The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Manfred Grasserbauer - One of the best experts on this subject based on the ideXlab platform.
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Development and evaluation of a Calibration Gas generator for the analysis of volatile organic compounds in air based on the injection method
Analytical and Bioanalytical Chemistry, 2001Co-Authors: Erwin Rosenberg, Rainer A. Hallama, Manfred GrasserbauerAbstract:The development and operational evaluation of a Calibration Gas generator for the analysis of volatile or ganic compounds (VOC) in air is described. Details of the construction, as well as of the evaluation of the apparatus are presented here. The performance of the test Gas generator is validated both by on-line GC analysis of the Calibration Gas produced and by off-line analysis of adsorptive samples taken from the generated Calibration Gas. Both, active and passive sampling have been used, and the results demonstrate the excellent accuracy and precision of the generated test Gas atmosphere: For the 11 investigated organic compounds (aromatic and halogenated compounds), the found values were in most cases within 5% of the target value with a reproducibility of better than 3% RSD (as determined by the analysis of the sampled adsorbent tubes). Custom made adsorbent tubes were used for active and passive sampling and in both cases were analysed by thermal-desorption GC. Particularly the combination of passive sampling and thermodesorption-GC analysis offers significant advantages over the commonly used active sampling on activated charcoal, followed by CS2 desorption in terms of avoidance of hazardous solvents, potential for automation and improved detection limits. Both sampling techniques are capable for monitoring VOCs at concentrations and under conditions relevant for workplace monitoring.
S C Herndon - One of the best experts on this subject based on the ideXlab platform.
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characterizing a quantum cascade tunable infrared laser differential absorption spectrometer qc tildas for measurements of atmospheric ammonia
Atmospheric Measurement Techniques, 2009Co-Authors: R A Ellis, J G Murphy, E Pattey, R Van Haarlem, J M Obrien, S C HerndonAbstract:Abstract. A compact, fast-response Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of ammonia (NH3) has been evaluated under both laboratory and field conditions. Absorption of radiation from a pulsed, thermoelectrically cooled QC laser occurs at reduced pressure in a 0.5 L multiple pass absorption cell with an effective path length of 76 m. Detection is achieved using a thermoelectrically-cooled Mercury Cadmium Telluride (HgCdTe) infrared detector. A novel sampling inlet was used, consisting of a short, heated, quartz tube with a hydrophobic coating to minimize the adsorption of NH3 to surfaces. The inlet contains a critical orifice that reduces the pressure, a virtual impactor for separation of particles, and additional ports for delivering NH3-free background air and Calibration Gas standards. The level of noise in this instrument has been found to be 0.23 ppb at 1 Hz. The sampling technique has been compared to the results of a conventional lead salt Tunable Diode Laser Absorption Spectrometer (TDLAS) during a laboratory intercomparison. The effect of humidity and heat on the surface interaction of NH3 with sample tubing was investigated at mixing ratios ranging from 30–1000 ppb. Humidity was seen to worsen the NH3 time response and considerable improvement was observed when using a heated sampling line. A field intercomparison of the QC-TILDAS with a modified Thermo 42CTL chemiluminescence-based analyzer was also performed at Environment Canada's Centre for Atmospheric Research Experiments (CARE) in the rural town of Egbert, ON between May–July 2008. Background tests and Calibrations using two different permeation tube sources and an NH3 Gas cylinder were regularly carried out throughout the study. Results indicate a very good correlation at 1 min time resolution (R2 = 0.93) between the two instruments at the beginning of the study, when regular background subtraction was applied to the QC-TILDAS. An overall good correlation of R2 = 0.85 was obtained over the entire two month data set, where the majority of the spread can be attributed to differences in inlet design and background subtraction methods.
Erwin Rosenberg - One of the best experts on this subject based on the ideXlab platform.
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Development and evaluation of a Calibration Gas generator for the analysis of volatile organic compounds in air based on the injection method
Analytical and Bioanalytical Chemistry, 2001Co-Authors: Erwin Rosenberg, Rainer A. Hallama, Manfred GrasserbauerAbstract:The development and operational evaluation of a Calibration Gas generator for the analysis of volatile or ganic compounds (VOC) in air is described. Details of the construction, as well as of the evaluation of the apparatus are presented here. The performance of the test Gas generator is validated both by on-line GC analysis of the Calibration Gas produced and by off-line analysis of adsorptive samples taken from the generated Calibration Gas. Both, active and passive sampling have been used, and the results demonstrate the excellent accuracy and precision of the generated test Gas atmosphere: For the 11 investigated organic compounds (aromatic and halogenated compounds), the found values were in most cases within 5% of the target value with a reproducibility of better than 3% RSD (as determined by the analysis of the sampled adsorbent tubes). Custom made adsorbent tubes were used for active and passive sampling and in both cases were analysed by thermal-desorption GC. Particularly the combination of passive sampling and thermodesorption-GC analysis offers significant advantages over the commonly used active sampling on activated charcoal, followed by CS2 desorption in terms of avoidance of hazardous solvents, potential for automation and improved detection limits. Both sampling techniques are capable for monitoring VOCs at concentrations and under conditions relevant for workplace monitoring.
M. Kulmala - One of the best experts on this subject based on the ideXlab platform.
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Technical Note: Quantitative long-term measurements of VOC concentrations by PTR-MS ? measurement, Calibration, and volume mixing ratio calculation methods
Atmospheric Chemistry and Physics Discussions, 2008Co-Authors: R. Taipale, T. M. Ruuskanen, J. Rinne, M. K. Kajos, H. Hakola, T. Pohja, M. KulmalaAbstract:Proton transfer reaction mass spectrometry (PTR-MS) is a technique for online measurements of atmospheric concentrations, or volume mixing ratios, of volatile organic compounds (VOCs). The aim of this paper is to give a detailed description of our measurement, Calibration, and volume mixing ratio calculation methods, which have been designed for long-term stand-alone field measurements by PTR-MS. We also show how the information obtained from a Calibration can be used to determine the instrument specific relative transmission curve, which enables quantitative mixing ratio calculation for VOCs which are not present in a Calibration Gas standard. To illustrate the functionality of our measurement, Calibration, and calculation methods, we present a one-month period of ambient mixing ratio data measured in a boreal forest ecosystem at the SMEAR II station in southern Finland. During the measurement period 27 March?26 April 2007, the hourly averages of mixing ratios were 0.1?0.5 ppbv for formaldehyde, 0.2?3.0 ppbv for methanol, 0.04?0.39 ppbv for benzene, and 0.03?1.25 ppbv for monoterpenes.
Horst Fischer - One of the best experts on this subject based on the ideXlab platform.
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real time measurements of atmospheric co using a continuous wave room temperature quantum cascade laser based spectrometer
Optics Express, 2012Co-Authors: Jingsong Li, U Parchatka, R Konigstedt, Horst FischerAbstract:A compact, mobile mid-infrared laser spectrometer based on a thermoelectrically (TE) cooled continuous-wave room temperature quantum cascade laser and TE-cooled detectors has been newly developed to demonstrate the applicability of high sensitivity and high precision measurements of atmospheric CO. Performance of the instrument was examined with periodic measurements of reference sample and ambient air at 1 Hz sampling rate and a 1-hourly Calibration cycle. The typical precision evaluated from replicate measurements of reference sample over the course of 66-h is 1.41 ppbv. With the utilization of wavelet filtering to improve the spectral SNR and minimize the dispersion of concentration values, a better precision of 0.88 ppbv and a lower detection limit of ~0.4 ppbv with sub-second averaging time have been achieved without reducing the fast temporal response. Allan variance analysis indicates a CO measurement precision of ~0.28 ppbv for optimal integration time of approximate 50 s. The absolute accuracy is limited by the Calibration Gas standard. This completely thermoelectrically cooled system shows the capability of long-term, unattended and continuous operation at room temperature without complicated cryogenic cooling.
