Version /02/2013. (Pilot Study CCQM-P110 Nitrogen dioxide in Nitrogen 10 μmol/mol_protocol B2) Final Report

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1 Study on the accuracy and uncertainty of FT-IR methods calibrated with synthetic spectra for NO 2 concentration measurements (Pilot Study CCQM-P110 Nitrogen dioxide in Nitrogen 10 μmol/mol_protocol B2) Final Report Edgar Flores *1, Joële Viallon 1, Robert Wielgosz 1, Teresa Fernández 2, Andrés Rojo 2, Sergio Ramírez 2, Nobuyuki Aoki 3, Kenji Kato 3, Lee Jeongsoon 4, Dongmin Moon 4, Jin-Seog Kim 4, A. Harling 5, M. Milton 5, David Griffith 6, Damian Smeulders 7, Pamela Chu 8, Lyn Gameson 8, Angelique Botha 9, James Tshilongo 9, Napo Godwill Ntsasa 9, Miroslava Valková 10, Leonid Konopelko 11, Y.A. Kustikov 11, D.V. Rumyantsev 11 and Elena Gromova Bureau International des Poids et Mesures (BIPM), Pavillon de Breteuil, F Sèvres Cedex. 2 Centro Español de Metrología (CEM), Calle Alfar, 2, Tres, Cantos (Madrid), Spain. 3 National Metrology Institute of Japan (NMIJ), Umesono, Tsukuba Ibaraki, Japan. 4 Korea Research Institute of Standards and Science (KRISS),1Doryong-Dong, Yuseong-Gu, Daejeon , Republic of Korea 5 National Physical Laboratory (NPL), Hampton Road, Teddington, Middx, TW11 0LW, UK. 6 University of Wollongong (UOW), Centre for Atmospheric Chemistry, Northfields Ave., Wollongong, NSW 2522, Australia. 7 National Measurement Institute Australia (NMIA), PO Box 264, Lindfield NSW 2070, Australia. 8 National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, MD , USA 9 National Metrology Institute of South Africa (NMISA), Building 4 West, M. Naude Road Brummeria, 0184, Pretoria, South Africa. 10 Slovak Institute of Metrology (SMU), Karloveská 63, SK Bratislava, Slovak Republic. 11 D.I.Mendeleyev Institute for Metrology (VNIIM), 19 Moskovsky pr., St. Petersburg, Russian Federation. Coordinating laboratories: Bureau International des Poids et Mesures (BIPM) VSL Study coordinator: Edgar Flores (BIPM) Correspondence to be addressed to: Edgar Flores edgar.flores@bipm.org (Tel: ) Field: Amount of substance Organizing Body: CCQM Page 1 of 97

2 Index 1. RATIONALE FOR COMPARISON 4 2. QUANTITIES AND UNITS 4 3. SCHEDULE 4 4. MEASUREMENT STANDARDS: RESULTS OF THE KEY COMPARISON CCQM-K REFERENCE VALUES FOR CYLINDERS 5 6. MEASUREMENT PROTOCOL 5 7. INSTRUMENTATION AND CALIBRATION 6 8. RESULTS NMIs submitted values Analysis by participant Discussion Recalculation of the participants results by the BIPM Analysis by participant Discussion Amount of substance fraction as calculated by the BIPM using its own measured spectra 22 9 CONCLUSIONS BIBLIOGRAPHY 24 ANNEX 1- BIPM VALUE ASSIGNMENT PROCEDURE 25 FT-IR Spectra acquisition 25 Control and acquisition software 26 Quantitative analysis of the absorbance spectra 26 Uncertainty budget 28 ANNEX 2 - BIPM MEASUREMENT RESULTS FOR CYLINDER # PRM 30 ANNEX 3 - MEASUREMENT REPORTS OF PARTICIPANTS 33 Centro Español de metrología (CEM) 33 Page 2 of 97

3 Korea Research Institute of Standards and Science (KRISS) 37 National Measurement Institute Australia (NMIA)/ University of Wollongong (UOW) 42 National Metrology institute of Japan (NIMJ) 45 National Institute of Standards and Technology (NIST) 51 National Physical Laboratory (NPL) 55 National Metrology Institute of South Africa (NMISA) 62 Slovak Institute of Metrology (SMU) 67 Mendeleyev Institute for Metrology (VNIIM) 73 Bureau International des Poids et Mesures (BIPM) 79 ANNEX 4 ABSORBANCE SPECTRA SUBMITTED BY PARTICIPANTS 85 National Metrology Institute of South Africa (NMISA) 85 Korea Research Institute of Standards and Science (KRISS) 86 Centro Español de metrología (CEM) 87 Mendeleyev Institute for Metrology (VNIIM) 88 National Metrology institute of Japan (NIMJ) 89 National Physical Laboratory (NPL) 90 National Institute of Standards and Technology (NIST) 91 Slovak Institute of Metrology (SMU) 92 Bureau International des Poids et Mesures (BIPM) 93 ANNEX 5 AMOUNT OF SUBSTANCE FRACTION AS CALCULATED BY THE BIPM USING ITS OWN MEASURED SPECTRA 94 Page 3 of 97

4 1. Rationale for comparison This comparison was designed to evaluate the level of comparability of laboratories nitrogen dioxide measurement procedures based on FT-IR spectroscopy as an absolute method of quantification with traceability of measurement results to line strength data. In this comparison, which is a variation of the key comparison CCQM-K74[1] and the pilot study FT-IR for comparisons of NO 2 in nitrogen standards [2], participants provided, in addition to the value and uncertainty of the nitrogen dioxide mole fraction, the infrared spectra and instrument parameters used in their calculations. In this manner the BIPM reproduced the participant s nitrogen dioxide mole fractions using its own synthetic spectra calibration procedure with values traceable to the line parameters contained in HITRAN 2004 to investigate the use of FT-IR as an absolute method of quantification. Additionally it was expected that the results of this comparison would provide further information on any biases in line strength data for nitrogen dioxide in the HITRAN database. 2. Quantities and Units In this protocol the measurand was the mole fraction of nitrogen dioxide in nitrogen* with measurement results being expressed in mol/mol and its multiples μmol/mol or nmol/mol. (*the nitrogen balance gas nominally contains 1000 µmol/mol of oxygen) 3. Schedule The revised schedule of the project was as follows: June 2009 Shipment of cylinders to the BIPM June 2009 August 2009 Analysis of mixtures at the BIPM September 2009 Shipment of cylinders from the BIPM to participants October 2009 January 2010 Analysis of mixtures by the participants February 2010 Shipment of cylinders back from participants to the BIPM March 2010 May nd set of analyses of mixtures at the BIPM February 2010 May 2010 Reports of the participants September 2010 Distribution of Draft A of this report and Workshop on NO 2 Comparisons CCQM-K74 and CCQM-P110 April 2011 Proposal of the Draft B report with updates from the Workshop September 2011 Distribution of the Draft B report April 2012 Distribution of the 1 st revised version of the Draft B report February 2013 Distribution of the 2 nd revised version of the Draft B report Page 4 of 97

5 4. Measurement standards: results of the key comparison CCQM-K74 Since this comparison was performed in parallel with the international key comparison CCQM-K74 all mixtures, with exception of the mixture assigned to NMIJ, were previously described in the Final Report of the CCQM-K74 comparison. The characteristics of the mixture , value assigned simultaneously by the BIPM with all the other mixtures of the CCQM-K74 comparison, are described in Annex 2 - BIPM measurement results for cylinder # PRM. 5. Reference Values for Cylinders The reference value of the cylinders is based on the 1st series of BIPM measurement results that corresponds to the KCRV as reported in Flores et Table 2). NMIJ did not take part in the CCQM-K74, and in their case the reference value was based on the procedure used to calculate KCRV values for all other cylinders in the study. 6. Measurement protocol The measurement protocol requested participants to evaluate the nitrogen dioxide mole fraction using synthetic spectra created with an atmospheric radiative transfer model and a database of molecular parameters such as HITRAN. In order to perform an in-depth investigation of the FT-IR methodology used, participants were required to report the following information in the result form CCQM- P110-R-B2: the value and uncertainty of the nitrogen dioxide mole fraction measured by the laboratory using synthetic spectra for calibration; a complete uncertainty budget; a description of the gas analysis procedure, including the FT-IR quantitative analysis procedure; and all the interferograms and infrared spectra (background and sample) used to calculate the nitrogen dioxide mole fraction. Wherever possible the BIPM used the laboratories submitted spectra and instrument data to recalculate nitrogen dioxide mole fractions using its own synthetic spectra calibration procedure with values traceable to line parameters contained in HITRAN The participant s reports are included in Annex 3 - Measurement reports of participants. Page 5 of 97

6 7. Instrumentation and calibration The instrument and experimental characteristics submitted by the participants were included in Annex 3 - Measurement reports of participants. Table 1 summarizes the main characteristics of the instrumentation and calibration methods used by each laboratory. 8. Results 8.1 NMIs submitted values The nitrogen dioxide mole fractions submitted by the participating laboratories are listed in Table 2. This includes the BIPM results obtained with the synthetic spectra calculation procedure described in Annex 1- BIPM Value assignment procedure. Details of the calculations made by participants can be found in Annex 3 - Measurement reports of participants. The evaluation of the level of consistency between the participating laboratories was done by comparison with the Key Comparison Reference Values (KCRV) of CCQM- K74 with exception of cylinder # PRM, assigned to NMIJ, that was not used in the CCQM-K74 comparison. However this cylinder was value assigned simultaneously with the cylinders used in the CCQM-K74 comparison and was part of the original batch of cylinders produced by VSL for this comparison. The level of consistency is presented in terms of the difference (D 1 ) expressed quantitatively in two terms: deviation from the reference value and the uncertainty of this deviation (at 95 % level of confidence). This difference is defined as: D 1 xlab xref (1) Where: x Lab denotes the amount of substance fraction as reported by the participants; and x ref is the assigned amount of substance fraction by the 1st series of BIPM measurement results that corresponds to the KCRV as reported in Flores et al. [1]1 (Table 2). The combined standard uncertainty associated with the difference D 1 can be expressed as: u 2 2 ( D1 ) ulab uref and the expanded uncertainty, at 95 % confidence level (2) Page 6 of 97

7 U D ) k u( ) (3) ( 1 D1 where k denotes the coverage factor, taken as k = 2 (normal distribution, ~95 % level of confidence). The difference (D 1 ) between the reference values and NMI s assigned values for each of the circulated gas standards is listed in Table 2 and plotted in Figure 1 where: Laboratory Cylinder x ref BIPM u(x ref ) x Lab u(x Lab ) D 1 u(d 1 ) is the acronym of the participating NMI; is the identification code of the cylinder received by the participating laboratory; is the assigned amount of substance fraction of a component by the (1st series of BIPM measurement results); is the uncertainty of the BIPM measurement result; is the FT-IR result as reported by the participating laboratory; is the standard uncertainty associated with the reported value as submitted by the participant x Lab ; is the difference in amount of substance fraction as measured by the laboratory and the 1st series of BIPM measurement results that corresponds to the KCRV as reported in Flores et al. [1]1 (Table 2). and is the standard uncertainty of the difference. Page 7 of 97

8 Laboratory NMIA NMISA BIPM NPL NIST SMU KRISS CEM VNIIM NMIJ (UOW) FT-IR spectrometer Nicolet 6100 Nicolet Magna Varian Monitoring Nicolet Nexus Nicolet 6700 Nicolet 6700 Bruker PerkinElmer IR 560 Excalibur Ldt, Russia JASCO Path length (m) * 7.36* 10.99* * Path length calibration method None None NO 2 Ethanol and measurements + CO gas mixture methane ratio to single measurements measurements path gas cell None None None None Slide gauge Path length uncertainty (%) None None Average gas cell temperature (K) Average gas cell pressure (kpa) Missing parameters in Table B2-5.2 of the result form CFL, CAD CFL None CFL CFL CFL None CFL None CFL Spectrometer software to: control Omnic Omnic Omnic-IMACC Omnic Omnic OPUS Spectrum Spectra Fspec software Manager acquire Omnic Omnic IMACC Omnic Omnic FT-IR Collection Manager analyze MALT+NLLSQ MALT+NLLSQ MALT+CLS Omnic MALT+NLLSQ IMACC SpectraLab Line-by-Line software to create the reference spectra MALT 5 MALT 5 MALT 4.4 NA HITRAN simulation program Spectrum software Fspec Own MALT 5 ETRANS SpectraLab Spectra Manager Spectra Manager MOLSPEC IV Spectral range used for the mole fraction determination(cm ) ( *) 3000 Measurement resolution (cm 1 ) 0.25/ Molecular Database HITRAN HITRAN04 HITRAN04 HITRAN04 NIST/PNNL HITRAN04 HITRAN04 HITRAN04 HITRAN04 HITRAN04 (or reference spectra) 96 Molecular database assigned None None None None uncertainty /% u(x Lab ) /% Table 1. FT-IR instrumentation, optical path of the gas cells, control, acquisition and analysis software and the molecular data. (*) Second region for extra information concerning the mole fraction determination of nitrogen dioxide. * Optical path value determined by the laboratory. CFL: Collimator Focal length. CDA: Collimator Diameter aperture. NLLSQ: Non-linear least squares. Page 8 of 97

9 Reference value from the 1 st series of BIPM measurement results*. Nitrogen dioxide value reported by participants (CCQM-P110 B2) Laboratory Cylinder x ref u(x ref ) x Lab u(x Lab ) D 1 u(d 1 ) 2u(D 1 ) NPL # PRM SMU # PRM NMIA/UOW # PRM NMISA # PRM NMIJ # PRM KRISS # PRM NIST** # PRM CEM # PRM VNIIM # PRM BIPM # PRM Table 2. Laboratory results for nitrogen dioxide measurements (μmol/mol). * These values, with exception to NMIJ, correspond to the KCRV reported in Flores et al.[1] 1 Table 2. ** For this comparison NIST used the same gas mixture (# PRM) than the BIPM. Page 9 of 97

10 D1 ( μmol/mol) NPL SMU NMIA/UOW NMISA NMIJ KRISS NIST CEM VNIIM BIPM Cylinder form Laboratory Figure 1. Difference between FT-IR participants results and the 1st series of BIPM measurement results. The error bar represents the expanded uncertainty at a 95 % level of confidence. Page 10 of 97

11 8.1.1 Analysis by participant The results of the comparison were presented and discussed during a workshop held in Singapore in November The discussion of results below is based on the information provided by the laboratories during the workshop and extra analysis provided by the BIPM NMIA/UOW The result submitted by NMIA/UOW does not agree with the CCQM-K74 reference value. The precision of the gas cell optical path length and the conversion of some NO 2 due to the heating of the gas cell used during the measurements (60 C) may be associated with this difference equivalent to ~6 % (see Page 42). However, the presence of other species apart from H 2 O, CO 2 and NO 2 was not confirmed when inspecting the infrared spectra submitted by the participant. Since NMIA/UOW did not consider any uncertainty contribution due the optical path length of the FT-IR gas cell and the HITRAN database, this participant reported the smallest standard uncertainty of the comparison: 0.6 % (see Table 1) NMISA The standard uncertainty in the value of the difference between the submitted NMISA result and the CCQM-K74 reference value would need to be enlarged by a factor of 2.32 in order to infer agreement between the submitted and reference values. The relative standard uncertainty of the measurement result submitted by NMISA did not consider the uncertainty contribution of the FT-IR gas cell used for the measurements or any uncertainty contribution from the HITRAN molecular database NMIJ The standard uncertainty in the value of the difference between the submitted NMIJ result and the 1st series of BIPM measurement results would need to be enlarged by a factor of 2.8 in order to infer agreement between the submitted and reference values. NMIJ did determine the optical path length of the gas cell experimentally and evaluated an associated uncertainty. Further consideration should be given to the magnitude of the uncertainty contribution from the optical path length determination and the need to include an uncertainty contribution for the values originating from the HITRAN molecular database. NMIJ determined the optical path length of the single gas cell by measuring the distance between the gas cell windows using a highly accurate slide gauge. Therefore, the uncertainty contribution of the determination of the gas cell optical path length was extremely small (0.13 %) compared to other participants that used multi-reflection gas cells. This combined with the omission of an uncertainty contribution for values taken from HITRAN resulted in a submitted relative standard uncertainty of 1 % (the second smallest of all submitted values). Page 11 of 97

12 An example of the infrared spectra submitted by all participants, including NMIJ, were plotted for review in ANNEX 4 Absorbance spectra submitted by participants. The consequence of using a single path absorption cell can be seen in the small absorbance values of the infrared spectra recorded by NMIJ compared to other spectra. The peak height signal of the nitrogen dioxide band was ~ absorbance units (Abs), when the range of the peak high signals of other participants was in the range (0.075 to 0.380) Abs. The NMIJ submitted value is close to the reference value, which indicates a limited influence of the low absorbances on the nitrogen dioxide mole fraction determination SMU The value submitted by SMU agrees with the CCQM-K74 reference value and the laboratory reported one of the lowest standard uncertainties submitted by any participant (1.3 %). SMU considered as 0.25 % the uncertainty contribution of the optical path length to the general uncertainty budget however the laboratory did not verify the optical path experimentally. SMU used a different version of HITRAN to the version originally specified in the Measurement protocol. SMU used HITRAN 96 instead of HITRAN 2004 for the generation of synthetic reference spectra. The use of a different version of the database was not considered to lead to considerable measurement bias. Calculations carried out by the BIPM indicate that the difference resulting from the use of the two versions of HITRAN for retrieving the nitrogen dioxide mole fractions is 0.1 % for the spectral region 1500 cm 1 to 1700 cm 1 and ~0.5 % for the region 2800 cm 1 to 3000 cm 1. The BIPM obtained these results using its own infrared spectra measured by a Nicolet infrared spectrometer, the Multiple Atmospheric Layer Transmission software (MALT) [3]3, developed at the University of Wollongong, and a Classical Least Squares algorithm CLS (also known as the K-Matrix method) [4] KRISS The result submitted by KRISS agrees with the CCQM-K74 reference value. The assigned uncertainty of the value submitted by KRISS is within the range of most of the standard uncertainties reported by the participants (2.2 % to 3.4 %). KRISS did not calibrate or verify the optical path length of the gas cell used for its measurements instead it assigned a relative standard uncertainty of 2.5 % to this component. The uncertainty obtained was similar to the other results submitted by participants that determined this value experimentally NIST The nitrogen dioxide value submitted by NIST agrees with the CCQM-K74 reference value. The relative standard uncertainty of 2.2 % assigned by NIST is within the range of standard uncertainties reported by most of the participants (2.2 % to 3.4 %). NIST determined the optical path length of the gas cell using ethanol and methane gas standards of known mole fraction. The relative standard uncertainty assigned by NIST to the optical path length of its gas cell was 2.15 %. Page 12 of 97

13 NIST used the spectral region 2840 cm -1 to 2940 cm -1 for its quantitative analysis, which was different from the other participants. This region is where water has no absorption but nitrogen dioxide absorbs 95 % less infrared radiation than in the spectral region (1500 cm -1 to 1700 cm -1 ). According to BIPM calculations i this difference in intensity can result in a difference of up to 2.5 % in the retrieved nitrogen dioxide mole fractions. Revaluation of the submitted NIST spectra using BIPM methodology led to a significant shift in the calculated NO 2 mole fraction as described in section VNIIM The result submitted by VNIIM is in agreement with the CCQM-K74 reference value. The relative standard uncertainty assigned by this participant is within the range of most of the standard uncertainties reported by the participants of 2.5 %. VNIIM did not calibrate or verify the optical path length of the FT-IR gas cell BIPM The result submitted by the BIPM is in agreement with the CCQM-K74 reference value. The stated relative uncertainty by the BIPM of 3.4 % is within the uncertainty range (2.2 % to 3.4 %) of most of the participants. The optical path length was determined experimentally using a single path FT-IR gas cell and a primary standard of highly concentrated nitrogen dioxide (100 μmol/mol). The contribution of the uncertainty associated with the optical path length, determined experimentally by the BIPM and included in the contribution of the MALT+CLS uncertainty budget, was estimated to be 61 %. This is fully described in Flores et al. [5] NPL The standard uncertainty in the value of the difference between the submitted NPL result and the CCQM-K74 reference value would need to be enlarged by a factor of 2.54 in order to infer agreement between the submitted and reference values. The NPL experimentally determined the optical path length of the gas cell ii and assigned the largest standard uncertainty submitted by all participants (~4.3 %). NPL was the only participant to choose a different reference than the HITRAN database recommended in the comparison protocol (section 6): reference spectra were taken from the NorthWest Infrared Vapor Phase InfraRed Spectral Library created by the Pacific Northwest National Laboratory (PNNL). The difference between the submitted result of NPL and the CCQM-K74 reference value cannot be explained by these spectra (PNNL) instead of the HITRAN database, as will be discussed in section i This calculation was carried out by retrieving MALT +HITRAN 2004 infrared absorbance spectra from the BIPM Nicolet spectrometer. ii NPL experimentally determined the optical path length of the gas cell using carbon monoxide gas mixtures of known mole fraction. The relative standard uncertainty of the optical path gas cell is 3 %, leading to a relative standard uncertainty of 4.3 % assigned by NPL to the reported nitrogen dioxide value. Page 13 of 97

14 CEM The standard uncertainty in the value of the difference between the submitted CEM result and the CCQM-K74 reference value would need to be enlarged by a factor of 12.9 in order to infer agreement between the submitted and reference values. According to further discussions with this participant, an error in the optical path length of the FT- IR gas cell used for the measurements could account for the origin of the difference Discussion Since similarities in the calibration methodologies, instrumentation and experimental conditions used by some of the participants could influence agreement with the CCQM- K74 reference value, a list of the most representative similarities observed in Table 1 is presented below. It was concluded that of the ten participating laboratories: - five laboratories used Nicolet spectrometers operated by the Omnic acquisition software; - four used the MALT software for the generation of their infrared reference spectra (NMIA, KRISS and NMI-SA used MALT 5 +NLLSQ and BIPM MALT 4.4 +CLS); - five used 10 m as the optical path length; - eight assigned an uncertainty contribution to the optical path length within the range of 0.1 % to 3 %; - four determined their optical path lengths experimentally; - eight used the spectral region within the range 1500 cm -1 to 1700 cm -1 for the quantification of the nitrogen dioxide mole fraction with only NIST and SMU using a spectral region within the range 2800 cm -1 to 3000 cm -1 for quantification (NPL used both regions); - most used HITRAN 2004 as their molecular database for high resolution line strength reference data, with only SMU using HITRAN 96 and NPL using NIST/PNNL infrared reference spectra; - six considered the standard uncertainty of the line parameters contained in the HITRAN database to be within the range 1 % to 5 % and three did not assign any contribution; - nine measured their gas mixtures near ambient conditions (297 K and ~100 kpa); and - the measurement spectral resolution used by the participants is within the range 0.25 cm -1 to 4 cm -1. Taking this information into account it is concluded that the uncertainty contribution assigned to the optical path length and to the molecular database HITRAN were the parameters that most influenced the agreement with the CCQM-K74 reference value. The relative standard uncertainties reported by participants that considered the uncertainty contributions of the optical path length and HITRAN were in the range 1.3 % to 4.3 % with the median value of all claimed uncertainties being 2.3 %. Page 14 of 97

15 8.2 Recalculation of the participants results by the BIPM As described in the comparison protocol (Section 6) the BIPM recalculated the results obtained by each laboratory using the laboratories submitted spectra, instrument data and BIPM synthetic spectra calculation procedure with values traceable to line parameters in the HITRAN database. This was undertaken to study the agreement between MALT+CLS+HITRAN 2004 users, as well as different software packages used by the participants to generate their synthetic references spectra and to differentiate result disagreements associated with the spectra acquisition and the calculation procedure. Unfortunately, only two of the ten participating laboratories reported the entire set of parameters requested by the protocol. In order to extract the maximum information the results of those participants that did not report the Collimator Focal Length (CFL) but used Nicolet spectrometers were reproduced using the standard CFL value of 152 mm instead. Indeed, according to BIPM simulations of a Nicolet spectrum using a CFL value in the range 148 mm to 162 mm by MALT the uncertainty contribution of this parameter is less than %. Only SMU, NMIJ and CEM used a different spectrometer and did not provide sufficient information to recalculate their results. The consistency between the participants results recalculated by the BIPM using the spectra submitted by the participants and the reference values (CCQM-K74) is presented in terms of the difference (D 2 ) expressed quantitatively in two terms: deviation from the reference iii value and the uncertainty of this deviation (at 95 % level of confidence). These differences are defined as: Where: D2 x BIPMSpectN x (4) MI ref x BIPMSpectNMI is the amount of substance fraction as calculated by the BIPM using laboratories submitted spectra, instrument data and BIPM synthetic spectra calculation procedure with values traceable to line parameters in the HITRAN database VERSION 2004; x ref was defined in section 8.1. The combined standard uncertainties associated with the difference in the relative difference can be expressed as: u 2 2 ( D2 ) u BIPMSpectN MI uref (5) and the expanded uncertainty at 95 % confidence level U ( D2 D2 ) k u( ) (6) iii The x ref value is the CCQM-K74 value determined by the BIPM. Page 15 of 97

16 where k denotes the coverage factor taken as k = 2 (normal distribution, ~95 % level of confidence). The differences D 2 between BIPM and the amount of substance as calculated by the BIPM using laboratories submitted spectra and instrument data are listed in Table 3 where: Laboratory Cylinder is the acronym of the participating NMI; is the identification code of the cylinder received by the participating laboratory; x ref and u(x ref ) was defined in section 8.1. x BIPMSpectNMI is the amount of substance fraction as calculated by the BIPM using laboratories submitted spectra, instrument data and BIPM synthetic spectra calculation procedure with values traceable to line parameters in the HITRAN database 2004; x ) is standard uncertainty associated with the reported value x BIPMSpectNMI equivalent to the uncertainty submitted by the participant u(x Lab ), see section 8.1; u( BIPMSpectNMI D 2 u(d 2 ) is the difference in amount of substance fraction as calculated by the BIPM using laboratory submitted spectra and the 1st series of BIPM measurement results that, with exception to NMIJ, correspond to the KCRV from the CCQM-K74 report (Table 2); and is the standard uncertainty of the difference of amount of substance; To simplify the evaluation of the agreement between the recalculated values by the BIPM, the submitted values by the participants and the CCQM-K74 reference values, the differences D 1 and D 2, see section 8.1, were plotted together in Figure 2. Page 16 of 97

17 Reference value from the 1 st series of BIPM measurement results that in this case correspond to the KCRV reported in the CCQM-K74 report (Table 2). Nitrogen dioxide value obtained by the BIPM using laboratories submitted spectra, instrument data and BIPM synthetic spectra calculation procedure in the spectral region 1500 cm 1 to 1660 cm 1 Laboratory Cylinder x ref u(x ref ) x BIPMSpectNMI u( x BIPMSpectNMI ) D 2 u(d 2 ) 2u(D 2 ) NPL # PRM NMIA/UOW # PRM NMISA # PRM KRISS # PRM NIST # PRM VNIIM # PRM BIPM # PRM Table 3. Nitrogen dioxide value obtained by the BIPM using laboratories submitted spectra, instrument data and BIPM synthetic spectra calculation procedure in the spectral region 1500 cm 1 to 1660 cm 1. Page 17 of 97

18 D2 (μmol/mol) NPL NMIA /UOW NMISA KRISS NIST VNIIM Cylinder from Laboratory BIPM Calculated values NMI's Submitted results Figure 2. Difference (D 2 ) between BIPM calculated values using laboratories submitted spectra and the CCQM-K74 reference values (red), together with the difference (D 1 ) between laboratories submitted results and CCQM-K74 reference values (blue). The error bar represents the expanded uncertainty at a 95 % level of confidence. Page 18 of 97

19 8.2.1 Analysis by participant Participants that did not report the CFL parameter but used Nicolet spectrometers NPL Excellent agreement was found between the average nitrogen dioxide mole fraction calculated by the BIPM using MALT+CLS+HITRAN2004 and NPL using PNNL infrared reference spectra and peak area integration. This result implies that the use of both methods is equivalent with an uncertainty of 4.3 % and that the source of the reported difference in section between the value reported by NPL and CCQM- K74 reference value may be related to the acquisition procedure of the infrared spectra and not to the mole fraction determination procedure NMIA/UOW The nitrogen dioxide mole fraction calculated by the BIPM agrees with the value submitted by NMIA/UOW. This result confirms the consistency in the use of MALT 5 +NLLSQ+HITRAN 2004 and MALT 4.4 +CLS+HITRAN 2004 by both participants and confirms that the discrepancies with the KCRV of the CCQM-K74 are not generated by the retrieval procedure NMISA The nitrogen dioxide mole fraction obtained by the BIPM is in agreement with the result submitted by NMISA. This participant, like NMIA/UOW, used MALT 5 +NLLSQ+HITRAN 2004 for the quantitative analysis NIST The nitrogen dioxide mole fraction calculated by the BIPM is not in agreement with the result submitted by NIST. The difference between both results is equivalent to 7.5 % despite the nitrogen dioxide mole fraction submitted by NIST agreeing with the CCQM- K74 reference value. In order to verify if this difference was the result of the use of a different spectral region by the BIPM analysis (1500 cm -1 to 1660 cm -1 ) the spectra were retrieved once again in the region 2840 cm -1 to 2940 cm -1. As result, a difference of ~0.1% was found between both results concluding that the observed difference between NIST and BIPM can not be explained by the difference in the spectral region. Page 19 of 97

20 Participants that submitted all parameters KRISS Excellent agreement was observed between the nitrogen dioxide mole fraction calculated by the BIPM and KRISS. This participants used MALT 5 +NLLSQ+HITRAN 2004 for their quantitative analysis VNIIM Excellent agreement as well was observed between the nitrogen dioxide mole fraction reported by VNIIM and the BIPM. VNIIM used HITRAN 2004 as the molecular database (also used by the BIPM) but the SpectraLab quantitative analysis software was used for data interpretation Discussion To characterize the differences between the submitted and BIPM recalculated results both nitrogen dioxide mole fractions were subtracted and plotted in Figure 3. From the recalculation of the participants results was concluded that: - a CFL standard value allowed the BIPM to correctly retrieve the nitrogen dioxide mole fractions of those laboratories that did not submit this parameter as predicted; - excellent agreement was observed between NMIA/OUW, NMISA, KRISS that used MALT 5 +NLLSQ+HITRAN 2004 and the BIPM that used MALT 4.4 +CLS+HITRAN 2004 with a difference in the nitrogen dioxide retrieved values of ~0.1 %; - excellent agreement was observed between the recalculated values obtained by the BIPM and VNIIM, which used SpectraLab software, and NPL which used infrared spectra from the PNNL database. Differences were equivalent to 0.3 % and 0.5 % respectively; and - no reason was found to explain the 7.5 % difference between the results calculated by the BIPM and submitted by the NIST. Page 20 of 97

21 Calc Diff / μmol/mol MALT5+NLLSQ +HITRAN 2004 MALT5+NLLSQ +HITRAN 2004 MALT5+NLLSQ +HITRAN 2004 MOLSPEC IV+HITRAN 2004 NIST/PNNL HITRAN+HITRAN NPL NMIA /UOW NMISA KRISS NIST VNIIM Laboratory Figure 3. Difference between BIPM calculated values using laboratories submitted spectra and FT-IR participants results. The error bar represents the expanded uncertainty at a 95 % level of confidence. Page 21 of 97

22 Version /03/ Amount of substance fraction as calculated by the BIPM using its own measured spectra The BIPM recalculated the nitrogen dioxide mole fraction of each gas standard used in the comparison using its own measured infrared spectra and calibration method to identify biases in the line strength measurements for nitrogen dioxide in the HITRAN database. The potential biases were evaluated in terms of the difference (D 3 ) defined as: where: D x BIPMSpectB x (7) 3 IPM K 74 x BIPMSpectBIPM is the amount of substance fraction as calculated by the BIPM using its own measured spectra and calculation procedure (traceable to HITRAN 2004); and x defined in section 8.1. ref The combined standard uncertainties associated with the difference D 3 and other details are fully explained in ANNEX 5 Amount of substance fraction as calculated by the BIPM using its own measured spectra. Figure 4 shows that D 3 according to the stated uncertainties given to the BIPM and the CCQM-K74 reference values are consistent. However, according to BIPM calculations such a difference is consistent and equivalent to ~6 % D3 (μmol/mol) NPL SMU NMIA NMISA NMIJ KRISS NIST CEM VNIIM BIPM Cylinder from Laboratory Figure 4. Difference between the calculated nitrogen dioxide values using own synthetic spectra (traceable to HITRAN 2004) and the 1st series of BIPM measurement results that, with exception to NMIJ, correspond to the KCRV from the CCQM-K74.

23 9 Conclusions This pilot study was designed to evaluate the level of comparability of laboratories nitrogen dioxide measurements based on FT-IR spectroscopy as an absolute method of quantification. Additionally, it was expected that the results of this comparison would provide further information on any biases in line strength measurements for nitrogen dioxide in the HITRAN database. To do so, the protocol required participants to produce results operating the FT-IR as a potentially primary method i.e. without calibration with nitrogen dioxide standards. Based on the BIPM methodology, it was expected that the major contributors to the uncertainty of results would come from uncertainties in the line strength data in the spectroscopic reference databases, optical path length values for the FT-IR gas cells, and gas temperature and pressure measurements. To further compare methodologies, the protocol also required participants to submit their infrared spectra and a detailed list of the experimental parameters used during the acquisition. This allowed the BIPM to recalculate the results of six of the ten participants. Looking at the results of this study, it was concluded that: a) Half of participants agreed with the reference values and a non-negligible spread in the results (relative standard deviation of 11% compared to 0.8% on the reference values) as well as in the standard uncertainties (from 0.6% to 4.3%) was observed; b) The average relative standard uncertainty attributed by participants was 2.3%, which is five times larger than the relative standard uncertainty of 0.4% attributed to the reference values based on calibration with the dynamic facility maintained by the BIPM [6]6, specifically continuous weighing of a nitrogen dioxide permeation tube; c) The spread in the values for measurement uncertainties submitted was mainly attributed to the underestimation of the uncertainty contributions coming from the optical path length and the values taken from the HITRAN molecular data base. These two contributions were, as expected, the parameters that most affected the level of agreement of the participants; d) When recalculating the nitrogen dioxide mole fraction of each gas standard using BIPM s measured infrared spectra a systematic bias with the reference values of 6% was noticed. However, due to the spread of values reported by participants, it was not possible to confirm the expectation that a constant bias in the results of this study would be observed as a result of a bias in line strength values in the HITRAN database; e) From the recalculation of the participant s results by the BIPM using the laboratories submitted experimental characteristics and infrared spectra, good agreement between calculation procedures was achieved. This however indicated the lack of harmonization in the experimental procedures applied by the different participants; Page 23 of 97

24 In conclusion, the level of participation in this study confirmed the interest for developing FTIR procedures with traceability to reference line strengths for use in gas metrology. The results however revealed a lack of harmonization measurement protocols, mainly in the experimental procedures, but also in the uncertainties associated with common reference values from the HITRAN database which is widely used, not only within the metrology community. Further work should be performed to identify best practices and limitations for the use of FTIR procedures with traceability to line strength data. The BIPM is currently contributing to this effort with a paper describing the study of sources of uncertainties in such methods which was undertaken in parallel to this study 5. A future comparison using a more detailed protocol could also be developed in the future, to better characterise the performance of these methods. 10 Bibliography (1) DWT Griffith: Synthetic calibration and quantitative analysis of gas phase FTIR spectra. Applied spectroscopy 50 (1996) (2) BJ Sønnik C.: A hot gas facility for high-temperature spectrometry. Meas. Sci. Technol 13 (2002) (3) DJ L.S. Rothman, A. Barbe, D. Chris Benner, M. Birk, L.R. Brown, M.R. Carleer, C. Chackerian Jr., K. Chancea, L.H. Couderth, V. Danai, V.M. Devic, J.-M. Flaudh,2, R.R. Gamachej, A. Goldmank, J.-M. Hartmannh,2, K.W. Jucksl, A.G. Makim, J. Y. Mandini, S.T. Massien, J. Orphalh,2, A. Perrinh,2, C.P. Rinslando, M.A.H. Smitho, J. Tennysonp, R.N. Tolchenovp, R.A. Tothe, J. Vander Auweraf, P. Varanasiq, G. Wagnerd: The HITRAN 2004 molecular spectroscopic database. Journal of Quantitative Spectroscopy & Radiative Transfer 96 (2005) Page 24 of 97

25 Version /03/2012 Annex 1- BIPM Value assignment procedure FT-IR Spectra acquisition A ThemoNicolet Nexus FT-IR spectrometer was configured with a MCT-high D* liquid N 2 -cooled mid-infrared detector and a 6.44±0.17 m pathlength multipass White cell (Gemini Scientific Instruments, USA) for the purposes of quantitative analysis for gas reference standards. The White cell has wetted surfaces of only electropolished stainless steel and gold (mirror coatings) to minimise surface interactions with reactive gas phase species. To keep the internal optical path of the spectrometer free of any interference species this ensemble has been placed in stainless steel enclosure which is constantly purged with ultra high purity nitrogen (dewpoint ~-95 C, i.e. ~200 nmol mol -1 H 2 O) flowing at ~15 L min -1. Waste Flow control ~400 ml/min T P Sample flow With Cell 6.4 m Path 750 ml vol. IR Source Purge ultra pure nitrogen Flow=~15L/min Dew point: ~95 C MCT-High D* detector LN 2 cooled range: cm -1 Interferometer KBr beamsplitter Figure 5: Schematic of FT-IR system used in the BIPM NO 2 Facility 6 for quantitative analysis of gas reference mixtures for NO 2, H 2 O and HNO 3. The gas sample from the high pressure cylinders, flows from the NO 2 facility sampling manifold through the White cell, and then to waste. The sample flow rate is controlled immediately downstream of the White cell at ~400 ml min -1. The sample pressure and temperature are measured on real time by means of a calibrated barometer (Series 6000 Digital Pressure Transducer, Mensor, USA) and a calibrated 100 Ω RTD temperature probe attached to the White cell.

26 Control and acquisition software The spectrometer user interface is by means of the IMACC software. IMACC allows the automatic setting of all instrument parameters into Thermo's proprietary Omnic software for the control, spectra acquisition and on-line analysis. For the acquisition of high quality spectra suitable for quantitative analysis, 120 scans are co-added over a period of 2 minutes to provide one single beam spectrum of a sample. This single beam spectrum is then ratioed with a similar spectrum of ultra pure nitrogen collected under similar conditions to provide an absorbance spectrum of the gas sample (relative to ultra pure nitrogen). The White cell has a volume of ~750 ml and the sample flows at ~400 ml min -1. Assuming perfect mixing in the cell we estimate that an initial sample at time t = 0 s has been 99.9 % replaced after 10 min of flow, and % replaced after 20 min. Accordingly, to ensure complete exchange of sample, spectrum acquisition started at t = 0 but only the measured spectra obtained after flowing the sample through the White cell for 30 min were used for the mole fraction determination. The absorbance spectra of gas reference standards obtained following this procedure had a very high signal: noise ratio, with the level of noise in the baseline being typically ~ abs 10 peak-peak. By comparison the main NO 2 peak had absorbance in the range ( ) abs 10. Quantitative analysis of the absorbance spectra Two codes developed in GRAMS software environment were used to analyse the absorbance spectra of the gas reference standards; the Multiple Atmospheric Layer Transmission software MALT 4 and a Classical Least Squares algorithm CLS. The Multiple Atmospheric Layer Transmission software MALT After reading an input file specified by the user, MALT reads the relevant line parameters from the HITRAN database and constructs a stick spectrum which is at the full high resolution of the database. MALT, then convolves this stick spectrum with the temperature, pressure, path length, resolution and instrument line shape function specified by the user in the input file. The output is a synthetic spectrum that closely simulates a spectrum of a real gas mixture acquired on the user s real (i.e. imperfect) FT-IR spectrometer. For the quantitative analysis MALT was run in a batch mode where it generated a set of 40 synthetic spectra which simulate a set of real spectra where the mole fraction of the component species vary independently of each other, and span a given range of mole fractions for each species. Table 4 lists a representative set of input parameters for MALT in the present study. 4 MALT is a piece of software developed at the University of Wollongong. Page 26 of 97

27 MALT input parameter Value range cm -1 primitive point spacing 0.02 cm -1 method LBL % width for Voigt calculation 5 # halfwidths for Voigt calculation 50 apodizaton Hamming (=Happ-Genzel) resolution (i.e. point spacing cm -1 ) collimator aperture diameter mm (equiv. to Nexus aperture setting 34) collimator focal length 152 mm y-scale absorbance log 10 pressure (of sample gas) Temperature (of sample gas) pathlength (of sample gas) line broadening option isotopic amounts component gas # hpa (typically) 29 C (typically) 6.45 m 1 (i.e. self-broadening) natural H 2O Component gas #2 NO 2 units for gas #1 ppm (=µmol mol -1 ) units for gas #2 ppm (=µmol mol -1 ) # of calibration spectra 40 seed for random numbers 7 baseline offset baseline slope gas #1 range gas #2 range min: 0 ppm; max: 3 ppm min: 8 ppm; max: 12 ppm baseline offset range min: ; max: baseline slope range min: ; max: Table 4. List of the input parameters to the MALT program to generate a set of 40 synthetic spectra which best model experimental spectra of NO 2 /N 2 mixtures acquired on the BIPM s Nexus FT-IR spectrometer. This input models spectra of NO 2 / N 2 mixtures with x in the range (8-12) µmol.mol -1 NO 2 and x in the range (0-3) µmol.mol -1. H 2 O The output of MALT run with this input is a set of 40 spectra at 1 cm -1 resolution of gas mixtures at 29 C and 1050 hpa where x NO varies in the range (8-12) µmol mol -1, x 2 H 2 O varies independently in the range (0-3) µmol mol -1, and the baseline offset and baseline slope of the spectra also vary independently over a small range. There are numerous input parameters and options for MALT other than those listed in Table 4. For the present study they were either not selected or were set to the default of zero. These 40 spectra and their corresponding mole fraction and baseline offset and slope values constitute a multivariate training (or calibration) set, which was used as input to the CLS algorithm. Page 27 of 97

28 The Classical Least Squares algorithm CLS For the quantification analysis of the spectra the multivariate algorithm CLS (an acronym for Classical Least Squares; a.k.a. the K-Matrix method) was used. The algorithm is first run in the forward (calibration) mode and then in the inverse (prediction) mode. The CLS-calibration mode takes as its primary input a matrix consisting of the spectral data of the 40-spectrum training set generated using MALT, as well as the mole fraction and baseline values associated with each spectrum. Using various matrix operations the CLS-calibration calculation derives a single vector corresponding to each measured parameter, in this case x NO, x 2 H 2 O, baseline offset and baseline slope. In the inverse mode the CLS-prediction algorithm takes as its input a real spectrum of unknown composition, acquired on our FT-IR spectrometer. An iterative process follows where a linear combination of the four vectors derived in the CLS-calibration mode is fitted to the real spectrum to provide the best fit according to a least squares criterion. The parameters of the CLS-prediction mode best fit are the estimated values of the x NO, x 2 H 2 O, baseline offset and baseline slope in the spectrum of the real mixture. Uncertainty budget The uncertainty budget used to calculate the uncertainty in the determination of NO 2 is the subject of an independent publication [5]5. The table below summarises the uncertainty sources and present the final combined uncertainty associated with the FT- IR measurements using MALT for synthetic calibration and CLS for the prediction of nitrogen dioxide values, at nominal mole fractions x in the range 5 µmol/mol to 15 µmol/mol, when using a 6.45 m optical path gas cell. Type A μmol/mol Stability Type B MALT 0.015x HITRAN 0.030x Combined uncertainty x 0. x 2 (10) Table 5: uncertainty budget associated with the FT-IR spectrometer used as an absolute method of quantification to determine the concentration of NO 2 in nitrogen. Three uncertainty sources were considered when using FT-IR spectroscopy as an absolute method of quantification: the stated uncertainty of HITRAN, the stability of the FT-IR spectrometer and calculation procedure of the synthetic spectra. The experimental standard uncertainty of the molecular line parameters of the HITRAN database version 2004 according to the authors is 3 %(3) 7. In the absence of any other reliable information contradicting this value the standard uncertainty of the database was considered as 3 % as well. Regarding the standard uncertainty of the response of the instrument an Allan variance analysis of the time series concluded that 20 nmol/mol Page 28 of 97

29 is the instrument standard uncertainty for a nitrogen dioxide range between 5 μmol/mol to 15 μmol/mol. MALT s contribution was calculated by a sensitivity study being the standard uncertainty u MALT =0.16 μmol/mol (or 1.5 %) when analyzing a gas mixture of 11 μmol/mol of nitrogen dioxide Standard uncertainty/ μmol/mol NO2 mole fraction / μmol/mol Figure 6: Plot of the standard uncertainty of nitrogen dioxide mole fraction x evaluated by FT-IR with MALT+CLS using the spectral region cm -1. Page 29 of 97

30 Version /03/2012 Annex 2 - BIPM measurement results for cylinder # PRM The nitrogen dioxide gas mixture was as all the other mixtures contained in a passivated aluminium cylinder of 5 L. The cylinder was pressurized at about 12 MPa. The nitrogen dioxide gas standards were produced by gravimetric preparation in accordance with the International Standard ISO 6142: The cylinder was value assigned by the BIPM with its gas facility in the same manner as has been fully described in the report International comparison CCQM-K74: Nitrogen dioxide, 10 μmol/mol (Draft A) ANNEX 1. The VSL and BIPM values and measurements for the mixture are given in Table 6 and Table 7 where: x VSL u prep (x VSL ) u ver (x VSL ) x BIPM1 u(x BIPM1 ) x BIPM2 u(x BIPM2 ) is the value assigned by VSL based on gravimetric preparation; the standard uncertainty of the VSL values with contributions due to gravimetry and purity analysis; the standard uncertainty including contributions from verification associated with the assigned value x VSL ; the first BIPM measurement result (prior to sending out cylinders to participants); the standard uncertainty of the first BIPM measurement result; the second BIPM measurement result (on return of cylinders from participants); the standard uncertainty of the second BIPM measurement result; Table 8 list the nitric acid mole fractions found in the gas standards where: Cylinder x HNO3(1) u(x HNO3(1) ) x HNO3(2) u(x HNO3(2) ) is the identification code of the cylinder received by the participating laboratory; the mole fraction of nitric acid measured in the standard by the BIPM (prior to sending standards to participants); the standard uncertainty associated with the nitric acid mole fraction measurement; the mole fraction of nitric acid measured in the standard by the BIPM (following return of standards to the BIPM); is the standard uncertainty associated with the nitric acid determination by FT-IR spectroscopy after the participants measurements. Table 4 lists the summation of nitrogen dioxide and nitric acid mole fractions for the standard based on BIPM measurements. 5 ISO 6142:2001: Gas analysis-preparation of calibration gas mixtures-gravimetric method.

31 Version /03/2012 VSL preparation values Gravimetric Certificate Preparation Number Assigned standard Certified standard NO 2 mole number date of Cylinder fraction uncertainty uncertainty x VSL uprep(x VSL ) uver(x VSL ) (μmol/mol) (μmol/mol) (μmol/mol) /04/2009 # PRM Table 6. Characteristics of gravimetric mixtures as provided by VSL. Number of Cylinder Measurement date 1 st measurement BIPM measurement results 1st BIPM Standard 2nd BIPM assigned Measurement assigned Standard NO 2 mole fraction uncertainty NO 2 mole measurement date fraction uncertainty Δx= x BIPM1 u(x BIPM1 ) (x BIPM2-2 nd measurement x BIPM2 u(x BIPM2 ) x BIPM1 ) u(δx) 2u(Δx) μmol/mol μmol/mol μmol/mol μmol/mol μmol/mol μmol/mol μmol/mol # PRM 31/08/ /04/ Table 7. Results of BIPM NO 2 mole fraction measurements. BIPM HNO 3 Measurements Measurement x HNO3(1) u(x HNO3(1) ) Measurement x HNO3(2) u(x HNO3(2) ) Δx= (x HNO3(2) - Cylinder date date x HNO3(1) -) u(δx) 2u(Δx) (μmol/mol) (μmol/mol) (μmol/mol) (μmol/mol) μmol/mol μmol/mol μmol/mol # PRM 12-Aug May Table 8. Nitric acid mole fraction measured in cylinder gas standards by the BIPM using FT-IR spectroscopy. * Insufficient gas for second measurement.

32 1st BIPM Standard 2nd BIPM Standard NO 2 mole fraction measurement uncertainty NO 2 mole fraction measurement uncertainty x BIPM1 2u x BIPM2 2u x BIPM1 u(x BIPM1 ) x BIPM2 u(x BIPM2 ) + (x BIPM1 + + u(x BIPM2 + (x BIPM2 + μmol/mol μmol/mol μmol/mol μmol/mol x HNO3(1) u(x BIPM1 + x HNO3(1) ) x HNO3(1) ) x HNO3(2) x HNO3(2) ) x HNO3(2) ) Table 9. Summary of nitrogen dioxide and nitric acid mole fractions for each standard based on BIPM measurements. Page 32 of 97

33 Version /03/2012 Annex 3 - Measurement reports of participants Centro Español de metrología (CEM) B2-1. General information Institute CENTRO ESPAÑOL DE METROLOGÍA (CEM) Address CALLE ALFAR, TRES CANTOS (MADRID) SPAIN Contact person TERESA E. FERNÁNDEZ VICENTE Telephone Fax * Serial number of cylinder received Cylinder pressure as received tefernandez@cem.mityc.es (D650059) 95 bar B2-2. Results Nitrogen dioxide mole fraction Expanded uncertainty Coverage factor x / μmol/mol U ) / μmol/mol NO2 ( x NO 2 7,24 0,49 2 B2-3. Uncertainty Budget The mathematical mode used to calculate the uncertainty in the composition of mixture analyzed is a linear combination of the sources of uncertainty due to the instrument used and the repeatability of the measurements. This leads to: u u u u u r shift bias L where u r is the standard deviation of the mean of the results obtained along the period of measurements considered, from the linear fit regression by means of the IFSS software; u is the uncertainty due to the error shift obtained by means of the IFSS software; u bias is the uncertainty due to HITRAN molecular database bias (5 %) and u L is the uncertainty of the path length due to the influence of the temperature and the pressure in the cell and the path length itself. Table 1 summarizes the uncertainties budget.

34 Uncertainty source r Assumed distribution Standard uncertainty / mol/mol Sensitivity coefficient Contribution to standard uncertainty / mol/mol u normal 0,05 1 0,05 u shift normal 0,08 1 0,08 u bias rectangular 0,21 1 0,21 u L normal 0,29-0,32 0,09 Combined standard uncertainty / mol/mol 0,25 Expanded uncertainty, k 6 = 2 / mol/mol 0,49 Table 1. Detailed uncertainty budget. B2-4. Description of the procedure used during the gas analysis Upon arrival the sample cylinder was rolled and stored in the laboratory under laboratory reference conditions. A pressure reducer was connected to the sample cylinder. The reducer was carefully flushed as prescribed in International Standard ISO 16664:2004 (Gas analysis Handling of calibration gases and calibration gas mixtures Guidelines). The sample cylinder was connected to a vacuum tree system connected to the FT-IR. When the vacuum in the cell was kpa and the vacuum in the tree was kpa, 16 background scans were collected. With the pressure in the cell set next to 102,3 kpa, 100 scans from the sample were collected. Due to the fact that the system lacks a sensor for the measurement of the temperature inside the gas cell, the experimental temperature corresponds to the environmental conditions in the laboratory, next to 293 K. Although the laboratory obtained spectra from seven independent working days (sample data reported in B2-6), the sample results reported come from the data obtained along three consecutive working days, from February the 16 th to the 18 th, because of their better uncertainty. Six synthetic spectra: 6 mol/mol, 7 mol/mol, 8 mol/mol, 9 mol/mol, 10 mol/mol and 16 mol/mol were used for a linear fit regression by means of IFSS software. Synthetic spectra were created in the conditions specified in Table 2: Software E-TRANS Database of molecular parameters HITRAN Temperature 296 K Pressure 765 torr Path length 6,4 m Laser frequency ,26 cm -1 Data point spacing 0, cm -1 Resolution 1 cm -1 Table 2. Experimental conditions for synthetic calibration spectra. Protocol B1 and B2 were carried out simultaneously. B2-5. FT-IR instrumentation and acquisition parameters B2-5.1 Instrumentation Spectrometer FT-IR 6 The coverage factor shall be based on approximately 95 % confidence. Page 34 of 97

35 Manufacturer Type Serial number Gas cell PerkinElmer GXI Manufacturer Specac Type SC Tornado T-20 Optical path (m) 20 m Operation software details Name of the software used to control the spectrometer Name of the software used to acquire spectra Name of the software used to analyse spectra Spectrum Software Spectrum Software IFSS (Imacc Software) B2-5.2 Acquisition parameters table Experimental conditions: Expanded Uncertainty U Gas cell path length / m 20 0,6 Instrument parameters (required): Nominal Resolution / cm -1 2 NA True Resolution ( Data point Spacing ) / cm -1 0,5 Negligible Laser frequency / cm ,01 NA Starting Wavenumber / cm NA Ending Wavenumber / cm NA Name of the apodization function used Strong NA Wavenumber shift related to HITRAN / cm -1 NA Collimator aperture diameter / mm 5,60 0,01 Collimator focal length / mm Scans 100 NA Page 35 of 97

36 Version /03/2012 B2-6 Recorded spectra names and parameters Measurement File name of the absorbance spectrum File name of the interferogram associated with the sample t File name of the sample spectra File name of the background interferogram associated with the sample spectrum File name of the background spectrum associated with the sample spectrum Temperature inside the gas cell Pressure inside the gas cell (Absorbance) T / K P / Muestra 1 incognita.spa NPL Muestra.SPA I0110k04 I0110k01 293,06 102,28 I0210k03 I0210k01 292,96 102,35 Muestra.SPA I0310k04 I0310k01 293,06 102,21 Muestra.SPA I0410k04 I0410k01 292,56 102,26 Muestra.SPA I0510k04 I0510k01 292,76 102,26 Muestra.SPA I0610k04 I0610k01 292,66 102,23 Muestra.SPA I0710k04 I0710k01 292,96 102,23 B2-7 Complementary information on the cylinder The value of the pressure left in the cylinder before shipment to the BIPM was 65 bar approximately.

37 Korea Research Institute of Standards and Science (KRISS) General information Institute Address Contact person KRISS 1 Korea Research Institute of Standards and Science (KRISS), P.O.Box 102, Yusong, Daejeon, Republic of Korea Lee, Jeongsoon for P110 B1 and b2 Telephone Fax * Serial number of cylinder received Cylinder pressure as received leejs@kriss.re.kr D bar Results Nitrogen dioxide mole fraction Expanded uncertainty Coverage factor x / μmol/mol U ) / μmol/mol NO2 ( x NO k = 2 Uncertainty Budget Please provide a complete uncertainty budget. The amount of substance for NO 2 can be determined by the following equation, C = R/(σ)(T/PV)(A/L), where (A = lni/lni 0 ). (1) In eq.(1), R is the gas constant of L atm K -1 mol -1, T is absolute temperature in unit of K, σ(λ, T, NO 2 ) is a cross section of a molecular NO 2, L is optical light pathlength of gas cell, P is pressure of gas cell, V is volume of gas cell and A(λ) is infrared absorbance of NO 2 at the wavelength and measured. Among variables in Eq. (1), σ is a B type variable obtained from HITRAN, and V and P are B type variables. Among them, an absorbance(a) is only measurand by FT-IR analyzer. Unfortunately the light path length was not calibrated in the laboratory for this comparison. Therefore the given value with uncertainty was used for uncertainty burget. Table. 1 Uncertainty Burget CCQM-P110_Protocol Page 37 of 97

38 Uncertainty factor type value Standard relative uncertainty [%] Expanded uncertainty [%] σ(λ) B 2 4 L B m P B kpa V B T B K A A cm Total Description of the procedure used during the gas analysis Measurement by FT-IR BIPM cylinder was measured several times with 10 m optical cell. Gas from the cylinder was introduced as: Cylinder >> regulator >> MFC >> gas Cell >> vent to atmosphere (when FT-IR measurement) or Vacuum during pumping (when purging). Followings are the procedures to acquire the spectrum; VACUUM less than 1.0 mb >> GAS CELL FILL with N2 TILL about 1013 mb (ambient pressure) >> measurement BG >> VACUUM less than 1.0 mb >> GAS CELL FILL with NO2 TILL 1013 mb >> measurement BIPM sample >> Analysis of FT-IR spectrum The spectrum measured by FT-IR was analyzed with the MALT program (Griffith et al. ver.5.2 ) which is well explained at Griffith et al. Details on the program are in the reference 5. FT-IR instrumentation and acquisition parameters Please specify the FT-IR instrumentation and the acquisition parameters used during the gas analysis. Spectrometer Manufacturer B2-5.1 Instrumentation Bruker Type TENSOR 27 Serial number T Gas cell Manufacturer Type OTSUKA MULTI PASS CELL CCQM-P110_Protocol Page 38 of 97

39 Optical path (m) Software FT-IR COLLECTION MANAGER (FCM) Name of the software used to control the spectrometer OPUS Name of the software used to acquire spectra FCM Name of the software used to analyse spectra FCM B2-5.2 Acquisition parameters table Experimental conditions: Parameter value Expanded Uncertainty U Gas cell path length / m % Temperature (K) % Pressure (KPa) % Instrument parameters (required): Nominal Resolution / cm NA True Resolution ( Data point spacing ) / cm Negligible Laser frequency / cm -1 15,798.0 NA Starting Wavenumber / cm NA Ending Wavenumber / cm NA Name of the Apodization function used Hamming (Happ-Genzel) NA Wavenumber shift related to HITRAN / cm NA Collimator aperture diameter / mm Collimator focal length / mm 69 Negligible Scans 128 NA Note: Section B2-7 shows the acquisition parameters of a Fourier transform Infrared Spectrometer device. Section B2-8 contains a short compendium of FT-IR terms and definitions. You may also find the acquisition parameters in your instrument manual, or in the software used for the spectra acquisition. CCQM-P110_Protocol Page 39 of 97

40 B2-6 Recorded spectra names and parameters Measurement File name of the File name of the File name of the File name of the File name of the absorbance spectrum interferogram associated with the sample spectrum sample spectra background interferogram associated with the sample spectrum background spectrum associated with the sample spectrum Temperature inside the gas cell Pressure inside the gas cell (Absorbance) T / K P / kpa 1 Work. 14 Work. 14 Work. 14 Work. 14 Work Work. 15 Work. 15 Work. 15 Work. 15 Work Work. 16 Work. 16 Work. 16 Work. 16 Work Work. 19 Work. 19 Work. 19 Work. 19 Work Work. 20 Work. 20 Work. 20 Work. 20 Work Please provide by to edgar.flores@bipm.org a single compressed file including all the interferograms and spectra used to calculate the nitrogen dioxide mole fraction of your cylinder gas mixture. If the compressed file is bigger than 2 megabytes, please split it in several 2 megabytes files. The spectra and interferograms need to be sent in one the follow formats: Spectra (SPA); J-Camp (JDX); Pcir (IRD); Nicolet SX/DX (NIC);Please note that an absorbance spectrum is considered as the result of the base 10 logarithm of 1/T (Abs=log 10 1/T) being T the ratio of a sample spectrum and a background spectrum. We are sending a OPUS format file to you named as work.20 which includes interferograms and transmittances of Bg and sample and absorbance. CCQM-P110_Protocol Page 40 of 97

41 B2-7 Complementary information on the cylinder Please report the value of the pressure left in the cylinder before shipment to the BIPM: PRESSURE LEFT: 52 BAR If any other component other than NO 2, nitrogen and oxygen was detected and/or quantified please report its mole fraction in the table below: N.A. Component Mole fraction / nmol/mol Expanded uncertainty Coverage factor Measurement technique CCQM-P110_Protocol Page 41 of 97

42 National Measurement Institute Australia (NMIA)/ University of Wollongong (UOW) General information Institute Address Contact person University of Wollongong Centre for Atmospheric Chemistry University of Wollongong Northfields Ave. Wollongong, NSW 2522 AUSTRALIA David Griffith Telephone Fax * Serial number of cylinder received Cylinder pressure as received griffith@uow.edu.au bar Results Nitrogen dioxide mole fraction Expanded uncertainty Coverage factor x / μmol/mol U ) / μmol/mol NO2 ( x NO (1.1%) 2 Uncertainty Budget This 1.1% stdev includes the systematic difference between the two spectral bands, and the real difference between the 4 samples in each case. The random error due to just the measurement is less than this Description of the procedure used during the gas analysis A Nicolet FT-IR was used to acquire the spectra of the unknown sample. The spectra were run at resolutions of 0.5cm -1 and 0.25cm -1 with an aperture setting of scans were obtained for each analysis. The background spectra was collected on the evacuated cell. Spectra were collected on a static gas sample with a temperature of 60ºC at a pressure of 650 Torr. The strong bands in the region cm -1 and the weaker bands in the region cm -1 were both used for quantitation. The analyses of the sample was repeated three times at each resolution with evacuation and flushing of the cell between tests. The analysis was performed on January 12th. FT-IR instrumentation and acquisition parameters Please specify the FT-IR instrumentation and the acquisition parameters used during the gas analysis. B2-5.1 Instrumentation Spectrometer Manufacturer Thermo Nicolet CCQM-P110_Protocol Page 42 of 97

43 Type 6100 Serial number AHR Gas cell Manufacturer Type Optical path (m) 10 Operation software details Thermo Nicolet Nickel plated aluminium. KBr windows Name of the software used to control the spectrometer Name of the software used to acquire spectra Name of the software used to analyse spectra Omnic Omnic MALT B2-5.2 Acquisition parameters table Experimental conditions: Gas cell path length / m 10 Expanded Uncertainty U Instrument parameters (required): Nominal Resolution / cm / 0.5 NA True Resolution ( Data point Spacing ) / cm / Negligible Laser frequency / cm NA Starting Wavenumber / cm NA Ending Wavenumber / cm NA Name of the apodization function used Hamming NA Wavenumber shift related to HITRAN / cm -1 <0.04 NA Collimator aperture diameter / mm Collimator focal length / mm Negligible Scans 100 NA Note: Section B2-7 shows the acquisition parameters of a Fourier transform Infrared Spectrometer device. Section B2-8 contains a short compendium of FT-IR terms and definitions. You may also find the acquisition parameters in your instrument manual, or in the software used for the spectra acquisition. CCQM-P110_Protocol Page 43 of 97

44 B2-6 Recorded spectra names and parameters Measurement File name of the File name of the File name of the File name of the File name of the absorbance spectrum interferogram associated with the sample spectrum sample spectra background interferogram associated with the sample spectrum background spectrum associated with the sample spectrum Temperature inside the gas cell Pressure inside the gas cell (Absorbance) Note: Interferograms were not saved as they were not required by the UOW. T / K P / kpa 1 Note : 0.25 cm-1 resolution K spa Bg spa K Bg spa K Bg spa K Bg spa Note : 0.5 cm-1 resolution K spa BG spa K BG spa K BG spa K BG spa Please provide by to edgar.flores@bipm.org a single compressed file including all the interferograms and spectra used to calculate the nitrogen dioxide mole fraction of your cylinder gas mixture. If the compressed file is bigger than 2 megabytes, pleas CCQM-P110_Protocol Page 44 of 97

45 National Metrology institute of Japan (NIMJ) Pilot Study CCQM-P110 Nitrogen dioxide in Nitrogen (10 μmol/mol) Protocol B2, Result form CCQM-P-110-B2 Project name: CCQM-P110 (Nitrogen dioxide, 10 μmol/mol). Comparison: Comparability study of laboratories measurement capabilities for nitrogen dioxide/nitrogen. Proposed dates: 12/2008 to 5/2010. Coordinating laboratories: Bureau International des Poids et Mesures Chemistry Section Pavillon de Breteuil Sevres Cedex, France. Nederlands Meetinstituut Van Swinden Laboratorium Department of Chemistry Thijsseweg JA Delft, the Netherlands. Study Coordinator: Edgar Flores Phone: +33 (0) Fax: +33 (0) Return of the form: Please complete and return the form preferably by to Protocol B2 Protocol B2 aims to evaluate the level of comparability of laboratories nitrogen dioxide measurement capabilities based on FTIR spectroscopy as an absolute method of quantification. The nitrogen dioxide reference value will be evaluated using synthetic spectra created with a line-by-line software and a data base of molecular parameters (for example HITRAN) 7. General information Institute National Metrology Institute of Japan Address Umesono, Tsukuba Ibaraki Contact person Nobuyuki Aoki Telephone Fax * Aoki-nobu@aist.go.jp 7 Protocol B2 is fully described in the document: Pilot Study CCQM-P110 Nitrogen dioxide in Nitrogen (10 μmol/mol) page 6. CCQM-P110_Protocol Page 45 of 97

46 Serial number of cylinder received Cylinder pressure as received APEX MPa Results Nitrogen dioxide mole fraction Expanded uncertainty Coverage factor x / μmol/mol U ) / μmol/mol NO2 ( x NO Uncertainty Budget The standard uncertainty of NO 2 fraction in sample was obtained from combination of standard uncertainties for the fractions determined using absorbances at wavenumber of cm -1 and cm -1. The standard uncertainties of NO 2 fraction at each wavenumber ( cm -1 and cm -1 ) were combination of reference uncertainty and measurement repeatability by FT-IR. The reference uncertainty was calculated from standard uncertainties of pressure, temperature, and pathlength. The uncertainty of pressure and temperature are uncertainty of the absolute pressure gauge and the platinum resistance thermometer. The uncertainty of pathlength are uncertainty combined from the standard uncertainty of measurement using a slide gauge and the difference of path lengths with and without multiple reflections. The effect of multireflection in the FTIR cell was estimated from total absorption of transmitted light through the FTIR cell considering reflection on the both surface of incident and exit windows for 0 to 10 reflection numbers. The reflectance on each surface was calculating using refractive index of window material (n= for IR with wavelengths of 1.5 to 8.5 micro meter). The measurement repeatability is standard deviation of four measurement values by FT-IR. Uncertainty of reference spectrum from HITRAN database Source of uncertainty Estimation Relative standard uncertainty Pressure(hPa) % rel. Temperature(K) % rel. Pathlength(cm) % rel. total 1.64 % rel. CCQM-P110_Protocol Page 46 of 97

47 Uncertainty of measurement Wave number(cm -1 ) absorbance average Relative standard uncertainty Uncertainty of NO 2 concentration Wave number(cm -1 ) Concentration ( mol/mol) Standard uncertainty ( mol/mol) average Description of the procedure used during the gas analysis NO 2 concentration in P-110 sample was quantified by comparison of the measured and reference spectra. The measured spectra were obtained using a JASCO FTIR-6100 spectrometer. While the reference spectra were calculated from a molecular database (HITRAN database(2004)). Reference spectra The reference spectra of NO 2 were calculated from convolution of the true line transmission and the instrument line shape (ILS) function. The true line transmission as function of wavenumber ( t ) is found from S( T ) l p c 1 t exp T 1 L c L where t is the optical transmission as a function of Wavenumber, Temperature T, Pathlength l, Linestrength S(T), Pressure p, Concentration c, linecenter c and lorentzian Halfwidth L. This calculation was performed by MOLSPEC IV using the spectroscopic parameters tabulated in a molecular database (HITRAN database(2004)). but an actual FT-IR spectrometer does not have infinite resolution, so when it measures radiation at a target wavenumber v i with FT-IR, it also measures nearby radiation in bandpass around v i. An instrument line shape (ILS) function accounts for this behaviour. The ILS function is the Fourier transform of the apodization function applied to the measured interferogram. In this work, with boxcar apodization, the ILS is the sinc function CCQM-P110_Protocol Page 47 of 97

48 2 2 ILS boxcar sinc R R where R is resolution of the FT-IR spectrometer and was 4 cm -1. Finally, reference transmittance spectrum can be obtained by convolving this ILS with the true transmittance spectrum. i ILS d measured i 0 The calculation were performed under conditions of the line shape function of Lorentzian, room temperature (298K), atmospheric pressure (1015hPa), a pathlength of cm, and resolution of 0.01 cm -1. Reference concentrations were 5.0, 7.5, 10.0, 12.5, and 15.0 mol/mol. Determination process The sample cylinder was stood at room temperature after arrival. Samples were transferred to a gas cell with a stainless steel pressure regulator. the regulator was evacuated before samples were introduced to gas cell. in addition, the measurement was performed about ten minutes after sample introduction to the gas cell. The measurement of sample was repeated 4 times for the determination of NO 2 concentration in nitrogen contained 1000 mol/mol of oxygen. The NO 2 concentration in sample was determined with two absorbance at wavenumber of cm -1 and cm -1. FTIR instrumentation and acquisition parameters B2-5.1 Instrumentation Spectrometer Manufacturer Type Serial number JASCO Corporation FTIR-6100 Gas cell Manufacturer Type Optical path (m) Operation software details JASCO Corporation 10cm gas cell Name of the software used to control the spectrometer Name of the software used to acquire spectra Name of the software used to analyse spectra Spectra Manager Spectra Manager Spectra Manager CCQM-P110_Protocol Page 48 of 97

49 B2-5.2 Acquisition parameters table Experimental conditions: Expanded Uncertainty U Temperature(K) Pressure(KPa) Gas cell path length / m Instrument parameters (required): Nominal Resolution / cm -1 4 NA True Resolution ( Data point Spacing ) / cm Negligible Laser frequency / cm NA Starting Wavenumber / cm NA Ending Wavenumber / cm NA Name of the apodization function used boxcar NA Wavenumber shift related to HITRAN / cm -1 Negligible NA Collimator aperture diameter / mm 7.1mm NA Collimator focal length / mm unknown Negligible Scans 256 NA CCQM-P110_Protocol Page 49 of 97

50 B2-6 Recorded spectra names and parameters Measurement File name of the File name of the File name of the File name of the File name of the absorbance spectrum interferogram associated with the sample spectrum sample spectra background interferogram associated with the sample spectrum background spectrum associated with the sample spectrum Temperature inside the gas cell Pressure inside the gas cell (Absorbance) T / K P / kpa S01 NA NA NA bak S02 NA NA NA bak S03 NA NA NA bak S04 NA NA NA bak Please provide by to edgar.flores@bipm.org a single compressed file including all the interferograms and spectra used to calculate the nitrogen dioxide mole fraction of your cylinder gas mixture. If the compressed file is bigger than 2 megabytes, please split it in several 2 megabytes files. The spectra and interferograms need to be sent in one the follow formats: Spectra (SPA); J-Camp (JDX); Pcir (IRD); Nicolet SX/DX (NIC); CSV Text (CSV); Grams/32 (SPC); Matson (IGM,ABS,DRT,SBM,RAS) or Spectacle (IRS). Please note that an absorbance spectrum is considered as the result of the base 10 logarithm of 1/T (Abs=log 10 1/T) being T the ratio of a sample spectrum and a background spectrum

51 National Institute of Standards and Technology (NIST) General information Institute Address Contact person National Institute of Standards and Technology Gas Metrology Group 100 Bureau Drive, Gaithersburg, MD , USA Pamela Chu and Lyn Gameson Telephone (301) (301) Fax * Serial number of cylinder received Cylinder pressure as received Results and APEX MPa Nitrogen dioxide mole fraction Expanded uncertainty Coverage factor x / μmol/mol U ) / μmol/mol NO2 ( x NO Uncertainty Budget Please provide a complete uncertainty budget. The final uncertainty was assigned from the dominant uncertainty from the path length, which had a relative uncertainty over an order of magnitude greater than any other uncertainty. There were several issues which we encountered. The data was acquired on an instrument that has been used as a comparator (e.g. comparisons to standards in the same range) and the data acquisition parameters were not optimized for absolute measurements. The expanded uncertainty for the path length is 4.3 %. The two measurements agreed within 0.26 % and the uncertainties in the pressure and temperature are both less than 0.1 %, see B2-5.2Acquisition parameters table. Description of the procedure used during the gas analysis Please describe in detail the analytical method(s) used during the gas analysis with the FTIR spectrometer. The NO2 component of CCQM-P110 sample APEX was analyzed by FTIR (Nicolet Model Nexus 670, NIST# ) equipped with a KBr beamsplitter and a mercury-cadmium-telluride (MCT) detector. A quartz gas cell with potassium bromide windows, a nominal 10 meter folding path, and 2 L internal volume (Specac, Model Cyclone 10C, NIST# ) was used as the sample cell. Sample flow (200 ml/min) through the gas cell was controlled by a needle valve. The sample was purged through the cell for 100 minutes followed by co-adding 512 scans (total collection time was 50 minutes). Four spectra were collected with the first two spectra being dismissed because they CCQM-P110_Protocol Page 51 of 97

52 were collected during the purge cycle of the analytical system. Furthermore, the first spectrum shows spectral features for water with significantly higher intensity than the water features subsequent spectra. The cell pressure (measured by a calibrated Mensor Series 6000 Pressure Transducer, Serial# ) was auto collected every minute throughout the FTIR acquisition; cell temperature was monitored manually using a calibrated thin film platinum thermometer affixed to the cell wall. The effective path length of the cell was obtained by measuring standards of known concentration for ethanol and methane with the same experimental parameters as the measurements of the CCQM-P110 sample. Integrated bands over the C-H stretch region from 2700 cm -1 to 3000 cm -1 were used for the analysis and compared to previously acquired infrared reference data (the reference data was acquired on a different infrared system). Backgrounds were subtracted from absorption spectra, by using a linear fit to the several points on either side of the absorption features. The uncertainties for the cell path length are significantly larger than expected. The large uncertainties are, in part, due to the initial data acquisition parameters used for the CCQM-P110 sample. Subsequent measurement comparisons suggest that the non-linearity of the MCT detector response remains an issue and the aperture and resolution settings potentially added additional uncertainties. Two measurements of the CCQM-P110 sample were analyzed by comparing the integrated band intensities in the 2900 cm -1 region against spectra generated from the HiTRAN04 database. There is significant amount of water in the final spectra and variations in the background in the 1560 cm -1 to 1660 cm -1 region, therefore the analysis was performed over 2840 cm -1 to 2940 cm -1, the overtone region. Backgrounds were subtracted from absorption spectra, by using a linear fit to the several points on either side of the absorption feature. The reference spectrum was generated from the line intensity data using a HiTRAN simulation program and assuming a Lorentzian line shape. The ratio of the sample spectra to the reference spectra, using the measured pressure, temperature, and path length, provided the concentration of the CCQM-p110 sample. FTIR instrumentation and acquisition parameters Please specify the FTIR instrumentation and the acquisition parameters used during the gas analysis. B2-5.1 Instrumentation Spectrometer Manufacturer Type Serial number AEQ Nicolet Nexus 670 (MCT Detector) Gas cell Manufacturer Specac Type Cyclone 10C (Quartz) Optical path (m) Nominal 10 m, Measured based on a number of measurements compared to reference data ( ± 0.47) m. Operation software details Name of the software used to control the spectrometer OMNIC V7.1 Name of the software used to acquire spectra OMNIC V7.1 Name of the software used to analyse spectra B2-5.2 Acquisition parameters table HiTRAN04 And a HiTRAN Simulation program to generate spectra. CCQM-P110_Protocol Page 52 of 97

53 Experimental conditions: Expanded Uncertainty U Temperature /K Pressure /KPa Gas cell path length / m Instrument parameters (required): Nominal Resolution / cm NA True Resolution ( Data point Spacing ) / cm Negligible Laser frequency / cm NA Starting Wavenumber / cm NA Ending Wavenumber / cm NA Name of the apodization function used Boxcar NA Wavenumber shift related to HITRAN / cm -1 NA Collimator aperture diameter / mm 4 Collimator focal length / mm Not Known Negligible Scans 512 NA Note: Section B2-7 shows the acquisition parameters of a Fourier transform Infrared Spectrometer device. Section B2-8 contains a short compendium of FTIR terms and definitions. You may also find the acquisition parameters in your instrument manual, or in the software used for the spectra acquisition. CCQM-P110_Protocol Page 53 of 97

54 B2-6 Recorded spectra names and parameters Measurement File name of the File name of the File name of the File name of the File name of the absorbance spectrum interferogram associated with the sample spectrum sample spectra background interferogram associated with the sample spectrum background spectrum associated with the sample spectrum Temperature inside the gas cell Pressure inside the gas cell (Absorbance) T / K P / kpa 1 QM3_0125 QM3_0125 QM3_0125 BGRD0125 BGRD QM4_0125 QM4_0125 QM4_0125 BGRD0125 BGRD CCQM-P110_Protocol Page 54 of 97

55 National Physical Laboratory (NPL) General information Institute Address National Physical Laboratory (NPL) Hampton Road, Teddington, Middlesex, TW11 0LW, UK Contact person * Serial number of cylinder received Cylinder pressure as received Alice Harling / Martin Milton alice.harling@npl.co.uk / martin.milton@npl.co.uk D bar Results Nitrogen dioxide mole fraction Expanded uncertainty Coverage factor x / μmol/mol U ) / μmol/mol NO2 ( x NO K = 2 Uncertainty Budget Determination of Path Length of cell by measurement of known amount fraction of CO Source of uncertainty Estimation Method Standard uncertainty Nominal value Relative standard uncertainty Spectral data A/B 2.5% Repeatability of A 0.35% measured area Spectral baseline B 1% allocation Certified amount fraction A 60 nmol/mol 10 mol/mol 0.6% of CO Cell pressure B 1 mbar 1050 mbar 0.1% Cell temperature B 0.5K 298 K 0.2% Combined uncertainty 24 cm 8 m 3% Determination of Amount Fraction of Nitrogen Dioxide in Unknown Page 55 of 97

56 Source of uncertainty Estimation Method Standard uncertainty Nominal value Relative standard uncertainty Spectral data A/B 2.5% Repeatability of A 0.3% measured area Spectral baseline B 1% allocation Cell pressure B 1 mbar 1050 mbar 0.1% Cell temperature B 0.5K 298 K 0.2% Cell path length (see Table above) A 24 cm 8 m 3% Combined uncertainty 12 mol/mol 4% The expanded uncertainty (k=2) is 1000 nmol/mol (8% rel). Description of the procedure used during the gas analysis Please describe in detail the analytical method(s) used during the gas analysis with the FTIR spectrometer. Measurement Procedure 1. The gas cell was evacuated to 5 x 10-4 mbar, and the FTIR system purged with Metrology Grade nitrogen for several hours. 2. The gas cell was filled with BIP N When the pressure in the cell (indicated on the Baratron pressure gauge) reached 1050 mbar, the exhaust to the cell was opened and the BIP N 2 left to flow through and flush the cell. During this time the reduction in carbon dioxide in the background spectrum was monitored. 4. After 10 minutes the background was collected (over 64 scans) 5. The BIP N 2 was stopped and the gas line and regulator from the FTIR system to the cylinder to be measured were purged and evacuated. 6. The gas cell was then re-evacuated to 5 x 10-4 mbar. 7. The sample was allowed to flow into the gas cell until the pressure read ~1050 mbar, then the exhaust was opened and the sample flowed through the cell during the measurements. 8. Five consecutive measurements were made for each sample (over 64 scans), using the same background. Results and spectroscopy The nitrogen dioxide peak at 1600 cm-1 was used for the measurements. The results from a second peak at 2860 to 2940 cm-1 are also given for information. The samples were run in the following sequence on 9th Dec 2009: Background Unknown D Page 56 of 97

57 The integration of the peak areas was carried out using the Thermo Scientific software OMNIC. The results were validated using a MATLAB code developed at NPL. The value of the unknown was calculated by means of a ratio of the FTIR response against the area of the peak from the standard reference spectra from the NorthWest Infrared Vapor Phase InfraRed spectral Library. In each case, the area counts given in the table are after background subtraction. The result given is the mean of the analysis carried out against the library spectra. FTIR instrumentation and acquisition parameters Please specify the FTIR instrumentation and the acquisition parameters used during the gas analysis. B2-5.1 Instrumentation Spectrometer Nicolet 6700 Manufacturer Thermo Scientific Type 6700 Serial number AHRO Gas cell Manufacturer Type Optical path Specac Cyclone C m Software Name of the software used to control the spectrometer Name of the software used to acquire spectra Name of the software used to analyse spectra OMNIC OMNIC OMNIC B2-5.2 Acquisition parameters table Experimental conditions: Expanded Uncertainty U Gas cell path length / m % Instrument parameters (required): Nominal Resolution / cm NA True Resolution ( Data point Spacing ) / cm Negligible Laser frequency / cm NA Starting Wavenumber / cm NA Ending Wavenumber / cm NA Page 57 of 97

58 Name of the apodization function used Happ-Genzel NA Wavenumber shift related to HITRAN / cm -1 0 NA Collimator aperture diameter / mm 17 Collimator focal length / mm Negligible Scans 64 NA Note: Section B2-7 shows the acquisition parameters of a Fourier transform Infrared Spectrometer device. Section B2-8 contains a short compendium of FTIR terms and definitions. You may also find the acquisition parameters in your instrument manual, or in the software used for the spectra acquisition. B2-7 Complementary information on the cylinder Please report the value of the pressure left in the cylinder before shipment to the BIPM: 40 bar If any other component other than NO 2, nitrogen and oxygen was detected and/or quantified please report its mole fraction in the table below: Component Mole fraction / nmol/mol Expanded uncertainty Coverage factor Measurement technique HNO K=2 FTIR (library spectra) Page 58 of 97

59 B2-6 Recorded spectra names and parameters Measurement File name of the File name of the File name of the File name of the File name of the absorbance spectrum interferogram associated with the sample spectrum sample spectra background interferogram associated with the sample spectrum background spectrum associated with the sample spectrum Temperature inside the gas cell Pressure inside the gas cell (Absorbance) T / K P / kpa 1 D _091209_1 BIPN2BKG_091209_ D _091209_2 BIPN2BKG_091209_ D _091209_3 BIPN2BKG_091209_ D _091209_4 BIPN2BKG_091209_ D _091209_5 BIPN2BKG_091209_ Please provide by to edgar.flores@bipm.org a single compressed file including all the interferograms and spectra used to calculate the nitrogen dioxide mole fraction of your cylinder gas mixture. If the compressed file is bigger than 2 megabytes, please split it in several 2 megabytes files. The spectra and interferograms need to be sent in one the follow formats: Spectra (SPA); J-Camp (JDX); Pcir (IRD); Nicolet SX/DX (NIC); CSV Text (CSV); Grams/32 (SPC); Matson (IGM,ABS,DRT,SBM,RAS) or Spectacle (IRS). Page 59 of 97

60 B2-7 Complementary information on the cylinder Please report the value of the pressure left in the cylinder before shipment to the BIPM: 40 bar If any other component other than NO 2, nitrogen and oxygen was detected and/or quantified please report its mole fraction in the table below: Component Mole fraction / nmol/mol Expanded uncertainty Coverage factor Measurement technique HNO K=2 FTIR (library spectra) Page 60 of 97

61 Results of analysis 9/12/2009 The NIST Spectrum refers to the calculated absorbance based on data from the NIST/PNNL database. The nitrogen dioxide peak at 1600 cm-1 was used for the measurements. The results from a second peak at 2860 to 2940 cm-1 are also given for information.note: the modified area counts are corrected from the measured pressure to a standard pressure of 1056 mbar. Page 61 of 97

62 National Metrology Institute of South Africa (NMISA) General information Institute Address Contact person National Metrology Institute of South Africa (NMISA) CSIR, Building 5 Meiring Naudé Road Brummeria, 0184 Pretoria South Africa A Botha Telephone +27(0) Fax +27(0) * Serial number of cylinder received Cylinder pressure as received Results abotha@nmisa.org D bar Nitrogen dioxide mole fraction Expanded uncertainty Coverage factor x / μmol/mol U ) / μmol/mol NO2 ( x NO 2 10,62 0,22 2 Uncertainty Budget Parameter Temperature Pressure Verification Stability Gravimetry Bias Standard uncertainty(u) 0,11% rel 0,09% rel 0,18% rel 0,10% rel 0,13% rel 1% rel Description of the procedure used during the gas analysis After the arrival of D cylinder in the laboratory, the cylinder was stabilised at room temperature (22 ºC ± 2 ºC) and humidity of (50 % ± 10%) before checking the pressure and doing measurements. The standards and sample were transferred directly to the FTIR using a system composed of pressure regulator, mass flow controller and control valves. The measurements of D received from the coordinator (BIPM) were made during January 2010 by direct comparison with four gravimetric preparation standards by NMISA containing 10 μmol/mol concentrations. The results reported all follow from a bracketing comparison strategy. Page 62 of 97

63 For FTIR measurements a NICOLET-Magna-IR-560 was used. A fixed optical path length gas cell of 10 m from Gemini-Mars was used. Measurement conditions: 0.5 cm -1 resolution, 64 scans, phase correction (Mertz), Happ-Genzel apodization, water correction performed by the OMNIC-Software, zero level of zero-filling, liquid nitrogen cooled mercury cadmium telluride (MCT/A) detector. Nominal measurement pressure for all samples: kpa. The optical bench set up was continuously purged with BIP TM + N 2 (6.0). For every measurements of cylinders a fresh Background BIP TM + N 2 (6.0) was used. Cylinders were measured randomly at continuous flow (i.e 1000 ml/min) controlled by mass flow controller. The quantification was performed by MALT version 5.2 software. FTIR instrumentation and acquisition parameters B2-5.1 Instrumentation Spectrometer Manufacturer Type Serial number: ADU Gas cell Manufacturer Type Optical path (m): 10 Operation software details Nicolet Instrument Corporation Magna IR 560 E.S.P Gemini Scientific Instruments Gemini-Mars Name of the software used to control the spectrometer Omnic version 8 Name of the software used to acquire spectra Omnic version 8 Name of the software used to analyse spectra Malt5 version 5.2 B2-5.2 Acquisition parameters table Experimental conditions: Expanded Uncertainty U Temperature (K) Pressure (KPa) Gas cell path length / m 10 NA Instrument parameters (required): Nominal Resolution / cm NA True Resolution ( Data point Spacing ) / cm Negligible Page 63 of 97

64 Laser frequency / cm NA Starting Wavenumber / cm NA Ending Wavenumber / cm NA Name of the apodization function used Hamming Happ- Genzel NA Wavenumber shift related to HITRAN / cm -1 NA Collimator aperture diameter / mm 17 Negligible Collimator focal length / mm Negligible Scans 64 NA Page 64 of 97

65 B2-6 Recorded spectra names and parameters Measurement File name of the File name of the File name of the File name of the File name of the absorbance spectrum interferogram associated with the sample spectrum sample spectra background interferogram associated with the sample background spectrum associated with the sample spectrum Temperature inside the gas cell Pressure inside the gas cell (Absorbance) T / K P / kpa 1 d650032_15.spc d650032_15.spc d650032_15.spc BKG_15.SPC BKG_15.SPC d650032_16.spc d650032_16.spc d650032_16.spc BKG_16.SPC BKG_16.SPC d650032_17.spc d650032_17.spc d650032_17.spc BKG_17.SPC BKG_17.SPC d650032_18.spc d650032_18.spc d650032_18.spc BKG_18.SPC BKG_18.SPC d650032_19.spc d650032_19.spc d650032_19.spc BKG_19.SPC BKG_19.SPC Please provide by to edgar.flores@bipm.org a single compressed file including all the interferograms and spectra used to calculate the nitrogen dioxide mole fraction of your cylinder gas mixture. If the compressed file is bigger than 2 megabytes, please split it in several 2 megabytes files. The spectra and interferograms need to be sent in one the follow formats: Spectra (SPA); J-Camp (JDX); Pcir (IRD); Nicolet SX/DX (NIC); CSV Text (CSV); Grams/32 (SPC); Matson (IGM,ABS,DRT,SBM,RAS) or Spectacle (IRS). Page 65 of 97

66 B2-7 Complementary information on the cylinder Please report the value of the pressure left in the cylinder before shipment to the BIPM: 23 bar If any other component other than NO 2, nitrogen and oxygen was detected and/or quantified please report its mole fraction in the table below: Component Mole fraction / nmol/mol Expanded uncertainty / nmol/mol Coverage factor Measurement technique HNO FTIR Page 66 of 97

67 Slovak Institute of Metrology (SMU) Page 67 of 97

68 Page 68 of 97