Results of the inter-laboratory comparison exercise for TC and EC measurements : PT OC&EC-2025-01.
Date: 2025-10-06
Institutions: Joint Research Centre
Subjects: aerosol, air quality, analytical chemistry, comparative analysis, environmental monitoring, quality standard, report, scientific research, standardisation, testing

ISSN 1831-9424 

Results of the inter-laboratory comparison 
exercise for TC and EC measurements  

PT OC&EC-2025-01 

Cavalli, F., Putaud, J.-P. 

2025 

 EUR 40391 

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JRC142729 

EUR 40391 

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ISBN 978-92-68-29860-2   ISSN 1831-9424   doi:10.2760/3149321 

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© European Union, 2025  

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How to cite this report: Cavalli, F. and Putaud, J.-P., Results of the inter-laboratory comparison exercise for TC and EC 
measurements - PT OC&EC-2025-01, Publications Office of the European Union, Luxembourg, 2025, 
https://data.europa.eu/doi/10.2760/3149321, JRC142729. 

 
 
 
 
 
 
 
 
 
 
 
Contents 

Abstract ...................................................................................................................................................................................................... 2 

1.

Introduction ....................................................................................................................................................................................... 3 

2. Organization ...................................................................................................................................................................................... 4 

2.1.  PT provider ............................................................................................................................................................................... 4 

2.2.  PT SAMPLES: production, distribution, homogeneity and stability ........................................................... 4 

2.3.  Participants ............................................................................................................................................................................. 5 

2.4.  Thermal-optical analysis ................................................................................................................................................. 7 

3. Data evaluation ............................................................................................................................................................................... 8 

3.1.  Laboratory performance.................................................................................................................................................. 8 

3.1.1.  Description ................................................................................................................................................................. 8 

3.1.2.  Results: Laboratory performance for TC ............................................................................................... 10 

3.1.3.  Results: Laboratory performance for EC/TC ........................................................................................ 12 

4. Conclusions ..................................................................................................................................................................................... 14 

References ............................................................................................................................................................................................. 16 

List of abbreviations and definitions ...................................................................................................................................... 17 

List of figures ....................................................................................................................................................................................... 18 

List of tables ......................................................................................................................................................................................... 19 

Annexes ................................................................................................................................................................................................... 20 

Annex A. Numerical results and z-scores ...................................................................................................................... 20 

Annex B. METHOD PERFORMANCE ..................................................................................................................................... 32 

B.1 Method performance for TC .................................................................................................................................. 33 

B.2 Method performance for EC/TC ........................................................................................................................... 35 

Annex C. QA MEASURES ........................................................................................................................................................... 38 

C.1 Calculation of QA variability = Random errors (2RSD) ........................................................................... 38 

C.2 Calculation of QA bias = systematic error (RB%) ...................................................................................... 40 

Annex D. Certificate of accreditation ............................................................................................................................... 44 

1 

Abstract 

The ACTRIS (Aerosol, Clouds and Trace Gases Research Infrastructure) Centre for Aerosol In-Situ 
measurements ECAC (European Centre for Aerosol Calibration) completed, in April 2025, the annual 
inter-laboratory exercise (ILC) for the measurement of Total, Elemental and Organic carbon (TC, EC, 
and OC) in particulate matter collected on filters. This exercise was conducted by the European 
Reference Laboratory for Air Pollution of the EC-Joint Research Centre, ERLAP. 

The overall scope of this ILC was to enhance the comparability and determine the uncertainty of the 
TC, OC and EC atmospheric concentration data produced across Europe. This ILC scheme was based 
on ambient PM2.5 aerosol samples collected on quartz fibre filters at a regional background site in 
Ispra, Italy. 

The primary goal was to assess participants’ performance in determining the TC loading and the 
EC/TC ratio in order to evaluate the accuracy of the instrument response throughout the analytical 
chain and the optical correction for charring, respectively. Thirty-six laboratories, with thirty-seven 
analyzers in total, participated in this exercise, all - except one - running EUSAAR_2 / Transmittance 
as their usual thermal-optical protocol with their usual analytical instrument.  

Participants’ performance was determined in terms of z-scores, a measure of the participants’ bias 
compared to an assigned value, associated with its standard deviation. Ten outliers and sixteen 
stragglers, and eleven outliers and sixteen stragglers were identified for TC mass loadings and 
EC/TC ratios, respectively.  

2 

 
 
 
1.  Introduction  

Total Carbon (TC), including Organic Carbon (OC) and Elemental Carbon (EC) is a relevant constituent 
of the fine fraction of particulate matter (PM), both from the perspective of health risks related to 
inhalation, and indication of air pollution sources (Putaud et al., 2025). For these reasons, 
requirements for measuring EC and OC in PM2.5 at rural and urban background locations have been 
included in the recently published Air Quality Directive 2024/2881.  

The Directive states that measurements should be made in a manner consistent with those of the 
cooperative programme for monitoring and evaluation of the long-range transmission of air 
pollutants in Europe (EMEP). The reference method for the measurement of elemental carbon and 
organic carbon in ambient air is that described in EN 16909:2017 which requires the use of 
thermal-optical analysis, and implementation of the thermal protocol EUSAAR_2 with a 
transmittance-based optical correction for pyrolysis (Cavalli et al., 2010). 

The European Reference Laboratory for Air Pollution (ERLAP) of the European Commission – Joint 
Research Centre (EC – JRC) completed in April 2025 the TC, OC and EC inter-laboratory comparison 
exercise (PT OC&EC-2025-01) as part of the support and services provided by the European Centre 
for Aerosol Calibration, the Thematic Centre for aerosol in-situ measurements of ACTRIS - ERIC 
(Aerosol, Clouds and Trace Gases Research Infrastructure - European Research Infrastructure 
Consortium). Participation in the ILC is compulsory for laboratories submitting OC and EC data to 
EBAS (ebas.nilu.no) under EMEP and ACTRIS, and open to any other, including National Air Quality 
Reference Laboratories participating in quality assurance programmes under Directive EU 
2024/2881.  

Thirty-six laboratories, with thirty-seven analyzers in total, participated in this exercise, all - except 
one laboratory using the QUARTZ thermal protocol - running the EUSAAR_2 protocol as their usual 
thermal-optical protocol with their usual analytical instrument. Amongst those, thirty-four are 
responsible for the aerosol chemical speciation at the EMEP/ACTRIS RI facilities located in their 
countries and /or National Reference Laboratories (namely in Germany, Spain, Slovenia, Poland, 
Norway, Czech Republic, The Netherlands, Croatia, Finland, United Kingdom, Belgium, France, Latvia, 
Italy, Austria, Greece, Cyprus, Sweden, Denmark plus the EC - JRC). 

The University of California Air Quality Research Center and the Sunset Laboratory BV in The 
Netherlands (private sector) also participated. 

3 

 
 
 
2.  Organization 

2.1.  PT provider 

The European Reference Laboratory for Air Pollution of the EC - JRC (via E. Fermi 2749, I-21027 
Ispra (VA)) took the legal responsibility for all activities of the proficiency testing (PT), because of 
the contract JRC N°36775 signed with TROPOS (the leading institution of the ACTRIS Thematic 
Centre for aerosol in-situ measurements). The European Reference Laboratory for Air Pollution of 
the EC – JRC, ERLAP is accredited according to the UNI CEI EN ISO/IEC 17043:2010, since 2024 
(Annex D). 

Personnel: 

- 

- 

Fabrizia Cavalli (PT coordinator and statistician) – fabrizia.cavalli@ec.europa.eu; jrc-
erlap@ec.europa.eu; 

Jean-Philippe Putaud (preparing test samples –from sampling to dispatch–, stability and 
homogeneity determination and testing). 

ERLAP did not make use of any externally provided products and/or services for any of the 
operations involved in the PT. 

2.2.  PT SAMPLES: production, distribution, homogeneity and stability 

The measurands of this ILC scheme were TC, OC and EC (in unit format µg cm-2) in PM2.5 deposited 
on quartz fibre filters, within the mass loading range in line with EN 16909:2017 standard (1.8-45 
µg cm-2 and 0.2-16 μg cm-2 for OC and EC, respectively). 

PRODUCTION: In lack of suitable certified reference material for atmospheric OC and EC, this 
proficiency testing scheme made use of ambient (outdoor) PM2.5 aerosol collected with a high-
volume sampler (namely a Tisch Environmental non-FRM PM2.5 sampler) on binder-free quartz fibre 
filters (Pallflex, Tissuquartz 2500 QAT UP, 20.32 x 25.4 cm) at the regional background site of Ispra, 
Italy. Filter samples were stored in a refrigerator at temperature of 3±2 °C after exposure. Selected 
PT samples’ OC and EC loadings were checked to be within the EN 16909:2017 standard range of 
applicability. 

DISTRIBUTION: Aliquots (according to participants needs to triplicate measurements) were punched 
out from 8 PT samples labelled 1, 2, …, 8). PT sample aliquots were then packaged in closed petri 
dishes and securely labelled.  

To limit the contribution of localized heterogeneities and/or contaminations to the occurrence and 
recurrence of poor results from a single participant, PT sample aliquots were distributed randomly 
to participants.  

PT samples aliquots were dispatched on 17.02.2025 to all participants - except to EC – JRC, the 
“local” participant, - via courier (limiting to a max of 3 days the time needed for transport) at 
ambient temperature. A single use USB temperature-data logger (Mini 1 way) was included to 
qualitatively monitor the temperature experienced by the PT samples from dispatch to analysis. The 
recorded temperature was in all cases below 25°C apart from 4 cases where temperature exceeded 
25°C for a maximum of 65°C h.  

4 

 
 
 
Participants treated PT samples in the same manner as routine samples, including handling and 
storage. 

HOMOGENEITY: the homogeneity of the filter samples was assessed by the PT provider for all 
measurands based on the recommendations listed in ISO 13528:2022, informative Annex B. 

Studies were conducted prior to the circulation of PT samples to evaluate possible impacts of 
inhomogeneity on the measurands. 

Ten (10) subsamples of 4.7 cm diameter were randomly taken from a specific filter sample across 
an area corresponding to the one used to punch the PT samples; three replicates of TC, OC and EC 
measurements were performed on each subsample. The sample homogeneity was assessed as the 
estimate of the between-sample standard deviation, calculated using the analysis of variance, 
according to ISO 13528:2022 (E) Annex B, par. B.3.  

The homogeneity resulted better than 5% for TC, OC and EC, as in the previous rounds of this PT 
scheme. Because 5% represents also the accepted repeatability value for the measurement of TC, 
OC and EC (EN 16909:2017 (E)), a homogeneity of 5% is considered sufficient. If sampling occurs 
under repeatable conditions, it is reasonable to assume that all PT samples have a similar 
homogeneity.  

STABILITY: The stability of the PT samples was assessed by the PT provider based on the 
recommendations listed in ISO 13528:2022, informative Annex B, for all measurands. 

Studies were conducted prior to the circulation of the PT samples to evaluate possible impacts of 
temperature conditions over the duration (including transport and storage) of the PT scheme round 
on the measurands. 

Based on the time and temperature limits for sample transport and storage described in 
EN16909:2017 (par. 7.2), and on the temperature conditions foreseeable during transport and 
storage at participants’ premises (as determined from previous PT scheme rounds), three 
subsamples from two specific samples were exposed to a temperature of 25 °C ± 0.5 for a period 
of ca. 6 weeks (i.e. duration of the proficiency testing scheme round). 

The effect of temperature conditions during transport and storage was assessed by comparing the 
measurement results at t=tf (i.e. 6 weeks later) to the initial value at t=t0 (in refrigerator at T of 3±2 
°C) for each measurand. Sample stability was assessed by determining if the difference of the 
means of the measurements performed at t=t0 and t=tf were statistically different from zero 
according to a t-test at the 99% level of confidence. Both samples resulted stable over the 
prescribed period for all measurands. It is reasonable to assume that also PT samples were 
similarly stable. 

2.3.  Participants  

Thirty-six (36) laboratories, with thirty-seven (37) analyzers in total, participated in this exercise.  

The list of participants is reported in Table 1. For brevity, and because participants agreed on 
disclosure of their own results, the number assigned to each participant/analyzer will be used in the 
remainder of the document. 

5 

 
 
 
 
Table 1. List of participants in the PT-OC&EC-2025-01, and contact persons. 

Code  Participant 

Acronym 

Contact 

1  Landesamt fur Natur, Umwelt und Verbraucherschutz 
2 
Instituto De Salud Carlos III 
3  Slovenian Environment Agency 
4  Chief Inspectorate of Environmental Protection 
5  Norwegian Institute for Air Research 
6  Czech Hydrometeorological Institute 
7  PEC Consulting BV 
8  EC JRC 
9 

Institute for Medical Research and Occupational Health 

10  Finnish Metereological Institute 
11  National Physical Laboratory 
12 

13 

Institut Scientifique de Service Public 
Institut National de l’Environnement Industriel et des 
Risques 
14  AirParif 
15  Latvian Environment, Geology and Meteorology Centre 
16  Umweltbundesamt 
18  Laboratoire d' aérologie 

LANUV 
ISCIII 
SEA 
GIOS 
NILU 
CHMI 
RIVM 
JRC 
IMI 
FMI_f82 
NPL 
ISSeP 

david.czorny@lanuv.nrw.de 
acazana@isciii.es 
judita.burger@gov.si 
i.kaluzinska@gios.gov.pl 
key@nilu.no 
lucie.bohmova@chmi.cz 
pecconsultingbv@gmail.com 
fabrizia.cavalli@ec.europa.eu 
rgodec@imi.hr 
minna.aurela@fmi.fi 
krzysztof.ciupek@npl.co.uk 
p.fays@issep.be 

INERIS 

hugues.biaudet@ineris.fr 

AIRPARIF 
LVGMC 
UBA-L 
LAERO 

chadia.kebbi@airparif.asso.fr 
georgijs.bakradze@lvgmc.lv 
Julian.Ruediger@uba.de 
veronique.pont@aero.obs-mip.fr 

19 

Global Change Research Institute, Czech Academy of 
Sciences 

20  Spanish Research Council 
21  Leibniz Institute for Tropospheric Research 
22  Technische Universität Wien 

CzechGlobe  mbengue.s@czechglobe.cz 

IDAEA-CSIC 
TROPOS 
TU Wien 

angeliki.karanasiou@idaea.csic.es 
poulain@tropos.de 
anneliese.kasper-giebl@tuwien.ac.at 

23 

Environmental Chemical Processes Laboratory_ Univer-
sity of Crete 

ECPL_UOC 

abougiat@noa.gr 

24  National Centre for Scientific Research Demokritos 
25  The Cyprus Institute 

NCSR D 
CyI 

ldiapouli@ipta.demokritos.gr 
j.sciare@cyi.ac.cy 

26 

27 

28 

29 

Institute of Chemical Process Fundamentals of the 
Czech Academy of Sciences 
Institute of Environmental Engineering Polish Academy 
of Sciences 
Laboratoire des Sciences du Climat et de l'Envi-
ronnement 
University of Vienna, Faculty of Physics, Aerosol Physics 
and Environmental Physics Group 

30  Sunset Laboratory B.V. 
31  Lund University 
32  UC Davis Air Quality Research Center 

33 

Department of Environmental Science, Stockholm Uni-
versity 

ICPF 

vodicka@icpf.cas.cz 

IPIS PAN 

barbara.mathews@ipispan.edu.pl 

LSCE 

nicolas.bonnaire@lsce.ipsl.fr 

UNIVIE 

agnieszka.kupc@univie.ac.at 

SLBV 
LU_Physics 
UCD AQRC  mvlangston@ucdavis.edu 

luis@sunlab.com 
adam.kristensson@nuclear.lu.se 

SU-ACES 

birgitta.noone@aces.su.se 

34  Foundation for Research and Technology, Hellas 

FORTH 

spyros@chemeng.upatras.gr 

35 

Institute of Natural Products and Agrobiology - Spanish 
National Research Council 
Istituto Nazionale di Fisica Nucleare - Sezione di Firenze 

36 
37  National Environmental Research Institute 
38  Finnish Metereological Institute 

IPNA-CSIC 

misabel.garcia@csic.es 

INFN 
ATMI 
FMI_f83 

chiari@fi.infn.it 
cno@dmu.dk 
minna.aurela@fmi.fi 

Source: JRC 2025. 

6 

 
 
 
2.4.  Thermal-optical analysis 

The thermal protocol EUSAAR_2 (Cavalli et al., 2010) with a transmittance-based optical correction 
for pyrolysis is the European standard thermal protocol for the measurements of TC and EC in PM2.5 
samples deposited on filters (EN16909:2017). In this ILC round, all participants applied it, except for 
participant 2 applying the protocol QUARTZ. 

All participants operated a Sunset carbon analyser, except participant 31 operating a DRI 
instrument. Participants 10, 19, 24, 26 and 38 used the semi-continuous Sunset carbon analyser 
model. 

7 

 
 
 
3.  Data evaluation  

Participants reported (through the web-based platform https://erlap-
intercomparison.jrc.ec.europa.eu) by the deadline of 20th April 2025: i) TC, OC and EC concentrations, 
in μg C cm-2 units with three significant digits, from three replicates of the eight PT samples 
(corresponding uncertainties were not required) and ii) the record of temperature conditions over 
the duration of the PT scheme round. 

To evaluate the accuracy of the instrument response throughout the analytical chain and the optical 
correction for charring, we focused on TC loadings (in μg cm-2) and EC/TC ratios, respectively. Indeed, 
TC represents the most robust (and protocol-independent) output of the thermal-optical analysis, 
while the EC/TC ratio is free from biases in the total carbon determination calibration, and reflects, 
instead, possible biases or differences among participants in the OC/EC split determination.  

On average, reported TC loadings ranged from 3.73 to 14.8 μg cm-2, corresponding to atmospheric 
concentrations ranging from ca. 0.78 to 3.1 μg m-3 collected for 24h at a face velocity of 54 cm s-1. 
EC/TC ranged, on average, from 0.062 to 0.206.  

All submitted results for TC, EC, OC (in μg cm-2) and EC/TC ratios are presented in Tables A1-A4 in 
Annex A. 

3.1.  Laboratory performance 

3.1.1.  Description 

The assessment of the laboratory performance aims at describing the laboratory bias compared to 
an assigned value associated with its standard deviation. As ambient PM collected on filters was 
used as PT samples (in absence of suitable certified reference material for atmospheric TC, OC and 
EC deposited on filters), the true values for TC loadings and EC/TC ratios were not known. For each 
PT sample, the TC loading and EC/TC ratio assigned values and their standard deviations were 
calculated as follows: 

- Determining the assigned value: among the available methods for determining the assigned value, 
the approach of the consensus value from participants to a round of a PT scheme was chosen. With 
this approach, the assigned value X for each PT sample is the robust average calculated, with a 
recursive algorithm, from the results reported by all participants (ISO 13528:2022)). The results 
coming from different measurement methods (i.e. participants 23) were also included, because the 
number was not sufficient in order to produce a statistically meaningful evaluation if treated 
separately. 

- Determining the standard deviation for PT scheme: among the available methods for determining 
the standard deviation for proficiency assessment (σ*), the approach of calculating σ* from data 
obtained in a round of a PT scheme was chosen. With this approach, σ* is the robust standard 
deviation calculated, with a recursive algorithm, from the results reported by all participants (See 
ISO 13528:2022, Annex C). 

For the current PT scheme, this approach is considered producing reliable assigned values and 
associated robust standard deviations because of the participation of a large number of 
experienced and expert laboratories, and due to the use of a (almost) single thermal-protocol. In 
addition, by experience from previous rounds, the robust standard deviations from all data in a 

8 

 
 
 
round of PT scheme are in the range of the overall method precision (repeatability and 
reproducibility). 

In general, this approach might become statistically ineffective (ISO 13528:2022), for example, if 
the number of participants is lower than twelve (12). Although this condition does not apply to the 
current PT scheme round, the robust mean and its standard deviation were also calculated applying 
the Q/Hampel method to verify their reliability (https://quodata.de/content/qhampel-webtool, as in 
ISO 13528:2022 (E)).  

The values obtained did not significantly differ (less than 1%) from those retrieved as the 
consensus value from participant results as listed in Tables 2 and 3, which were then used for 
further elaboration. 

Each participant’s performance was determined in terms of z-scores, a measure of the deviation 
from the assigned value taking into account its standard deviation. 

For each laboratory i and PT sample j, a z-score zij was calculated as:  

Equation 1. z-score 

where xij is the result from the participant i for PT sample j; Xj is the assigned value for PT sample j; 
and σj* is the standard deviation for proficiency assessment for PT sample j. 

When a participant reports an entry that produces a bias greater than +3 z or less than -3 z (i.e. 
deviating from the assigned value for more than 3 standard deviations), this entry is considered to 
give an “action signal”. Likewise, a laboratory bias above +2 z or below -2 z (i.e. deviating from the 
assigned value for more than 2 but less than 3 standard deviations) is considered to give a 
“warning signal”. A laboratory bias between -2 z and +2 z indicates a satisfactory laboratory 
performance with respect to the standard deviation for proficiency assessment. 

9 

zij = (xij-Xj)/ σj*  
 
 
 
 
 
3.1.2.  Results: Laboratory performance for TC 

The assigned values, X [and their standard uncertainty, u(X)] and the related standard deviations for 
proficiency assessment σ* calculated from the entire database for each PT sample, are reported in 
Table 2.  

Table 2. Assigned values, X [and their standard uncertainty, u(X)] and standard deviations for proficiency 
assessment σ* from data obtained in a round of a proficiency testing scheme for TC. 

assigned value, 
X 
[standard un-
certainty, u(X)] 
standard devia-
tion, σ* 
1σ* 
2σ* 
3σ* 

Source: JRC 2025. 

1 

2 

3 

4 

5 

6 

7 

8 

μg/cm2 

9.39 
[0.121] 

11.5 
[0.120] 

3.73 
[0.069] 

7.61 
[0.093] 

6.29 
[0.086] 

7.06 
[0.078] 

14.9 
[0.148] 

8.09 
[0.074] 

μg/cm2  0.589 

0.586 

0.334 

0.455 

0.421 

0.378 

0.720 

0.362 

6% 
13% 
19% 

5% 
10% 
15% 

9% 
18% 
27% 

6% 
12% 
18% 

7% 
13% 
20% 

5% 
11% 
16% 

5% 
10% 
15% 

4% 
9% 
13% 

An indication of the performance of individual participants (i.e. z-scores) for each PT sample is 
reported in Table A5 of Annex A and shown in Figure 1.  

Ten (10) outliers are identified: 19/2, 19/3, 34/3, 33/4, 19/5, 18/6, 19/6, 18/7, 18/8, and 19/8 
(participant/sample); in addition, sixteen (16) stragglers are identified: 18/1, 19/1, 36/1, 8/2, 18/2, 
13/3, 18/3, 27/3, 36/3, 2/4, 18/4, 18/5, 36/5, 8/7, 8/8, 31/8 (participant/ sample). 

For each PT sample, twenty-four (24) to twenty-seven (27) out of thirty-seven (37) entries show 
deviations from the assigned values within +/- 1 σ* (i.e. within 1 z-score) as listed in Table 2. Eighty-
six percent (86%) of all entries are within 10% of the assigned value.  

Several participants show the systematic tendency (i.e. for all PT samples and more than ± 5%, on 
average) of overestimating - i.e. participants 2, 8, 24, 26, and 31- or underestimating -  i.e. 
participants 10, 18, 20, 37 and 38- the assigned TC values (Table A7 in Annex A). 

A contribution of filter heterogeneities to poor laboratory performances cannot be completely 
excluded. However, participants showing large (|z-scores|> 2) and/or systematic biases shall 
carefully examine their procedures and identify appropriate corrective actions that are likely to 
prevent the recurrence of significant deviations in the future. A more accurate determination of the 
instrument’s calibration constant (e.g. implementing CO2 calibration, where possible) would probably 
reduce the observed variability in TC determination. 

10 

 
 
 
  
  
 
 
 
Figure 1. z-scores for TC calculated using σ* from data obtained in a round of a proficiency testing scheme. 
The z-score axis is set to ±5. 

5

4

3

2

1

0

-1

-2

-3

-4

-5

s
e
r
o
c
s
-
z

123456789

0
1

1
1

2
1

3
1

4
1

5
1

6
1

8
1

9
1

0
2

1
2

2
2

3
2

4
2

5
2

6
2

7
2

8
2

9
2

0
3

1
3

2
3

3
3

4
3

5
3

6
3

7
3

8
3

1

2

3

4

5

6

7

8

laboratory

Source: JRC 2025. 

11 

 
 
 
 
 
 
3.1.3.  Results: Laboratory performance for EC/TC 

The assigned values, X, [and their standard uncertainty, u(X)] and the related standard deviations for 
proficiency assessment, σ*, are reported in Table 3.  

Table 3. Assigned values, X [and their standard uncertainty, u(X)] and standard deviations for proficiency 
assessment σ* from data obtained in a round of a proficiency testing scheme for EC/TC. 

1 

2 

3 

4 

5 

6 

7 

8 

assigned 
value X, 
[standard 
uncertainty, 
u(X)] 

standard de-
viation, σ* 
σ* 
2σ* 
3σ* 

Source: JRC 2025. 

ratio 

0.155 
[0.003] 

0.179 
[0.004] 

0.062 
[0.004] 

0.169 
[0.003] 

0.142 
[0.005] 

0.151 
[0.004] 

0.171 
[0.004] 

0.206 
[0.004] 

ratio 

0.016 

0.016 

0.019 

0.016 

0.022 

0.021 

0.018 

0.019 

10% 
21% 
31% 

9% 
18% 
27% 

31% 
61% 
91% 

10% 
19% 
29% 

16% 
32% 
47% 

14% 
27% 
41% 

10% 
21% 
31% 

9% 
18% 
28% 

An indication of the performance of individual participants (i.e. z-scores) for each PT sample is 
reported in Table A6 of Annex A and shown in Figure 2. 

Eleven (11) outliers – 2/1, 26/2, 9/3, 16/3, 26/3, 2/4, 26/4, 16/5, 26/5, 26/6, 2/8 (participant/ 
sample)- and sixteen (16) stragglers – 26/1, 34/1, 36/1, 2/2, 32/2, 34/2, 18/3, 34/3, 36/3, 2/5, 2/6, 
16/6, 2/7, 26/7, 19/8, 26/8 (participant /sample)– were identified.  

For each PT sample, twenty-two (22) to twenty-seven (27) out of thirty-seven (37) entries show 
deviations from the assigned values within +/- 1 σ* (i.e. within 1 z-score) as listed in Table 3. Sixty-
one percent (61%) of all entries were within 10% of the assigned value and eighty-four percent 
(84%) were within 20% of the assigned EC/TC ratio value. 

Several participants show a systematic tendency (i.e. for all PT samples and more than ± 5%, on 
average) of overestimating - i.e. participants 5, 9, 14, 18, 21, 23, 26, 32, and 38 - or 
underestimating - i.e. participants 2, 6, 12, 15, 22, 29, 31, 33, 34, and 36- the assigned EC/TC ratio. 
Participant 2, applying the QUARTZ thermal protocol, underestimated EC/TC ratio by 33% ± 6, in line 
with previous exercises. 

A contribution of filter heterogeneities to poor laboratory performances cannot be completely 
excluded. However, participants showing large (|z-scores|> 2) and/or systematic biases shall 
carefully examine their procedures and identify appropriate corrective actions that are likely to 
prevent the recurrence of such results in the future. A more solid and stable in time instrument set-
up in terms of i) laser stability; ii) FID response in He and He/O2 phases; iii) oven temperature 
calibration iv) selection of the time period for determining the initial laser signal and v) transit time 
would improve such performances and reduce the observed biases in EC/TC ratio determination. 

12 

 
 
 
  
  
 
 
 
Figure 2. z-scores for EC/TC ratio calculated using σ* from data obtained in a round of a proficiency testing 
scheme. 

5

4

3

2

1

0

-1

-2

-3

-4

-5

s
e
r
o
c
s
-
z

123456789

0
1

1
1

2
1

3
1

4
1

5
1

6
1

8
1

9
1

0
2

1
2

2
2

3
2

4
2

5
2

6
2

7
2

8
2

9
2

0
3

1
3

2
3

3
3

4
3

5
3

6
3

7
3

8
3

1

2

3

4

5

6

7

8

laboratory

Source: JRC 2025. 

13 

 
 
 
 
 
 
4.  Conclusions  

The inter-laboratory exercise PT OC&EC-2025-01 for the measurement of total carbon, elemental 
carbon and organic carbon in PM2.5 deposited on filters involved thirty-six (36) laboratories, with 
thirty-seven (37) analyzers in total, all applying the thermal-optical method, and the EUSAAR_2 
thermal protocol, except one laboratory using the QUARTZ thermal protocol.  

In absence of a suitable certified reference material for atmospheric OC and EC, the PT samples 
used to assess laboratories’ performance consisted of atmospheric PM2.5 deposited on filters.  

The assigned values for TC loadings and EC/TC ratios in the PT samples and the corresponding 
standard deviations were calculated as robust averages and standard deviations from all data 
obtained in this round of the PT scheme. 

Laboratory performances were assessed for both TC loadings and EC/TC ratios based on z-scores. 

For TC filter loadings, ten outliers and sixteen stragglers - mainly from two participants- were 
identified; 86% of all entries were within 10% of the assigned TC concentration value. Several 
participants showed the systematic tendency of overestimating (five participants) or 
underestimating (five participants) the assigned TC concentrations.  

A contribution of filter heterogeneities to poor laboratory performances cannot be completely 
excluded. However, participants showing large (|z-scores|> 2) and/or systematic biases shall 
carefully examine their procedures and identify appropriate corrective actions that are likely to 
prevent the recurrence of such results in the future. A more accurate determination of the 
instrument’s calibration constant (e.g. implementing CO2 calibration where possible) would correct 
this tendency. 

Regarding EC/TC ratios, eleven outliers and sixteen stragglers were identified. 61% of all entries 
were within 10% of the assigned value and 84% were within 20% of the assigned EC/TC ratio 
value. Several participants showed the systematic tendency of overestimating (nine participants) or 
underestimating (ten participants) the assigned EC/TC ratio. Participant 2, applying the QUARTZ 
thermal protocol, underestimated EC/TC ratio by 33% ± 6, on average. 

A contribution of filter heterogeneities to poor laboratory performances cannot be completely 
excluded. However, participants showing large (|z-scores|> 2) and/or systematic biases shall 
carefully examine their procedures and identify appropriate corrective actions that are likely to 
prevent the recurrence of such results in the future. A more solid and stable in time instrument set-
up in terms of i) laser stability; ii) FID response in He and He/O2 phases; iii) oven temperature 
calibration iv) determination of the initial laser signal and v) transit time would improve such 
performances and reduce the observed variability in EC/TC ratio determination. 

For informative purposes only, results from this inter-laboratory comparison round were also used 
to determine the repeatability and reproducibility of the standard measurement method described 
in EN16909:2017, according to the ISO 5725-2:2019 (ANNEX B). The measurement method 
repeatability and reproducibility standard deviations for TC ranged across samples 1 to 8 from 2% 
to 7%, and from 6% to 13% (as one relative standard deviation), respectively. For the EC/TC ratio, 
repeatability and reproducibility standard deviations ranged from 3% to 14% and from 9% to 40%, 
respectively. Combining the repeatability (sr) and reproducibility (sR) relative standard deviations for 
the EUSAAR_2 protocol obtained during the previous ILC exercises and the present one, we observed 
that the method precision (both sr and sR) for TC determination becomes exponentially poorer 

14 

 
 
 
toward lower TC contents, i.e. <10 µgC / cm². For EC/TC determination, the method precision (sR and 
less evident for sr) can become poorer toward lower EC/TC ratios and exceptionally poor only for 
EC/TC ratios <0.07. 

In addition, based on the results from the present inter-laboratory comparison and for the purpose 
of documenting the TC, OC and EC mass concentrations reported to the EBAS database, quality 
control measures, i.e. percentage bias and variability, were calculated for TC, OC and EC 
determination for each participant (ANNEX C). 

15 

 
 
 
References  

EU Directive 2024/2881 on ambient air and cleaner air for Europe. 

ISO/IEC 17043. Conformity assessment - General requirements for the competence of proficiency 
testing providers. ISO, Geneva, 2010 and 2023. 

EN 16909. Ambient air – Measurement of elemental carbon (EC) and organic carbon (OC) collected 
on filters. CEN, Brussels, 2017. 

Cavalli F., Putaud J., Viana M., Yttri K., Genberg J., Toward a Standardised Thermal-Optical Protocol 
for Measuring Atmospheric Organic and Elemental Carbon: The EUSAAR Protocol. Atmospheric 
Measurement Techniques, Vol. 3, No 1, 2010, pp. 79-89. 

ISO GUIDE 13528. Statistical methods for use in proficiency testing by inter-laboratory 
comparisons. ISO, Geneva, 2022. 

ISOGUIDE  5725-2. Accuracy (trueness and precision) of measurement methods and results - Part 
2: Basic method for the determination of repeatability and reproducibility of a standard 
measurement method. ISO, Geneva, 2019. 

Putaud J. P., Cavalli F. et al., A worldwide aerosol phenomenology: Elemental and organic carbon in 
PM2.5 and PM10. Atmospheric Environment, Vol. 358, 2025, p. 121338, 
https://doi.org/10.1016/j.atmosenv.2025.121338. 

16 

 
 
 
 
 
List of abbreviations and definitions 

Abbreviations 

Definitions 

ACTRIS 

Aerosol, Cloud and Trace Gases Research InfraStructure 

TC 

EC 

OC 

EMEP 

ERLAP 

PT 

PM 

ILC 

Total Carbon 

Elemental Carbon 

Organic Carbon 

Cooperative programme for monitoring and evaluation of 
the long-range transmission of air pollutants in Europe 

European Reference Laboratory for Air Pollution 

Proficiency Testing 

Particulate Matter 

Inter-Laboratory Comparison 

17 

 
 
 
 
List of figures  

Figure 1. z-scores for TC calculated using σ* from data obtained in a round of a proficiency testing 
scheme. ..................................................................................................................................................................................................... 11 

Figure 2. z-scores for EC/TC ratio calculated using σ* from data obtained in a round of a proficiency 
testing scheme. The z-score axis is set to ±5. ................................................................................................................... 13 

18 

 
 
 
 
 
List of tables  

Table 1. List of participants in the PT-OC&EC-2025-01, and contact persons. ............................................... 6 

Table 2. Assigned values and standard deviations for proficiency assessment σ* from data 
obtained in a round of a proficiency testing scheme for TC. ..................................................................................... 10 

Table 3. Assigned values and standard deviations for proficiency assessment σ* from data 
obtained in a round of a proficiency testing scheme for EC/TC. .............................................................................. 12 

19 

 
 
 
 
Annexes  

Annex A. Numerical results and z-scores  

(“-“ corresponds to a “no entry”) 

Table A1. Total carbon (µg/cm2) reported by each participant. 

1 

2 

3 

4 

5 

6 

7 

8 

Laboratory 
1 
1 

1 
2 
2 
2 
3 
3 
3 
4 
4 
4 
5 
5 
5 
6 
6 
6 
7 
7 
7 
8 
8 
8 
9 
9 
9 
10 
10 
10 
11 
11 
11 
12 
12 
12 
13 
13 
13 
14 
14 
14 
15 
15 
15 
16 
16 
16 

9.15 
9.30 

9.42 
9.55 
10.70 
9.91 
9.09 
8.98 
9.33 
9.27 
8.52 
9.18 
9.62 
9.42 
9.40 
9.18 
9.37 
9.34 
8.97 
8.91 
8.94 
10.86 
10.36 
10.40 
9.18 
9.17 
9.30 
8.75 
9.04 
8.84 
9.54 
9.49 
9.19 
9.66 
9.21 
9.21 
9.06 
9.15 
9.12 
9.40 
9.00 
9.11 
9.16 
9.02 
9.10 
8.61 
8.64 
8.47 

11.7 
11.7 

11.6 
12.4 
11.9 
11.7 
11.3 
11.5 
11.7 
10.4 
11.1 
11.5 
11.9 
12.2 
12.0 
12.3 
11.9 
11.8 
11.7 
11.5 
11.2 
12.9 
12.7 
12.9 
11.1 
11.6 
11.4 
10.6 
10.6 
10.5 
11.7 
11.4 
11.7 
11.6 
11.6 
11.4 
12.4 
11.5 
11.3 
11.4 
11.3 
11.7 
11.1 
11.2 
11.3 
10.6 
10.6 
 - 

3.49 
3.66 

3.57 
3.96 
4.35 
3.99 
3.69 
3.75 
3.75 
3.22 
3.22 
3.25 
3.85 
3.81 
3.85 
4.10 
3.62 
3.73 
3.81 
3.71 
3.71 
4.02 
4.00 
4.18 
3.55 
3.55 
3.49 
3.22 
3.61 
3.24 
3.55 
3.60 
4.00 
3.72 
3.64 
3.66 
6.68 
3.47 
3.74 
3.63 
3.70 
3.62 
3.80 
3.65 
3.88 
3.29 
3.17 
3.18 

6.39 
6.24 

6.51 
8.49 
6.20 
6.40 
6.07 
6.06 
6.61 
6.08 
6.92 
6.69 
6.33 
6.41 
6.39 
6.12 
6.72 
6.74 
6.28 
6.16 
6.18 
6.86 
6.84 
6.89 
6.14 
5.94 
6.18 
5.57 
5.71 
5.54 
6.11 
6.06 
6.38 
6.31 
6.19 
6.53 
6.96 
6.73 
6.42 
6.31 
6.09 
6.22 
6.12 
6.41 
6.24 
5.76 
5.72 
5.93 

7.47 
7.51 

7.77 
7.72 
9.78 
8.16 
7.39 
7.19 
7.67 
7.02 
8.13 
7.02 
7.94 
7.76 
7.75 
7.61 
7.58 
7.81 
7.53 
7.28 
7.45 
8.37 
8.32 
8.20 
7.20 
7.46 
7.25 
6.97 
6.99 
7.17 
7.66 
7.91 
7.85 
7.64 
7.39 
7.58 
7.42 
7.47 
7.44 
7.53 
7.59 
7.51 
7.52 
7.64 
7.59 
6.92 
6.97 
7.05 

20 

7.13 
7.04 

7.35 
7.17 
7.08 
7.49 
6.94 
6.91 
6.77 
6.69 
7.28 
7.11 
7.14 
7.23 
7.37 
7.10 
7.13 
7.13 
7.04 
7.08 
6.86 
7.66 
7.91 
7.82 
7.10 
7.05 
6.85 
6.33 
6.99 
6.44 
6.95 
7.14 
7.17 
7.26 
7.44 
7.10 
6.94 
6.92 
6.98 
7.00 
7.29 
7.12 
6.79 
6.73 
6.85 
6.78 
6.60 
6.52 

14.8 
14.9 

15.7 
15.4 
15.9 
15.5 
14.8 
14.4 
14.6 
14.5 
15.6 
16.0 
15.3 
15.6 
16.0 
15.2 
15.2 
14.8 
14.6 
14.7 
14.0 
16.5 
17.0 
16.9 
15.2 
15.0 
14.8 
13.6 
13.8 
13.4 
13.8 
14.4 
13.6 
16.1 
15.3 
15.6 
14.8 
14.7 
14.8 
15.2 
15.4 
15.1 
15.1 
14.8 
14.7 
14.0 
14.5 
-  

7.90 
7.96 

8.25 
8.55 
8.45 
8.18 
8.16 
8.57 
7.87 
7.76 
7.47 
7.63 
8.38 
8.47 
8.42 
7.86 
8.00 
8.03 
7.78 
7.86 
7.78 
8.89 
9.11 
9.24 
7.73 
7.73 
8.01 
7.67 
7.52 
7.33 
8.50 
8.00 
8.23 
9.24 
8.72 
8.45 
7.82 
8.20 
7.75 
8.10 
8.07 
8.38 
8.05 
8.15 
8.20 
7.59 
8.05 
7.74 

 
 
 
 
 
 
 
 
 
 
 
 
18 
18 
18 
19 
19 
19 
20 
20 
20 
21 
21 
21 
22 
22 
22 
23 
23 
23 
24 
24 
24 
25 
25 
25 
26 
26 
26 
27 
27 
27 
28 
28 
28 
29 
29 
29 
30 
30 
30 
31 
31 
31 
32 
32 
32 
33 
33 
33 
34 
34 
34 
35 
35 
35 
36 
36 
36 
37 
37 
37 
38 

8.15 
7.85 
7.68 
9.71 
11.18 
11.07 
8.77 
8.86 
8.91 
9.25 
8.96 
9.04 
9.35 
9.24 
9.21 
9.72 
9.27 
9.30 
10.22 
10.23 
11.20 
10.03 
9.76 
9.70 
9.79 
10.67 
10.25 
9.61 
10.02 
9.64 
9.03 
9.19 
9.50 
9.72 
9.73 
9.99 
9.73 
9.82 
9.74 
10.03 
10.60 
10.58 
9.34 
9.22 
9.30 
9.57 
9.15 
9.41 
9.59 
8.53 
8.45 
9.07 
9.12 
9.33 
12.06 
11.09 
10.19 
8.80 
8.57 
8.54 
8.76 

9.6 
9.8 
9.9 
12.4 
13.9 
14.8 
10.8 
10.8 
11.0 
11.1 
11.1 
11.9 
11.3 
11.3 
11.4 
11.3 
11.7 
11.0 
12.3 
12.1 
12.3 
12.1 
11.7 
11.8 
12.2 
11.8 
12.3 
11.1 
11.7 
11.1 
11.6 
11.7 
11.6 
12.0 
11.7 
11.6 
11.4 
11.7 
11.5 
12.6 
12.1 
12.4 
11.3 
11.2 
11.4 
11.6 
11.1 
11.0 
11.9 
10.6 
13.6 
10.9 
11.1 
11.1 
13.0 
11.6 
12.7 
10.5 
10.3 
10.3 
11.1 

3.09 
2.92 
2.83 
5.89 
4.91 
5.37 
3.45 
3.44 
3.43 
3.35 
3.52 
3.38 
3.93 
3.68 
3.74 
3.75 
3.55 
3.54 
3.80 
3.83 
4.03 
3.58 
3.59 
3.78 
3.84 
3.91 
3.54 
4.70 
4.13 
4.42 
3.63 
3.69 
3.58 
4.14 
3.61 
3.72 
3.93 
4.08 
3.78 
3.53 
3.94 
3.71 
3.98 
3.48 
3.46 
3.90 
3.62 
4.28 
3.43 
6.41 
5.32 
3.76 
3.73 
3.68 
5.79 
4.05 
3.68 
3.34 
3.29 
3.33 
3.70 

7.29 
6.35 
6.00 
7.84 
8.35 
7.93 
7.08 
7.22 
7.13 
7.58 
7.69 
7.28 
7.44 
7.86 
7.62 
7.28 
7.55 
7.35 
8.71 
8.01 
7.91 
7.82 
7.68 
7.57 
7.53 
8.17 
8.06 
7.80 
7.80 
7.52 
7.46 
7.74 
7.64 
8.18 
7.74 
8.07 
8.08 
7.98 
8.37 
8.61 
8.10 
8.00 
7.51 
7.50 
7.48 
7.56 
7.20 
13.23 
7.65 
6.65 
6.52 
7.57 
7.95 
7.55 
8.54 
7.95 
6.75 
7.01 
6.84 
6.81 
7.26 

21 

5.08 
5.06 
5.06 
8.54 
8.33 
6.68 
5.88 
5.98 
5.94 
5.92 
6.09 
5.96 
6.37 
6.20 
6.04 
6.51 
6.56 
6.11 
6.29 
6.29 
6.35 
6.44 
6.38 
6.22 
7.06 
6.41 
6.67 
6.70 
6.16 
6.59 
6.65 
6.21 
6.34 
7.15 
6.63 
6.42 
7.18 
6.59 
6.31 
6.58 
7.03 
7.16 
5.92 
6.14 
6.13 
6.05 
6.07 
5.96 
6.50 
5.82 
6.68 
6.35 
6.22 
6.19 
6.90 
5.72 
2.59 
5.90 
5.67 
5.73 
5.96 

5.90 
5.69 
5.61 
8.67 
9.68 
7.57 
6.66 
6.49 
6.58 
6.59 
6.65 
6.85 
7.01 
6.86 
7.00 
6.75 
6.88 
7.09 
8.03 
7.44 
7.41 
7.03 
7.17 
7.24 
7.83 
7.40 
7.78 
7.19 
7.26 
7.41 
6.93 
6.82 
6.92 
7.26 
7.45 
7.54 
7.72 
7.49 
7.38 
7.73 
7.34 
7.53 
6.93 
6.93 
6.72 
6.83 
6.81 
7.03 
6.95 
7.15 
7.34 
7.02 
7.04 
7.00 
7.91 
7.12 
6.86 
6.35 
6.46 
6.23 
6.65 

12.3 
12.7 
12.6 
14.5 
14.5 
15.1 
14.2 
14.2 
14.3 
14.4 
14.1 
14.1 
14.7 
15.0 
14.9 
14.8 
14.7 
14.0 
15.5 
15.9 
15.7 
14.9 
14.8 
14.5 
15.3 
15.6 
15.4 
14.4 
14.8 
14.6 
15.0 
15.2 
15.0 
15.4 
15.7 
15.6 
16.0 
15.2 
15.7 
16.1 
15.4 
16.1 
14.6 
14.1 
14.6 
15.1 
15.4 
14.5 
16.1 
15.8 
14.0 
14.7 
14.8 
14.7 
16.0 
14.8 
15.3 
13.6 
14.0 
13.6 
13.8 

7.21 
7.08 
6.50 
8.19 
10.18 
9.39 
7.98 
7.81 
8.09 
7.62 
7.55 
7.67 
8.37 
8.09 
7.79 
8.24 
8.31 
8.48 
8.33 
8.04 
7.87 
8.09 
7.88 
8.21 
8.42 
8.71 
8.68 
8.32 
8.22 
8.27 
7.82 
8.53 
8.08 
8.53 
8.20 
8.39 
8.10 
8.05 
8.08 
9.48 
8.86 
8.75 
8.02 
7.78 
7.88 
7.88 
8.11 
8.20 
8.71 
7.46 
7.50 
8.35 
8.26 
8.14 
8.18 
8.30 
7.58 
8.21 
7.50 
7.72 
7.39 

 
 
 
38 
38 

8.72 
9.04 

11.0 
10.6 

3.37 
3.00 

7.12 
7.23 

5.03 
5.72 

6.58 
6.55 

13.7 
13.1 

7.36 
7.37 

Source: JRC 2025. 

Table A2. Elemental carbon / total carbon (ratio) calculated from the results reported by each participant. 

1 

2 

3 

4 

5 

6 

7 

8 

Laboratory 
1 
1 

1 
2 
2 
2 
3 
3 
3 
4 
4 
4 
5 
5 
5 
6 
6 
6 
7 
7 
7 
8 
8 
8 
9 
9 
9 
10 
10 
10 
11 
11 
11 
12 
12 
12 
13 
13 
13 
14 
14 
14 
15 
15 
15 
16 
16 
16 
18 
18 
18 

0.140 
0.149 

0.153 
0.096 
0.092 
0.102 
0.154 
0.178 
0.143 
0.148 
0.156 
0.162 
0.175 
0.175 
0.181 
0.154 
0.149 
0.147 
0.164 
0.162 
0.164 
0.167 
0.169 
0.161 
0.172 
0.168 
0.173 
0.174 
0.169 
0.151 
0.152 
0.148 
0.153 
0.148 
0.158 
0.151 
0.152 
0.146 
0.148 
0.163 
0.166 
0.206 
0.142 
0.137 
0.142 
0.182 
0.127 
0.186 
0.163 
0.167 
0.160 

0.181 
0.179 

0.178 
0.176 
0.120 
0.123 
0.188 
0.169 
0.168 
0.207 
0.187 
0.198 
0.207 
0.210 
0.214 
0.174 
0.172 
0.177 
0.189 
0.197 
0.201 
0.179 
0.183 
0.173 
0.204 
0.201 
0.194 
0.190 
0.191 
0.185 
0.179 
0.189 
0.179 
0.168 
0.171 
0.169 
0.169 
0.170 
0.171 
0.198 
0.182 
0.191 
0.174 
0.165 
0.169 
0.204 
0.202 
 - 
0.177 
0.192 
0.185 

0.057 
0.061 

0.058 
0.064 
0.033 
0.041 
0.072 
0.045 
0.048 
0.075 
0.065 
0.071 
0.086 
0.087 
0.065 
0.037 
0.047 
0.046 
0.044 
0.049 
0.048 
0.065 
0.060 
0.055 
0.121 
0.126 
0.119 
0.087 
0.081 
0.072 
0.060 
0.058 
0.063 
0.041 
0.034 
0.042 
0.029 
0.046 
0.047 
0.066 
0.070 
0.065 
0.061 
0.065 
0.060 
0.126 
0.129 
0.130 
0.095 
0.100 
0.111 

0.129 
0.132 

0.127 
0.122 
0.073 
0.071 
0.142 
0.151 
0.128 
0.132 
0.124 
0.148 
0.166 
0.162 
0.167 
0.133 
0.117 
0.123 
0.146 
0.151 
0.154 
0.155 
0.154 
0.160 
0.162 
0.178 
0.173 
0.173 
0.180 
0.170 
0.133 
0.132 
0.134 
0.137 
0.137 
0.131 
0.123 
0.116 
0.129 
0.152 
0.150 
0.160 
0.132 
0.121 
0.124 
0.231 
0.222 
0.224 
0.160 
0.174 
0.165 

0.197 
0.173 

0.167 
0.112 
0.094 
0.111 
0.171 
0.159 
0.158 
0.170 
0.173 
0.161 
0.185 
0.191 
0.183 
0.160 
0.158 
0.145 
0.179 
0.183 
0.179 
0.179 
0.179 
0.180 
0.197 
0.192 
0.197 
0.182 
0.183 
0.169 
0.157 
0.177 
0.168 
0.168 
0.164 
0.155 
0.164 
0.166 
0.164 
0.186 
0.186 
0.185 
0.161 
0.156 
0.174 
0.186 
0.208 
0.155 
0.156 
0.177 
0.184 

22 

0.143 
0.133 

0.139 
0.097 
0.102 
0.089 
0.140 
0.143 
0.144 
0.152 
0.140 
0.174 
0.168 
0.178 
0.176 
0.134 
0.140 
0.139 
0.164 
0.172 
0.170 
0.162 
0.155 
0.157 
0.182 
0.180 
0.188 
0.165 
0.139 
0.164 
0.146 
0.158 
0.139 
0.152 
0.142 
0.150 
0.142 
0.145 
0.142 
0.165 
0.162 
0.161 
0.143 
0.142 
0.145 
0.196 
0.199 
0.201 
0.153 
0.170 
0.164 

0.178 
0.183 

0.180 
0.115 
0.126 
0.121 
0.182 
0.184 
0.182 
0.169 
0.174 
0.166 
0.201 
0.199 
0.204 
0.162 
0.174 
0.170 
0.190 
0.193 
0.191 
0.163 
0.165 
0.175 
0.188 
0.187 
0.196 
0.162 
0.173 
0.156 
0.191 
0.182 
0.196 
0.172 
0.155 
0.157 
0.167 
0.178 
0.169 
0.172 
0.179 
0.172 
0.159 
0.156 
0.157 
0.153 
0.153 
-  
0.170 
0.178 
0.171 

0.215 
0.212 

0.217 
0.129 
0.134 
0.131 
0.216 
0.189 
0.205 
0.227 
0.218 
0.219 
0.236 
0.237 
0.233 
0.190 
0.188 
0.197 
0.220 
0.225 
0.226 
0.211 
0.210 
0.203 
0.245 
0.243 
0.236 
0.207 
0.214 
0.207 
0.200 
0.221 
0.216 
0.182 
0.191 
0.196 
0.206 
0.202 
0.203 
0.216 
0.214 
0.216 
0.193 
0.183 
0.184 
0.233 
0.222 
0.229 
0.199 
0.203 
0.215 

 
 
 
 
 
 
 
 
 
 
 
 
19 
19 
19 
20 
20 
20 
21 
21 
21 
22 
22 
22 
23 
23 
23 
24 
24 
24 
25 
25 
25 
26 
26 
26 
27 
27 
27 
28 
28 
28 
29 
29 
29 
30 
30 
30 
31 
31 
31 
32 
32 
32 
33 
33 
33 
34 
34 
34 
35 
35 
35 
36 
36 
36 
37 
37 
37 
38 
38 
38 

0.169 
0.152 
0.161 
0.146 
0.140 
0.143 
0.169 
0.177 
0.161 
0.160 
0.141 
0.148 
0.165 
0.178 
0.191 
0.142 
0.144 
0.130 
0.156 
0.152 
0.154 
0.206 
0.198 
0.201 
0.155 
0.167 
0.165 
0.152 
0.156 
0.147 
0.134 
0.143 
0.137 
0.155 
0.155 
0.159 
0.138 
0.130 
0.130 
0.166 
0.177 
0.173 
0.136 
0.147 
0.137 
0.124 
0.123 
0.123 
0.152 
0.155 
0.150 
0.099 
0.133 
0.128 
0.143 
0.149 
0.153 
0.173 
0.161 
0.170 

0.174 
0.167 
0.168 
0.174 
0.176 
0.168 
0.193 
0.190 
0.187 
0.181 
0.160 
0.179 
0.203 
0.196 
0.200 
0.155 
0.167 
0.168 
0.181 
0.178 
0.181 
0.230 
0.233 
0.234 
0.185 
0.189 
0.195 
0.169 
0.176 
0.180 
0.165 
0.170 
0.169 
0.180 
0.181 
0.184 
0.167 
0.165 
0.163 
0.204 
0.228 
0.209 
0.157 
0.172 
0.173 
0.139 
0.160 
0.116 
0.180 
0.177 
0.177 
0.162 
0.162 
0.152 
0.178 
0.173 
0.170 
0.200 
0.198 
0.191 

0.043 
0.042 
0.040 
0.056 
0.054 
0.057 
0.096 
0.090 
0.094 
0.062 
0.043 
0.041 
0.080 
0.074 
0.056 
0.082 
0.058 
0.052 
0.041 
0.040 
0.053 
0.136 
0.119 
0.108 
0.063 
0.069 
0.066 
0.063 
0.063 
0.060 
0.049 
0.057 
0.053 
0.060 
0.059 
0.060 
0.071 
0.066 
0.054 
0.065 
0.070 
0.079 
0.056 
0.061 
0.049 
0.045 
0.000 
0.001 
0.089 
0.063 
0.063 
0.026 
0.032 
0.002 
0.051 
0.053 
0.058 
0.090 
0.084 
0.079 

0.102 
0.091 
0.115 
0.140 
0.138 
0.154 
0.148 
0.151 
0.152 
0.143 
0.122 
0.124 
0.144 
0.142 
0.157 
0.143 
0.144 
0.141 
0.154 
0.149 
0.145 
0.213 
0.223 
0.216 
0.121 
0.130 
0.136 
0.139 
0.145 
0.145 
0.121 
0.128 
0.129 
0.118 
0.129 
0.133 
0.129 
0.125 
0.117 
0.189 
0.205 
0.166 
0.131 
0.137 
0.149 
0.095 
0.109 
0.107 
0.131 
0.142 
0.139 
0.115 
0.111 
0.159 
0.137 
0.138 
0.140 
0.174 
0.187 
0.185 

0.170 
0.158 
0.149 
0.162 
0.161 
0.163 
0.183 
0.176 
0.190 
0.169 
0.142 
0.159 
0.200 
0.197 
0.199 
0.156 
0.166 
0.170 
0.162 
0.164 
0.163 
0.233 
0.229 
0.234 
0.166 
0.155 
0.163 
0.165 
0.161 
0.166 
0.147 
0.150 
0.151 
0.163 
0.159 
0.155 
0.146 
0.163 
0.165 
0.189 
0.191 
0.187 
0.155 
0.168 
0.092 
0.123 
0.141 
0.146 
0.174 
0.165 
0.171 
0.129 
0.142 
0.170 
0.168 
0.173 
0.172 
0.196 
0.181 
0.177 

23 

0.119 
0.111 
0.130 
0.147 
0.140 
0.148 
0.169 
0.177 
0.169 
0.120 
0.135 
0.134 
0.173 
0.184 
0.185 
0.150 
0.153 
0.154 
0.139 
0.151 
0.147 
0.227 
0.238 
0.238 
0.139 
0.136 
0.135 
0.148 
0.153 
0.150 
0.137 
0.135 
0.138 
0.152 
0.150 
0.146 
0.124 
0.140 
0.137 
0.170 
0.173 
0.182 
0.146 
0.145 
0.144 
0.105 
0.115 
0.124 
0.157 
0.148 
0.151 
0.121 
0.122 
0.132 
0.145 
0.140 
0.143 
0.182 
0.186 
0.157 

0.174 
0.179 
0.174 
0.165 
0.165 
0.164 
0.184 
0.188 
0.196 
0.173 
0.169 
0.159 
0.194 
0.191 
0.185 
0.153 
0.148 
0.144 
0.186 
0.185 
0.188 
0.207 
0.212 
0.212 
0.165 
0.180 
0.180 
0.165 
0.164 
0.171 
0.167 
0.157 
0.167 
0.167 
0.171 
0.174 
0.141 
0.156 
0.146 
0.201 
0.212 
0.191 
0.151 
0.147 
0.155 
0.120 
0.145 
0.154 
0.171 
0.171 
0.170 
0.151 
0.144 
0.146 
0.176 
0.170 
0.169 
0.193 
0.175 
0.162 

0.171 
0.146 
0.159 
0.198 
0.197 
0.200 
0.231 
0.232 
0.224 
0.182 
0.197 
0.209 
0.224 
0.234 
0.216 
0.196 
0.198 
0.206 
0.219 
0.206 
0.219 
0.258 
0.242 
0.254 
0.200 
0.194 
0.197 
0.210 
0.204 
0.215 
0.194 
0.203 
0.191 
0.197 
0.214 
0.205 
0.175 
0.194 
0.191 
0.219 
0.229 
0.226 
0.190 
0.190 
0.186 
0.156 
0.184 
0.186 
0.198 
0.215 
0.214 
0.177 
0.179 
0.178 
0.190 
0.207 
0.201 
0.214 
0.209 
0.207 

 
 
 
Source: JRC 2025. 

Table A3. Elemental carbon loadings (µg/cm2) reported by each participant. 

1 

2 

3 

4 

5 

6 

7 

8 

Laboratory 
1 
1 

1 
2 
2 
2 
3 
3 
3 
4 
4 
4 
5 
5 
5 
6 
6 
6 
7 
7 
7 
8 
8 
8 
9 
9 
9 
10 
10 
10 
11 
11 
11 
12 
12 
12 
13 
13 
13 
14 
14 
14 
15 
15 
15 
16 
16 
16 
18 
18 
18 
19 
19 

1.28 
1.39 

1.44 
0.92 
0.99 
1.01 
1.40 
1.60 
1.33 
1.37 
1.33 
1.49 
1.68 
1.65 
1.70 
1.41 
1.40 
1.37 
1.47 
1.44 
1.46 
1.81 
1.75 
1.67 
1.58 
1.54 
1.61 
1.52 
1.53 
1.33 
1.45 
1.41 
1.41 
1.43 
1.45 
1.39 
1.38 
1.34 
1.35 
1.53 
1.50 
1.88 
1.30 
1.24 
1.29 
1.57 
1.09 
1.57 
1.33 
1.31 
1.23 
1.65 
1.70 

2.12 
2.10 

2.06 
2.18 
1.43 
1.44 
2.13 
1.94 
1.96 
2.15 
2.08 
2.28 
2.46 
2.56 
2.57 
2.14 
2.05 
2.08 
2.21 
2.25 
2.25 
2.32 
2.32 
2.23 
2.25 
2.34 
2.22 
2.02 
2.03 
1.94 
2.09 
2.16 
2.11 
1.94 
1.98 
1.93 
2.09 
1.95 
1.93 
2.25 
2.06 
2.23 
1.94 
1.85 
1.92 
2.16 
2.15 
 - 
1.70 
1.89 
1.83 
2.15 
2.32 

0.20 
0.23 

0.21 
0.26 
0.15 
0.17 
0.27 
0.17 
0.18 
0.24 
0.21 
0.23 
0.33 
0.33 
0.25 
0.15 
0.17 
0.17 
0.17 
0.18 
0.18 
0.26 
0.24 
0.23 
0.43 
0.45 
0.41 
0.28 
0.29 
0.23 
0.21 
0.21 
0.25 
0.15 
0.13 
0.15 
0.20 
0.16 
0.18 
0.24 
0.26 
0.24 
0.23 
0.24 
0.23 
0.41 
0.41 
0.41 
0.30 
0.29 
0.31 
0.25 
0.21 

0.83 
0.83 

0.83 
1.04 
0.46 
0.46 
0.86 
0.91 
0.84 
0.80 
0.86 
0.99 
1.05 
1.04 
1.07 
0.81 
0.79 
0.83 
0.92 
0.93 
0.95 
1.06 
1.05 
1.10 
0.99 
1.06 
1.07 
0.96 
1.03 
0.94 
0.81 
0.80 
0.86 
0.86 
0.85 
0.86 
0.86 
0.78 
0.83 
0.96 
0.91 
0.99 
0.81 
0.77 
0.77 
1.33 
1.27 
1.33 
0.81 
0.88 
0.84 
0.87 
0.76 

1.47 
1.30 

1.30 
0.87 
0.92 
0.91 
1.26 
1.14 
1.21 
1.19 
1.41 
1.13 
1.47 
1.48 
1.42 
1.22 
1.20 
1.13 
1.34 
1.33 
1.33 
1.50 
1.49 
1.48 
1.42 
1.43 
1.43 
1.27 
1.28 
1.21 
1.20 
1.40 
1.32 
1.29 
1.21 
1.17 
1.22 
1.24 
1.22 
1.40 
1.41 
1.39 
1.21 
1.19 
1.32 
1.29 
1.45 
1.09 
1.14 
1.12 
1.10 
1.33 
1.32 

24 

1.02 
0.94 

1.02 
0.70 
0.73 
0.67 
0.97 
0.99 
0.97 
1.02 
1.02 
1.24 
1.20 
1.29 
1.30 
0.95 
1.00 
0.99 
1.15 
1.22 
1.16 
1.24 
1.23 
1.23 
1.29 
1.27 
1.29 
1.04 
0.97 
1.06 
1.02 
1.13 
1.00 
1.10 
1.06 
1.06 
0.98 
1.00 
0.99 
1.15 
1.18 
1.15 
0.97 
0.96 
0.99 
1.33 
1.32 
1.31 
0.90 
0.97 
0.92 
1.03 
1.07 

2.64 
2.72 

2.83 
1.77 
2.01 
1.88 
2.70 
2.65 
2.65 
2.46 
2.70 
2.65 
3.07 
3.11 
3.27 
2.47 
2.64 
2.51 
2.77 
2.83 
2.68 
2.69 
2.81 
2.96 
2.85 
2.81 
2.90 
2.21 
2.40 
2.08 
2.64 
2.61 
2.67 
2.77 
2.37 
2.46 
2.47 
2.61 
2.50 
2.62 
2.76 
2.60 
2.39 
2.30 
2.31 
2.13 
2.22 
 - 
2.09 
2.27 
2.15 
2.54 
2.58 

1.70 
1.69 

1.79 
1.10 
1.13 
1.07 
1.76 
1.62 
1.61 
1.76 
1.63 
1.67 
1.98 
2.01 
1.96 
1.50 
1.50 
1.58 
1.71 
1.77 
1.76 
1.88 
1.91 
1.88 
1.89 
1.88 
1.89 
1.59 
1.61 
1.52 
1.70 
1.77 
1.78 
1.68 
1.67 
1.66 
1.61 
1.66 
1.57 
1.75 
1.73 
1.81 
1.55 
1.49 
1.51 
1.77 
1.79 
1.78 
1.43 
1.44 
1.40 
1.40 
1.49 

 
 
 
 
 
 
 
 
 
 
 
 
19 
20 
20 
20 
21 
21 
21 
22 
22 
22 
23 
23 
23 
24 
24 
24 
25 
25 
25 
26 
26 
26 
27 
27 
27 
28 
28 
28 
29 
29 
29 
30 
30 
30 
31 
31 
31 
32 
32 
32 
33 
33 
33 
34 
34 
34 
35 
35 
35 
36 
36 
36 
37 
37 
37 
38 
38 
38 

1.78 
1.28 
1.24 
1.27 
1.57 
1.58 
1.46 
1.50 
1.30 
1.36 
1.60 
1.65 
1.78 
1.45 
1.47 
1.45 
1.57 
1.49 
1.49 
2.01 
2.12 
2.06 
1.49 
1.67 
1.60 
1.37 
1.44 
1.40 
1.30 
1.39 
1.36 
1.51 
1.52 
1.55 
1.38 
1.38 
1.38 
1.55 
1.63 
1.61 
1.30 
1.34 
1.29 
1.19 
1.05 
1.04 
1.38 
1.41 
1.40 
1.20 
1.47 
1.30 
1.26 
1.28 
1.31 
1.51 
1.41 
1.54 

2.48 
1.88 
1.90 
1.85 
2.14 
2.11 
2.23 
2.05 
1.81 
2.04 
2.30 
2.30 
2.20 
1.90 
2.02 
2.07 
2.19 
2.08 
2.14 
2.80 
2.75 
2.87 
2.06 
2.21 
2.17 
1.96 
2.05 
2.08 
1.98 
1.98 
1.96 
2.06 
2.12 
2.11 
2.10 
2.00 
2.02 
2.31 
2.55 
2.38 
1.83 
1.91 
1.90 
1.65 
1.70 
1.57 
1.96 
1.96 
1.97 
2.10 
1.88 
1.93 
1.87 
1.78 
1.75 
2.21 
2.18 
2.02 

0.22 
0.19 
0.19 
0.20 
0.32 
0.32 
0.32 
0.24 
0.16 
0.15 
0.30 
0.26 
0.20 
0.31 
0.22 
0.21 
0.15 
0.14 
0.20 
0.52 
0.46 
0.38 
0.30 
0.28 
0.29 
0.23 
0.23 
0.21 
0.20 
0.21 
0.20 
0.23 
0.24 
0.23 
0.25 
0.26 
0.20 
0.26 
0.24 
0.27 
0.22 
0.22 
0.21 
0.15 
0.00 
0.01 
0.33 
0.24 
0.23 
0.15 
0.13 
0.01 
0.17 
0.17 
0.19 
0.33 
0.28 
0.24 

Source: JRC 2025. 

0.98 
0.98 
0.91 
0.97 
1.11 
1.18 
1.16 
0.84 
0.93 
0.94 
1.16 
1.27 
1.31 
1.21 
1.14 
1.14 
0.98 
1.09 
1.07 
1.78 
1.76 
1.85 
1.00 
0.99 
1.00 
1.03 
1.04 
1.04 
1.00 
1.01 
1.04 
1.17 
1.13 
1.08 
0.96 
1.03 
1.03 
1.18 
1.20 
1.22 
0.99 
0.99 
1.01 
0.73 
0.83 
0.91 
1.10 
1.04 
1.06 
0.96 
0.87 
0.91 
0.92 
0.91 
0.89 
1.21 
1.23 
1.03 

2.63 
2.34 
2.35 
2.35 
2.65 
2.64 
2.77 
2.55 
2.53 
2.37 
2.86 
2.81 
2.59 
2.38 
2.34 
2.26 
2.76 
2.74 
2.72 
3.17 
3.31 
3.27 
2.37 
2.67 
2.63 
2.49 
2.49 
2.56 
2.57 
2.47 
2.61 
2.67 
2.60 
2.73 
2.26 
2.41 
2.36 
2.93 
2.99 
2.79 
2.27 
2.26 
2.25 
1.93 
2.30 
2.15 
2.52 
2.53 
2.50 
2.42 
2.13 
2.23 
2.39 
2.38 
2.30 
2.67 
2.39 
2.12 

1.49 
1.58 
1.54 
1.62 
1.76 
1.75 
1.71 
1.52 
1.59 
1.63 
1.85 
1.95 
1.83 
1.63 
1.59 
1.62 
1.77 
1.63 
1.80 
2.18 
2.10 
2.21 
1.66 
1.59 
1.63 
1.64 
1.74 
1.74 
1.65 
1.66 
1.61 
1.60 
1.72 
1.66 
1.66 
1.72 
1.67 
1.76 
1.78 
1.78 
1.50 
1.54 
1.53 
1.36 
1.37 
1.39 
1.65 
1.78 
1.74 
1.45 
1.48 
1.35 
1.56 
1.55 
1.55 
1.58 
1.54 
1.53 

0.77 
0.82 
0.83 
0.92 
0.88 
0.92 
0.90 
0.91 
0.76 
0.75 
0.94 
0.93 
0.96 
0.90 
0.90 
0.90 
0.99 
0.95 
0.90 
1.51 
1.43 
1.44 
0.81 
0.80 
0.89 
0.92 
0.90 
0.92 
0.87 
0.85 
0.83 
0.84 
0.85 
0.84 
0.85 
0.88 
0.84 
1.12 
1.26 
1.02 
0.79 
0.83 
0.89 
0.62 
0.63 
0.71 
0.83 
0.88 
0.86 
0.79 
0.64 
0.41 
0.81 
0.78 
0.80 
1.04 
0.94 
1.06 

1.19 
1.15 
1.16 
1.16 
1.39 
1.35 
1.38 
1.26 
1.12 
1.21 
1.45 
1.49 
1.46 
1.36 
1.33 
1.35 
1.27 
1.26 
1.24 
1.76 
1.87 
1.88 
1.29 
1.21 
1.23 
1.23 
1.24 
1.27 
1.20 
1.16 
1.22 
1.32 
1.27 
1.30 
1.26 
1.32 
1.32 
1.42 
1.43 
1.40 
1.17 
1.21 
1.21 
0.94 
0.94 
0.95 
1.32 
1.31 
1.29 
1.10 
1.13 
1.15 
1.18 
1.18 
1.17 
1.42 
1.29 
1.28 

25 

 
 
 
Table A4. Organic carbon (µg/cm2) reported by each participant. 

1 

2 

3 

4 

5 

6 

7 

8 

Laboratory 
1 
1 

1 
2 
2 
2 
3 
3 
3 
4 
4 
4 
5 
5 
5 
6 
6 
6 
7 
7 
7 
8 
8 
8 
9 
9 
9 
10 
10 
10 
11 
11 
11 
12 
12 
12 
13 
13 
13 
14 
14 
14 
15 
15 
15 
16 
16 
16 
18 
18 
18 
19 
19 
19 
20 

7.87 
7.90 

7.99 
8.64 
9.77 
8.90 
7.69 
7.38 
8.00 
7.90 
7.19 
7.69 
7.94 
7.77 
7.70 
7.77 
7.98 
7.97 
7.50 
7.46 
7.48 
9.05 
8.61 
8.74 
7.60 
7.63 
7.70 
7.23 
7.51 
7.51 
8.09 
8.09 
7.78 
8.23 
7.76 
7.82 
7.68 
7.81 
7.77 
7.87 
7.51 
7.23 
7.86 
7.78 
7.81 
7.04 
7.55 
6.90 
6.83 
6.54 
6.46 
8.06 
9.49 
9.29 
7.49 

9.54 
9.56 

9.52 
10.3 
10.5 
10.3 
9.22 
9.57 
9.74 
8.25 
9.05 
9.21 
9.47 
9.67 
9.43 
10.1 
9.84 
9.69 
9.45 
9.20 
8.97 
10.6 
10.4 
10.6 
8.80 
9.26 
9.20 
8.61 
8.61 
8.56 
9.61 
9.28 
9.64 
9.61 
9.59 
9.49 
10.3 
9.56 
9.42 
9.10 
9.28 
9.43 
9.19 
9.36 
9.41 
8.42 
8.50 
 - 
7.89 
7.95 
8.06 
10.2 
13.9 
12.3 
8.96 

3.29 
3.44 

3.36 
3.71 
4.22 
3.83 
3.43 
3.58 
3.57 
2.98 
3.01 
3.02 
3.53 
3.48 
3.60 
3.95 
3.45 
3.56 
3.64 
3.52 
3.54 
3.76 
3.76 
3.95 
3.12 
3.10 
3.07 
2.94 
3.32 
3.00 
3.34 
3.39 
3.75 
3.57 
3.51 
3.50 
3.49 
3.31 
3.56 
3.39 
3.44 
3.39 
3.57 
3.42 
3.65 
2.87 
2.77 
2.77 
2.80 
2.62 
2.52 
5.65 
4.70 
5.16 
3.25 

5.57 
5.41 

5.69 
7.44 
5.75 
5.95 
5.21 
5.15 
5.76 
5.28 
6.06 
5.70 
5.29 
5.37 
5.32 
5.31 
5.93 
5.91 
5.37 
5.23 
5.22 
5.80 
5.79 
5.80 
5.15 
4.89 
5.11 
4.61 
4.68 
4.60 
5.30 
5.26 
5.53 
5.45 
5.35 
5.68 
6.10 
5.95 
5.60 
5.35 
5.18 
5.22 
5.31 
5.63 
5.46 
4.43 
4.45 
4.60 
4.27 
4.18 
4.23 
7.68 
7.57 
5.91 
5.06 

6.00 
6.21 

6.47 
6.85 
8.87 
7.26 
6.13 
6.05 
6.46 
5.83 
6.72 
5.89 
6.46 
6.28 
6.33 
6.39 
6.39 
6.68 
6.18 
5.95 
6.12 
6.88 
6.84 
6.71 
5.78 
6.03 
5.82 
5.70 
5.71 
5.96 
6.46 
6.51 
6.53 
6.35 
6.18 
6.41 
6.20 
6.24 
6.21 
6.14 
6.18 
6.12 
6.32 
6.46 
6.26 
5.64 
5.52 
5.96 
6.15 
5.22 
4.90 
6.50 
7.03 
6.74 
5.94 

26 

6.11 
6.10 

6.33 
6.49 
6.36 
6.84 
5.97 
5.92 
5.80 
5.67 
6.26 
5.87 
5.94 
5.95 
6.07 
6.15 
6.14 
6.14 
5.89 
5.86 
5.70 
6.42 
6.68 
6.58 
5.81 
5.79 
5.56 
5.29 
6.03 
5.39 
5.94 
6.02 
6.18 
6.16 
6.38 
6.04 
5.95 
5.92 
5.99 
5.85 
6.11 
5.97 
5.82 
5.77 
5.86 
5.45 
5.29 
5.21 
4.99 
4.73 
4.68 
7.64 
8.61 
6.59 
5.68 

12.1 
12.2 

12.9 
13.6 
13.9 
13.7 
12.1 
11.7 
12.0 
12.1 
12.9 
13.4 
12.3 
12.5 
12.8 
12.7 
12.5 
12.3 
11.8 
11.9 
11.3 
13.8 
14.2 
13.9 
12.3 
12.2 
11.9 
11.4 
11.4 
11.3 
11.2 
11.7 
11.0 
13.3 
12.9 
13.2 
12.3 
12.1 
12.3 
12.6 
12.7 
12.6 
12.7 
12.5 
12.4 
11.8 
12.2 
-  
10.2 
10.4 
10.4 
12.0 
11.9 
12.4 
11.8 

6.20 
6.27 

6.46 
7.46 
7.32 
7.10 
6.40 
6.94 
6.26 
6.00 
5.84 
5.96 
6.40 
6.46 
6.45 
6.36 
6.50 
6.44 
6.07 
6.09 
6.02 
7.00 
7.20 
7.35 
5.84 
5.85 
6.13 
6.08 
5.91 
5.81 
6.81 
6.23 
6.46 
7.56 
7.06 
6.80 
6.21 
6.54 
6.17 
6.35 
6.34 
6.58 
6.51 
6.66 
6.69 
5.82 
6.26 
5.97 
5.78 
5.64 
5.10 
6.79 
8.70 
7.90 
6.40 

 
 
 
 
 
 
 
 
 
 
 
 
20 
20 
21 
21 
21 
22 
22 
22 
23 
23 
23 
24 
24 
24 
25 
25 
25 
26 
26 
26 
27 
27 
27 
28 
28 
28 
29 
29 
29 
30 
30 
30 
31 
31 
31 
32 
32 
32 
33 
33 
33 
34 
34 
34 
35 
35 
35 
36 
36 
36 
37 
37 
37 
38 
38 
38 

7.62 
7.65 
7.68 
7.38 
7.59 
7.85 
7.94 
7.85 
8.12 
7.61 
7.52 
8.77 
8.76 
9.75 
8.47 
8.27 
8.21 
7.78 
8.55 
8.19 
8.12 
8.35 
8.05 
7.65 
7.76 
8.10 
8.42 
8.34 
8.62 
8.22 
8.30 
8.19 
8.65 
9.21 
9.20 
7.79 
7.59 
7.69 
8.27 
7.81 
8.12 
8.40 
7.48 
7.42 
7.69 
7.72 
7.93 
10.9 
9.62 
8.89 
7.54 
7.29 
7.23 
7.25 
7.31 
7.51 

8.91 
9.11 
8.93 
9.00 
9.70 
9.24 
9.50 
9.32 
9.03 
9.42 
8.77 
10.4 
10.1 
10.2 
9.91 
9.60 
9.67 
9.38 
9.04 
9.40 
9.06 
9.46 
8.97 
9.62 
9.60 
9.51 
10.0 
9.69 
9.66 
9.36 
9.59 
9.35 
10.5 
10.1 
10.4 
9.04 
8.68 
9.03 
9.82 
9.18 
9.06 
10.3 
8.95 
12.0 
8.96 
9.16 
9.11 
10.9 
9.70 
10.8 
8.58 
8.52 
8.58 
8.85 
8.79 
8.58 

3.26 
3.23 
3.03 
3.20 
3.07 
3.68 
3.52 
3.59 
3.45 
3.28 
3.34 
3.49 
3.61 
3.82 
3.44 
3.45 
3.58 
3.32 
3.44 
3.16 
4.40 
3.85 
4.13 
3.40 
3.46 
3.37 
3.93 
3.40 
3.52 
3.69 
3.84 
3.55 
3.28 
3.68 
3.51 
3.72 
3.24 
3.19 
3.68 
3.40 
4.07 
3.28 
6.41 
5.31 
3.43 
3.50 
3.45 
5.64 
3.92 
3.67 
3.17 
3.12 
3.13 
3.36 
3.10 
2.77 

Source: JRC 2025. 

5.58 
5.61 
5.47 
5.47 
5.69 
6.17 
5.94 
6.06 
5.58 
5.61 
5.78 
6.82 
6.30 
6.27 
6.05 
6.08 
6.18 
6.06 
5.64 
5.93 
6.19 
6.27 
6.40 
5.90 
5.78 
5.88 
6.27 
6.44 
6.50 
6.55 
6.37 
6.30 
6.77 
6.30 
6.50 
5.75 
5.74 
5.51 
5.83 
5.82 
6.02 
6.22 
6.32 
6.42 
5.92 
6.00 
5.94 
6.95 
6.24 
5.95 
5.43 
5.55 
5.34 
5.44 
5.36 
5.52 

11.9 
11.9 
11.7 
11.4 
11.4 
12.1 
12.4 
12.5 
11.9 
11.9 
11.4 
13.1 
13.5 
13.4 
12.1 
12.1 
11.7 
12.1 
12.3 
12.1 
12.0 
12.2 
11.9 
12.6 
12.7 
12.4 
12.8 
13.2 
13.0 
13.4 
12.6 
12.9 
13.8 
13.0 
13.8 
11.7 
11.1 
11.8 
12.8 
13.2 
12.3 
14.1 
13.5 
11.8 
12.2 
12.2 
12.2 
13.6 
12.7 
13.1 
11.2 
11.6 
11.2 
11.2 
11.3 
11.0 

6.27 
6.46 
5.87 
5.79 
5.95 
6.85 
6.50 
6.15 
6.40 
6.36 
6.65 
6.70 
6.44 
6.25 
6.32 
6.25 
6.41 
6.25 
6.61 
6.47 
6.66 
6.63 
6.64 
6.18 
6.78 
6.34 
6.87 
6.54 
6.79 
6.51 
6.33 
6.42 
7.82 
7.14 
7.08 
6.26 
6.00 
6.10 
6.38 
6.57 
6.67 
7.35 
6.09 
6.11 
6.70 
6.49 
6.40 
6.73 
6.81 
6.23 
6.65 
5.95 
6.16 
5.81 
5.82 
5.85 

5.15 
5.03 
5.04 
5.17 
5.05 
5.46 
5.45 
5.29 
5.57 
5.63 
5.15 
5.39 
5.38 
5.45 
5.45 
5.43 
5.32 
5.55 
4.98 
5.23 
5.88 
5.36 
5.69 
5.72 
5.30 
5.42 
6.29 
5.78 
5.59 
6.34 
5.75 
5.48 
5.74 
6.14 
6.32 
4.80 
4.88 
5.10 
5.26 
5.24 
5.07 
5.88 
5.18 
5.97 
5.52 
5.33 
5.33 
6.11 
5.08 
2.18 
5.09 
4.88 
4.93 
4.92 
4.09 
4.66 

6.06 
5.97 
6.20 
6.33 
5.89 
6.18 
6.74 
6.41 
5.83 
6.06 
5.89 
7.36 
6.68 
6.56 
6.55 
6.42 
6.33 
5.78 
6.30 
6.18 
6.50 
6.59 
6.29 
6.23 
6.50 
6.37 
6.98 
6.59 
6.85 
6.76 
6.71 
7.07 
7.35 
6.78 
6.68 
6.09 
6.06 
6.09 
6.39 
6.00 
12.0 
6.71 
5.71 
5.56 
6.25 
6.64 
6.27 
7.44 
6.82 
5.60 
5.84 
5.66 
5.65 
5.84 
5.83 
5.94 

27 

 
 
 
 
 
Table A5. z-scores for TC. 

1 

2 

3 

4 

5 

6 

7 

8 

Laboratory 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

-0.16 

1.14 

-0.43 

-0.67 

0.16 

-0.15 

-0.76 

1.96 

-0.29 

-0.86 

0.04 

-0.05 

-0.47 

-0.37 

-0.50 

-1.38 

-2.53 

2.16 

-0.91 

-0.51 

-0.20 

0.07 

1.98 

0.76 

1.45 

0.63 

-0.25 

0.73 

0.64 

1.73 

-0.17 

-0.01 

-0.90 

-0.36 

2.93 

-1.27 

-0.92 

0.28 

0.85 

0.00 

-0.47 

1.11 

0.00 

-0.84 

-1.50 

0.91 

0.81 

-0.09 

2.27 

-0.25 

-1.56 

0.22 

0.02 

0.40 

-0.08 

-0.47 

-1.51 

-2.95 

3.68 

-1.08 

-0.22 

-0.28 

-0.28 

1.25 

0.62 

0.99 

-0.33 

0.18 

0.45 

0.05 

1.47 

-0.34 

-0.46 

0.93 

-0.80 

1.59 

-1.93 

-1.07 

0.32 

0.26 

0.04 

1.01 

-0.61 

-1.13 

-0.05 

-0.18 

2.69 

-0.24 

0.14 

-1.55 

-2.35 

4.98 

-0.87 

-0.94 

0.16 

-0.35 

0.46 

-0.24 

0.10 

2.06 

-0.29 

0.27 

0.59 

-0.01 

-0.27 

0.61 

3.96 

-0.02 

2.33 

-1.23 

-1.12 

Source: JRC 2025. 

0.29 

0.48 

-0.50 

-0.10 

0.48 

0.14 

-0.19 

1.94 

-0.16 

-1.25 

0.07 

0.53 

-0.31 

0.19 

-0.72 

-1.14 

-3.52 

4.16 

-1.29 

-0.97 

-0.28 

-0.42 

1.48 

0.22 

1.61 

0.58 

-0.46 

0.94 

1.23 

1.24 

-0.54 

-0.46 

0.21 

-0.12 

0.60 

-1.90 

-1.25 

0.35 

1.00 

-0.39 

0.68 

1.05 

0.24 

-0.63 

2.65 

0.14 

-1.79 

-1.31 

1.11 

-0.16 

0.52 

-0.05 

-0.93 

-3.27 

-0.26 

-0.90 

-0.95 

-0.02 

-0.53 

1.11 

-0.23 

0.79 

-0.39 

0.28 

0.93 

1.07 

1.37 

-0.62 

0.16 

0.56 

-0.20 

0.67 

-1.59 

-1.87 

-0.14 

0.85 

0.31 

-1.29 

0.93 

-0.35 

-0.78 

2.75 

-0.72 

-1.61 

0.44 

1.98 

-0.45 

0.27 

0.13 

-0.81 

-3.20 

3.23 

-0.35 

-1.31 

-0.01 

0.71 

-0.02 

-0.08 

1.43 

0.50 

0.15 

0.80 

-0.03 

2.61 

-0.53 

-0.07 

-0.55 

0.45 

-0.19 

-0.77 

-1.97 

-0.06 

2.07 

-0.43 

-0.48 

0.45 

0.13 

-0.42 

1.51 

-0.67 

-1.25 

0.43 

-0.16 

-0.37 

-0.15 

-0.06 

-1.38 

-2.35 

0.94 

-1.03 

-0.21 

0.07 

-0.48 

1.32 

0.17 

0.68 

0.21 

0.00 

0.86 

1.17 

1.38 

-0.25 

3.78 

-1.48 

0.18 

0.30 

-1.59 

-0.90 

0.21 

1.76 

-0.11 

0.65 

0.20 

0.55 

-0.20 

1.36 

-0.49 

-1.63 

-0.25 

0.13 

0.98 

-0.20 

-0.08 

-1.16 

-2.91 

3.70 

-0.85 

-0.72 

-0.21 

0.24 

0.04 

0.13 

1.00 

0.45 

0.25 

1.05 

0.96 

1.50 

-0.54 

-0.63 

0.10 

-0.09 

-2.91 

-1.25 

-1.72 

28 

 
 
 
 
 
 
 
 
 
 
 
 
 Table A6. z-scores for EC/TC ratio. 

1 

2 

3 

4 

5 

6 

7 

8 

Laboratory 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

-0.48 

-3.65 

0.20 

0.02 

1.36 

0.06 

-2.37 

-0.22 

1.15 

1.94 

-0.34 

-0.25 

0.51 

0.64 

0.98 

0.59 

-0.24 

-0.17 

-0.38 

1.45 

-0.92 

0.61 

0.50 

0.35 

-0.77 

0.87 

-0.34 

1.44 

-1.04 

-0.07 

2.91 

0.45 

-0.20 

-1.08 

0.08 

-1.40 

1.06 

-0.95 

-2.00 

-0.17 

-2.20 

-0.40 

0.81 

1.05 

0.00 

1.31 

0.60 

0.24 

-0.57 

-0.54 

0.73 

-0.55 

1.50 

0.37 

-0.54 

-0.35 

0.71 

-0.31 

1.31 

-0.93 

0.08 

3.30 

0.68 

-0.21 

-0.66 

0.20 

-0.82 

2.15 

-0.67 

-2.47 

-0.03 

-1.22 

-0.30 

1.08 

-0.17 

-0.82 

-0.35 

0.43 

0.90 

-0.97 

-0.79 

-0.11 

3.14 

0.95 

-0.10 

-1.20 

-1.12 

0.27 

0.00 

3.48 

2.11 

-1.06 

-0.33 

1.65 

-0.70 

0.44 

0.09 

-0.91 

3.09 

0.21 

0.00 

-0.47 

-0.14 

0.08 

0.49 

-0.34 

-2.46 

0.50 

-2.20 

-0.42 

1.18 

Source: JRC 2025. 

-0.62 

-2.66 

-0.43 

0.22 

1.12 

-0.66 

0.84 

0.34 

1.56 

0.23 

-0.17 

-0.16 

-0.40 

0.56 

-0.37 

2.29 

0.55 

-1.52 

-0.30 

1.00 

-1.03 

1.42 

0.06 

-0.24 

4.01 

-0.70 

-0.04 

-0.69 

-0.08 

-0.84 

1.15 

-0.29 

-1.74 

0.04 

-1.25 

-0.40 

1.16 

0.51 

-2.87 

0.64 

-0.11 

1.71 

-0.15 

1.13 

-0.19 

1.09 

-0.42 

1.03 

-0.56 

-0.01 

0.16 

-0.80 

-1.04 

0.09 

0.25 

-0.37 

1.02 

-0.24 

1.06 

-1.31 

0.85 

2.22 

0.20 

-0.27 

-0.42 

-0.05 

-1.34 

1.70 

-1.17 

-1.79 

-0.03 

-1.38 

0.02 

0.30 

0.47 

-3.91 

-0.14 

0.81 

1.55 

-0.73 

0.94 

0.12 

1.86 

0.18 

0.34 

-0.85 

-0.11 

0.50 

-1.01 

1.17 

-0.01 

-2.46 

-0.38 

1.20 

-0.52 

0.99 

-0.31 

0.46 

2.38 

-0.47 

0.20 

-0.51 

-0.03 

-1.00 

0.99 

-0.88 

-1.60 

0.16 

-1.45 

-0.35 

0.22 

0.63 

-3.84 

-0.39 

-0.04 

1.08 

-0.87 

0.69 

0.67 

1.63 

0.56 

-0.08 

-0.38 

-0.23 

1.04 

-0.31 

0.86 

0.22 

-0.57 

-0.41 

0.87 

-0.72 

1.81 

-0.28 

-0.32 

3.87 

-0.45 

-0.29 

-1.18 

-0.58 

-0.64 

1.24 

-1.87 

-1.95 

0.08 

-1.32 

0.14 

0.98 

-0.57 

-2.37 

-0.10 

-0.34 

1.02 

-0.79 

0.35 

0.60 

1.27 

1.43 

-0.40 

-0.33 

-0.88 

0.51 

-0.74 

3.71 

1.06 

-1.78 

0.07 

0.36 

-0.56 

0.24 

0.02 

0.31 

3.35 

-0.60 

0.03 

-0.73 

-0.71 

-0.82 

1.98 

-0.16 

-1.72 

-0.23 

-0.62 

-0.17 

1.76 

29 

 
 
 
 
 
 
 
 
 
 
 
 
Table A7. percentage deviation (%) from assigned value for TC. 

3 

4 

5 

6 

7 

8 

Laboratory 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

1 

-1 

7 

-3 

-4 

1 

-1 

-5 

12 

-2 

-5 

0 

0 

-3 

-2 

-3 

-9 

-16 

14 

-6 

-3 

-1 

0 

12 

5 

9 

4 

-2 

5 

4 

11 

-1 

0 

-6 

-2 

18 

-8 

-6 

Source: JRC 2025. 

2 

1 

4 

0 

-4 

5 

4 

0 

12 

-1 

-8 

1 

0 

2 

0 

-2 

-8 

-15 

19 

-6 

-1 

-1 

-1 

6 

3 

5 

-2 

1 

2 

0 

7 

-2 

-2 

5 

-4 

8 

-4 

10 

0 

-13 

3 

2 

0 

9 

-5 

-10 

0 

-2 

24 

-2 

1 

-14 

-21 

44 

-8 

-8 

1 

-3 

4 

-2 

1 

18 

-3 

2 

5 

0 

-2 

5 

35 

0 

21 

-10 

-5 

-11 

-10 

2 

3 

-3 

-1 

3 

1 

-1 

10 

-1 

-7 

0 

3 

-2 

1 

-4 

-6 

-19 

22 

-7 

-5 

-2 

-2 

8 

1 

9 

3 

-2 

5 

7 

7 

-3 

-2 

1 

-1 

3 

-10 

-7 

2 

5 

-2 

3 

5 

1 

-3 

13 

1 

-9 

-6 

5 

-1 

3 

0 

-5 

-16 

-1 

-4 

-5 

0 

-3 

5 

-1 

4 

-2 

1 

4 

5 

7 

-3 

1 

3 

-1 

3 

-8 

-9 

-1 

4 

1 

-6 

4 

-2 

-3 

12 

-3 

-7 

2 

9 

-2 

1 

1 

-4 

-14 

14 

-2 

-6 

0 

3 

-0.1 

0 

6 

2 

1 

4 

0 

12 

-2 

0 

-2 

2 

-1 

-3 

-9 

0 

12 

-3 

-3 

3 

1 

-3 

9 

-4 

-7 

3 

-1 

-2 

-1 

0 

-8 

-14 

6 

-6 

-1 

0 

-3 

8 

1 

4 

1 

0 

5 

7 

8 

-1 

23 

-9 

1 

2 

-10 

-5 

1 

12 

-1 

4 

1 

4 

-1 

9 

-3 

-11 

-2 

1 

7 

-1 

-1 

-8 

-19 

25 

-6 

-5 

-1 

2 

0.2 

1 

7 

3 

2 

7 

6 

10 

-4 

-4 

1 

-1 

-19 

-8 

-11 

30 

 
 
 
 
 
 
 
 
 
 
 
 
Table A8. percentage deviation (%) form assigned value for EC/ TC ratio. 

Laboratory 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

1 

-5 

-38 

2 

0 

14 

-3 

5 

7 

10 

6 

-2 

-2 

-4 

15 

-9 

6 

5 

4 

-8 

9 

-4 

15 

-11 

-1 

30 

5 

-2 

-11 

1 

-14 

11 

-10 

-21 

-2 

-23 

-4 

8 

2 

1 

-22 

-2 

11 

18 

-2 

10 

0 

12 

6 

2 

-5 

-5 

7 

-5 

14 

3 

-5 

-3 

7 

-3 

12 

-8 

1 

30 

6 

-2 

-6 

2 

-8 

20 

-6 

-23 

0 

-11 

-3 

10 

3 

-5 

-25 

-11 

13 

28 

-30 

-24 

-3 

96 

29 

-3 

-37 

-34 

8 

-0.1 

107 

65 

-33 

-10 

51 

-22 

14 

3 

-28 

95 

6 

0 

-14 

-4 

3 

15 

-11 

-75 

15 

-67 

-13 

36 

4 

6 

-37 

-4 

0 

11 

-8 

7 

6 

16 

5 

-1 

-4 

-2 

10 

-3 

8 

2 

-6 

-4 

8 

-7 

18 

-3 

-3 

38 

-4 

-3 

-12 

-6 

-6 

12 

-18 

-19 

1 

-13 

1 

10 

Source: JRC 2025. 

5 

6 

-8 

-36 

-6 

3 

15 

-9 

11 

5 

21 

3 

-2 

-2 

-6 

8 

-5 

31 

7 

-21 

-4 

14 

-14 

19 

1 

-3 

55 

-10 

-1 

-9 

-1 

-11 

16 

-4 

-24 

1 

-17 

-5 

16 

-9 

-37 

-2 

-5 

16 

-12 

6 

10 

20 

23 

-6 

-5 

-14 

8 

-12 

59 

17 

-28 

1 

6 

-9 

4 

0.3 

5 

53 

-9 

0 

-12 

-11 

-13 

31 

-3 

-27 

-4 

-10 

-3 

28 

31 

7 

5 

8 

4 

-29 

-36 

7 

-1 

18 

-2 

12 

-2 

11 

-4 

11 

-6 

-0.12 

2 

-8 

-11 

1 

3 

-4 

10 

-2 

11 

-1 

8 

14 

-7 

9 

1 

17 

2 

3 

-8 

-1 

5 

-9 

11 

0 

-23 

-4 

11 

-5 

9 

-13 

-2.9 

9 

23 

2 

-3 

-4 

0 

-14 

17 

-12 

-18 

0 

-14 

0 

3 

4 

22 

-4 

2 

-5 

0 

-9 

9 

-8 

-15 

2 

-14 

-3 

2 

 
 
 
 
 
 
 
 
 
 
 
 
Annex B. METHOD PERFORMANCE  

The assessment of the method performance aims at deriving, from the results of the present 
exercise, the precisions of the standard measurement method described in EN16909:2017, in terms 
of repeatability and reproducibility standard deviations. For this, the consistency of the dataset is 
evaluated by means of Cochran’s test and Grubbs’ test [ISO5725-2] for possible outliers (i.e. 
observations greater than the critical value at the 99% confidence level) or stragglers (i.e. 
observations greater than the critical value at the 95% confidence level but less or equal to the 
critical value at the 99% confidence level). 

Cochran’s test verifies the within-laboratory consistency (repeatability). The critical values for 
Cochran’s test (i.e. outlier and straggler) vary upon the number of participants and replicate 
measurements. In this comparison exercise, all thirty-seven participants provided three replicates 
for every PT sample except participants 16 (two replicates for PT samples 2 and 7). However, 
Cochran’s critical values for three replicates were used for all PT samples, i.e. 0.204 (outlier) and 
0.168 (straggler). 

For each test filter separately, Cochran’s criterion is applied to test the consistency of the highest 
standard deviation value (repeatability) among those reported by all participants. After the removal 
of the outlier, if any, the test is repeated on the remaining standard deviations values. 

Grubb’s test verifies the between-laboratory consistency (reproducibility) and is applied to test, at 
the first place, the significance of the largest observation (or two as for G2), and then the 
significance of the smallest observation (or two as for G2). For an inter-laboratory comparison 
among thirty-seven participants, the critical values for Grubb’s test are 3.343 and 0.564 -outliers 
for G1 and G2, respectively- and 3.003 and 0.6247 - stragglers for G1 and G2, respectively. 

Based on the outcomes of above statistical analyses, outliers are discarded. From the retained 
values and for each PT sample separately, the mean values and the method repeatability (sr) and 
reproducibility (sR) standard deviations are calculated. Subsequently, the dependence of precision 
(i.e. repeatability and reproducibility) upon the mean values is investigated [ISO5725-2]. 

32 

 
 
 
 
 
B.1 Method performance for TC 

Within-laboratory consistency. In Figure B1, the standard deviations on the three replicates reported 
by each participant for each PT sample are presented grouped by participant. Cochran’s test 
identifies 19/1, 36/1, 19/2, 34/2, 13/3, 34/3, 2/4, 33/4, 2/5, 36/5, 19/6, 36/6, 34/7, 19/8 and 34/8 
(participant/sample) as outliers; no stragglers (participant/ sample). 

Figure B1. Standard deviation on the three replicates reported for each test filters, grouped by participant. 

3,5

3,0

2,5

2,0

1,5

1,0

0,5

0,0

²

m
c
/
C
g
µ

,

n
o
i
t
a
i
v
e
d
d
r
a
d
n
a
t
s

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9

0
1

1
1

2
1

3
1

4
1

5
1

6
1

8
1

9
1

0
2

1
2

2
2

3
2

4
2

5
2

6
2

7
2

8
2

9
2

0
3

1
3

2
3

3
3

4
3

5
3

6
3

7
3

8
3

Laboratory

Source: JRC 2025. 

Between-laboratory consistency. In Figure B2, the average values from the replicates reported by 
each participant for each PT sample are presented. 

The G1 and G2 Grubbs’ tests identifies 19/2, 19/3, 19/5, and 19/6 as stragglers (participant/sample), 
and 33/4 (participant/sample) as outliers. 

33 

 
 
 
 
 
 
 
 
 
Figure B2. TC average values from three replicates reported by participants for each test sample, grouped by 
participant. 

²

m
c

/
C
g
µ

l

e
u
a
v
e
g
a
r
e
v
A

20

15

10

5

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9

0
1

1
1

2
1

3
1

4
1

5
1

6
1

8
1

9
1

0
2

1
2

2
2

3
2

4
2

5
2

6
2

7
2

8
2

9
2

0
3

1
3

2
3

3
3

4
3

5
3

6
3

7
3

8
3

Laboratory

Source: JRC 2025. 

Localized sample heterogeneities or contaminations cannot be rigorously excluded, but the 
occurrence of several outliers and/or stragglers from a single participant most probably suggests 
unsatisfactory laboratory precision for the determination of the TC loadings as compared to the 
other participants. 

The entries identified as outliers by the statistical tests were discarded from the dataset, and from 
the retained values and for each PT sample separately, the mean value, the method repeatability 
(sr) and reproducibility (sR) standard deviations were calculated. The general means and values of 
sr and sR for the eight PT samples are listed in Table B1.  

Table B1: General mean, repeatability (sr) and reproducibility (sR) standard and relative standard 
deviations for TC. 

PT sample 

general 
mean  
µgC / cm² 

sr 

µgC / cm² 

1 

2 

3 

4 

5 

6 

7 

8 

9.34 

11.5 

3.74 

7.56 

6.30 

7.02 

14.8 

8.08 

0.256 

0.279 

0.264 

0.298 

0.290 

0.161 

0.318 

0.221 

Source: JRC 2025. 

% 

2.7 

2.4 

7.1 

3.9 

4.6 

2.3 

2.1 

2.7 

sR 

µgC / cm² 

0.604 

0.651 

0.475 

0.471 

0.526 

0.422 

0.842 

0.463 

34 

% 

6.5 

5.7 

13 

6.2 

8.3 

6.0 

5.7 

5.7 

 
 
 
  
 
 
 
 
 
Combining the repeatability and reproducibility relative standard deviations of the EUSAAR_2 
protocol obtained during the previous ILCs and the present one, we observe that the method 
precision (both sr and sR) for TC measurement becomes exponentially poorer toward lower TC 
contents i.e. < 10 µgC / cm² (Fig. B3). 

Figure B3. Repeatability (squares) and reproducibility (triangles) relative standard deviation of the EUSAAR_2 
protocol for TC measurement obtained during the previous inter-laboratory comparisons and the present one. 

0,30

0,25

0,20

0,15

0,10

0,05

0,00

0

m
/
R
s

,

m

/
r
s

2014-2024

OCEC2025-1

2014-2024

OCEC2025-1

10

20

30

40

50

TC, µgC / cm²

Source: JRC 2025. 

B.2 Method performance for EC/TC 

Within-laboratory consistency. In Figure B4, the standard deviations of the replicates reported for 
each PT sample are presented grouped by participant.  

Cochran’s test identifies entries 16/1, 14/1, 2/2, 34/2, 34/3, 16/4, 33/4, 2/5, and 36/5 
(participant/sample) as outliers and 4/6 and 34/7 (participant/sample) as stragglers.  

35 

 
 
 
 
 
Figure B4. Standard deviation on the EC/TC ratio replicates reported for each test filters, grouped by 
participant. 

n
o
i
t
a
i
v
e
d
d
r
a
d
n
a
t
s

0,045

0,040

0,035

0,030

0,025

0,020

0,015

0,010

0,005

0,000

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9

0
1

1
1

2
1

3
1

4
1

5
1

6
1

8
1

9
1

0
2

1
2

2
2

3
2

4
2

5
2

6
2

7
2

8
2

9
2

0
3

1
3

2
3

3
3

4
3

5
3

6
3

7
3

8
3

Laboratory

Source: JRC 2025. 

Between-laboratory consistency. In Figure B5, the EC/TC ratio average values from the replicates 
reported by all participants for PT sample are presented grouped by participant.  

Grubbs’ test identifies entries 26/4, 26/6 and 2/8 (participant/sample) as stragglers and no outliers.  

36 

 
 
 
 
 
 
Figure B5. EC/TC average ratios from the replicates reported by participants for each PT sample, grouped by 
participant. 

0,30

0,25

0,20

0,15

l

e
u
a
v
e
g
a
r
e
v
A

0,10

0,05

0,00

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9

0
1

1
1

2
1

3
1

4
1

5
1

6
1

8
1

9
1

0
2

1
2

2
2

3
2

4
2

5
2

6
2

7
2

8
2

9
2

0
3

1
3

2
3

3
3

4
3

5
3

6
3

7
3

8
3

Laboratory

Source: JRC 2025 

The entries identified as outliers by the statistical tests are discarded from the dataset, and the 
mean value, the repeatability (sr) and the reproducibility (sR) standard deviations for EC/TC are 
calculated for each PT sample from the retained values (Table B2).  

Table B2: General mean, repeatability (sr) and reproducibility (sR) standard and relative standard 
deviations for EC/TC.  

PT sample 

1 

2 

3 

4 

5 

6 

7 

8 

general 
mean  
M, ratio 

0.153 

0.183 

0.064 

0.169 

0.146 

0.152 

0.171 

0.205 

sr 

0.007 

0.006 

0.009 

0.008 

0.007 

0.007 

0.006 

0.007 

Source: JRC 2025. 

sR 

0.020 

0.017 

0.026 

0.022 

0.028 

0.025 

0.019 

0.023 

% 

4.7 

3.2 

14 

4.8 

5.0 

4.5 

3.7 

3.6 

% 

13 

9.2 

40 

13 

19 

17 

11 

11 

Combining the repeatability and reproducibility relative standard deviation of the EUSAAR_2 
protocol obtained during the previous four ILCs and the present one, we observe that the method 
precision (sR and possibly sr) of EC/TC ratio measurement can become poorer at lower EC/TC ratios 
and exceptionally poor only for EC/TC ratios <0.070 (Fig. B6). 

37 

 
 
 
 
  
       
        
 
 
Figure B6. Repeatability (squares) and reproducibility (triangles) relative standard deviation for the 
EUSAAR_2 protocol for EC/TC measurement obtained during the previous inter-laboratory comparisons and 
the present one. 

2014-2024

OCEC2025-1

2014-2024

OCEC2025-1

0,70

0,60

0,50

0,40

0,30

0,20

0,10

0,00

m
/
R
s

,

m

/
r
s

0,000

0,050

0,100

0,150

0,200

0,250

0,300

0,350

EC/TC ratio

Source: JRC 2025. 

Annex C. QA MEASURES  

Based on the results from the present inter-laboratory comparison and for the purpose of 
documenting the TC, OC and EC mass concentrations reported to the EBAS database, quality control 
measures, i.e. percentage bias and variability, were calculated for TC, OC and EC determination for 
each participant. 

C.1 Calculation of QA variability = Random errors (2RSD) 

It is assumed that laboratories taking part in inter-laboratory comparisons will obtain results near 
the expected ones when this bias is removed, and that the differences between expected and 
obtained results will be more often close to zero than not. Based upon this assumption, a triangular 
distribution can be used to quantify the random errors in the laboratory results (Eurachem, 2000; 
EMEP CCC report 6/2003). 

38 

 
 
 
  
 
Figure C1. Triangular distribution. 

Source: Eurachem, 2000; EMEP CCC report 6/2003. 

The triangle distribution is symmetric with a baseline 2a. The height in the triangle will be 1/a when 
the triangle area equals 1. The standard uncertainty is given by 

Equation C.1 

The distance from –a to a (i.e. 2a) is called the range. When applied on the inter-laboratory 
comparison results, the range equals the distance between the largest and smallest of the 
differences between expected and found concentrations. L and T represent the laboratories’ and the 
expected concentrations respectively, and D is the relative difference:  

The range (2a) is then the difference between the highest and minimum differences (Dmax – Dmin) 
and the uncertainty 

, for the differences becomes 

Equation C.2 

and more than 95 % of the data will be within  
relative standard deviation (RSD) given by the 95% confidence limit, thus:  

. The QA variability is defined as the 

Equation C.3 

Equation C.4 

39 

)(Du)(2Du      -a 0 a   x  6)(axu=Di = (Li – Ti)/ Ti  ()()62)(minmax−=DDDu QA variability   =   %6)(%100)(221minmax1==−==niiniiTDDnnTDuRSD  
 
 
 
 
 
 
 
 
 
C.2 Calculation of QA bias = systematic error (RB%) 

An estimation of bias in single measurements requires a long data series, and only a few samples 
in an inter-laboratory comparison will only give a very coarse estimate or indication of the bias. 
However, looking at the bias in inter-laboratory comparison over years will give a good indication of 
the performance of the laboratory. 

The absolute bias may be dependent upon the concentrations, but the relative bias is considered 
approximate constant for the concentrations range used in the comparison. The differences Di, as 
defined above are calculated as relative difference, and a median of these relative difference is 
defined as the QA bias. Median is chosen instead of average to avoid that one outlier get too high 
influence on the results.  

Equation C.5 

In Table C1 are reported the assigned values for TC, OC and EC calculated as described in par. 2.2.1. 
In Tables C2-4 are reported QA measures for TC, OC and EC from the present inter-laboratory 
comparison. If the tendency is observed for more than 75% of the test samples, the bias is 
considered systematic. 

Table C1. Assigned values for TC, OC and EC in μg cm-2. 

Assigned values 

TC 

OC 

EC 

1 

9.39 

7.91 

1.45 

2 

11.5 

9.35 

2.09 

3 

3.73 

3.47 

0.23 

4 

7.61 

6.31 

1.28 

5 

6.29 

5.38 

0.89 

6 

7.06 

5.99 

1.06 

7 

14.9 

12.3 

2.53 

8 

8.09 

6.41 

1.65 

Source: JRC 2025. 

40 

 QA bias   =  RB = median %iiTD  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table C2: QA bias and QA variability for TC. 

QA_bias  QA_variability 

Systematic 

Laboratory 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 

Source: JRC 2025. 

LANUV 
ISCIII 
SEA 
GIOS 
NILU 
CHMI 
RIVM 
JRC 
IMI 
FMI_f82 
NPL 
ISSeP 
INERIS 
AIRPARIF 
LVGMC 
UBA-L 
LAERO 
CzechGlobe 
IDAEA-CSIC 
TROPOS 
TU Wien 
ECPL_UOC 
NCSR D 
CyI 
ICPF 
IPIS PAN 
LSCE 
UNIVIE 
SLBV 
LU_Physics 
UCD AQRC 
SU-ACES 
FORTH 
IPNA-CSIC 
INFN 
ATMI 
FMI_f83 

0.5% 
6.0% 
-1.3% 
-3.6% 
2.8% 
1.0% 
-1.9% 
11.0% 
-2.5% 
-7.7% 
0.3% 
0.5% 
-1.2% 
-0.7% 
-0.5% 
-7.7% 
-15.8% 
16.6% 
-5.7% 
-4.7% 
-0.7% 
-1.8% 
5.9% 
0.9% 
5.7% 
2.6% 
0.3% 
4.5% 
5.2% 
7.9% 
-2.4% 
-0.2% 
0.9% 
-0.6% 
3.2% 
-8.9% 
-7.8% 

2.4% 
4.0% 
1.7% 
7.2% 
1.7% 
2.3% 
2.1% 
1.6% 
2.5% 
2.2% 
3.6% 
4.3% 
11.0% 
2.0% 
2.1% 
4.2% 
2.9% 
18.7% 
2.5% 
3.0% 
1.2% 
2.6% 
5.1% 
2.8% 
3.3% 
8.3% 
1.7% 
1.9% 
2.9% 
4.8% 
1.1% 
10.9% 
18.1% 
2.5% 
16.4% 
3.1% 
2.5% 

no 
high 
no 
no 
high 
no 
low 
high 
low 
low 
no 
no 
no 
no 
no 
low 
low 
high 
low 
low 
no 
no 
high 
no 
high 
no 
no 
high 
high 
high 
low 
no 
no 
no 
no 
low 
low 

41 

 
 
 
 
 
 
 
 
 
 
 
Table C3: QA bias and QA variability for OC. 

QA_bias  QA_variability 

Systematic 

Laboratory 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 

LANUV 
ISCIII 
SEA 
GIOS 
NILU 
CHMI 
RIVM 
JRC 
IMI 
FMI_ f82 
NPL 
ISSeP 
INERIS 
AIRPARIF 
LVGMC 
UBA-L 
LAERO 
CzechGlobe 
IDAEA-CSIC 
TROPOS 
TU Wien 
ECPL_UOC 
NCSR D 
CyI 
ICPF 
IPIS PAN 
LSCE 
UNIVIE 
SLBV 
LU_Physics 
UCD AQRC 
SU-ACES 
FORTH 
IPNA-CSIC 
INFN 
ATMI 
FMI_f83 

Source: JRC 2025. 

0.4% 
13.3% 
-0.8% 
-3.3% 
0.6% 
2.6% 
-3.3% 
10.6% 
-5.3% 
-7.9% 
0.9% 
2.2% 
-0.6% 
-1.4% 
1.1% 
-9.6% 
-16.2% 
24.4% 
-4.6% 
-6.0% 
0.8% 
-3.2% 
8.2% 
1.2% 
-1.4% 
3.5% 
0.6% 
6.2% 
5.9% 
10.1% 
-4.6% 
2.0% 
5.5% 
-0.5% 
6.5% 
-8.2% 
-9.1% 

2.7% 
4.8% 
2.1% 
7.8% 
1.3% 
2.6% 
3.3% 
2.3% 
3.8% 
3.1% 
4.6% 
4.6% 
4.7% 
2.9% 
2.5% 
7.0% 
4.0% 
20.5% 
2.5% 
3.8% 
1.6% 
3.1% 
5.9% 
3.2% 
3.3% 
8.6% 
1.9% 
2.2% 
3.5% 
5.8% 
2.4% 
13.2% 
20.0% 
2.0% 
16.7% 
2.9% 
3.6% 

no 
high 
no 
no 
no 
high 
low 
high 
low 
low 
no 
high 
no 
no 
no 
low 
low 
high 
low 
low 
no 
no 
high 
no 
no 
no 
no 
high 
high 
high 
low 
no 
no 
no 
no 
low 
low 

42 

 
 
 
 
 
 
 
 
 
 
 
Table C4: QA bias and QA variability for EC. 

QA_bias  QA_variability 

Systematic 

Laboratory 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 

LANUV 
ISCIII 
SEA 
GIOS 
NILU 
CHMI 
RIVM 
JRC 
IMI 
FMI_ f82 
NPL 
ISSeP 
INERIS 
AIRPARIF 
LVGMC 
UBA-L 
LAERO 
CzechGlobe 
IDAEA-CSIC 
TROPOS 
TU Wien 
ECPL_UOC 
NCSR D 
CyI 
ICPF 
IPIS PAN 
LSCE 
UNIVIE 
SLBV 
LU_Physics 
UCD AQRC 
SU-ACES 
FORTH 
IPNA-CSIC 
INFN 
ATMI 
FMI_f83 

Source: JRC 2025. 

-2.5% 
-28.3% 
-2.6% 
0.8% 
19.4% 
-7.5% 
5.4% 
15.1% 
13.5% 
-2.8% 
0.0% 
-2.5% 
-5.5% 
7.1% 
-8.4% 
5.3% 
-12.4% 
-1.0% 
-9.8% 
6.2% 
-6.0% 
12.0% 
1.2% 
3.4% 
43.3% 
-0.3% 
-2.3% 
-5.0% 
1.2% 
-2.8% 
12.4% 
-7.2% 
-23.6% 
-0.1% 
-12.8% 
-10.6% 
3.4% 

6.9% 
6.6% 
6.6% 
3.0% 
7.1% 
11.7% 
14.1% 
6.2% 
31.7% 
11.6% 
5.2% 
15.8% 
9.5% 
3.4% 
5.3% 
37.8% 
18.2% 
12.1% 
5.4% 
14.9% 
7.3% 
4.5% 
7.0% 
15.2% 
28.2% 
13.2% 
2.5% 
5.4% 
4.3% 
4.1% 
8.5% 
2.0% 
25.0% 
8.7% 
21.5% 
6.6% 
12.2% 

no 
low 
no 
no 
high 
no 
high 
high 
high 
no 
no 
no 
low 
high 
low 
no 
low 
no 
low 
high 
low 
high 
no 
no 
high 
no 
no 
low 
high 
no 
high 
low 
low 
no 
low 
low 
no 

43 

 
 
 
 
 
 
 
 
 
 
 
Annex D. Certificate of accreditation  

44 

 
 
 
 
 
NAME 

VERSION 

DATE 

Editing 

Review 

F. CAVALLI (PT Coordinator) 

FINAL 

06.06.2025 

J.-P PUTAUD (Technician) 

FINAL 

30.06.2025 

Approval 

F. PEKAR (Unit head) 

FINAL 

03/07/2025 

Authorisation 

SZYMANSKI, P. (Director) 

Published 

11/07/2025 

End of document

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