ࡱ> )+(7 8bjbjUU "7|7|8 l0000000D$$$$ 0 DuHHHHHHHH$+ K`0HHHHH00HH/HR0H0HH 00H< ÓD$: E0u  DD0000Hydrogen measurements are made using an RGA3 analyzer fitted with a mercuric oxide reduction gas detector (Trace Analytical, Inc., California). The hydrogen measurements are referenced against a calibration scale developed at CSIRO (Commonwealth Scientific and Industrial Research Organization). The hydrogen scale was bootstrapped from a gravimetrically derived methane-in-air calibration scale by the following procedure. A short section of stainless steel tubing was used to connect two valves, with the volume isolated between the valves being ~0.4 mL. With the valves open this volume could be flushed (to vent) with either high purity hydrogen or high purity methane. This volume was also connected to the valve of a 22-L stainless steel cylinder in which the calibration mixture was prepared. The cylinder was first flushed and filled to approximately ~1 atm with zero air. The sample volume was then flushed and filled to ambient pressure with hydrogen, followed by rapid flushing into the cylinder with zero air. For hydrogen this procedure was performed only once. The sample volume was then flushed and filled with methane and similarly flushed into the cylinder with zero air. For methane this process was repeated twice more. To complete the preparation of the mixture, sufficient zero air was then added to achieve hydrogen and methane mixing ratios close to present-day atmospheric values and in a precisely determined ratio of 1:3. The methane mixing ratio was determined by gas chromatographic analysis to be 1585.5 ppb, adjusted from the CSIRO94 CH4 scale to the gravimetrically derived scale of Meteorological Research Institute, Japan [Matsueda, 1993], that is more accurate in absolute terms. The hydrogen content of this mixture could then be determined as 528.5 ppb mole fraction in dry air. The zero air used was verified to be free of both hydrogen and methane, at least to the detection limits of the analytical techniques used (<2 ppb for both species). Our experience has shown that hydrogen-in-air mixtures show good long-term stability in clean stainless steel containers. The hydrogen scale was propagated (by analysis) to a suite of 14 natural air standards stored in high-pressure stainless steel cylinders. These standards have been regularly analyzed over a period of up to 6 years, over which time it has been possible to establish experimentally that the suite of standards has the property of relative stability. Because the hydrogen mixing ratios in the suite span a reasonable range (~500-550 ppb) and the pressures in these cylinders have spanned a significant range (10-400 psig), we feel confident in concluding from the finding of relative stability that the suite is likely to also exhibit absolute stability. The hydrogen calibration scale developed at CSIRO has also been regularly intercompared with the hydrogen calibration scale of the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory (NOAA CMDL). There is an absolute calibration difference of 3 1.0% between the two independent scales, with the CSIRO scale giving higher atmospheric values. A detailed description of the calibration scale, including the methods used, and the evaluation of its long-term stability are given by R. L. Langenfelds et al. (manuscript in preparation), [see also Francey et al., 1996]. * % &  (278h 6CJh6CJCJH*CJhCJ*, QS3478] 8]8^ 8 &P/ =!"#$% i0@0 Normal_HmH sH tH <A@< Default Paragraph FontDOD Text$ d$]a$ CJtH uHH Level 1 head$d"xa$5CJ8 *,Q S 3 4 7 : 0000008 8 8.0eh '  " :  S  : 3333:  Peter Simmonds2C:\windows\TEMP\AutoRecovery save of Document1.asdPeter SimmondsC:\My Documents\H2Absolute.docPeter SimmondsC:\My Documents\H2Absolute.docPeter SimmondsC:\My Documents\H2Absolute.doc Ray H.J. Wang'C:\agage\agage_24\header\H2standard.doc: @7 7 47 7 8 @UnknownGz Times New Roman5Symbol3& z Arial"qh\r\\r\ E& d#20b 2Hydrogen measurements are made using an RGA3 analyzer fitted with a mercuric oxide reduction gas detector (Trace Analytical, IncPeter Simmonds Ray H.J. WangOh+'0$0HTd |    Hydrogen measurements are made using an RGA3 analyzer fitted with a mercuric oxide reduction gas detector (Trace Analytical, InceydrPeter SimmondseeteNormaliRay H.J. Wange2y Microsoft Word 9.0t@Ik@2m@X@X ՜.+,0| hp  ]University of Bristoleb  Hydrogen measurements are made using an RGA3 analyzer fitted with a mercuric oxide reduction gas detector (Trace Analytical, Inc Title !"#$%&'*Root Entry F?ߓ,1TableWordDocument"SummaryInformation(DocumentSummaryInformation8 CompObjjObjectPool?ߓ?ߓ  FMicrosoft Word Document MSWordDocWord.Document.89q