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Vertical Profiles of Pollution Particle Concentrations in the Boundary Layer above Paris (France) from the Optical Aerosol Counter LOAC Onboard a Touristic Balloon

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Atmospheric pollution by particulate matter represents a significant health risk and needs continuous monitoring by air quality networks that provide mass concentrations for PM10 and PM2.5 (particles with diameter smaller than 10 m and 2.5 m, respectively). We present here a new approach to monitor the urban particles content, using six years of aerosols number concentration measurements for particles in the 0.2−50 m size range. These measurements are performed by the Light Optical Aerosols Counter (LOAC) instrument onboard the tethered touristic balloon “Ballon de Paris Generali”, in Paris, France. Such measurements have allowed us first to detect at ground a seasonal variability in the particulate matter content, due to the origin of the particles (anthropogenic pollution, pollens), and secondly, to retrieve the mean evolution of particles concentrations with height above ground up to 150 m. Measurements were also conducted up to 300 m above ground during major pollution events. The vertical evolution of concentrations varies from one event to another, depending on the origin of the pollution and on the meteorological conditions. These measurements have shown the interest of performing particle number concentrations measurements for the air pollution monitoring in complement with regulatory mass concentrations measurement, to better evaluate the intensity of the pollution event and to better consider the effect of smallest particles, which are more dangerous for human health.
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Sensors2020,20,1111;doi:10.3390/s20041111www.mdpi.com/journal/sensors
Article
VerticalProfilesofPollutionParticleConcentrations
intheBoundaryLayeraboveParis(France)fromthe
OpticalAerosolCounterLOACOnboarda
TouristicBalloon
JeanBaptisteRenard1,*,VincentMichoud2andJérômeGiacomoni3
1LPC2E,CNRS/Universitéd’Orléans,45071OrléansCEDEX2,France
2LISA,CNRS/UniversitéParisEstCréteil,UniversitédeParis,InstitutPierreSimonLaplace(IPSL),
94010CréteilCEDEX,France;Vincent.Michoud@lisa.upec.fr
3AerophileSAS,75015Paris,France;giacomoni@aerophile.com
*Correspondence:jeanbaptiste.renard@cnrsorleans.fr;Tel.:+33632917742
Received:21December2019;Accepted:15February2020;Published:18February2020
Abstract:Atmosphericpollutionbyparticulatematterrepresentsasignificanthealthriskandneeds
continuousmonitoringbyairqualitynetworksthatprovidemassconcentrationsforPM10and
PM2.5(particleswithdiametersmallerthan10mand2.5m,respectively).Wepresenthereanew
approachtomonitortheurbanparticlescontent,usingsixyearsofaerosolsnumberconcentration
measurementsforparticlesinthe0.250msizerange.Thesemeasurementsareperformedbythe
LightOpticalAerosolsCounter(LOAC)instrumentonboardthetetheredtouristicballoon“Ballon
deParisGenerali”,inParis,France.Suchmeasurementshaveallowedusfirsttodetectatgrounda
seasonalvariabilityintheparticulatemattercontent,duetotheoriginoftheparticles
(anthropogenicpollution,pollens),andsecondly,toretrievethemeanevolutionofparticles
concentrationswithheightabovegroundupto150m.Measurementswerealsoconductedupto
300mabovegroundduringmajorpollutionevents.Theverticalevolutionofconcentrationsvaries
fromoneeventtoanother,dependingontheoriginofthepollutionandonthemeteorological
conditions.Thesemeasurementshaveshowntheinterestofperformingparticlenumber
concentrationsmeasurementsfortheairpollutionmonitoringincomplementwithregulatorymass
concentrationsmeasurement,tobetterevaluatetheintensityofthepollutioneventandtobetter
considertheeffectofsmallestparticles,whicharemoredangerousforhumanhealth.
Keyworks:particulatematter;urbanpollution;numberconcentrations;tetheredballoon
_______________________________________________________________________________
1.Introduction
Atmosphericpollutionbyparticulatematter(PM)isagrowingconcern,particularlyinurban
environmentsthatconcentratealargeportionofthepopulationandtheparticle’semissionsources.
Theseparticlescanbeprimary,directlycomingfromnaturalsources(dusts,salts,pollen)andfrom
anthropogenicsources(transport,heating,industries,agriculture)orsecondary,comingfrom
chemicalreactionsinvolvingsunlightoratmosphericoxidants.
Suchparticlesrepresentasignificanthealthrisk[1–3].ThePM10fraction(particleswith
aerodynamicdiametersmallerthan10m)canpenetratebeyondthenasopharyngealtractinthe
bronchianduptothepulmonaryalveoli.Thesmallerparticles,below1m,candiffuseinthebody
andbefoundinvarioushumanorgans[4–6].Thesmallertheparticlesare,thedeepertheycan
penetrateanddiffuseinthebody.Thus,detectingandcountingthesubmicronicpollutionparticles
isamajorareaofinterestforpublichealth.ExceedingtheWHO(WorldHealthOrganization)
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guidelinevaluesforPM2.5(particleswithaerodynamicdiametersmallerthan10m)of10gm3isthe
causeforabout20,000prematuredeathsormoreeachyearinmajorEuropeancities[7].Inparticular,
ithasbeenestimatedthatifthesestandardswouldhavebeenreacheditwouldhaveresultedina
gainofsixmonthsoflifeexpectancyformorethan11millioninhabitantsoftheParisregion[8].
TheParisregionischaracterizedbyrelativelyfewindustries.Ataregionalscale,theurban
backgroundconditionsaredrivenbylongdistancetransportofpollutants,accountingfor70%in
averageofPM2.5massconcentration[9–13].Localsourcesofprimaryparticlesaredominatedin
massbytrafficemissionandbyresidentialheatinginwinter,asinmanyotherurbanenvironments
[14,15].Thespatialdistributionofparticlesconcentrationsatthesurfacecanstronglydifferatthe
urbanscale,alsodependingonairmassdispersionconstrainedbytheurbantopography.
Atground,thePMcontentiscontinuouslymonitoredbyairqualitynetworks,whichprovide
themassconcentrationsofPM10usingmicrobalancesorsimilarinstruments.Somestationscanalso
provideanestimateofPM2.5massconcentrations.InParisandthe“IledeFrance”region(which
includesthecityofParis)theseregulatorymeasurementsareconductedbyAirparif[16].However,
thetechniquesdeployedacrosstheairqualitymonitoringnetworksarebylaworientedtowardthe
measurementoftheaerosolmassconcentration,whileitisknownthatthesmallestparticles,which
penetratedeeperintothehumanorganism,mostlydominatethenumberconcentrationand
contributeonlyweaklytothemass.Then,complementarymeasurementsprovidingparticlenumber
concentrationsinadditiontomassconcentrationscanbeproposedtomonitortheurbanparticle
contentandbetterunderstanditsdistributionanddynamics.Verticalprofilesmeasurementsofthe
aerosolscontentabovemajorcities,performedduringspecificcampaigns,canbeusedtobetter
understandtheverticaltransportandthedispersionoftheparticles[1719].
Theaimofthispaperistopresentsixyearsofaerosolsnumberconcentrationmeasurements
performedbytheLightOpticalAerosolsCounter(LOAC)instrumentonboardatetheredtouristic
ballooninParis.Suchconditionsofmeasurementsallowustobetterdeterminethemeanseasonal
variationsofparticlescontentfordifferentsizeclasses,andalsotoevaluatethemeanvertical
evolutionofparticlesandtofocusonsomespecificpollutionevents.
2.TheLightOpticalAerosolsCounter(LOAC)
TheLOACisaprototypeinstrumentdevelopedforgroundandballoonbasedmeasurements[20].
Particlesaredrawnuptotheopticalchamberthroughanisostatictubebyasmallpumpandcrossa
laserbeamworkingat650nm.Thescatteredlightisrecordedbytwophotodiodesatscatteringangles
of~15°and~65°,andphotonstraveldirectlytothephotodiodesthoughpipeswithoutalens(Figure1,
updatedfrom[21]).Atotalof19sizeclassesaredefinedintheparticlediameterrangebetween0.2
and~50m.Thesizeclassesarechosenasagoodcompromisebetweentheinstrumentsensitivityand
theexpectedsizedistributionofambientairparticles.Fora10minintegrationtime,theuncertaintyof
totalconcentrationsisabout±20%forconcentrationshigherthan10particlecm3upto±60%for
concentrationslowerthan101particlecm3.Theuncertaintiesinthesizedeterminationisof±0.025m
forparticlessmallerthan0.6m,5%forparticlesinthe0.72mrange,andof10%forparticlesgreater
than2m.
Themeasurementsat15°arealmostinsensitivetotherefractiveindexoftheirregularshaped
aerosolparticlesandcanbeusedtodeterminetheconcentrations[22].Ontheotherhand,
measurementsatsidescatteringaround65°areverysensitivetotherefractiveindexoftheirregular
particles[23].Anindicationofthetypologyofsuchparticlescanbeobtainedusinga“speciation
index”,retrievedbycombiningthe15°and65°channelsmeasurements.Thisindexissensitivetothe
imaginarypartoftherefractiveindexoftheparticles,andthustotheiropticalabsorbingproperties.
LaboratoryreferencesforthespeciationindexeshavebeendeterminedwithLOACfor4naturesof
particles:carbonaceous,mineraldust,salts,andliquiddroplet[20].Thespeciationindexesobtained
fromLOACobservationsintheambientairarecomparedtotheselaboratorydatatoderivethe
estimateddominanttypologyofparticlesindifferentsizeclasses.Theidentificationofthenatureof
theparticlesworkswellincaseofahomogeneousmediumbutismorequestionableincaseofa
heterogeneousmediumthatcausethespeciationindextobemorescattered.
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
Figure1.LightOpticalAerosolsCounter(LOAC)principleofmeasurementsattwoscatteringangles
(updatedfromRenardetal.,2018).
Finally,theconcentrationscanbeconvertedtomassconcentrations(ingm3)assumingspherical
particlesandmassdensitybetween1.2and2.2gcm3dependingonthedetectedtypologyofthe
particles.Forcarbonaceousparticlessmallerthan1m,themassdensityisassumedtobe2.0gcm3,
whilethedensityisassumedtobeof1.2gcm3forparticlesgreaterthan1m.Formineralparticles
thedensityisassumedtobeof2.2gcm3;incaseofnoidentification,thedensityisassumedtobeof
2.0gcm3(thesevaluesareupdatedfrom[20]).Theerrorbarsarecalculatedconsideringthe
uncertaintiesinsizedetermination.TheLOACaveragemassconcentrationsaccuracyisofabout
±5gm3whencomparedtomicrobalancemeasurementsinlaboratory[20].
TheperformancesofLOAChavebeenestablishedduringnumeroussessionsofintercomparison
withotherinstrumentsdedicatedtothecounting,sizedistribution,extinctions,andmass
concentrationsofsolidaerosolsintheatmosphere[20].ThesesessionshaveshownthatLOACcan
beusedforstudiesonurbanaerosols.
3.MeasurementsConditionsattheTouristic“BallondeParisGenerali”inParis(France)
TheLOAChasbeenmountedonthegondolaofthetouristictetheredballoon“BallondeParis
Generali”(Figure2)inthepark“AndréCitroën”inthesouthwestofParis,France(48.8414°N,
2.2740°E),sincemid2013andworkscontinuously[24].Dependingonthemeteorologicalconditions,
150to200daysperyeararefavorableforflying.TheheightismeasuredbyaGPS,withavertical
accuracyofabout±15m.Theballoonnominalmaximumheightabovegroundis150mandupto50
flightscanbeperformedperday.Someflightscanalsobeconducteduptoaheightof300mwhen
thewindspeedisverylow(<fewm1).Theurbanpollutioneventsoccurmainlyduringanticyclonic
conditionswhenthewindspeedislow;thus,theballooncanoftenflyduringsuchevents.
DuetotheballoonlocationinoneofthelargestparksinPariswithnomainhighwaysinthe
directvicinity,thegroundbasedmeasurementscanbereferredasbackgroundurbanconditions
(Figure3).Thehighestbuildingsclosetotheparkhaveaheightbelow50m.Therefore,wecanexpect
tomeasuremeanpersistenturbanpollutionwhentheballoonheightisabove50m.Nevertheless,
thesemeasurementsareconductedjustatonelocationinParis,thustheresultspresentedbelow
couldbenotrepresentativeofthegeneralpicture.

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Figure2.(a)LOACmountedonthegondolaofthe“BallondeParisGenerali”;(b)Theballooninthe
parkAndréCitroën(Paris,France).
Figure3.Mapofthevicinityofthe“ParcAndréCitroën”(thegreendotrepresentstheballoon
location,mapfrommappy.com).
LOACprovidesmeasurementsevery10s.Duringtheballoonflight,datamustbeintegrated
overatleast30storeducethemeasurementnoise.Sincetheballoonascentspeedisof1ms1,the
verticalresolutionforanindividualLOACconcentrationsprofileisofabout30m.Individualprofiles
canbealsodailyaveragedtoreducethenaturaldispersionoftheconcentration’smeasurements.For
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measurementsatground,thedatacanbeaveragedover10mintoreducethedispersionofthe
measurements.
4.MeasurementsatGround
Figure4presentsthe20132019evolutionoftheparticlenumberconcentrationswithtimefor
the19sizeclassesofLOACwhentheballoonisatgroundandoutsidemajorLOACand/orballoon
maintenanceperiod.Dataduringfogandheavyraineventshavebeenremovedbecauseofthe
presenceofdropletsthatcanskewtheretrievalofthesolidparticles.Forclarityreason,thedatahave
beensmoothedbyaslidingsmoothingprocedurewithawidthof2days.Thehighestconcentrations
correspondingtostrongpollutionseventswererecordedatthebeginningofwinter2013,andatthe
beginningof2014and2015.Itcanbenoticedthatthemeanlevelofconcentrationsforparticles
smallerthan10mmeasuredbyLOACishigherinthe2013periodthanafter(Figure4),duetostrong
buildingactivitiesclosetotheParcAndréCitroën(unfortunatelynoAirparifstationisclosetothis
locationtovalidatetheseobservations).
Figure4.Temporalevolutionofnumberconcentrationsforthe19LOACsizeclasseswhentheballoon
isatground(thedatahavebeensmoothedbyaslidingsmoothingprocedurewithawidthof2days).
ThePM10massconcentrationsobtainedbytheAirparifairqualitynetworkforastationinthe
suburbofParis(Vitry,backgroundurbanconditions,48.7778°N,2.3779°E)andforastationinarural
areainthesouthofParisregion(RuralSouth,48.3667°N,2.2333°E)alsoshowtheconcentrations
enhancementsduringpollutionevents(Figure5).ThemassconcentrationsderivedfromtheLOAC
measurementsarealsoplottedinFigure5andaregloballyingoodagreementwiththeAirparif
measurements(allthedatahavebeenalsosmoothedwiththesameprocedureasforLOACnumber
concentrations).Excludingthe2013periodwiththebuildingactivitiesclosetothepark,themean
LOACmassconcentrationsmeasurementsare6.5mm3and0.5mm3lowerthantheVitryandRural
Southstations,withastandarddeviationof10mm3and9.5mm3respectively.
Whenconsideringthesixyearsofmeasurements,aseasonalcycleseemstobepresentforthe
particlessmallerthanabout1m,withmaximumconcentrationsinwinterandminimum
concentrationsinsummer(Figure6).Thiscouldberelatedtotheheatingandtrafficduringwinter
butalsototheseasonalvariationoftheboundarylayerheight[25]andtothemeteorological
conditions.Theconcentrationsforparticleslargerthanabout15mexhibitalsoaseasonalcycle,
anticorrelatedwiththeseasonalcycleofthesmallerparticles;thehighestconcentrationsareobtained
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duringsummer(Figure6).Apossibleexplanationisthedetectionofpollens,sincemostofthepollens
areindeedinthe1550msizerangeandtheirseasonalityissimilartotheonedetectedbyLOAC.
Figure5.TemporalevolutionofthePM10massconcentrationsfromLOACatthe“BallondeParis
Generali”andfromtheAirparifairqualitynetworkforstationsinthesuburbofParis(Vitry)andin
theruralareainthesouthofParisregion(thedatahavebeensmoothedbyaslidingsmoothing
procedurewithawidthof2days).
Figure6.Annualevolutionoftheconcentrationsforthesmallestparticles(a)andthebiggestparticles
(b)detectedbyLOACforthesixyearperiod;theverticalbarscorrespondtothemeanabsolute
deviationoftheconcentrations.
5.VerticalProfiles
5.1.DailyProfiles
Duringthe20132019period,976dayswithflightsperformedduringdaytimeareavailable.
Amongthem148dayswithflightsuptotheheightof300mwereperformed.Sincemostoftheflights
wereconducteduptotheheightof150m,wewillconsidertheseflightstoestimatethemean
evolutionoftheconcentrationswithheight.Ontheotherhand,thefewflightspermonthuptothe
heightof300mcanbeusedtostudysomespecificevents.
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Tostudythemeanverticaltrend,theconcentrationsareintegratedover7heightranges:020m,
2040m,4060m,6080m,80100m,100120m,and120150m.Theverticalprofilesaredaily
averagedtoreducethevariabilityoftheindividualmeasurements.Thisvariabilityoriginatesfrom
themeasurementaccuracy(Poissondistribution)butalsofromvariationsinthewindconditions.
Globally,thedailystandarddeviationoftheconcentrationprofilesisinthe20%60%range.Thus,
thedailyprofilespresentedinthefollowingsubsectionscontainserrorbarsthatrepresentthe
standarddeviationforeachsizeclassandheightrange.
5.2.BackgroundConditions
Thedailyprofilesexhibitatemporalvariabilityofabouttwoordersofmagnitudedependingon
theweatherandonthepollutionconditions.Asexamples,Figure7presentstwonumber
concentrationsprofilesobtainedinsummertime,8July2016and20September2017,duringlow
pollutionconditions(theLOACPM10massconcentrationswereofabout10gm3atgroundforboth
casesandinthe515gm3rangeinflight).Thetwoprofilesexhibitdifferentverticalevolutionsand
sizedistributions;inparticular,theprofileofthe8July2016presentsanexcessoflargeparticlesin
the1030msizerange,probablyduetoapollenepisode.
Figure7.Evolutionwithheightofnumberconcentrationsforthe19sizeclassesofLOACwhenthe
urbanpollutionislow.(a)8July2016;(b)20September2017.
Ateachheightrange,thehistogramofthenumberconcentrationsobtainedduringthesixyearsof
measurementsdonotfollowagaussiandistribution.Ontheotherhand,agaussiandistributioncanbe
obtainedwhenconsideringthelogarithmoftheconcentrations.Fourbroadrangeclassesaredefined:
0.21.0m,13µm,310m,and1550m.Then,foreachheightrangeandforthe4broadrangeclasses,
thehistogramofthelogarithmoftheconcentrationsisfittedbyagaussianfunction,toestimatethe
modeofnumberconcentrations(correspondingtothemostfrequentconcentrationsoverthefulltime
periodofmeasurements,examplesaregiveninFigure8).
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Figure9presentstheevolutionwithheightofthemorefrequentconcentrationsforthe4
broadrangeclasses.Itmustbenoticedthattheseverticalprofilesmightnotbeindividually
consistentandarenotthemodalverticalprofilesbutareasequenceofindividualmodal
concentrationforeachheightrange.Forthesubmicronicparticles,noevolutionisdetected,whilethe
concentrationsslightlydecreaseofabout20%inthefirsttensofmetersforthelargestparticles.This
couldresultoftheparticlessensitivitytoupwarddiffusion,dependingontheirsizes,shapes,and
densities,butthisanalysisrequiresfurtherinvestigation.
Figure8.Examplesofthehistogramofthelogarithmoftheconcentrationsattwoheightrangesfor
thesixyearsofmeasurements,forthe13msizerange.(a)measurementsatground;(b)
measurementsattheheightof120150m.
Figure9.Evolutionwithheightofthemodeofnumberconcentrationsforthesixyearsof
measurements.(a)broadrangeclass0.21.0µm;(b)broadrangeclass13µm;(c)broadrangeclass
310µm;(d)broadrangeclass1550µm.
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5.3.MainPollutionEvents
Duringmostofthepollutionevents,thewindswerelow,thusflightsuptoaheightof300mwere
available.WepresentbelowthemainpollutioneventsobservedbyLOACinthe20132019period.
5.3.1.WinterEvent
PollutionisoftenencounteredinParisduringanticyclonicconditionsinwinter,typicallyin
December,withparticulatesoriginatingfromtrafficandheating[26].Duringsuchevents,the
concentrationoftheparticlescanbefrom10to100timeshigherthanduringthesummerbackground
conditions.Thestrongerwintereventrecordedinthe20132019periodbyLOACoccursinDecember
2013.Figure10presentstheprofilesforthestrongpollutioneventin11December2013.Theprofile
exhibitsastrongconcentrationincreaseataheightof200mforthesmallestparticles<0.4mwhilethe
concentrationsareabouttentimeslowerabove,duetoatemperatureinversionlayerresultingfromthe
anticyclonicconditions.TheLOACPM10massconcentrationsatgroundareofabout50gm3at
ground,ofabout60gm3ataheightof130mduetoanincreaseofconcentrationsofparticlesinthe
510µmsizerange,onlyof45gm3ataheightof200malthoughtheincreaseofsubmicronicparticles
concentrations,andofabout35gm3above.Thus,theheightvariabilityinmassconcentrationsdo
notfullyreflectthemorecomplexheightvariabilityofthenumberconcentrationsforthevarious
sizeclasses.
Figure10.EvolutionwithheightofLOACconcentrationsforthe11December2013pollutionevent.
(a)numberconcentrations;(b)PM10massconcentration.
5.3.2.SpringEvent
Anothertypeofpollutionisoftenencounteredinbeginningofspring,typicallyinMarch,mainly
originatingfromthecombinationoflocalpollutionandthetransportofpollutantsfromagricultural
activitiesaroundParis[27,28].TheverticalprofilesinFigure11forthe14March2014and17March
2015differfromthosemeasuredinwinter(Figure10).Theconcentrationsoftheparticlesaremore
constantwithheight,becauseboundarylayeristhickerduetomoreverticallymixedairmasses,
whileconcentrationsofthebiggestparticlesslightlydecreasewithheight.TheLOACPM10mass
concentrationsdecreasefrom110gm3atgroundtoabout65gm3at300mforthe17March2015
anddecreasefromabout40gm3atgroundtoabout20gm3at300m(Figure12).
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Figure11.EvolutionwithheightofLOACnumberconcentrationsduringthespringpollutionevents.
(a)14March2014;(b)17March2015.
Figure12.EvolutionwithheightofLOACPM10massconcentrationsduringthespringpollution
events.(a)14March2014;(b)17March2015.
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5.3.3.SummerEvent
Pollutioneventscanbealsopresentduringsummer,dependingontheweatherconditions.
Althoughnomajorpollutioneventwasdetectedatgroundduringthe20142019period,anincreasein
aerosolconcentrationswasdetectedfrom24to30Juneaboveaheightofabout100m.Forthe25June
2019profile,thenumberconcentrationswereupto10timeshigherforparticlessmallerthan5minthe
100200mheightrangethanatground,themassconcentrationwerefivetimeshigher(Figure13).This
eventwasnotdetectedfromgroundbasedstation,showingtheinterestofballoonborne
measurements.
Noexplainableextrasource(smoke,industrialactivities)wasidentifyduringthisperiodatthe
vicinityofthemeasurementlocation.TheLOACtypologyindicationdiffersstronglyfromthoseof
theotherpollutioneventsanddonotcorrespondtotheusualLOACtypologyforconventionalurban
pollutionparticles(carbonaceous,mineral,sulfate,ammoniumnitrate).Atpresentnoexplanation
canbeproposedfortheoriginofthiseventandforthenatureoftheparticles,andfurther
investigationsareneeded.
Figure13.EvolutionwithheightofLOACconcentrationsforthe25June2019pollutionevent.(a)
numberconcentrations;(b)PM10massconcentration.
6.Discussion
Theconcentrationsoftheparticlesandtheirverticalevolutionvariesfromonepollutionepisode
toanother.Tobetterevaluatethevariability,wecanconsidertheprevious4broadrangeclasses,now
appliedtothe6verticalprofilespresentedinFigures7,10,11and13.Afactorofmorethan50occurs
betweenlowpollutionandhighpollutioneventsforthe3firstbroadrangeclasses(particleswith
diametersmallerthan10m),asshowninFigure14.Asexpected,thehighestconcentrationsofthe
submicronicparticlesoccurfortheDecember2013eventandfortheMarch2014and2015events.For
theparticlesinthe13msizerange,thehighestconcentrationsweredetectedduringtheMarch2014
event,duringtheMarch2015event,andduringtheJune2019eventinflight.Inparticular,theMarch
2015eventwasdominatedbysecondaryaerosols(moreparticularlyofammoniumnitrate,as
reportedin[28]).Theconcentrationofthe13mparticlesduringtheDecember2013eventis
significantlylowerthanfortheMarch2014event.Thetendencyforthe310mparticlesisrelatively
similartotheoneforthe13mparticles,exceptfortheMarch2015concentrationsthatarecloserto
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thebackgroundconditions.Finally,noobviouscorrelationbetweenpollutionandconcentrationsof
thelargestparticles(1550m)canbepointedout,since,aspreviouslymentioned,theseparticlesare
likelymainlyoriginatingfrompollenevents.
WhenconsideringthemassconcentrationsvaluesfromLOAC,thehighestpollutioneventswere
onMarch2014andMarch2015(withmaximumvaluesupto110gm3andupto90gm3,
respectively).Whenconsideringthenumberofallparticleslargerthan0.2m,thehighest
concentrationsweredetectedonDecember2013,althoughthemassconcentrationswereonlyofup
to80gm3.Thesedifferencescouldbeduetotheoriginofthepollution,typicallyprimary
(carbonaceous)particlesversussecondaryaerosols.
MassconcentrationvariabilityfromlowpollutiontohighpollutionlevelsinParisisaboutone
orderofmagnitude,whilethevariabilityisoftwoordersofmagnitudefornumberconcentration.
Mostofthestudiesonthepollutiontrendincitiesarebasedonmassconcentrations[29].Itisoften
establishedthatthemassconcentrationofPM10isdecreasinginEuropeancities,mainlydueto
changesindieselenginesandparticlesfilters[30].Nevertheless,possiblechangeinthesizedistribution,
aspossibleincreaseinnumberconcentrationofsubmicronicparticles,cannotbeestimatedwithsuch
measurements.Also,theverticalevolutionofparticlesnumberconcentrationscanchangedepending
ontheoriginofthepollutionevents.Numberconcentrationmeasurementsasthosepresentedabove,
mainlyforsubmicronicthatcanbethemostdangerousforhealth[4–6],maybemoreefficientthan
massconcentrationstoevaluatethehealthimpactofpollutionseventsandtoestablishthetemporal
trendofnumberconcentrationof(anthropogenic)pollutionparticles.Obviously,suchtrendscannotbe
retrievedfrommeasurementsonlyatonelocation;thus,anetworkof(optical)counterinstruments
mustbeimplantedinparallelwithregulatorymassconcentrationinstruments.
Figure14.Evolutionwithheightofaerosolsconcentrations.(a)broadrangeclass0.21.0µm;(b)
broadrangeclass13µm;(c)broadrangeclass310µm;(d)broadrangeclass1550µm.
7.Conclusions
ThesixyearsofnumberconcentrationmeasurementsperformedinParis,France,bytheLOAC
instrumentforparticlesinthe0.250msizerangeallowedustodetectaseasonalvariabilityinthe
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PMcontent,expectedlyduetotheoriginoftheparticles(anthropogenicpollution,pollens).Sincethe
instrumentismountedonboardthetouristictetheredballoon“BallondeParisGenerali”,themean
evolutionofparticlesconcentrationswithheightwasobtainedforbackgroundconditionsuptoa
heightof150m.Theconcentrationsofsubmicronicparticlesremainconstantwithheight,whilethe
concentrationsslightlydecreaseinthefirsttensofmetersforthelargestparticles.Measurements
werealsoconductedduringmajorpollutionevents,withparticlesconcentrationsseveraltensof
timeshigherthanduringbackgroundconditions.Theverticalevolutionofconcentrationsvariesfrom
oneeventtoanotherone,dependingontheoriginofthepollutionandonthemeteorological
conditions.Inparticular,anaccumulationlayerwassometimesdetectedataheightofabout200m
inwinterduetotemperatureinversionlayer.
Thesemeasurementshaveshowntheinterestofperformingparticlenumberconcentrations
measurementsfortheairpollutionmonitoringincomplementwithregulatorymassconcentrations
measurements,tobetterevaluatetheintensityofthepollutioneventandtobetterconsidertheeffect
ofsmallestparticles.
WehavepresentedherethefirstresultsobtainedwithLOACattheParistouristicballoon.
FuturestudiescouldbeconductedusingthisLOACdatabase,asmodelingworksonthevertical
transportofparticles,studiesonthecorrelationofthevariabilityoftheparticle’sconcentrationsand
theirsizedistributionwiththemeteorologicalconditions,andstudiesontheevolutionoftheparticle
concentrationsafterrain.Finally,aLOACisalsomountedinanothertouristicballoon,the“Ballon
TerraBotanica”inasmallercity,Angers(WestofFrance);itsmeasurementswillbecomparedsoon
tothoseofParistobetterestablishthesimilaritiesandthedifferencesfortheverticalevolutionofthe
pollutionparticlesdependingonthemeasurementlocations.
NewmeasurementscouldbeproposedbymountingtheLOACinstrumentonboardthevarious
touristictetheredballoonsavailableintheworld,tobetterevaluatetheverticaltransportoftheurban
pollutionparticles.
Authorcontribution:TheinstrumentconceptionandthedataanalysiswereconductedbyJ.B.Renard.The
measurementsinterpretationwasdonebyJ.B.RenardandV.Michoud.Thefundingacquisitionswereconducted
byV.Michoud,J.B.RenardandG.Giacomoni.The“BallondeParis”facilitieswereprovidedbyJ.Giacomoni.
Funding:ThisprojectwaspartlyfundedbyADEME(projectMESUrPOP)CORTEA/contractnumber
1762C0004andbytheLabex“ÉtudedesgéofluidesetdesVOLatils–Terre,AtmosphèreetInterfacesRessources
etEnvironnement”(VOLTAIRE)(ANR10LABX10001)managedbytheUniversityofOrleans.
Acknowledgments:TheregulatorymassconcentrationsareprovidedbytheairqualitynetworkAirparif.The
authorswanttothankthepilotsofthetouristicballooninParis,andG.Berthet,P.Formenti,J.F.Doussin,and
IsabellaAnnesiMaesanoforfruitfuldiscussionsthathelpimprovingourpaper.
ConflictsofInterest:Theauthorsdeclarenoconflictofinterest.Thefundershadnoroleinthedesignofthe
study;inthecollection,analyses,orinterpretationofdata;inthewritingofthemanuscript,orinthedecisionto
publishtheresults.
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©2020bytheauthors.LicenseeMDPI,Basel,Switzerland.Thisarticleisanopenaccess
articledistributedunderthetermsandconditionsoftheCreativeCommonsAttribution
(CCBY)license(http://creativecommons.org/licenses/by/4.0/).
... Another similar study is that of Renard et al. [15], in which the vertical profiles of airborne particle concentrations within the boundary layer were measured above Paris (France) utilizing an optical particle counter onboard a balloon used for touristic purposes. During the long-term monitoring campaign, concentrations were measured at various levels up to a height above ground of 150 m. ...
... The same holds for PM 2.5 and the alveolic fraction. The inhalable fraction would be roughly equivalent to the total suspended particulate matter or PM 15 . The cyclone sampling head fitted to the inlet of the optical particle counter used in this study had a 15 µm cut-off, as detailed previously. ...
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Preliminary monitoring campaigns in three (nonindustrial) indoor environments (a corridor, a coffee room with a kitchenette, and a single-occupancy office, all located in the same public building) were carried out, in which the vertical concentration profiles of airborne particulate matter (inhalable, thoracic, and alveolic fractions, as well as PM10 and PM2.5) and carbon dioxide were determined using two distinct, purpose-built sequential sampling systems. One of the systems was specifically built for use with gas monitors and is based on the organ-pipe sequential air sampling technique. The second system better suited the sequential air sampling of particulate matter. Both systems were electronically controlled. Six receptor levels at heights of 0.25, 0.95, 1.25, 1.65, 2.15, and 2.75 m above the ground/floor were considered. The outcomes of the campaigns are presented. The larger-size particle fractions exhibited the most vertical variation in concentration. With respect to measurements at a height of 1.25 m above the floor, percentage differences as high as 80% were recorded. Given the appreciable measured variation in concentration over a height of approximately three meters, further investigation is warranted, especially in view of the exposure of humans of different heights, e.g., adults and children, and possibly different circumstances, e.g., standing and sitting.
... Beenose is based on light scattered by particles crossing a laser beam in the visible domain, which has been reported to help in distinguishing some pollen families from other ones in several studies [24][25][26][27][28][29][30]. The same principle has also been used to develop optical counters with typology determination capabilities, to distinguish between anthropogenic pollution particles, natural mineral particles, and pollens [31,32]. Beenose has already been tested in laboratory conditions, demonstrating its capacity to discriminate pollen particles from other particles and to characterize some pollen taxa [33]. ...
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... Other parameters such as the number concentration and the size distribution of the particles must be considered. They can provide some valuable information about the origin of the particles, their mode of production, and their transport scheme [29,30]. Also, the number concentration provides better information on what is actually inhaled by a person, targeting the concentration of particles that enter deeper in the body with respect to the particle size. ...
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... Apart from dust episodes, in Europe mainly coming from Sahara [38], the main PM peaks are due to anthropogenic activities. The peaks occur during periods of anticyclonic conditions when pollutants accumulate and cannot be dispersed by winds [36,39]. The primary and secondary PM originate from vehicular traffic throughout the year (mainly carbonaceous particles), from industrials activities (all kinds of particles), from heating in winter (mainly carbonaceous particles), and from agricultural activities in autumn and spring (mainly ammonium). ...
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A secondary organic aerosol (SOA) model, H2O (Hydrophilic/Hydrophobic Organic), is evaluated over the Paris area. This model treats the formation of SOA with two kinds of surrogate species: hydrophilic species (which condense preferentially on an aqueous phase) and hydrophobic species (which condense only on an organic phase). These surrogates species are formed from the oxidation in the atmosphere of volatile organic compounds (VOC) by radicals (HO and NO3) and ozone. These VOC are either biogenic (isoprene, monoterpenes and sesquiterpenes) or anthropogenic (mainly aromatic compounds). This model includes the formation of aerosols from different precursors (biogenic precursors, aromatics), and semi-volatile organic compounds (SVOC) from traffic. The H2O aerosol model was incorporated into the Polyphemus air quality modeling platform and applied to the Paris area and evaluated by comparison to measurements performed during the Megapoli campaign in July 2009. The comparison to measurements in the suburbs and in the city center of Paris shows that the model gives satisfactory results for both elemental carbon (EC) and organic carbon (OC). However, the model gives a peak of OC concentrations in the morning due to high emissions from traffic, which does not appear in measurements. Uncertainties in the modeled temperature, which can affect the gas-particle partitioning, in the partitioning of primary SVOC or underestimation of primary organic aerosol (POA) evaporation by the model could explain the differences between model and measurements. Moreover, using a theoretical mechanism for the oxidation of primary SVOC and intermediate volatility organic compounds (IVOC), POA concentrations were found to be likely overestimated by models due to the use of simple partitioning constants (which do not take into account the affinity of a compound with the liquid aerosol solution) or due to the assumption that the organic aerosol solution is a one-phase ideal solution. The organic aerosol in the city center of Paris was found to be originating mostly from distant sources with only 30 to 38% due to local sources.
Article
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We have investigated the behaviour of light scattering by particulates of various sizes (0.1 μm to 100 μm) at a small scattering angle (below 20°). It has been previously shown that, for a small angle, the scattered intensities are weakly dependent upon the particulates' composition (Renard et al., 2010). Particles found in the atmosphere exhibit roughness that leads to large discrepancies with the classical Mie solution in terms of scattered intensities in the low angular set-up. This article focuses on building an effective theoretical tool to predict the behaviour of light scattering by real particulates at a small scattering angle. We present both the classical Mie theory and its adaptation to the case of rough particulates with a fairly simple roughness parameterisation. An experimental device was built, corresponding to the angular set-up of interest (low scattering angle and therefore low angular aperture). Measurements are presented that confirm the theoretical results with good agreement. It was found that differences between the classical Mie solution and actual measurements – especially for large particulates – can be attributed to the particulate roughness. It was also found that, in this low angular set-up, saturation of the scattered intensities occurs for relatively small values of the roughness parameter. This confirms the low variability in the scattered intensities observed for atmospheric particulates of different kinds. A direct interest of this study is a broadening of the dynamic range of optical counters: using a small angle of aperture for measurements allows greater dynamics in terms of particle size. Thus it allows a single device to observe a broad range of particle sizes whilst utilising the same electronics.
Article
During March 2015, a severe and large-scale particulate matter (PM) pollution episode occurred in France. Measurements in near real-time of the major chemical composition at four different urban background sites across the country (Paris, Creil, Metz and Lyon) allowed the investigation of spatiotemporal variabilities during this episode. A climatology approach showed that all sites experienced clear unusual rain shortage, a pattern that is also found on a longer timescale, highlighting the role of synoptic conditions over Wester-Europe. This episode is characterized by a strong predominance of secondary pollution, and more particularly of ammonium nitrate, which accounted for more than 50% of submicron aerosols at all sites during the most intense period of the episode. Pollution advection is illustrated by similar variabilities in Paris and Creil (distant of around 100 km), as well as trajectory analyses applied on nitrate and sulphate. Local sources, especially wood burning, are however found to contribute to local/regional sub-episodes, notably in Metz. Finally, simulated concentrations from Chemistry-Transport model CHIMERE were compared to observed ones. Results highlighted different patterns depending on the chemical components and the measuring site, reinforcing the need of such exercises over other pollution episodes and sites.