influence of particle-bound water on aerosol mass measurementszenzors.com/kikuseminar/swietlicki...
TRANSCRIPT
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Influence of particle-bound water on aerosol mass
measurements
Erik Swietlicki
Division of Nuclear Physics,Lund University
P.O. Box 118, SE-21100 Lund, Sweden.
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Effect of hygroscopic particles on PM measurements
• Water mass added to PM mass.Regulating water?
• Particles might grow in size past the cut-off of the PM10/PM2.5 inlet.
Loose PM mass at high RH?
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European PM10 ConcentrationsEuropean PM10 Concentrations
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European PM2.5 ConcentrationsEuropean PM2.5 Concentrations
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Water vapour – liquid equilibrium
Raoult’s law (ideal solutions) states that the equilibriumwater vapour pressure is reduced over a salt solution:
wwsw
w
w annn
PPRH =+== *
RH relative humidity; nw moles of water; ns moles of salt ions in solutionsw
w miMa
+=
11
Water activity:
H2O(g)Pw(T,ms) < Pw*(T)RH<100%
Salt + H2O(l)
H2O(g)Vapour pressure Pw*(T)RH=100%
Pure H2O(l)
Molality of salt in solution: ms mol / kg water
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Cloud dropRH>100%
Humidified particleRH=90%Dry particle
Water solutionSalt
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RH Hysteresis EffectAmmonium Sulphate
RH Hysteresis
0.8
1
1.2
1.4
1.6
1.8
2
0 10 20 30 40 50 60 70 80 90 100
Relative Humidity (%)
Dia
met
er G
row
th F
acto
r
Crystallisation
Particle Dry Diameter = 100 nm
Deliquescence
Increasing Relative Humidity
Supersaturated Salt Solution
Dry Particle
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Hygroscopic Tandem Differential Mobility AnalyserH-TDMA
Excess Air
HumidifiedSheath Air
HumidAerosolCPC
Excess Air
Dry Sheath Air
Monodisperse Aerosol
Ambient Aerosol
DMA1 DMA2Aerosol
Humidifier
Bip
olar
C
harg
er
CPC
Drie
r
Division of Nuclear Physics, Lund University
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Hygroscopic properties (H-TDMA)265 nm (Forsdala)
Hygroskopiska egenskaperLTHs H-TDMA, Forsdala, Lycksele 2002
Torrstorlek = 265 nm
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
13/1 15/1 17/1 19/1 21/1 23/1 25/1 27/1 29/1 31/1 2/2 4/2 6/2 8/2 10/2 12/2 14/2 16/2 18/2 20/2 22/2 24/2 26/2 28/2 2/3 4/3 6/3 8/3 10/3
Datum 2002
Dia
met
ertil
lväx
t (r.f
. = 9
0%)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Aer
osol
ande
l
Mindre-hygroskopisk Hydrofob Mer-Hygroskopisk
Background
Fresh wood burning
Pure salts
“Hydrophobic”
Gro
wth
fact
or a
t 90%
RH
Aer
osol
frac
tion
⋅hygroscopic, ⋅intermediate, ⋅hydrophobic
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GFEMN Model Predictions for NaCl/Na2SO4(Ansari and Pandis, Atmos. Environ., 1999)
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5measured (Tang, 1997)}deliquescence
efflorescenceGFEMN
Part
icle
Mas
s C
hang
e, W
/Wo
Relative Humidity
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Effect of Soluble Fraction
Dry particle Humidified particle
Water solutionSaltFully
soluble
SaltOnly partly
soluble Insoluble
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Effect of SolubilityAmmonium Sulphate
Diameter Growth Factors at various Soluble Volume Fractions
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
0 10 20 30 40 50 60 70 80 90 100
Relative Humidity (%)
Dia
met
er G
row
th F
acto
r
Epsilon=1.0
Epsilon=0.5
Epsilon=0.1
Molality30 mol/kg
Molality6 mol/kg
Particle Dry Diameter = 100 nm
5.0=ε
1.0=ε
1=ε
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ZSR Model for Water Uptake of MixturesZSR mixing rule to estimate the water activity of a mixture,
based on the water activity of the pure compounds:
ms is the molality of compound s in the mixture,mo,s is the molality of the single electrolyte solution of
component s for which the water activity equals that of the solution mixture.
The ZSR method can also be expressed as
masswater_tot is the mass of water in the mixture at the given water activity,
masswater_s is the mass of water that would have been associated with the amount of the single electrolyte present in the mixed particle at the given water activity.
( )( )∑=
s wso
ws
amam
,
1
∑=s
swatertotwater massmass __
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H-TDMA Hygroscopic Diameter Growth Factors
Organic-Inorganic MixturesZSR Model for Water Uptake of Mixtures
ZSR model shows good agreement for MIX1 and MIXBIO.
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
20 30 40 50 60 70 80 90 100
Water activity
Gro
wth
fact
or
MIX1, measuredZSR, MIX1MIXBIO, measuredZSR, MIXBIO, no succinic acidZSR, MIXBIO, solubility of succinic acid
MIX1
MIXBIO
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Wet and Dry PM Size Distributions(Pittsburgh Air Quality Study, PAQS, Pandis et al.)
101 102 1030
5000
10000
15000
101 102 1030
5
10
15x 1010
Diameter, nm
NUMBER
VOLUME
Dry, 20% RH
Wet, 68% RH
Increase due to water
Aerosol water =
ρw(Vwet-Vdry)
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Aerosol Water During January 2002Aerosol Water During January 2002
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
RHwet, %
V w
et /
V d
ry
DRYDRY
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Aerosol Water During July 2001Aerosol Water During July 2001
0
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
RHwet, %
V w
et /
V d
ry
Wet particles at RH< 60%Wet particles at RH< 60%
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Aerosol Water During Spring 2002Aerosol Water During Spring 2002
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
Ambient RH
Vol
ume
Gro
wth
Fac
tor*
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
Ambient RH
Volu
me
Gro
wth
Fac
tor*
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
Ambient RH
Vol
ume
Gro
wth
Fac
tor* February March
April May
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100
Ambient RH
Volu
me
Gro
wth
Fac
tor*
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Mass Discrepancy and Atmospheric Acidity
0
0 . 5
1
1 . 5
2
2 . 5
3
3 . 5
4
A m m o n i u m B i s u l f a t e
N e u t r a l
mol
eq to
tal a
vail
amm
oniu
m
2 x
mol
eq S
O4
0
1 5
3 0
4 5
6 0
7 5
7/20
/01
00:0
0
06:0
0
12:0
0
18:0
0
7/21
/01
00:0
0
06:0
0
12:0
0
18:0
0
7/22
/01
00:0
0
06:0
0
12:0
0
18:0
0
7/23
/01
00:0
0
06:0
0
12:0
0
18:0
0
7/24
/01
00:0
0
06:0
0
12:0
0
18:0
0
7/25
/01
00:0
0
PM2.
5 (ug/
m^3
)
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Fine PM Composition
0
10
20
30
40
50
60
70
6/30
/01
7/8/
01
7/16
/01
7/24
/01
8/1/
01
8/9/
01
8/17
/01
8/25
/01
Date
PM2.
5 M
ass
(ug/
m3 )
CrustalECNH4NO3SO4OC*1.8FRM PM 2.5
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Comparison with theory
• GFEMN (Ansari and Pandis, 1999)• Input :
– hourly data of inorganic species: • Sulfate• Total nitrate, ammonium, chloride, sodium, etc. from the
steam sampler– OC and EC from 4 hour filter measurements – OC contribution to aerosol water is neglected
• Calculates equilibrium PM volume at the RH of dry and ambient measurements
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Predicted and Measured Water
1 8 15 22 290
20
40
60
PM2.
5w
ater
(µg
m-3
)
Date (July 2001)
MeasuredPredicted
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Mass Balance Closure – July 2001
0
10
20
30
40
50
60
WaterCrustalNO3SO4NH4ECOC*1.8FRM
PM2.
5 (µ
g m
-3)
1 4 7 10 13 16 19 22 25 28 31
Date (July 2001)
Good mass balance was achieved for the winter months
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Hygroscopic particles might grow past the cut-off of the PM10 Inlet
0,0
0,5
1,0
1,5
2,0
2,5
0,1 1 10 100Geometrisk diameter [µm]
dm/d
logD
p [m
g/m
³]
30 km/h 031008 11:54-12:14
50 km/h 031008 14:11-14:31
70 km/h 031008 16:17-16:37
70 km/h 030603 13:02-15:17
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Lung Deposition av particles - ICRP
Total
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Depositionincreases
Depositiondecreases
Lungdeposition och hygroskopisk tillväxt vid r.f.=99.5%
0%
20%
40%
60%
80%
100%
1 10 100 1000
Torrdiameter (nm)
Dep
oner
ad a
ndel
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
Tillv
äxtfa
ktor
(r
.f.=9
9.5%
)
Lungdeposition - fuktadLungdeposition - torrtTIllväxtfaktor
Dry Particle Diameter (nm)
Dep
osite
d Fr
actio
n
Hyg
rosc
opic
Gro
wth
Fac
tor
(at R
H=9
9.5%
)
Lung Deposition and Hygroscopic Growth(at RH=99.5%)
Hygroscopic particles shift the minimum in the deposition curve to smaller sizes.
Deposition – HumidifiedDeposition – HumidifiedGrowth Factor
Hygroscopic particles affect deposition:• More particle mass (>200 nm) is deposited in the
upper airways.• Fewer very small (<100 nm) particles are deposited
in the lower airways (number).
Particle hygroscopic propertiesImportance for deposition in the lungs
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Particle hygroscopic propertiesLung deposition (Forsdala)
Medelstorleksfördelningar och lungdeposition Antal - Yta - Volym
Forsdala, Lycksele 2002 (LTHs DMPS)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
1 10 100 1000
Torr partikeldiameter (nm)
Ant
alsk
onc.
dN
/dlo
gDp (
cm-3
)
0
1
2
3
4
5
6
7
8
9
Voly
mko
nc. d
V/dl
ogD
p (µm
3 /cm
3 )10
*Ytk
onc.
dS/
dlog
Dp (
µm2 /c
m3 )
AntalDeponerad antalsandelYtaDeponerad ytandelVolymDeponerad volymsandel
NumberDeposited NumberSurfaceDeposited SurfaceVolumeDeposited Volume
Particle lung deposition (number, surface area,volume) can be calculated with a time resolution of 10 minutes.
Dry Particle Diameter (nm)
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European PM10 CompositionEuropean PM10 Composition
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European Coarse Mode CompositionEuropean Coarse Mode CompositionPM10PM10--PM2.5PM2.5
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European PM2.5 CompositionEuropean PM2.5 Composition
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A European Aerosol PhenomenologyPhysical and chemical characteristics of particulate matterat kerbside, urban, rural and background sites in Europe.
Jean-P. Putaud et al. EU-JRC 2003 (EUR 20411 EN)
Conclusion 10:“When all main chemical components of the aerosol are
measured, they account for about 70% or more of the PM10 and PM2.5 mass. The rest is thought to be due to the presence of water or to the underestimation of the molecular mass – to – carbon mass ratio when calculating organic matter concentrations.”
As much as 30% of the aerosol mass can be water!
“This may be an important source of inconsistency between the PM mass concentrations determined according to the EN 12341 norm and TEOMs.”
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Effect of hygroscopic particles on PM measurements
• Water mass added to PM mass.Regulating water?
• Particles might grow in size past the cut-off of the PM10/PM2.5 inlet.
Loose PM mass at high RH?
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Thank you for your attention!