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Mt. Kenya
-CO-
| Observation |
| Category |
: |
Air sampling observation |
| Situation |
: |
ongoing |
| Time zone |
: |
UTC |
| Sampling |
| Sampling height |
: |
4.5 |
| Description |
: |
continuous |
| Sampling and analysis frequency |
: |
Continuous sampling with 1-minute averages stored on external data logger. |
| Sampling environment |
: |
The MKN station is situated on the north-western slope of Mt. Kenya at an altitude of 3680 m a.s.l. and is surrounded by alpine grassland and brushes. As part of the Mt.Kenya National Park the whole mountain area is protected and there are no local anthropogenic emissions, making the site suitable for continuous observations of the background free tropospheric composition. The closest human settlement with rather low emission sources is situated 17 km in north-westerly direction. |
| Description for sampling analysis |
: |
A rain and snow protected air inlet system is mounted 4.5 m
above ground and is connected to a glass manifold (length 3
m, diameter 5 cm) to which individual instruments are connected. The manifold is permanently flushed by a high volume pump. Residence times were estimated to be below 10 s.
Sample air is taken from the glass manifold through a 1.5 m, 4 mm diameter teflon tubing at a flow rate of 1 lpm. A 47 mm teflon filter (5-6 micron) is installed before the sample gas inlet and is regularly
exchanged. To reduce the interference with water vapor, a nafion
dryer (PERMAPURE PD-50-24'') is installed in the sampling line,
operating in reflux mode using a critical orifice. |
| Instrument and Analysis |
| Measurement method |
: |
NDIR |
| Current status and history of instrument |
: |
TEI 48C TL (SN: 66838-352) installed 2002-08-01
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| Description of instrument |
: |
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| Calibration |
| Current scale employed in the measurement |
: |
WMO-2000 |
| Measurement calibration |
: |
Automatic zero and span calibration are performed every 2 hours (20 minutes zero, 10 minutes span).
Zero air is generated using a custom built system consisting of a rubin gel cartridge, a SOFNOCAT 423 (Molecular Products Ltd) cartridge, inlet and outlet filters.
The span gas concentration is created using a higher concentration laboratory standard (traced back to WMO-2000 CO scale by GAW World Calibration Center (WCC), Empa), which is diluted with zero air (using Bronckhorst mass flow controllers) and fed into the span gas inlet.
In addition, manual span gas checks directly using 1 ppm laboratory standards (WMO-2000) are performed by the station operators once per month.
|
| Scale and calibration(treasability) |
: |
WMO-2000
See audit reports 2002, 2005, 2006. |
| Data Processing |
| Measurement unit |
: |
ppbv |
| Data processing |
: |
Due to the CO zero drift, zero conditions during ambient air sampling are interpolated from zero air measurements using local regression models. A span correction is applied in a similar way. The combined uncertainty of every individual 1-min CO measurement is then determined from the contributions of the uncertainty of the CO analyzer, the uncertainty of the zero correction and the uncertainty of the span correction.
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| Processing for averaging |
: |
Processing for Hourly Data:
All aggregate calculations based on 1-minute aggregates, 40% availability required for aggregate. Uncertainty of aggregate following ISO 11222.
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| Data flag |
: |
All measurements are submitted with an individual estimate of their uncertainty. Only valid measurements are reported. No additional flag is provided. Regional pollution events are not filtered. |
| Data remarks |
: |
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| Other Information |
| Scientific aim |
: |
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| Reference |
: |
ISO, 2002: 11222:2002 Air quality - Determination of the uncertainty of the time average of air quality measurements11222:2002, 20 pp.
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| submitted by Kenya Meteorological Department / Swiss Federal Laboratories for Materials Testing and Research |
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