Intercomparison of an Aerosol Chemical Speciation Monitor (ACSM)

13 Pages·2014·1.15 MB·English

Atmos.Meas.Tech.,7,1929–1941,2014
www.atmos-meas-tech.net/7/1929/2014/
doi:10.5194/amt-7-1929-2014
©Author(s)2014.CCAttribution3.0License.
Intercomparison of an Aerosol Chemical Speciation Monitor
(ACSM) with ambient fine aerosol measurements in downtown
Atlanta, Georgia
S.H.Budisulistiorini1,M.R.Canagaratna2,P.L.Croteau2,K.Baumann3,E.S.Edgerton3,M.S.Kollman4,
N.L.Ng4,5,V.Verma5,S.L.Shaw6,E.M.Knipping7,D.R.Worsnop2,J.T.Jayne2,R.J.Weber5,andJ.D.Surratt1
1DepartmentofEnvironmentalSciencesandEngineering,GillingsSchoolofGlobalPublicHealth,TheUniversityofNorth
CarolinaatChapelHill,ChapelHill,NC27599,USA
2AerodyneResearch,Inc.,Billerica,MA01821,USA
3AtmosphericResearch&Analysis,Inc.,Cary,NC27513,USA
4SchoolofChemicalandBiomolecularEngineering,GeorgiaInstituteofTechnology,Atlanta,GA30332,USA
5SchoolofEarthandAtmosphericSciences,GeorgiaInstituteofTechnology,Atlanta,GA30332,USA
6ElectricPowerResearchInstitute,PaloAlto,CA94304,USA
7ElectricPowerResearchInstitute,Washington,D.C.20036,USA
Correspondenceto:J.D.Surratt([email protected])
Received:6November2013–PublishedinAtmos.Meas.Tech.Discuss.:19December2013
Revised:19May2014–Accepted:22May2014–Published:2July2014
Abstract.Currently,therearealimitednumberoffieldstud- measurements. This suggests that adjusting the ambient
iesthatevaluatethelong-termperformanceoftheAerodyne aerosol continuous measurements with results from filter
Aerosol Chemical Speciation Monitor (ACSM) against es- analysisintroducedadditionalbiastothemeasurements.We
tablishedmonitoringnetworks.Inthisstudy,wepresentsea- also recommend to calibrate the ambient aerosol monitor-
sonal intercomparisons of the ACSM with collocated fine inginstrumentsusingaerosolstandardsratherthangas-phase
aerosol (PM ) measurements at the Southeastern Aerosol standards.ThefittingapproachforACSMrelativeionization
2.5
Research and Characterization (SEARCH) Jefferson Street for sulfate was shown to improve the comparisons between
(JST) site near downtown Atlanta, GA, during 2011–2012. ACSM and collocated measurements in the absence of cal-
IntercomparisonoftwocollocatedACSMsresultedinstrong ibrated values, suggesting the importance of adding sulfate
correlations (r2>0.8) for all chemical species, except chlo- calibrationintotheACSMcalibrationroutine.
ride (r2=0.21) indicating that ACSM instruments are ca-
pable of stable and reproducible operation. In general, spe-
ciated ACSM mass concentrations correlate well (r2>0.7)
with the filter-adjusted continuous measurements from JST, 1 Introduction
although the correlation for nitrate is weaker (r2=0.55) in
summer.CorrelationsoftheACSMNR-PM (non-refractory Atmosphericfineparticulatematterwithaerodynamicdiam-
1
particulate matter with aerodynamic diameter less than or eters less than or equal to 2.5µm (PM2.5) have adverse ef-
equal to 1µm) plus elemental carbon (EC) with tapered el- fectsonhumanhealth(Dockeryetal.,1993),reducevisibil-
ementoscillatingmicrobalance(TEOM)PM andFederal ity,andplayaroleinEarth’sclimate(IPCC,2013).Asare-
2.5
ReferenceMethod(FRM)PM massarestrongwithr2>0.7 sult,therehasbeenanongoingneedtoresolvethechemical
1
andr2>0.8,respectively.Discrepanciesmightbeattributed compositionofPM2.5inordertoidentifytheirexactsources,
to evaporative losses of semi-volatile species from the fil- andthus,developeffectivecontrolstrategies.Organicmatter
ter measurements used to adjust the collocated continuous (OM) contributes a major fraction (25–70%) of the submi-
cron (PM ) mass in the troposphere; however, its sources,
1
PublishedbyCopernicusPublicationsonbehalfoftheEuropeanGeosciencesUnion.
1930 S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements
composition, and atmospheric chemical transformations re- integratedPM andPM massmeasurementsbasedonthe
2.5 1
main unclear (Jimenez et al., 2009). Inorganic aerosol con- FederalReferenceMethod(FRM).
stituents,suchassulfate(SO2−),nitrate(NO−),ammonium In the discussion that follows, we first compare individ-
4 3
(NH+),andchloride(Cl−)canalsobemajorcomponentsof ualspecies(i.e.,OM,SO2−,NO−,NH+,andCl−)andtotal
4 4 3 4
PM2.5,dependingonlocationandtimeofyear. NR-PM1 mass measured from collocated ACSMs during a
Numerous methods for measuring the mass and chemi- shortperiodbetweenJanuaryandFebruary2012.Secondly,
calcompositionofPMhavebeenputforward,includingin- wecomparespeciesmeasurements(minuschloride)andto-
tegrated filter samplers with subsequent laboratory analysis tal mass from the ACSM with organic carbon (OC), SO2−,
4
− +
(e.g., Baumann et al., 2003; Solomon et al., 2003b), semi- NO ,NH ,andPM fromcontinuousandfiltermeasure-
3 4 2.5
continuousmethods(e.g.,Weberetal.,2003a,b;Limetal., ments at the Jefferson Street (JST) site during summer and
2003),andreal-timeinstruments(e.g.,Gardetal.,1997;Lee fall2011.WecomparemassfromtheACSMwithtotalmass
etal.,2002;Jimenezetal.,2003).Differencesbetweensam- from integrated FRM measurements in three short periods
pling techniques may occur for a host of reasons, including ofJanuary–February,April–May,andJuly2012.Lastly,we
design, analysis methods, and assumptions used in data re- estimateaerosoldensityfromcontinuousmeasurementsbe-
duction. Hence, comparison of new sampling methods with tween17Octoberto20November2012.Fromthisintercom-
establishedtechniquesallowsonetodetermineitssuitability parison,wehavegainedmoreknowledgeoncontinuousam-
forlong-termairqualitymonitoring. bientaerosolmeasurements,includingtheimportanceofcal-
The Aerodyne Aerosol Chemical Speciation Monitor ibratingtheroutinemonitoringaerosolinstrumentswithtrue
(ACSM, Ng et al., 2011) is designed for reliable long-term aerosolstandardsratherthangas-phasestandards,aswellas
operation with minimal user intervention. The key differ- sulfate calibration as additional routine calibration for the
ences between the ACSM and the aerosol mass spectrom- ACSM.
eter (AMS, Jayne et al., 2000) is that the former lacks
a particle beam chopper and uses a relatively lower sen-
2 Experimentalsection
sitivity quadrupole and, therefore, data must be averaged
over a longer period to obtain sufficient signal-to-noise for
2.1 Sitedescription
quantification. Recent studies showed that the ACSM data
are strongly correlated (r2>0.8) with the Aerodyne high-
Ambient aerosol from Atlanta, Georgia, was collected at
resolution time-of-flight aerosol mass spectrometer (HR- the Jefferson Street (JST) site (33.7775◦N, 84.4166◦W),
ToF-AMS) (Ng et al., 2011), time-of-flight ACSM (ToF-
whichislocatedinamixedindustrial–residentialareaabout
ACSM), and compact time-of-flight AMS (Fröhlich et al.,
4.2kmnorthwestofdowntownAtlanta(Hansenetal.,2003;
2013). Comparisons of SO2− aerosol showed good correla-
4 Solomon et al., 2003a). The JST site is one of the research
tionsbetweentheACSMandtheparticle-into-liquidsampler
sitesofSoutheasternAerosolResearchandCharacterization
coupledtoanionchromatograph(PILS-IC),andtheThermo
(SEARCH) network that is equipped with a suite of gas,
ScientificSulfateParticulateAnalyzer(model5020i),where
particle,andmeteorologicalmeasurements.Detailsofthese
the ACSM measured 31% lower for SO2− than these two
4 measurements are described in subsequent sections. The
−
instruments. For NO3 aerosol, the ACSM measured 25% University of North Carolina at Chapel Hill (UNC) ACSM
lower than the PILS-IC (Ng et al., 2011). A recent deploy- wasoperatedcontinuouslyatJSTfrom27July2011through
mentoftheACSMinBeijing,China,reportedagoodcorre- 21 September 2012, while the GIT ACSM was deployed at
lationbetweenthetotalnon-refractoryPM1 (NR-PM1)esti- thissitefrom31Januarythrough29February2012.Thepe-
mated from the sum of all species measured by the ACSM riod when both ACSMs were collocated at JST is used to
withthePM2.5 measuredbythetaperedelementoscillating evaluate the ACSM performance, and the extended periods
microbalance(TEOM),wheretheACSMNR-PM1 reported in2011and2012areusedtoevaluatetheaccuracyofACSM
64%oftheTEOMPM2.5mass(Sunetal.,2012). measurementsagainstestablishedmonitoringnetworkmea-
The present study compares ambient NR-PM1 measured surements.
by the ACSM with a suite of collocated particle measure-
mentsinAtlanta,Georgia.Thecollocatedparticlemeasure- 2.2 NR-PM andchemicalmeasurementsbytheACSM
1
mentsincludeanotherACSMoperatedbytheGeorgiaInsti-
tuteofTechnology(GIT),continuousSO2−,NO−,andNH+ DuringFebruary2012,NR-PM1 wasmeasuredbytwoAC-
4 3 4
measurements operated by Atmospheric Research & Anal- SMs that belong to UNC and GIT, and placed in an air-
ysis Inc. (ARA), semi-continuous organic carbon/elemental conditionedtraileratJST.SamplingconditionsforbothAC-
carbon(OC/EC)measurements,total PM massmeasured SMsaredescribedinTable1.BothACSMswereoperatedto
2.5
by TEOM, integrated SO2−, NO−, and NH+ by parti- scan150mass-to-charge(m/z)ratiosoffragmentedionsata
cle composition monitor (P4CM) d3eveloped by4ARA, and rateof500msamu−1.Vaporizerandheaterbiasesweresetat
600◦Cand100.30V,respectively,withthebiasvoltagecho-
sen to maximize the N (m/z28) signal. Particle-laden and
2
Atmos.Meas.Tech.,7,1929–1941,2014 www.atmos-meas-tech.net/7/1929/2014/
S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements 1931
Table1.UNCandGITACSMssamplingsetupattheJSTsiteforashortperiodbetweenJanuary–February2012.
UNC GIT
Samplinginlet PM2.5cyclone PM2.5cyclone
Samplinglinelength 5.00m 5.00m
Samplinglinediameter 0.64cmODand0.46cmID 1.27cmIDfor1moflength
stainlesssteeltube 0.95cmIDfor4moflength
Sampledrying 50-tubeNafiondryer(PermaPurePD- 200-tubeNafiondryer(PermaPure
50T-24SS)with7.00Lmin−1ofsheath PD-200T-12MPS)runningwith
aircomingfromdry/zeroairsystem 0.50Lmin−1sheathairflow(under
vacuum)
ACSMsamplingflowrate 3.00Lmin−1 3.00Lmin−1
RFNO3 calibration 3.79×10−11 3.97×10−11
RIENH4 calibration 6.00 4.30
RIESO4 fitting 0.79 0.54
RIENO3 default 1.10 1.10
RIECldefault 1.30 1.30
RIEOrganicdefault 1.40 1.40
Referenceflow(Qcalincm3s−1) 1.39 1.35
Dataacquisitionsoftware ACSMDAQv1.4.2.2 ACSMDAQv1.4.2.5
Dataanalysisprocedure ACSMLocalv1.5.2.0 ACSMLocalv1.5.2.0
particle-freeairweresampledinterchangeablyandaveraged An air beam signal (i.e., m/z28) was used to normalize
over∼30minintervalsforeachmeasurement.Wecalibrated the measurements with respect to instrument measurement
theACSMonsite.TheACSMswerecalibratedforresponse sensitivity (i.e., secondary electron multiplier (SEM) gain
factor (RF) and relative ionization efficiency (RIE) using a decay) and sampling flow rate. The effusive naphthalene
separatecalibrationsystemforUNCandGIT.Theresulting source was not used due to lower signal-to-noise compared
values for each instrument are reported in Table 1, and for tom/z28anditsdependencyoneffusionflowand/orback-
UNC ACSM, different calibration values were used for dif- ground contamination. Moreover, the changes in flow rate
ferentseasons. needtobeaccountedforbyusingthefilteredairbeam.The
Data acquisition software provided by ARI was used to ACSMusesafilteredairmassspectrumtoaccountforback-
process the measurements to obtain total organic and inor- grounds(e.g.,N andCO).Thesesignalswillvarywithflow
2
ganic (i.e., SO2−, NO−, NH+, and Cl−) aerosol mass con- rateorslowlydesorbingmaterial.Contributionoftheslowly
4 3 4
centrations. Further details of the concentration calculation desorbingmaterial,however,isgenerallysmallcomparedto
arediscussedbyNgetal.(2011)andshowninEq.(1). theN signalatm/z28.
2
RIE for species s was determined from calibrations of
s
C = CEs × 1012 ×Qcal×Gcal × 1 XIC (1) laboratory-generated aerosols of each species using Aero-
s T RIE RF Q×G s,i dyne AMS (Alfarra et al., 2004; Canagaratna et al., 2007).
m/z s NO3 alli
SincetheACSMparticlevaporizationandionizationsource
Speciesmassconcentration(C )iscalculatedbasedonmea- are similar but not identical in design to that of the AMS,
s
suredioncurrent(ICinamps)atfragmentioni.CE iscol- there may be differences in RIE values compared to those
s
lectionefficiencyforspeciess,andRF isinstrumentre- referencedabove.ThevaporizerisidenticalbetweenACSM
NO3
sponsefactorfromcalibration.T iscorrectionforthem/z andAMSsystems.TheionformationchamberintheACSM
m/z
dependent ion transmission efficiency of the quadrupole. is somewhat smaller than in the AMS. The ion source vol-
Q and G are the volumetric sample flow rate and mul- ume in the ACSM is calculated to be 370mm3 and that of
cal cal
tipliergain,respectively,andweredeterminedfromcalibra- the AMS is 580mm3. We note, however, that the effective
tion,whileQandGareobtainedduringthemeasurements. volume is really defined by the electric fields and it is not
During data processing, calibrated and measured Q and G easily calculated. In both systems the diameter of the ex-
cancel each other out as part of air beam correction factor traction into the ion optic lens region is 3mm. The smaller
(Eq. 2), and no separate correction is applied for flow rate. ionsourcevolume(withtighterspatiallydistributedelectric
Theairbeamcorrectionisappliedasitisuncertainwhether fields) in the ACSM could result in larger variability of the
airbeamsignalchangesduetogainorflowchanges. relativeionizationefficiencieswithrespecttopreciseparticle
beamalignment,whichiscurrentlybeinginvestigated.
Q ×G
Airbeamcorrectionfactor= cal cal (2)
Q×G
www.atmos-meas-tech.net/7/1929/2014/ Atmos.Meas.Tech.,7,1929–1941,2014
1932 S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements
Table2.StatisticsofcalibrationvaluesobtainedfromUNCandGITACSMssincemid2011toearly2013.
UNCACSM GITACSM
∗ ∗
Date RFNO3 RIENH4 RIESO4 RFNO3 RIENH4 RIESO4
Mean 4.17×10−11 5.71 0.67 3.26×10−11 4.40 0.59
1-stddeviation 1.53×10−11 1.01 0.09 1.26×10−11 0.38 0.04
%uncertainty 37% 18% 14% 39% 9% 7%
∗Sulfateaerosolcalibrationswerenotconducteduntilearly2013.
The default RIE value for ammonium (RIE ) was 3.5; dataanalysisduetooperationalandmaintenanceissues,such
NH4
the value obtained from ACSM calibrations was approxi- asshutdownduringcalibrations.Aerosolmassspectrometer
mately 5.71 (Table 2). The default RIE of sulfate was 1.2, uncertainty was estimated 20–35% (Bahreini et al., 2009)
whichtherealvaluecouldbeestimatedbyfittingmeasured which included CE uncertainty of 30%. A recent study of
sulfate and predicted sulfate values, derived from NH composition dependent CE parameterization (Middlebrook
4,pred
equation(Eq.3).Measuredsulfate(SO )issulfatethat et al., 2012) has substantially contributed to narrow the un-
4,meas
ismeasuredbytheACSM,whilepredictedsulfate(SO ) certainty of AMS, which could be used as a guideline for
4,pred
is the estimated value of sulfate from ion balance approach ACSMaccuracy(∼30%).
(Eq.4).
2.3 Chemical constituents measured by integrated and
(cid:18) (cid:19)
NH =2 MWNH4 SO (3) continuousparticlemeasurementsatJSTsite
4,pred 4,meas
MWSO
4
(cid:18) (cid:19) (cid:18) (cid:19) DetailsoftheJSTsitemeasurementsareprovidedelsewhere
MWNH MWNH
+ 4 NO + 4 Cl (Hansenetal.,2003;Edgertonetal.,2005,2006).Inletsfor
3,meas meas
MWNO MWChl
3 particlesamplersaremountedontherooftopofthesampling
trailer about 5m above ground level. The particle measure-
ments consist of 24h filter sampling conducted every third
SO = (4)
4,pred
day(dailyforPM andPM mass),andofcontinuousand
(cid:16) (cid:17) (cid:16) (cid:17) 2.5 1
NH4,meas− MMWWNNOH34 NO3,meas− MMWWNCHhl4 Clmeas semi-continuous measurements by instruments placed in an
(cid:16) (cid:17) air-conditionedtrailer.Integrated,semi-continuous,andcon-
2 MWNH4
MWSO4 tinuous PM2.5 measurements are listed in Table 3, and de-
scribedbrieflybelow.FieldblankloadingsofJSTsitemea-
ThepreviousvalueofRIESO4 1.2isthenmultipliedbyslope surements are generally insignificant for SO24−, NH+4 and
obtained from fitting SO versus SO and used as −
4,pred 4,meas OC, but can be significant for NO and EC mostly due to
3
the RIE value of this study. UNC ACSM applied fitted
SO4 loadings at or below detection limit of those components
RIE values of 0.95, 0.77, 0.79, 1.1, 0.73, and 0.44 for
SO4 (Edgerton et al., 2005). We emphasize here that the JST
summerandfall2011,winter,spring,summer,andfall2012
siteaerosolinstrumentsarebasedongasphasedetectionof
data sets, respectively. Explicit calibration of RIESO4 by at- aerosol conversion products (e.g., SO2 from SO42− and NO
omizing(NH4)2SO4usingthesamecalibrationsystemfrom fromNO−),therefore,arecalibratedwithstandardgasesin-
UNCduringwinter2013yieldedavalueof0.67±0.09indi- 3
steadofdirectlybyparticlemassgeneratedfromanatomizer
catingthatthefittingapproachvalue(0.79±0.22)isconsis-
combined with scanning electrical mobility sizer (SEMS)
tentwiththecalibrations,withalargeruncertainty(Table2).
mixing condensation particle counter (MCPC) as done for
WefoundthatSO2− percentdifferencebetweenACSMand
4 theACSM.
collocated measurement at JST was improved from about
50%tolessthan30%.Therefore,inadditiontoregularcal- Particlecomponentsmeasurements
ibration using NH NO , we recommend additional calibra-
4 3
tionusing(NH ) SO toobtainanRIE valuespecificfor Details of the semi-continuous and continuous PM sam-
4 2 4 SO4 2.5
theACSM. plingandanalysisareprovidedinEdgertonetal.(2006)and
A CE of 0.5 was used to calculate mass concentration. in the supporting information. Briefly, PM mass is mea-
2.5
We used a Nafion dryer to dry ambient air samples; inves- sured continuously using an R&P Model 1400a/b TEOM
tigationofspecies-dependentCE(Middlebrooketal.,2012) operated at 30◦C to reduce losses of semi-volatile com-
suggestedthatCEisnotinfluencedbyhighlyacidicaerosol poundsandwithmainflowrateof3Lmin−1.Sampleairwas
(Fig. S1 in the Supplement) or ammonium nitrate (Fig. S2 pulledthroughaPM inletfollowedbyaPM VerySharp
10 2.5
in the Supplement) as provided in the supplemental infor- Cut Cyclone (BGI Incorporated) that goes inside the trailer
mation.Somemeasurementperiodswereexcludedfromthe where a multi-tube Nafion drier (Perma Pure) is installed
Atmos.Meas.Tech.,7,1929–1941,2014 www.atmos-meas-tech.net/7/1929/2014/
S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements 1933
Table3.Summaryofintegrated,semi-continuous,andcontinuousPM2.5analysesatJST.
Analyte Instrument Analyticalmethod DetectionLimit(mgm−3) Frequency/TimeResolution
Integratedsamples
Mass FRM(Teflon,47mm) Gravimetry 0.2 daily
SO2− PCM1(Teflon,47mm) IC 0.05 3-day
4
−
NO PCM1(Teflon,47mm) IC 0.01 3-day
3
+
NH PCM1(Teflon,47mm) AC 0.03 3-day
4
−
Volatile-NO PCM1(Nylon,47mm) IC 0.02 3-day
3
+
Volatile-NH PCM1(Citricacid-coatedcellulose,47mm) AC 0.04 3-day
4
OC PCM3(Quartz,37mm) TOR 0.08 3-day
Continuoussamples
Mass R&P1400a/bTEOM(modified) Oscillatingmicrobalance 2.0 5min
SO24− HSPH(modified) ReductiontoSO2/PF 0.4 1min
−
NO ThermoScientific ReductiontoNO/CL 0.25 1min
3
+
NH ThermoScientific OxidationtoNO/CL 0.07 1min
4
OC/TC SunsetOC/ECAnalyzer CombustiontoCO2/NDIR 0.5 60min
Notes:Volatile-NO−3 andVolatile-NH+4 arecollectedonbackfiltersasHNO3andNH3dissociationonthefrontfilter;ICrepresentsionchromatographytechnique;ACrepresentsautomated
colorimetrymethod;TORindicatesthermal/opticalreflectancemethod;PFrepresentspulsedfluorescencetechnique;CLindicatesozone-NOchemiluminescencemethod;HSPHstandsforHarvard
SchoolofPublicHealth.
to dry the sample. SO2− is measured continuously using a PM valueswereobtainedbyaddingblank-correctedPCM
4 2.5
−
modified Harvard School of Public Health (HSPH) Sulfate measurementstogetherwithvolatileNO fromPCMnylon,
3
ParticulateAnalyzer.NH+ andNO− weremeasuredusinga volatileNH+andvolatileOMfromPCMbackfilter.
4 3 4
three-channelcontinuousdifferencingmethoddevelopedby FRM filter samples were collected for 24h using dual
ARA, Inc. (Edgerton et al., 2006). Total carbon (TC) was R&P Model 2025 sequential FRM monitors to determine
semi-continuouslymeasuredbyaSunsetOC/ECinstrument both PM and PM mass. 47mm diameter Teflon filters
2.5 1
(model3),whichcollectsparticlesonafilter.Oncecollection (2µmporesize)wereusedforthesemeasurements,andthe
iscomplete(after∼50min),theovenispurgedwith10%O2 collection,processing,andanalysisofthesefiltersfollowed
inHe,andthenrampeduptoasetpointof850◦Caccording FRMprotocol(CodeofFederalRegulations,2001).PM fil-
1
totheNIOSH5040analysisprotocol. ters were sampled during three separate sampling periods:
Inorganics, OC, and total mass concentrations from the JanuarytoFebruary,April,andJuly2012,representingwin-
continuousanalyzerswereadjustedtomatchthefilter-based ter,spring,andsummerseasons,respectively.
datavialinearregressionsincethecontinuousanalyzershave
beenshowntodriftovertime.Newadjustmentsareapplied 2.5 Aerosoldensityestimation
every1–2months,dependingonthestabilityoftheindivid-
ual analyzer. With respect to carbon measurements, OC is Total PM1 volume measurements were obtained using
calculated as the difference between filter-adjusted TC and the Brechtel Manufacturing Incorporated (BMI) SEMS
filter-adjusted EC, and OM is estimated from applying an equipped with a cylindrical-geometry differential mobility
OM/OCratioof1.4(Edgertonetal.,2006). analyzer (DMA) and coupled to an MCPC (Sorooshian et
Thecomponentmassloadingsfromeachfilterwereblank- al., 2008). The DMA was set to size particles between 10–
corrected using SEARCH network-wide average loadings 1000nm in diameter for both up and down scans. Differen-
from field blanks, then the corrected loading was normal- tialmobilityanalyzersheathairflowratewassetto5Lmin−1
izedbysamplingvolume.Detailsoftheintegratedmeasure- and particles were sampled at 0.5Lmin−1. Particle volume
mentsattheJSTsiteareprovidedinEdgertonetal.(2005). concentrationfromeachscanwascollectedevery120s,and
This study will focus on comparison between ACSM and bothupanddownscanswereaveragedtogetonedatapoint
JST filter-adjusted continuous measurements (Figs. S3, S4 every4minand30s,whichincludesthescanningdelaytime.
and S5 in the Supplement). Results of intercomparison be-
tween ACSM and filter measurements are presented in the
3 Results
supportinginformation(Figs.S6andS7intheSupplement).
TheACSMmeasuredabout11.6µgm−3 ofOM,3.2µgm−3
2.4 Totalparticlemassmeasurements ofSO2−,and0.61µgm−3ofNO−duringsummer2011.The
4 3
numbers decreased in the fall 2011, except for nitrate (Ta-
PM2.5 mass concentrations were obtained by several meth- bleS1intheSupplement).TheACSMmeasuredchlorideon
ods during this campaign. Continuous total mass concen- average of 0.02 to 0.04µgm−3 in summer and fall, respec-
trations were obtained with the TEOM (after adjustment to tively.
matchtheintegratedPCM-basedPM ).TheJST-integrated
2.5
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1934 S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements
3.1 IntercomparisonbetweentheUNCand Table4.CorrelationsbetweentheACSMandthecollocatedmea-
GITACSMs surements at JST site. Slope and intercept±1 standard deviation
fromeachlinearregressioncorrelationsarepresented.
TheUNCandGITACSMswerecollocatedfrom10January
to 23 February 2012. Intercomparisons of chemical species JSTContinuousc
betweenthetwoACSMsshowninFig.1indicatestrongcor-
Summer2011 Fall2011
relations (r2>0.8), except for chloride (r2=0.21). Slopes
Massa
and intercepts of the linear regression are provided in Ta-
r2 0.71 0.83
ble4.Weakercorrelationsofchloridemightbeduetoitslow
Slope 1.50±0.02 2.10±0.02
concentrationinAtlanta.
Intercept −2.89±0.31 −4.36±0.20
3.2 IntercomparisonofACSMwithcollocated OMvs.OCb
JSTmeasurements r2 0.86 0.93
Slope 4.85±0.05 3.85±0.02
Intercomparisons of species and total mass measurements Intercept −7.34±0.19 −2.99±0.09
by the ACSM, continuous particle measurements from JST, SO2−
Sunset OC analyzer (model 3), and TEOM PM2.5 (model r2 4 0.84 0.83
1400a/b) at the JST site are given in Table 4 for summer Slope 1.04±0.01 1.44±0.02
(8 August to 14 September) and fall (17 October to 21 De- Intercept −0.73±0.04 −0.54±0.03
cember)2011samplingperiods.Collocatedmassandchem-
−
NO
ical constituent measurements were averaged to the ACSM 3
r2 0.55 0.81
sampling times to allow for a direct intercomparison. Pre-
Slope 2.14±0.04 1.77±0.02
vious intercomparison studies conducted at the same site
Intercept 0.06±0.01 0.08±0.02
have been limited to the summer season (Solomon et al.,
+
2003a); therefore, results from this study could reveal pos- NH
4
sibleaerosolmeasurementsvariationacrossseasonsandin- r2 0.79 0.76
strumentationdifferencesinaerosolmeasurements. Slope 1.20±0.02 1.51±0.02
Intercept −0.19±0.02 −0.61±0.01
3.2.1 Speciescomparison aACSMPM1iscalculatedfromsumofACSMspeciesand
SunsetEC.bForACSM-to-ACSMcomparison,itisOMvs.
ACSM OM is strongly correlated with OC from the Sunset OM.cJSTmeasuresPM2.5massandchemicalconstituents.
OC/EC analyzer (r2 values are 0.86 and 0.92 for summer
and fall, respectively); the resulting ratios (from the linear
regressionslopesinTable4)ofOM/OCare4.85±0.05and −
IntercomparisonsbetweenACSMNO andJSTcontinu-
3.85±0.02insummerandfall,respectively.AerosolChem- ous NO− result in percent differences of3114% (r2=0.55)
ical Speciation Monitor OM versus Sunset OC correlations 3
and 77% (r2=0.81) in the summer and fall, respectively.
are likely higher since they are both real-time and not af-
The weaker correlation and larger discrepancy in the sum-
fected by storage related losses, such as that from the filter −
mermightbeduetothelowNO loadingsandevaporative
measurements. 3
ACSM SO2− is strongly correlated with that from JST lossesfromfiltersthatwillbediscussedlater.
4
continuousmeasurementsinthesummer(r2=0.84)andfor
someperiodsinthefall(r2=0.83;September–November); 3.2.2 Totalmasscomparison
however, the correlation is weaker for some periods in De-
cember (r2=0.22) when JST measured several instances ACSM PM mass was determined from the sum of ACSM
1
of very high SO2− aerosol. Percent differences between OM, SO2−, NO−, NH+, and Cl− as well as EC from the
4 4 3 4
the measurements are 4 and 44% for summer and fall, re- SunsetOC/ECanalyzer.TheintercomparisonoftheACSM
spectively. These results are close to previous sulfate inter- PM and TEOM PM shows a good correlation, with r2
1 2.5
comparisons between ACSM and collocated measurements values of 0.71 and 0.83, respectively, and discrepancies of
(slope=0.95, 0.69, and 0.69, for HR-ToF-AMS, PILS-IC, 50 and 110% for summer and fall, respectively (Table 4).
and sulfate particulate analyzer, respectively) (Ng et al., AsinthespeciatedACSMandPCMmeasurementcompar-
2011). isons,discrepanciesinthefallmighthaveresultedfromposi-
For NH+ comparison, correlations are high (r2=∼0.8) tivebiasesofspeciesmeasurementsbytheACSM.Sincethe
4
andinterceptsforbothsummerandfallareinsignificant.Dif- TEOMmeasurementsareadjustedtomatchfiltermasscon-
ferences between ACSM and JST measurements are 20% centrations,itisalsopossiblethattheadjustedTEOMvalues
(r2=0.79)forsummerand51%(r2=0.76)forfall. arelowerthantheACSMPM valuesbecauseofevaporation
1
Atmos.Meas.Tech.,7,1929–1941,2014 www.atmos-meas-tech.net/7/1929/2014/
S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements 1935
(a) r2=0.95 r2=0.95 (b) UNC Org GIT Org
f(x)=(-0.06±0.07) f(x)=(0.20±0.01) 40
+(1.14±0.01)x 12 +(0.73±0.01)x 30
Org 4300 2-O4180 21000
UNC 2100 UNC S 642 1162 UNC SO42- GIT SO42-
0 0 8
-C NO3 640rf ( 2 x= 1) 0 =G+0.(8(00I9.T.1293 08O±±00r3.g.00021))x40 +C NH432..000rf ( 2 x= ) G0 =4+.(8I(01T2..2 280S1±±O00.14.002212-))x16 -3Concentration (µg m) 3.6420400 UUNNCC N NHO43+- GGIITT NNHO43+-
UN 2 UN1.0 ass 2.0
M 1.0
0 0.0 M 0.0
0 G2IT N4O3-6 0.0 G1IT.0 NH42+.0 ACS 4 UNC Cl- GIT Cl-
r2=0.21 r2=0.92 3
f(x)=(0.01±0.00) f(x)=(0.08±0.12) 2
0.30 +(0.60±0.04)x +(1.09±0.01)x 1
0.25 M150 0
-UNC Cl0000....21100505 UNC NR-P43210000 5432100000 UNC NR-PM1 GIT NR-PM1
0.00 0 0
0.00 0.10 0.20 0 10203040 2/10/2012 2/20/2012
GIT Cl- GIT NR-PM1 Date and Time (Local)
Figure1.(a)Linearregressioncorrelationand(b)timeseriesplotsoforganicandinorganicconstituentsmeasuredbytheUNCandGIT
ACSMs.ACSMmeasurementsfromUNCarecoloredbyspecieswhilethosefromGITarecoloredinblack.
ofsemi-volatileorganicsandnitratesfromthefiltersduring (79%) are due to its significantly lower concentration in
storage. Atlanta during the entire sampling period. This resulted in
TheACSMdatawereaveragedtotheFRMfiltersampling weaker correlation between the two instruments although
times, which was 24h (midnight to midnight) during each bothinstrumentscapturesimilarlargepeaksofCl−forsome
sampling period. Comparison between the ACSM NR-PM periods.
1
and FRM PM in winter, spring, and summer 2012 shows
1
a good correlation, with r2 values of >0.80 (Fig. 2), and 4.2 OM/OCratio
themassconcentrationsdifferencesvaryfrom10%insum-
mer to 73% in winter. For the same period, comparison of TheOM/OCratiosderivedfromtheregressionlinearslopes
ACSM NR-PM and FRM-PM shows a good correlation arelargerthanmostOM/OCratiospreviouslyreportedinthe
1 2.5
r2>0.80).Thetightercomparisonsduringsummer(r2>0.8) literature.Thesevaluesaresignificantlyhigherthanthetra-
comparedtowinter(r2=∼0.6)mightsuggestmeteorologi- ditionally used values of 1.6 for urban aerosol and 2.1 for
calinfluenceontotalmassmeasurementsduetopositivebias non-urban aerosol (Turpin and Lim, 2001; Lim and Turpin,
from filter measurement during colder seasons (Solomon et 2002; Russell, 2003). They are also larger than those found
al.,2003a,b). fromrecentHR-ToF-AMSintercomparisonswiththeSunset
OC/EC analyzer that report ∼1.8 from September in Pitts-
burgh(Zhangetal.,2005a),1.8and1.6fromsummerandfall
4 Discussion in Tokyo (Takegawa et al., 2005), 1.41–2.15 from March in
Mexico(Aikenetal.,2008),2.59fromAugustinNewYork
4.1 IntercomparisonbetweenACSMinstruments City (Sun et al., 2011) and 3.3 from summer in Pasadena
(Hayesetal.,2013).StudiesinAtlantaalsoreportedahigh
Slopes of the linear regression from UNC ACSM vs. GIT variabilityofOM/OCratio,from1.23–3.44inAugust1999
ACSM (Table 4) suggest percentage differences of speci- (Baumannetal.,2003)and1.77inDecember1999to2.39in
atedmassconcentrationsare4to38%betweentwoindepen- July 1999 (El-Zanan et al., 2009). These suggest variability
dentACSMmeasurements.TheSO2−differenceof25%can inOM/OCratiosbasedonlocation,timeandmeteorological
4
be attributed to uncertainty in the instrument RIE fitting re- conditions,and/orthattheACSMismeasuringorganicmass
sults.Thepercentuncertaintyofthefittingapproachislarger muchhigherthanitshouldsinceitisusingAMS-basedRIE
(28%) than calibration results (7–14%) recently conducted valuesfororganic(i.e.,RIE=1.4)ratherthanthosethathave
at both ACSMs. Larger differences of Cl− measurements beenexplicitlymeasuredforACSMinstruments.
www.atmos-meas-tech.net/7/1929/2014/ Atmos.Meas.Tech.,7,1929–1941,2014
1936 S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements
(a) r2=0.89 r2=0.88
30 f(x)=(-1.44±1.35)+(1.73±0.14)x 30 f(x)=(-1.55±1.42)+(1.53±0.13)x
20 20
10 10
3) 0 3) 0
-m 0 5 10 15 20 -m 0 5 10 15 20
µg (b) r2=0.86 µg r2=0.83
(1 12 f(x)=(-0.06±0.54)+(0.81±0.06)x (1 12 f(x)=(0.05±0.60)+(0.70±0.06)x
M 8 M 8
P P
R- 4 R- 4
N N
M 0 M 0
S 0 4 8 12 S 0 4 8 12
C C
A 25 (c) r2=0.91 A 25 r2=0.76
20 f(x)=(0.40±0.65)+(1.10±0.08)x 20 f(x)=(-1.07±1.30)+(1.07±0.13)x
15 15
10 10
5 5
0 0
0 4 8 12 16 0 4 8 12 16
-3 -3
FRM PM (µg m ) FRM PM (µg m )
1 2.5

Figure2.CorrelationofACSMNR-PM1measurementswiththoseofFRMPM1andPM2.5methodsduring(a)winter,(b)spring,and(c)
summer2012,respectively.
ThelargeOM/OCratiosmightalsobeattributedtounder- incomplete photochemical oxidation leading to more labile
estimationofOCduetoevaporationofsemi-volatileorganic functional groups and intermediates. An offline polarity-
compounds (SVOCs) from the Sunset OC analyzer, and/or based analysis suggested values of 1.9 to 2.1 for OM/OC
overestimation of OC due to condensation of SVOC or ad- ratios due to aging and oligomerization processes in the at-
sorptionofVOConthefilter(Couvidatetal.,2013).Thisis mosphere(Polidori,2008).Inaddition,water-solubleorganic
reflectedinalargeoffsetattheSunsetOC(Figs.S4andS5 aerosol was observed to have higher OM/OC ratios than
in the Supplement). The presence of a denuder on the inlet that of less water-soluble organics, ranging from 2.1–2.3 in
ofSunsetOC/ECanalyzer,forexample,mightcauseevapo- theGreatSmokyMountainsto3.3indowntownLosAnge-
ration of particulate OC from the collection filter due to re- les (Turpin and Lim, 2001). Furthermore, ratios of 2–3.12
partitioning of SVOC after removal of gaseous organics by were observed from organic fractions that could not be ex-
the denuder (Grover et al., 2008). Also, 20% of Sunset OC tractedusingorganicsolvent(Polidori,2008),indicatingthat
uncertainty(Peltieretal.,2007)togetherwithACSMuncer- compound-specificpolaritymightberelatedtosourcesofor-
taintymightpropagatetheOM/OCratio. ganic aerosol. Therefore, besides overestimation of OM by
OverestimationofOMbytheACSMcouldarisefromun- ACSM as noted above, high OM/OC ratios might indicate
derestimation of the RIE value of organic species. The RIE thattheorganicaerosolismorewater-solubleinnature.
values used in this study are based on experiments examin-
ing a suite of organic standards using the AMS instrument
4.3 SO2−andNH+measurementsvariations
(Jimenez et al., 2003; Alfarra et al., 2004). Since the two 4 4
instruments rely on the same vaporizer and ionization con-
ditions (i.e., electron ionization), it was assumed that the SulfatemeasurementsfromACSMandthefiltershowagood
RIE values for organics should be similar. However, based trend (r2>0.7, see Fig. S7 in the Supplement) for the De-
on the high OM/OC ratios observed from our intercompar- cember period, suggesting that the large discrepancies ob-
ison study, sets of authentic organic standards covering a served between the ACSM and JST data might be caused
wide range of chemical classes as well as secondary or- by some unknown issues with either the JST continuous
ganicaerosolgeneratedfromlaboratoryexperiments,suchas measurements or ACSM during this sampling period. Both
isoprene-derivedsecondaryorganicaerosol(SOA)(Kleindi- ACSM and continuous measurements show that the slopes
+ +
enstetal.,2006;Linetal.,2012),needtobesystematically of NH measured versus NH predicted (neutralized) are
4 4
analyzedinfutureworkinordertodeterminetheRIEvalue slightly less than 1 (Fig. S8 in the Supplement). This sug-
fororganicsintheACSM. gests during both summer and fall 2011, the aerosol was
The large OM/OC ratios might also suggest photochemi- slightly acidic. Investigation of the period where correla-
cally,well-aged,andwell-mixedairmassescontainparticle- tion between ACSM and collocated measurement is low in
phase organics that are more oxygenated and less-volatile fallseasonsuggestsomeorganicinterferences(hydrocarbon-
compared to more stagnant air masses where less polar likeorganicaerosol/HOA)insulfatefragments,inparticular
and more volatile organics can be found possibly due to m/z81(Fig.S9intheSupplement).
Atmos.Meas.Tech.,7,1929–1941,2014 www.atmos-meas-tech.net/7/1929/2014/
S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements 1937
-3m) 40 (a) ASECMSMS PNMR1-P vMol1u mmaes cso cnocn.c. (b) 40 rf (2 x= )0 =+.(8(019..3519±±00..1021))x
-3µg m; µm c 3200 -3PM (µg m)13200
n ( R-
o N
ati M
centr 10 ACS 10
n
o
C
0 0
10/21/2012 10/31/2012 11/10/2012 11/20/2012 0 5 10 15 20 25
Date and Time (Local) SEMS PM1 (µm3 cm-3)
Figure3.(a)Timeseriesand(b)correlationoftotalaerosolmassmeasuredbyACSM(NR-PM1)andSEMSDMA/MCPCduringperiodof
17Octoberto20November,2012.Aerosoldensitywasestimatedfromthelinearregressionslopeof1.59multipliedby1.10toaccountfor
the10%ofelementalcarbon(EC)componentthatisnotmeasuredbyACSM.Thisresultsinestimatedaerosoldensityof1.75gcm−3.
Previous comparison of SO2− measurements from the anylonfilter(PCM2)(Edgertonetal.,2005).Bothsystems
4
Thermo Electron 5020 Sulfate Particulate Analyzer with were denuded to remove artifacts of HNO and NH , thus
3 3
filter-based methods from laboratory and field studies ob- thermodynamicsshouldfavormetathesisofNH NO .Sum-
4 3
servedgoodcorrelations(i.e.,slopederivedfromfieldstudy mer results showed that PCM1 agreed with PCM2 within
wascloserto1thanthatoflaboratorystudy)(Schwabetal., 5%andthat>95%oftheNO fromPCM1wasontheny-
3
2006).ItshouldbenotedthatSchwabetal.(2006)suggested lonbackupfilter.Fallresultsshowedagreementwithin10%
that the slope differences are due to ambient SO2− from and with >90% on the nylon filter (Edgerton et al., 2005).
4
−
the field study being catalytically converted to SO faster WhiletheuseofnylonbackupfilterslikelyminimizedNO
2 3
than the laboratory-generated SO2−. During this study, the lossesduringsampling,additionallossesduringfilterstorage
4
ACSMSO2− measurementsdiscrepanciesare4–44%com- andconditioningbeforeoff-linechemicalanalysiscannotbe
4
pared to that of the continuous modified HSPH sulfate an- ruledoutandcouldhavecontributedtotheobserveddiscrep-
alyzer, with the largest difference occurring during colder ancy.
months (fall season). This difference is within the expected Changesinmeteorologicalconditionsfromsummertofall
accuracyoftheACSMmeasurements,butsincetheJSTcon- might influence the equilibrium partitioning behavior of ni-
tinuousSO2− valuesareobtainedafteradjustingtothefilter trogenous compounds. Low temperatures and high relative
4
data,thebiascouldbeduetoartifactsfromthefilterdata. humidity (RH) in the fall could create thermodynamic con-
−
ditions that favor the partitioning of gaseous NO to the
3
4.4 DiscrepanciesofNO−measurements aerosol phase (Hennigan et al., 2008; Rastogi et al., 2011).
3 −
The fact that the observed NO discrepancies are larger in
3
ACSM NO− measurements are based on the measured the fall than the summer is consistent with evaporative loss
3 −
m/z30 and m/z46 ion signals. Positive biases at m/z30 of NO from the filter samples and reflected in the filter-
3
arepossiblyduetocontributionstothisionfromNO+ frag- adjustedcontinuousdata.
−
ments of organic nitrates and/or contributions from organic Insummary,itisunclearifthehigherACSMNO load-
3
CH O+ ions. A detailed investigation of the interference of ings reflect true NO− levels which include contributions
2 3
m/z30isprovidedinthesupplementalsection.Therelation- fromorganicnitratenotcapturedbyJSTNO−,orifitisfrom
3
ship of estimated excess signal of m/z30 linked to organic inaccurate subtraction of m/z30 originating from oxidized
andoxygenatedorganicaerosolisfoundtobeheteroscedas- organic aerosol. Also, it is possible the discrepancy may be
tic.Thus,oxygenatedorganicspeciescouldnotbesuggested due to the underestimation of JST NO− due to volatility
3
todirectlyinfluencenitratefragments. lossesfromthefilterswhichareusedtoscaletheJSTNO−
− 3
The continuous NO data are adjusted to the integrated data.Itislikelysomecombinationofalloftheabove,which
3
−
NO data, which can impose measurement biases, espe- cannotbeclearlydeterminedfromthisdataset,explainsthe
3
ciallyforsemi-volatilecompoundssuchasNO−.Heringand differencesbetweenNO−measurements.
3 3
−
Cass (1999) reported lower aerosol NO mass from Teflon
3
filters compared to that from denuded nylon filters. For this 4.5 Totalmassmeasurementsvariations
study, the PCM filter samples utilized both Teflon and ny-
lon filters downstream of a denuder in order to account for ACSMPM issumofACSMNR-PM (i.e.,organicandin-
1 1
− −
NO losses.PreviousSEARCHresultshavecomparedNO organics) plus EC measurements from JST site. This study
3 3
measurements with parallel systems: one with a Teflon pre- shows that total mass differences between ACSM PM and
1
filterandnylonbackupfilter(PCM1)andtheotherwithjust TEOM PM are 50–110%. Previous intercomparisons of
2.5
www.atmos-meas-tech.net/7/1929/2014/ Atmos.Meas.Tech.,7,1929–1941,2014
1938 S.H.Budisulistiorinietal.:IntercomparisonofanACSMwithambientfineaerosolmeasurements
the same instruments in summer in Beijing suggested that 5 Conclusions
ACSM NR-PM measured ∼30% less than TEOM PM
1 2.5
(Sun et al., 2012). Since the ACSM PM mass is a sum of Thisstudyaimstocomparespeciesandtotalmassmeasure-
1
species concentrations, the discrepancies in species specific mentsfromtheACSMtothecollocatedmeasurementsatthe
intercomparisons described above result in high discrepan- JSTsite(i.e.,ACSM,JSTcontinuousandfiltersamplers,and
cies of PM mass. Uncertainties in RIE values, particularly FRMfilters)overdifferentseasons.Massconcentrationsob-
1
for organic species, may be partly responsible for overesti- tainedfromthetwoACSMsagreewithin4–38%,exceptfor
mationofcertainspeciesresultinginoverestimationofNR- Cl−.Overall,thepercentagedifferencesofACSMspeciated
PM mass. On the other hand, loss of semi-volatile species massconcentrationsagreewithin4–51%fromtheSEARCH
1
−
from the filters (which are used together to adjust TEOM network measurements, except for NO (77–114%). Com-
3
loadings)couldalsoresultinlowerTEOMPM concentra- parison of ACSM OM to JST Sunset OC yielded OM/OC
2.5
tion.Thisissupportedbythefactthatinfall,whenthemete- ratiosof4.85and3.85forsummerandfallperiods,respec-
orologicalconditionsfavorsemi-volatileorganicaerosolen- tively.DiscrepanciesbetweenACSMPM1andTEOMPM2.5
hancement,theslopeoftheACSMPM toTEOMPM is are50–110%,whilediscrepanciesbetweenACSMPM1and
1 2.5
muchhigherthanthatinsummer(i.e.,slopeof1.80infallto FRMPM1 are10–73%.Estimatedaerosoldensitybasedon
1.19insummer). ratioofmasstovolumeconcentrationis1.75gcm−3.
Differences between NR-PM masses measured by the DiscrepanciesfoundintheintercomparisonsoftheACSM
1
ACSM and PM mass measured by the FRM method are andthecollocatedmeasurementsmightbeexplainedbythe
1
about 10–73%, with the lowest difference observed in the following:(1)RIEvaluesoforganicsmighthavedependen-
summer data set (Fig. 2; Table S2 in the Supplement). ciesonsourcesoforganicaerosol;(2)possibleinterferences
Discrepancies between the ACSM and FRM methods are from organic and organic-nitrate-specific fragments to the
−
larger during winter and spring compared to that of sum- m/z30ionsignalthatconstituteACSMinorganicNO sig-
3
mer, and the direction of the discrepancy is different in nal;and(3)evaporativelossesofsemi-volatilespeciesfrom
spring (ACSM<FRM) as compared to winter and summer the filter measurements used in the collocated continuous
(ACSM>FRM).Thismightbeduetopositiveartifactsofthe measurementadjustment.Futureworkshouldsystematically
filtersamplingmethod,whicharelikelyenhancedincolder examine all of the possibilities. Additionally, calibration of
months(Solomonetal.,2003a,b).Ontheotherhand,uncer- the continuous instruments used at monitoring sites should
tainties in RIE values may also result in inaccurate ACSM alsoberoutinelycheckedwithastandardaerosolinaddition
chemical constituent measurements leading to over- or un- tothestandardgascalibrationthatistypicallyperformed.
derestimationofACSMNR-PM mass.
1
The slope resulting from the intercomparison of ACSM
TheSupplementrelatedtothisarticleisavailableonline
NR-PM mass concentration and SEMS PM volume con-
1 1
atdoi:10.5194/amt-7-1929-2014-supplement.
centrationcan be usedto estimateaerosol density.Compar-
ison suggests a slope of 1.59 (Fig. 3); however, this num-
berwillbelargerwhentherefractorycomponents(i.e.,EC)
are added to NR-PM . Since the EC measurement for this
1 Acknowledgements. We thank the Electric Power Research Insti-
period (October–November 2012) are not available, we es-
tute(EPRI)fortheirsupport.WethankJerryBrownandMikeBoaz
timated that EC contributes about 10% to total PM based
of Atmospheric Research and Analysis (ARA) for their mainte-
on available data (i.e., October–November 2011). Hence, nance of the ACSM at the JST site. We thank Fred Brechtel for
the estimated aerosol density in Atlanta is 1.75gcm−3 for his inputon SEM-MCPCoperation anddata analysis.S. H.Bud-
fall2012.Inaddition,weestimatedtypicaldryaerosolden- isulistiorini is supported by a Fulbright Presidential Fellowship
sity based on average particle composition of 60.1% of or- (2010–2013) for attending the University of North Carolina at
ganics, 30.8% of inorganics, plus 10% of EC, and the as- Chapel Hill. We also thank Wendy Marth for her assistance in
sumption of organic, inorganics, and EC densities are 1.2, setting up the ACSM at the JST site and Sriram Suresh for his
1.77, and 1.77gcm−3 (Zhang et al., 2005b, and references assistance in ACSM fitting RIE formula derivation. GIT ACSM
measurements were supported by US EPA grant # RD83479901
therein). This approached resulted in typical dry density of
1.61gcm−3.Thesenumbersareconsistentwithrecentambi- as part of the Emory/Georgia Tech Clean Air Center (SCAPE).
RegardingtheGITACSMdata;thecontentsofthispaperaresolely
entaerosoldensityestimations,suchas1.61gcm−3 inBei-
the responsibility of the grantee and do not necessarily represent
jing(Huetal.,2012)and1.46gcm−3inPasadena(Hayeset
the official views of the US EPA. These agencies do not endorse
al.,2013). thepurchaseofanycommercialproductsorservicesmentionedin
thepublication.
Editedby:P.Herckes
Atmos.Meas.Tech.,7,1929–1941,2014 www.atmos-meas-tech.net/7/1929/2014/