A Method for Measurement of Fine Aerosol H2O Content:

The Dry-Ambient Aerosol Size Spectrometer (DAASS)

2

Authors

Charles StanierUniversity of IowaChemical and Biochemical Engineeringcharles-stanier@uiowa.edu

Andrey KhlystovDuke UniversityCivil and Environmental Engineeringandrey@duke.edu

Spyros PandisUniversity of Patras, GreeceCarnegie Mellon UniversityChemical Engineeringspyros@andrew.cmu.edu

3

Abstract (1)

Hygroscopic growth of atmospheric particles affects a number of environmentally important aerosol properties.

But aerosol water content is typically estimated, not measured, using models and assumptions that may be in error – therefore, we want to measure the water content.

The systemConsists of two Scanning Mobility Particle Sizers (SMPS) and an Aerodynamic Particle Sizer (APS) covering 3 nm to 10 micronInlets either ambient RH or dried through Nafion driers (switched every 7.5 minutes)Sheath air RH for SMPS also dried or ambient

Aerosol water is measured and growth factors are calculated fromthe difference or ratio between aerosol volumes

Published As: Stanier, C., Khlystov, A., Chan, W.R., Mandiro, M., and Pandis, S.N., “A Method for the In-situ Measurement of Fine Aerosol Water Content of Ambient Aerosol: the Dry-Ambient Aerosol Size Spectrometer (DAASS)”, Aerosol Science and Technology, Vol 28(S1), 2004, pp. 215-228.

4

Abstract (2)

Benefits of combined systemWhen sampling in dry only mode

After data processing, provides a single dry number size distribution for the entire rangeAerosol volume through 2.5 microns was highly correlated with dried TEOM using this technique

When sampling in dry-wet mode, can calculate aerosol waterThe measured value of aerosol water was found to be more accurate than f(RH) or modeled values in the following applications:

estimating light scatteringnitrate partitioningphysical state of the aerosol

Amount of absorbed water also used to calculate water uptake by organics

5

Organization of This Poster

Background

Experimental Setup

Example Results (Dry Only)

Example Results on H2O Content

Panels6-8

Panels8-12

Panels13-15

Panels16-18

6

Pittsburgh Air Quality Study (PAQS)

2 Year Collaborative Study17 Participating GroupsFunded by

Environmental Protection AgencyDepartment of Energy

Main goalsCharacterize Pittsburgh aerosols

SourcesAtmospheric ProcessesInstruments

MeasurementsMeteorologyAtmospheric gasesAerosol parametersParticle size distribution, ambient relative humidityParticle size distribution, dried

This MethodPresented in

this work

7

Pittsburgh AirQuality Study – Schenley Park Station

Schenley ParkSampling Site

View TowardDowntown

Particle SizeSampling Instruments

8

Aerosol Water Content – Review

Which “branch” or state are particles generally inhydrated or dried?

What is the crystallization relative humidity?How well can we model water uptake?What is the role of organic compounds in water uptake?

0 .5

1

1 .5

2

2 .5

0 20 40 60 80 100

Relative Humidity

Hyd

rate

d D

iam

eter

----

----

----

----

----

----

----

----

-

Drie

d D

iam

eter

Ammonium Sulfate Hygroscopicity of “f(RH)”

9

Dry-Ambient Aerosol Size Spectrometer

Reconfigured commercial instrumentsRH control systemInlet particle losses characterizationCustom control, data acquisition, and data reduction software

10

Dry-Ambient Aerosol Size Spectrometer

RH

APSAPS

Dry sheath airfor Nafion dryers

Vent excessdry air1 LPM

RH

RH

LL -- DM

AD

MA

NN-- D

MA

DM

ARH

HEPA MFHEPA

HEPA

RH

HEPAMFHEPA

HEPA

AmbientAir In

Dry AirExhaust

CPCCPC

CPCCPC

AmbientAir In

AerosolInlets

MF

Clean, Dry &Regulated Air

3-Way Plug Valvew/ Solenoid Actuator∆P Flowmeter

Ball Valve, Air Actuated

Mass Flow Meter

Bipolar Charger

Nafion DryerRotameter

RH

RH

APSAPSAPSAPS

Dry sheath airfor Nafion dryers

Vent excessdry air1 LPM

RH

RH

RHRH

LL -- DM

AD

MA

NN-- D

MA

DM

ARHRH

HEPAHEPA MFMFHEPAHEPA

HEPAHEPA

RHRH

HEPAHEPAMFMFHEPAHEPA

HEPAHEPA

AmbientAir In

Dry AirExhaust

CPCCPC

CPCCPC

AmbientAir In

AerosolInlets

MFMF

Clean, Dry &Regulated Air

3-Way Plug Valvew/ Solenoid Actuator∆P Flowmeter

Ball Valve, Air Actuated

Mass Flow Meter

Bipolar Charger

Nafion DryerRotameter

11

SMPS and APS OverlapSize Particles under very low Reynolds Number conditionsFviscous >> Finertial

Mass & density do not effect measured sizeOnly physical size and shape

( ) ( )1

2ln32

rr

shst

st

qLVne

DCD

µ=

2/1pstaero DD ρ≈

Sizing under high RePhysical size, shape, and density matter

12

SMPS and APS Overlap

June 14, 2002 – 6 AM – 10 AM

Shift using densityof 1.6 g/cm3

Effective density for shift determined independently for each hour

13

Calculating Aerosol Mass with DAASS

Density estimate (for volume to mass conversion) madefrom speciation measurements

(mainly OC and ammonium sulfate)

0

20

40

60

7/1 0:00 7/2 0:00 7/3 0:00 7/4 0:00 7/5 0:00 7/6 0:00 7/7 0:00 7/8 0:00

TEOM

DAASS & Density Estimate

14

0 10 20 30 40 50 60 70 80 90

0

10

20

30

40

50

60

70

80

PM

2.5,

µg/

m3

Particulate Volume (PV2.5), µm3/cm3

y = x

Comparison to Independent Measurement

Aero

sol M

ass

(µg

m-3)

Aerosol Volume (10-6cm3 m-3)

WithoutAPS Shift Correction

Algorithm

15

0 10 20 30 40 50 60

0

10

20

30

40

50

60

70

80

PM2.

5, µ

g/m

3

Particulate Volume (PV2.5), µm3/cm3

y = 1.4 x

Comparison to Independent Measurement

WithAPS Shift Correction

Algorithm

Aero

sol M

ass

(µg

m-3)

Aerosol Volume (10-6cm3 m-3)

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Example Result, Dry-Wet Operation

0

5,000

10,000

15,000

20,000

25,000

1 10 100 1,000 10,000

smps, dried

smps, ambient

nano-smps, dried

nano-smps, ambient

aps, dried

aps, ambient

14% RH, 150 nm64% RH, 175 nm

Particle Mobility Diameter (nm)

dN/d

logD

p(c

m-3

)

0

5,000

10,000

15,000

20,000

25,000

1 10 100 1,000 10,000

smps, dried

smps, ambient

nano-smps, dried

nano-smps, ambient

aps, dried

aps, ambient

14% RH, 150 nm64% RH, 175 nm

Particle Mobility Diameter (nm)

dN/d

logD

p(c

m-3

)

17

Example Results for Aerosol Water

0

10

20

300

20

40

60

80

100

Rel

ativ

eH

umid

ityAe

roso

l Wat

erC

onte

nt (µ

g/m

3 )R

elat

ive

Hum

idity

Aero

sol W

ater

Con

tent

(µg/

m3 )

(a)

(b)Equation (5)

Equation (10)

RH at SMPS Aerosol Charger, Ambient Scans

SMPS Sheath RH, Ambient Scans

(a)

(b)Equation (5)

Equation (10)

RH at SMPS Aerosol Charger, Ambient Scans

SMPS Sheath RH, Ambient Scans

0.0

0.2

0.4

0.6

0.8

1.0

7/1 0:00 7/2 0:00 7/3 0:00 7/4 0:00 7/5 0:00 7/6 0:00 7/7 0:00 7/8 0:00

0

20

40

60

PM2.

5 (µ

g/m

3 )Ae

roso

l Wat

er /

TEO

M P

M2.

5PM

2.5

(µg/

m3 )

Aero

sol W

ater

/TE

OM

PM

2.5

(c)

(d)

(c)

(d)

TEOM

DAASS & Density EstimateRH PM2.5

H2O

0.07/1 0:00 7/2 0:00 7/3 0:00 7/4 0:00 7/5 0:00 7/6 0:00 7/7 0:00 7/8 0:00

H2O / PM2.5

Dry at 30-60% RH

Hydrated at 30-60% RH

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Aerosol Water & Nephelometer Bscat

0

100

200

300

400

0 100 200 300 400

Summer

Estim

ated

Bsp

(Mm

-1)

Measured Bsp (Mm-1)

1:1

0 100 200 300 400

Summer

Measured Bsp (Mm-1)

1:1

H2O estimated asf(RH, Chemical Composition)

H2O from DAASS measurement

19

Acknowledgements

US Environmental Protection Agency Contract R82806101 US Department of Energy National Energy Technology Laboratory Contract DE-FC26-01NT41017

Related PresentationsPoster 12-PD16 Particle Density And Shape Factors Estimated From Merging Aerodynamic And Mobility Size DistributionsPoster 12-PA9 Light Scattering by Fine Particles During PAQS: Measurements and ModelingPoster 12-PD13 Ambient Aerosol Size Distributions Measured During PAQSTalk 19-C2 (Friday 10:20) Aerosol Water Content During Pittsburgh Air Quality Study: Observations And Model Comparison