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Applicationsofcavityring-downspectroscopy(CRDS)inatmosphericchemistryAndrewJ.Orr-EwingBristol,UnitedKingdomScotlandEnglandWalesBristolUniversityofBristolBristolCliftonSuspensionBridge1836-1864Overview•Absorptionspectroscopy•Principlesofcavityring-downspectroscopy•Applicationsinatmosphericchemistry•Sensingoftraceconstituents(C2H2,NO2,IO)•Aerosolparticles•Molecularphotochemistry4.3mm15mmBendingVibrationl=15mmAsymmetricStretchl=4.3mm1.AbsorptionspectroscopyCO2sensorAbsorptionspectroscopyI0IBeer-LambertLaw:I=I0exp{s[X]}Samplewithconcentration[X]•Trapapulseoflightbetweentwohigh-reflectivitymirrors•Placethegassamplebetweenthemirrors(inthecavity)•Measurethelifetimeofthelightpulseinthecavity–dependsonconcentrationofsample2.Cavityring-downspectroscopyApplicationsofCRDS•AtmosphericChemistry•Tracegassensing•Isotopologueratios•Aerosolopticalproperties•Photochemistry•Otherresearchfields•Chemistryofplasmasandflames•Breathanalysis(medicaldiagnosis)•Astrochemistry•etc.DiamondCVDplasmaEaglenebulaAnalysisofbreathsamples•Volatilecomponentsofhumanbreathcontainsignaturesofavarietyofmedicalconditions.•Non-invasivemethodofdiagnosis.•Currentmedicalpracticeinvolvesbagcollection,pre-concentrationofsamplesandanalysisbygaschromatography.•Laserspectrometersoffercheaper,fasteralternatives.•Examples:NO,ethane,13CO2CO2isotopologueanalysis•Helicobacterpyloriisleadingcauseofduodenalandgastriculcers•ItconvertsureatoHCO3-whichisexhaledasCO2•Ingestionof13C-labelledureaistestforH.pylori•Measure13CO2/12CO2•CRDSgivesd13C(relativetostandard)withprecisionof0.2‰Crossonetal.,Anal.Chem.74,2003(2002)Wavenumber/cm-1Cavityring-downspectroscopyLdcs]X[011Foranemptycavity:Withanabsorber:R10cL(R)ring-downbuild-upPZTvoltageTEM00modesForR=0.9999andL=50cm:TEM00modespacing=300MHzCavitymodeFWHM=10kHzDiodelaserbandwidth~1MHzCavitymodesc/2L3.TheEarth’satmosphereOzonelayerSept2005ChemistryinthetroposphereNO2VOCsparticulatesSO2N2OOVOCsChemistrystudiedbyCRDS•Radicalphotochemistryandreactionkinetics:ClO,IO,FCO•HCHOphotochemistryandquantumyields•Absorptioncrosssectionsathighresolution:O2,IO,NO2,Volatileorganiccompounds•Effectsofpressurebroadening•Tracedetection–CH4,C2H2,C2H4,NO2,IOandVOCs•Atmosphericaerosolparticles4.Diode-lasertracegassensors•Distributedfeedback(DFB)andexternalcavitydiodelasersavailableinnear-IRandvisible•Outputpowers~1–10mW•Bandwidths~1MHz2n3bandat1.65mm•Pressurebroadeninginairdegradessensitivity•Detectionlimit~25ppbvwith=9.0ms•ForotherVOCs,detectionlimitsarehigherandmixingratiosarelower50mTorrof1%CH4inAr3.2ppmvCH4inlabairMeasurementofatmosphericCH4DetectionofatmosphericC2H2+•AtmosphericC2H2hasmostlyanthropogenicsources•Atmosphericlifetimes~daystoweeks•Tracerforpollutedairmasses•Mixingratios0.8–2.5ppbvinruralareas•MonitorviaP(17)lineofn1+n3bandat1535.393nm•CRDSdetectionlimitin1atmair~2.5ppbv(=14ms)•Limitingabsorptioncoefficient:•AllanVarianceanalysistooptimizeaveraging;•Pressurebroadening(g=0.073cm-1atm-1)–workatreducedsamplepressure;•Trappingandpre-concentration(25)ofC2H2fromair;•DetectionlimitforC2H2is8pptv.CRDSdetectionlimits0min0mincdL19min0mincm1090.1%08.0Allanvarianceanalysis212212AAAsABcwCRDSapparatusTestsofcwCRDSmeasurements•ApelReimerstandardmixtureof75VOCs(C2–C11)•ComparisonofcwCRDSandGC-FIDforindoorairsamplecwCRDS8.60.6ppbvManufacturer8.70.05ppbvM.Pradhanetal.,Appl.Phys.B90,1(2008)cwCRDS3.87±0.22ppbvGC-FID3.90±0.23ppbvMonitoringC2H2inlabairWednesday09/04/08Sunday06/04/08MonitoringatmosphericC2H2Isotopologuemeasurements•Measured13CforC2H2incigarettesmoke(atestsource)•UseH13C12CHandH12C12CHabsorptionlines•R=13C/12C•RVPDB=0.01117973131012dVPDBRRCExtensiontothemid-IR•Strongfundamentalvibrationaltransitionsinmid-IR•DifferencefrequencygenerationinPPLNwaveguide•200mWatawavelengthof3.2mm•12%W-1conversionefficiencySpectraobtainedwithDFGsystemWavelengthmodulationspectraof1.1%C2H4/Arin15-cmlongcellNO2measurements•NO2formsinpollutedtroposphereandproducesozone•[NO2]100pptinremotesitesand5ppbinurbanairM.Mazurenkaetal.,Chem.Phys.Lett.367,1(2003)andAppl.Phys.B81,135(2005)NO2absorptionspectruminthevisibleregionAtmosphericNO2•Ring-downsystemhas=32.5ms•DetectionlimitforNO2is~100pptv(in~50s)•1mmteflonfilterininlettoremoveaerosolsR.Wadaetal.,Analyst130,1595(2005)NO2measurementsinBristolair25March2005R.Wadaetal.,Analyst130,1595(2005)11:0012:0013:0014:0015:0016:0017:0018:0005101520253035[NO2]/ppbvTimeofdayComparisonofCRDSwithchemiluminescenceanalyserIodinemonoxideinmarineairl~437nm•SeaweedsreleaseI2andalkyliodideswhichoxidizetoIO•IO(16ppt)identifiedatcoastalsitesbylong-path(4km)DOAS•Localizedmixingratiosmaybe~60-100pptv.•Fora32msring-downtime,[IO]min=7x107cm-3(3pptv).PulsedlaserCRDSapparatusdeployedinRoscofftomeasureatmosphericIO.IntercomparisonwithDOASandLIF/FAGEinstruments.RHaMBLecampaignSept2006RHaMBLecampaignSept2006DrRyuichiWadaRoscoffIOmeasurementsbyCRDSElevatedconcentrationsofIOradicals(upto50pptv)causeburstsofiodineoxideaerosolparticles.8thSeptember200625thSeptember2006●MeasuredIO○Detectionlimit5.Optica
本文标题:Cavity-Ring-Down-Spectroscopy-腔衰荡光谱
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