Post on 07-Jan-2016
description
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