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!