aerosols and nephelometers
TRANSCRIPT
European Commission – Joint Research Centre, Institute for Environment and
Sustainability, Air-Climate and Human Interactions (AIRCLIM) Ispra, Italy
F. KARAGULIAN, Claudio A. Belis, Friedrich Lagler, Maurizio Barbiere and, Michel Gerboles
Evaluation of the performances of SidePak AM510 nephelometer compared to the Tapered Element
Oscillating Microbalance (TEOM) method for PM2.5 mass measurement
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Applications: - Personal exposure monitoring/IH studies - Ambient/work area monitoring - Trending/screening - Engineering studies - Epidemiology health studies - Environmental sampling
The “Candidate”SidePak AM510 (TSI)
The “Reference”TEOM-FDMS 8500(Thermo Scientific)
Nephelometer vs TEOM-FDMS
Portable nephelometer
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Sampling conditions
SidePak AM510: - Laser beam for light scattering TSI ~ 670 nm- 50% cut off at 2.5 µm- Flow rate of 1.7 L/min for PM2.5 sampling - Original factory calibration with the ISO standard 12103-1, A1 Arizona Test Dust - In situ re-calibration of the flow rate with a Gilan Gilibrator-2 Air Flow Calibrator (Sensidyne)
TEOM-FDMS 8500: - sampling head with 50% cut off at 2.5 µm
SidePak AM510 - - - > TSI valuesTEOM-FDMS- - - > TEOM values
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Site Locations
Rural and kerbsiteUrban site
Northern Po Valley (Italy)
January-February 2010
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Experimental Setup
TOPAS Gmbh LAP 321(aerosol size spectrometer)
SidePak in raw for calibration
Mobile laboratory with equipment for
meteorological data
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Principle of operation for a nephelometer
Light scattering from particle passing through a monochromatic light:
βαTSIddm,λ,dPdfCR p
0
TSIpλpn
radiance
p
0
3pppnm ddd
6
πdfρCc
particle number
concentration
d
ppλp
d
p3
pp
pmd(ddPdf
d(dd6
πdf
ρRc)
)
light flux :
4
TSI
2
2
23
p4
pλ λ
1
2m
1md4πm),(dP
m: refraction index of dp: particle size d: particle density
probability density function
particle mass concentration of polidisperse aerosol
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Rayleigh approximation
2
2
23
4TSIp
m
2m
1m24π
λRρc
)f(d p )dδ(d p
limit of Rayleigh scattering
Sampled particle diameter < 0.5 TSI
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Implications due to relative humidity (RH)
-γRH)-(1GF
Hygroscopic growth factor GF(RH) for a particle in humid environment:
parameterizes the light scattering and its hygroscopic dependence
complex refraction index
3
3evwetdry
GF
1GFRmRmm
dry
mdry and mwet are the partioned dry and wet refraction index, respectively
/TEOMTEOMR evev
evdrydry R-1/TEOMTEOMR
...evaporative (Rev) and dry (Rdry) PM fraction measured by TEOM-FMDS:
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Rev determination
In order to confirm the evaporative fraction Rev, PM2.5 were sampled on quartz filters by a PM sampler
Ion chromatography was carried out to determine the amount of NO3
-, SO4-2 and NH4
+ on PM2.5
~ 24.8% of the total PM2.5 mass was assigned to ammonium nitrate which is also the main component of TEOMev (Favez..)
Rev measured by TEOM-FDMS ~ 0.25
Agreement with TEOM-FDMS measurements
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Calibration through modeling
2
23γ23γevwetevdry
23γ23γevwetevdry
3
4TSIpi
mRH11RH1RmR-1m
RH121RH1RmR-1m
24π
λρβTSIαc
Total mass concentration measured by TEOM-FDMS:
fitting of parameters , mdry , mwet
Calibration of SidePak AM510 (“Modeled” TSI data)
13γ23
evwetevdry
3γ23evwetevdry
0Modeled aRH11GFRmR-1m
RH121GFRmR-1mTSIaTSI
2
34TSI0 24πγλαa
34TSI1 24πγλ a
PM2.5 data from TEOM measurements
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The goal
calculation of fitting parameters (, , , mdry ,mwet ) related to humidity and site typology
Attempt to calibrate the SidePak at different sites without necessary presence of a TEOM-FDMS
Calculation of new TSImodeled values for SidePaks where TEOM-FDMS was located at the same measuring site
calibration
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Example: fitting parameters for a SidePak
JRC Blg 44(3)
rural
EMEP(4)
rural
Varese(6)
urban
Varese(8)
urban
TEOM (µg/m³) 36 to 129 24 to 110 74 to 124 22 to 47
Temperature (ºC) -2.5 to 3.9 -6.1 to 1.6 -3 to 4 -2 to 3
RH (%) 65 to 93 64 to 94 58 to 90 62 to 94
Sampling time 25 hrs 85 hrs 24 hrs 9 hrs
0.198 0.229 0.194 0.229
0 -4.9 -6.9 -4.9
mdry 0.703 0.773 0.735 0.773
mwet 1.110 1.187 1.100 1.187
0.251 0.226 0.143 0.226
Fitting parameters Calibration factors for the SidePak
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Modeled TSI vs TEOM
bTEOM aTSIModeled
after modeling, new slope b closer to 1* (regression coefficients a and b) enhanced coefficient of determination R2 between TSI and TEOM
*Guide for the Demonstration of Equivalence of Ambient Air in Measurement Methods http://ec.europa.eu/environmental/air/quality/legislation/pdf/equivalence.pdf, 2009
regression line
bTEOM aTSI regression
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Example: results from calibration of a SidePak
JRC BLG 44(4)
rural
EMEP (5)
Rural
Varese(6)
urban
Varese(8)
urban
b ± u(b)a ± u(a)
U/RRSS/R²
0.96±0.01 0.75±0.01 0.72±0.2 1.08±0.06
4.5±0.8 11.2±0.5 28.1±1.8 6.1±2.1
7.4/6.2/0.977 14.0/8.1/0.924 7.2/6.4/0.867 21.8/12.0/0.217
1.14±0.01 0.97±0.01 0.92±0.02 1.47±0.07
-9.9±1.0 1.5±0.6 25.2±1.9 -7.3±2.3
9.0/7.8/0.976 10.9/10.5/0.910 34.8/6.8/0.905 23.0/13.6/0.309
1.24±0.01 0.95±0.01 1.04±0.02 1.07±0.05
-18.6±1.1 -5.6±0.7 -3.5±1.8 -6.3±1.6
10.0/9.4/0.972 21.7/11.8/0.881 7.1/6.3/0.935 11.8/8.0/0.556
1.26±0.02 0.93±0.01 1.04±0.02 1.00±0.04
-14.2±1.3 -1.2±0.8 -2.4±1.9 0.3±1.2
18.2/11.0/0.962 18.6/14.1/0.831 8.2/7.1/0.918 6.2/5.5/0.724
Regression with fitting parameters calculated with TEOM-FDMS and
SidePak at the same site:
….TEOM-FDMS and SidePak different sites:
Better performance of the TSImodeled vs TEOM only if we use calibration factors calculated when SidePak were located at the same site of the TEOM-FDMS
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Improvements in R2
larger improvements in R2 were measured when larger GF was observed
(usally associated to larger RH variations)
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Sensitivity analysis
Average |u(Xi)/Xi| |δcm/δXi/cm.u(Xi)/Xi|
α 0.245 27.% 27%
β -4.5 -300% 4%
mdry 0.589 49% 13%
mwet 1.281 48% 15%
0.205 25% 0.3%
1.6 31% 31%
RH 82% 11% 1.9%
Rev 0.278 10% 3.1%
uc(cm)/cm 46%
How the variation (uncertainty) in PM2.5 can
be attributed to variations in the inputs of this model? Relative contribution
of each parameterto the total uncertainty
Mean Relative Standard Deviation