Ambient ammonia measurements using laser photo-acoustic spectroscopy

Ammonia concentrations reached minimal levels (approximately 0.1 ppb) in early winter, followed by a sudden later winter increase. A direct relationship between ambient ammonia levels and air temperature was inferred from the data (linear correlation coefficient r=0.53). Ammonia concentrations were determined to be directly related to the absolute humidity of the air (r=0.72); a weaker relationship between ammonia concentrations and relative humidity was discovered (r=0.37). The data also indicated that ammonia levels were generally higher within continental air masses than those of maritime origin. Soil parameters such as pH and moisture content were found to have a major bearing on the release of gaseous ammonia from soils in the region

An optimized sampling system for highly reproducible isotope ratio measurements (δ 13C and δ 18O) of pure CO2 gas by infrared spectroscopy

partially_open8sìThe characteristics of an optimized sampling system for measurements of isotope ratios in pure CO2 gas with Isotope Ratio Infrared Spectroscopy measurement systems that has achieved reproducible measurement of δ 13 C and δ 18O values with 0.02‰ reproducibility (1 σ) is described. The key elements of the sampling system revolve around almost identical treatment of sample and reference gases allowing two-point calibration of up to 14 samples, and appropriate flushing protocols to remove any biases from memory effects of previously sampled gases. Measurements are performed by the Isotope Ratio Infrared Spectroscopy system at a mole fraction of nominally 700 μmol mol−1 CO2 in air, by dilution of pure CO2 gas controlled by individual low-flow mass flow controllers (0.07 ml min−1), and with a feedback loop to control mole fractions to ensure that differences between references and sample gas mole fraction stay below 2 μmol mol−1. This level of control is necessary to prevent biases in measured isotope ratios, the magnitude of which has also been studied with a sensitivity study. The system has been validated using pure CO2 samples which range in δ 13 C delta values of −1‰ and −45‰ vs VPDB-CO2, and in all cases measurement reproducibility over several days of testing of 0.02‰ or better (1 σ) was achieved for both δ 13 C and δ 18O, with negligible memory effects. The amount of sample gas used for each measurement was less than 5 ml of CO2 at (RTP), making the system easily deployable for isotope ratio value assignment of bulk CO2 gas, and adaptable to atmospheric mole fractions of CO2 in air, and for value assignments of standards. Using the sampling system described the measurement reproducibility of current Isotope Ratio Infrared Spectroscopy systems approaches measurement reproducibility that can be achieved with some IRMS systems.openViallon, Joële; Flores, Edgar; Moussay, Philippe; Chubchenko, Ian; Rolle, Francesca; Zhang, Tiqiang; Mussell Webber, Eric B; Wielgosz, Robert IViallon, Joële; Flores, Edgar; Moussay, Philippe; Chubchenko, Ian; Rolle, Francesca; Zhang, Tiqiang; Mussell Webber, Eric B; Wielgosz, Robert

Metrology in Gas Analysis at the Federal Office of Metrology METAS

Gas analysis as a metrological discipline has a history of about 25 years in Switzerland. Starting with the requirement of reliable reference gas mixtures for legal applications the Swiss Federal Office of Metrology (METAS) had to increasingly find also calibration solutions for the ambient air level. Thereby the metrological principles of traceability, uncertainty evaluation and verification as well as the use of unambiguous terminology for quantities and units were in the focus of the activities. Using three examples different ways of implementing these principles are explained. For the emission range, traceability is mainly achieved by gravimetrically prepared certified gas mixtures in pressurised cylinders using high purity gases and a highly reproducible comparison method. The reactivity and limited stability of the important analytes in the ambient range ask for dynamic methods to secure traceability to the international system of units (SI). The dynamic methods requiring additionally high accuracy gas flow measurement techniques and trace gas analysis will be the focus for further developments at METAS

Amount of Carbon Dioxide Fraction Determination by TDLAS: Evidences for a Potential Primary Method Directly Applied in Gas Analysis

Tunable diode laser absorption spectroscopy (TDLAS) is a very powerful measurement technique. Compared with other traditional methods used in gas analysis, TDLAS is very selective and fit for field measurements. This work regards its ability to perform calibration-free measurements of amount of substance fractions serving as a potential primary method of measurement directly applied (PMDA) in gas analysis. This PMDA effectively reduces the uncertainty of field measurement results being independent of relatively large traceability chains supported by e. g. primary gas mixtures. The method based on the application of the Beer-Lambert law. The measurement equation of the method considered all significant uncertainty sources and all correction factors that substantially contribute to the uncertainty budget. For the first time a GUM-compliant, transparent and complete uncertainty budget for calibration-free amount of carbon dioxide fraction measurements by TDLAS is given. The performance of the calibration-free method was proved measuring amount of carbon dioxide fractions xCO2 of gravimetrically prepared CO2 in N2 gas mixtures in the interval of 10 to 100 mmol/mol. The TDLAS based xCO2 results were compared with respective gravimetric values and exhibited no bias, i. e. within their uncertainties. To improve the TDLAS-based method a new traceable linestrength value for the R12 line of the 2 µm band of CO2 was measured. The uncertainty of this line was improved from 2 - 5 % given in HITRAN to 1.1 % (k=2). The performance of the PMDA-TDLAS method was also proved in two applications at extreme opacity conditions: the measurement of xCO2 in a commercially certified multi-component gas mixture with xCO2 = 140 mmol/mol and in CO2 measurements in room air with xCO2 = 400 µmol/mol. The TDLAS measurements for both of them also rendered unbiased measurement results when they were compared with reference values.Diodenlaserabsorptionsspektroskopie (TDLAS) ist eine leistungsfähige Messtechnik. Verglichen mit anderen traditionellen Messverfahren der Gasanalytik besitzt TDLAS eine höhere Selektivität und ist für Feldmessungen geeignet. Diese Arbeit behandelt die Durchführbarkeit kalibrationsfreier Messungen von Stoffmengenanteilen als ein potentielles direkt angewandtes Primärverfahren (PMDA) in der Gasanalytik. Ein PMDA könnte die Unsicherheit von Feldmessungen wirksam verringern, da es unab- hängig von Rückführungsketten wäre, die auf Primärgasgemischen basieren. Das Messverfahren basiert auf der Anwendung des Beer-Lambertsches Gesetzes. Die Modellgleichung des Verfahrens betrachtet alle signifikanten Unsicherheitsquellen und Korrektionsfaktoren, die zum Unsicherheitsbudget beitragen. Erstmals wird ein GUM-kompatibles, transparentes und vollständiges Unsicherheitsbudget für kalibrationsfreie Messungen von Stoffmengenanteilen mit TDLAS angegeben. Die Performance des TDLAS-Verfahrens wurde anhand von Messungen des Stoff- mengenanteils xCO2 in gravimetrisch hergestellten Gasgemischen mit 10 bis 100 mmol/mol CO2 in N2 nachgewiesen. Dazu wurden die laserbasierten xCO2-Werte mit gravimetrisch bestimmten Messergebnissen verglichen. Die TDLAS-basierten Werte zeigten innerhalb der Unsicherheit keine Abweichung. Um das TDLAS-basierte Messverfahren zu verbessern, wurde ein neuer, rück- führbarer Wert der R12-Linienstärke in der 2-µm-Bande gemessen, dessen Unsicher- heit gegenüber der von HITRAN mit 2-5 % angegebenen auf 1,1 % (k=2) verringert wurde. Die Leistungsfähigkeit des TDLAS-Messverfahrens als PMDA wurde in zwei An- wendungen unter extremeren optischen Dichten erprobt: die Messung von xCO2 in einem kommerziellen zertifizierten Mehrkomponentengasgemisch mit xCO2 = 140 mmol/mol und in Raumluft mit xCO2 = 400 µmol/mol. Die TDLAS- Messungen lieferten für beide Anwendungen keine Abweichungen von den entsprechenden Referenzwerten

A study of multicomponent gas mixtures using various analytical methods for stack emission measurements

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfillment of the requirements for the degree Master of Science. Johannesburg, 2017.Multicomponent gas mixtures are inherently challenging to produce in the laboratory because of matrix effects, boiling points and reactivity amongst other factors. Therefore, methods must be continuously developed to control these challenges. The purpose of this work was to study these complex gas mixtures to improve their measurements with emphasis on the reduction of uncertainty. There are three critical steps to be followed in gas metrology for primary reference gas mixtures of the highest metrological level; purity analysis of source gases, gravimetric preparation and verification/validation which includes stability testing. Purity analysis of select source gases was quantified using various techniques. This methodology incorporated the use of molar masses and their uncertainties in order to obtain purity values for the chemical composition of gas mixtures. While many preparation methods such as permeation and dynamic methods are available, a static gravimetric method was used to prepare the complex stack and automotive gas mixtures following International Standard Organisation: 6142-1. For the mole fraction range of interest, four components (carbon dioxide, carbon monoxide, sulphur dioxide and nitric oxide) excluding propane, were obtained from analysis by non-dispersive spectroscopy techniques calibrated by several standard gas mixtures of different mole fractions. Propane was analysed by a gas chromatograph coupled with flame ionisation detection. Multipoint calibration was used to evaluate the linearity or nonlinearity of the detector. The final results for the stack gas mixture components showed an achievement of 0.4% to 0.8% percentage relative expanded uncertainty and 0.4% to 1.3% for carbon dioxide depending on the matrix of the standard gas mixtures used, 0.5% to 1% for propane, 0.8% to 1.8% for nitric oxide, 2% to 6% for carbon monoxide and 0.3% to 2.3% for sulphur dioxide. One of the most important suppositions drawn was the incidence of synergistic effects associated with calibration by nonrepresentative standard gas mixtures when these were used for analysis for some of the components of stack mixtures. To evaluate improvements in measurement capability, the results of the current work were compared to the data of the laboratory in 2008-2011 and there was an improvement in the measurement of carbon dioxide, carbon monoxide, propane and nitric oxide. These improvements are attributed to rigorous purity analysis of starting materials, reduction of uncertainty and developments in measurement expertise. In this work, different measurement and calibration methods were used to analyse the components of the new stack gas mixtures. The stability of these components was evaluated by analysing them at different times and the statistical D-test was used to check for significant instability. An unknown stack sample was compared with the standard gas mixtures prepared for this work. In combination with same matrix and same concentrations, single point calibration was found suitable for stack gas measurement. To reiterate the concept of matrix effect, the results of carbon dioxide in a mixture containing carbon monoxide and oxygen as well in nitrogen, were used to show how differences in matrix often give erroneous results and same conclusions cannot be made for different mixtures. While the data of this measurement was unsatisfactory, an improved method developed for this type of emission multicomponent was very successful. Emission industries also require automotive primary reference gas mixtures. These are equally important and complex multicomponent mixtures measured and improved in this work. A very precise and repeatable single point method was developed for the analysis of the components of automotive mixtures. The repeatability of the gas chromatography method was 0.2% for oxygen, 0.1% for carbon monoxide, 0.5% for carbon dioxide and 0.3% for propane. The percentage relative expanded uncertainty was 0.4% for oxygen, 0.8% for carbon monoxide, 0.8% for carbon dioxide and 0.5% for propane. However, its limitation was the use of different calibration gases for each analysis. This led to inconsistencies in the calculated mole fractions, non-predictability and instability. A proficiency testing scheme was coordinated by the laboratory for automotive emission as part of this study. Given the complexity of the samples, the work aimed to check any improvements that could be made to the capability of measurement over the years. This new method using gas chromatography coupled with different detectors (residual gas analyser) was successful in verifying the gravimetric values very V accurately. Finally, the results of the stack gas mixtures were ≤1% relative except carbon monoxide and ≤1% for automotive mixtures. This work aimed to support the emission industry by providing it with representative and accurate reference gas mixtures, extend the accreditation scope of the laboratory and improve its calibration and measurement capability for multicomponent gas mixtures.LG201

CCQM-K90, formaldehyde in nitrogen, 2 μmol mol− 1 Final report

The CCQM-K90 comparison is designed to evaluate the level of comparability of national metrology institutes (NMI) or designated institutes (DI) measurement capabilities for formaldehyde in nitrogen at a nominal mole fraction of 2 μmol mol−1. The comparison was organised by the BIPM using a suite of gas mixtures prepared by a producer of specialty calibration gases. The BIPM assigned the formaldehyde mole fraction in the mixtures by comparison with primary mixtures generated dynamically by permeation coupled with continuous weighing in a magnetic suspension balance. The BIPM developed two dynamic sources of formaldehyde in nitrogen that provide two independent values of the formaldehyde mole fraction: the first one based on diffusion of trioxane followed by thermal conversion to formaldehyde, the second one based on permeation of formaldehyde from paraformaldehyde contained in a permeation tube. Two independent analytical methods, based on cavity ring down spectroscopy (CRDS) and Fourier transform infrared spectroscopy (FTIR) were used for the assignment procedure. Each participating institute was provided with one transfer standard and value assigned the formaldehyde mole fraction in the standard based on its own measurement capabilities. The stability of the formaldehyde mole fraction in transfer standards was deduced from repeated measurements performed at the BIPM before and after measurements performed at participating institutes. In addition, 5 control standards were kept at the BIPM for regular measurements during the course of the comparison. Temporal trends that approximately describe the linear decrease of the amount-of-substance fraction of formaldehyde in nitrogen in the transfer standards over time were estimated by two different mathematical treatments, the outcomes of which were proposed to participants. The two treatments also differed in the way measurement uncertainties arising from measurements performed at the BIPM were propagated to the uncertainty of the trend parameters, as well as how the dispersion of the dates when measurements were made by the participants was taken into account. Upon decision of the participants, the Key Comparison Reference Values were assigned by the BIPM using the largest uncertainty for measurements performed at the BIPM, linear regression without weight to calculate the trend parameters, and not taking into account the dispersion of dates for measurements made by the participant. Each transfer standard was assigned its own reference value and associated expanded uncertainty. An expression for the degree of equivalence between each participating institute and the KCRV was calculated from the comparison results and measurement uncertainties submitted by participating laboratories. Results of the alternative mathematical treatment are presented in annex of this report

Scale down of a dynamic generator of VOC reference gas mixtures

A system for the dynamic preparation of reference gas mixtures based on the diffusion technique has been developed by the National Metrology Institute of Italy i.e. the Istituto Nazionale di Ricerca Metrologica (INRIM). The gravimetric method used for the estimation of the diffusion rate and consequent concentration, gives the system the property to be a primary standard. The system can generate mixtures with low uncertainty and high stability in the 20 nmol.mol-1 - 2.5 µmol.mol-1 concentration range with a 5% (k = 2) expanded uncertainty for mixtures of acetone in air. Based on this system, a transportable device for the generation of VOC reference gas mixtures to be used as calibration standard was designed and developed. The methodology used for the scale down included several steps. An initial characterization and modelling of the primary device was done using computational tools. Based on the response of the computational model to the different physical quantities, a set of design parameters was identified. The thresholds for this set of parameters were established and translated into a set of design criteria to consider in order to keep the metrological performance target. After the design and development of the transportable device, a metrological characterization was carried out, to verify its capabilities. The metrological characterization of the generator was done in the Dutch National Metrology Institute i.e. the Van Swinden Laboratory (VSL) trough Cavity Ring Down Spectroscopy (CRDS) analyses to evaluate the linearity, the reproducibility and the short term stability. The results for the generation of methanol mixtures with molar fractions in the 80-150 nmol.mol-1 range, were 99.6% linear, with a reproducibility after 3 days within 2,9% and a short term stability better than 1% per hour. Repeatable measurements of the generated concentration were obtained for three different molar fractions, with the use of both CRDS (VSL) and the GC/FID (INRIM). A flow of the desired dry pure carrier gas can be connected to the device. The presence of water in the system has not been taken into account and further analyses should be done before introducing it to the system. Water presence might affect the adsorption rate, and consequently the flushing time before normal operation. This transportable device is able to perform in-situ calibration of instruments and has been designed to generate gas mixtures of up to four species at a time

Indoor Air Quality Design and Control in Low-Energy Residential Buildings, International Energy Agency, EBC Annex 68, Subtask 5 Final Report: Field measurements and case studies

IEA-EBC Annex 68: Indoor Air Quality Design and Control in Low Energy Residential Buildings investigates how to ensure that future low energy buildings are able to improve their energy performance while still providing comfortable and healthy indoor environments. More specifically, Subtask 5 of Annex 68 has dealt with generation of data for the verification of the models and strategies developed in the other Annex 68 Subtasks through controlled field tests and case study presentations

Global tropospheric chemistry: Chemical fluexes in the global atmosphere

In October 1987, NSF, NASA, and NOAA jointly sponsored a workshop at Columbia University to assess the experimental tools and analysis procedures in use and under development to measure and understand gas and particle fluxes across this critical air-surface boundary. Results are presented for that workshop. It is published to summarize the present understanding of the various measurement techniques that are available, identify promising new technological developments for improved measurements, and stimulate thinking about this important measurement challenge