenceintheffCO2accuracy,giventhattheCOandAPO
methodsarereliantontwocompletelyindependenttracers.
TheUKgovernmentstatesthatUKannualfossilfuelCO2emissionsfor2013areknown
towithin±2%uncertainty,basedonbottom‐upinventorymethodsanda95%confidence
level.Whilethisuncertaintysoundsverysmall,itisapproximatelyequivalenttotheUKmean
annualCO2footprintsofover950,000people.Inaddition,theuncertaintiesassociatedwiththe
UKinventoryarenotquantifiedforhigherspatialresolutionthannational,orforhigher
temporalresolutionthanannual(StephenForden,DECC;personalcommunication,2016).
Severalstudieshaveshownthatemissionsuncertaintiesincreasewithincreasingspatialand
temporalresolution,andcanreach100%ormorefor1°latitude/longituderesolutions(also
fora95%confidencelevel)(Andresetal.,2012;Andresetal.,2016).Thus,evenifnational
scaleuncertaintiesinfossilfuelemissionsarerelativelysmallandareassumedtobewell‐
known,largedifferencescanbefoundatsmallerscales,asdemonstratedby(Ackermanand
222
Sundquist,2008),whofounddifferencesofupto25%inindividualUSApowerplantCO2
emissionscompiledbydifferentgovernmentagencies.
InordertobeabletosuccessfullyreduceanthropogenicCO2emissions,weneedto
haveaccesstohighresolution(spatialandtemporal)informationthatenablesustodetermine
whichbehaviourscauseincreasesanddecreasesinanthropogenicCO2emissions.For
example,howdoUKfossilfuelCO2emissionschangeifthereisanunexpectedlycoldwinter,or
ifelectriccarsbecomedominantoverpetrolcars,orifhouse‐holdelectricityandgassmart
metersaremadecompulsoryinUKhouseholds?Inthischapter,IhavecomparedffCO2from
APOandCOmeasurementswithmodelledffCO2frominventoryestimates.Thecomparison
indicatesthatboththeCOFFEE(derivedfromEDGAR)andtheUKNAEIinventoriesmaybe
over‐estimatingCO2emissionsinNorfolk.InthecaseoftheUKNAEI,someofthisdisparity
maybeexplainedbythefactthatIhavecompared2014ffCO2fromtheatmosphericdatato
modelledffCO2basedon2013values,becausethe2014valuesarenotcurrentlyavailable;
however,thereductionintheNorfolkNAEICO2emissionsbetweensummer2013and
summer2014wouldneedtoberelativelylargeinordertobringtheinventoryffCO2estimates
in‐linewiththeffCO2fromtheatmosphericmeasurements.Itshouldalsobenotedthatthe
modelledffCO2fromtheinventoriesthatIhavepresentedinthischapterarecalculatedusinga
singleatmospherictransportmodel.FurthersensitivityanalysisonthemodelledffCO2
emissionsshouldbecarriedoutusingotheratmospherictransportmodels,suchasSTILT
(StochasticTime‐InvertedLagrangianTransportmodel)(Linetal.,2003)andTM3
(HeimannandKörner,2003),toensurethatthemodelledffCO2isnotbiasedbymychoiceof
atmospherictransportmodel.
Tomyknowledge,therearecurrentlynocontinuoushigh‐precisionatmosphericO2
measurementsmadeinurbansettingsforthepurposeofffCO2quantification,andyet~70%of
allanthropogenicCO2emissionsarefromcities(IEA,2012a).Ithereforeproposeanew
directionforhigh‐precisionO2measurements,byadvocatingthatatmosphericO2isacurrently
under‐exploitedtoolforffCO2quantificationinurbanenvironments,andhasthepotentialto
provideprecise,accurate,hightemporalandspatialresolutionffCO2quantification,whichcan
alsobeusedinregionsthatareseverelyaffectedbygas‐coolednuclearpowerplantemissions,
suchaswesternEurope,Japan,easternUSAandCanada.Itshouldbenotedthatinordertouse
atmosphericO2measurementstosuccessfullyquantifyffCO2,veryprecisemeasurementsare
required(ontheorderof~5permegover1‐2minutes)andahighlevelofdataqualitycontrol
isrequired.Nevertheless,asdemonstratedinthischapter,itiscurrentlypossibletoachieve
suchmeasurementprecisionanddataqualitycontrolrequirementsinordertosuccessfully
quantifyffCO2evenatruralandcoastallocations,whereffCO2emissionsarerelativelylow.I
223
thereforeproposethatacombinationofatmosphericO2measurementsandinversemodelling
couldenablerobusttop‐downquantificationofCO2emissionsatbothnational,butalso
perhapsurbanscales,andatsub‐annualtemporalresolutions,dependingonthedensityofthe
atmosphericO2measurementnetwork,andlimitationsofatmospherictransportmodelsand
inversemodellingmethodologies.
References
Ackerman,K.V.andSundquist,E.T.:ComparisonoftwoUSpower‐plantcarbondioxideemissionsdatasets,EnvironmentalScience&Technology,42,5688‐5693,2008.
Andres,R.J.,Boden,T.A.,Breon,F.M.,Ciais,P.,Davis,S.,Erickson,D.,Gregg,J.S.,Jacobson,A.,Marland,G.,Miller,J.,Oda,T.,Olivier,J.G.J.,Raupach,M.R.,Rayner,P.,andTreanton,K.:Asynthesisofcarbondioxideemissionsfromfossil‐fuelcombustion,Biogeosciences,9,1845‐1871,2012.
Andres,R.J.,Boden,T.A.,andHigdon,D.M.:Griddeduncertaintyinfossilfuelcarbondioxideemissionmaps,aCDIACexampleAtmosphericChemistryandPhysicsDiscussions,2016.
Bergamaschi,P.,Hein,R.,Heimann,M.,andCrutzen,P.J.:InversemodelingoftheglobalCOcycle1.InversionofCOmixingratios,JournalofGeophysicalResearch‐Atmospheres,105,1909‐1927,2000.
Bergamaschi,P.,Krol,M.,Dentener,F.,Vermeulen,A.,Meinhardt,F.,Graul,R.,Ramonet,M.,Peters,W.,andDlugokencky,E.J.:InversemodellingofnationalandEuropeanCH4emissionsusingtheatmosphericzoommodelTM5,AtmosphericChemistryandPhysics,5,2431‐2460,2005.
Breon,F.M.,Broquet,G.,Puygrenier,V.,Chevallier,F.,Xueref‐Remy,I.,Ramonet,M.,Dieudonne,E.,Lopez,M.,Schmidt,M.,Perrussel,O.,andCiais,P.:AnattemptatestimatingParisareaCO2emissionsfromatmosphericconcentrationmeasurements,AtmosphericChemistryandPhysics,15,1707‐1724,2015.
Carslaw,D.C.andRopkins,K.:Openair—anRpackageforairqualitydataanalysis.,EnvironmentalModelling&Software,27‐28,52‐61,2012.
Gamnitzer,U.,Karstens,U.,Kromer,B.,Neubert,R.E.M.,Meijer,H.A.J.,Schroeder,H.,andLevin,I.:Carbonmonoxide:AquantitativetracerforfossilfuelCO2?,JournalofGeophysicalResearch‐Atmospheres,111,2006.
Graven,H.D.:Impactoffossilfuelemissionsonatmosphericradiocarbonandvariousapplicationsofradiocarbonoverthiscentury,ProceedingsoftheNationalAcademyofSciencesoftheUnitedStatesofAmerica,112,9542‐9545,2015.
Graven,H.D.andGruber,N.:Continental‐scaleenrichmentofatmospheric14CO2fromthenuclearpowerindustry:potentialimpactontheestimationoffossilfuel‐derivedCO2,AtmosphericChemistryandPhysics,11,12339‐12349,2011.
Gurney,K.R.,Chen,Y.H.,Maki,T.,Kawa,S.R.,Andrews,A.,andZhu,Z.X.:SensitivityofatmosphericCO2inversionstoseasonalandinterannualvariationsinfossilfuelemissions,JournalofGeophysicalResearch‐Atmospheres,110,2005.
Heimann,M.andKörner,S.:TheGlobalAtmosphericTracerModelTM3,Max‐Planck‐InstitutforBiogeochemistry,Jena,2003.
IEA:InternationalEnergyAgency:Worldenergyoutlook,2012a.IEA:TechnologyRoadmap:BioenergyforHeatandPower,InternationalEnergyAgency(IEA),
2012b.
224
Jones,A.R.,Thomson,D.J.,Hort,M.,andDevenish,B.:TheU.K.MetOffice'snext‐generationatmosphericdispersionmodel,NAMEIIIIn:AirPollutionModelinganditsApplicationBorrego,C.andNorman,A.L.(Eds.),XVII(Proceedingsofthe27thNATO/CCMSInternationalTechnicalMeetingonAirPollutionModellinganditsApplication),Springer,2007.
Kossoy,A.,Peszko,G.,Oppermann,K.,Prytz,N.,Klein,N.,Blok,K.,Lam,L.,Wong,L.,andBorkent,B.:StateandTrendsofCarbonPricing2015(September),WorldBank,Washington,DC.,2015.
Levin,I.,Hammer,S.,Eichelmann,E.,andVogel,F.R.:Verificationofgreenhousegasemissionreductions:theprospectofatmosphericmonitoringinpollutedareas,PhilosophicalTransactionsoftheRoyalSocietya‐MathematicalPhysicalandEngineeringSciences,369,1906‐1924,2011.
Levin,I.,Kromer,B.,Schmidt,M.,andSartorius,H.:AnovelapproachforindependentbudgetingoffossilfuelCO2overEuropeby14CO2observations,GeophysicalResearchLetters,30,2003.
Lin,J.C.,Gerbig,C.,Wofsy,S.C.,Andrews,A.E.,Daube,B.C.,Davis,K.J.,andGrainger,C.A.:Anear‐fieldtoolforsimulatingtheupstreaminfluenceofatmosphericobservations:TheStochasticTime‐InvertedLagrangianTransport(STILT)model,JournalofGeophysicalResearch‐Atmospheres,108,2003.
Manning,M.R.,Lowe,D.C.,Melhuish,W.H.,Sparks,R.J.,Wallace,G.,Brenninkmeijer,C.A.M.,andMcGill,R.C.:Theuseofradiocarbonmeasurementsinatmosphericstudies,Radiocarbon,32,37‐58,1990.
Moxley,J.M.andCape,J.N.:Depletionofcarbonmonoxidefromthenocturnalboundarylayer,AtmosphericEnvironment,31,1147‐1155,1997.
Nisbet,E.andWeiss,R.:Top‐DownVersusBottom‐Up,Science,328,1241‐1243,2010.Peylin,P.,Houweling,S.,Krol,M.C.,Karstens,U.,Rodenbeck,C.,Geels,C.,Vermeulen,A.,
Badawy,B.,Aulagnier,C.,Pregger,T.,Delage,F.,Pieterse,G.,Ciais,P.,andHeimann,M.:ImportanceoffossilfuelemissionuncertaintiesoverEuropeforCO2modeling:modelintercomparison,AtmosphericChemistryandPhysics,11,6607‐6622,2011.
Ruckstuhl,A.F.,Henne,S.,Reimann,S.,Steinbacher,M.,Vollmer,M.K.,O'Doherty,S.,Buchmann,B.,andHueglin,C.:Robustextractionofbaselinesignalofatmospherictracespeciesusinglocalregression,AtmosphericMeasurementTechniques,5,2613‐2624,2012.
Severinghaus,J.P.:StudiesoftheterrestrialO2andcarboncyclesinsanddunesgasesandinBiosphere2,Ph.D.thesis,ColumbiaUniversity,1995.
Staufer,J.,Broquet,G.,Breon,F.M.,Puygrenier,V.,Chevallier,F.,Xueref‐Remy,I.,Dieudonne,E.,Lopez,M.,Schmidt,M.,Ramonet,M.,Perrussel,O.,Lac,C.,Wu,L.,andCiais,P.:Afirstyear‐longestimateoftheParisregionfossilfuelCO2emissionsbasedonatmosphericinversion,AtmosphericChemistryandPhysicsDiscussions,2016.
Steinbach,J.,Gerbig,C.,Rodenbeck,C.,Karstens,U.,Minejima,C.,andMukai,H.:TheCO2releaseandOxygenuptakefromFossilFuelEmissionEstimate(COFFEE)dataset:effectsfromvaryingoxidativeratios,AtmosphericChemistryandPhysics,11,6855‐6870,2011.
Stephens,B.B.,Keeling,R.F.,Heimann,M.,Six,K.D.,Murnane,R.,andCaldeira,K.:TestingglobaloceancarboncyclemodelsusingmeasurementsofatmosphericO2andCO2concentration,GlobalBiogeochemicalCycles,12,213‐230,1998.
Turnbull,J.,Rayner,P.,Miller,J.,Naegler,T.,Ciais,P.,andCozic,A.:Ontheuseof14CO2asatracerforfossilfuelCO2:Quantifyinguncertaintiesusinganatmospherictransportmodel,JournalofGeophysicalResearch‐Atmospheres,114,2009.
Turnbull,J.C.,Miller,J.B.,Lehman,S.J.,Tans,P.P.,Sparks,R.J.,andSouthon,J.:Comparisonof14CO2,CO,andSF6astracersforrecentlyaddedfossilfuelCO2intheatmosphereandimplicationsforbiologicalCO2exchange,GeophysicalResearchLetters,33,2006.
vanderLaan,S.,Karstens,U.,Neubert,R.E.M.,VanderLaan‐Luijkx,I.T.,andMeijer,H.A.J.:Observation‐basedestimatesoffossilfuel‐derivedCO2emissionsintheNetherlands
225
using14C,COand222Radon,TellusSeriesB‐ChemicalandPhysicalMeteorology,62,389‐402,2010.
Vogel,F.R.,Hammer,S.,Steinhof,A.,Kromer,B.,andLevin,I.:Implicationofweeklyanddiurnal14CcalibrationonhourlyestimatesofCO‐basedfossilfuelCO2atamoderatelypollutedsiteinsouthwesternGermany,TellusB,512‐520,2010.
Vogel,F.R.,Levin,I.,andWorthy,D.E.J.:ImplicationsforderivingregionalfossilfuelCO2estimatesfromatmosphericobservationsinahotspotofnuclearpwerplant14CO2emissions,Radiocarbon,55,1556‐1572,2013.
Weiss,R.F.andPrinn,R.G.:Quantifyinggreenhouse‐gasemissionsfromatmosphericmeasurements:acriticalrealitycheckforclimatelegislation,PhilosophicalTransactionsoftheRoyalSocietya‐MathematicalPhysicalandEngineeringSciences,369,1925‐1942,2011.
Zondervan,A.andMeijer,H.A.J.:IsotopiccharacterisationofCO2sourcesduringregionalpollutioneventsusingisotopicandradiocarbonanalysis,TellusSeriesB‐ChemicalandPhysicalMeteorology,48,601‐612,1996.
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