the ‘next generation’ aethalometer model ae33 - magee ......magee scientific and aerosol co. are...

The‘Next‐Generation’Aethalometer®

ModelAE33

www.mageescientific.com

Berkeley,LjubljanaJuly2014

©MageeScientific,2014www.mageescientific.com Page1

The‘Next‐Generation’Aethalometer®ModelAE33

SummaryThenewmodelAE33Aethalometerisaveryconsiderableimprovementandmodernizationoftheexistingwell‐provenandruggeddesign.Theenhancedfeaturesinclude:

Patented‘DualSpot’technologyeliminatesthedataartifactduetofilterloading. Analysisatmultiplewavelengthsidentifiesbiomassemissions. Timeresolutionasrapidas1secondpermitsstudiesofemissionsources. SamplecollectiononTeflon‐coatedglassfiberfiltertapereducestheeffectsof

varyingRelativeHumidity(air‐conditionerperturbations). Automaticflowcalibrationprocedureusingexternalstandardensuresaccuracy. Built‐in‘zero’testfrominternalclean‐airsourcechecksleakageandnoise. ‘Span’testofopticaldetectorsusingexternalstandardsvalidatesperformance. Networkconnectionprovidesremoteaccess,operationanddataretrieval. Front‐panelUSBportsprovidelocaldownloadwithoutinterruptionofdata. Lowpowerconsumption(25W)permitsoff‐griduse. Completelyautomaticoperationuponpower‐upprovidescontinuity. Hermeticsealspreventingressofdustandmoisture. DirectcouplingtoCO2sensor(optionalaccessory)integratesBCandCO2data. Directcouplingtometeorologysensor(optionalaccessory)reportsP,TandRH,

permitscalculationofBCconcentrationdataunder‘local’conditions.


The‘Next‐Generation’Aethalometer®ModelAE33

Magee Scientific and Aerosol Co. are pleased to announce the ‘Next Generation’Aethalometer®, Model AE33. This development incorporates scientific and technicaladvances designed to offer improved measurement performance, user features,communications and interface, and the ability to perform routine performance tests toverifycorrectoperation. Mostimportantly,thenewinstrumentincorporatesthepatentedDualSpot™measurementmethod.Thisprovidestwosignificantadvantages:eliminationofthechanges inresponsedueto ‘aerosol loading’effects;andareal‐timecalculationof the‘loadingcompensation’parameterwhichoffersinsightsintoaerosolopticalproperties,andhasbeeninterpretedinmodelsofaerosoloriginsandaging.The Model AE33 Aethalometer has been developed with input from the research andmonitoringcommunities,andisdesignedforreliableoperationunderallconditionsrangingfromstate‐of‐the‐artresearchtocompliancemonitoring.TheleadinginnovationsincorporatedintotheModelAE33include:

1. TheDualSpot™measurementmethod,whichsolvestheeffectscommontoallfilter‐based real‐time monitors, in which the instrumental response factor shows adependenceontheloadingofmaterialonthefilter.

2. Features forautomatic ‘dynamiczero’ testingundera flowof internally‐generated

clean air; ‘span’ testing of the response of the optical sources and detectors;calibrationoftheresponseoftheinternalmassflowmeters,ifanexternalstandardflowcalibratorisconnected;andvalidationofthephotometricresponsebyuseofakitof ‘NeutralDensity’optical filterswhosepropertiesmaybetracedtoreferencestandards.

3. User and communications interfaces, permitting remote monitoring of operation;

data retrieval; performance of internal tests; and reporting of ‘state‐of‐health’parameters.

4. Modularconstructiondesignedforeaseofroutinemaintenanceservice.

In addition to the above new features, the Model AE33 Aethalometer offers real‐timeaerosolabsorptionanalysisatsevenopticalwavelengths,withtimeresolutionto1second.Thispermitsthemeasurementofoptically‐absorbingaerosols–‘Black’Carbonand‘Brown’Carboncomponentsofparticulatematter–inapplicationsincludingroutinemonitoringofambient air quality for regulatorypurposes;measurements of the concentration ofBC inurban,suburban,regional,ruralandremotelocations;sourcetesting;andlaboratory‐basedresearch.


1. ‘DualSpot™’technologyTheModelAE33AethalometerusesthepatentedDualSpot™methodtocompensateforthe‘spot loading effect’; and also toprovide a real‐timeoutput of the ‘loading compensation’parameter, which may provide additional information about the physical and chemicalpropertiesoftheaerosol.

The‘spotloadingeffect’isavariablephenomenonwhichappearsasagradualreductionofinstrumentalresponseastheaerosoldepositdensityofthefiltertapeincreasesfromzeroto thepredetermined limitof ‘MaximumAttenuation’. Whenthe filter tapeadvances toafresh spot, the data undergoes a discontinuous jump from its previous lower value,calculatedwhenthespotwasheavilyloaded;toahighervalue,calculatedfromcollectionona fresh spot at zero loading. In the Aethalometer the reduction of data at increasingloadingsiswelldescribedbya linearfunctionofattenuation,but itsmagnitudecannotbepredicted: some aerosols in some locations in some seasons may show a small or zero‘loading effect’; while under other conditions, the effect may be larger and noticeable.Empirically,itisfoundthatfresheraerosolsclosertotheircombustionsourceswillshowalarger ‘spotloadingeffect’;whilewell‐agedaerosolsunderatmosphericconditionsofhighchemical activity andoxidative processingmay showan almost zero effect. The effect isrevealed statistically by processing data collected over a large number of tape advances,representingmanydatapointscollectedatloadings(‘ATNvalues’)rangingfromzerotothepresetmaximum.Thedataiscollectedintobinsaccordingtoloading(attenuation,ATN).Ifthereisasystematicreductionofthecalculatedresultasafunctionofloading,thedatawillshowaclearnegativeslope,withtheinterceptrepresentingthe‘zeroloading’value.Figure1illustratestwodatasetsfromurbanlocationswithloadingeffectseitherpresentornot.

Figure1:Aethalometerdatasortedandaveragedaccording to loading (attenuation,ATN)onspot.Left:roadsidelocationinLondon,UK;right:urbansiteinBoston(Roxbury),USA.

The London data show a systematic reduction at increasing loadings;while the Roxburydata do not. This demonstrates that any method intended to compensate for the ‘spotloadingeffect’mustbeauto‐adaptiveandabletoadjustdynamicallytodifferentsituations.An instrument based on firmwarewith a fixed ‘loading non‐linearity’ parameterwill notoperatecorrectlyatalllocations.The‘loadingnon‐linearity’parametermustbemeasured.

London Oct-Dec 2006

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It is clear that the effect, when present, is linear with loading (‘ATN’). This can berepresentedas

BC(reported)=BC(zeroloading)*{1‐k·ATN}

whereBC (zero loading) is the desired ambient BC value that would be obtained in theabsence of any loading effect; and k is the ‘loading compensation parameter’ (similar toVirkkulaetal.,2007).Theanalysisofalargenumberofdatasetsfromawidevarietyoflocationsshowsthatthisrelationship is linear in all cases studied; but with different values of k. It is thereforepossible to eliminate the ‘loading effect’ of k by making two simultaneous identicalmeasurementsBC1andBC2atdifferentdegreesofloadingATN1andATN2.

BC1=BC*{1‐k·ATN1}BC2=BC*{1‐k·ATN2}

Fromthesetwolinearequationswemaycalculatethe‘loadingcompensationparameter’k;andthedesiredvalueofBCcompensatedbacktozeroloading.TheModel AE33Aethalometer analyzes theBlack Carbon component of aerosols on twoparallel spots drawn from the same input stream, but collected at different rates ofaccumulation,i.e.atdifferentvaluesofATN.Bycombiningthedataaccordingtotheaboveequations,theAE33yieldsthevalueofBCextrapolatedbackto‘zeroloading’;aswellasareal‐timeoutputofthe‘loadingcompensationparameter’kwhichprovidesinsightsintotheaerosol nature and composition (see Figure 8 below). This process is performed in realtimeforallwavelengths:examinationofthe‘k’valuesasafunctionofwavelengthprovidesfurther information about the aerosol composition. An example of the real‐time loadingcompensationprocessisshowninFig.2forextremeconcentrationsofblackcarbon.

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Figure2:Thetime‐seriesofAE33rawandcompensatedBCconcentrationswith1secondtimebase–notetheextremeconcentrationsandloadingeffects.


Note that ‘spot loading effects’ are also exhibited by other filter‐based BC‐measuringinstruments(Kanayaetal.,2008;Virkkula,2010;Hyvärinenetal.,2013).Publishedresultsshowthat theeffect isnot linearandconsequentlynot readilyamenable tomathematicalcompensationwithoutmakingassumptionsaboutthenatureoftheaerosol.DatafromonesuchinstrumentisobservedtosaturateatBCconcentrationsabove~7 g/m3(Kanayaetal.,2008).andexhibitjumpsattapeadvances(Hyvärinenetal.,2013).

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Figure3:Loadingeffectinanotherfilter‐basedBC‐measuringinstrument.Datasortedandaveraged according to cumulative loading on spot; 1month of data from the eastern US(top),and1weekofdatafromnorthernEurope(bottom).


2. UserandCommunicationsInterfaces

TheModelAE33Aethalometer incorporates the followinguser,dataandcommunicationsfeatures:

Largecolorgraphicstouch‐screenfordatadisplayandlocaluserinterface; USBportsforinsertionofamemorystickforlocaldatadownload; USB ports for connection of a keyboard, if necessary for initial setup of

parameters,suchasstationidentification; RS‐232COMportfordatatransmissiontodigitaldatalogger; Ethernetportforfullnetworkaccessandcontrol,including

i. Remotedataacquisition,eitherbatchorstreamingii. Remoteretrievalofinstrumentstatusandstate‐of‐healthiii. Remotecontrolofinstrumentoperatingparameters

3. ModularConstruction

TheModelAE33Aethalometerisconstructedwithamodulardesign,sothatsub‐unitsmaybeeasilyserviced.Theonlyitemrequiringattentioninroutineuseiscleaningoftheopticalinsert toremoveaccumulateddustorothercontaminationwhichmaybebrought inwiththe sample air stream. The optical chamber is attachedwith a bayonet fitting for quickremoval; easy cleaning; and reliable re‐assembly. The entire instrument is hermeticallysealedtoreducetheentryofdustandmoisture.


4. AutomaticZeroandSpan

ZeroTheModelAE33Aethalometeroffersthecapabilityforautomaticallycheckingthe‘zero‐air’responseoftheinstrumentunderdynamicaloperatingconditions.Thistestisimplementedby back‐flushing the inlet connection with an excess flow of internally‐filtered air andcirculating the filtered air in the instrument. The data reported during this period areanalyzed for themeanvalue and thepoint‐to‐point variation. Themeanvalue shouldbeclose to zero under ideal conditions; any positive value greater than zero represents theleakageofBC‐containingroomairintotheinstrument’sanalyticalzone.Thepoint‐to‐pointvariation represents the instrument’s measurement noise level under actual operatingconditionsofactualflow–i.e.,a‘dynamic’test.Thepoint‐to‐pointvariationwhenthetime‐baseissettoonesecondis60timeslargerthantheone‐minutevariation.Intheexampleshownbelow,aone‐secondnoise levelof125ng/m3 is equivalent toonly2ng/m3whenaverageduptoone‐minutetimeresolution.

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131 ng/m3 119 ng/m3

Point-to-point variation @ 1 second:

126 ng/m3

Figure4:‘Zero‐air’check.TheModelAE33Aethalometerswitchesfromsamplingambientairtofilteredair.One‐seconddatais60timesnoisierthantheone‐minuteaverage.


SpanTheresponseoftheopticaldetectorsoftheModelAE33AethalometermaybeverifiedbyuseofakitofNeutralDensityoptical filtersasshowninFigure5below. Theseareglasselementswitha rangeofknownandstableopticalabsorptions, from light todark,whichare traceable from manufacturing records back to primary standards. When these areinserted into theAE33Aethalometer, thephotodetectorswillgiveacertainoutputsignal.The stability and reproducibility of the relationship between optical signal andND Filterdensity fromonevalidation test to another; and the comparisonwith theoriginal factoryvalues;isameasureoftheconsistencyofperformanceoftheinstrument’soptics.

Figure5: Optical ValidationKit consisting of traceable standardNeutralDensityOpticalFilters,whichareinsertedintotheAE33opticalpathtodeterminethereproducibilityoftherelationshipbetweenLEDopticalsourceintensityanddetectorresponse.


5. SummaryandIllustrations

ThenewmodelofAethalometer,theAE33,isaveryconsiderableimprovementandmodernizationoftheexistingwell‐provenandruggeddesign.Theenhancedfeaturesinclude:

a) Patented‘DualSpot’technologytoeliminatethedataartifactduetofilterloading.i. SeeFigure2above.

b) Analysisatmultipleopticalwavelengthswithtimeresolutionasrapidas1second(usefulfordirectcombustionstudies).

ii. SeeFigure2above,showing1‐Hzdata.c) SamplecollectiononTeflon‐coatedglassfiberfiltertape,toreducetheeffectsonthe

opticalanalysisofvaryingRelativeHumidity(air‐conditionerperturbations).iii. SeeFigure6below.

d) Instrumentishermeticallysealedtopreventingressofdustandmoisture.e) Built‐insoftwareanalyzesthemulti‐wavelengthdata,toprovidereal‐timesource

apportionmentoftheBCattributedtodieseloroilcombustion;versustheBCattributedtobiomassburning.

iv. SeeFigure7belowforscientificdataexample.v. SeeFigure8belowforscreendisplayexample

f) CapabilityofdirectcouplingtoCO2sensor(optionalextraaccessory),withintegrationofBCandCO2data.Thispermitsdirect,real‐timedeterminationoftheEmissionFactorofBCduringcombustion.

vi. SeeFigure9below.g) CapabilityofdirectcouplingtometeorologysensorforP,TandRH(optionalextra

accessory),withintegrationofdatah) Built‐in‘zero’testfrominternalclean‐airsource.

vii. SeeFigure4above.i) Optionalverificationtestofopticaldetectors,usingexternally‐insertedoptical

standards.viii. SeeFigure5above.

j) Networkconnectionforremoteaccess,operationanddataretrieval.Localdatadownloadfromfront‐panelUSBports.RearpanelCOMports.Colortouch‐screenuserinterface.

k) Lowpowerconsumption(25W),automaticoperationuponpower‐up.Maybeoperatedatremotesitesfromoff‐gridinverter,batteries,and/orsolarpanels.


Figure6:PerturbationofdatainducedbyfluctuationinroomairRelativeHumiditywhensubject to anon‐off cycling air‐conditioner. “Legacy” instrumentsusingquartz fiber tapeshow large perturbation,while the effects on the AE33 are greatly reduced. However, aSampleStreamDryer(optionalaccessory)isrecommendedforbestresults.

Figure 7: Example of analysis of multi‐wavelength data to determine the ‘AngstromExponent’ of optical absorption by ambient aerosols, and separate the total BC intocontributionsfrom“traffic”versus“biomasssmoke”,accordingtothemodelofSandradewietal.,2008.


Figure8:AE33displayscreenshowingspectraldataanalysisrepresentedasaPercentageoftotalBCattributabletobiomassburning

Figure9: Highly‐correlatedBCandCO2data from integratedsensorwithcombineddatastream. Thecorrelationspermitadeterminationof theBCEmissionFactorof thesourcecreatingthetransientplume.


6. References

Hyvärinenetal.,2013,CorrectionforameasurementartifactoftheMulti‐AngleAbsorptionPhotometer(MAAP)athighblackcarbonmassconcentrationlevels,Atmos.Meas.Tech.,6,81‐90.

Kanayaetal.,2008,MassconcentrationsofblackcarbonmeasuredbyfourinstrumentsinthemiddleofCentralEastChinainJune2006,Atmos.Chem.Phys.,8,7637–7649.

Sandradewietal.,2008,Usingaerosol lightabsorptionmeasurementsforthequantitativedetermination of wood burning and traffic emission contributions to particulate matter,Environ.Sci.Technol.,42,3316–3323.

VirkkulaA.etal.,2007,ASimpleProcedureforCorrectingLoadingEffectsofAethalometerData,J.Air&WasteManage.Assoc.,57,1214–1222.

Virkkula A., 2010, Correction of the Calibration of the 3‐wavelength Particle SootAbsorptionPhotometer(3λPSAP),AerosolSci.Tech.,44,706‐712.


7. Contactwww.mageescientific.comwww.aerosol.siInEurope,Asia,andAfrica,pleasecontact:Aerosold.o.o.,Kamniška41,SI‐1000Ljubljana,Slovenia,EUtel:+38659191220fax:+38659191221IntheUS,pleasecontact:MageeScientificCorporation,1916AM.L.KingJr.Way,BerkeleyCA94704,USAtel:+15108452801fax:+15108457137orthedistributorresponsibleforyourcountry.

www.mageescientific.com

www.aerosol.si

Berkeley,Ljubljana,July2014

the ‘next generation’ aethalometer model ae33 - magee ......magee scientific and aerosol co. are...

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