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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.
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?
European PM10 ConcentrationsEuropean PM10 Concentrations
European PM2.5 ConcentrationsEuropean PM2.5 Concentrations
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
Cloud dropRH>100%
Humidified particleRH=90%Dry particle
Water solutionSalt
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
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
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
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
Effect of Soluble Fraction
Dry particle Humidified particle
Water solutionSaltFully
soluble
SaltOnly partly
soluble Insoluble
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
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 __
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
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)
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
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%
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*
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
)
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
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
Predicted and Measured Water
1 8 15 22 290
20
40
60
PM2.
5w
ater
(µg
m-3
)
Date (July 2001)
MeasuredPredicted
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
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
Lung Deposition av particles - ICRP
Total
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
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)
European PM10 CompositionEuropean PM10 Composition
European Coarse Mode CompositionEuropean Coarse Mode CompositionPM10PM10--PM2.5PM2.5
European PM2.5 CompositionEuropean PM2.5 Composition
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.”
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?
Thank you for your attention!