Particle Size Distributions:Data Analysis

Susanne Hering,Mark Stolzenburg,Nathan Kreisberg,

Aerosol Dynamics Inc.

Size DistributionMeasurement System

• SMPS– scanning mobility particle spectrometer– particle sizing by electrical mobility,– (assume equilibrium charge distribution)– size range: 10 nm - 350 nm

• LASAIR– optical sizing– size range: 120 nm to 2000 nm (2 µm)

• Climet– optical sizing– size range: 500 nm to 10000 nm (10 µm)

Combined Data: Number Distribution

10-2

10-1

100

101

102

103

104

105

106

Parti

cle N

umbe

r Dist

ribut

ion

(dN/

Dlog

Dp, #

/cm

3)

102 3 4 5 6

1002 3 4 5 6

10002 3 4 5 6

Particle Diameter (nm)

SMPS Mobility Sizing LASAIR Optical Sizing Climet Optical Sizing

SMPS: 2/1/2001 19:09LASAIR: 2/1/2001 19:10Climet: 2/1/2001 19:10

Fresno First Street

Same Data as Particle Volume Distribution

120

100

80

60

40

20

0

Parti

cle V

olum

e Di

stribu

tion

(dV/

Dlog

Dp, µ

m3/

cm3)

102 3 4 5 6

1002 3 4 5 6

10002 3 4 5 6

Particle Diameter (nm)

Volume Distribution SMPS LASAIR Climet

SMPS: 2/1/2001 19:09LASAIR: 2/1/2001 19:10Climet: 2/1/2001 19:10

30x103

25

20

15

10

5

0

Num

ber C

once

ntra

tion

(#/cm

3)

12/15/2000 12/17/2000 12/19/2000 12/21/2000 12/23/2000 12/25/2000 12/27/2000 12/29/2000

110-220 nm

LASair Counts SMSP Counts

4000

3000

2000

1000

0

Num

ber C

once

ntra

tion

(#/cm

3)

12/15/2000 12/17/2000 12/19/2000 12/21/2000 12/23/2000 12/25/2000 12/27/2000 12/29/2000

220-316 nm

LASair Counts SMSP Counts

Systematic Difference Among Instruments

Lowest LASair channel fewer counts at peaks

Second LASair channel always higher than SMPS

Why the Differences ?

• SMSP has assumes an equilibrium particle charge distribution, andcorrects measured counts for this assumed charge fraction

• Optical and mobility sizing differ, but performed DOS and PSLcalibrations on optical instruments. Differences persist with eithercalibration factors.

How to Handle these Differences ?• Treat each sizing method independently.

– Ultrafine=> SMPS; Accumulation=> LasAir; Coarse => Climet

• Merging into a single distribution will produce inherent “bumps” attransition.

40x103

30

20

10

Parti

cle N

umbe

r Dist

ribut

ion (d

N/Dl

ogDp

, #/c

m3)

102 3 4 5 6 7 8 9

1002 3

Particle Diameter (nm)

SMPSNumber

2/1/2001 23:59

2/2/2001 08:00

Midnight

Following Morning, 8am

SMPS Particle Number Distribution

See multiple modes

SMPS Distributions:Bimodal, Lognormal Deconvolution

,2

,,

ln( / )exp log( )

2(ln )2 ln

a b

p pm aaa p

g ag a

dN dN dN

D DNdN d Dσπ σ

= +

= −

Each size distribution is expressed as a sum oftwo lognormal distributions:

Size Distribution MovieFresno First Street

Feb 1 – 3, 2001

Look for:• How well the bimodal deconvolution generally captures

the major characteristics of the distribution.

• Differences in character from nighttime and day timedistributions.

Can we use the Bimodal, LogNormal Parametersto Quantify these Observations?

For each mode:

N = number of particles

Dgm = geometric mean diameter

σg = geometric standard deviation

With two modes => 6 parameters.

How well do these parameters to characterize thetemporal and spatial variablity of the size distributions?

Mode Diameters: Jan 31-Feb 3, 2001 Data

200

150

100

50

0

Mod

e Di

amet

er, n

anom

eter

s

12:00 AM1/31/2001

12:00 PM 12:00 AM2/1/2001

12:00 PM 12:00 AM2/2/2001

12:00 PM 12:00 AM2/3/2001

12:00 PM

Mode A Dp Mode B Dp

larger ultrafine particle size midday

Comparison with Black Carbon80x103

60

40

20

0

Num

ber C

once

ntra

tion

(#/c

m3)

12:00 AM1/31/2001

12:00 PM 12:00 AM2/1/2001

12:00 PM 12:00 AM2/2/2001

12:00 PM 12:00 AM2/3/2001

12:00 PM

20

15

10

5

0

Black Carbon (ug/m

3)

Black Carbon (ug/m3) SMPS Number Concentration

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Frac

tion

in M

ode

A (s

mal

lest

)

12:00 AM1/31/2001

12:00 PM 12:00 AM2/1/2001

12:00 PM 12:00 AM2/2/2001

12:00 PM 12:00 AM2/3/2001

12:00 PM

20

15

10

5

0

Black Carbon (ug/m

3)

Fraction in smallest mode Black Carbon (ug/m3)

•Ultrafine number tracks black carbon •Lower fraction of particle number in smallest mode

Summary: Size Distribution Analysis

• Discrepancies among instruments makes it difficult to synthesizedata into a uniform distribution.

• Modal analysis from one instrument (SMPS) provides means to– Investigate temporal variations– Comparison with chemical constituents

• Ultrafine distributions more stable at night– Small mode (A) appears in early morning– Larger mode (B) has larger diameter midday

• Black carbon and SMSP number track, while the fraction associatedwith the small mode (A) varies inversely with BC level.

TEMPORAL AND SPATIALDISTRIBUTION OF PARTICULATE

NITRATE AND LIGHTSCATTERING

Susanne Hering, Nathan Kreisberg,Aerosol Dynamics Inc.,

Judith Chow, John Watson,Desert Research Institute,

L. Willard Richards,Sonoma Technology Inc.

Sites and Constituentscompared using 10-min database

Multiday trends separated fromdaily pattern.

Each frequency domaincompared separately.

605040302010

0PM2.

5 N

itrat

e (u

g/m

3)

12/21/00 1/10/01 1/30/01

800

600

400

200

0

Parti

cle

Scat

terin

g at

<70

% R

H (M

m-1

)

BAKERSFIELD: 24-hr Running Average Nitrate Bsp

-40

-20

0

20

40

PM2.

5 N

itrat

e (u

g/m

3)

12/21/00 1/10/01 1/30/01

-500

0

500

Parti

cle

Scat

terin

g at

<70

% R

H (M

m-1

)

Bakersfield: Residual (24-hr running average subtracted) Nitrate Bsp

80

60

40

20

0PM2.

5 N

itrat

e (u

g/m

3)

12/21/00 1/10/01 1/30/01

120010008006004002000

Parti

cle

Scat

terin

g at

<70

% R

H (MBAKERSFIELD: Raw Data

Nitrate Bsp

=

+

=

Comparison among sites for 24-hr average

40

30

20

10

0

PM2.

5 Ni

trate

(ug/

m3)

12/11/2000 12/21/2000 12/31/2000 1/10/2001 1/20/2001 1/30/2001

1000

800

600

400

200

0

Parti

cle

Scat

terin

g at

<70

% R

H (M

m-1

)

Running 24-hr Average ANGIOLA Nitrate ANGIOLA Bsp FRESNO Nitrate FRESNO Bsp

Residual, after subtracting running 24-hr average

-40

-20

0

20

40

PM2.

5 Ni

trate

(ug/

m3)

12/11/2000 12/21/2000 12/31/2000 1/10/2001 1/20/2001 1/30/2001

-500

0

500

Parti

cle

Scat

terin

g at

<70

% R

H (M

m-1

)

Bakersfield: Residual (24-hr running average subtracted) Nitrate Bsp

Comparison among Constituents in 24-hr Pattern

-4

-2

0

2

4

PM2.

5 Ni

trate

(ug/

m3)

20151050

Hour of Day

-100

0

100

Parti

cle S

catte

ring

at <

70%

RH

(Mm

-1)

Bakersfield Nitrate Bsp

-1.0

-0.5

0.0

0.5

1.0

PM2.

5 Ni

trate

(ug/

m3)

20151050

Hour of Day

-60

-40

-20

0

20

40

60

Parti

cle S

catte

ring

at <

70%

RH

(Mm

-1)

Angiola Nitrate Bsp

-2

0

2

PM2.

5 Ni

trate

(ug/

m3)

20151050

Hour of Day

-200

-100

0

100

200

Parti

cle S

catte

ring

at <

70%

RH

(Mm

-1)

Fresno Nitrate Bsp

-4

-3

-2

-1

0

1

2

3

4

PM2.

5 Ni

trate

(ug/

m3)

20151050

Hour of Day

-60

-40

-20

0

20

40

60

Parti

cle S

catte

ring

at <

70%

RH

(Mm

-1)

Sierra Nevada Foothills Nitrate Bsp

Bsp and Nitrate Analysis

• Subtract out overall multi-day pattern to discern the daily pattern,and how this varies among constituents and sites

• Nitrate maxima occurs earlier in the day at Bakersfield and Fresnothan at Angiola or Sierra Nevada Foothills.

• Note there is also a seasonal pattern -- not shown here.