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Alert - EC
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| Category |
Air sampling observation |
| Sampling Type |
continuous |
| Sampling Height/Depth |
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| Sampling and Analysis Frequency |
Hourly |
| Sampling Environment |
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| Measurement Method |
Gas Chromatography (FID) |
| Current status and history of Instruments |
GC-FID |
| Description of Instruments |
Agilent 6890N |
| Time Zone |
UTC |
| Data Period |
1988-01-01 - 2008-12-31 |
| Data Type |
hourly, daily, monthly |
| Parameter detail |
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| Other Descriptions for Sampling and Analyses |
The continuous measurement of CH4 at Alert, Fraserdale, Candle Lake and Sable Island is currently being made using an Aglilent (formerly Hewlett Packard) gas chromatographs (Model 6890N)employing flame ionization detection. In November 1999, the CH4 gas chromatographic (Hewlett Packard 5890) system that was initially installed at Alert in September 1987 (along with the desk top integrator, data logger collection and automation software) was replaced with the Agilent 6890N GC. This system is fully automated via HP Chemstation software (described in the data section). A similar gas chromatographic system was installed at Fraserdale in October 2002, replacing the original HP 5890 GC that was installed in December 1990).
At all sites, ambient air is delivered to the GC at approximately 5 L min-1 by a vacuum pump via a dedicated 0.95 cm o.d. sample line that extends to the top of a nearby tower. The air passes through a membrane filter, then through a pressure relief valve set at ~1 atmosphere to release excess pressure and is then dried to a dew point of around -60 degress C by passing the air through a glass trap submerged in an -80 degree C methanol bath. All standard gases are supplied to the GC from pressurized gas cylinders equipped with high-purity, two-stage gas regulators.
For CO and CH4, the analysis is done in a similar manner. CO and CH4 are first passed on to a 4'x1/8" pre-column (Molesieve 5a) and then passed on to 4'x1/8" analytical column (Unibeads 1s). The pre-column is back flushed allowing late eluting components and contamination to be passed back to the room. All columns are contained in the same oven and maintained at 80¡C. An electronic pressure controller is used to control the nitrogen carrier gas flow rate (~60 ml/min). CH4 elutes at ~2 minutess and CO at ~4 minutes after injection. After the CH4 elutes, a 1/16¡É 6-port two-position valve is switched, allowing the CO to pass through a heated Nickel catalyst. The catalyst converts the CO to CH4, permitting the analysis of CO to be done on the FID. The shunting configuration also avoids having the oxygen to pass through the catalyst, thus eliminating potential contamination as well as a large air peak that can cause baseline irregularities to occur near the CH4 peak.
Measurement cycles consist of repeated series of standard gas and ambient air injections. The peak height for the standard injection is used to calculate the CH4 mole fraction of the ambient injections.
All CH4 measurements at Alert and Fraserdale are reported in nmole mole-1 (abbreviated ppm, or parts per million, mole fraction), dry air,relative to the NOAA04 CH4 standard scale. Analytical precision based on replicate injections for standard tank gas is approximately 1.5 ppb for CH4 and 2 ppb for CO. |
| Scientific Aim |
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| Supporting Contributor(s) |
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| Last update |
2009-08-28 |
| Situation |
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This site is maintained by the Japan Meteorological Agency
in cooperation with the World Meteorological Organization
(Created : 2001/07/02 Modified : 2010/09/02)
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WMO World Data Centre for Greenhouse Gases
c/o Japan Meteorological Agency
1-3-4, Otemachi, Chiyoda-ku
Tokyo 100-8122, Japan
| Tel: |
+81-3-3287-3439 |
| Fax: |
+81-3-3211-4640 |
| E-mail: |
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WDCGG Data Submission and Dissemination Guide (PDF 1.2Mbyte)
WDCGG leaflet (PDF 2.7MByte, July 2008)