Teledyne 633 Carbon Monoxide Alarm User Manual


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Teledyne Advanced Pollution Instrumentation Model 633 Aethalometer
®
Black Carbon Monitor User Manual
07645A DCN6170 7
The‘spotloading effect’is avariablephenomenon whichappearsasagradualreductionof
instrumentalresponseastheaerosoldepositdensityofthefiltertapeincreasesfromzeroto
thepredeterminedlimitof‘MaximumAttenuation’(Gundel1984,Weingartner2003,Arnott
2005,Virkkula2007,Kanaya2008).Whenthefiltertapeadvancestoafreshspot,thedata
undergoesadiscontinuousjumpfromitspreviouslowervalue,calculatedwhenthespotwas
heavilyloaded;toahighervalue,calculatedfromcollectiononafreshspotatzeroloading.In
the Aethalometer the reduction of data at increasing loadings is welldescribed by a linear
functionofattenuation,butitsmagnitudecannotbepredicted: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, it is found that fresher
aerosolsclosertotheircombustionsourceswillshowalarger‘spotloadingeffect’;whilewell‐
agedaerosolsunderatmosphericconditionsofhighchemicalactivityandoxidativeprocessing
may show an almost zero effect. The effect is revealed statistically by processing data
collectedover alargenumber oftapeadvances, representingmanydatapointscollectedat
loadings(‘ATNvalues’)rangingfromzerotothepresetmaximum.Thedataiscollectedinto
binsaccordingtoloading(attenuation,ATN).Ifthereisasystematic reduction of the
calculatedresultasafunctionofloading,thedatawillshowaclearnegativeslope,withthe
interceptrepresentingthe‘zeroloading’value.Figure2illustratestwodatasetsfromurban
locationswithloadingeffectseitherpresentornot.
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