Aerosols and Nephelometers

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

MANCHESTER 9 September 2011 – EAC2011 1

MANCHESTER 9 September 2011 EAC 2011 2

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


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


Site Locations

Rural and kerbsiteUrban site

Northern Po Valley (Italy)

January-February 2010


Experimental Setup

TOPAS Gmbh LAP 321(aerosol size spectrometer)

SidePak in raw for calibration

Mobile laboratory with equipment for

meteorological data


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


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


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:


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


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


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


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


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


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


Improvements in R2

larger improvements in R2 were measured when larger GF was observed

(usally associated to larger RH variations)


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

Aerosols and Nephelometers

Technology

Transcript of Aerosols and Nephelometers