Proficiency testing scheme, Measurement of inorganic gaseous pollutants (SO2, CO, O3, NO and NO2) in filtered ambient air, 11-14 March 2024 : European Commission harmonisation programme for air quality measurements.
Date: 2024-11-29
Institutions: Joint Research Centre
Subjects: EU environmental policy, air quality, anti-pollution device, directive (EU), environmental cooperation, environmental impact, environmental law, environmental monitoring, pollution control, quality standard, testing

PROFICIENCY TESTING SCHEME, 
Measurements of inorganic gaseous 
pollutants (SO2, CO, O3, NO and NO2) in 
filtered ambient air, 11-14 March 2024 
Ispra, Italy 

European Commission harmonisation programme for air quality 
measurements 

Barbiere, M.G., Tarricone, C., Borowiak, A. 

2024 

 EUR 40126 

This document is a publication by the Joint Research Centre (JRC), the European Commission’s science and knowledge 
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Contact information 
Name: Annette Borowiak 
Address: European Commission, Joint Research Centre, Via E. Fermi 2749, 21027 Ispra (VA), Italy 
Email: annette.borowiak@ec.europa.eu 
Tel.: +39 0332 789956 

EU Science Hub 
https://joint-research-centre.ec.europa.eu 

JRC139418 

EUR 40126 EN 

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ISBN 978-92-68-22423-6   ISSN 1831-9424   doi:10.2760/3118813 

KJ-01-24-164-EN-N 

Luxembourg: Publications Office of the European Union, 2024 

© European Union, 2024  

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How  to  cite  this  report:  European  Commission,  Joint  Research  Centre,  Barbiere,  M.G.,  Tarricone,  C.  and  Borowiak,  A., 
PROFICIENCY  TESTING  SCHEME,  Measurements  of  inorganic  gaseous  pollutants  (SO2,  CO,  O3,  NO  and  NO2)  in  filtered 
ambient  air,  11-14  March  2024  Ispra,  Italy,  Publications  Office  of  the  European  Union,  Luxembourg,  2024, 
https://data.europa.eu/doi/10.2760/3118813, JRC139418. 

 
 
 
 
 
 
 
 
 
 
Contents 

Abstract ................................................................................................................................................................................................................................. 3 
Acknowledgements ...................................................................................................................................................................................................... 4 
1  Introduction ................................................................................................................................................................................................................ 5 
2  Proficiency test organisation ....................................................................................................................................................................... 5 
3  Participants ................................................................................................................................................................................................................. 6 
4  Preparation of test mixtures ........................................................................................................................................................................ 7 
5  The evaluation of laboratory’s measurement proficiency .................................................................................................. 9 
5.1  z-score and z’–score ............................................................................................................................................................................... 9 
5.2  En-score .......................................................................................................................................................................................................... 17 
6  Conclusions .............................................................................................................................................................................................................. 24 
References ....................................................................................................................................................................................................................... 28 
List of abbreviations ................................................................................................................................................................................................ 31 
Mathematical Symbols .......................................................................................................................................................................................... 32 
List of figures ................................................................................................................................................................................................................ 33 
List of tables .................................................................................................................................................................................................................. 34 
Annex A. Reference values ................................................................................................................................................................................. 35 
Homogeneity .......................................................................................................................................................................................................... 37 
Annex B: Results reported by participants............................................................................................................................................. 39 
Annex C: Repeatability and reproducibility............................................................................................................................................ 58 
1  Introduction ............................................................................................................................................................................................................. 58 
2  Results ......................................................................................................................................................................................................................... 60 
3  Conclusions .............................................................................................................................................................................................................. 65 
Annex D: Confidentiality ....................................................................................................................................................................................... 66 
Annex E: Accreditation certificate ................................................................................................................................................................. 67 

1 

EUROPEAN REFERENCE LABORATORY FOR AIR POLLUTION - ERLAP 

PROFICIENCY TESTING SCHEME 

Measurement of inorganic gaseous pollutants  
(SO2, CO, O3, NO and NO2) in filtered ambient air 
(11-14 March 2024, Ispra-Italy) 

European Commission harmonisation programme 
for air quality measurements 

Barbiere M.G., Tarricone C., Borowiak A. 

PTP N° 0018 P

2 

EUR XXXXX XX 

Abstract 
Within the harmonisation programme of Air Quality monitoring in Europe  the European 
Reference Laboratory of Air Pollution (ERLAP) organises Proficiency Tests (PT).  
During the period 11-14 of March 2024, including ERLAP, ten Laboratories of AQUILA (Network 
of European Air Quality Reference Laboratories) met for a laboratory comparison exercise in Ispra 
(IT) to evaluate their proficiency in the analysis of inorganic gaseous air pollutants (NO, NO2, SO2, CO 
and O3) covered by the European Air Quality Directive 2008/50 EC [1] and following amendments 
[42].  The proficiency evaluation, which assesses each participant's performance against  the 
criteria z/z' score, provides the European Commission with insights into the status and capabilities of 
participants. In addition, considering that the evaluation scheme should be useful to participants for 
accreditation according  to  ISO  17025,  they  are  requested  to  include  their  measurement 
uncertainty.  Hence, participants’  results  (measurement  values  and  uncertainties)  are  also 
compared  to  the  reference values applying the En–score method [13]. The results can be used by 
participants to implement or enhance their quality control system. 
Based only on the z/z’-score evaluation all results reported were 98.2% satisfactory. Considering 
the En-score,  92.5%  of  all  values  were  found  satisfactory,  but  the  overall  performance  of  both 
the indicators can be considered good. 
Considering the repeatability and reproducibility evaluation, the results among AQUILA 
participants at the highest generated concentration levels are satisfactory for measurements of all 
pollutants. 

3 

Acknowledgements 
Thank you for the participation to: 
GABRYSCH Mario, STUMMER Manfred, BEAUJEAN François, ROME Bertrand, BOŽIKOVIĆ Borna, RUPCIC 
Mladen,  BERNBERG  Stephan,  NORDSTROEM  Claus,  LACONDEMINE  Gérald,  LIEGEY  Clément, 
MAGDELENAT  Perrine,  CAPOBIANCO  Diego,  CENTIOLI  Damiano,  JURCOVIC  Maros,  LENGYEL  Jozef, 
BRADSHAW Christopher, BUTTERFIELD David, HERCOG Predrag, BLAŽICKO Ranko. 

Editing 

NAME 
A. BOROWIAK (PT Coordinator)
M. BARBIERE (Technician/QO)
C. TARRICONE (Technician)
JRC 
(proof reading check with minor remarks) 
Approval 
F. PEKAR (Head of Unit)
Authorization  P. SZYMANSKI (Director)

Editorial 

Review 

Review 

Board 

VERSION 

DATE 

FINAL REV. 0 

30/06/2024 

FINAL REV. 1 

14/10/2024 

FINAL REV. 1 
FINAL REV. 1 

20/09/2024 
22/11/2024 

4 

1  Introduction 

The Directive 2008/50/EC [1] and its last amendments 2015/1480/EC [42] on ambient air quality and 
cleaner air for Europe sets a framework for a harmonised air quality assessment in Europe.  
One important objective of the Directive [1] is that the ambient air quality shall be assessed based 
on common methods and criteria. It deals with the air pollutants sulphur dioxide (SO2), nitrogen dioxide 
(NO2) and nitrogen monoxide (NO), particulate matter, lead, benzene, carbon monoxide (CO) and ozone 
(O3). Among others it specifies the reference methods for measurements and Data Quality Objectives 
(DQOs) for the accuracy of measurements.  
The  European  Commission  (EC)  has  supported  the  development  and  publication  of  reference 
measurement methods for CO [2], SO2 [3], NO-NO2 [4] and O3 [5] as European standards. Appropriate 
calibration  methods  [6],  [7]  and  [8]  have  been  standardised  by  the  International  Organization  for 
Standardization (ISO). 
As foreseen in the Air Quality Directive [1, 42], the European Reference Laboratory of Air Pollution 
(ERLAP)  of  the  Directorate  for  Energy,  Mobility  and  Climate  at  the  Joint  Research  Centre  (JRC) 
organises Proficiency Tests (PT) to assess and improve the status of comparability of measurements 
of National Reference Laboratories (NRL) of the Member States of the European Union.  
The  World Health  Organization  Collaborating  Centre  for  Air  Quality Management  and  Air  Pollution 
Control, Berlin (WHO CC) is carrying out similar activities since 1994 [9] [10], [24], [31], [35], [38], [45] 
and [50], but with a view to obtaining harmonised air quality data for health related studies. Their 
programme integrates within the WHO EURO region, which includes public health institutes and other 
national  institutes  -  especially  from Central  Eastern  Europe,  Caucasus  and  countries  from  Central 
Asia. 
Starting in 2004, it has been decided to bring together the efforts of both the JRC-ERLAP and WHO 
CC and to coordinate activities as far as possible, with a view to optimise resources and improve 
international harmonisation.  
This report deals with the PT that took place in Ispra (IT) in the period 11-14 of March 2024. 
Since 1990 ERLAP has organised PT in order to evaluate the comparability of measurements carried 
out  by  NRLs  and  promote  information  exchange  among  the  expert  laboratories.  Recently,  a  more 
systematic  approach  has  been  adopted,  in  agreement  with  the  Network  of  National  Reference 
Laboratories for Air Quality (AQUILA) [11], aiming to both provide an alert mechanism for the purposes 
of the EC legislation and support the implementation of quality schemes by NRLs.  
ERLAP is accredited to the standard ISO 17043 for the pollutants and EN standard methods used 
during this proficiency test (EN 14211:2012-NO/NO2, EN 14212:2012-SO2, EN 14625:2012-O3, EN 
14626:2012-CO) as proved by the certificates in Annex E. 
The methodology for the organisation of PT was developed by ERLAP in collaboration with AQUILA 
and is described in a paper on the organisation of laboratory comparison exercises for gaseous air 
pollutants [12].  
This evaluation scheme was adopted by AQUILA in December 2008 and has been applied to all PT 
since then. The evaluation scheme implements the z/z’-score method [13] as performance indicator. 
According to the above-mentioned document [12], NRLs with an unsatisfactory performance in the 
z/z’-score  evaluation  (one  unsatisfactory  or  two  questionable  results  per parameter)  are  asked  to 
repeat their participation in the following PT in order to demonstrate remediation measures [12].  
In addition, considering that the evaluation scheme should be useful to participants for accreditation 
according  to  ISO  17025,  they  are  requested  to  include  their  measurement  uncertainty.  Hence, 
participants’  results  (measurement  values  and  uncertainties)  are  also  compared  to  the  reference 
values applying the En–score method [13]. 
Besides  the  proficiency  of  participating  laboratories,  the  repeatability  and  reproducibility  of 
standardised  measurement  methods  [14],  [15]  and  [16]  are  evaluated  as  well.  These  group 
evaluations are useful indicators of trends in measurement quality over different proficiency tests.  

2  Proficiency test organisation 

The PT was announced in September 2023 to the members of the AQUILA network and the WHO 
CC representative. Registration was opened in November 2023 and closed the first week of March 

5 

2024. Every participant, together with the registration confirmation, received a detailed protocol with 
all  the  necessary  information  about  the  PT.  Each  laboratory  was  required  to  bring  their  own 
measurement  instruments,  data  acquisition  equipment  and  travelling  standards  (to  be  used  for 
calibrations or checks during the PT). The participants were invited to arrive on Monday, 11 of March 
2024, for their equipment installation. The calibration of NOx and O3 analysers was carried out the 
morning of the following day and the generation of NOx and O3 gas mixtures started at 11:00 on 
Tuesday. The calibration of SO2 and CO analysers was carried out on Wednesday afternoon and the 
generation of CO and SO2 gas mixtures started at 20:00 of the same day. The test gases generation 
and measurements finished on Thursday at 9:00. 

3   Participants 

All  participants  (Table  1)  were  organisations  dealing  with  the  routine  ambient  air  monitoring  or 
institutions involved in environmental or public health protection. The national representatives came 
from, France, Belgium, Denmark, Croatia, Italy, United Kingdom, Austria, and Slovakia. 

Table 1: List of participating organizations. 

Laboratory Acronym 
AIRPARIF 
CELINE 
DCE 
DHMZ-LIKZ 
EKONERG 
ISPRA 
ERLAP 
NPL 
OOE 
SHI 
Source: JRC 2024 

Complete laboratory name 

Country 

AirParif 
Belgian Interregional Environment Agency 
National Environmental Research Institute 
Meteorological and Hydrological Service - TEST 
Energy and Environmental Protection Institute 
Italian Institute for Environmental Protection and Research 
European Reference Laboratory for Air Pollution 
National Physical Laboratory 
Upper Austria Regional Government 
Slovak Hydrometeorological Institute 

FR 
BE 
DK 
HR 
HR 
IT 
IT 
UK 
AT 
SK 

The following Table 2 reports the manufacturer and model of the instrumentations used by every 
participant during the proficiency test, including those used in the calculation of the reference values. 
The list contains technical information and cannot be considered as an implicit or explicit endorsement 
by the organisers of any specific instrumentation. This list is used to identify the presence of cluster 
during the data evaluation.  

Table 2: List of instruments used by participants. 

Analyser CO 

Analyser NO/NO2 

Analyser O3 

Laboratory  Analyser SO2 
Thermo 43 C 
AIRPARIF 
Thermo FS 43i 
CELINE 
DCE 
Teledyne API T100 
DHMZ-LIKZ  Teledyne API T100 
EKONERG 
ISPRA 
ERLAP 
NPL 
OOE 
SHI 

Horiba APSA 370 
Thermo FS 43 i 
Thermo FS 43 i-TLE  Horiba APMA 370 
Thermo FS 43 i-TLE  Thermo FS 48i 
Thermo FS 43 i-TLE  Horiba APMA 370 
Horiba APMA 360 
Horiba APSA 370 

Thermo electron 48C  Environnement SA AS32M 
Thermo FS 48i 
Teledyne API T300 
Horiba APMA 370 
Horiba APMA 370 
Thermo FS 48i 

Thermo FS 42i 
Teledyne API T200 
Teledyne API T200 
Horiba APNA 370 
Thermo FS 42i 
Thermo FS 42i TL 
Thermo FS 42i 
Horiba APNA 370 

/ 

Environnement SA O342e 
Horiba APOA 370 
Teledyne API T400 
Teledyne API T400 
Horiba APOA 370 
Thermo FS 49i 
Thermo FS TEI 49 i 

/ 

Thermo FS TEI 49 i 
Horiba APOA-360 

Source: JRC 2024 

SHI laboratory did not participate to the testing exercise for NO/NO2 and NPL laboratory for O3. 

6 

4  Preparation of test mixtures 

The ERLAP PT facility has been described in several reports [17], [18]. During this PT, gas mixtures 
were prepared for SO2, CO, O3, NO and NO2 at concentration levels around limit values, critical levels 
and assessment thresholds set by the European Air Quality Directive [1].  

Table 3: Sequence program of generated test gases with indicative pollutant concentrations. 

Run 

Component  Day  Start time  Duration 

NO 

NO2 

O3 

SO2 

CO 

0 

1 

2 

1 

3 

4 

2 

5 

6 

3 

7 

8 

4 

9 

10 

5 

0 

1 

2 

3 

4 

5 

/ 
/ 

1st 

09:00 

2nd 
NO-NO2-O3  2nd 

08:00 

11:00 

NO-NO2 
NO-NO2 
O3 
NO-NO2 
NO-NO2 
O3 
NO-NO2 
NO-NO2 
O3 
NO-NO2 
NO-NO2 
O3 
NO-NO2 
NO-NO2 
O3 
/ 
CO-SO2 
CO-SO2 
CO-SO2 
CO-SO2 
CO-SO2 
CO-SO2 

2nd 

12:00 

2nd 

14:00 

2nd 

16:00 

2nd 

18:00 

2nd 

20:00 

2nd 

22:00 

00:00 

02:00 

04:00 

06:00 

08:00 

10:00 

12:00 

14:00 

16:00 

18:00 

20:00 

21:00 

23:00 

01:00 

03:00 

05:00 

07:00 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

3rd 

4th 

4th 

4th 

4th 

4th 

h 

3 

1 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

1 

2 

2 

2 

2 

2 

2 

Source: JRC 2024 

09:00  END 

nmol/mol 

µmol/mol 

Installation 

Calibration 

Zero air 

0 

10 

0 

10 

0 

25 

7 

200 

4 

120 

60 

20 

180 

90 

120 

Calibration 

X 

X 

X 

X 

Zero air 

120 

0.7 

35 

5 

15 

50 

9 

1 

2 

5 

Zero air (not to be reported) 

200 

190 

30 

20 

60 

45 

480 

280 

300 

180 

7 

The sequence program of generated test concentrations requested is given in Table 3. In addition, the 
PT provider, in agreement with the participants, also requested the concentrations of SO2 indicated in 
Table 3 with an X. 
The test mixtures were prepared by gas dilution from cylinders containing high concentrations of NO, 
SO2, or CO using thermal mass flow controllers [8]. O3 was added using an ozone generator and NO2 
was  produced  applying  the  gas  phase  titration  method  [19]  in  a  condition  of  NO  excess  or  as  a 
presence of NO2 in NO cylinders. 
The participants were required to report three half-hour-mean measurements for each concentration 
level (run) in order to evaluate the repeatability of standardised measurement methods. Zero value 
concentration levels were generated for one hour and was requested to be reported one half-hour-
mean measurement, so no repeatability was calculated for this run.  

8 

 
 
 
 
 
5  The evaluation of laboratory’s measurement proficiency  

To evaluate the participant’s measurement proficiency, the methodology described in ISO 13528 [13] 
was applied and measurement results of ERLAP were used as the reference values [12].  
The traceability of ERLAP’s measurement results and the reference values list are presented in Annex 
A.  
In the following proficiency evaluations, the uncertainty of test gas homogeneity (Annex A) was added 
to the uncertainties of ERLAP’s measurement results. 
In Annex B for each participant and for each run, the values of measurement submitted, the mean 
value, the uncertainties, σpt calculated, z-score or z’-score (z/z’-score) and En-score are reported. The 
data are reported in a table and a graphical format, with all values plotted against the established 
reference value.   
As described in the AQUILA document 37 [12], the proficiency of the participants was assessed by calculating 
two performance indicators (z/z’-score and En-score).  
The  performance  indicators  z/z’-score  verify  if  the  difference  between  the  participants  measured 
value and the reference value remains within the limits of a common criterion. The selection of the 
appropriate indicator, z-score or z’-score, depends on whether the uncertainty of the reference value 
(uref) meets the criterion uref < 0,3σpt from ISO 13528 (paragraph 9.2) [13]. When the criterion is met 
the z-score value is applied, in the other case z’-score is used.  
The  second  performance  indicator  (En-score)  verifies  if  the  difference  between  the  participants 
measured values and reference value remains within the limits of a criterion calculated, from the 
uncertainty of the participant measurement result and the uncertainty of the reference value. 
During  the  evaluation  a  process  of  detection  of  exceptional  errors  (error  during  typing,  slip  in 
performing  the  measurement  or  the  calculation,  wrong  averaging  interval,  malfunction  of 
instrumentation,  etc.)  is  applied.  In  this  procedure  a  data  consistency  evaluation  is  carried  out  as 
described in ISO 13528 [13].  
Before  the  release  of  the  draft  report,  laboratories  showing  clear  blunders  are  requested  to 
investigate the cause of discrepancies and are allowed to correct their results in case of identification 
of exceptional errors. After blunders (exceptional error) data are considered definitive, and z/z’-scores 
calculation is used to estimate the participant performance. 

5.1  z-score and z’–score 

The z/z’- score performance indicators are calculated according to ISO 13528 (par. 9.4 and 9.5) [13] 
as: 

Equation 1 

(𝒙𝒍𝒂𝒃 − 𝑿𝒓𝒆𝒇)

𝒛 =  

𝟐
√𝝈𝒑𝒕

=  

(𝒙𝒍𝒂𝒃 − 𝑿𝒓𝒆𝒇)
√(𝒂  .  
𝑿𝒓𝒆𝒇 + 𝒃)𝟐

                                                                          Equation 2 

(𝒙𝒍𝒂𝒃 − 𝑿𝒓𝒆𝒇)

√(𝒂  .  

𝑿𝒓𝒆𝒇 + 𝒃)𝟐 + 𝒖𝒓𝒆𝒇

𝟐

𝒛′ =  

(𝒙𝒍𝒂𝒃 − 𝑿𝒓𝒆𝒇)
𝟐 + 𝒖𝒓𝒆𝒇

√𝝈𝒑𝒕

𝟐

=  

z = z-score 
z’ = z’-score 
xlab = participant average values 
Xref = reference value 
uref = uncertainty of the reference value 
σpt = Standard deviation for proficiency assessment 
a = slope see table 4 
b = intercept see table 4 

9 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
In the NO2, SO2, CO and O3 EN Standards [2, 3, 4, 5] the uncertainties for calibration gases used in 
ongoing  quality  control  are  prescribed.  In  fact,  it  is  stated  that  maximum  permitted  expanded 
uncertainty for calibration gases at the calibration point (75% of certification range) is 5% and that 
‘zero gas’ shall not give instrument reading higher than the detection limit. The ‘standard deviation 
for proficiency assessment’ (pt) is derived in a fitness-for-purpose manner from requirements given 
in the EN standards, where in place of detection limits criteria, the specifications for purity of zero 
gas used in type approval as defined in EN Standards are taken. 
Over the whole measurement range pt is calculated by linear interpolation between the uncertainty 
of  2.5%  at  the  calibration  point  (75%  of  certification  range)  and  the  uncertainty  at  zero  level 
concentration (“b”). 

Table 4: Standard deviation for proficiency assessment (pt). 

Gas 
SO2 
CO 
O3 
NO 
NO2 

a 
0.022 
0.024 
0.020 
0.024 
0.028 

b (nmol/mol) 
1 
100 
1 
1 
1.4 

Source: JRC 2024 

pt is a linear function of concentration (c) with parameters in Table 4 identified “a” as slope and “b” 
as intercept. 

Equation 3 

𝝈𝒑𝒕
= (𝒂  .  
+ 𝒃 

𝑿𝒓𝒆𝒇)

σpt = Standard deviation for proficiency assessment 
a = slope see table 4 
Xref = reference value 
b = intercept see table 4 

The  parameters  in  table  4  have  been  discussed  and  agreed  with  the  AQUILA  network  through  a 
document named N37 [12].  

The assessment of results in z/z`-score evaluation is made according to the following criteria: 
|z/z’| ≤ 2 are considered satisfactory.  
2 < |z/z’| < 3 are considered questionable. 
|z/z’| ≥ 3 are considered unsatisfactory. Scores falling in this range are very unusual and are taken as 
evidence that an anomaly has occurred that should be investigated and corrected. 

According to z/z’-score calculation,  values  between 2 and 3 are considered  questionable and they 
deserve a specific check.  

In  this  report,  within  all  the  results,  no value  was  found  unsatisfactory  and  only  few values  were 
identified as questionable as reported in table 5.  

10 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table 5: Unsatisfactory/questionable results according to z/z’-score. 

Laboratory 

NPL 
NPL 
NPL 
NPL 
NPL 
EKONERG 

Source: JRC 2024 

Component 

CO 
CO 
NO 
NO 
NO 
NO2 

Run 

2 
5 
5 
6 
10 
7 

z/z'-score           

value 
2.95 
2.57 
-2.30 
-2.16 
-2.29 
-2.76 

z/z'-score 
evaluation 
questionable 
questionable 
questionable 
questionable 
questionable 
questionable 

11 

 
 
 
The overall performance of all participants related to the z/z’-score parameters is shown in Figures 1 
to 5 as colored graphical matrix, where on the x axis the runs (concentration levels) are shown and 
the y-axis the participants are plotted. The figures, through a bi-dimensional graphical representation, 
identifies, with different colors according to the criteria explained above, the participant’s values of 
z/z’-score for each concentration level analysed during the PT.  
The values of z/z’-score calculated for each participant and each tested concentration level (run) are 
reported in the following matrix cells. 

Figure 1: graphical matrix of z/z’-score evaluations of CO measurements in μmol/mol 

Source: JRC 2024 

Underestimated  unsatisfactory  results  are  marked  in  red,  in  yellow  underestimated  questionable 
results,  in  green  satisfactory  results,  in  orange  overestimated  questionable  results  and  in  brown 
overestimated unsatisfactory results.  
For  this  pollutant,  the  graphical  representation  shows  a  general  satisfactory  performance  for  all 
concentration levels generated. 

In figure 1 only 2 measurements of NPL were found questionable.  

12 

 
 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2: graphical matrix of z/z’-score evaluations of NO measurements in nmol/mol 

Source: JRC 2024 

Underestimated  unsatisfactory  results  are  marked  in  red,  in  yellow  underestimated  questionable 
results,  in  green  satisfactory  results,  in  orange  overestimated  questionable  results  and  in  brown 
overestimated unsatisfactory results.   

SHI laboratory did not participate to the measurement of this pollutant. 

For this pollutant, the graphical representation shows a  general  satisfactory performance t for all 
concentration levels generated. 

In figure 2 only 3 measurements of NPL were found questionable.  

13 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3: graphical matrix of z/z’-score evaluations of NO2 measurements in nmol/mol 

Source: JRC 2024 

Underestimated  unsatisfactory  results  are  marked  in  red,  in  yellow  underestimated  questionable 
results,  in  green  satisfactory  results,  in  orange  overestimated  questionable  results  and  in  brown 
overestimated unsatisfactory results.  
SHI laboratory did not participate to the measurement of this pollutant. 

For this pollutant, the graphical representation shows a general satisfactory performance of every 
participant for all concentration levels generated. 

In figure 3 only 1 measurement of EKONERG was found questionable.  

14 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 4: graphical matrix of z/z’-score evaluations of O3 measurements in nmol/mol 

Source: JRC 2024 

z/z’-score values are given for each participant and each tested concentration level (run).  
Underestimated  unsatisfactory  results  are  marked  in  red,  in  yellow  underestimated  questionable 
results,  in  green  satisfactory  results,  in  orange  overestimated  questionable  results  and  in  brown 
overestimated unsatisfactory results.   

NPL laboratory did not participate in the measurement of this pollutant. 

For this pollutant, the graphical representation shows a satisfactory performance of every participant 
for all concentration levels generated. 

15 

 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 5: graphical matrix of z/z’-score evaluations of SO2 measurements in nmol/mol 

Source: JRC 2024 

z/z’-score values are given for each participant and each tested concentration level (run).  
Underestimated  unsatisfactory  results  are  marked  in  red,  in  yellow  underestimated  questionable 
results,  in  green  satisfactory  results,  in  orange  overestimated  questionable  results  and  in  brown 
overestimated unsatisfactory results.   

For this pollutant, the graphical representation shows a satisfactory performance of every participant 
for all concentration levels generated. 

16 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5.2  En-score  

In order to evaluate the participant’s ability to have results close to the reference values within their 
reported uncertainties, the En-score parameters (En) were calculated according to:  

Equation 4 

𝒙𝒍𝒂𝒃 − 𝑿𝒓𝒆𝒇

𝑬𝒏 =

√𝑼𝒍𝒂𝒃

𝟐 + 𝑼𝒓𝒆𝒇

𝟐

En = En-score 
xlab = participant average values 
Xref = reference value 
Ulab= expanded uncertainty of the participants 
Uref= expanded uncertainty of the reference value 

The overall performance of all participants related to the En-score parameters is shown in Figures 6 
to 15 as colored graphical matrix, where on the x-axis are the runs (concentration levels) shown and 
the y-axis the participants are plotted. The figures, through a bi-dimensional graphical representation, 
identify,  with  different  colors,  the  participant’s  values  of  En-score  for  each  concentration  level 
analysed  during  the  PT.  Results  with  |En-score|<1  are  considered  satisfactory,  all  the  others  are 
unsatisfactory. The values of En-score, calculated for each participant, are reported in the matrix cells. 
At the bottom of each figure, the legend explains with different colors the identification of the results: 
in red are marked underestimated unsatisfactory results, in green satisfactory results and in brown 
overestimated unsatisfactory results.  

Table 6: Unsatisfactory/questionable results according to En-score. 

Laboratory 
NPL 
AIRPARIF 
NPL 
AIRPARIF 
NPL 
AIRPARIF 
NPL 
AIRPARIF 
NPL 
NPL 
NPL 
NPL 
NPL 
NPL 
DCE 
DCE 
DCE 
NPL 
DCE 
EKONERG 
DCE 
DCE 
EKONERG 
DCE 
AIRPARIF 
              Source: JRC 2024 

Component 
CO 
CO 
CO 
CO 
CO 
CO 
CO 
CO 
CO 
NO 
NO 
NO 
NO 
NO 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
SO2 

Run 
1 
2 
2 
3 
3 
4 
4 
5 
5 
3 
4 
5 
6 
10 
1 
2 
6 
6 
7 
7 
8 
9 
9 
10 
1 

En-score 
1.90 
3.88 
1.60 
1.86 
1.81 
2.51 
1.55 
3.86 
1.72 
-1.16 
-1.15 
-1.71 
-2.06 
-1.28 
-1.21 
-1.53 
-1.24 
-1.06 
-1.05 
-1.70 
-1.00 
-1.19 
-1.20 
-1.39 
-1.26 

En evaluation 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 
unsatisfactory 

17 

 
 
              
                                        
 
 
 
 
 
 
 
The  En  evaluation  reported  in  Figures  6,  8,  10,  12,  14  underline  some  unsatisfactory  results  for 
different parameters and concentrations, as reported in table 6. 
In Annex B, from table 11 to 19 are reported all En values calculated for each participant, parameter 
and concentration level. 
The  differences  between  individual  participants’  values  and  reference  values  (bias  xlab-Xref)  are 
evaluated and presented for each concentration level in the figures 7, 9, 11, 13, 15.  
The expanded uncertainties reported by participants are shown in the graphs for each run as error 
bar.  
These plots represent also the En-score evaluations where, considering the En criterion (|En-score|<1), 
all results are satisfactory if the error bars cross the red line representing the reference value.  
Reported standard uncertainties of the participants, larger than the “standard deviation for proficiency 
assessments” (pt), are considered not fit-for-purpose (see Annex B).  

18 

 
 
 
Figure 6: En-score for CO measurements in matrix view 

Source: JRC 2024 

Figure 7: Bias of participant’s CO measurement results in μmol/mol 

Source: JRC 2024 

Laboratories NPL and AIRPARIF overestimate the measurement and uncertainties for this pollutant 
obtaining unsatisfactory En values (in brown). 

19 

 
 
 
 
 
 
 
 
 
 
 
 
Figure 8: En-score for NO measurements in nmol/mol in matrix view 

Source: JRC 2024 

Figure 9: Bias of participant’s NO measurement results in nmol/mol 

Slovak Republic laboratory (SHI) did not participate to the PT for this pollutant.  

Source: JRC 2024 

For  this  pollutant,  both  graphical  representations  show  a  satisfactory  performance  from  every 
participant.  Only  for  NPL  laboratory,  in  run  3-4-5-6-10,  can  a  measurement  underestimation  be 
observed and due to the very small uncertainty reported the En-score is unsatisfactory. 

20 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 10: En-score for NO2 measurements in nmol/mol in matrix view 

Source: JRC 2024 

Figure 11: Bias of participant’s NO2 measurement results in nmol/mol.  

Source: JRC 2024 

For this pollutant, both graphical representations show a good performance for around 90% of all 
results.  For EKONERG in run 7 and 9, NPL in run 6 and DCE in run 1, 2, 6, 7, 8, 9 and 10, can be 
observed a En unsatisfactory.    

21 

 
 
 
 
  
 
 
 
 
 
 
 
 
 
Figure 12: En-score for O3 measurements in nmol/mol in matrix view 

Source: JRC 2024 

Figure 13: Bias of participant’s O3 measurement results in nmol/mol 

Source: JRC 2024 

National Physics laboratory (NPL) did not participate to the PT for this pollutant.  

For this pollutant, both graphical representations show a general satisfactory performance of every 
participant. 

22 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 14: En-score for SO2 measurements in nmol/mol in matrix view 

Source: JRC 2024 

Figure 15: Bias of participant’s SO2 measurement results in nmol/mol 

Source: JRC 2024 

For this pollutant, both graphical representations show a general satisfactory performance of every 
participant. 
AIRPARIF,  in  run  1,  shows  an  underestimated  measurement  reported  and  the  EN-score  value  is 
unsatisfactory.    

23 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
6  Conclusions 

The  proficiency  evaluation  scheme  has  assessed  the  participants’  measured  values  and  their 
evaluated uncertainties through calculating two performance indicators (z/z’-score and En-score).  

z/z’-scores calculation is used to estimate the participant performance.  

Statistical unsatisfactory results obtained at this stage are not considered as extraordinary errors, 
but due to significant difference in participant’s standard operating procedure.  
The precision of standardised measurement methods reported in Annex C are calculated using  the 
whole data pool submitted.  
In this exercise 98.2% of the results in the z/z’-score evaluations are satisfactory. 
Regarding  the  En-score  parameter  92.5%  of  the  results  are  found  satisfactory  and  7.5% 
unsatisfactory according to the limits explained in paragraph 5.2.  

As  in  previous  PT,  the  adopted  criteria  for  high  concentrations  were  the  standard  deviations  for 
proficiency assessment, deriving from the European Standards’ uncertainty requirements.   
The reproducibility standard deviation obtained and described in Annex C, like previous PTs [20], [21], 
[22], [23], [24], [25], [33], [34], [35], [36], [37], [38], [39], [40], [41], [43], [44], [45], [46], [47], [48], [49], 
[50], [51], [52], [53], [54] and [55] is comparable to the mentioned criteria. On the other hand, the 
uncertainty criteria for zero levels were those set in AQUILA’s position paper [12].  
The following figure 16 is reporting a histogram representation of the overview of the performance 
indicator z/z’-score results obtained in this PT. All charts indicate the results of each participant for 
every component analysed at all concentrations generated.  
Generally,  the  overall  performance  of  all  laboratories  is  good  and  no  unsatisfactory  results  are 
identified for z/z’-score indicator while a small number of values were found unsatisfactory for the 
En-score.    
The result of this PT is in line with the performances of previous years as shown by the following 
Table 7 where the results of z/z’-score in all PT organized in JRC Ispra site from 2005 till 2024 are 
presented. 

24 

 
 
 
 
 
 
 
 
Figure 16: Overview about z/z’-score final evaluation 

Source: JRC 2024 

25 

 
 
 
 
 
 
 
 
Table 7: z/z’-score summary results of PT organized in JRC Ispra site from 2005 to 2024. 

Site 

Satisfactory (%) 

Questionable (%) 

Unsatisfactory (%) 

PT 

Jun_05 

Jun_07 

Apr_08 

Ispra (IT) 

Ispra (IT) 

Ispra (IT) 

Oct_08_I 

Ispra (IT) 

Oct_08_II 

Ispra (IT) 

Oct_09 

Jun_10 

Sep_11 

Oct_11 

Jun_12 

Sep_13 

Oct_13 

May_14 

Ispra (IT) 

Ispra (IT) 

Ispra (IT) 

Ispra (IT) 

Ispra (IT) 

Ispra (IT) 

Ispra (IT) 

Ispra (IT) 

Oct_15_I 

Ispra (IT) 

Oct_15_II 

Ispra (IT) 

Jun_16 

Ispra (IT) 

Jun_17_I 

Ispra (IT) 

Jun_17_II 

Ispra (IT) 

Jun_18 

Ispra (IT) 

May_19_I 

Ispra (IT) 

May_19_II 

Ispra (IT) 

Mar-22(I) 

Ispra (IT) 

Mar_22_II 

Ispra (IT) 

Apr_22_III 

Ispra (IT) 

Mar_23 

Mar_24 

Ispra (IT) 

Ispra (IT) 

Source: JRC 2024 

3.0 

0.3 

4.1 

2.9 

0.0 

0.0 

0.0 

0.3 

0.0 

0.0 

0.0 

0.0 

1.1 

0.0 

2.2 

0.0 

0.4 

1.9 

0.0 

0.0 

0.0 

1.7 

0 

5.3 

0 

0 

94.7 

97.8 

93.8 

92.9 

97.0 

98.2 

97.0 

99.4 

98.7 

100.0 

100.0 

99.3 

98.1 

99.4 

93.7 

100 

98.9 

96.2 

100 

98.7 

97.5 

97.2 

99.3 

91.5 

100 

98.2 

2.3 

1.9 

2.1 

4.2 

3.0 

1.8 

3.0 

0.3 

1.3 

0.0 

0.0 

0.7 

0.7 

0.6 

4.1 

0.0 

0.7 

1.9 

0.0 

1.3 

2.5 

1.1 

0.7 

3.2 

0 

1.8 

26 

 
 
 
 
 
 
During this PT, in agreement with all participants, an extra set of values has been asked to be reported. 
In order to verify the impact of the interference of NO/NO2 during SO2 measurement, all participants 
quantified sulphur dioxide while, in the sampling tube, was generated high concentration of NO and 
NO2. In table 8 are summarised the reading of all laboratories and the correspondent instrument used. 
In annex E of the EN 14212 standard is described the type approval required for the instrument used 
for SO2 analysis. In table E.1 of this document are listed the relevant performance characteristics and 
criteria for SO2 measurement in presence of NO and NO2 (for NO with concentration 500 nmol/mol 
SO2 reading ≤ 5.0 nmol/mol, for NO2 with concentration 200 nmol/mol SO2 reading ≤ 5.0 nmol/mol).     
This test is pure indicative and does not have the goal of reaching any conclusion about any of the 
instrumentation used. 

Table 8: SO2 measurement during NO gas generation. 

ERLAP1 

ERLAP2 

ISPRA 

OOE 

NPL 

EKONERG 

IRCEL-
CELINE 

AIRPARIF 

DCE 

DHMZ-
LIKZ 

SHMU 

Run 

7 
7 
7 
8 
8 
8 
9 
9 
9 
10 
10 
10 

NO ref 
value 

479 
479 
478 
250 
252 
253 
300 
300 
300 
165 
165 
165 

3.2 
3.2 
3.2 
1.7 
1.8 
1.7 
2.0 
2.0 
2.0 
1.3 
1.2 
1.2 

2.3 
2.4 
2.4 
1.5 
1.5 
1.5 
1.8 
1.8 
1.8 
1.1 
1.0 
1.0 

3.5 
3.5 
3.7 
2 
1.7 
2 
2.3 
2.4 
2.7 
1.7 
1.7 
1.6 

3.2 
3.2 
3.2 
1.7 
1.7 
1.7 
2 
2 
2 
1.1 
1.1 
1.1 

2.5 
2.5 
2.4 
1.3 
1.3 
1.3 
1.6 
1.5 
1.5 
0.92 
0.84 
0.88 

SO2 nmol/mol 

2.09 
2.36 
2.33 
1.01 
0.76 
0.87 
1.29 
1.47 
1.5 
0.8 
0.82 
0.87 

horiba 
APSA -
370 

3.1 
3.1 
3.1 
1.6 
1.7 
1.7 
2 
2 
1.9 
1.1 
1.1 
1.1 

2.7 
2.7 
2.7 
1.4 
1.4 
1.4 
1.7 
1.7 
1.7 
1 
1 
1 

6.5 
6.46 
6.41 
3.46 
3.47 
3.47 
3.96 
3.96 
4.01 
2.15 
2.1 
2.11 

2.4 
2.4 
2.4 
1.3 
1.3 
1.3 
1.6 
1.6 
1.6 
1 

1.69 
1.63 
1.59 
1.01 
1.23 
1.14 
1.05 
0.97 
1.01 
1.0 
0.89  0.95 
0.58  0.96 

Thermo 
43i 

Thermo 43C 

Teledyne 
API 
T100 

Teledyne 
API 
T100 

Horiba 
APSA-
370 

Instrument 

Thermo 
FS 
43iTLE 

horiba 
APSA -
370 

Thermo 
FS 43i 

Thermo 
FS 
43iTLE 

Thermo 
43i 

  Source: JRC 2024 

27 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Measurements of inorganic gaseous pollutants (SO2, CO, O3, NO and NO2) in filtered ambient 
air, 04-07 April 2022 Ispra, Italy. EUR 31348 

56. Barbiere  M.,  Lagler  F.,  Tarricone  C.,  Borowiak  A.,  PROFICIENCY  TESTING  SCHEME, 
Measurements of inorganic gaseous pollutants (SO2, CO, O3, NO and NO2) in filtered ambient 
air, 27-30 March 2023 Ispra, Italy. EUR 31694 

30 

 
 
 
 
 
List of abbreviations 

AQUILA 
BIPM 
CEN 
CO 
CRM 
DQO 
ERLAP 
EC 
GPT 
PT 
ISO 
JRC 
NO 
NO2 
NOX 
NRL 
O3 
PT 
SO2 
VDI 
WHO-CC 

Network of National Reference Laboratories for Air Quality 
Bureau international des poids et mesures 
European Committee for Standardization 
Carbon monoxide 
Certified Reference Material 
Data Quality Objective 
European Reference Laboratory for Air Pollution 
European Commission 
Gas Phase Titration 
Proficiency Test 
International Organization for Standardization 
Joint Research Centre 
Nitrogen monoxide 
Nitrogen dioxide  
The oxides of nitrogen, the sum of NO and NO2  
National Reference Laboratory 
Ozone 
Proficiency Test 
Sulphur dioxide 
Verein Deutscher Ingenieure 
World Health Organization Collaborating Centre for Air Quality Management and Air 
Pollution Control, Berlin 

31 

 
 
 
 
 
 
 
Mathematical Symbols 

Ec 
En 
r 
R 
σpt 
x* 
s* 
sr 
sR 
Uref 
Ulab 
uref 
Xref 
xlab 

z’ 
z 

Converter efficiency for NO analyser 
En–score statistic (ISO 13528) 
repeatability limit (ISO 5725) 
reproducibility limit (ISO 5725) 
standard deviation for proficiency assessment (ISO 13528) 
robust average (Annex C ISO 13528) 
robust standard deviation (Annex C ISO 13528) 
estimate of repeatability variance (ISO 5725) 
estimate of reproducibility variance (ISO 5725) 
expanded uncertainty of the reference value (ISO 13528) 
expanded uncertainty of the participant’s value (ISO 13528) 
standard uncertainty of the reference value (ISO 13528) 
reference value (ISO 13528) 
average of 3 values reported by the participant i (for each parameter and concentration 
level) 
z’-score statistic (ISO 13528) 
z-score statistic (ISO 13528) 

32 

 
 
 
 
 
 
List of figures 
Figure 1: graphical matrix of z/z’-score evaluations of CO measurements in μmol/mol ................................................ 12 
Figure 2: graphical matrix of z/z’-score evaluations of NO measurements in nmol/mol ................................................ 13 
Figure 3: graphical matrix of z/z’-score evaluations of NO2 measurements in nmol/mol .............................................. 14 
Figure 4: graphical matrix of z/z’-score evaluations of O3 measurements in nmol/mol ................................................. 15 
Figure 5: graphical matrix of z/z’-score evaluations of SO2 measurements in nmol/mol .............................................. 16 
Figure 6: En-score for CO measurements in matrix view .................................................................................................................... 19 
Figure 7: Bias of participant’s CO measurement results in μmol/mol ......................................................................................... 19 
Figure 8: En-score for NO measurements in nmol/mol in matrix view ....................................................................................... 20 
Figure 9: Bias of participant’s NO measurement results in nmol/mol ........................................................................................ 20 
Figure 10: En-score for NO2 measurements in nmol/mol in matrix view .................................................................................. 21 
Figure 11: Bias of participant’s NO2 measurement results in nmol/mol. .................................................................................. 21 
Figure 12: En-score for O3 measurements in nmol/mol in matrix view ...................................................................................... 22 
Figure 13: Bias of participant’s O3 measurement results in nmol/mol ....................................................................................... 22 
Figure 14: En-score for SO2 measurements in nmol/mol in matrix view ................................................................................... 23 
Figure 15: Bias of participant’s SO2 measurement results in nmol/mol .................................................................................... 23 
Figure 16: Overview about z/z’-score final evaluation .......................................................................................................................... 25 
Figure 17: Graphical report of results of Laboratory AirParif (France) ....................................................................................... 40 
Figure 18: Graphical report of results of Laboratory Celine (Belgium). ..................................................................................... 42 
Figure 19: Graphical report of results of Laboratory DCE (Denmark). ........................................................................................ 44 
Figure 20: Graphical report of results of Laboratory DHMZ-LIKZ (Croatia). ............................................................................ 46 
Figure 21: Graphical report of results of Laboratory EKONERG (Croatia). ............................................................................... 48 
Figure 22: Graphical report of results of Laboratory ISPRA (Italy). ............................................................................................... 50 
Figure 23: Graphical report of results of Laboratory NPL (United Kingdom). ........................................................................ 52 
Figure 24: Graphical report of results of Laboratory OOE (Austria). ............................................................................................ 54 
Figure 25: Graphical report of results of Laboratory SHI (Slovak Republic). ........................................................................... 56 
Figure 26: The R and r of SO2 standard measurement method as a function of concentration. .............................. 60 
Figure 27: The R and r of CO standard measurement method as a function of concentration. ................................ 61 
Figure 28: The R and r of O3 standard measurement method as a function of concentration. ................................. 62 
Figure 29: The R and r of NO standard measurement method as a function of concentration. ................................ 63 
Figure 30: The R and r of NO2 standard measurement method as a function of concentration. .............................. 64 

33 

List of tables 
Table 1: List of participating organizations. .....................................................................................................................................................6 
Table 2: List of instruments used by participants. .......................................................................................................................................6 
Table 3: Sequence program of generated test gases with indicative pollutant concentrations. ....................................7 
Table 4: Standard deviation for proficiency assessment (pt). ......................................................................................................... 10 
Table 5: Unsatisfactory/questionable results according to z/z’-score. ......................................................................................... 11 
Table 6: Unsatisfactory/questionable results according to En-score. .......................................................................................... 17 
Table 7: z/z’-score summary results of PT organized in JRC Ispra site from 2005 to 2024. ....................................... 26 
Table 8: SO2 measurement during NO gas generation. ........................................................................................................................ 27 
Table 9: Reference values (X) ................................................................................................................................................................................ 36 
Table 10: Homogeneity test. .................................................................................................................................................................................. 38 
Table 11: Reported values, uncertainties and performance evaluation results for Laboratory AirParif (France).
 .................................................................................................................................................................................................................................................... 41 
Table 12: Reported values, uncertainties and performance evaluation results for Laboratory Celine (Belgium).
 .................................................................................................................................................................................................................................................... 43 
Table 13: Reported values, uncertainties and performance evaluation results for Laboratory DCE (Denmark).
 .................................................................................................................................................................................................................................................... 45 
Table 14: Reported values, uncertainties and performance evaluation results for Laboratory DHMZ-LIKZ 
(Croatia)................................................................................................................................................................................................................................. 47 
Table 15: Reported values, uncertainties and performance evaluation results for Laboratory EKONERG 
(Croatia)................................................................................................................................................................................................................................. 49 
Table 16: Reported values, uncertainties and performance evaluation results for ISPRA (Italy). .............................. 51 
Table 17: Reported values, uncertainties and performance evaluation results for NPL (United Kingdom). ....... 53 
Table 18: Reported values, uncertainties and performance evaluation results for OOE (Austria). ........................... 55 
Table 19: Reported values, uncertainties and performance evaluation results for SHI (Slovak Republic). ......... 57 
Table 20: Critical values of t used in the repeatability (r) and reproducibility (R) evaluation. ..................................... 59 

34 

Annex A. Reference values 
The reference values of tested concentration levels (run) were derived, as an average of two set of 
instruments, from ERLAP’s measurements, which are calibrated against the certified reference values 
of CRMs and are traceable to international standards. In this perspective the reference values are 
defined as described in the ISO 13528 [13].  
To foster its reference function ERLAP is participating regularly to key comparisons of the Gas Analysis 
Working Group within the framework of BIPM’s CCQM and it is yearly confirming the compliance to 
standard to ISO 17043, through an annual audit run by the competent Italian accreditation body (see 
annex E). 
During  this  PT  ERLAP’s  SO2,  CO  and  NO  analysers  were  calibrated  according  to  the  methodology 
described  in  the  standard ISO  6143  [6].  Reference  gas  mixtures  were produced  from  the primary 
reference materials (produced and certified by NMi Van Swinden Laboratorium) by dynamic dilution 
method using mass flow controllers [8].  
All flows were verified with a certified molbloc/molbox1 system. For O3 measurements, the analysers 
were  calibrated  using  the  JRC  SRP42  primary  standard  (constructed  by  NIST),  which  has  been 
compared  to  BIPM  primary  standard  [26].  The  photometer  absorption  cross  section  uncertainty 
(1.06%) was included in the uncertainty budget [27], [28].  
The calibration functions parameters and uncertainties associated were carried out using VDI 2449 
Part3 [30]. The contribution to the uncertainty budget “uref” include repeatability, certified reference 
material standard uncertainty, drift and homogeneity. For extending calibration from the NO to NO2 
channel of NOX analyser, the GPT test was performed to establish the efficiency of NO2-converter and 
its contribution is added to the uncertainty.  
In table 9 the reference values are reported together with their uncertainties. 

35 

Ref exp 
unc 
0.02 
0.02 
0.08 
0.02 
0.02 
0.04 
1.4 
2.5 
2.4 
1.5 
1.5 
1.6 
1.5 
5.0 
2.9 
3.3 
2.2 
1.5 
2.0 
2.0 
1.5 
1.5 
1.5 
1.6 
3.6 
3.9 
2.6 
2.7 
0.43 
0.95 
0.45 
2.8 
1.4 
2.0 
1.0 
2.1 
1.2 
1.2 
1.1 
1.3 

sigmaPT 

Unit 

z or z' 

0.10 
0.11 
0.31 
0.12 
0.15 
0.22 
1.00 
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4 
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00 
2.3 
1.4 
5.0 
2.9 
3.6 
1.00 
3.8 
1.9 
1.1 
1.5 
2.2 

µmol/mol 
µmol/mol 
µmol/mol 
µmol/mol 
µmol/mol 
µmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 

z 
z 
z 
z 
z 
z 
z’ 
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z 
z 
z 
z 
z 
z 
z’ 
z 
z’ 
z’ 
z’ 
z 

Table 9: Reference values (X) 

Component 

CO 
CO 
CO 
CO 
CO 
CO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3 
O3 
O3 
O3 
O3 
O3 
SO2 
SO2 
SO2 
SO2 
SO2 
SO2 
Source: JRC 2024 

Run 

Ref value 

Ref unc 

0 
1 
2 
3 
4 
5 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0 
1 
2 
3 
4 
5 
0 
1 
2 
3 
4 
5 

0.00 
0.62 
8.8 
0.92 
1.9 
4.8 
0.20 
202 
193 
31 
21 
61 
42 
478 
252 
300 
165 
-0.01
0.28 
10 
0.09 
9.7 
-0.04
29 
6.7 
234 
3.8 
139 
-0.10
66 
21 
197 
97 
129 
0.20 
127 
41 
5.2 
21 
56 

0.01 
0.01 
0.04 
0.01 
0.01 
0.02 
0.72 
1.2 
1.2 
0.74 
0.73 
0.78 
0.76 
2.5 
1.5 
1.7 
1.1 
0.73 
1.0 
1.0 
0.74 
0.74 
0.76 
0.78 
1.8 
1.9 
1.3 
1.3 
0.21 
0.47 
0.22 
1.4 
0.68 
0.99 
0.50 
1.0 
0.59 
0.59 
0.54 
0.66 

36 

Homogeneity 
This type of PT for inorganic gases foresees a generation in real time of gas mixture that is analysed 
immediately. The gas is not stored  nor manipulated before the participant’s measurement. In this 
condition, the stability and homogeneity verification of test item is not fully applicable.  

ERLAP  verify  the  homogeneity  of  the  mixture  gases,  using  a  ozone  mixture  because  is  the  most 
reactive gas. The readings of two identical analysers (Thermo Fisher Scientific 49i), calibrated against 
an SRP photometer primary standard, are compered, while an ozone concentration is running in the 
sampling  line.  The  sampling  line  has  20  positions  with  2  connection  ports  in  each  position.  An 
analysers  measures  ozone  at  the  port  20a,  the  last  of  the  sampling  line,  and  the  other  one 
sequentially in the other ports. 

The test is considered acceptable when the absolute difference between the initial measurement and 
all  the  others  is  below  0.5%(during this  PT  equivalent  to  2,18  nmol/mol).  Assuming  a  rectangular 
distribution, it constitutes an uncertainty of 0.3% of each concentration level This test is performed 
before each inorganic gas PT organised by ERLAP in Ispra.    
The homogeneity results are reported in Table10.  

37 

 
 
 
 
 
 
 
 
 
Table 10: Homogeneity test. 
Bench  
position 
20a/b 
1a 
1b 
2a 
2b 
3a 
3b 
4a 
4b 
5a 
5b 
6a 
6b 
7a 
7b 
8a 
8b 
9a 
9b 
10a 
10b 
11a 
11b 
12a 
12b 
13a 
13b 
14a 
14b 
15a 
15b 
16a 
16b 
17a 
17b 
18a 
18b 
19a 
19b 
20a 
20b 
21a 
21b 
22a 
22b 
22c 
22d 
23a 
23b 
23c 
23d 
Source: JRC 2024 

Sample 
Analyzer SN14 
447 
446 
446 
447 
448 
449 
449 
448 
449 
449 
449 
448 
448 
448 
450 
449 
449 
450 
450 
449 
449 
449 
450 
450 
450 
450 
450 
450 
450 
450 
450 
450 
449 
451 
451 
450 
450 
451 
450 
450 
451 
452 
451 
450 
450 
450 
449 
448 
450 
449 
449 

Ref 
Analyzer SN15 
436 
436 
435 
436 
436 
437 
437 
436 
438 
437 
438 
438 
438 
438 
438 
438 
438 
439 
439 
438 
438 
438 
438 
439 
439 
439 
439 
439 
439 
438 
439 
439 
438 
438 
439 
439 
438 
439 
439 
439 
439 
440 
439 
439 
439 
439 
439 
439 
438 
439 
438 

Difference 

0.00 
-1.00 
0.00 
0.00 
0.50 
1.00 
1.00 
0.80 
0.30 
0.60 
0.40 
-1.10 
-1.00 
-1.00 
0.20 
-0.40 
-0.40 
0.40 
0.40 
-0.40 
-0.50 
-0.50 
0.50 
0.40 
0.40 
0.30 
0.30 
0.20 
0.20 
1.00 
0.40 
0.40 
-0.30 
1.7 
1.3 
0.30 
0.50 
1.3 
0.30 
0.70 
1.4 
1.00 
0.60 
-0.40 
0.20 
0.40 
-0.60 
-2.00 
1.00 
-1.10 
-0.50 

38 

Unit 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 
nmol/mol 

<0.5% passed? 

Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 

 
 
Annex B: Results reported by participants 
In this annex are reported all results submitted by the participants and they are presented both as 
graphs and tables. 
In  the  graph,  from  the  left  and  top  down,  for  each  pollutant  is  represented  the  submitted 
measurement  result  compared  to  the  reference  value,  the  z/z’-score  and  En-score  calculated  and 
compared to criteria explained in paragraph 5.  
In the table are reported all values obtained from the data evaluation of this PT.  
From the left “Runs” indicate all gas mixture concentrations generated. In the column “Lab mean 
value” is shown the average of the 3 results (Step 1,2,3) representing a measurement of 30 minutes 
each that every laboratory is asked to report.  
The combined and expanded uncertainties of the participant are listed in column “Lab unc” and “Lab 
unc exp”, expressed in mol/mol units.  
“sigmaPT” column shows the results of the calculation described in paragraph 5.1 using the parameter 
in Table 4. In column “z/z’-score value” and “En-score” are listed the performance indicators values 
obtained by each participant. “z/z’ selection” column indicates for each pollutant’s run if it was used 
z or z’ according to the criteria explained in paragraph 5.  

39 

Figure 17: Graphical report of results of Laboratory AirParif (France) 

Source: JRC 2024 

40 

Table 11: Reported values, uncertainties and performance evaluation results for Laboratory AirParif (France). 

AIRPARIF 

Lab 
mean 
value 
0.10
0.69 
9.4 
1.1 
2.2 
5.2 
0.00
199 
190 
30 
21 
59 
40 
468 
246 
293 
162 
0.00
1.5 
11 
1.8 
11 
0.57 
29 
6.5 
229 
3.5 
137 
0.00
65 
21 
197 
97 
130 
0.10
122 
40 
4.8 
20 
54 

Step 
1

Step 
2

Step 
3

0.10
0.69 
9.3 
1.1 
2.2 
5.2 
0.00
199 
190 
30 
21 
59 
40 
467 
246 
293 
162 
0.00
1.1 
10 
1.1 
11 
0.50 
30 
6.7 
229 
3.6 
136 
0.00
65 
21 
197 
97 
130 
0.10
122 
40 
4.3 
20 
54 

0.69 
9.4 
1.1 
2.1 
5.2 

199 
190 
30 
21 
59 
40 
468 
246 
293 
162 

1.9 
11 
2.0 
11 
0.60 
29 
6.6 
228 
3.5 
137 

65 
21 
197 
97 
129 

122 
40 
5.0 
20 
54 

0.69 
9.4 
1.1 
2.2 
5.2 

199 
190 
30 
21 
59 
40 
468 
247 
294 
162 

1.5 
11 
2.2 
10 
0.60 
29 
6.1 
228 
3.3 
137 

65 
21 
198 
97 
129 

122 
40 
5.2 
20 
54 

Lab 
unc

0.06
0.05 
0.06 
0.05 
0.05 
0.04 
0.60
2.2 
2.1 
0.70 
0.90 
0.90 
0.80 
5.2 
2.7 
3.2 
1.8 
0.60
0.90 
0.90 
0.90 
0.90 
0.60 
0.80 
0.90 
2.6 
0.90 
1.7 
0.60
1.3 
0.70 
2.4 
1.3 
1.7 
0.60
1.6 
0.80 
0.90 
0.70 
0.90 

unit

Lab 
unc 
exp 
µmol/mol
0.12
0.11  µmol/mol 
0.13  µmol/mol 
0.11  µmol/mol 
0.10  µmol/mol 
0.09  µmol/mol 
nmol/mol
1.2
nmol/mol 
4.3 
nmol/mol 
4.1 
nmol/mol 
1.4 
nmol/mol 
1.8 
nmol/mol 
1.7 
nmol/mol 
1.5 
nmol/mol 
10 
nmol/mol 
5.3 
nmol/mol 
6.3 
nmol/mol 
3.6 
nmol/mol
1.2
nmol/mol 
1.9 
nmol/mol 
1.9 
nmol/mol 
1.9 
nmol/mol 
1.9 
nmol/mol 
1.2 
nmol/mol 
1.5 
nmol/mol 
1.8 
nmol/mol 
5.2 
nmol/mol 
1.8 
nmol/mol 
3.3 
nmol/mol
1.2
nmol/mol 
2.6 
nmol/mol 
1.4 
nmol/mol 
4.8 
nmol/mol 
2.6 
nmol/mol 
3.4 
nmol/mol
1.2
nmol/mol 
3.2 
nmol/mol 
1.6 
nmol/mol 
1.7 
nmol/mol 
1.3 
nmol/mol 
1.8 

sigmaPT

0.10
0.11 
0.31 
0.12 
0.15 
0.22 
1.00
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00
2.3 
1.4 
5.0 
2.9 
3.6 
1.00
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
1.0
0.61 
1.9 
1.7 
1.7 
1.8 
-0.16
-0.61
-0.59
-0.39
-0.35
-0.62
-0.52
-0.83
-0.75
-0.79
-0.66
0.01
0.70 
0.35 
1.1 
0.57 
0.38 
0.02 
-0.08
-0.71
-0.17
-0.42
0.10
-0.27
-0.08
-0.02
0.03 
0.20 
-0.09
-1.27
-0.74
-0.30
-0.57
-0.90

z/z' 
selection

En-
score

z
z 
z 
z 
z 
z 
z’
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z
z 
z 
z 
z 
z 
z’
z 
z’ 
z’ 
z’ 
z 

0.87
0.63 
3.9 
1.9 
2.5 
3.9 
-0.11
-0.71
-0.70
-0.36
-0.25
-0.69
-0.66
-0.90
-0.87
-0.90
-0.78
0.01
0.44 
0.25 
0.70 
0.43 
0.31 
0.02 
-0.05
-0.88
-0.11
-0.53
0.08
-0.23
-0.08
-0.02
0.03 
0.18 
-0.07
-1.26
-0.74
-0.19
-0.53
-0.90

Component

Run

CO
CO 
CO 
CO 
CO 
CO 
NO
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3
O3 
O3 
O3 
O3 
O3 
SO2
SO2 
SO2 
SO2 
SO2 
SO2 

0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 

Source: JRC 2024 

41 

 Figure 18: Graphical report of results of Laboratory Celine (Belgium). 

Source: JRC 2024 

42 

Table 12: Reported values, uncertainties and performance evaluation results for Laboratory Celine (Belgium). 

CELINE 

Lab 
mean 
value 
-0.01
0.64 
8.9
0.91 
1.9 
4.9 
-0.10
204 
194 
31 
21 
62 
42 
484 
254 
302 
166 
0.00
0.17 
9.8 
0.03 
9.9 
-0.03
30 
5.4 
237 
2.9 
140 
0.10
66 
22 
199 
98 
130 
0.00
124 
40 
5.3
20 
55 

Step 
1

Step 
2

Step 
3

-0.01
0.64 

0.91 
1.9 
4.9 
-0.10
204 
195 
31 
21 
62 
42 
483 
254 
302 
166 
0.00
0.10 
9.6 
0.10 
9.9 
0.00 
30 
5.7 
237 
2.9 
140 
0.10
66 
21 
199 
98 
130 
0.00
124 
40 

20 
55 

0.64 
8.9
0.91 
1.9 
4.9 

204 
194 
31 
21 
62 
42 
484 
255 
302 
166 

0.30 
10.0 
0.00 
9.9 
-0.10
30 
5.2 
237 
2.9 
140 

66 
22 
199 
98 
130 

124 
40 
5.3
20 
55 

0.64 
8.9
0.91 
1.9 
4.9 

204 
194 
31 
21 
62 
42 
484 
254 
302 
166 

0.10 
9.9 
0.00 
9.8 
0.00 
30 
5.2 
237 
3.0 
140 

67 
22 
199 
98 
130 

125 
40 
5.4
20 
55 

Lab 
unc

0.07
0.10 
0.14
0.10 
0.10 
0.10 
1.1
3.5 
3.4 
2.2 
2.2 
2.2 
2.2 
7.6 
4.2 
4.8 
3.0 
1.2
1.1 
1.1 
1.4 
1.4 
1.4 
1.4 
2.4 
7.7 
1.5 
3.2 
0.77
1.2 
1.2 
2.4 
1.4 
1.6 
0.87
5.4 
2.0 
1.1
1.3 
2.5 

unit

Lab 
unc 
exp 
µmol/mol
0.14
0.20  µmol/mol 
0.28
µmol/mol
0.19  µmol/mol 
0.19  µmol/mol 
0.20  µmol/mol 
nmol/mol
2.2
nmol/mol 
6.9 
nmol/mol 
6.7 
nmol/mol 
4.3 
nmol/mol 
4.3 
nmol/mol 
4.4 
nmol/mol 
4.3 
nmol/mol 
15 
nmol/mol 
8.3 
nmol/mol 
9.7 
nmol/mol 
6.0 
nmol/mol
2.4
nmol/mol 
2.2 
nmol/mol 
2.2 
nmol/mol 
2.7 
nmol/mol 
2.7 
nmol/mol 
2.7 
nmol/mol 
2.8 
nmol/mol 
4.9 
nmol/mol 
15 
nmol/mol 
3.1 
nmol/mol 
6.4 
nmol/mol
1.5
nmol/mol 
2.5 
nmol/mol 
2.4 
nmol/mol 
4.8 
nmol/mol 
2.8 
nmol/mol 
3.3 
nmol/mol
1.7
nmol/mol 
11 
nmol/mol 
3.9 
nmol/mol
2.3
nmol/mol 
2.7 
nmol/mol 
5.0 

sigmaPT

0.10
0.11 
0.31
0.12 
0.15 
0.22 
1.00
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00
2.3 
1.4 
5.0 
2.9 
3.6 
1.00
3.8 
1.9 
1.1
1.5 
2.2 

z/z'-
score 
value 
-0.05
0.17 
0.38
-0.05
0.00 
0.25 
-0.24
0.28 
0.23 
0.00 
-0.17
0.41 
0.18 
0.45 
0.38 
0.28 
0.12 
0.01
-0.07
-0.12
-0.03
0.11 
0.00 
0.26 
-0.54
0.34 
-0.44
0.23 
0.20
0.23 
0.41 
0.32 
0.40 
0.34 
-0.18
-0.68
-0.50
0.11
-0.49
-0.53

z/z' 
selection

En-
score

z
z 
z
z 
z 
z 
z’
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z
z 
z 
z 
z 
z 
z’
z 
z’ 
z’
z’ 
z 

-0.04
0.10 
0.41
-0.03
0.00 
0.27 
-0.11
0.22 
0.18 
0.00 
-0.06
0.23 
0.09 
0.36 
0.31 
0.22 
0.10 
0.01
-0.04
-0.08
-0.02
0.07 
0.00 
0.19 
-0.21
0.18 
-0.22
0.17 
0.13
0.20 
0.24 
0.29 
0.38 
0.32 
-0.10
-0.23
-0.25
0.05
-0.26
-0.23

Component

Run

CO
CO 
CO
CO 
CO 
CO 
NO
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3
O3 
O3 
O3 
O3 
O3 
SO2
SO2 
SO2 
SO2
SO2 
SO2 

0
1 
2
3 
4 
5 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
0
1 
2 
3
4 
5 

Source: JRC 2024 

43 

Figure 19: Graphical report of results of Laboratory DCE (Denmark). 

Source: JRC 2024 

44 

 
 
 
 
 
 
Table 13: Reported values, uncertainties and performance evaluation results for Laboratory DCE (Denmark). 

Lab 
mean 
value 
0.05
0.66 
8.9 
0.93 
1.9 
4.9 
0.18
203 
193 
31 
22 
61 
43 
474 
256 
297 
166 
-0.20
-2.70
6.3 
-1.13
7.9 
-1.60
26 
2.6 
222 
0.30 
129 
-0.88
63 
20 
196 
95 
127 
-0.20
127 
41 
5.0 
21 
56 

Step 1

Step 
2

Step 
3

0.05
0.67 
8.9 
0.93 
1.9 
4.9 
0.18
203 
194 
31 
22 
61 
43 
473 
255 
296 
166 
-0.20
-2.80
6.2 
-1.30
7.8 
-1.50
26 
2.9 
222 
0.20 
129 
-0.88
63 
19 
196 
95 
127 
-0.20
127 
41 
4.5 
21 
56 

0.66 
8.9 
0.93 
1.9 
4.9 

203 
193 
31 
22 
61 
43 
475 
256 
298 
166 

-2.80
6.4 
-1.00
7.9 
-1.50
27 
2.3 
222 
0.12 
128 

63 
20 
196 
95 
127 

127 
41 
5.2 
21 
56 

0.65 
8.8 
0.93 
1.9 
4.9 

202 
193 
31 
22 
61 
43 
475 
257 
296 
166 

-2.50
6.2 
-1.10
8.1 
-1.80
26 
2.5 
221 
0.59 
129 

64 
20 
196 
96 
127 

127 
41 
5.2 
21 
56 

DCE 

Lab 
unc

0.07
0.07 
0.17 
0.07 
0.08 
0.11 
0.68
3.4 
3.2 
0.85 
0.77 
1.2 
0.97 
7.8 
4.2 
4.9 
2.8 
0.68
0.68 
0.69 
0.68 
0.71 
0.68 
0.96 
0.68 
5.8 
0.68 
3.4 
0.63
1.6 
0.77 
4.5 
2.3 
3.0 
0.64
2.3 
0.95 
0.64 
0.73 
1.2 

unit

Lab 
unc 
exp 
µmol/mol
0.14
0.14  µmol/mol 
0.34  µmol/mol 
0.14  µmol/mol 
0.15  µmol/mol 
0.22  µmol/mol 
nmol/mol
1.4
nmol/mol 
6.8 
nmol/mol 
6.5 
nmol/mol 
1.7 
nmol/mol 
1.5 
nmol/mol 
2.4 
nmol/mol 
1.9 
nmol/mol 
16 
nmol/mol 
8.5 
nmol/mol 
9.8 
nmol/mol 
5.6 
nmol/mol
1.4
nmol/mol 
1.4 
nmol/mol 
1.4 
nmol/mol 
1.4 
nmol/mol 
1.4 
nmol/mol 
1.4 
nmol/mol 
1.9 
nmol/mol 
1.4 
nmol/mol 
12 
nmol/mol 
1.4 
nmol/mol 
6.8 
nmol/mol
1.3
nmol/mol 
3.2 
nmol/mol 
1.5 
nmol/mol 
9.0 
nmol/mol 
4.5 
nmol/mol 
5.9 
nmol/mol
1.3
nmol/mol 
4.5 
nmol/mol 
1.9 
nmol/mol 
1.3 
nmol/mol 
1.5 
nmol/mol 
2.3 

sigmaPT

0.10
0.11 
0.31 
0.12 
0.15 
0.22 
1.00
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00
2.3 
1.4 
5.0 
2.9 
3.6 
1.00
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
0.55
0.35 
0.27 
0.11 
0.00 
0.25 
-0.02
0.05 
0.05 
0.00 
0.43 
0.03 
0.65 
-0.30
0.62 
-0.37
0.12 
-0.12
-1.72
-1.93
-0.77
-0.95
-0.98
-1.29
-1.70
-1.59
-1.77
-1.92
-0.78
-1.07
-1.00
-0.29
-0.51
-0.50
-0.36
0.03 
-0.00
-0.20
0.16 
-0.08

z/z' 
selection

En-
score

z
z 
z 
z 
z 
z 
z’
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z
z 
z 
z 
z 
z 
z’
z 
z’ 
z’ 
z’ 
z 

0.39
0.28 
0.24 
0.10 
0.00 
0.25 
-0.01
0.04 
0.04 
0.00 
0.34 
0.02 
0.67 
-0.22
0.49 
-0.29
0.10 
-0.09
-1.21
-1.53
-0.60
-0.85
-0.75
-1.24
-1.05
-1.00
-1.19
-1.39
-0.57
-0.74
-0.90
-0.15
-0.32
-0.29
-0.25
0.02 
-0.00
-0.14
0.13 
-0.07

Component

Run

CO
CO 
CO 
CO 
CO 
CO 
NO
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3
O3 
O3 
O3 
O3 
O3 
SO2
SO2 
SO2 
SO2 
SO2 
SO2 

0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
Source: JRC 2024 

45 

Figure 20: Graphical report of results of Laboratory DHMZ-LIKZ (Croatia). 

Source: JRC 2024 

46 

Table 14: Reported values, uncertainties and performance evaluation results for Laboratory DHMZ-LIKZ 
(Croatia). 

Step 1

Step 
2

Step 
3

0.00
0.63 
8.9 
0.92 
1.9 
4.9 
-0.13
199 
190 
30 
21 
59 
41 
470 
248 
296 
163 
-0.06
0.05 
9.3 
-0.21
8.6 
0.07 
28 
6.2 
230 
2.3 
137 
0.14
65 
21 
195 
96 
127 
0.37
123 
40 
4.8 
21 
55 

0.63 
8.9 
0.92 
1.9 
4.9 

200 
191 
30 
20 
60 
40 
472 
247 
296 
163 

-0.25
9.7 
-0.29
9.2 
-0.45
28 
5.5 
230 
3.0 
136 

65 
21 
195 
96 
127 

123 
40 
5.5 
21 
55 

0.63 
8.9 
0.92 
1.9 
4.9 

200 
191 
30 
21 
59 
41 
472 
248 
296 
163 

-0.09
9.4 
-0.67
9.0 
0.01 
28 
5.2 
230 
2.5 
136 

65 
21 
195 
96 
127 

124 
40 
5.6 
21 
55 

DHMZ-LIKZ 

Lab 
unc

0.06
0.06 
0.16 
0.06 
0.07 
0.10 
0.58
2.5 
2.4 
0.75 
0.77 
1.0 
1.1 
5.6 
3.1 
3.6 
2.1 
0.61
0.76 
0.75 
0.67 
0.75 
0.72 
0.78 
0.77 
3.0 
0.78 
1.9 
0.61
1.6 
0.78 
4.5 
2.2 
3.0 
0.59
2.2 
0.91 
0.59 
0.69 
1.1 

unit

Lab 
unc 
exp 
0.12
µmol/mol
0.12  µmol/mol 
0.32  µmol/mol 
0.12  µmol/mol 
0.14  µmol/mol 
0.20  µmol/mol 
nmol/mol
1.2
nmol/mol 
5.0 
nmol/mol 
4.8 
nmol/mol 
1.5 
nmol/mol 
54 
nmol/mol 
2.1 
nmol/mol 
2.1 
nmol/mol 
11 
nmol/mol 
6.1 
nmol/mol 
7.2 
nmol/mol 
4.2 
nmol/mol
1.2
nmol/mol 
1.5 
nmol/mol 
1.5 
nmol/mol 
1.3 
nmol/mol 
1.5 
nmol/mol 
1.4 
nmol/mol 
1.6 
nmol/mol 
1.5 
nmol/mol 
5.9 
nmol/mol 
1.6 
nmol/mol 
3.7 
nmol/mol
1.2
nmol/mol 
3.2 
nmol/mol 
1.6 
nmol/mol 
8.9 
nmol/mol 
4.5 
nmol/mol 
5.9 
nmol/mol
1.2
nmol/mol 
4.4 
nmol/mol 
1.8 
nmol/mol 
1.2 
nmol/mol 
1.4 
nmol/mol 
2.2 

Lab 
mean 
value 
0.00
0.63 
8.9 
0.92 
1.9 
4.9 
-0.13
200 
191 
30 
21 
59 
41 
471 
248 
296 
163 
-0.06
-0.10
9.5 
-0.39
8.9 
-0.12
28 
5.6 
230 
2.6 
136 
0.14
65 
21 
195 
96 
127 
0.37
123 
40 
5.3 
21 
55 

sigmaPT

0.10
0.11 
0.31 
0.12 
0.15 
0.22 
1.00
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00
2.3 
1.4 
5.0 
2.9 
3.6 
1.00
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
0.07
0.09 
0.38 
0.03 
0.00 
0.25 
-0.27
-0.46
-0.42
-0.53
-0.37
-0.62
-0.44
-0.54
-0.56
-0.45
-0.48
-0.03
-0.22
-0.30
-0.30
-0.40
-0.05
-0.59
-0.43
-0.54
-0.61
-0.47
0.24
-0.35
-0.06
-0.49
-0.28
-0.50
0.15
-0.94
-0.50
0.07 
0.16 
-0.53

z/z' 
selection

En-
score

z
z 
z 
z 
z 
z 
z’
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z
z 
z 
z 
z 
z 
z’
z 
z’ 
z’ 
z’ 
z 

0.06
0.08 
0.36 
0.03 
0.00 
0.27 
-0.18
-0.49
-0.44
-0.47
-0.01
-0.61
-0.42
-0.54
-0.58
-0.46
-0.50
-0.03
-0.15
-0.24
-0.24
-0.35
-0.04
-0.62
-0.26
-0.61
-0.40
-0.54
0.19
-0.24
-0.05
-0.26
-0.17
-0.29
0.11
-0.74
-0.46
0.05 
0.14 
-0.46

Component

Run

CO
CO 
CO 
CO 
CO 
CO 
NO
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3
O3 
O3 
O3 
O3 
O3 
SO2
SO2 
SO2 
SO2 
SO2 
SO2 

0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
Source: JRC 2024 

47 

Figure 21: Graphical report of results of Laboratory EKONERG (Croatia). 

Source: JRC 2024 

48 

Table 15: Reported values, uncertainties and performance evaluation results for Laboratory EKONERG 
(Croatia). 

EKONERG 

Lab 
mean 
value 
0.00 
0.64 
9.1 
0.95 
2.0 
5.0 
0.32 
200 
191 
31 
21 
61 
41 
474 
250 
297 
166 
-0.41 
0.04 
9.5 
0.01 
9.5 
0.01 
29 
0.00 
223 
0.23 
131 
-0.02 
65 
21 
199 
95 
126 
0.29 
125 
39 
4.2 
19 
54 

Step 1  Step 
2 

Step 
3 

0.01 
0.64 
9.1 
0.95 
2.0 
5.0 
0.32 
200 
191 
31 
21 
61 
42 
473 
250 
296 
171 
-0.41 
-0.07 
9.5 
0.02 
9.6 
-0.04 
29 
0.10 
223 
0.15 
126 
-0.02 
65 
21 
199 
96 
127 
0.24 
124 
39 
4.1 
19 
54 

0.00 
0.65 
9.1 
0.95 
2.0 
5.0 

200 
191 
31 
21 
61 
41 
474 
250 
297 
164 

-0.01 
9.5 
-0.13 
9.5 
0.06 
29 
-0.07 
223 
0.02 
133 

65 
21 
199 
95 
126 
0.34 
125 
39 
4.3 
19 
54 

0.00 
0.64 
9.1 
0.95 
2.0 
5.0 

200 
190 
31 
21 
61 
41 
474 
250 
297 
164 

0.20 
9.6 
0.15 
9.5 
0.00 
29 
-0.02 
223 
0.52 
133 

65 
21 
198 
95 
124 
0.29 
125 
39 
4.3 
19 
54 

Lab 
unc 

0.03 
0.04 
0.19 
0.05 
0.07 
0.12 
0.69 
4.8 
4.6 
1.3 
1.1 
1.9 
1.5 
10 
5.8 
6.8 
4.1 
0.76 
0.75 
1.00 
0.75 
1.0 
0.75 
1.6 
0.75 
7.1 
0.75 
4.5 
0.90 
1.8 
1.3 
3.5 
2.2 
2.6 
0.51 
3.0 
1.3 
0.59 
0.90 
1.6 

unit 

Lab 
unc 
exp 
0.07  µmol/mol 
0.09  µmol/mol 
0.39  µmol/mol 
0.10  µmol/mol 
0.14  µmol/mol 
0.24  µmol/mol 
nmol/mol 
1.4 
nmol/mol 
9.6 
nmol/mol 
9.2 
nmol/mol 
2.6 
nmol/mol 
2.2 
nmol/mol 
3.8 
nmol/mol 
3.1 
nmol/mol 
21 
nmol/mol 
12 
nmol/mol 
14 
nmol/mol 
8.2 
nmol/mol 
1.5 
nmol/mol 
1.5 
nmol/mol 
2.0 
nmol/mol 
1.5 
nmol/mol 
2.0 
nmol/mol 
1.5 
nmol/mol 
3.1 
nmol/mol 
1.5 
nmol/mol 
14 
nmol/mol 
1.5 
nmol/mol 
9.0 
nmol/mol 
1.8 
nmol/mol 
3.7 
nmol/mol 
2.5 
nmol/mol 
7.0 
nmol/mol 
4.4 
nmol/mol 
5.2 
nmol/mol 
1.0 
nmol/mol 
5.9 
nmol/mol 
2.5 
nmol/mol 
1.2 
nmol/mol 
1.7 
nmol/mol 
3.1 

sigmaPT 

0.10 
0.11 
0.31 
0.12 
0.15 
0.22 
1.00 
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4 
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00 
2.3 
1.4 
5.0 
2.9 
3.6 
1.00 
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
0.10 
0.20 
1.0 
0.28 
0.69 
0.72 
0.10 
-0.41 
-0.42 
0.00 
-0.17 
0.03 
-0.13 
-0.35 
-0.23 
-0.37 
0.19 
-0.25 
-0.14 
-0.27 
-0.05 
-0.07 
0.03 
-0.16 
-2.76 
-1.42 
-1.80 
-1.54 
0.08 
-0.35 
-0.06 
0.25 
-0.51 
-0.87 
0.08 
-0.59 
-1.01 
-0.78 
-1.13 
-0.98 

Component  Run 

CO 
CO 
CO 
CO 
CO 
CO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3 
O3 
O3 
O3 
O3 
O3 
SO2 
SO2 
SO2 
SO2 
SO2 
SO2 

0 
1 
2 
3 
4 
5 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0 
1 
2 
3 
4 
5 
0 
1 
2 
3 
4 
5 
Source: JRC 2024 

z/z' 
selection 

En-
score 

z 
z 
z 
z 
z 
z 
z’ 
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z 
z 
z 
z 
z 
z 
z’ 
z 
z’ 
z’ 
z’ 
z 

0.14 
0.25 
0.80 
0.33 
0.70 
0.64 
0.06 
-0.24 
-0.25 
0.00 
-0.11 
0.02 
-0.09 
-0.20 
-0.14 
-0.22 
0.11 
-0.19 
-0.10 
-0.19 
-0.04 
-0.05 
0.02 
-0.11 
-1.70 
-0.76 
-1.20 
-0.87 
0.04 
-0.21 
-0.03 
0.16 
-0.32 
-0.56 
0.06 
-0.36 
-0.72 
-0.58 
-0.87 
-0.65 

49 

 
 
 
 
 
 
 
 
 
 
 
 
Figure 22: Graphical report of results of Laboratory ISPRA (Italy). 

Source: JRC 2024 

50 

Table 16: Reported values, uncertainties and performance evaluation results for ISPRA (Italy). 

Component  Run 

CO 
CO 
CO 
CO 
CO 
CO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3 
O3 
O3 
O3 
O3 
O3 
SO2 
SO2 
SO2 
SO2 
SO2 
SO2 

0 
1 
2 
3 
4 
5 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0 
1 
2 
3 
4 
5 
0 
1 
2 
3 
4 
5 
Source: JRC 2024 

Lab 
mean 
value 
0.01 
0.68 
8.9 
0.98 
2.0 
5.0 
0.09 
202 
192 
31 
21 
60 
41 
479 
253 
297 
164 
0.09 
0.96 
11 
0.28 
9.6 
0.36 
29 
7.1 
227 
4.2 
137 
-0.16 
66 
21 
201 
98 
130 
0.40 
128 
41 
5.5 
21 
57 

Step 1  Step 
2 

Step 
3 

0.01 
0.67 
8.9 
0.97 
2.0 
5.0 
0.09 
202 
192 
31 
21 
60 
41 
479 
254 
297 
164 
0.09 
0.92 
11 
0.24 
9.5 
0.31 
29 
7.1 
227 
4.2 
137 
-0.16 
66 
21 
200 
98 
131 
0.40 
128 
41 
5.6 
21 
58 

0.68 
8.9 
0.98 
2.0 
5.0 

202 
191 
31 
21 
60 
41 
480 
253 
296 
164 

0.98 
11 
0.30 
9.6 
0.43 
29 
7.1 
227 
4.2 
138 

66 
21 
201 
98 
130 

127 
42 
5.4 
21 
57 

0.68 
8.9 
0.98 
2.0 
5.0 

202 
192 
31 
21 
60 
41 
479 
253 
298 
164 

0.97 
11 
0.29 
9.6 
0.35 
29 
7.2 
227 
4.1 
137 

67 
21 
201 
98 
130 

128 
42 
5.4 
21 
57 

ISPRA 

Lab 
unc 

0.06 
0.06 
0.13 
0.07 
0.07 
0.09 
0.59 
4.2 
4.0 
1.8 
1.7 
2.0 
1.8 
9.0 
5.0 
6.0 
3.5 
0.58 
1.7 
1.7 
1.7 
1.7 
1.7 
1.7 
1.7 
4.6 
1.7 
3.1 
0.65 
1.2 
0.70 
3.2 
1.7 
2.1 
0.80 
3.3 
1.3 
0.80 
1.00 
1.6 

unit 

Lab 
unc 
exp 
0.13  µmol/mol 
0.13  µmol/mol 
0.26  µmol/mol 
0.13  µmol/mol 
0.14  µmol/mol 
0.18  µmol/mol 
nmol/mol 
1.2 
nmol/mol 
8.4 
nmol/mol 
8.0 
nmol/mol 
3.5 
nmol/mol 
3.4 
nmol/mol 
4.0 
nmol/mol 
3.7 
nmol/mol 
19 
nmol/mol 
10.0 
nmol/mol 
12 
nmol/mol 
7.1 
nmol/mol 
1.2 
nmol/mol 
3.3 
nmol/mol 
3.3 
nmol/mol 
3.3 
nmol/mol 
3.3 
nmol/mol 
3.3 
nmol/mol 
3.5 
nmol/mol 
3.3 
nmol/mol 
9.3 
nmol/mol 
3.3 
nmol/mol 
6.2 
nmol/mol 
1.3 
nmol/mol 
2.4 
nmol/mol 
1.5 
nmol/mol 
6.4 
nmol/mol 
3.3 
nmol/mol 
4.3 
nmol/mol 
1.6 
nmol/mol 
6.5 
nmol/mol 
2.6 
nmol/mol 
1.7 
nmol/mol 
1.9 
nmol/mol 
3.3 

sigmaPT 

0.10 
0.11 
0.31 
0.12 
0.15 
0.22 
1.00 
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4 
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00 
2.3 
1.4 
5.0 
2.9 
3.6 
1.00 
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
0.11 
0.50 
0.36 
0.50 
0.60 
0.61 
-0.09 
-0.09 
-0.26 
-0.21 
-0.05 
-0.26 
-0.13 
0.10 
0.24 
-0.33 
-0.32 
0.06 
0.39 
0.30 
0.12 
-0.05 
0.25 
-0.08 
0.19 
-0.91 
0.18 
-0.26 
-0.06 
0.29 
0.11 
0.67 
0.49 
0.48 
0.17 
0.21 
0.23 
0.20 
0.20 
0.41 

z/z' 
selection 

En-
score 

z 
z 
z 
z 
z 
z 
z’ 
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z 
z 
z 
z 
z 
z 
z’ 
z 
z’ 
z’ 
z’ 
z 

0.08 
0.43 
0.41 
0.46 
0.61 
0.71 
-0.06 
-0.06 
-0.18 
-0.11 
-0.02 
-0.15 
-0.08 
0.07 
0.16 
-0.22 
-0.21 
0.05 
0.17 
0.15 
0.05 
-0.03 
0.11 
-0.05 
0.09 
-0.72 
0.09 
-0.21 
-0.04 
0.26 
0.10 
0.48 
0.41 
0.36 
0.10 
0.12 
0.16 
0.12 
0.14 
0.26 

51 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 23: Graphical report of results of Laboratory NPL (United Kingdom). 

Source: JRC 2024 

52 

Table 17: Reported values, uncertainties and performance evaluation results for NPL (United Kingdom). 

NPL 

Lab 
mean 
value 
0.00
0.71 
9.7 
1.0 
2.1 
5.4 
0.01
194 
184 
28 
19 
55 
37 
466 
241 
285 
154 
0.32
0.06 
9.4 
0.10 
8.9 
0.06 
27 
4.6 
230 
2.6 
133 
0.05
129 
42 
4.6 
21 
57 

Step 
1

Step 
2

Step 
3

0.00
0.70 
9.7 
1.1 
2.1 
5.4 
0.01
195 
184 
29 
19 
55 
37 
465 
240 
285 
154 
0.32
0.18 
9.2 
0.09 
8.9 
0.13 
27 
5.2 
230 
2.8 
134 
0.05
128 
42 
3.2 
21 
57 

0.71 
9.7 
1.00 
2.1 
5.4 

194 
184 
28 
19 
55 
37 
467 
241 
285 
154 

0.00 
9.3 
0.17 
8.9 
0.01 
27 
4.3 
230 
2.5 
133 

129 
42 
5.2 
21 
57 

0.71 
9.7 
1.00 
2.1 
5.4 

194 
184 
28 
19 
55 
37 
467 
241 
285 
154 

0.01 
9.6 
0.05 
8.9 
0.05 
27 
4.4 
230 
2.6 
133 

129 
42 
5.4 
21 
57 

Lab 
unc

0.00
0.02 
0.29 
0.03 
0.06 
0.16 
0.14
5.5 
5.2 
0.88 
0.67 
1.6 
1.1 
13 
6.8 
8.0 
4.3 
0.13
2.9 
0.49 
0.23 
0.32 
0.59 
0.80 
0.91 
6.5 
0.64 
3.8 
0.14
5.1 
1.7 
0.43 
0.86 
2.3 

unit

Lab 
unc 
exp 
µmol/mol
0.01
0.04  µmol/mol 
0.57  µmol/mol 
0.06  µmol/mol 
0.13  µmol/mol 
0.32  µmol/mol 
nmol/mol
0.29
nmol/mol 
11 
nmol/mol 
10 
nmol/mol 
1.8 
nmol/mol 
1.3 
nmol/mol 
3.1 
nmol/mol 
2.1 
nmol/mol 
26 
nmol/mol 
14 
nmol/mol 
16 
nmol/mol 
8.6 
nmol/mol
0.26
nmol/mol 
5.7 
nmol/mol 
0.98 
nmol/mol 
0.45 
nmol/mol 
0.64 
nmol/mol 
1.2 
nmol/mol 
1.6 
nmol/mol 
1.8 
nmol/mol 
13 
nmol/mol 
1.3 
nmol/mol 
7.6 
nmol/mol
0.29
nmol/mol 
10 
nmol/mol 
3.4 
nmol/mol 
0.85 
nmol/mol 
1.7 
nmol/mol 
4.6 

sigmaPT

0.10
0.11 
0.31 
0.12 
0.15 
0.22 
1.00
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
0.06
0.76 
3.0 
0.96 
1.4 
2.6 
-0.15
-1.37
-1.61
-1.41
-1.36
-2.30
-2.16
-0.94
-1.56
-1.79
-2.29
0.21
-0.13
-0.36
0.01 
-0.42
0.06 
-1.01
-0.84
-0.54
-0.59
-1.03
-0.13
0.47 
0.50 
-0.49
0.16 
0.36 

z/z' 
selection

En-
score

z
z 
z 
z 
z 
z 
z’
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z’
z 
z’ 
z’ 
z’ 
z 

0.34
1.9 
1.6 
1.8 
1.6 
1.7 
-0.13
-0.72
-0.86
-1.16
-1.15
-1.71
-2.06
-0.44
-0.79
-0.90
-1.28
0.23
-0.04
-0.31
0.01 
-0.47
0.05 
-1.06
-0.50
-0.32
-0.41
-0.68
-0.14
0.17 
0.28 
-0.42
0.12 
0.17 

Component

Run

CO
CO 
CO 
CO 
CO 
CO 
NO
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
SO2
SO2 
SO2 
SO2 
SO2 
SO2 

0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 

Source: JRC 2024 

53 

Figure 24: Graphical report of results of Laboratory OOE (Austria). 

Source: JRC 2024 

54 

Table 18: Reported values, uncertainties and performance evaluation results for OOE (Austria). 

Lab 
mean 
value 
-0.01
0.61 
8.8 
0.91 
1.9 
4.9 
0.75
201 
192 
32 
22 
61 
42 
475 
251 
298 
165 
-0.05
1.7 
11 
0.23 
9.7 
0.41 
29 
8.5 
233 
4.9 
138 
0.16
66 
22 
198 
97 
129 
0.09
123 
40 
5.0 
20 
55 

Step 1

Step 
2

Step 
3

-0.01
0.61 
8.8 
0.92 
1.9 
4.9 
0.75
201 
192 
32 
22 
61 
42 
475 
250 
298 
165 
-0.05
1.6 
11 
0.21 
9.6 
0.37 
30 
8.6 
233 
5.0 
138 
0.16
66 
22 
198 
97 
129 
0.09
123 
40 
4.5 
20 
55 

0.61 
8.8 
0.91 
1.9 
4.9 

201 
192 
31 
22 
61 
42 
475 
251 
298 
165 

1.6 
11 
0.33 
9.7 
0.46 
29 
8.5 
232 
4.9 
138 

66 
22 
198 
97 
129 

123 
40 
5.1 
20 
55 

0.61 
8.8 
0.91 
1.9 
4.9 

201 
192 
31 
22 
61 
42 
475 
251 
298 
165 

1.8 
11 
0.16 
9.7 
0.41 
29 
8.5 
233 
4.9 
138 

66 
22 
198 
97 
129 

124 
40 
5.3 
20 
55 

OOE 

Lab 
unc

0.02
0.02 
0.16 
0.03 
0.04 
0.09 
0.46
2.4 
2.3 
0.50 
0.46 
0.80 
0.59 
5.7 
3.0 
3.6 
2.0 
0.78
0.78 
0.78 
0.78 
0.78 
0.78 
0.78 
0.78 
2.8 
0.78 
1.7 
0.82
1.1 
0.87 
2.5 
1.4 
1.8 
0.42
1.6 
0.65 
0.64 
0.50 
0.79 

unit

Lab 
unc 
exp 
µmol/mol
0.04
0.05  µmol/mol 
0.32  µmol/mol 
0.05  µmol/mol 
0.08  µmol/mol 
0.18  µmol/mol 
nmol/mol
0.92
nmol/mol 
4.8 
nmol/mol 
4.6 
nmol/mol 
1.00 
nmol/mol 
0.92 
nmol/mol 
1.6 
nmol/mol 
1.2 
nmol/mol 
10 
nmol/mol 
6.1 
nmol/mol 
7.1 
nmol/mol 
4.0 
nmol/mol
1.6
nmol/mol 
1.6 
nmol/mol 
1.6 
nmol/mol 
1.6 
nmol/mol 
1.6 
nmol/mol 
1.6 
nmol/mol 
1.6 
nmol/mol 
1.6 
nmol/mol 
5.7 
nmol/mol 
1.6 
nmol/mol 
3.4 
nmol/mol
1.6
nmol/mol 
2.3 
nmol/mol 
1.7 
nmol/mol 
5.0 
nmol/mol 
2.9 
nmol/mol 
3.6 
nmol/mol
0.84
nmol/mol 
3.1 
nmol/mol 
1.3 
nmol/mol 
1.3 
nmol/mol 
1.00 
nmol/mol 
1.6 

sigmaPT

0.10
0.11 
0.31 
0.12 
0.15 
0.22 
1.00
5.9 
5.6 
1.7 
1.5 
2.5 
2.0 
12 
7.0 
8.2 
5.0 
1.4
1.4 
1.7 
1.4 
1.7 
1.4 
2.2 
1.6 
8.0 
1.5 
5.3 
1.00
2.3 
1.4 
5.0 
2.9 
3.6 
1.00
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
-0.03
-0.07
0.20 
-0.02
0.06 
0.16 
0.44
-0.27
-0.26
0.28 
0.37 
0.11 
0.18 
-0.25
-0.12
-0.23
-0.15
-0.02
0.79 
0.51 
0.09 
0.00 
0.28 
0.04 
0.77 
-0.22
0.57 
-0.22
0.26
0.19 
0.45 
0.13 
0.21 
0.16 
-0.10
-0.94
-0.60
-0.20
-0.43
-0.71

z/z' 
selection

En-
score

z
z 
z 
z 
z 
z 
z’
z 
z 
z’ 
z’ 
z’ 
z’ 
z 
z 
z 
z 
z’
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z’ 
z 
z’ 
z 
z
z 
z 
z 
z 
z 
z’
z 
z’ 
z’ 
z’ 
z 

-0.07
-0.16
0.19 
-0.04
0.11 
0.19 
0.32
-0.29
-0.28
0.30 
0.36 
0.13 
0.28 
-0.27
-0.13
-0.24
-0.16
-0.02
0.54 
0.39 
0.07 
0.00 
0.21 
0.04 
0.47 
-0.25
0.37 
-0.27
0.15
0.18 
0.35 
0.11 
0.20 
0.14 
-0.09
-0.96
-0.67
-0.14
-0.46
-0.77

Component

Run

CO
CO 
CO 
CO 
CO 
CO 
NO
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO 
NO2
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
NO2 
O3
O3 
O3 
O3 
O3 
O3 
SO2
SO2 
SO2 
SO2 
SO2 
SO2 

0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
Source: JRC 2024 

55 

Figure 25: Graphical report of results of Laboratory SHI (Slovak Republic). 

Source: JRC 2024 

56 

Table 19: Reported values, uncertainties and performance evaluation results for SHI (Slovak Republic). 

Lab 
mean 
value 
0.01
0.62 
8.7 
0.91 
1.9 
4.8 
0.18
66 
22 
197 
97 
129 
0.15
125 
40 
5.1 
20 
55 

Step 
1

Step 
2

Step 
3

0.01
0.62 
8.7 
0.91 
1.9 
4.8 
0.18
66 
21 
197 
97 
129 
0.15
125 
40 
5.0 
20 
55 

0.62 
8.7 
0.91 
1.9 
4.8 

66 
22 
197 
97 
129 

125 
40 
5.1 
20 
55 

0.62 
8.7 
0.91 
1.9 
4.8 

66 
22 
197 
97 
128 

125 
40 
5.2 
20 
55 

SHI 

Lab 
unc

0.10
0.11 
0.19 
0.11 
0.12 
0.15 
0.50
1.5 
0.82 
3.5 
2.0 
2.4 
0.50
3.6 
1.5 
0.63 
1.00 
1.9 

unit

Lab 
unc 
exp 
µmol/mol
0.20
0.21  µmol/mol 
0.37  µmol/mol 
0.22  µmol/mol 
0.24  µmol/mol 
0.30  µmol/mol 
nmol/mol
1.00
nmol/mol 
3.0 
nmol/mol 
1.6 
nmol/mol 
6.9 
nmol/mol 
3.9 
nmol/mol 
4.9 
nmol/mol
1.00
nmol/mol 
7.2 
nmol/mol 
3.0 
nmol/mol 
1.3 
nmol/mol 
2.0 
nmol/mol 
3.8 

sigmaPT

0.10
0.11 
0.31 
0.12 
0.15 
0.22 
1.00
2.3 
1.4 
5.0 
2.9 
3.6 
1.00
3.8 
1.9 
1.1 
1.5 
2.2 

z/z'-
score 
value 
0.12
0.00 
-0.26
-0.05
0.00 
-0.21
0.28
0.09 
0.41 
-0.08
0.06 
-0.03
-0.05
-0.50
-0.50
-0.09
-0.49
-0.53

z/z' 
selection

En-
score

z
z 
z 
z 
z 
z 
z
z 
z 
z 
z 
z 
z’
z 
z’ 
z’ 
z’ 
z 

0.06
0.00 
-0.22
-0.03
0.00 
-0.15
0.26
0.06 
0.35 
-0.06
0.04 
-0.02
-0.04
-0.25
-0.31
-0.07
-0.33
-0.29

Component

Run

CO
CO 
CO 
CO 
CO 
CO 
O3
O3 
O3 
O3 
O3 
O3 
SO2
SO2 
SO2 
SO2 
SO2 
SO2 

0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 
0
1 
2 
3 
4 
5 

Source: JRC 2024 

57 

Annex C: Repeatability and reproducibility 

1  Introduction 

In this PT the standard ISO 5725 was used to confirm the test method's validity and reliability through 
the calculation of repeatability and reproducibility. 
Reproducibility is defined as the closeness of the agreement between the results of measurements 
of the same measurand carried out under various conditions: different operators, different equipment, 
different equipment calibration etc. 
During the PT the  participants were invited to use, as much as possible, their own  everyday work 
procedure. 
The reproducibility limit (R) is a quantitative measure indicating the maximum difference in  results 
that can be expected under reproducibility conditions for a given level of probability, usually 95%. 
The  repeatability  refers  to  the  closeness  of  the  agreement  between  the  results  of  successive 
measurements of the same measurand carried out under the same measurement conditions: same 
procedure, same operator, same measuring instrument, etc.  
The  repeatability  limit (r) is  a  value below  which  the  absolute difference between  two  single  test 
results  obtained  under  repeatability  conditions  may  be  expected  to  lie  with  a  certain  probability, 
typically 95%. 
For the main purpose of monitoring trends between different PT undertaken by ERLAP, the precision 
of standardized SO2, CO, O3 and NOX measurement methods [2], [3], [4] and [5] as implemented by 
NRLs, is evaluated. Due to the small number of participants the reproducibility results doesn’t give an 
accurate response about the quality of the methods application during the PT. 
Applied methodology is described in ISO 5725-1, 5725-2 and 5725-6 [14], [15] and [16].  
The  precision  experiment  has  involved  a  maximum  of  ten  laboratories,  the  actual  number  of 
laboratories (p) is listed in Table 20 according to the data reported.  
Six concentration levels (for run 0 only one value is requested so repeatability cannot be evaluated) 
were tested for O3, CO, SO2 and NO2, and eleven for NO. Performance tests for each participant are 
performed and results are reported in Annex B. 
In ISO 5725 repeatability (r) and reproducibility (R) limits are defined. These limits are the values less 
than  or  equal  to  which  the  absolute  difference  between  two  test  results,  obtained  under  either 
repeatability or reproducibility conditions, may be expected to be with (1 - α) probability level.   
The  repeatability  standard  deviation  (sr)  was  calculated  as  the  square  root  of  average  within-
laboratory variance at the 95% confidence level. The repeatability limit (r) is calculated using Equation 
5 [16].  

Equation 5 
𝒓 = 𝒕𝝂/𝜶 ∙ √𝟐 ∙ 𝑺𝒓 

r = repeatability limit 
t/α = t Student distribution value 
Sr = estimate of repeatability standard deviation 

The reproducibility standard deviation (SR) was calculated as the square root of sum of reproducibility 
of  between-laboratory  variance  at  the  95%  confidence  level  ().  The  reproducibility  limit  (R)  is 
calculated using Equation 6 [16]. 

Equation 6 
𝑅 = 𝑡ν/α ∙ √2 ∙ 𝑆𝑅 

R = reproducibility limit 
t/α = t Student distribution value 
SR = standard deviation of between-lab reproducibility 

58 

The  repeatability  standard  deviation  was  evaluated  with  (p  *(3-1))  degrees  of  freedom  ()  and 
reproducibility  standard  deviation  with  (p-1)  degrees  of  freedom  ()  where  p  is  the  number  of 
participants.  
The  critical  range  Student  factors,  for  r  and  R,  corresponding  to  defined  confidence  level  ()  and 
degree of freedom () are reported in Table 20. 

Table 20: Critical values of t used in the repeatability (r) and reproducibility (R) evaluation. 

parameter 
CO 
NO 
NO2 
O3 
SO2 

Source: JRC 2024 

run 
1,2,3,4,5 
1,2,3,4,5,6,7,8,9,10 
2,4,6,8,10 
1,2,3,4,5 
1,2,3,4,5 

p 
10 
9 
9 
9 
10 

t critical value 95% for r 
2.086 
2.101 
2.101 
2.101 
2.086 

t critical value 95% for R 
2.262 
2.306 
2.306 
2.306 
2.262 

59 

2  Results 

The repeatability (r) and reproducibility (R) limits of measurement methods are presented from Figure 
26  to  Figure  30.  It  is  reported  also  the  ‘reproducibility  from  common  criteria  (Ref.)’  calculated  by 
substituting SR in Equation 6 with a ‘standard deviation for proficiency assessment’ (see Table 4). 
Comparison between R and Ref. serves to indicate that σpt is realistic [13] or from the other point of 
view, that the general methodology implemented by NRLs is appropriate for σpt. 

Figure 26: The R and r of SO2 standard measurement method as a function of concentration. 

Source: JRC 2024 

60 

Figure 27: The R and r of CO standard measurement method as a function of concentration. 

Source: JRC 2024 

61 

Figure 28: The R and r of O3 standard measurement method as a function of concentration. 

Source: JRC 2024 

62 

Figure 29: The R and r of NO standard measurement method as a function of concentration. 

Source: JRC 2024 

63 

Figure 30: The R and r of NO2 standard measurement method as a function of concentration. 

Source: JRC 2024 

64 

3  Conclusions 

The evaluation of reproducibility was conducted using all the data received during the proficiency test 
(PT). The relative reproducibility limits, at the highest concentration levels examined, are 5.6% for 
SO2, 10.9% for CO, 2.8% for O3, 3.8% for NO, and 7.1% for NO2, all of which fall within the objectives 
representation  of 
derived 
reproducibility/repeatability, neither the blue line (R) nor the green one (r) intersects the reference red 
line, indicating an overall good performance for all the pollutants assessed. 

from  criteria  set  by  EN  standards. 

In  every  graphical 

65 

Annex D: Confidentiality 
The PT results evaluation is disseminated in alignment with the stipulations laid out in the AQUILA-
N37 document [12], which has received unanimous consent from all NRL members within the AQUILA 
network.  ERLAP  is  committed  to  preserving  the  confidentiality  of  laboratory  data  through  the 
following measures:  
- All  administrative  details  furnished  by  the  laboratory  are  deemed  confidential  and  will  not  be
disclosed to external parties.
- Entry  to  ERLAP  premises  is  strictly  limited  to  JRC-C5  Unit  members  and  individuals  granted
permission (including cleaning, maintenance, safety, and security personnel). Unique passwords for
the web-based data submission portal are issued upon successful PT enrollment. These passwords
remain active until the conclusion of the PT. Participating laboratories have the option to modify their
passwords through the online platform.

As part of their initial PT engagement with ERLAP, participants are required to sign a Confidentiality 
Involvement Form during their first participation to a PT organized by ERLAP. 

66 

Annex E: Accreditation certificate 

End of report 

67 

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