2005 Aerosol Sci. Technol. Zervas E. Interlaboratory Test of Exhaust PM Using ELPI

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Interlaboratory Test of Exhaust PM Using ELPIE. Zervas

a, P. Dorlhne

a, L. Forti

b, C. Perrin

b, J. C. Momique

c, R. Monier

c, H. Ing

d

B. Lopezd

aRenault, 1, Alle Cornuel, Lardy, France

bInstitut Franais du Ptrole (IFP), Rueil-Malmaison, France

cPSA Peugeot Citren, La Garenne-Colombes, France

dUnion Technique de l'Automobile, du Motocycle et du Cycle (UTAC), Autodrome de Linas

Montlhry, Montlhry, France

Version of record first published: 23 Feb 2007

To cite this article: E. Zervas, P. Dorlhne, L. Forti, C. Perrin, J. C. Momique, R. Monier, H. Ing & B. Lopez (2005):Interlaboratory Test of Exhaust PM Using ELPI, Aerosol Science and Technology, 39:4, 333-346

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Aerosol Science and Technology, 39:333346, 2005

Copyright c American Association for Aerosol ResearchISSN: 0278-6826 print / 1521-7388 online

DOI: 10.1080/027868290930222

Interlaboratory Test of Exhaust PM Using ELPI

E. Zervas,1 P. Dorlhene,1 L. Forti,2 C. Perrin,2 J. C. Momique,3 R. Monier,3

H. Ing,4

and B. Lopez4

1Renault, 1, Allee Cornuel, Lardy, France2Institut Francais du P etrole (IFP), Rueil-Malmaison, France3PSA Peugeot Citr oen, La Garenne-Colombes, France4Union Technique de lAutomobile, du Motocycle et du Cycle (UTAC), Autodrome de Linas-Montlh ery,

Montlhery, France

The Particulate Measurement Programme (PMP) works on thedevelopment of an improved method for the exhaust particulate

matter (PM) measurement, which can include, if feasible and nec-essary, the measurement of particle number. The French PMPsubgroup, composed of IFP, PSA Peugeot-Citroen, Renault, andUTAC, has defined a measurement protocol based on electricallow-pressure impactor (ELPI) and conducted an interlaboratorytest to evaluate its performances. The technical programwas basedon tests carried out on three Euro3 passenger cars(one gasoline op-erating under stoichiometric conditions, one Diesel, and one Dieselequipped with a diesel particulate filter (DPF)) that were testedon the New European Driving Cycle (NEDC). The regulated pollu-tants are also measured, as indicators of test repeatability and goodworking conditions. The interlaboratory reproducibility value ofthetunnel background tests is quite high (337%)due to lowparticlenumbers. Therepeatabilityvalues increase at lowparticle numbersindependently of the vehicle used. On the NEDC, the reproducibil-ity of total particle number is 59, 47, and 131% for the gasoline,

Diesel, and DPF-equipped Diesel vehicles, respectively (compare to67, 29, and 164% for PM collected on filters). These results showthat the protocol used in this study allows a reliable measurementof exhaust particle number in the case of vehicles emitting at leasttwo orders of magnitude more than the tunnel background. In theother cases, the measurement variability is too high, especially forregulatory purposes, without taking into account other metrologi-cal aspects, such as calibration.

INTRODUCTION

Current European regulations are basedon a gravimetricmea-

surement of exhaust particles emitted from Diesel passenger

cars. However, as health concerns and instrument capabilitiesincrease, more research is focused on number and size of emit-

ted particles. The Particle Measurement Programme (PMP) of

theWorkingPartyon Pollutionand Energy (GRPE)of theUnited

Received 1 July 2004; accepted 31 January 2005.Address correspondence to Efthimios Zervas, Renault,1 Allee Cor-

nuel, 91510 Lardy, France. E-mail: [email protected]

Nations at Geneva is mandated to work on the development of an

improved method for the particulate matter (PM) measurement,

which can include, if feasible and necessary, the measurement

of the particle number of the exhaust particles (UNECE 2001).Currently there are many methods for the particle number

and size determination. The method most commonly used in the

case of vehicle exhaust gas are the electrical low-pressure im-

pactor (ELPI; Keskinen et al. 1992; Ahlvik et al. 1998; Pattas

et al. 1998; Khalek 2000; Maricq et al. 2000; Witze et al. 2004),

scanning mobility particle sizer (SMPS; Wang and Flagan 1990)

andparticle counters (Willeke andBaron 1993; Hinds 1999), but

many others are also presented in literature. Burtscher (2001)

and Mohr and Lehmann (2003) give a detailed description of

several analytical methods. Because SMPS has an insufficient

resolution time (some minutes) it cannot be used for the analy-

sis of particle distribution on the New European Driving Cycle

(NEDC).Particles are composed of solid carbonaceous matter, other

solids such as metals, and adsorbed components such as water,

sulphates,and volatile organic compounds (Degobert 1992). The

very fine particles are not always solids but can be condensate

aerosol (Lunders et al. 1998; Matter et al. 1999). Several of the

methods used for the measurement of the particle number can-

not distinguish the solid particles from the volatiles (Burtscher

2001). Forthis reason, several methods, such as thermodenuders

or thermodiluters have been developed to eliminate the volatiles

before measurements (Wehner et al. 2002), but as sampling con-

ditions play a very important role on the particle size measure-

ments (Lunders et al. 1998; Khalek et al. 1999; Maricq et al.

1999; Ntziachristos and Samaras 2000) a standard procedure is

not well established yet.

Several authors evaluate the performances of ELPI.

Marjamaki et al. (2000) evaluate the collection efficiency of

the impactor and the performances of the charger. Maricq et al.

(2000) and Van Gulijk et al. (2003, 2004) perform a comparison

between ELPI and SMPS, while Witze et al. (2004) compares

ELPI with LII and TEOM.

333


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334 E. ZERVAS ET AL.

One specific point before the validation of an analytical

methodis the determinationof its repeatabilityand reproducibil-

ity. Round robin test is themost adequate methodfor thispurpose

(Hoekman et al. 1995; Lanning et al. 1997; Tejada et al. 1997).

However, no interlaboratory comparison on ELPI performances

has yet been presented.

This article presents the results of the French PMP subgroup,

composed by IFP, PSA Peugeot-Citroen, Renault, and UTAC, of

an interlaboratory comparison of particle number measurement

using ELPI. An interlaboratory comparison of particle counters

will be presented in a future article. Three Euro3 passenger cars

(PC) are used in this study: a gasoline vehicle operating un-

der stoichiometric conditions and two Diesel PC, one with and

one without diesel particulate filter (DPF). A pragmatic pro-

tocol based on the European regulatory conditions (tests on the

NEDC)is used. The intralaboratoryvariability, repeatability, and

reproducibility values are presented in the case of the three vehi-

cles. The CO2, fuel consumption (FC), and regulated pollutants

are also measured, and their repeatability and reproducibility

are compared with these of the particle number. Other particu-

lar measurement aspects that can influence the obtained results

and are not very well established today (Choi et al. 2003), such

as accurate day-to-day calibration of the analytical instruments,

are not treated here.

TECHNICAL BACKGROUND OF ELPI

Keskinen et al. (1992) present the operation principles of

ELPI (charger, impactor cut diameters, and electrometer) and

compare it with SMPS. An atomizer was used to generate an

aerosol, which is measured by SMPS and ELPI. This work con-

cludes that both instruments measure the same particle distri-

bution. Marjamaki et al. (2000) evaluates the performances ofELPI at a nominal flow rate of 10 l/min. The impactor, charger,

and their calibration using two differentaerosol-generation tech-

niques are presented. This article presents the impactor collec-

tion efficiency and charger performance (both are estimated sat-

isfactory) and the comparison of the size distribution obtained

by ELPI and SMPS using a di-octyl-sebacate (DOS) aerosol.

Both techniques give similar particle distribution.

ELPI is used for the measurement of exhaust gasparticle

number and distribution, but it is also used to estimate the parti-

cle mass. Ahlvik et al. (1998) uses ELPI to measure the particle

number distribution of a passenger car (model year 1993) and

a heavy-duty engine on two driving cycles (European Driving

Cycle (EDC) and Federal Test Procedure (FTP) for the pas-senger car, and US transient cycle and European Steady-state

Cycle (ESC) for the heavy-duty engine). A differential mobil-

ity analyzer (DMA) is also used for these measurements. The

effective particle density is estimated from the DMA and used

to estimate the particle mass from ELPI distribution; however,

the authors do not examine this method deeply. The effect of

dilution ratio and driving cycle on particle distribution is also

presented. Pattas et al. (1998) examine the effect of DPF on par-

ticle size distribution using ELPI. The influence of sulphur and

Ce content in the fuel on particle distribution is presented on the

NEDC. It is shown that DPF decreases the particle number, but

no information about repeatability is given. Shi et al. (1999) use

ELPI to study the number and distribution of particles emitted

from a Diesel engine tested on an 11-mode steady-state cycle.

A comparison of particle emissions at different engine load and

speeds is performed using ELPI and SMPS, where both tech-

niquesgive similar results. Theauthors present that theestimated

particle mass is 1.31.6 times higher than the mass collected on

filters.

Maricq et al. (2000) presents a comparison of particle distri-

bution of three diesel and three gasoline vehicles (model years

19951997) operating in steady states and on the FTP and mea-

sured by SMPS and ELPI. The effective density of particles

is also estimated and used to calculate the particle mass, but no

comparison with the mass collected on filters is given.

Tsukamoto et al. (2000) uses ELPI to measure the particle num-

ber distribution of a heavy-duty engine. The emitted particle

mass is estimated from ELPI measurements and compared with

the mass collected on filters. Generally, the estimated mass is

1.52 times higher than the mass collected on filters. Khalek

(2000) analyzes the particle number distribution of a heavy-duty

engine on FTP. Similar to Tsukamoto et al. (2000), he concludes

that ELPI overestimates total mass emissions comparing to filter

mass measurements. Andrews et al. (2001) estimate the particle

effective density as a function of size to 1.50.2 g/cm3. Thiswork

concludes that the estimated mass can be very different from the

mass collected on filters. This difference can be very important

for particles bigger than 1 m. One reason is that ELPI overes-

timates the particle number by up to two orders of magnitude

at this particle size. Virtanen et al. (2002) estimate the particleeffective density to 1.11.2 g/cm3 as a function of their size.

This work suggests that dilution has a strong effect on density

values. Ristimaki et al. (2002) use ELPI and SMPS to estimate

the effective density of different aerosols but not of exhaust gas

particles. Choi et al. (2003) use ELPI to study the emissions

of nanoparticles of a HSDI diesel engine and the effect of the

oxidation catalyst on mass and distribution of emitted particles.

Maricq and Xu (2004) use DMA and ELPI to determine the ef-

fective density and fractal dimension of particles emitted from

flames and motor vehicle exhaust gas. The effective densities of

particles emitted from two diesel engines and a direct-injection

SI engine are identical.

However, ELPI has some limitation for particle number mea-surements. Van Gulijk et al. (2001, 2003) presents a list of non-

ideal behavior of ELPI, as particle bounce, wall or interstage

loss, overloading or surface buildup, and losses due to electro-

static effects and to charger nonideal efficiency. Using a steady-

state speed, a continual decrease of small particles and a con-

tinual increase of bigger ones is observed. The authors explain

that this is due to impactor overloading. In our point of view,


4/15

INTERLABORATORY TEST OF EXHAUST PM USING ELPI 335

TABLE 1

Main characteristics of the three passenger cars used

Vehicle 1 Vehicle 2 Vehicle 3

Type Renault Megane Peugeot 307 Peugeot 307

Fuel Gasoline Diesel Diesel

Inertia class (kg) 1130 1360 1360

Displacement (cm3) 1600 1997 1997

Number of cylinders 4 4 4

Valves per cylinder 4 2 4

Injection system MPI Common rail Common rail

Combustion system HDI HDI

Max. power (kW) 66 66 80

Emission limits Euro3 Euro3 Euro3

EGR type Electric closed loop Electric closed loop

After-treatment device TWC DOC DOC + DPF

even if a part of these changes is due to impactoroverloading, an

extremely constant source of particles and different analytical

methods must be combined to validate these conclusions.

Van Gulijk et al. (2004) present that ELPI underestimates the

apparent size of particles and, as a result, that their number is

overestimated.

Three other program must be mentioned. ACEA conducted

two important research programs studying the emissions of fine

particles (ACEA 1999, 2002). In the first study, 11 diesel and

5 gasoline vehicles were tested on NEDC and steady speeds by

two laboratories. The emissions of regulated pollutants and par-

ticle number (determined by SMPS) are presented in the final

report, but no repeatability or reproducibility values are given.

ELPI is not used in this work. Three diesel and four gasoline

passenger cars were tested in the second program. The stability

of ELPI is determined over 18 weeks (one test per week) us-

ing a reference vehicle at a steady speed of 100 km/h. Within

the same laboratory, the repeatability 1.96*RSD value (Relative

Standard Deviation, defined in the experimental section) is 31%

(data extracted from this report). With no apparent explanation,

the particle number decreases by about 35% between the begin-

ning and the end of this program. No other repeatability results

are presented. The third program is the Swiss contribution to

the GRPE particle measurement program (Mohr and Lehmann

2003b). In this study, 24 particle-measurement techniques were

tested using a heavy-duty engine and a combustion aerosol gen-

erator. As only one laboratory is involved, no reproducibility

values can be given. The repeatability values (1.96*RSD) ofELPI during the European Transient Cycle (ETC) are 20 and

57%, respectively, for a configuration without and with a par-

ticulate filter. The respective values are 16% and 39% for the

gravimetric method and 4% and 47% for the CPC. Other tests

on steady-state speeds are also performed. The 1.96*RSD of the

tunnel background measurements are 38% for ELPI, 55% for

the gravimetric method, and 95% for the CPC. The correlation

between particle number measured by ELPI or CPC and particle

mass is poor. The limits of detection (LOD) of ELPI are found

to be very close (90%) to the measured particle concentration

when a particulate filter is used.

EXPERIMENTAL SECTION

Three passenger cars were used in this study: a gasoline PC

operating under stoichiometric conditions (vehicle 1), a diesel

PC (vehicle 2) and a diesel PC equipped with a DPF (vehicle 3).

Table 1 provides their main characteristics. Twenty fiveparts per

million of commercially used, Ce-based additive were added in

the fuel in the case of the DPF-equipped vehicle to decrease the

necessary temperature for the DPF regeneration from about 650

to 550C. The addition of Ce-based additive does not change

the particle distribution.As fuel sulphur can influence the nanoparticle formation due

to sulphates emission, (Mohr2003a), fuels withless than 10 ppm

of sulphur were used for this study. The main characteristics

of these fuels are presented in Table 2. The same lubricant,

which contains less than 0.4% of sulphur, was used for all three

vehicles.

Three tests were performed on the NEDC (cold start)and reg-

ulated pollutants, CO2, and fuel consumption were measured ac-

cording to current European regulations (EU Directive 70/220).

Theexperimental procedureused is thefollowing: a cold NEDC,

24 h of conditioning at 20C, and three cold NEDCs with a con-ditioning of 24 h between each cycle. The results of the last

three NEDC are taken into consideration. In the case of theDPF-equipped diesel PC, a DPF regeneration is performed at

each laboratory before these cycles.

Number and size distribution measurements were performed

using a DEKATI ELPI, covering particle cut size from 8 to

10 m. Three laboratories used an ELPI sampling of 10 l/min,

while Lab 1 used an ELPI sampling of 20 l/min. As thermode-

nuders can induce high particle losses (OICA 2003; Zervas et al.

2004), a DEKATI ejector-type dilutor, heated at 130C with hot


5/15


TABLE 2

Fuel characteristics

Characteristic Diesel Characteristic Gasoline

Density at 15C (kg/m3) 834 Density at 15C (kg/m3) 762Viscosity at 40C (cSt) 3.00 H/C ratio 1.82Cetane number 53.8 Octane number (MON/RON) 89.1/100.2

Flash Point (C) 82 Distillation (C)Distillation (C) Initial Boiling Point 34.9

Initial Boiling Point 197 10% 62.9

10% 222 20% 77.4

20% 235 50% 107.0

50% 278 90% 144.8

90% 331 95% 154.8

95% 347 Final Boiling Point 184.8

Final Boiling Point 359 E 70C (vol%) 15E 250C (vol%) 30.4 E 100C (vol%) 38.3E 300C (vol%) 69.6 E 150C (vol%) 92.5E 350C (vol%) 95.9 Composition

Composition Total paraffins (vol%) 59.4Sulphur (mg/kg) 8 Total olefins (vol %) 0

Polycyclic Hydrocarbons (wt%) 4.5 Total aromatics (vol%) 49.6

Ce (ppm, the DPF vehicle only) 25 Benzene (vol%) 1.73

Polyaromatics (wt%) 4.5

Total oxygenates (vol%)


6/15


FIG. 1. Experimental setup.

T4 =

i

n2i [7]

T5 =

i

(ni 1)RSD2i [8]

s L2 =

T2T3 T21T3(k

1)

T5

T3(k 1)T23

T4

[9]

Intralaboratory variability:

ILVi = 1.96 RSDi [10]

Repeatability = 1.96 100

T5/(T3 k)T1/T3

[11]

Reproducibility = 1.96 100

T5/(T3 k) + s L2T1/T3

[12]

where ni = the number of measurements ofi laboratory, mi,j =the value of j measurements ofi laboratory, and k= number oflaboratories.

RESULTS AND DISCUSSION

Emissions of Regulated Pollutants, CO2,and Fuel Consumption

Table 3 presents the emission of regulated pollutants, CO 2,

and FC of the three vehicles. In the case of CO, the mean

exhaust values are 0.7, 0.22, and 0.16 g/km for the gasoline,

diesel, and DPF-equipped diesel vehicle, respectively. The cor-

responding 1.96*RSD intralaboratory variability is within 215,

834%, and 1084%, respectively, for the three vehicles. The

corresponding reproducibility 1.96*RSD value is 13, 21, and

113%, respectively, while the corresponding repeatability value

is 11, 20, and 38%, respectively. The last reproducibility value

is due to the high CO mean value of Lab2 (more than double

that of the other three laboratories, probably due to the deac-

tivation of the oxidation catalyst). Nevertheless, this value is

not considered as an outlier and is not extracted form the cal-

culations. The 1.96*RSD values are more important at lower

emissions.

The 1.96*RSD of intralaboratory hydrocarbon (HC) vari-

ability is within 1116, 1021, and 1050% for the gasoline,

diesel, and DPF-equipped diesel vehicles, respectively. The re-

producibility 1.96*RSD value is 27, 22.5,and 67%, respectively,

for the three vehicles, while the corresponding repeatability

value is 14, 18, and 27.5%, respectively. Once more, the last

reproducibility value is due to the high HC emissions measured

by Lab 2 (probably due to the deactivation of the catalyst), but

this value is not considered as an outlier and is not extractedfrom the calculations. Like in the case of CO emissions, the

RSD values are more important at lower emissions.

The NOx 1.96*RSD intralaboratory variability values are

within 1467, 25.5, and 57% for the gasoline, diesel and

DPF-equipped diesel vehicles, respectively. The reproducibility

1.96*RSD value of these emissions is 47, 11, and 17%, respec-

tively, for the three vehicles, while the corresponding repeata-

bility value is 46, 4, and 6%. The gasoline vehicle has a higher


7/15

TABLE3

Average,foreachlaboratory,emissionofregulatedpollutants,C

O2(ing/km)andfuelconsumption(in

L/100km),intralaboratoryvariability

(IVL),repeatability

(RPT),andreproducibility(RPD)1.96RSDvalues(%)forthe

threevehiclesused

CO

HC

NOx

PM

CO2

FC(inl/100km)

(g/km)

G

D

D+

DPF

G

D

D+

DPF

G

D

D+

DPF

G

D

D+

DPF

G

D

D+DPFG

D

D+

DPF

Lab1

0.67

0.2

0.12

0.116

0.034

0.033

0.045

0.333

0.254

0.0008

0.0233

0.0006

156.4137.1

136.5

6.645.2

5.14

Lab2

0.73

0.24

0.28

0.147

0.032

0.054

0.037

0.344

0.295

0.0275

0.0007

155.8137.9

135.9

6.595.23

5.09

Lab3

0.67

0.23

0.12

0.122

0.035

0.031

0.04

0.319

0.279

0.0011

0.0313

0.001

159.6136.1

135.9

6.75.23

5.18

Lab4

0.73

0.22

0.1

0.112

0.029

0.028

0.051

0.36

0.307

0.0313

0.001

161.7137.6

139.8

6.815.22

5.29

MEAN

0.7

0.22

0.16

0.124

0.032

0.036

0.043

0.339

0.284

0.001

0.0284

0.0008

158.4137.2

137

6.685.22

5.17

ILV(%)

Lab1

11

33.9

24.9

11.4

20.8

9.8

27.5

3.4

6

88.3

12.8

72

1.8

1.6

1.4

1.71.4

1.3

Lab2

2.6

10

10.3

15.8

13.2

13.8

14

2.4

7.4

0

5

169.7

0.8

0.9

0.3

0.71.1

0.4

Lab3

11.9

18.2

84.1

13.7

21.4

50.2

35.7

3.2

5.1

37.2

14.4

261.1

1.4

2.4

1.6

1.32.4

1.3

Lab4

15.2

8.1

41.1

14

10.4

34.9

67.3

5.5

6.5

0

13

122.2

0.7

0.9

1.3

0.80.9

1.3

RPT(%)11.2

20.4

37.6

14.2

18.3

27.5

45.9

4

6.4

60.4

12.9

191

1.2

1.6

1.2

1.21.6

1.2

RPD(%)13.1

21.3

113.1

27.2

22.6

67.2

47.2

10.9

16.7

67.8

29.3

163.9

3.6

1.7

2.9

2.91.4

3.3

G,gasolinevehicle;D,d

iese

lvehicle;D+

DPF,DPF-equippeddieselvehicle.

338


8/15


intralaboratory variability, repeatability, and reproducibility

(lower 1.96*RSD values) than the two diesel ones due to lower

emissions.

The PM emissions are less repeatable than the previous pol-

lutants in the case of the low-emitting vehicles. The 1.96*RSD

intralaboratory variability values are within 3788 (with the mea-

surements of only two laboratories), 514, and 72261% for the

gasoline, diesel, and DPF-equipped diesel vehicles,respectively.

The reproducibility 1.96*RSD value of these emissions is 67,

29, and 164%, respectively, for the three vehicles, while the

corresponding repeatability value is 60, 12.7, and 191%. The

gasoline vehicle and the DPF-equipped diesel vehicle have high

RSD values due to their very low emissions, which are similar

to the tunnel backgrounds.

The repeatability of CO2 and fuel consumption is better than

this of the regulated pollutants: the 1.96*RSD intralaboratory

variability values are less than 2.4%, with no significant dif-

ferences between CO2 and FC values. The reproducibility and

repeatability 1.96*RSD values of these emissions ranged from

1.2 to 3.6%.

The 1.96*RSD ILV values increase with the decrease of the

mean emitted value in the case of CO, HC, NOx, and PM emis-

FIG. 2. 1.96RSD intralaboratory variability values versus the mean value ofthe regulated pollutants (in g/km), CO2 (in g/km), and fuel consumption (in

l/100 km) of the three vehicles used (PM: particulate matter).

FIG. 3. Particle number of the tunnel background tests before and after each

NEDC for the four laboratories and the three vehicles used.

sions (Figure 2). This correlation seems independent of the ve-

hicle and technology used, even if more data are necessary tovalidate this statement. Within the observed range, this correla-

tion is not valid in the case of CO2 and FC.

Particle Number of the Tunnel Background Tests

Figure 3 presents the particle number of the tunnel back-

grounds, before and after the tests, for the four laboratories and

the three vehicles used. The particle number is quite similar be-

fore and after each NEDC, indicating that the tunnel is found

at its initial stage after each cycle. The difference of the tunnel

temperature before and after the tests is less than 5C; moreover,particle numbers after the tests arenot systematically higherthan

before the tests. These statements indicate that there is no par-

ticle desorption from the higher tunnel temperature after eachNEDC. The tunnel background values before tests are used in

the rest of this work.

Figure 4 presents the particle number of the tunnel back-

ground tests as a function of laboratory. This number depends

on the tunnel used at each laboratory, but it is generally around

1 1011 1/km. The particle number observed in the Lab 3 gaso-line tunnel is the lowest due to its cleanness. The higher num-

bers of the diesel tunnel are due to the particle deposit on the


9/15


FIG. 4. Tunnel background tests. Lower bars: tunnel background particle

numbersmeasuredat eachlaboratory(mean of three tests); meanvalueof alltests

andELPI limits of detectionand quantification (LOD= 5.3 1010 1/km/LOQ=1.59 1011 1/km) for the three vehicles used. Upper bars: 1.96RSD of eachlaboratory ILV (left bars), and reproducibility and repeatability (right bars). Lab

3 has two tunnels, one for gasoline vehicles (3G) and one for diesel vehicles

(3D).

walls during the tests and the dropping during the measurements

(Andrews et al. 2000). All of these tests are not very repeatable

due to the low particle number; repeatability is also very depen-

dent on the tests performed previously due to the dropping of

the deposed particles (Andrews et al. 2000). For each labora-

tory, the 1.96*RSD intralaboratory variability values are within

43 and 153%. Mohr (2003b) presents an ILV of 38%, but for aheavy-duty engine. The reproducibility 1.96*RSD value of tun-

nel background tests is 200%, while repeatability 1.96*RSD is

163%. Figure 4 shows that the particle number of blank mea-

surements is very near or even below the ELPI LOD or limits

of quantification (LOQ = 3 LOD), which are 5.3 1010 and1.5 1011 1/km, respectively.

Particle Number on the NEDC

Figure 5 presents the particle number of the gasoline vehicle

emitted on the NEDC. The mean total particle numbermeasured

is1.3

10121/km, thesameorderof magnitudeas ACEA (2002).

The 1.96*RSD values are quite high due to low particle numbers(Zervas et al. 2004). The intralaboratory 1.96*RSD variability

values are 2469%, while the corresponding reproducibility and

repeatability values are 59 and 45%. These values are much

lower than those of the tunnel background tests of this vehicle,

which is 174%.

The mean total particle number of the diesel vehicle without

DPF is two orders of magnitude higher than the particle number

of the gasoline vehicle: 1.3 10141/km (Figure 6), as already

FIG. 5. Lower bars: particle number (in 1/km) of the gasoline vehicle mea-sured at each laboratory (mean of 3 tests), mean value of all tests and ELPI

limits of detection and of quantification (LOD = 5.3 1010 1/km/LOQ =1.59 1011 1/km). Blank= mean of all four laboratories blanks for this vehi-cle. Upper bars: blank reproducibility 1.96RSD values (left bars), 1.96RSDintralaboratory variability values (middle bars), and reproducibility and repeata-

bility 1.96RSD values (right bars).

FIG. 6. Lower bars: particle number (in 1/km) of the diesel vehicle measured

at each laboratory (mean of 3 tests), mean value of all tests and ELPI limits of

detection and of quantification (LOD = 5.3 1010 1/km/LOQ= 1.59 10111/km). Blank=mean of allfourlaboratories blanksfor this vehicle.Upperbars:blank reproducibility 1.96RSD values (left bars), 1.96RSD intralaboratoryvariability values (middle bars), and reproducibility and repeatability 1.96RSDvalues (right bars).


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FIG. 7. Lower bars: particle number (in 1/km) of the DPF-equipped diesel

vehicle measured at each laboratory (mean of 3 tests), mean value (MV) of all

tests, and ELPI limits of detection and of quantification (LOD = 5.3 10101/km/LOQ = 1.59 1011 1/km). Blank= mean of all four laboratories blanksfor this vehicle. Upper bars: blank reproducibility 1.96RSD values (left bars),1.96RSD intralaboratory variability values (middle bars), and reproducibilityand repeatability 1.96RSD values (right bars).

presented (ACEA 2002; Zervas et al. 2004). The intralabora-

tory 1.96*RSD variability values are 1020%. These values are

lower than the corresponding values of the gasoline vehicle due

to higher particle number (Figure 5). The corresponding repro-

ducibility and repeatability 1.96*RSD values are 47 and 14%,

quite low compared to the values of this vehicle tunnel back-ground tests, which is 166%. It must be noted that this vehicle

is representative of the current European fleet (Euro3).

Figure 8 presents that the mean total particle number of the

DPF-equipped diesel vehicle is lower than the particle num-

ber of the two previous ones: 1.8 10111/km, as already pre-sented (ACEA 2002; Zervas et al. 2004). The intralaboratory

1.96*RSD variability values are within 18135%, while the cor-

responding reproducibility and repeatability values are 131 and

96%. These last values are quite close to the tunnel background

tests of this vehicle, which is 137%. The variability values are

higher than the values of the diesel vehicle due to the lower

particle numbers (Figure 3). It must be noted that the particu-

late emissions of this vehicle are representative of the emissionsof the future European passenger cars. The particle number of

this vehicle is very close or even lower than the ELPI limits of

detection or quantification, which induces high values of repro-

ducibility (as in the case of mass measurements). These high

values of reproducibility might not be adapted for regulatory

purposes.

There are some correlations between the 1.96*RSD values

and particle number. The lower curve of Figure 8 shows that the

FIG. 8. Lower curve: intralaboratory standard deviation (1.96SD) of particlenumber versus particle number on the NEDC. Upper curve: intralaboratory

1.96SD of particle number of each ELPI stage. All points for the three vehiclesused.

intralaboratory standard deviation (1.96*SD) of the measured

total particle number on the NEDC is linear with this number,

independent of the vehicle and technology used, indicating that

the error of this number determination using ELPI is quite con-

stant (Zervas et al. 2004). The same linear relation also exists in

the case of particle number 1.96*SD at each ELPI stage (upper

curves of Figure 8).

Figure 9 presents the ELPI 1.96*RSD ILV, reproducibility,and repeatability values as a function of particle number for the

threevehicles tested. Uppercurves show that reproducibility and

repeatability values increase at low particle numbers. The order

observedis tunnel backgrounds blanks>Diesel+DPF>Gaso-line > Diesel. The DPF-equipped diesel vehicle emits slightly

more particles that the blanks, but the 1.96*RSD reproducibil-

ity and repeatability values present a very important increase

between these two points. This statement indicates that ELPI

repeatability is critical for future vehicles. The lower curves

present the intralaboratory variability. The points are more scat-

tered, but three blocks of points are observed: one with low

1.96*RSD values due to high particle numbers (Diesel vehicle),

one with intermediary particle numbers and 1.96*RSD values(gasoline vehicle), and one with very disperse 1.96*RSD values

due to very low particle numbers. This last block corresponds to

DPF-equipped Diesel vehicle and blanks of the three vehicles.

This statement indicates that even within the same laboratory

the 1.96*RSD values are very dispersed in the case of future ve-

hicles. A probable correlation between repeatability of emitted

particle numbers andeach laboratory is searched but no tendency

is found.


11/15


FIG. 9. Lower curves: ELPI 1.96RSD intralaboratory variability values as afunction of each laboratory average particle number, for the three vehicles used

and the tunnel background tests of each vehicle. Upper curves: ELPI 1.96RSDreproducibility and repeatability values as a function of the average particle

number, for the three vehicles used and the tunnel background tests.

Mean Particle Size Distribution

Figure 10 presents the mean particle size distribution of the

three vehicles. These distributions are quite similar for the four

laboratories. Furthermore, size distribution shows that there is

no nucleation during the measurements. The particle numbers

emitted from the gasoline vehicle (mean value of all tests) are

about one order of magnitude higher than particle numbers oftunnel blanks, up to about 300 nm (Figure 11, lower curves).

For bigger particles, the ratio between exhaust gas particles and

tunnel background ones drops to only two. The particle number

of the diesel vehicle is, on the entire distribution, 23.5 orders of

magnitude higher than the particle number of the tunnel blank

measurements, while the particle number of the DPF-equipped

diesel vehicle remains very close to the blank measurements

for the entire distribution, especially in the area of very fine

particles. For the three vehicles tested, the maximum of this

ratio is observed at the third ELPI stage (63109 nm). Upper

curves of Figure 11 present the ratio between the mean number

of emitted particles and ELPI LOD; the limits of quantification

are also presented. It is clearly shown that the particle numbersof tunnel blanks of the DPF-equipped diesel PC and of the upper

part of the gasoline PC distribution are very close or even lower

to the LOD and LOQ.

The repeatability 1.96*RSD values of each ELPI stage are

4182, 0.6188, and 18259%, respectively, for the gasoline,

diesel, and DPF-equipped diesel vehicles. These values remain

lowerthan 133, 35,and 211%, respectively, forthe three vehicles

at the four first stages of the ELPI, where the majority of the

FIG. 10. Mean particle size distribution of the tunnel background (average of

all tests), and of the gasoline PC (lower curves), diesel PC (middle curves), and

DPF-equipped diesel PC (upper curves) measured at each laboratory (mean of

3 tests).

particles are measured (99, 96, and 97%, respectively, for the

three vehicles). The corresponding reproducibility 1.96*RSD

values are 63178, 20161, and 129208%.

Comparison Between the Particle Number and Mass

ELPI gives the particle distribution, but some authors calcu-

late the particle mass from this distribution. To achieve it the

particle density must be first determined. Different particle den-

sities are used in literature: an average density of 1.0 g/cm3(Shi

et al. 1999; Tsukamotoet al. 2000), or 1.7 g/cm3(Ulfvarson et al.

1997), or 0.5 g/cm3(Witze et al. 2004). But particle density is a

function of size (Ulfvarson et al. 1997; Ahlvik 1998; Andrews

et al. 2001, Virtanen et al. 2002, Witze et al. 2004). The smallerparticles are spherical, and the effective diameter determines the

particle density. The larger the particles are the more primary

particles they contain, leading to much lower values of effective

density (Ahlvik et al. 1998). The values of 1 g/cm 3 at 50 nm

and 0.3 g/cm3 at 300 nm (Witze et al. 2004), or 1.50.2 g/cm3

(Andrews et al. 2001), or 1.20.3 g/cm3 (Maricq et al. 2004) or

1.60.2 g/cm3 (Ahlvik et al. 1998), or 1.11.2 g/cm3 (Virtanen

et al. 2002) are suggested.


12/15


FIG. 11. Lowercurves:ratio between the mean numbers of theparticles emit-ted from each vehicle and the number of the tunnel background tests. Upper

curves: ratio between the mean particle numbers and the ELPI LOD.

A correlation between the particle mass obtained from cal-

culations and the mass measured on filters is performed. The

conclusions of Tzsukamoto et al. (2000) are that an average

density cannot be assumed for all particle size and that ELPI,

due to the several assumptions used (same density of particles

FIG. 12. Comparison between particle mass collected on filters and estimated from ELPI using the lower, mean, and upper diameter for each stage. Lower

curves: all ELPI stages. Upper curves: six first ELPI stages.

of each size, each particle size of each stage, charge efficiency,

etc.), generally predicts 1.52 times more particle mass. Shiet al.

(1999) found that ELPI and SMPS predict 1.31.6 times more

mass than this collected on filters. Khalek (2000) also concludes

that ELPI overestimates the total mass emissions comparing to

filter mass measurements in the case of a heavy-duty engine.

Andrews et al. (2001) conclude that estimated mass can be very

different from the mass collected on filter. Witze et al. (2004)use

only the first 6 ELPI stages and an empirical method to adjust

particle density to the mass obtained on the filters.

The correlation between the particle mass estimated from

ELPI and the mass collected on filters is presented here. For the

estimation of particle mass from ELPI, the following procedure

is used: the particle mass is the sum of the particle mass of

each stage over the NEDC. The particle mass of each stage is

calculated as the product of particle numbers and the effective

density of each stage. The density values of Ahvil et al. (1998)

are used for these estimations. Two methods are applied: using

all or only the first six ELPI stages, as Witze et al. (2004).

These resultsare presented in Figure12. This figure is divided

in four parts. Lower part of this figure presents the particle mass

estimated from ELPI versus this collected on filters when all

ELPI stages are taken into consideration. The lower, upper, and

mean (defined as Di =mean upper) diameter of each ELPIstage is used for these calculations. The upper curves present the

same estimations using only the six first stages. As the emissions

of diesel vehicle are much higher comparing to the other two

vehicles, the right part of this figure presents the estimation of


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TABLE 4

The a, b, and r2 of the best-fit lines y = ax+ b of theestimated versus measured particle mass

a b r2

All ELPI stages

Upper diameter 15.60

0.016 0.90

Mean diameter 6.85 0.0066 0.92Lower diameter 0.917 0.0008 0.95

First six ELPI stages

Upper diameter 4.92 0.0048 0.96Mean diameter 2.61 0.0026 0.95Lower diameter 0.454 0.0005 0.93

thediesel vehicle,whilethe left onethe estimationof thegasoline

and diesel + DPF passenger cars.The best-fit linesy= ax+ b and the coefficient of determina-

tion (r2) of the estimated versus measured values are calculated

for each diameter. Table 4 presents the values of a, b, and r2

forthese configurations.

From a macroscopicpoint of view, the use of upper and mean

diameter gives much higherparticlemass than themeasuredone;

the use of lower diameter using only the six first ELPI stages

estimates very lower mass. The use of lower diameter using all

ELPI stages gives the quite good best-fit line: y = 0.917*x0.0008, with r2 = 0.95, and it could predict the measured mass.However, if each vehicle is examined in detail, the obtained

results are less good.

In the case of the diesel vehicle, Figure12 shows that globally

the estimated and measured mass points are found on a straight

line. However:

the use of upper diameter estimates higher mass thanthe measured one (in average 14 times more mass than

the measured one when all the ELPI stages are taken

into account, while the 6 first stages give, on average,

4.6 times more mass), the use of mean diameter also estimates higher mass

than the measured one (in average 6.3 times more mass

than the measured one when all the ELPI stages are

taken into account, while the 6 first stages give in av-

erage 2.4 times more mass), and the use of lower diameter estimates lower mass than the

measured one (in average 15% less than the measured

mass when all the ELPI stages are taken into account,while the 6 first stages give in average 68% less mass

than the measured one).

In the case of the low-emitting particles passenger cars,

Figure 12 shows that ELPI cannot estimate the measured mass.

The points are too dispersed. Moreover:

the use of upper diameter estimates higher mass thanthe measured one in the case of all ELPI stages (6.6

and 11 times more for the gasoline and Diesel+DPFvehiclesrespectively), while theuse of thefirst sixELPI

stages estimates lower mass (in average 47 and 78%

less mass than the measured one for the gasoline and

diesel + DPF vehicles respectively); the use of mean diameter gives similar results as the

upper one (2.6 and 4.3 times more mass for thegasoline

and Diesel+DPF vehicle, respectively, when all ELPIstages are taken into account; while the 6 first stages

give respectively 73% and 89% less mass); and the use of lower diameter estimates lower mass than

the measured one in all cases (all ELPI stages: 71 and

96% less mass than the measured one for the gasoline

and diesel + DPF vehicles, respectively; 6 first ELPIstages: 53 and 98%, respectively, less mass).

A coefficient can be applied to each stage density and adjust

the estimated values to the measured ones. This method can give

slightly better results, but only in the case of the diesel PC, while

the estimated emissions of gasoline and diesel

+DPF vehicle

are not improved. For all the above reasons, the use of ELPIresults is not recommended for the estimation of particle mass.

Comparison Between the Reproducibility andRepeatability of Regulated Pollutants and ParticleNumber Measurements Using ELPI

Figure 13 presents the reproducibility and repeatability of

regulated pollutants and particle numbers determined by ELPI.

The CO2 and FC corresponding values are very low and are not

FIG. 13. Reproducibility (R1) and repeatability (R2) of CO, HC, NOx, PM

(in g/km), and ELPI particle number of the tunnel background tests (Number

Blank) and on the NEDC (1/km, Number ELPI) for the three vehicles used. G,

gasoline; D, diesel; D + DPF, DPF-equipped diesel vehicle.


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presented in this figure. The 1.96*RSD of particle emissions de-

termined by filters is, for each vehicle, higher than for the other

three regulated pollutants. This difference is not very important

in the case of the diesel vehicle: reproducibility of 14% and

repeatability of 30% against 1224% for the other pollutants.

As the other two vehicles emit very low particle mass, these

differences become quite important: 61 and 69% for the PM

emissions versus 1247% for the other three pollutants in the

case of the gasoline vehicle, and 165 and 190% against 6114%

for the DPF-equipped diesel passenger car. The ELPI repro-

ducibility over the entire NEDC is not very different from that

of PM emissions: 68, 29, and 164% for the PM determination

against 59, 47, and 131% for the ELPI, for the three vehicles,

respectively; the corresponding repeatability values are 61, 14

and 190% for the PM versus 45, 14, and 96% for ELPI.

CONCLUSIONS

The French subgroup of the Particulate Measurement Pro-

gramme, composed by IFP, PSA Peugeot-Citroen, Renault, and

UTAC, conducted an interlaboratory test on the determinationof exhaust particle number using ELPI. Three Euro3 passen-

ger carsone gasoline operating under stoichiometric condi-

tions, one diesel, and one DPF-equipped dieselare tested on

the NEDC. Only the metrological aspects related to repeatability

and detection limits are studied here, without touching on other

features not well established today, such as calibration of ana-

lytical instruments. The results of this study show the following:

The reproducibility 1.96*RSD values are 13, 21, and113%, respectively, for the three vehicles in the case of

CO; 27, 23, and 67% inthecase ofHC;47,11,and17%

in the caseof NOx; and 68, 29, and 164% in the caseof

particles collected on filters. For these pollutants, theintralaboratory variability 1.96*RSD values increase

quite regularly with the decrease of the mean emitted

values, independently of the vehicle and technology

used. The reproducibility 1.96*RSD values of CO2 emis-

sions and fuel consumption are always less than 3.6%

and much lower than the RSD values of the regulated

pollutants. There is very little difference between the

1.96*RSD values of CO2 and FC. There is no obvious

link between the 1.96*RSD values of CO2 emission

or fuel consumption and the vehicle used or the mean

value.

There is no effect of the ELPI sampling volume, be-tween 10 and 20 l/min, as the results of the Lab 1 are

similar to these of the other laboratories. The reproducibility 1.96*RSD of the tunnel background

tests is quite high (200%), due to low particle numbers,

very close to the ELPI detection limits. The 1.96*SD of the measured particle number (on the

NEDC or at each ELPI stage) is linear with this num-

ber, independently of the vehicle and technology used,

indicating that the error of this number determination

is quite constant. On theentire NEDC, thereproducibilityof total particle

number determined by ELPI is 59, 47, and 131% for

the gasoline, diesel, and DPF-equipped diesel vehicles,

respectively. These values are quite similar to those of

the mass particle determination. The particle number emitted from the DPF-equipped

diesel engine is very close or even lower to ELPI LOD

and LOQ. ELPI can be used, with some approximations, to esti-

mate the mass of emitted particles, but only for Euro3

Diesel passenger cars, and it fails to estimate the emit-

ted mass of the low-particle-emitting vehicles. Even if size distribution is given by ELPI with

insufficient reliability, it allows to check that there

is no nucleation mode due to inadequate dilution

parameters. These results show that the protocol used in this study

allows the reliable measurement of exhaust particle

number in the case of vehicles emitting at least two

orders of magnitude more than the tunnel background.

In the other cases, the measurement variability is too

high, especially for regulatory purposes.

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2005 Aerosol Sci. Technol. Zervas E. Interlaboratory Test of Exhaust PM Using ELPI

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