Using theAerodynamic Particle Sizer

to Measure PM-coarse

Thomas PetersThe University of Iowa

Robert VanderpoolUS EPA

Sanjay NatarajanRTI International

Disclaimer

Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.

Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Acknowledgements Thanks to Ricky Holm at TSI for useful discussions and to TSI for

loaning the two APS units that were used during this study.

Aerodynamic Particle Sizer (APS)

• Counts and sizes particles – Aerodynamic diameter from 0.5 um to 20 um– Number concentration

• Rapid, entire size distribution in seconds

• Ideal for measuring coarse aerosols– Estimate PM-coarse

Must convert from particle number to mass distribution

Convert Number to Mass DistributionMass = Number x Volume x Density

p3ve ρ D

6

π dN dM

volume equivalent diametervep

ae0aeve Cρ

Cρ D D

2/1p

2/3

ve

ae03ae

ρ

1

C

Cρ D

6

π dN dM

APS Diameter Cubed

APS Counts Shape Factor

Particle Density

Counting Efficiency of the APS

1 102 3 5 20

Aerodynamic Diameter, µm

0

20

40

60

80

100

Co

un

tin

g E

ffic

ien

cy, %

L iquidInner Nozzle Loss

Liquid

Solid Fluorescent PSL Ammonium Fluorescein

Solid particles bouncedemonstrates capability of optics and processing scheme to count near 100% particles

Volckens and Peters (submitted to JAS)

Droplets hit inner nozzle

Hypothesis: Data from the APS can be used to estimate PM-coarse

• Many coarse aerosols are solid, bouncy material– Counting efficiency near 100%

• Only need shape factor and density

Goal of this work:

Compare PM-Coarse estimated with the APS 3321 with that measured with filter-based FRM samplers

Methods• Co-located samplers

– Two APS 3321– Three FRM PM-2.5– Three PM-10

• Three US cities– Riverside, CA– Phoenix, AZ– Gary, IN

• Thirty days each

APS Sampling ConfigurationPM-10 inlet on roof

Isokinetic FlowSplitter

APS3321

No conditioner on inlet,but trailer at 20-25ºC

Data Analysis• Measured by Federal Reference Method (FRM)

– PM-Coarse = PM-10 – PM-2.5

• Estimated from APS 3321 data– Calculate particle mass concentration by size

• density = 2 g/cm3

• shape factor = 1.4– Sum mass concentration above 2.5 um

Reference p g/cm3 Stein et al. (1969)

Pittsburgh2.2 ---

Noll et al. (1988)

Chicago2.0 1.4

Lin et al. (1992)

Chicago

1.77 (fine)

2.64 (coarse)1.4

Phoenix, AZ

P hoenix, A Z - 1 Phoenix, A Z - 2

0 20 40 60 80 100

FR M PM -C , µg m -3

0

20

40

60

80

100

AP

S P

M-C

, µg

m-3

0 50 100 150 200 250

FR M PM -C , µg m -3

0

50

100

150

200

250

AP

S P

M-C

, µg

m-3

y = 0.92 x + 0.97r2 = 0.98

y = 1.0 x + 0 .27r2 = 0 .99

Riverside, CA

0 20 40 60

FR M PM -C , µg m -3

0

20

40

60

AP

S P

M-C

, µg

m-3

R ivers ide, C A

y = 1.05 x - 2 .6r2 = 0 .84

Gary, IN

0 20 40 60 80 100

FR M PM -C , µg m -3

0

20

40

60

80

100A

PS

PM

-C, µ

g m

-3

y = 0.68 x + 1.7r2 = 0.53

G ary, IN

Eliminate Outliers

y = 0.59 x + 0.83r2 = 0.91

APS Event Information Similar

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

%Event1 %Event2 %Event3 %Event4

Per

cen

t o

f T

ota

l Co

un

ts in

24

Ho

urs Gary

Phoenix - 1

Riverside

Phoenix - 2

Meteorology

-10

0

10

20

30

40

Me

an

Te

mp

era

ture

, Ce

lciu

s

0

20

40

60

80

100

Re

lativ

e H

um

idity

, %

A

B

• In Gary– Temperature lowest

– Relative humidity greatest

– Often relative humidity greater than deliquescence point

If water is associated with particles - density lower - shape nearer to one (drops) - liquid losses

Negative bias in mass estimate

2/1p

2/3

ve

ae03ae

ρ

1

C

Cρ D

6

π dN dM

Conclusions

• APS can estimate PM-Coarse– Must apply density and shape factor

• Measurement affected by water uptake– Need to dry aerosol before entering APS

• APS provides additional information– Number, surface area, mass concentration– Great temporal resolution for source apportionment

Future Work

• Planned lab work– Compare mass concentration by size estimated with

APS to aerosols with known density and shape factors– Controlled temperature / relative humidity experiments

• Two additional field studies planned– Research Triangle Park, Feb. 2005– Phoenix, AZ, May 2005

• Resolve counting efficiency for liquid drops