Main text As part of the ongoing key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of China maintained by the National Institute of Metrology (NIM) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM). The instruments have been compared over a nominal ozone amount fraction range of 0 nmol mol−1 to 500 nmol mol−1. To 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 https://www.bipm.org/kcdb/. 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).

Main text As part of the ongoing key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of Singapore maintained by the National Metrology Centre, A*STAR (NMC, A*STAR) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM), via a transfer standard maintained by the National Institute of Standards and Technology (NIST). The instruments have been compared over a nominal ozone amount-of-substance fraction range of 0 nmol/mol to 500 nmol/mol. To 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 https://www.bipm.org/kcdb/. 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).

Primary mercury gas standards, traceable to the SI, have been developed which can be used to underpin a NIST traceability framework for the calibration of vapor phase continuous emission monitoring systems (CEMS). A gas standard, which is based on a commercial gas generator, has been certified for gaseous elemental mercury output at specified generator output set points. The standard, termed the NIST Prime (NP) was certified at selected set points in the range 0.25 mu g/m(3) to 38 mu g/m(3) by isotope dilution inductively coupled plasma - mass spectrometry (ID-ICP-MS) using two alternative approaches, based on directly coupled gas sampling, and activated carbon sorbent trapping. Both approaches have been used to provide NIST traceability for electric utility mercury CEMS. The directly coupled method yielded expanded measurement uncertainties ranging from approximately 5.5% relative at 0.5 mu g/m(3), to approximately 1% relative at 38 mu g/m(3), and an estimated limit of quantization (LOQ) of 0.06 mu g/m(3). The sorbent trapping method in contrast, yielded expanded uncertainties of approximately 1% relative at all sampling points, with an LOQ of 0.001 mu g/m(3).

We present a direct comparison between two independent methods for the measurement of gaseous elemental mercury (GEM) mass concentration: isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS) and laser absorption spectroscopy (LAS). The former technique combined with passive sorbent tube sampling is currently the primary method at NIST for mercury gas standards traceability to the International System of Units (SI). This traceability is achieved via measurements on a mercury-containing reference material. The latter technique has been recently developed at NIST and involves real-time measurements of light attenuation caused by GEM, with SI traceability based in part on the known spontaneous emission lifetime of the probed 6 1S0-6 3P1 intercombination transition of elemental mercury (Hg0). Using a steady-flow Hg0-in-air generator to produce samples measured by both methods, we use LAS to measure the sample gas and in parallel we collect the Hg0 on sorbent tubes to be subsequently analyzed using ID-CV-ICP-MS. Over the examined mass concentration range (41 μg/m3 to 287 μg/m3 Hg0 in air), the relative disagreement between the two approaches ranged from (1.0 to 1.8)%. The relative combined standard uncertainty on average is 0.4% and 0.9%, for the LAS and MS methods, respectively. Our comparison studies help validate the accuracy of the ID-CV-ICP-MS primary method as well as establish the LAS technique as an attractive alternative primary method for SI-traceable measurements of GEM.

The performance characteristics of explosive and narcotic trace detectors are mission critical to agencies worldwide that are charged with protection of the public, defense for mass transit and infrastructure, illicit drug interdiction, and the safety of first responders. Commercial trace detectors can measure signals from nanogram-size analytes in complex matrices, but even with proper maintenance, detector performance can degrade over time. Sensitive indicators of performance include the limit of detection and the minimum consistently detectable amount (MCDA), which are distinctive for each analyte in each detector for a given set of operating parameters. ASTM Subcommittee E54.01, with help from industry and agency stakeholders, recently approved ASTM E2677-14, Standard Test Method for Determining Limits of Detection in Explosive Trace Detectors. This method allows a well-characterized MCDA to be estimated in accordance with International Organization for Standardization and International Union of Pure and Applied Chemistry (IUPAC) measurement, detection, and uncertainty concepts. Challenges of background interference, response nonlinearity, heteroskedastic behavior, and truncation by signal filters were considered. Data are input into a web-based calculator on a National Institute of Standards and Technology (NIST) cloud server in which data quality is assessed, calculations are performed, and results are returned to the user. This method is gaining use worldwide as a well-documented mechanism to estimate MCDA values and is now being considered by ASTM for a wider audience of users. We describe some of the details of this method and demonstrate two other applications: (1) ozone measurements that were simultaneously collected on two commercial monitors and the NIST Standard Reference Photometer; and (2) trace opioid samples that were measured using a variety of techniques: ion mobility spectrometry, gas chromatography/mass spectrometry, and thermal desorption-direct analysis in real time-quadrupole mass spectrometry. We believe many environmental applications could benefit from such an approach.

In response to the environmental impact of mercury and the neuro-toxic risk associated with trophic transfer of methyl mercury to humans, the reduction of mercury emissions from coal-fired electric utilities, a significant anthropogenic source, is now receiving global attention. To address impending regulations for mercury reduction, there is a need to establish a mercury emissions measurement framework, which has demonstrated accuracy and traceability to national and international standards. To support this effort, the National Institute of Standards and Technology (NIST) has been working jointly with the United States Environmental Protection Agency (EPA) to develop a traceability system which links the output of elemental mercury calibration instrumentation sited at the power utilities, to the SI (International System of Units). This system is based on a reference (NIST Prime) elemental mercury generator standard, which is used by NIST to certify elemental mercury generators from the instrument vendors. These in turn are used by the instrument vendors to provide NIST traceable calibration for the instrumentation supplied to each electric utility. The NIST Prime generator is certified using a primary analytical method for the determination of mercury using sorbent trap analysis with isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS).

As part of the ongoing key comparison BIPM.QM-K1, a comparison has been performed between the ozone standard of Norway maintained by the Norwegian Institute for Air Research (NILU) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM). The instruments have been compared over a nominal ozone amount-of-substance fraction range from 0 nmol/mol to 500 nmol/mol. Main text To 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).

There are many gas phase compounds present in the atmosphere that affect and influence the earth's climate. These compounds absorb and emit radiation, a process which is the fundamental cause of the greenhouse effect. The major greenhouse gases in the earth's atmosphere are carbon dioxide, methane, nitrous oxide, and ozone. Some halocarbons are also strong greenhouse gases and are linked to stratospheric ozone depletion. Hydrocarbons and monoterpenes are precursors and contributors to atmospheric photochemical processes, which lead to the formation of particulates and secondary photo-oxidants such as ozone, leading to photochemical smog. Reactive gases such as nitric oxide and sulfur dioxide are also compounds found in the atmosphere and generally lead to the formation of other oxides. These compounds can be oxidized in the air to acidic and corrosive gases and contribute to photochemical smog. Measurements of these compounds in the atmosphere have been ongoing for decades to track growth rates and assist in curbing emissions of these compounds into the atmosphere. To accurately establish mole fraction trends and assess the role of these gas phase compounds in atmospheric chemistry, it is essential to have good calibration standards. The National Institute of Standards and Technology has been developing standards of many of these compounds for over 40 years. This paper discusses the development of these standards.

As part of the on-going key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of the Directorate of Measures and Precious Metals (DMDM) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM), via a transfer standard maintained by the National Institute of Standards and Technology (NIST). The instruments have been compared over a nominal ozone amount-of-substance fraction range of 0 nmol/mol to 500 nmol/mol Main text To 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).

Ambient ozone measurements in the United States and many other countries are traceable to a National Institute of Standards and Technology Standard Reference Photometer (NIST SRP). The NIST SRP serves as the highest level ozone reference standard in the United States, with NIST SRPs located at NIST and at many U.S. Environmental Protection Agency (EPA) laboratories. The International Bureau of Weights and Measures (BIPM) maintains a NIST SRP as the reference standard for international measurement comparability through the International Committee of Weights and Measures (CIPM). In total, there are currently NIST SRPs located in 20 countries for use as an ozone reference standard. A detailed examination of the NIST SRP by the BIPM and NIST has revealed a temperature gradient and optical path-length bias inherent in all NIST SRPs. A temperature gradient along the absorption cells causes incorrect temperature measurements by as much as 2 degrees C. Additionally, the temperature probe used for temperature measurements was found to inaccurately measure the temperature of the sample gas due to a self-heating effect. Multiple internal reflections within the absorption cells produce an actual path length longer than the measured fixed length used in the calculations for ozone mole fractions. Reflections from optical filters located at the exit of the absorption cells add to this effect. Because all NIST SRPs are essentially identical, the temperature and path-length biases exist on all units by varying amounts dependent upon instrument settings, laboratory conditions, and absorption cell window alignment. This paper will discuss the cause of, and physical modifications for, reducing these measurement biases in NIST SRPs. Results from actual NIST SRP bias upgrades quantifying the effects of these measurement biases on ozone measurements are summarized.Implications: NIST SRPs are maintained in laboratories around the world underpinning ozone measurement calibration and traceability within and between countries. The work described in this paper quantifies and shows the reduction of instrument biases in NIST SRPs improving their overall agreement. This improved agreement in all NIST SRPs provides a more stable baseline for ozone measurements worldwide.

A comparison of the ozone primary reference standard photometer serial number 45 (SRP45) against the National Institute of Standards and Technology (NIST) instruments, serial number 0 (SRP0) and 2 (SRP2), has been performed in order to establish the traceability and comparability of ozone measurements made by the Chilean atmospheric science community. A complete uncertainty budget was developed for SRP45, using a GUM approach. The results of the comparisons allow us to conclude that SRP45. SRP0 and SRP2 are comparable according to internationals criteria over an ozone mole fraction range of 0 nmol mol(-1) to at least 500 nmol mol(-1). The official result for the validation of SRP45 is x(ozone)(SRP45) = [0.013 + 0.99806x(ozone)(SRP2)] nmol mol(-1) with an expanded uncertainty of 2 x root(0.27)(2) + (1.18 x 10(-2) x x(ozone))(2) from 0 to 500 nmol mol(-1). (C) 2011 Elsevier B.V. All rights reserved.

As part of the on-going key comparison BIPM. QM-K1, a comparison has been performed between the ozone national standard of the National Physical Laboratory of India (NPLI) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM), via a transfer standard maintained by the National Institute of Standards and Technology (NIST). The instruments have been compared over a nominal ozone mole fraction range of 0 nmol/mol to 500 nmol/mol.

As part of the on-going key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of the Directorate General Joint Research Centre (JRC) and the common reference standard of the key com parison, maintained by the Bureau International des Poids et Mesures (BIPM), via a transfer standard maintained by the National Institute of Standards and Technology (NIST). The instruments have been compared over a nominal ozone mole fraction range of 0 nm ol/mol to 500 nmol/mol.

We report a pilot study organized within the Consultative Committee for Amount of Substance (CCQM), in which the ozone reference standards of 23 institutes have been compared to one common reference, the BIPM ozone reference standard, in a series of bilateral comparisons carried out between July 2003 and February 2005. The BIPM, which maintains as its reference standard a standard reference photometer (SRP) developed by the National Institute of Standards and Technology (NIST, United States), served as pilot laboratory. A total of 25 instruments were compared to the common reference standard, either directly (16 comparisons) or via a transfer standard (9 comparisons). The comparisons were made over the ozone mole fraction range 0 nmol/mol to 500 nmol/mol.

Intercomparison experiments were made between two independent techniques for ozone (O3) reference standards often used as the primary standards in air quality monitoring networks. These techniques include ultraviolet absorption photometry of O3 at the 253.7‐nm Hg line and gas‐phase titration of O3 with excess NO. For ultraviolet photometry, a well‐designed and maintained standard reference photometer (SRP) built by the National Institute of Standards and Technology (USA) was employed. For gas‐phase titration (GPT), an existing system was significantly modified by the National Institute for Environmental Studies (Japan) by using gravimetric NO/N2 standard gases, accurate flow measurement systems based on laminar flow elements, and two chemiluminescence NO detectors to minimize uncertainty in the measurements, which had previously been a major shortcoming of this method. Uncertainty in the improved GPT system was reduced to less than 0.4% above 100 nmol mol−1 O3 mole fraction. A series of comparison runs between the two methods over the course of 13 months from August 2004 to August 2005 showed a significant discrepancy, which cannot be explained by the measurement uncertainties attributed to either SRP or GPT in the range of 80–800 nmol mol−1 O3, where GPT was about 2% higher than SRP. This result indicates possible biases in the currently existing O3 reference standards and warrants further studies to identify and characterize possible sources of the systematic discrepancy.