aerosol science and technology calibration of condensation

PLEASE SCROLL DOWN FOR ARTICLE

This article was downloaded by: [UAST - Aerosol Science and Technology]On: 21 November 2009Access details: Access Details: [subscription number 768370741]Publisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Aerosol Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713656376

Calibration of Condensation Particle Counters for Legislated VehicleNumber Emission MeasurementsB. Giechaskiel a; X. Wang b; H. -G. Horn c; J. Spielvogel d; C. Gerhart d; J. Southgate e; L. Jing f; M.Kasper g; Y. Drossinos a; A. Krasenbrink a

a European Commission, Joint Research Centre, Institute for Environment and Sustainability,Transport and Air Quality Unit, Ispra, VA, Italy b TSI Incorporated, Shoreview, MN, USA c TSI GmbH,Aachen, Germany d GRIMM Aerosol Technik, GmbH & Co KG, Ainring, Germany e AEA Energy andEnvironment, Oxfordshire, U.K. f Jing Ltd, Zollikofen, BE, Switzerland g Matter Eng. AG, Wohlen,Switzerland

First published on: 01 December 2009

To cite this Article Giechaskiel, B., Wang, X., Horn, H. -G., Spielvogel, J., Gerhart, C., Southgate, J., Jing, L., Kasper, M.,Drossinos, Y. and Krasenbrink, A.(2009) 'Calibration of Condensation Particle Counters for Legislated Vehicle NumberEmission Measurements', Aerosol Science and Technology, 43: 12, 1164 — 1173, First published on: 01 December 2009(iFirst)To link to this Article: DOI: 10.1080/02786820903242029URL: http://dx.doi.org/10.1080/02786820903242029

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf

This article may be used for research, teaching and private study purposes. Any substantial orsystematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply ordistribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directlyor indirectly in connection with or arising out of the use of this material.

http://www.informaworld.com/smpp/title~content=t713656376

http://dx.doi.org/10.1080/02786820903242029

http://www.informaworld.com/terms-and-conditions-of-access.pdf

Aerosol Science and Technology, 43:1164–1173, 2009Copyright © American Association for Aerosol ResearchISSN: 0278-6826 print / 1521-7388 onlineDOI: 10.1080/02786820903242029

Calibration of Condensation Particle Counters for LegislatedVehicle Number Emission Measurements

B. Giechaskiel,1 X. Wang,2∗ H.-G. Horn,3 J. Spielvogel,4 C. Gerhart,4 J.Southgate,5 L. Jing,6 M. Kasper, 7 Y. Drossinos,1 and A. Krasenbrink1

1European Commission, Joint Research Centre, Institute for Environment and Sustainability, Transportand Air Quality Unit, Ispra (VA), Italy2TSI Incorporated, Shoreview, MN, USA3TSI GmbH, Aachen, Germany4GRIMM Aerosol Technik, GmbH & Co KG, Ainring, Germany5AEA Energy and Environment, Oxfordshire, U.K.6Jing Ltd, Zollikofen BE, Switzerland7Matter Eng. AG, Wohlen, Switzerland

Light duty vehicle emissions legislation requires calibration andvalidation of Condensation Particle Counters (CPCs). A workshopwas organized at the European Commission’s Joint Research Cen-tre (JRC, Ispra, Italy) to study the effect of test aerosol materials (oftheir chemical composition) on CPC calibration results. The count-ing efficiencies of Combustion Aerosol STandard (CAST) particlesat 23 nm (steep part of the counting efficiency curve) were found tobe similar (0.53) to those of heavy duty diesel engine particles (0.57),the counting efficiencies of Emery oil were either similar (0.53) orhigher (0.72), while those of tetracontane (C40H82) particles weremuch higher (0.86). However, tests performed at JRC after theworkshop found much lower counting efficiencies for tetracontaneparticles (almost 0 at 23 nm) and variable results for NaCl (0.6or lower for 23 nm) indicating the importance of the generationmethod and the thermal treatment of the generated aerosol. Mea-surement issues including calibration against an electrometer or areference CPC, the effect of multiply charged particles on countingefficiencies, stability, repeatability, reproducibility and compara-bility of CPCs and electrometers of different manufacturers werealso investigated.

[Supplementary materials are available for this article. Go to thepublisher’s online edition of Aerosol Science and Technology toview the free supplementary files.]

Recieved 30 April 2009; accepted 3 August 2009.The authors thank L. Keck for his helpful comments. The assistance

of M. Carriero, S. Alessandrini, F. Forni, H. Jorgl, and G. Winklerduring the tests is also highly appreciated.

∗Current address: Desert Research Institute, 2215 Raggio Pkwy.,Reno, NV 89512, USA.

Address correspondence to Y. Drossinos, European Commission,Joint Research Centre, Institute for Environment and Sustainability,Transport and Air Quality Unit, I-21027 Ispra (VA), Italy. E-mail:[email protected]

1. INTRODUCTIONParticle number measurement has been introduced in Euro

5/6 light duty vehicles legislation based on the findings ofthe Particle Measurement Programme (PMP) (e.g., Giechaskielet al. 2008a, b). The particle number measurement system con-sists of two main parts: the volatile particle remover (or samplepreconditioning unit) and the particle number counter. The mainrequirements for the particle number counter according to thelegislation are (Regulation 83):

• To operate under full flow operating conditions (nobypass flow).

• To have a linear response to particle concentrationsover the full measurement range in single particle countmode.

• To have a counting accuracy of ± 10% across the rangefrom 1 cm−3 to the upper threshold of the single particlecount mode against a traceable standard (with up to10% coincidence correction).

• To have 0.50 ± 0.12 and >0.90 counting efficienciesat particle electrical mobility diameters of 23 ± 1 nmand 41 ± 1 nm, respectively.

Condensation Particle Counters (CPC) compliant with theselegislative requirements are known as PMP CPCs. These CPCsshould be calibrated at least annually with one of the followingtwo calibration methods:

• Primary method: By comparison of the response ofthe CPC under calibration (test CPC) with that of acalibrated aerosol electrometer (AE) when simultane-ously sampling electrostatically classified calibrationparticles, or

1164

Downloaded By: [UAST - Aerosol Science and Technology] At: 04:42 21 November 2009

CALIBRATION OF LEGISLATIVE CPCs 1165

• Secondary method: By comparison of the response ofthe CPC under calibration with that of a second one(reference CPC) which has been directly calibrated bythe primary method.

These calibration procedures are not new. Both methodshave been used by CPC manufacturers and research labs (e.g.,Wiedensohler et al. 1997; Sem 2002). The advantage of theprimary method is that the electrometer measurement can betraceable to international standards. Its disadvantages are thatthe particle charge state has to be known, and electrometer noiseintroduces measurement errors at low concentrations. On theother hand, the secondary method is less affected by the particlecharge state, and it is able to measure very low concentrations.However, very few studies have compared the equivalence ofthese two methods (e.g., Fletcher et al. 2009).

Another open issue on the CPC calibration procedures, andmaybe the most important, is the selection of the test aerosol ma-terial. CPC’s counting efficiencies strongly depend on aerosolproperties, thus the calibration curve is strictly valid for the testaerosol (e.g., Kesten et al. 1991; Sem 2002; Ankilov et al. 2002).As different CPC manufacturers may use different aerosol ma-terials for calibration (e.g., TSI uses Emery oil and GRIMMuses NaCl), CPCs from different manufacturers may have dif-ferent counting efficiencies. Since the PMP CPCs will be usedto measure engine emissions, it would be desirable to use dieselengine exhaust aerosols for calibration. The properties of dieselaerosol, however, depend on many parameters (e.g., engine type,engine load, fuel) and diesel aerosol can contain a wide range ofmaterials (e.g., soot, sulfuric acid, hydrocarbons). As it is verydifficult to define a “diesel engine” aerosol, the main objectiveof this study is to identify a material with behavior similar todiesel exhaust aerosol. Moreover, to our knowledge no previ-ous studies have investigated the calibration of n-butanol-basedCPCs with diesel engine particles.

Another concern is how robust, complete and applicable arethe proposed calibration/validation procedures. So far, CPC cal-ibration was conducted by manufacturers (e.g., Sem 2002) orhighly specialized labs (e.g., Stolzenburg and McMurry 1991;Wiedensohler et al. 1997; Kulmala et al. 2007). In the future,all labs that measure vehicle emissions will have to validatethe performance of their CPCs on site. A clear CPC calibrationprocedure is needed. Furthermore, it is necessary to identifymeasurement uncertainties, such as CPC performance stability(one day), repeatability (different days), reproducibility (differ-ent labs). Specifically, the effect of multiply charged particlesand mitigation approaches should be clearly addressed. Theseuncertainties, although well known (e.g., Rose et al. 2008), havenot been clearly discussed or quantified so far for “every day” labapplication. A workshop was organized by the European Com-mission’s Joint Research Centre (JRC, Ispra, Italy) in December2007 to address these issues. Various companies participated inthis workshop with CPCs (GRIMM, TSI) and particle genera-tors (TSI, GRIMM, AEA, Matter Eng.). JRC provided heavyduty diesel particles, tested the applicability of the required val-idation procedures, and coordinated the data analysis.

2. EXPERIMENTAL

2.1. Experimental Set UpThe schematic of the set up for CPC calibration is shown in

Figure 1 (Marshall and Sandbach 2007). Each company sam-pled polydisperse aerosol from a generator. The aerosol firstpassed through a dilution bridge that controlled its concentra-tion. Next, a differential mobility analyzer (DMA) was usedto select particles of a given mobility diameter. The sheath-to-aerosol flow rate ratio of the DMA was set at >5:1 to ensure anarrow “monodisperse” size distribution of different sizes (23,41 nm and a larger diameter (>50) for linearity tests). Filtered

FIG. 1. Schematic of the set up for the calibration of CPCs.


1166 B. GIECHASKIEL ET AL.

makeup flow air was added downstream of the DMA to maintaina flow balance. A mixing orifice was used to enhance turbulentmixing and to ensure uniform aerosol concentration. The aerosolflow was then split to the “test” CPC (with a nominal 50% cut-point (d50) around 23 nm), the “reference” CPC (d50 around 3nm), and the aerosol electrometer. Short, conductive tubes thatled to similar diffusion losses were used (Hinds 1999). Whenattainable, the counting efficiencies at 23 nm and 41 nm weremeasured at concentrations of ∼6000 cm−3 to avoid uncertain-ties due to coincidence correction or electrometer noise. For theengine tests at 23 nm the concentration was only about 2500cm−3. Electrometers have ±1 fA noise at 1 s averaging time(±375 cm−3 at a flow rate of 1 L/min) (Sem 2002), which trans-lates to an uncertainty of 15% for the engine tests at 23 nm and6% for the other tests. Linearity was measured at a size >50nm at concentrations of 10000, 8000, 6000, 4000, 2000, and0 cm−3. Each data point was recorded for 2 min at 1 Hz dataacquisition rate.

Before the beginning and after the end of the measurements aScanning Mobility Particle Sizer (SMPS) (or the DMA was con-nected to the reference CPC) was used to measure the size distri-bution that entered the DMA. TSI and GRIMM used their owninstrumentation and similar set ups and in most cases they mea-sured in parallel. Each company performed separately the dataacquisition, and the raw data were provided to JRC for analysis.

2.2. InstrumentationParticle Generators

The generators used in this workshop included a heavy dutydiesel engine as well as electrospray, evaporation-condensation,and CAST generators. The particle generators will be describedbriefly below.

Diesel EngineAn INECO Cursor 8 heavy duty engine without any af-

tertreatment was used as the diesel soot source. The TSI in-struments sampled from the tailpipe through a 20 m line inparallel with an extra pump to reduce the residence time inthis line (estimated 2.5 s). At medium load and speed (referredas “load”) the size distribution was monomodal (mean 60 nm,standard deviation σ = 1.8). At idle (referred as “idle”), thesize distribution was bimodal, with mean 60 nm, σ = 1.8 andmean 18.5 nm, σ = 1.28, even though a thermodenuder was in-stalled upstream of the DMA. Giechaskiel et al. (2009) showedthat a thermodenuder without hot dilution is not adequate toremove completely semi-volatiles if their concentration is high,thus some semi-volatiles might have remained on the particlesat the idle condition. For the engine tests GRIMM measuredindependently from the full dilution tunnel (CVS) downstreamof a thermodenuder and an ejector dilutor at the same mediumload and speed (referred as Engine “CVS” tests). Due to lowparticle concentrations (1000 cm−3) these measurements hadhigh uncertainty (>35%).

Evaporation-Condensation TechniqueThe aerosol generators (AEA prototypes) consisted of a ce-

ramic crucible heated via an electric Bunsen. The bulk material(NaCl or tetracontane) was placed in the ceramic crucible andheated to near its boiling point. A small air flow was introducedinto the crucible to displace vapor from the surface of the bulkmaterial to a cooler region of the generator where condensa-tion occurred. Filtered air was also added to dilute and cool thesample and to increase the flow rate. Particle diameters couldbe varied by controlling the rate of vapor transport from thecrucible (via the crucible displacement air flow) and/or the sub-sequent dilution and cooling rate of the vapor (via the carrierair flow). Two different aerosol generators were used for NaCl(mean 75 nm, σ = 1.3) and for tetracontane particles (mean 21nm and σ = 1.4, or mean 41 nm and σ = 1.6). A few addi-tional tests were conducted by the JRC after the workshop withtwo different (but similar) tetracontane and NaCl evaporation-condensation generators. The main difference was that filteredN2 was used as the displacement flow.

Electrospray TechniqueThis method refers to the generation of liquid droplets by

feeding a liquid solution or suspension through a capillary tubeand applying an electric field to the liquid at the capillary tip(Chen et al. 1995). The electric field draws the liquid from thetip into a conical jet from which ultrafine charged droplets areemitted. Air (and optionally CO2) is merged with the dropletsand the liquid evaporates while the charge is neutralized by anionizer. The result is a neutralized, monodisperse aerosol that ispractically free of solvent residue. This method was used (TSImodel 3480, S/N: 70515032) to electrospray Emery oil (PAO 4cSt) for CPC calibration (mean diameters of 22, 40, and 54 nmwith σ = 1.1). Emery oil is supposed to provide spherical par-ticles of chemical composition representative of synthetic lubeoil particles. Emery oil, a highly branched isoparaffinic polyal-phaolefin (1-decene (tetramer) mixed with 1-decene (trimer),hydrogenated), usually consists of 82–85% C30H60 and 13–16%C40H80 polyalphaolefins by volume.

CAST (Combustion Aerosol STandard)The CAST generators use a diffusion flame to form soot

particles during pyrolysis. Within the soot-generating burner theflame is mixed with a quenching gas at a definite flame height.Consequently, combustion is quenched and a particle flow arisesfrom the flame that leaves the combustion chamber. Sufficientquenching stabilizes soot particles and inhibits condensation inthe particle stream when it escapes from the flame unit intoambient air. Subsequently, air is supplied to dilute the particlestream. The state of the flame and the features of generatedsoot particles are primarily a function of the flow settings ofthe gases. The mini-CAST generator from GRIMM (numberdistribution mean 20 or 30 nm with σ = 1.4, S/N: 001) andthe CAST generator (mean 40 nm, σ = 1.4, S/N: 100907) fromMatter Eng. were used.



ElectrometersAerosol electrometer (AE) is a primary standard that mea-

sures the net charge of an aerosol. The charge is measured ina Faraday cup where the charge initiates a small current thatis converted to a voltage using a high resistance resistor. TheGRIMM model 5.705 (flow rate 1.5 L/min, S/N: 57050503) andthe TSI 3068B (flow rate 1 L/min, S/N: 70601289) electrometerswere used.

Particle Number CountersGRIMM and TSI each tested at least 3 counters. Due to space

limitations only the most representative results will be presentedin this article. The results were similar for the other counters.GRIMM used one CPC (Model 5.403, S/N: 003) with d50 at 3nm as a reference CPC for the secondary calibration method,and one test CPC (Model 5.404, S/N: 608) with d50 at 4.5 nm.All GRIMM CPCs operated at 1.5 L/min. The CPCs had beencalibrated 6 months (test CPC) and 3 years (reference CPC)before the workshop using nebulised NaCl particles. TSI useda 3790 (S/N: 70721012) as test CPC (with d50 at 23 nm) witha flow rate of 1 L/min. It had been calibrated with Emery oilparticles 6 months before the workshop.

Differential Mobility AnalyzersGRIMM used a Vienna-Type M-DMA (5 to 350 nm, S/N:

5UP60710) (Reischl et al. 1997). It was controlled and set to thespecified sizes with a DMA controller. It had been last calibrated7 months before the workshop. TSI used a 3080 electrostaticclassifier with a nano-column DMA (calibrated 6 months beforethe workshop, S/N: 70424125). The flow rates of DMAs werecontrolled internally.

Flow, Temperature, and Pressure MeasurementsFlow rate measurements were conducted with a soap bubble

meter (mini-BUCK Calibrator M-5) (1–6000 cm3/min) with a±0.5% accuracy of the display reading. The ambient tempera-ture and pressure remained constant during the measurements(21.5 ± 1◦C and 98.5 ± 1.5 kPa, respectively). These ambientconditions were similar to those that the companies had dur-ing their calibrations, so no extra correction for the ambientconditions was needed.

2.3. GRIMM–TSI ComparisonFor a limited number of tests some of the TSI and GRIMM in-

struments were used in parallel to compare directly the electrom-eters and the CPCs. Particles were generated by the TSI elec-trospray and classified by the GRIMM classifier. The GRIMMelectrometer, the GRIMM test CPC model 5.404, the TSI elec-trometer and the TSI test CPC 3790 sampled the monodisperseaerosol in parallel (figure not shown). Only counting efficienciesat 23 nm and 41 nm were measured.

2.4. Effect of Multiply Charged ParticlesBesides the monodisperse singly charged particles that exit

a DMA, there is a smaller amount of multiply charged parti-cles with the same electrical mobility but larger size (Baronand Willeke 2005). Multiply charged particles have a two foldeffect:

• The electrometer overestimates particle concentrationdue to the higher current generated by multiply chargedparticles. This can lead to lower test CPC linearityslopes and lower test CPC counting efficiencies.

• The test CPCs seem to have higher counting effi-ciency because multiply charged particles are largerthan singly charged particles with the same mobilitydiameter.

The contribution of these effects is difficult to calculate pre-cisely, so the multiply charged fraction should be minimized.One rigorous way to correct the experimental error due to multi-ple charging is to carry out a Tandem Differential Mobility Anal-ysis (TDMA) experiment to determine the fraction of multiplycharged particles and correct the efficiency data. One simplerway to minimize multiple charging effects is to sample the test“monodisperse” aerosol from the right-hand side of the modeof the polydisperse aerosol size distribution. This procedurewas followed for the measurements described in this article.The equations used to estimate the fraction of doubly to singlycharged particles and its effect on the counting efficiencies canbe found in the Supplemental information.

2.5. Effect of DMA Transfer Function on CPC CountingEfficiencies

The particle size selected by a DMA is not strictly monodis-perse. Instead, it has a narrow size range defined by the DMAtransfer function, even if contamination by multiply chargedparticles is not considered (Knutson and Whitby 1975). For asheath-to-sample flow rate ratio of 5:1, the mobility range ofparticles exiting the DMA is Z∗± 0.2Z∗, where Z∗ is the DMAcentroid mobility. This corresponds to a size range dl−du (lowerand upper diameters) of 21.0–25.7 nm for 23 nm, 37.4–45.9 nmfor 41 nm, 54.7–67.2 nm for 60 nm. To estimate the effect of thetransfer function on the counting efficiency at 23 nm (i.e., theeffect of particles with Z different from Z*), we used a hypo-thetical PMP CPC with a steep counting efficiency curve (0.35at 20 nm to 0.63 at 26 nm) to integrate concentrations of DMAclassified particles. The different polydisperse aerosols prior toDMA classification were assumed to have lognormal distribu-tion with different mean diameters and standard deviation. TheDMA transfer function was assumed to be triangular (Knut-son and Whitby 1975). We found that the transfer function hadnegligible effects on the measured counting efficiency (<0.01or <2% for counting efficiency 0.5) for size distributions withσ > 1.2 or size distributions with σ < 1.2 and peak around 23nm (±2 nm). Similar conclusions were drawn by Alofs et al.



(1995) and Rose et al. (2008). The effect would be even smallerfor sheath-to-sample flow rate ratio of 10:1.

The broadening of the DMA transfer function due to particlediffusion was found to be negligible for particles larger than 20nm and the flow rates selected (Stolzenburg 1988) and was nottaken into account (Reischl et al. 1997; Mamakos et al. 2007).

2.6. CalculationsIn the following results, the average of the 2 min electrome-

ters readings were corrected for the zero levels (drift or offset)and their flow rates (although the correction was negligible). Ingeneral, the electrometer drift after the end of the tests with eachmaterial (30–60 min) was small (±0.5 fA) with the exceptionof the engine tests where the drift was higher (±2 fA) and thesignal was unstable. The CPCs were not externally corrected forcoincidence as both TSI 3790 and GRIMM 5.404 have inbuiltcorrections. They were neither corrected for their flow rates,because users should have only one value to correct their resultsand not separately the flow and the slope. This effect wouldbe around 1.2% for TSI 3790 (which had a flow rate of 0.988L/min) and negligible for the GRIMM CPC 5.404. The effectof multiple charges was calculated through Equation (S9) (pri-mary method) or Equation (S11) (secondary method), otherwiseEquation (S15) or (S16) was used: equation numbers refer tothe equations in the Supplemental information. We assumed thatparticle losses in sampling lines from the DMA outlet to test in-struments were the same: no correction for sampling losses wasconsidered.

The gradient (slope) and the square of the Pearson productmoment correlation coefficient (R2) during linearity test werecalculated by forcing the fit to pass through the origin. As theslope and the R2 are not adequate indications of linearity andclose agreement of two instruments (Fletcher et al. 2009 andGiechaskiel and Stilianakis 2009), the ratio of the CPC (undercalibration) to the electrometer was calculated for each concen-tration. This ratio, according to legislation, should be between

0.9 and 1.1 for all concentrations tested. This ratio was also cal-culated for the 23 and 41 nm cases (it should be 0.38–0.62 and>0.9, respectively). The coefficient of variance (CoV) of theseratios, the ratio of the standard deviation to the mean value,during the 2 min recordings was also calculated (stability ofmeasurements).

For some tests, referred to as “repeated,” the method adoptedby the Japanese National Institute of Advances Industrial Sci-ence and Technology (AIST) was followed: the DMA voltagewas turned on/off alternatively for one minute and each measure-ment was repeated 3 times. The electrometer zero offset mea-sured when the DMA voltage was off was subtracted from eachmeasurement to reduce uncertainties due to electrometer drift.

3. RESULTS

3.1. Comparability of ElectrometersGRIMM and TSI electrometers showed similar concentra-

tions when measuring in parallel (see section 2.3). The GRIMMelectrometer measured 5% higher at 23 nm (concentration 8500cm−3) and 1.5% higher at 41 nm (concentration 4500 cm−3).Hence, if the two companies calibrated the same CPC, the cali-bration factors would have <5% difference. The 5% differenceof the electrometers was considered acceptable as the uncer-tainty at these concentrations is 4–8% (noise 1 fA or 375 cm−3)(Sem 2002). In an earlier workshop conducted by TSI and AIST,the TSI electrometer was found to agree within 3% in the sizerange of 3.7–150 nm with the AIST electrometer (Wang et al.2007).

3.2. Primary MethodThe counting efficiencies and slopes of various materials for

the three CPCs examined are presented in Tables 1–3. Theseresults were not corrected for multiply charged particles (i.e.,Equation (S15) was used).

TABLE 1Test TSI CPC 3790 calibration counting efficiencies according to the primary method without multiple charge correction

(Supplemental information, Equation (S15)). Number in parenthesis after the material is the size (in nm) at which the linearitychecks were conducted (for the last 3 columns). The fourth column gives the minimum and maximum ratios of the test CPC to

electrometer concentrations. Numbers after ± indicate the CoV (ratio of the standard deviation to the mean value) of the ratio ofthe test CPC to the electrometer during the 2 min measurement

Material (nm) 23 nm 41 nm >50 nm Slope R2

NaCl (80) — — 0.856–0.919 0.894 0.9995Tetracontane (70) 0.862(±2.9%) 1.033(±2.6%) 0.938–0.970 0.943 0.9999CAST (60) 0.543(±1.1%) 0.931(±2.6%) 0.921–0.945 0.926 0.9999Mini-CAST (50) 0.522(±1.3%) 0.916(±4.8%) 0.911–0.976 0.924 0.9981Emery oil (55) 0.724(±0.9%) 0.984(±1.9%) 0.948–0.975 0.973 1.0000Emery oil (repeated) 0.532(±0.8%) 0.947(±1.8%) 0.945–0.987 0.951 0.9998Engine idle (120) 0.835(±4.4%) 0.941(±1.9%) 0.772–0.844 0.784 0.9984Engine load (120) 0.573(±2.3%) 0.919(±3.2%) 0.874–1.058 0.885 0.9966



TABLE 2Test GRIMM CPC 5.404 calibration counting efficiencies according to the primary method


NaCl (50) — — 0.766–0.790 0.785 0.9997Tetracontane (70) 0.810(±5.7%) 0.935(±5.6%) 0.908–0.996 0.913 0.9999CAST (60) 0.599(±6.9%) 0.911(±2.8%) 0.905–0.945 0.919 0.9997Mini-CAST (50) 0.566(±5.1%) 0.865(±3.4%) 0.887–0.944 0.936 0.9998Emery oil (55) 0.726(±5.9%) 0.954(±3.1%) 0.949–0.963 0.954 0.9999Emery oil (combined) 0.624(±5.2%) 0.913(±4.4%) — — —Engine CVS (70) — 0.806(±8.2%) 0.721–0.762 0.731 0.9996

TSI 3790As shown in Table 1 the concentration ratios and the slopes

were between 0.91 and 0.99 (requirement 0.9–1.1) except forthe NaCl and engine cases. The R2 was greater than 0.996 (0.97required) for all materials in the concentration range tested (upto 10000 cm−3). The slope of the TSI CPC 3790 accordingto the original calibration was 0.932 (with Emery oil). In thisworkshop, it was 0.95–0.97 (with Emery oil). This 0.03 differ-ence of the slope (3%) indicates that a <5% (reproducibility)uncertainty should be expected.

The 41 nm counting efficiency requirement (>0.9) was metfor all materials. The CoV of the tests was <5% indicating theexpected stability of the measurements. Similar uncertainty wasreported by Liu et al. (2005) who calibrated 3010 and 3010DCPCs and by Hermann et al. (2007). The 23 nm counting effi-ciency of the TSI test CPC 3790 met the requirements (0.38–0.62) for diesel (load), CAST, and Emery oil (repeated) (Table1 and Figure 2). The engine exhaust at idle mode had very highcounting efficiency at 23 nm (0.83), but lower efficiency at 120nm (0.78). This unexpected behaviour may be attributed to: (1)The size distribution at idle was bimodal, therefore a large frac-tion of particles were multiply charged when the DMA selected23 nm or 41 nm particles; or (2) The number concentration dur-ing these measurements was 2500 cm−3, thus the uncertaintyof the electrometer was 15%. Tetracontane particles had signifi-cantly higher counting efficiencies at 23 nm (0.86) than the othermaterials. These results will be further discussed in Section 3.4.

The Emery oil data taken with the standard experimentalprocedure had a higher efficiency (0.72) than earlier calibration

data for the same unit (see calibration data in Figure 2). Thecounting efficiency at 41 nm was also higher compared to theEmery oil (repeated) and the factory calibration value. It wassuspected that the isopropanol alcohol buffer solution used forelectrospray had not evaporated completely before entering theCPC, resulting in higher counting efficiencies. A counting effi-ciency test was conducted at TSI after the workshop by passingthe electrosprayed Emery oil particles through a diffusion dryerfilled with activated charcoal (or bypassing the diffusion dryer)before the DMA. However, no difference in the CPC counting ef-ficiency was observed with or without passing particles throughthe diffusion dryer. The high Emery oil efficiency in this testcould be partly due to the uneven concentration split betweenthe electrometer and CPC or due to electrometer drift duringthe duration of this particular test. However, the most probableexplanation is that the Emery oil has higher efficiencies than theCAST particles at 23 nm. Comparison of the original Emeryoil calibration data with the workshop results (0.13 differencewith normal data and 0.05 with repeated data) gives an indica-tion of the (reproducibility) uncertainty at the steep part of thecurve. These uncertainties are similar to the difference Heim etal. (2004) observed at the counting efficiency measurements ofa GRIMM CPC over a two years period (differences in count-ing efficiencies of ∼0.1 at the slope and much less at biggerdiameters). High uncertainty (20%) of the slope of the countingefficiency was also reported by Hermann et al. (2007).

Figure 2 shows the counting efficiencies reported in Ta-ble 1 for the TSI 3790 (for diameters >50 nm the slope isgiven). For the sake of clarity, error bars with measurement

TABLE 3Reference GRIMM CPC 5.403 calibration counting efficiencies according to the primary method


NaCl (50) — — 0.822–0.878 0.854 0.9994Tetracontane (70) 0.946(±5.6%) 0.965(±5.4%) 0.914–0.985 0.960 0.9992CAST (60) 0.968(±6.3%) 0.964(±2.8%) 0.945–0.969 0.951 0.9999Mini-CAST (50) 0.905(±4.2%) 0.946(±3.3%) 0.963–1.000 0.986 0.9992Emery oil (55) 0.952(±5.6%) 0.976(±3.1%) 0.960–1.026 1.007 0.9986Engine CVS (70) — 0.853(±8.5%) 0.718–0.777 0.730 0.9980



FIG. 2. Primary method counting efficiency of TSI CPC 3790 (accordingto Equation (S15), Supplemental information). Error bars give the countingefficiency corrected for doubly charged particles (Equation (S9)).

uncertainties, which have been reported in Table 1, are not dis-played. However, error bars are given that show the efficiencycalculated after correcting for doubly charged particles (Equa-tion (S9) with measured f++). This effect was important forthe engine (load) (correction +0.075 for 41 and 120 nm) andNaCl cases (correction +0.055 for the 80 nm) and negligiblefor the rest (correction <0.02). When this correction is appliedto the NaCl and engine data, their slopes become similar to theslopes of the other materials, indicating the importance of thiscorrection.

GRIMM 5.404Similar results with the TSI test CPC were also found for

the counting efficiencies of the test GRIMM model 5.404 CPC(Table 2). It is important to note the low slope with NaCl particles(size 50 nm). This has to do only partly with the multiply chargedparticles. Even if this correction is taken into account, the slopeis less than with the other materials. The lower slope can beexplained by the fact that the 50 nm size is still at the increasingpart of the counting efficiency curve (Wang et al. 2007). Thiseffect was not observed at the TSI 3790 in this workshop becausethe measurements were conducted with 80 nm particles. Thus,for linearity tests it is very important to choose a size that thecounting efficiency has reached its maximum value. In Table 2,a test is named “Emery oil combined,” where the two companiesmeasured in parallel. The “combined” counting efficiency at 23nm was 0.62, while during the measurements with the standardprocedure it was 0.72. These tests show that at the steep part ofthe counting efficiency curve the (repeatability) uncertainty ishigh (0.1 or 16%). The tests with this CPC also showed that thecounting efficiency of Emery oil particles at 23 and 41 nm isthe same or slightly higher (+0.1) than the counting efficiency

of CAST particles. The diesel engine (CVS) tests had veryhigh uncertainty (>35%) due to the low concentration measured(1000 cm−3): thus, no sound conclusions can be drawn.

GRIMM 5.403The GRIMM reference CPC had 23 nm efficiencies of 0.91–

0.95 for all materials and 0.94–0.98 for 41 nm (except for theengine case, Table 3). The ratios and slopes of the linearitychecks were 0.95–1.0 (lower for NaCl and engine) and the R2

values were >0.998.

3.3. Secondary MethodAccording to the secondary method, the CPCs under eval-

uation are compared with a CPC calibrated with the primarymethod. The reference CPC used by GRIMM was CPC model5.403 (d50 at 3 nm). No (counting efficiency) correction wasapplied to the reference CPC. This correction should have been∼0.93, ∼0.96, and ∼0.99 (see Table 3) for the 23, 41, and >50nm cases (depending also on the material of the primary cali-bration of the reference CPC). The secondary calibration resultsare shown in Table 4. The 23 nm efficiencies were 0.62 forCAST particles but higher for Emery oil (0.76) and even higherfor tetracontane (0.87). The 41 nm efficiencies were >0.91 forall materials. Note that 41 and 70 nm diesel particles had highefficiencies (0.94) regardless of their low concentration (1000cm−3). With the primary method the results were 0.72–0.80 (Ta-ble 2). The secondary method is much less susceptible to lowconcentrations than the primary method. The linearity slope forthe CPC model 5.404 was ∼0.95. The gradient seemed to bematerial independent for diesel, CAST, tetracontane and Emeryoil particles. The gradient for NaCl was ∼0.03 less mainly dueto the effect of doubly charged particles. However, the effectwas much lower compared to the primary method (where thedoubly charged particles effect on the slope was >0.1). Thiscan be explained by the different effects of the doubly chargedparticles on the CPCs and the electrometers (Equation (S13)and (S14), see discussion of Figure S1b). The R2 was greaterthan 0.997 (0.97 required) for all materials in the concentrationrange tested (up to 10000 cm−3).

Comparison of the results of the primary and secondary meth-ods for the GRIMM test CPC model 5.404 shows that the slopeswith the secondary method were slightly higher (∼0.02). How-ever, if the slope of the reference CPC model 5.403 was takeninto account then there would be no difference. The countingefficiencies at 23 nm and 41 nm with the secondary methodwere around 0.05 and 0.03 higher, respectively. This had to dowith the 0.93 and 0.96 efficiency of the reference CPC at thesediameters. These corrections should be taken into account foraccurate results.

Legislation doesn’t specify that the reference CPC shouldhave efficiencies ∼1 at diameter >23 nm. Thus, in principle,one CPC with a d50 around 23 nm could be used. Such a testwas conducted by comparing the test CPC model 5.404 with a



TABLE 4Test GRIMM CPC model 5.404 calibration counting efficiencies according to the secondary method.

No linearity (slope) correction for the reference CPC

Material (nm) 23 nm 41 nm > 50 nm Slope R2

NaCl (50) — — 0.889–0.933 0.919 0.9999Tetracontane (70) 0.867(±5.5%) 0.970(±5.2%) 0.940–1.011 0.951 0.9994CAST (60) 0.618(±4.4%) 0.945(±2.2%) 0.948–0.975 0.960 0.9996Mini-CAST (50) 0.619(±3.9%) 0.915(±2.5%) 0.891–0.968 0.950 0.9998Emery oil (55) 0.762(±2.9%) 0.977(±2.7%) 0.927–1.003 0.947 0.9985Engine CVS (70) — 0.944(±4.7%) 0.973–1.015 1.000 0.9992

“reference” CPC with d50 at 23 nm. The ratio of the concentra-tions of the two CPCs was 1 ± 0.02 for all the sizes and materialstested (with one exception at 23 nm that had 0.08 difference).When using a reference CPC with d50 at 23 nm, its counting ef-ficiencies must be known to calculate the counting efficienciesof the test CPC. However, the efficiency uncertainty near 23 nmis high. Small deviation can lead to large errors. Therefore, itis recommended that the reference CPC has counting efficiency∼1 near 23 nm.

3.4. Validation at LabsFigure 3 compares the results of the JRC workshop with ear-

lier measurements at JRC for the same 3790 CPC with dieselengine particles from the same heavy duty engine at the samemedium load and speed. Error bars show the counting efficien-cies corrected for double charges. Note that multiple chargingis important for 41 and 120 nm with the primary method. How-ever, for the secondary method, although there is a considerableamount of doubly charged particles (10%), the effect is negligi-ble due to the high counting efficiency (>0.9) of the test CPCat 41 and 120 nm (see Supplemental information, Figure S1b).At 10 and 23 nm the doubly charged fraction is low (2.5%) soits effect is small. The two calibration results are in very goodagreement, indicating that labs can do the validation tests (withthe secondary method).

Figure 4 shows the tetracontane and NaCl efficiency datafrom the JRC workshop. Counting efficiencies of tetracontaneand NaCl for another TSI CPC 3790 measured by the JRC labwith the secondary method are also plotted in Figure 4. Thetetracontane and NaCl particles were generated by two different(but similar) evaporation-condensation generators. The NaClcounting efficiency was measured with and without passing theaerosol through a thermodenuder (at 300◦C).

Significant differences in counting efficiencies for thermallyor non-thermally treated NaCl particles were observed withthe later having higher counting efficiencies. Higher countingefficiencies of NaCl particles with relative humidity of 50%compared to relative humidities of 25% and 0% were also re-ported in Sem (2002). One possible explanation is that non-thermally treated NaCl particles contain water (NaCl is very

hygroscopic) that could have condensed from the carrier air ofthe generator or the sheath air in the DMA. Since n-butanol issoluble in water, wet NaCl will have higher efficiencies than dryNaCl particles. Another possible explanation is the differencesin particle shape and structure due to the thermal treatment of theaerosol. The particles generated by evaporation-condensationtechnique (and possibly the dry particles downstream of the ther-modenuder) are highly agglomerated. After exposure to watervapour at relative humidity below the deliquescence threshold(75%) they become more compact with reduced shape factor(Kramer et al. 2000).

Larger differences were observed with the tetracontane parti-cles, probably due to differences in their generation. In the JRCtests the displacement flow was filtered N2, to avoid contami-nation from particles, and condensation took place at ambienttemperature. In the JRC workshop the tetracontane particleswere generated using air as the displacement flow that wasnot dried and condensation took place at <5◦C. It is possiblethat some water had condensed on the tetracontane particles,

FIG. 3. Comparison of JRC workshop results with earlier measurements atJRC for the same CPC for heavy duty diesel engine particles (engine at mediumload).



FIG. 4. Results from the JRC workshop TSI 3790 CPC (with the primarymethod, solid symbols) and from JRC lab with another TSI 3790 CPC (sec-ondary method, open symbols) for NaCl (squares and triangles) and tetracontane(circles) particles.

thereby increasing their counting efficiencies. In addition, im-purities of the displacement flow might have also contributed tothese higher efficiencies. Hering et al. (2005) found differencesin the counting efficiencies of DOS particles in a water CPC dueto contamination of NaCl. As extra solubility tests didn’t showany significant solubility of tetracontane in n-butanol, the JRClab results should be more representative of the tetracontanebehavior.

Some extra tests were also conducted to investigate the ef-fect of mixing and splitting of the flow (no figure shown). Itwas found that there must be a mixing orifice after the DMA,or at least the tube must be long enough (>20 diameters) toensure adequate mixing. The splitting is also important espe-cially when the flows of the instruments are different. A Y-typesplitter should be used. All the above tests show that althoughsome results might be repeatable, they are not necessary accu-rate. Labs that use their own generators and calibration systemsshould make sure that they control humidity and impurities intheir experimental set ups, and that the aerosol concentration isuniformly split to instruments.

4. SUMMARY AND CONCLUSIONSRecently the particle number method was introduced in the

Euro 5/6 light duty regulation. Calibration of Condensation Par-ticle Counters (CPCs) includes linearity measurements (slope0.9–1.1, R2 > 0.97) and counting efficiency measurements (at23 nm it should be 0.38–0.62, at 41 nm >0.9). Labs will haveto demonstrate compliance of their counters with a traceablestandard within a 12-month period prior to the vehicle emis-sions test. Compliance can be demonstrated by either the pri-mary (comparison of the test CPC with an electrometer) orsecondary method (comparison with a CPC already calibrated

with the primary method). Proper calibration of CPCs is neces-sary as the concentration linearity slope will have to be takeninto account for the calculations of particle number emissions.

A workshop was organised at the European Commission’sJoint Research Centre (JRC) to investigate the effect of theaerosol material (chemical composition) and the uncertaintiesof the calibration procedures. GRIMM and TSI provided CPCs,while AEA, Matter Eng., GRIMM and TSI provided parti-cle generators (evaporation-condensation, CAST, electrospray).Heavy duty diesel engine (w/o aftertreatment) particles werealso produced at idle and at a medium load modes. The datawere evaluated by JRC. The main conclusions are discussed inthe following sections.

Multiply Charged Particles EffectMulti-charge effect is important when f++ (ratio of doubly

to singly charged particles) is >5%. This translates to size dis-tributions with σ > 1.3 and measurements of large particles(>50 nm), assuming that the selected size is on the right side ofthe mean of the size distribution.

Primary MethodFor the linearity tests the material or size (>50 nm) was

small (with f++ <3%) (i.e., slopes were within ±0.02). A highmulti-charge effect (f++ ∼6%, polydisperse size distribution atDMA inlet with mean 60 nm and σ = 1.82) led to lower slopeestimation for NaCl and engine particles (0.05 less than the trueone). An underestimation of the slope was also observed with50 nm NaCl particles because the counting efficiency at this sizewas not maximum (i.e., this size was still at the increasing part ofthe counting efficiency curve). The R2 was >0.997 for all cases.

The counting efficiency at the steep part of the curve (23 nm)was found to depend significantly on the chemical compositionof the aerosol particles. Tetracontane particles showed the high-est efficiencies (0.86); CAST particles had similar efficiencies(0.53) with non-volatile diesel engine soot (0.57); Emery oilparticles had also similar efficiencies (0.53) or slightly higher(0.72). The uncertainty of the measurements (expressed as dif-ference between two measurements on different days or fromdifferent labs) was generally 0.05 for counting efficiencies >0.9and 0.1 for counting efficiencies at the steep part of the countingefficiency curve. Thus, manufacturers should aim for a slopearound unity and a counting efficiency at 23 nm of 0.5 to havebest performance safety margin. Labs that check their CPCsshould use the same material with the one that the CPC hadbeen calibrated. If a different material is used its effect on thecounting efficiencies should be taken into account.

Secondary MethodGenerally, similar counting efficiencies, slopes and R2 were

found with the secondary method as with the primary methodwhen using a reference CPC with a low cut-off size (3 nm). Ifthe counting efficiencies of the reference CPC were taken into



account, the primary and secondary methods were equivalent.With the secondary method the multi-charge effect was muchsmaller, as it was partially cancelled out from the two CPCs. Thesecondary method is highly recommended for labs that want toverify the proper operation of their CPCs, provided that theyhave a reliable reference CPC.

Validation at LabsExperiments at the JRC after the workshop measured count-

ing efficiencies of thermally treated (through a thermodenuderat 300◦C) NaCl particles that were almost 0.2 lower than theefficiencies of non-thermally treated NaCl particles. Tetracon-tane particles were found to have lower counting efficienciesthan the workshop results (almost 0 at 23 nm). However, ex-periments with diesel aerosol measured efficiencies similar tothe workshop results. Thus, labs should be extremely carefulin their aerosol generation method. Special attention should bepaid to humidity and impurities, as they were found to influenceconsiderably the measured counting efficiencies.

REFERENCESAlofs, D. J., Lutrus, C. K., and Hagen, D. E. (1995). Intercomparison

Between Commercial Condensation Nucleous Counters and an Alternat-ing Temperature Gradient Cloud Chamber, Aerosol Sci. Technol. 23:239–249.

Ankilov, A., Baklanov, A., Colhoun, M., Enderle, K.–H., Gras, J., Julanov,Y., Kaller, D., Lindner, A., Lushnikov, A. A., Mavliev, R., McGovern, F.,O’Conner, T. C., Podzimek, J., Preining, O., Reischl, G. P., Rudolf, R., Sem,G. L., Szymanski, W. W., Vrtala, A. E., Wagner, P. E., Winklmayr, W., andZagaynov, V. (2002). Particle Size Dependent Response of Aerosol Counters,Atmos. Res. 62:209–237.

Baron, P., and Willeke, K. (2005). Aerosol Measurement: Principles, Tech-niques, and Applications. Wiley-Interscience, John Wiley and Sons, 2nd edi-tion.

Chen, D.-R., Pui, D. Y. H., and Kaufman, S. L. (1995). Electrospraying ofConducting Liquids for Monodisperse Aerosol Generation in the 4 nm to 1.8µm Diameter Range, J. Aerosol Sci. 26:963–977.

Fletcher, R. A., Mulholland, G. W., Winchester, M. R., King, R. L., andKlinedinst, D. B. (2009). Calibration of a Condensation Particle CounterUsing a NIST Traceable Method, Aerosol Sci Technol. 43:425–441.

Giechaskiel, B., Dilara, P., and Andersson, J. (2008a). Particle Measure-ment Programme (PMP) Light-Duty Inter-Laboratory Exercise: Repeatabilityand Reproducibility of the Particle Number Method, Aerosol Sci. Technol.42:528–543.

Giechaskiel, B., Dilara, P., Sandbach, E., and Andersson, J. (2008b). Parti-cle Measurement Programme (PMP) Light-Duty Inter-Laboratory Exercise:Comparison of Different Particle Number Measurement Systems, Measure-ment Sci. Technol. 19:095401.

Giechaskiel, B., Carriero, M., Martini, G., Krasenbrink, A., and Scheder, D.(2009). Calibration and Validation of Various Commercial Particle NumberMeasurement Systems, SAE 2009–01–1115.

Giechaskiel, B., and Stilianakis, N. (2009). A Note on the Comparison of ParticleNumber Counters, Meas. Sci. Technol. 20:077003.

Heim, M., Kasper, G., Reischl, G. P., and Gerhart, C. (2004). Performance ofa New Commercial Electrical Mobility Spectrometer, Aerosol Sci. Technol.38(S2):3–14.

Hering, S. V., Stolzenburg, M. R., Quant, F. R., Oberreit, D. R., and Keady,P. B. (2005). A Laminar-Flow, Water-Based Condensation Particle Counter(WCPC), Aerosol. Sci. Technol. 39:659–672.

Hermann, M., Wehner, B., Bischof, O., Han, H.-S., Krinke, T., Liu, W., Zerrath,A., and Wiedensohler, A. (2007). Particle Counting Efficiencies of New TSICondensation Particle Counters, J. Aerosol Sci. 38:674–682.

Hinds, W. (1999). Aerosol Technology: Properties, Behavior, and Measurementof Airborne Particles, Wiley-Interscience, John Wiley & Sons. 2nd edition.

Kesten, J., Reineking, A. and Porstendorfer, J. (1991). Calibration of a TSIModel 3025 Ultrafine Condensation Particle Counter, Aerosol Sci. Technol.15:107–111.

Knutson, E. O., and Whitby K. T. (1975). Aerosol Classification by ElectricMobility: Apparatus, Theory, and Applications, J. Aerosol Sci. 6:443–451.

Kramer, L. Poschl, U., and Niessner, R. (2000). Microstructural Rearrange-memnt of Sodium Chloride Condensation Aerosol Particles on Interactionwith Water Vapor, J. Aerosol Sci. 31:673–685.

Kulmala, M., Mordas, G., Petaja, T., Gronholm, T., Aalto, P. P., Vehkamaki,H., Hienola, A. I., Herrmann, E., Sipila, M., Riipinen, I., Manninen, H. E.,Hameri, K., Stratmann, F., Bilde, M., Winkler, P. M., Birmili, W., and Wagner,P. E. (2007). The Condensation Particle Counter Battery (CPCB): A NewTool to Investigate the Activation Properties of Nanoparticles, J. Aerosol. Sci.38:289–304.

Liu, W., Osmondson, B. L., Bischof, O. F., and Sem, G. J. (2005). Calibrationof Condensation Particle Counters, SAE 2005–01–0189.

Mamakos, A., Ntziachristos, L., and Samaras, Z. (2007). Diffusion BroadeningOf DMA Transfer Functions. Numerical Validation of Stolzenburg Model, J.Aerosol Sci. 38:747–763.

Marshall, I., and Sandbach, E. (2007). Particle Number Counter Calibra-tion/Validation Procedures. Report to the Department for Transport. Availableat http://www.unece.org/trans/doc/2008/wp29grpe/PMP-21-07e.pdf.

Regulations No. 83 (Emissions of M1 and N1 categories of vehicles). Availableat http://www.unece.org/trans/main/wp29/wp29regs81-100.html.

Reischl, G. P., Makela, J. M., and Necid, J. (1997). Performance of a Vienna TypeDifferential Mobility Analyzer at 1.2–20 Nanometer, Aerosol Sci. Technol.27:651–672.

Rose, D., Gunthe, S. S., Mikhailov, E., Frank, G. P., Dusek, U., Andreae,M. O., and Poschl, U. (2008). Calibration and Measurement Uncertainties ofa Continuous-Flow Cloud Condensation Nuclei Counter (DMT-CCNC): CCNActivation of Ammonium Sulfate and Sodium Chloride Aerosol Particles inTheory and Experiment, Atmos. Chem. Phys. 8:1153–1179.

Sem, G. J. (2002). Design and Performance Characteristics of Three Continuous-Flow Condensation Particle Counters: A Summary, Atmos. Res. 62:267–294.

Stolzenburg, M. R. (1988). An Ultrafine Aerosol Size Distribution MeasuringSystem. Ph.D. Thesis, University of Minnesota.

Stolzenburg, M. R., and McMurry, P. H. (1991). An Ultrafine Aerosol Conden-sation Nucleous Counter, Aerosol Sci. Technol. 14:48–65.

Wang, X., Sakurai, H., Hama, N., Caldow, R., and Sem G. (2007). Evaluationof TSI 3068B Aerosol Electrometer and 3790 Engine Exhaust CPC. Pre-sented at 26th Annual Conference of AAAR in Reno, NV, Sep. 24–Sep. 28,2007.

Wiedensohler, A., Orsini, D., Covert, D. S., Coffmann, D., Cantrell, W.,Havlicek, M., Brechtel, F. J., Russell, L. M., Weber, R. J., Gras, J., Hudson,J. G., and Litchy, M. (1997). Intercomparison Study of the Size-DependentCounting Efficiency of 26 Condensation Particle Counters. Aerosol Sci. Tech-nol. 27:224–242.


aerosol science and technology calibration of condensation

Documents