Primary Standard Gas Mixtures Research Articles

Intercomparison of in situ measurements of ambient NH3: instrument performance and application under field conditions

Abstract. Ammonia (NH3) in the atmosphere affects both the environment and human health. It is therefore increasingly recognised by policy makers as an important air pollutant that needs to be mitigated, though it still remains unregulated in many countries. In order to understand the effectiveness of abatement strategies, routine NH3 monitoring is required. Current reference protocols, first developed in the 1990s, use daily samplers with offline analysis; however, there have been a number of technologies developed since, which may be applicable for high time resolution routine monitoring of NH3 at ambient concentrations. The following study is a comprehensive field intercomparison held over an intensively managed grassland in southeastern Scotland using currently available methods that are reported to be suitable for routine monitoring of ambient NH3. In total, 13 instruments took part in the field study, including commercially available technologies, research prototype instruments, and legacy instruments. Assessments of the instruments' precision at low concentrations (< 10 ppb) and at elevated concentrations (maximum reported concentration of 282 ppb) were undertaken. At elevated concentrations, all instruments performed well and with precision (r2 > 0.75). At concentrations below 10 ppb, however, precision decreased, and instruments fell into two distinct groups, with duplicate instruments split across the two groups. It was found that duplicate instruments performed differently as a result of differences in instrument setup, inlet design, and operation of the instrument. New metrological standards were used to evaluate the accuracy in determining absolute concentrations in the field. A calibration-free CRDS optical gas standard (OGS, PTB, DE) served as an instrumental reference standard, and instrument operation was assessed against metrological calibration gases from (i) a permeation system (ReGaS1, METAS, CH) and (ii) primary standard gas mixtures (PSMs) prepared by gravimetry (NPL, UK). This study suggests that, although the OGS gives good performance with respect to sensitivity and linearity against the reference gas standards, this in itself is not enough for the OGS to be a field reference standard, because in field applications, a closed path spectrometer has limitations due to losses to surfaces in sampling NH3, which are not currently taken into account by the OGS. Overall, the instruments compared with the metrological standards performed well, but not every instrument could be compared to the reference gas standards due to incompatible inlet designs and limitations in the gas flow rates of the standards. This work provides evidence that, although NH3 instrumentation have greatly progressed in measurement precision, there is still further work required to quantify the accuracy of these systems under field conditions. It is the recommendation of this study that the use of instruments for routine monitoring of NH3 needs to be set out in standard operating protocols for inlet setup, calibration, and routine maintenance in order for datasets to be comparable.

Verification of nitrous oxide primary standard gas mixtures by gas chromatography and cavity ring-down spectroscopy for ambient measurements in South Africa

Nitrous oxide (N2O) is an important greenhouse gas and is the third-largest contributor to global warming with a global warming potential (GWP) higher than that of carbon dioxide. Ambient N2O is monitored globally and described at nanomole per mole (nmol mol−1) levels. Metrologically traceable and highly accurate N2O gas standards are required to understand the behaviour of the greenhouse gases in the atmosphere and GWP. A group of primary standard gas mixtures (PSGMs) in aluminium cylinder material has been prepared in synthetic air for the calibration of analytical instruments for measurement of N2O at an ambient level. An automatic weighing system with a mass comparator and a fully automated circular rotary plate, as well as a gas filling station, was used in the preparation of the gas mixtures. Analytical methods such as gas chromatography coupled with micro-electron capture detector and cavity ring-down spectroscopy were adopted in the verification process. Four PSGMs in the final preparation step were used to analyse unknown background and filtered air samples at the ambient level. An expanded uncertainty relative to the gravimetric amount fraction was found to be 0.02 %. Results show that the background air samples lie within the calibration range with 329 to 330 nmol mol−1 obtained and 135 nmol mol−1 obtained for filtered air sample.

Development of 100 μmol mol−1 HCl primary standard gas mixtures in high-pressure cylinders

To develop a 100 μmol mol−1 hydrogen chloride (HCl) primary standard gas mixture in a high-pressure cylinder, pure HCl gas was diluted in two or three steps with pure N2 in high-pressure aluminum and nickel-coated manganese steel cylinders. To check the consistency between the HCl gas mixtures in the different cylinders, the HCl mixing ratios were analyzed by Fourier transform infrared spectroscopy. Four cylinders of 100 μmol mol−1 HCl gas mixtures agreed within 0.2 μmol mol−1. A previous study showed that 0.29 μmol mol−1 of HCl was adsorbed on the inner surface of aluminum cylinders that contained 100 μmol mol−1 HCl gas mixtures. The long-term stability test showed that the 100 μmol mol−1 HCl gas mixture in the aluminum cylinder decreased by 0.8 μmol mol−1 over 2 years, whereas that in the nickel-coated manganese steel cylinder decreased by 6 μmol mol−1. This result suggested that the nickel-coated manganese steel cylinder is not suitable for developing 100 μmol mol−1 HCl gas mixtures. From the verification test between gas cylinders and the long-term stability test, the 100 μmol mol−1 HCl standard gas mixture in the aluminum cylinder was successfully developed with an expanded uncertainty of 1.65 μmol mol−1 (k = 2%, 95% confidence level). The 100 μmol mol−1 HCl standard gas mixture was validated using an online ion chromatograph with a liquid Cl− certified reference material (CRM). The HCl gas mixture agreed with the liquid Cl− CRM within an expanded uncertainty of 1.5%.

Validation of ammonia diffusive and pumped samplers in a controlled atmosphere test facility using traceable Primary Standard Gas Mixtures

We report the determination of ammonia (NH3) diffusive sampling rates for six different designs of commercial diffusive samplers (CEH ALPHA sampler, Gradko diffusion tube, Gradko DIFRAM-400, Passam ammonia sampler, and ICS Maugeri Radiello radial sampler (blue and white turbulence barriers)), together with the validation test results for a pumped sampler (CEH DELTA denuder). The devices were all exposed in the UK's National Physical Laboratory's (NPL) controlled atmosphere test facility (CATFAC). For each of the seven diffusive sampler exposure tests there were traceable concentrations of ammonia (in the range 3–25 μg m−3) generated under well-defined conditions of temperature, relative humidity and wind speed, which are applicable to a variety of ambient monitoring environments. The sampler exposure time at each concentration was 28 days, except for the radial devices, which were exposed for 14 days. The work relied on the dilution of newly developed stable Primary Standard Gas Mixtures (PSMs) prepared by gravimetry in passivated gas cylinders as a method of improving the metrological traceability of ammonia measurements. The exposed diffusive samplers were sent blind to the participants for analysis and the reported NH3 concentrations were then compared against the known reference concentration. From the results for each sampler type a diffusive sampling rate was calculated and compared against the rate used routinely by the participants. Some measurement results were in good agreement with the known traceable reference concentration (particularly for one diffusive sampler design (ALPHA)), while other devices exhibited over-reading and under-reading (each with a clear bias). The new diffusive sampling rates determined in the laboratory study were then applied to measurements in a field comparison campaign, and this was found to deliver an improvement in agreement between the different devices deployed.

유해대기오염물질 중 14종의 휘발성유기화합물 1차 표준가스개발 (1 μmol/mol 수준)

유해대기오염물질 중 14종의 휘발성유기화합물 1차 표준가스개발 (1 μmol/mol 수준)

Long‐Term Stability Evaluation of 0.5‐7.0 nmol/mol Dimethyl Sulfide Primary Standard Gas Mixtures by Comparison with Traceable Dynamically Diluted Gas Mixtures

Dimethyl sulfide (DMS) is a crucial precursor in the formation of aerosols that play important roles in climate change. Stable and traceable primary standard gas mixtures (PSMs) are critical for accurate measurement of the trace amounts of reactive DMS reported at sub‐nanomole per mole (nmol/mol) levels at remote monitoring sites. However, the preparation of DMS at ambient levels in high‐pressure cylinders is challenging because of its instability. This study examined the long‐term stability of 0.5–7.0 nmol/mol DMS PSMs prepared in specially treated cylinders. Ten months after the PSM preparation, the DMS PSMs were compared with traceable dynamically diluted gas mixtures (DDMs). The DMS PSMs at 2–7 nmol/mol levels were stable for 10 months with uncertainties of less than 2.5% (k = 2). However, the amount‐of‐substance fraction (i.e., mole fraction) of the DMS PSM at 0.5 nmol/mol was 5.4% less than the gravimetrically determined mole fraction, which exceeds the uncertainty of 3.5%. These findings indicate that DMS PSMs at 2–7 nmol/mol levels are sufficiently stable for use as primary standards for long‐term monitoring of trace‐level DMS in remote areas, whereas DMS PSM at 0.5 nmol/mol is not sufficiently stable.

Development of accurate dimethyl sulphide primary standard gas mixtures at low nanomole per mole levels in high-pressure aluminium cylinders for ambient measurements

Dimethyl sulphide (DMS) plays an important role in atmospheric chemistry and climate change. Ambient DMS is monitored in a global network and reported at sub-nanomole per mole (nmol/mol) levels. Developing traceable, accurate DMS standards at ambient levels is essential for tracking the long-term trends and understanding the role of DMS in the atmosphere. Gravimetrically prepared gas standards in cylinders are widely used for calibrating instruments. Therefore, a stable primary standard gas mixture (PSM) is required for traceable ambient DMS measurement at remote sites. In this study, to evaluate adsorption loss on the internal surface of the gas cylinder, 6 nmol mol−1 DMS gas mixtures were prepared in three types of aluminium cylinders: a cylinder without a special coating on its internal surface (AL), an Aculife IV + III-treated cylinder (AC), and an Experis-treated cylinder (EX). There was little adsorption loss on the EX cylinder, whereas there was substantial adsorption loss on the other two cylinders. The EX cylinder was used to prepare 0.5, 2, 5, and 7 nmol mol−1 DMS PSMs with relative expanded uncertainties of less than 0.4%. The DMS PSMs were analytically verified and consistent within a relative expanded uncertainty of less than 1.2%. The long-term stability of the 7 nmol mol−1 DMS PSM was assessed by tracking the ratio of the DMS to the internal standard, benzene. The results showed that the DMS was stable for about seven months and it was projected to be stable for more than 60 months within a relative expanded uncertainty of 3%.

Validation and Comparison of Calibration Techniques for Measurements of Carbon Dioxide in Atmospheric Air Standards

The increase in the concentration of carbon dioxide (CO2) in the atmosphere has led the scientific community to investigate the adverse effects on humanity and nature, including the greenhouse effect, which contributes to global warming and can lead to climate change, besides the risks associated with human health. Due to the importance of metrological issues in the current scenario, the Laboratory of Gas Analysis (Lanag) of the National Institute of Metrology, Quality and Technology (Inmetro) is developing the methodology of preparation of such primary standard gas mixtures through gravimetry. For the preparation of these standards, an analysis verification step is necessary, carried out by means of an analytical technique of comparison, at low levels of concentration, by cavity ringdown (CRDS) and by gas chromatography using a flame ionization detector coupled to a methaniser catalyst (GC-FIDmeth). This work presents the method validation of both methodologies developed to analyze a range of concentration of atmospheric standards of CO2 at a matrix of synthetic clean dry air (SCDA) by CRDS and GC-FIDmeth, of which the analysis results can compromise the measurements on atmospheric air quality. The objective is to compare results of method validation of both analytical methods for low CO2 concentration through the use of primary reference mixtures developed and also by certified reference material. The validation measurement results were analyzed according to the requirements of ISO 5725: 1994 parts 1 and 2, and the calculation of measurement uncertainty followed the methodology described in ISO 6143:2001, with results showing satisfactory consistent between both selected techniques. According to the work presented here, the obtained validation results for CRDS are better than the GC results, such as the relative uncertainty of samples evaluated for CRDS was 0.4% and 2.7% for GC_FID meth.

Regional key comparison SIM.QM-K111—propane in nitrogen

This key comparison is one of a series of key comparisons in the gas analysis area assessing core competences (track A key comparisons). Such competences include, among others, the capabilities to prepare primary standard gas mixtures (PSMs), perform the necessary purity analysis on the materials used in the gas mixture preparation, the verification of the composition of newly prepared PSMs against existing ones, and the capability of calibrating a gas mixture. For this key comparison, a binary mixture of propane in nitrogen has been chosen at a nominal amount-of-substance fraction level of 1000 μmol mol−1 [6]. The key comparison design follows that of the key comparisons for gas mixture that are prepared gravimetrically.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Determination of physical adsorption loss of primary standard gas mixtures in cylinders using cylinder-to-cylinder division

Primary standard gas mixtures (PSMs) are typically prepared in cylinders and the amount-of-substance fractions are determined by purity analysis and gravimetric method. However, the actual amount-of-substance fraction can be different from the gravimetrically determined value due to adsorption loss onto the internal surface of cylinders. The resulted difference due to the adsorption loss can be larger than the PSM uncertainty. In this study, the cylinder-to-cylinder division method is proposed to evaluate any potential physical adsorption loss onto the internal surface of cylinders. A method for estimating the amount of adsorption loss, the corrected amount-of-substance fraction and its uncertainty due to the adsorption loss is described.

Development of primary standard gas mixtures containing 10 µmol/mol oxygen in nitrogen with verification by a two-oven GC-TCD system for effective separation of oxygen from argon in presence of plenty of nitrogen

Primary standard gas mixtures (PSMs) containing 10 µmol/mol oxygen in nitrogen were prepared in aluminum alloy cylinders from pure nitrogen and oxygen gases according to ISO 6142-1. We developed a system consisting of a gas chromatograph with a thermal conductivity detector (GC-TCD) and two ovens to verify precisely the amount-of-substance fraction of oxygen in the PSMs at a level of 10 µmol/mol. As pure nitrogen gas usually contains argon as an impurity, it is necessary to separate the oxygen peak from the argon peak in order to verify the amount-of-substance fraction of oxygen in the PSMs. Although the use of packed columns is essential in order to achieve high precision using a GC-TCD system, it is notoriously difficult to separate oxygen and argon by this method. To overcome this problem, we used two gas chromatograph ovens: The first oven separates oxygen and argon from the nitrogen, whereas the second oven—held at −15 °C or below—separates oxygen and argon. The two-oven GC-TCD system was able to achieve good resolution between the oxygen and argon peaks. The relative uncertainty in the determination of the oxygen fraction obtained using this system was 0.35 %. In order to avoid adsorption of oxygen onto the inner surface of the aluminum cylinder, we pretreated each cylinder by filling it with a standard gas mixture of oxygen in nitrogen at an oxygen partial pressure similar to that of the PSMs. The cylinders were then evacuated and used for the preparation of the target PSMs. From long-term monitoring using the GC-TCD system, we found the PSMs containing 10 µmol/mol oxygen in nitrogen to be stable for at least 30 months. The expanded combined uncertainties for the PSMs (k = 2) were found to be 0.026 µmol/mol to 0.036 µmol/mol, according to ISO 6142-1.

International comparison CCQM-K111—propane in nitrogen

This key comparison aims to assess the core capabilities of the participants in gas analysis. Such competences include, among others, the capabilities to prepare primary standard gas Mixtures (PSMs), perform the necessary purity analysis on the materials used in the gas mixture preparation, the verification of the composition of newly prepared PSMs against existing ones, and the capability of calibrating the composition of a gas mixture. According to the Strategy for Key Comparisons of the Gas Analysis Working Group, this key comparison is classified as a track A key comparison, which means that the results of this key comparison can be used to underpin calibration and measurement capabilities using the flexible scheme, and for propane under the default scheme.The artefacts were binary mixtures of propane in nitrogen at a nominal amount-of-substance fraction level of 1000 μmol/mol. The values and uncertainties from the gravimetric gas mixture preparation were used as key comparison reference values (KCRVs). Each transfer standard had its own KCRV. The results are generally good. All results but one are within ± 0.2 % of the KCRV.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

International comparison Euramet.QM-K111—propane in nitrogen

This key comparison aims to assess the core capabilities of the participants in gas analysis. Such competences include, among others, the capabilities to prepare Primary Standard gas Mixtures (PSMs), perform the necessary purity analysis on the materials used in the gas mixture preparation, the verification of the composition of newly prepared PSMs against existing ones, and the capability of calibrating the composition of a gas mixture. According to the Strategy for Key Comparisons of the Gas Analysis Working Group, this key comparison is classified as an RMO track A key comparison.The artefacts were binary mixtures of propane in nitrogen at a nominal amount-of-substance fraction level of 1000 μmol/mol. The values and uncertainties from the gravimetric gas mixture preparation were used as key comparison reference values (KCRVs). Each transfer standard had its own KCRV. The results are generally good. All results are within ± 1 % of the KCRV.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

International comparison CCQM-K111.1—propane in nitrogen

This key comparison aims to assess the core capabilities of the participants in gas analysis. Such competences include, among others, the capability of preparing Primary Standard gas Mixtures (PSMs), performing the necessary purity analysis on the materials used in the gas mixture preparation, the verification of the composition of newly prepared PSMs against existing ones, and the capability of calibrating the composition of a gas mixture. According to the Strategy for Key Comparisons of the Gas Analysis Working Group, this subsequent key comparison is classified as a track B key comparison, which means that the results of this key comparison can be used to underpin calibration and measurement capabilities for propane under the default scheme.The artefact was a binary mixture of propane in nitrogen at a nominal amount-of-substance fraction level of 1000 μmol/mol. The values and uncertainties from the gravimetric gas mixture preparation were used as key comparison reference values (KCRVs). Each transfer standard had its own KCRV. The result of the participating laboratory is consistent with the key comparison reference value within the respective expanded uncertainties and deviates less than 0.1 %.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The application of a cavity ring-down spectrometer to measurements of ambient ammonia using traceable primary standard gas mixtures

A correction for the undesirable effects of direct and indirect cross-interference from water vapour on ammonia (NH3) measurements was developed using an optical laser sensor based on cavity ring-down spectroscopy. This correction relied on new measurements of the collisional broadening due to water vapour of two NH3 spectral lines in the near infra-red (6548.6 and 6548.8 cm−1), and on the development of novel stable primary standard gas mixtures (PSMs) of ammonia prepared by gravimetry in passivated gas cylinders at 100 μmol mol−1. The PSMs were diluted dynamically to provide calibration mixtures of dry and humidified ammonia atmospheres of known composition in the nmol mol−1 range and were employed as part of establishing a metrological traceability chain to improve the reliability and accuracy of ambient ammonia measurements. The successful implementation of this correction will allow the extension of this rapid on-line spectroscopic technique to exposure chamber validation tests under controlled conditions and ambient monitoring in the field.

대기 중 모노테르펜 (α-피넨, 3-카렌, R-리모넨, 1,8-시네올) 측정을 위한 혼합표준가스개발

대기 중 모노테르펜 (α-피넨, 3-카렌, R-리모넨, 1,8-시네올) 측정을 위한 혼합표준가스개발

Development of traceable precision dynamic dilution method to generate dimethyl sulphide gas mixtures at sub-nanomole per mole levels for ambient measurement

Dimethyl sulphide (DMS) is an important compound in global atmospheric chemistry and climate change. Traceable international standards are essential for measuring accurately the long-term global trend in ambient DMS. However, developing accurate gas standards for sub-nanomole per mole (nmol/mol) mole fractions of DMS in a cylinder is challenging, because DMS is reactive and unstable. In this study, a dynamic dilution method that is traceable and precise was developed to generate sub-nmol/mol DMS gas mixtures with a dynamic dilution system based on sonic nozzles and a long-term (>5 years) stable 10μmol/mol parent DMS primary standard gas mixtures (PSMs). The dynamic dilution system was calibrated with traceable methane PSMs, and its estimated dilution factors were used to calculate the mole fractions of the dynamically generated DMS gas mixtures. A dynamically generated DMS gas mixture and a 6nmol/mol DMS PSM were analysed against each other by gas chromatography with flame-ionisation detection (GC/FID) to evaluate the dilution system. The mole fractions of the dynamically generated DMS gas mixture determined against a DMS PSM and calculated with the dilution factor agreed within 1% at 6nmol/mol. In addition, the dynamically generated DMS gas mixtures at various mole fractions between 0.4 and 11.7nmol/mol were analysed by GC/FID and evaluated for their linearity. The analytically determined mole fractions showed good linearity with the mole fractions calculated with the dilution factors. Results showed that the dynamic dilution method generates DMS gas mixtures ranging between 0.4nmol/mol and 12nmol/mol with relative expanded uncertainties of less than 2%. Therefore, the newly developed dynamic dilution method is a promising reference method for generating sub-nmol/mol DMS gas standards for accurate ambient measurements.

Comparison of primary standard gas mixtures: gravimetric production of carbon monoxide in nitrogen (3 μmol/mol)

COOMET.QM-S3 is a supplementary comparison of primary standard gas mixtures—'Carbon monoxide in Nitrogen (3 μmol/mol)'. This is a bilateral comparison between VNIIM and INMETRO and it was conducted in 2013. Carbon monoxide is a toxic gas and in concentrations higher than 3–5 μmol/mol it is hazardous to human health. Therefore, it is important for NMIs to have the capability of an accurate carbon monoxide measurements.This comparison has shown that primary standard gas mixtures of carbon monoxide in nitrogen on the level of 3 μmol/mol, prepared in VNIIM and Inmetro, do not agree—the pair-wise degree of equivalence D (0.77%) is higher than the appropriate expanded uncertainty U(D) (0.29%).Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

International Comparison of a Hydrocarbon Gas Standard at the Picomol per Mol Level

Studies of climate change increasingly recognize the diverse influences of hydrocarbons in the atmosphere, including roles in particulates and ozone formation. Measurements of key nonmethane hydrocarbons (NMHCs) suggest atmospheric mole fractions ranging from low picomoles per mol (ppt) to nanomoles per mol (ppb), depending on location and compound. To accurately establish mole fraction trends and to relate measurement records from many laboratories and researchers, it is essential to have accurate, stable, calibration standards. In February of 2008, the National Institute of Standards and Technology (NIST) developed and reported on picomoles per mol standards containing 18 nonmethane hydrocarbon compounds covering the mole fraction range of 60 picomoles per mol to 230 picomoles per mol. The stability of these gas mixtures was only characterized over a short time period (2 to 3 months). NIST recently prepared a suite of primary standard gas mixtures by gravimetric dilution to ascertain the stability of the 2008 picomoles per mol NMHC standards suite. The data from this recent chromatographic intercomparison of the 2008 to the 2011 suites confirm a much longer stability of almost 5 years for 15 of the 18 hydrocarbons; the double-bonded alkenes of propene, isobutene, and 1-pentene showed instability, in line with previous publications. The agreement between the gravimetric values from preparation and the analytical mole fractions determined from regression illustrate the internal consistency of the suite within ±2 pmol/mol. However, results for several of the compounds reflect stability problems for the three double-bonded hydrocarbons. An international intercomparison on one of the 2008 standards has also been completed. Participants included National Metrology Institutes, United States government laboratories, and academic laboratories. In general, results for this intercomparison agree to within about ±5% with the gravimetric mole fractions of the hydrocarbons.

Evaluation of changes in cylinder volume due to gas filling and subsequent release

This paper provides useful and important information in gas metrology especially where high-precision gas mixtures are essential. Buoyancy effects due to cylinder expansion are taken into account as a source of uncertainty in weighing for the preparation of primary or standard gas mixtures by gravimetric methods. Potential effects of cylinder construction materials, nominal volumetric capacity and filling gas species on cylinder volume during the preparation of primary standard gas mixtures remain unknown in the current literature. It is also difficult to find experimental evidence to demonstrate the theory that cylinder expansion upon pressurization is linear. We therefore devised an indirect measurement method to measure apparent volume changes and ultimately estimate changes in the volume of highly pressurized cylinders. We found that changes in the volumes of some gas cylinders varied significantly with construction material and nominal volumetric capacity. The relative volume changes for aluminium alloy cylinders were about 30% higher than those for manganese steel cylinders regardless of the nominal volumetric capacity and the filling gas species. We also provide experimental evidence verifying that changes in cylinder volume follow nearly linear patterns within the pressure range from 12 MPa to 0.1 MPa. Our estimate for the volume expansion of an aluminium alloy cylinder of 5 dm3 capacity with a pressure difference of 15 MPa is (15 ± 2) cm3. The reported value of about 20 cm3 in ISO 6142 : 2001 would be regarded as a rough estimate.