UBC Faculty Research and Publications

Isotopic composition of CO2 in gasoline, diesel and natural gas combustion exhaust in Vancouver, BC,… Semmens, Caitlin; Ketler, Rick; Schwendenmann, Luitgard; Nesic, Zoran; Christen, Andreas 2014

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   Isotopic composition of CO2 in gasoline, diesel and natural gas  combustion exhaust in Vancouver, BC, Canada !!Caitlin!Semmens(1),!Rick!Ketler(1),!Luitgard!Schwendenmann(2),!Zoran!Nesic(1,3),!Andreas!Christen(1)!(1)!University!of!British!Columbia,!Department!of!Geography,!Vancouver,!BC,!Canada!(2)!University!of!Auckland,!Auckland,!New!Zealand!(3)!University!of!British!Columbia,!Faculty!of!Land!and!Food!Systems,!Vancouver,!BC,!Canada!!!A!technical!report!of!the!University!of!British!Columbia!!!Supported!by!the!Natural!Sciences!and!Engineering!Research!Council!of!Canada!(NSERC)!through!Discovery!Grant!#155713180,!the!Canada!Foundation!for!Innovation!(#17141),!the!British!Columbia!Knowledge!Development!Fund!(BCKDF)!and!the!University!of!British!Columbia’s!AURA!program!!! !Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 2&Abstract The!isotopic!composition!(δ13C!and!δ18O)!in!atmospheric!carbon!dioxide!(CO2)!originating!from!gasoline!and!diesel!vehicle!exhaust!and!from!natural!gas!combustion!was!determined.!Gasoline!and!diesel!samples!were!taken!in!the!exhaust!of!representative!vehicles!of!the!fleet!in!Vancouver,!BC,!Canada!between!November!2013!and!May!2014.!The!fleet!average!gasoline!exhaust!(which!contained!a!fraction!bioethanol)!was!determined!with!a!δ13C!of!Z27.27!(±0.93)!‰!and!a!δ18O!of!Z12.46!(±3.45)!‰!(w.r.t.!VPDZCO2).!The!fleet!average!for!diesel!vehicles!exhibited!a!slightly!lower!δ13C!of!Z28.81!(±0.40)!‰!and!a!δ18O!of!Z18.63!(±0.72)!‰!close!to!unfractionated!combustion.!For!natural!gas,!samples!were!taken!from!a!open!torch!using!the!city’s!natural!gas!supply!network!at!different!dates!over!the!year.!The!mean!δ13C!for!natural!gas!samples!was!Z41.64!(±0.82)‰,!while!the!mean!δ18O!was!lower!than!for!internal!combustion!engines!at!Z22.74!(±0.56)‰.!In!conclusion,!δ13C!depends!on!the!fuel!type!and!origin!and!there!is!evidence!that!δ18O!is!fractionated!in!the!combustion!process!and!presence!and!state!of!catalytic!converters!causes!different!δ18O.!Introduction The!urban!atmosphere!contains!carbon!dioxide!(CO2)!usually!above!the!global!background.!Urban!air!is!enriched!by!CO2!originating!from!fuel!emissions!(vehicle!exhaust,!heating!systems,!gas!stoves)!and!human,!soil!and!plant!respiration!(possibly!modulated!by!photosynthesis).!For!urbanZscale!emission!monitoring!it!is!essential!to!separate!those!sources!(Christen,!2014).!Due!to!the!range!of!varying!sources,!determining!the!relative!contribution!to!the!observed!total!concentrations!of!CO2!in!an!urban!atmosphere!is!challenging.!Utilizing!the!isotopic!signatures!of!CO2!can!add!valuable!information.!For!example,!the!geological!processes!involved!in!the!formation!of!different!types!of!fossil!fuels!influence!the!relative!ratio!of!the!abundant!12CO2!to!the!heavier!13CO2!(the!normalized!ratio!of!the!two!is!expressed!as!δ13C!in!CO2).!By!analyzing!the!δ13C!in!CO2,!previous!work!has!been!able!to!distinguish!between!CO2!emitted!via!gasoline!combustion!(less!depleted!in!δ13C)!vs.!or!natural!gas!combustion!(more!depleted!in!δ13C)!(e.g.!Pataki!et!al.,!2003).!Likewise,!the!abundant!16O!in!CO2!may!be!substituted!with!18O,!giving!12C18O16O.!The!difference!between!12C18O16O!and!12C16O2!is!expressed!as!δ18O!in!CO2.!During!combustion,!the!oxygen!originates!from!the!atmosphere.!δ18O!of!atmospheric!oxygen!is!usually!assumed!to!be!constant.!Hence!differences!in!δ18O!are!not!caused!by!differences!of!the!fuel!or!background,!but!differences!in!the!combustion!process!and!the!consequent!catalytic!conversion!(if!applicable)!and!could!be!used!as!another!indicator!of!sources.!Fuel!for!vehicles,!like!gasoline,!can!originate!from!a!number!of!different!commercial!suppliers!which!sell!fuel!from!differing!geographic!origins.!Consequently,!the!isotopic!signatures!of!fuels!have!been!shown!to!vary!over!time,!mostly!due!to!changes!in!fuel!imports!from!different!geographic!locations!(Bush!et!al.,!2007).!Each!urban!region!and!time!might!therefore!have!slightly!different!values!in!δ13C.!The!aim!of!this!study!is!to!determine!the!extent!to!which!fuels!from!varying!sources!influence!the!isotopic!composition!of!the!CO2!emitted!in!Vancouver,!BC,!Canada!over!the!course!of!8!months.!Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 3&Quantifying!the!typical!isotopic!signature!of!CO2!emitted!from!different!sources!will!generate!valuable!data!for!and!emission!source!attribution!efforts!or!multiple!source!mixing!models!(e.g.!Djuricin!et!al.,!2010)!specifically!for!the!Metro!Vancouver!region.!Methods Exhaust!samples!were!taken!and!analyzed!from!a!number!of!different!vehicles!including!motorbikes,!small!cars,!trucks,!and!buses,!as!well!as!natural!gas.!Using!a!laser!spectrometer,!it!was!possible!to!analyze!the!composition!of!the!CO2!and!acquire!the!δ13C!and!δ18O!values!in!CO2!for!each!sample!in!several!repeating!samples.!Field sampling Vehicle Exhaust Sampling Setup:&Exhaust!samples!were!taken!using!a!rubberZcoated!metal!tube!connected!to!a!plastic!tube,!which!was!connected!to!a!10!litre!‘lung!sampler’!(Scentroid!Vacuum!Chamber,!IDES!Canada!Inc.,!Markham,!ON,!Canada).!The!purpose!of!the!metal!tube!was!to!avoid!melting!any!part!of!the!sampling!apparatus!while!sampling!the!hot!exhaust!in!the!exhaust!pipe!(Figure!1).!Inside!the!lung!sampler!is!a!3!l!TEDLAR!bag.!A!Pall!Corporation!Acro!50!filter!(1.0µm!PTFE)!is!located!between!tube!and!the!TEDLAR!bag!to!filter!aerosols!and!black!carbon.!Procedure:!Once!sampling!is!ready!to!begin!(vehicle!in!idling!mode),!the!metal!tube!is!placed!in!the!exhaust!pipe!of!the!vehicle.!The!end!of!the!tube!is!placed!approximately!10!cm!into!the!exhaust!pipe!to!ensure!high!CO2!concentrations!and!that!the!elevated!CO2!is!originating!from!the!exhaust!and!not!from!the!operator!or!any!other!sources.!Immediately!before!turning!the!lung!sampler!on,!a!syringe!is!used!to!flush!the!tube!and!filter!and!replace!any!air!already!present!in!the!tube!with!exhaust!air!while!running!the!engine.!Then!a!TEDLAR!bag!is!attached!and!the!vacuum!chamber!is!closed!and!turned!on.!Sampling!takes!approximately!one!minute!per!bag,!and!the!bags!are!filled!to!about!80Z90!percent!capacity.!The!exact!time!the!bag!sampling!begins!and!ends!is!recorded,!along!with!information!on!the!vehicle’s!age,!model,!fuel!type,!and!location!(gas!station)!of!last!fuelZup,!if!available.!From!each!vehicle!at!least!two!and!up!to!four!bags!are!sampled.!Between!sampling!different!vehicles,!the!tubes!are!flushed!with!ambient!air!using!a!syringe!to!purge!from!them!any!residual!exhaust.!In!addition,!one!or!two!bag!samples!of!ambient!air!from!the!sampling!site!are!taken!each!time!to!account!for!background!air!values!(unless!measurements!were!done!on!the!campus!of!the!University!of!British!Columbia!(UBC),!where!background!atmospheric!air!was!continuously!measured).!Many!different!vehicles!were!sampled,!including!small!cars,!semi!trucks,!buses,!and!motorbikes,!all!with!varying!fuel!types.!A!total!of!31!cars!and!trucks,!4!buses!and!1!motorbike!were!sampled!in!this!study!from!November!2013!to!May!2014.!Only!samples!exceeding!10’000!ppm!CO2!are!considered!in!the!subsequent!analysis.!Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 4&Natural Gas Sampling Setup:&The!natural!gas!samples!are!all!taken!indoors!in!an!unoccupied!laboratory!on!UBC!campus!(MCML!building!Rm!102A).!There!is!one!natural!gas!supplier!in!Vancouver!that!also!supplies!to!UBC.!With!the!vacuum!chamber!and!bag!ready,!a!Bunsen!burner!hooked!up!to!a!natural!gas!source!on!campus!is!lit!and!run.!A!3000!ml!Pyrex!beaker!is!placed!upside!down!over!the!flame,!so!that!the!top!of!the!burner!is!the!same!level!as!the!edge!of!the!beaker.!To!support!the!beaker,!a!metal!ring!stand!is!placed!over!the!burner!(see!Figure!2).!The!metal!tube!attached!to!the!vacuum!chamber!is!placed!up,!and!into!the!downturned!beaker!that!accumulates!the!exhaust!by!about!2!cm.!The!tube!is!not!placed!too!far!into!the!beaker!as!the!apparatus!gets!extremely!hot.!Procedure:!Similar!to!the!vehicle!exhaust!samples,!the!tube!is!flushed!with!ambient!room!air!using!a!syringe!before!sampling,!and!ambient!room!air!samples!are!taken!before!and!after!any!measurements.!!Once!the!vacuum!chamber!is!switched!on!and!a!sample!is!being!drawn,!anyone!present!leaves!the!room!to!reduce!excessive!exhaled!CO2!affecting!measurements.!Only!samples!exceeding!10’000!ppm!CO2!are!considered!in!the!subsequent!analysis.!A!total!of!15!samples!collected!between!February!2014!and!May!2014!were!considered!in!the!subsequent!analysis.!Sampling!was!spaced!a!few!weeks!apart!to!account!for!any!possible!shift!in!geographic!gas!origin.!! !Figure'1'–!Taking!exhaust!measurements!from!a!metal!tube!inserted!into!the!idling!car’s!exhaust!pipe!using!the!lungZsampler!(black!box).! Figure'2'–!The!setup!for!sampling!natural!gas.!A!Bunsen!burner!is!placed!under!a!downturned!beaker!which!is!resting!on!a!ring!stand.!The!lung!sampler!(to!the!right)!draws!a!sample!of!gas!via!the!metal!tube!placed!just!inside!the!beaker.!Lab analysis Once!samples!were!collected!they!were!analyzed!using!a!tuneable!laser!spectrometer!(TGA200,!Campbell!Scientific!Inc.,!Logan!UT,!USA).!However,!before!a!detailed!analysis!can!be!done,!samples!need!to!be!diluted.!With!the!TGA!in!uncalibrated!mode!samples!were!drawn!from!the!undiluted!bag!samples,!and!an!a!priori!estimate!of!the!CO2!mixing!ratios!was!performed!on!each!bag!to!calculate!the!required!amount!to!reach!a!CO2!mixing!ratio!between!380!and!480!ppm.!The!reason!to!be!between!380!and!480!Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 5&ppm!is!because!the!laser!spectrometer’s!response!is!calibrated!to!this!range,!using!two!bracket!gases!of!roughly!380!and!480!ppm.!A!clean!3!litre!TEDLAR!bag!is!filled!with!Ultra!Zero!Air!for!every!sample!(bag!of!undiluted!exhaust,!ambient!air,!and/or!natural!gas).!Using!a!syringe,!the!appropriate!amount!of!undiluted!sample!is!carefully!added!to!the!bag!of!Ultra!Zero!Air!(Praxair).!The!syringe!is!always!properly!cleaned!with!Ultra!Zero!Air!between!bags,!and!is!attached!before!the!bag’s!nozzle!is!opened!to!avoid!leakage!or!contamination.!Once!the!bags!of!diluted!samples!have!been!assembled,!the!diluted!samples!are!analyzed!by!the!TGA.!The!TGA!automatically!switches!between!sampling!the!diluted!bag,!and!3!other!sources;!It!switches!between!sampling!a!“low”!calibration!tank,!a!“high”!calibration!tank,!a!flush!of!ambient!air!in!the!range!of!the!sample!(collected!via!the!vacuum!chamber),!and!the!diluted!sample!being!analyzed.!Each!sample!is!run!through!the!TGA!twice,!and!during!each!analysis!the!TGA!must!run!through!one!full!cycle.!The!cycle!is!as!follows:!Low!Tank!–!Flush!–!Sample!–!Flush!–!High!Tank!–!Flush!–!Sample!–!Flush!–!Low!Tank.!‘Flush’!refers!to!three!seconds!of!sampling!of!a!bag!of!ambient!concentration!to!avoid!pressure!differences.!Table!2!shows!the!concentrations!used!over!time!for!the!“low”!and!“high”!calibration!gases!during!this!study.!All!results!in!this!report!are!shown!against!the!VPDBZCO2!standard!(Coplen,!1995).!!Table1:!Mixing!ratios,!δ13C,!and!δ18O!for!CO2!in!each!calibration!tank!used!as!either!low!brackets!or!high!brackets!w.r.t.!VPDZCO2.!The!secondary!calibration!tanks!below!have!been!calibrated!in!several!iterations!each!relative!to!global!National!Oceanic!and!Atmospheric!Administration!(NOAA)!standards!at!390!and!460!ppm.!Those!primary!standards!were!analyzed!for!isotopes!at!the!Stable!Isotope!Lab!(SIL)!at!INSTAAR,!University!of!Colorado,!in!cooperation!with!the!Global!Monitoring!Division!of!NOAA.!Calibration!tank!ID! Total!CO2!(ppm)! δ13C!!(‰)! δ18O!(‰)! Start!Date/Time!–!End!Date/Time!(UTC)!of!use!of!tank!(Low!bracket)!CO2Z007! 399.095! Z33.424! Z8.636! 2013/10/25!(00:00)!–!2014/01/14!(20:10)!(Low!bracket)!CO2Z009! 369.880! Z33.471! Z8.779! 2014/01/14!(20:10)!–!2014/05/02!(23:00)!(Low!bracket)!CO2Z012! 380.027! Z40.691! Z23.634! 2014/05/02!(23:00)!–!2014/05/26!(00:06)!(High!bracket)!CO2Z008! 457.820! Z37.165! Z15.318! 2013/10/25!(00:00)!–!2014/01/14!(20:10)!(High!bracket)!CO2Z011! 456.872! Z37.135! Z15.463! 2014/01/14!(20:10)!–!2014/05/26!(00:06)!!Once!the!mixing!ratios!of!the!diluted!samples!of!CO2!in!ppm,!δ13C‰,!and!δ18O!‰!have!been!determined,!results!are!either!accepted!or!rejected!based!on!how!closely!the!2!samples!match.!For!an!analysis!to!be!verified,!the!difference!in!the!acquired!CO2!concentrations!and!isotope!ratios!between!the!first!and!second!blocks!need!to!be!below!thresholds!set!by!the!instrument’s!noise.!Figure!3!shows!how!this!can!be!determined!graphically;!an!analysis!is!verified!if!after!the!150th!sample!(15!seconds)!the!red!and!blue!lines!have!converged,!as!well!as!the!pink!and!orange!lines.!For!acceptable!samples,!the!δ13C!and!δ18O,!as!well!as!the!total!mixing!ratios!of!the!samples!are!averaged!between!the!two!runs!compiled!into!a!spreadsheet!for!further!analysis.!Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 6&!Figure'3:!Measurements!taken!by!the!TGA!at!10!Hz!resolution!while!a!sample!bag!is!connected.!The!green!and!blue!lines!are!the!two!cycles!from!the!low!tank!and!the!high!tank!to!the!sample.!The!sample!volume!of!the!TGA!needs!to!be!flushed!!(contains!calibration!gas!at!time!0!seconds)!and!replaced!by!the!bag!content.!The!two!cycles!are!converging!at!around!the!100th!reading!(10!seconds),!and!remaining!stable!thereafter.!Only!data!after!the!150th!reading!(15!seconds)!is!considered!and!used!in!the!analysis.!Corrections Measurements!are!then!corrected!for!‘contamination’!by!background!CO2!as!follows:!!!"C = !!!!"C!"#$ 1[ CO!!" ]!where!!!"C!is!the!corrected!final!isotope!ratio!of!sample.!!!"C!"#$!is!the!measured!isotope!ratio!of!the!sample!(measured!by!the!TGA!contains!a!small!fraction!of!background!air!CO2),!and![ CO!!" ]!is!the!undiluted!mixing!ratio!of!the!sample.!The!slope!s!of!the!Keeling!plot!is!calculated!based!on!the!simultaneously!taken!background!air!sample!(undiluted):!s = !!"C!"#$ − !!"C!"#$)( !!!!!" !"#$ − !!!!!" !"#$)!!!"C!"#$ !is!the!measured!isotope!ratio!of!CO2!in!the!background!air!at!the!sampling!site!(for!natural!gas!this!is!indoor!air).Because!all!exhaust!samples!had!high!mixing!ratios!(>10,000!ppm!or!1!%,!usually!rather!10%),!the!correction!was!usually!not!very!substantial,!yet!was!applied.!3. Results and Discussion The!three!fuel!types!(gasoline,!diesel!and!natural!gas)!are!reported!separately.!The!mean!and!standard!deviation!of!δ13C!and!δ18O!were!calculated!for!all!samples!and!compiled!into!3!tables!based!on!fuel!type!below!(Tables!2,!3,!and!4).!Because!there!are!replicates!of!most!samples!(all!samples!have!at!least!two!replicates,!but!some!are!not!included!as!they!failed!the!analysis),!the!average!δ13C!and!δ18O!of!the!Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 7&replicates!for!each!vehicle!is!calculated!and!shown!on!each!line!of!tables!2,!3!or!4.!For!example,!CAR023!was!analyzed!four!times,!yielding!four!replicates.!The!average!of!the!four!replicates!is!taken!to!reduce!uncertainty.!In!order!to!derive!the!average!δ13C!and!δ18O!for!all!of!the!gasoline/diesel/natural!gas!samples,!the!average!of!all!subsequent!vehicles/samples!is!taken.!The!purpose!of!averaging!twice!ensures!that!some!vehicles!are!not!weighed!more!than!others!based!on!sample!abundance.!Gasoline exhaust The!fleet!gasoline!exhaust!was!determined!to!have!a!δ13C!value!of!Z27.27!(±0.93)!‰!and!a!δ18O!value!of!Z12.46!(±3.45)!‰!(Table!2).!Two!factors!explain!the!variability!of!samples.!For!δ13C,!gasoline!comes!from!different!suppliers,!which!have!fuels!from!different!geographic!origin!and!hence!isotopic!signatures!might!slightly!vary!(Bush!et!al.,!2007).!Secondly,!in!British!Columbia!gasoline!can!be!a!blend!of!up!to!10%!bioethanol,!which!also!affects!the!isotopic!composition.!For!δ18O,!it!is!important!to!know!thatcars!built!before!1988!(CAR003)!are!not!required!to!have!a!catalytic!converter!in!British!Columbia!(after!1988!a!three!way!catalytic!convertor!is!mandatory!by!law),!and!effectiveness!of!the!catalytic!converters!may!affect!the!δ18O.!The!δ18O!values!for!CAR017,!CAR020,!and!the!motorbike!(MTB001)!are!substantially!lower!than!the!rest!of!the!fleet!and!comparable!to!the!values!obtained!from!diesel!vehicles!(Table!3).!Table'2:!The!average,!maximum,!and!minimum!values!obtained!from!gasoline!vehicle!exhaust!w.r.t.!VPDZCO2.!The!‘number!of!replicates’!refers!to!the!number!of!bags!analyzed!from!this!particular!vehicle.!Based!on!individual!vehicles,!the!fleet!total!average!δ13C!and!total!average!δ18O,!as!well!as!the!standard!deviation!for!δ13C!and!δ18O!are!noted!at!the!bottom!of!the!table.!Vehicle!ID! Number!of!Replicates! Average!of!corrected!end!member!δ13C(‰)!Max!of!corrected!end!member!δ13C(‰)!Min!of!corrected!end!member!δ13C(‰)!Average!of!corrected!end!member!δ18O(‰)!Max!of!corrected!end!member!δ18O(‰)!Min!of!corrected!end!member!δ18O(‰)!CAR001! 6! 427.90' Z27.74! Z28.06! 414.96' Z13.63! Z15.86!CAR002! 3! 427.83' Z27.56! Z28.00! 413.25' Z12.01! Z15.42!CAR003(a)! 3! 427.28' Z27.22! Z27.33! 418.42' Z18.11! Z18.85!CAR004! 3! 427.95' Z27.84! Z28.02! 410.72' Z10.17! Z11.63!CAR005! 3! 428.69' Z28.35! Z28.86! 413.36' Z13.07! Z13.63!CAR006! 2! 427.70' Z27.46! Z27.94! 413.44' Z12.99! Z13.88!CAR008! 4! 427.43' Z27.36! Z27.47! 414.19' Z12.49! Z15.87!CAR010! 1! 427.24' Z27.24! Z27.24! 410.75' Z10.75! Z10.75!CAR013! 2! 427.35' Z27.33! Z27.37! 411.90' Z11.89! Z11.90!CAR015! 2! 426.78' Z26.76! Z26.80! 48.41' Z8.22! Z8.60!CAR016! 1! 427.51' Z27.51! Z27.51! 414.47' Z14.47! Z14.47!CAR017! 2! 428.47' Z28.32! Z28.62! 419.41' Z19.33! Z19.48!CAR019! 2! 427.00' Z26.95! Z27.06! 412.16' Z12.01! Z12.30!CAR020! 2! 427.12' Z27.06! Z27.19! 418.20' Z18.15! Z18.25!CAR021! 2! 427.28' Z27.10! Z27.46! 48.46' Z8.38! Z8.54!CAR022! 2! 427.26' Z27.12! Z27.40! 411.29' Z11.08! Z11.49!Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 8&CAR023! 4! 426.45' Z26.22! Z26.69! 49.00' Z8.79! Z9.17!CAR024! 1! 427.05' Z27.05! Z27.05! 410.73' Z10.73! Z10.73!CAR028! 2! 427.00' Z26.95! Z27.04! 49.42' Z9.40! Z9.43!CAR029! 2! 425.13' Z25.12! Z25.15! 48.95' Z8.72! Z9.19!CAR031! 2! 424.74' Z24.71! Z24.77! 46.32' Z6.27! Z6.36!MTB001! 1! 428.74' Z28.74! Z28.74! 416.40' Z16.40! Z16.40!Fleet'average' 427.27' Min:!Z28.74! Max:!Z24.77! 412.46' Min:!Z19.33' Max:!Z6.36'Standard'Deviation' 0.93! ' ' 3.45! ' '(a)This!vehicle,!built!in!1954,!has!no!catalytic!converter!only!a!muffler!(all!other!cars!are!age!1988!or!younger!and!have!catalytic!convertors).!!Diesel exhaust The!fleet!average!for!diesel!vehicles!exhibited!a!slightly!lower!δ13C!of!Z28.81!(±0.40)!‰!and!s!substantially!lower!δ18O!of!Z18.63!(±0.72)!‰!(Table!3).!Table'3:!The!average,!maximum,!and!minimum!values!obtained!from!exhaust!sampling!for!diesel!vehicles!w.r.t.!VPDZCO2.!The!‘number!of!replicates’!refers!to!the!number!of!bags!analyzed!from!this!particular!vehicle.!Based!on!individual!vehicles,!the!fleet!total!average!δ13C!and!total!average!δ18O,!as!well!as!the!standard!deviation!for!δ13C!and!δ18O!are!noted!at!the!bottom!of!the!table.!Vehicle!ID! Number!of!Replicates! Average!of!corrected!end!member!δ13C!(‰)!Max!of!corrected!end!member!δ13C!(‰)!Min!of!corrected!end!member!δ13C!(‰)!Average!of!corrected!end!member!δ18O!(‰)!Max!of!corrected!end!member!δ18O!(‰)!Min!of!corrected!end!member!δ18O!(‰)!BUS001! 2! 428.94' Z28.87! Z29.00! 418.00' Z17.92! Z18.08!BUS002! 2! 428.23' Z28.13! Z28.34! 417.61' Z17.52! Z17.71!BUS003! 2! 428.81' Z28.74! Z28.88! 418.11' Z18.01! Z18.21!BUS004! 2! 428.48' Z28.45! Z28.51! 417.51' Z17.50! Z17.53!CAR007! 4! 428.56' Z28.48! Z28.71! 418.70' Z18.55! Z18.86!CAR009(a)! 2! 427.95' Z27.83! Z28.07! 419.04' Z18.90! Z19.19!CAR011! 1! 429.29' Z29.29! Z29.29! 419.15' Z19.15! Z19.15!CAR012! 2! 429.09' Z29.07! Z29.12! 418.28' Z18.25! Z18.32!CAR014! 2! 428.77' Z28.77! Z28.77! 418.77' Z18.76! Z18.79!CAR018! 2! 429.00' Z28.85! Z29.16! 419.90' Z19.82! Z19.98!CAR025! 2! 429.21' Z29.17! Z29.25! 419.64' Z19.47! Z19.80!CAR026! 2! 429.17' Z29.11! Z29.22! 418.73' Z18.70! Z18.76!CAR027! 2! 429.08' Z29.07! Z29.09! 418.79' Z18.75! Z18.82!Fleet'average' 428.81' Min:!Z27.83! Max:!Z29.29! 418.63' Min:!Z17.50' Max:!Z19.98'Standard'Deviation' 0.40! ' ' 0.72! ' '(a)Vehicle!fueled!with!‘biodiesel’!that!contains!up!to!5%!bioethanol! !Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 9&Natural gas exhaust For!natural!gas,!the!average!δ13C!value!was!Z41.64!(±0.82)‰,!while!the!average!δ18O!value!was!Z22.74!(±0.56)‰.!The!results!show!that!there!is!little!change!in!the!isotopic!composition!of!natural!gas!over!the!duration!of!observations.!Table'4:!The!average,!maximum,!and!minimum!values!obtained!from!exhaust!sampling!for!natural'gas'exhaust!samples!w.r.t.!VPDZCO2.!The!‘number!of!replicates’!refers!to!the!number!of!bags!analyzed!from!this!particular!vehicle.!Based!on!individual!vehicles,!the!fleet!total!average!δ13C!and!total!average!δ18O,!as!well!as!the!standard!deviation!for!δ13C!and!δ18O!are!noted!at!the!bottom!of!the!table.!Sample!ID! Number!of!Replicates! Average!of!corrected!end!member!δ13C!(‰)!Max!of!corrected!end!member!δ13C!(‰)!Min!of!corrected!end!member!δ13C!(‰)!Average!of!corrected!end!member!δ18O!(‰)!Max!of!corrected!end!member!δ18O!(‰)!Min!of!corrected!end!member!δ18O!(‰)!NG002! 2! 442.22' Z42.19! Z42.25! 423.41' Z23.39! Z23.42!NG003! 1! 441.75' Z41.75! Z41.75! 423.43' Z23.43! Z23.43!NG004! 2! 441.48' Z41.42! Z41.54! 423.09' Z22.93! Z23.25!NG005! 1! 441.18' Z41.18! Z41.18! 423.25' Z23.25! Z23.25!NG006! 1! 441.46' Z41.46! Z41.46! 423.34' Z23.34! Z23.34!NG007! 2! 440.38' Z40.34! Z40.42! 422.27' Z22.20! Z22.34!NG008! 2! 439.98' Z39.92! Z40.03! 421.90' Z21.74! Z22.06!NG009! 1! 440.37' Z40.37! Z40.37! 421.68' Z21.68! Z21.68!NG010! 2! 441.88' Z41.82! Z41.94! 423.22' Z23.14! Z23.31!NG011! 1! 442.30' Z42.30! Z42.30! 422.47' Z22.47! Z22.47!NG012! 2! 442.46' Z42.44! Z42.48! 422.76' Z22.75! Z22.76!NG013! 2! 441.92' Z41.92! Z41.92! 422.18' Z22.12! Z22.24!NG014! 2! 442.35' Z42.33! Z42.36! 422.62' Z22.52! Z22.73!NG015! 2! 442.31' Z42.17! Z42.46! 422.89' Z22.55! Z23.24!NG016! 2! 442.48' Z42.46! Z42.51! 422.85' Z22.84! Z22.85!Average' 441.64' Min:!439.92! Max:!Z42.51! 422.74' Min:!Z21.68' Max:!Z23.43'Standard'Deviation' 0.82! ' ' 0.56! ' '' !Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 10&Conclusions The!variation!of!δ13C!values!of!all!three!fossil!fuel!types!are!relatively!narrow!and!depend!on!fuel!type!(see!Figure!4).!In!contrast,!the!δ18O!values!vary!significantly!for!gasoline!likely!due!to!types!and!efficiency!of!convertors!(Schumacher!et!al.,!2011).!The!δ18O!values!for!CAR003!(no!converter),!CAR017,!CAR020,!and!the!motorbike!(MTB001)!are!clearly!lower!than!the!rest!of!the!fleet!and!comparable!to!the!values!obtained!from!diesel!vehicles!and!predicted!for!unfractionated!combustion!(δ18O!!=!Z17‰,!Schumacher!et!al.,!2011).!For!both,!δ13C!and!δ18O,!natural!gas!is!well!separated!from!diesel!and!gasoline,!although!it!is!currently!unclear!why!δ18O!is!significantly!lower!that!the!unfractionated!prediction.!Schumacher!et!al.,!2011!suggest!that!fires!with!an!unlimited!O2!availability!such!as!the!current!gas!torch,!could!also!include!a!diffusive!step!in!the!supply!of!oxygen!which!might!question!the!unfractionated!prediction!and!lower!δ18O!of!the!produced!CO2.!!Figure'4:!All!samples!in!δ13C!vs.!δ18O!space.!Samples!shown!are!corrected!for!background!air!influence.!Analytical!errors!were!reduced!by!only!accepting!samples!which!met!the!strict!standards!imposed!during!the!analysis!such!as!the!required!reproducibility!of!the!2!cycles.!However,!it!is!possible!that!errors!may!still!have!been!introduced!during!the!sampling!and!dilution!process.!Occasionally!small!amounts!of!Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 11&water!would!condense!in!the!sampling!tube,!which!may!have!caused!temporary!H2OZCO2!isotope!exchanges.!Urban!atmospheric!CO2!originates!from!numerous!sources,!one!of!which!being!the!combustion!of!fossil!fuels.!By!utilizing!the!isotopic!signatures!of!CO2!reported!here,!the!degree!to!which!different!sources!contribute!to!the!overall!abundance!could!be!examined!using!mixing!models.!This!study!determined!the!typical!isotopic!composition!of!CO2!emitted!from!gasoline!burning!vehicles,!diesel!burning!vehicles,!and!natural!gas!burning!in!Vancouver,!BC,!between!November!2013!and!May!2014.!For!a!complete!picture,!source!characteristics!for!soil,!plant!and!human!respiration!are!needed!and!reported!in!a!different!study.!References Bush,!S.!E.,!Pataki,!D.!E.,!Ehleringer,!J.!R.(2007):!‘Sources!of!variation!in!delta!CZ13!of!fossil!fuel!emissions!in!Salt!Lake!City,!USA’.!Applied&Geochemistry22,!715–723.!Christen!A.!(2014):!‘Atmospheric!measurement!techniques!to!quantify!greenhouse!gas!emissions!from!cities’.!Urban&Climate,!10.1016/j.uclim.2014.04.006.!Coplen,!T.B.!(1995):‘Reporting!of!stable!carbon,!hydrogen,!and!oxygen!isotopic!abundances,!in!Reference!and!intercomparison!materials!for!stable!isotopes!of!light!elements’.!Vienna,!International!Atomic!Energy!Agency,!IAEAZTECDOCZ825,!p.!31Z34.!!Djuricin,!S.,!Pataki,!D.!E.,!Xu,!X.(2010):!‘A!comparison!of!tracer!methods!for!quantifying!CO2!sources!in!an!urban!region.’J.&Geophys.&Res.115.!Pataki!D.E.,!Bowling!D.R.,!Ehleringer!J.R.!(2003):‘The!seasonal!cycleof!carbon!dioxide!and!its!isotopic!composition!in!an!urban!atmosphere:!anthropogenic!and!biogenic!effects’.!Journal&of&Geophysical&Research,!108,!4735.!Popa!M.!E.,!Vollmer!M.!K.,!Jordan!A.,!Brand!W.!A.,!Pathirana!S.!L.,!Rothe!M.,$Röckmann$T.$(2014):‘Vehicle!emissions!of!greenhouse!gases!and!related!tracers!from!a!tunnel!study:!CO!:!CO2,!N2O!:!CO2,!CH4!:!CO2,!O2!:!CO2!ratios,!and!the!stable!isotopes!13C!and!18O!in!CO2!and!CO.’,&Atmos.&Chem.&Phys.,!14,!2105–2123,!2014!!Schumacher!M.,!Werner!R.!A.,!Meijer!H.!A.J.,!Jansen!H.!G.,!Brand!W.!A.,!Geilmann!H.,!and!Neubert!R.!E.!M.!(2011):!'Oxygen!isotopic!signature!of!CO2!from!combustion!processes.',!Atmos.&Chem.&Phys.,!11,!1473–1490,!2011!!!!  Semmens&et&al.&–&Isotopic&composition&of&CO2&from&fossil&fuel&exhaust&in&Vancouver,&BC& 12&Appendix - Sampled vehicles ! Car'ID' Fuel'type' Vehicle'manufacturer'model' Year'built' Date'samples'taken'BUSZ01! Diesel! (TranslinkPassenger!Bus)' 2009! 2014Z04Z25!BUSZ02! Diesel! (TranslinkPassenger!Bus)' 1998! 2014Z04Z25!BUSZ03! Diesel! (TranslinkPassenger!Bus)' 2009! 2014Z04Z25!BUSZ04! Diesel! (TranslinkPassenger!Bus)' 2000! 2014Z04Z25!CAR001! Gasoline! Dodge!Caravan' 2006! 2013Z11Z12!CAR002! Gasoline! Toyota!Tacoma' 2006! 2013Z11Z12!CAR003! Gasoline! Ford!FZ100!pickup!' 1954! 2013Z11Z12!CAR004! Gasoline! Mazda!Protoge!5' 2002! 2013Z11Z13!CAR005! Gasoline! Volvo!V50' 2006! 2013Z11Z13!CAR006! Gasoline! Toyota!Prius' 2010! 2013Z11Z14!CAR007! Diesel! Ford!FZ350' ! 2013Z11Z19!CAR008! Gasoline! Dodge!Caravan' 2006! 2013Z11Z19!CAR009! Biodiesel! Dodge!Sprinter' ! 2013Z11Z19!CAR010! Gasoline! Ford!transit' ! 2014Z02Z14!CAR011! Diesel! –' 2006! 2014Z02Z14!CAR012! Diesel! RTV900' 2008! 2014Z02Z14!CAR013! Gasoline! Ford!Transit' 2013! 2014Z02Z14!CAR014! Diesel! Dodge!Sprinter' 2006! 2014Z02Z14!CAR015! Gasoline! Ford!Transit!' 2010! 2014Z02Z14!CAR016! Gasoline! Honda!Civic' ! 2014Z03Z07!CAR017! Gasoline! Chevrolet!1!ton!Cube' 1994! 2014Z03Z14!CAR018! Diesel! GMC!W4500' ! 2014Z03Z14!CAR019! Gasoline! Chevrolet!1!ton!Cube' 1994! 2014Z03Z14!CAR020! Gasoline! Chevrolet!1!ton!Cube' 1994! 2014Z03Z14!CAR021! Gasoline! Ford!Transit!Connect' 2010! 2014Z03Z14!CAR022! Gasoline! Ford!FZ450!' ! 2014Z03Z14!CAR023! Gasoline! Toyota!Tundra' 2014! 2014Z03Z14!CAR024! Gasoline! Chevrolet!SZ10' 1993! 2014Z03Z21!CAR025! Diesel! Mercedes!Sprinter!Bluetech!2500' 2000! 2014Z03Z21!CAR026! Diesel! Dodge!Sprinter!3599' 2000! 2014Z03Z21!CAR027! Diesel! Ford!LCF' ! 2014Z03Z21!CAR028! Gasoline! Chevrolet!SZ10' 1993! 2014Z03Z21!CAR029! Gasoline! Ford!Ranger' 2005! 2014Z05Z05!CAR030! Gasoline! Mazda!3' 2012! 2014Z05Z05!CAR031! Gasoline! Toyota!RAV!4!' 2008! 2014Z05Z05!MTB001! Gasoline! Triumph!Street!Triple!2012!(Motorbike)' 2012! 2013Z11Z13!!

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