particle size distributions: data analysisarb.ca.gov/airways/crpaqs/workshop/adi1.pdf · summary:...
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Particle Size Distributions:Data Analysis
Susanne Hering,Mark Stolzenburg,Nathan Kreisberg,
Aerosol Dynamics Inc.
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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)
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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
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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
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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
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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.
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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
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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:
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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.
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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?
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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
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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
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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.
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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
=
+
=
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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
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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
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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
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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.