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CPO134S00
-N2O-
| Observation |
| Frequency |
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every 15 minutes |
| Method |
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GC-ECD |
| Instrument |
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SHIMADZU |
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| Description |
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Two freezing units (-4 and -45 ºC respectively) are used in series to dry the ambient air prior to analysis. Sampling is continuous, using a gas chromatograph (GC) with and Electron Capture Detector (ECD). The oven temperature is approximately 40 ºC and the ECD temperature 355 °C.
The primary column is a 1/8" x 3 m stainless steel, packed with Porapak N, 80/100 mesh, whilst a pre-column (1/4" x 20 cm s/steel packed with sodium asbestos) is used to extract any CO2. N2 (5.0) is used as carrier gas and the sampling loop (s/steel, 2 mm OD x 2.2 m) has a volume of 7 ml.
The data have been recorded at 15 min intervals (96 samples per day) and mixing ratios stored as hourly means (1994 until 2002). From mid-99 onwards, the 15-min intervals have been used to create half-hourly means. These in turn form the basis for the daily and monthly averages.
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The height of the air intake is 260 m above sea level from the top of a 30 m high mast.
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| Calibration |
| Scale |
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| Description |
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One working standard is used every hour and multi calibrations involving five (CMDL certified) laboratory standards (range: 286 - 347 ppb N2O) are utilised approximately once every 4 months to verify the working gas concentration. A target gas is also run once daily as a check on instrumental stability.
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| Data Processing |
| Unit |
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ppb |
| Description |
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All data with obvious sampling or analytical error are rejected. Furthermore, a statistical filter (moving percentiles) is applied for the selection of background concentrations. |
| Average Procedure |
| Hourly |
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| Daily |
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| Monthly |
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