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Bukit Koto Tabang
-CO-
| Observation |
| Category |
: |
Air sampling observation |
| Situation |
: |
ongoing |
| Time zone |
: |
Local time 7 |
| Sampling |
| Sampling height |
: |
4.5 |
| Description |
: |
continuous |
| Sampling and analysis frequency |
: |
Observations are continuous, 1-minute data are aggregated. |
| Sampling environment |
: |
|
| Description for sampling analysis |
: |
All tubing is teflon, inlets are open-face, protected from the rain with an upside-down cup. Inlet filters are used to protect the instruments, and the ambient air is dried using a Nafion dryer. |
| Instrument and Analysis |
| Measurement method |
: |
NDIR |
| Current status and history of instrument |
: |
A TEI48C TL instrument (S/N 66839-352) was installed by Empa in July 2001. The sample air is drawn from above the roof of the station through a ¼” Teflon line (ca. 10 m) and is dried using a Peltier cooling element (Hamamatsu, DH-109) and a Nafion dryer (Permapure, PD-625-24PP) operated in reverse flow mode before it enters the instrument. The TEI48C TL was operated as a self-contained unit and measurement as well as auxiliary data (5-minute aggregates) were downloaded periodically from the internal data logger. |
| Description of instrument |
: |
|
| Calibration |
| Current scale employed in the measurement |
: |
WMO2000 |
| Measurement calibration |
: |
The TEI 48C TL is a correlation-filter wheel instrument that required frequent zero-checks (15 minutes every 2 hours) to correct for substantial zero drift. This was accomplished by switching the inlet to the ZERO gas position, to which a Sofnocat unit was connected. Occasionally (but very infrequently), manual span checks were conducted, whereby a zero check was followed by challenging the instrument with CO calibration gas with a mixing ratio around 1 ppm. In March 2004, the set-up was amended with a dilution unit (2 red-y MFCs, a separate zero-air unit (silica gel drying cartridges followed by a pump followed by Purafil and Sofnocat) and a span gas with mixing ratios between 10 and 50 ppm) that was configured to deliver a constant span gas concentration nominally around 400 ppb CO (see below for details). Subsequently, automatic zero/span checks were performed every 2 hours and consisted of 20 minutes zero followed by 10 minutes of span at the beginning of odd hours.
Regular maintenance included changing the zero filter and periodically inspecting and cleaning the cell.
Between 10 October, 2005, and 3 January, 2006, the instrument experienced electronic failure and was shut down. After repair and maintenance, it continued to operate until 25 November 2007. After that, the instrument malfunctioned, and data were no longer considered reliable. |
| Scale and calibration(treasability) |
: |
All standard cylinders used were either prepared or purchased by WCC-Empa and were calibrated against the WMO-2000 scale.
The instrument was audited several times by WCC-Empa. Audit reports are available at http://gaw.empa.ch/gawsis. |
| Data Processing |
| Measurement unit |
: |
ppb |
| Data processing |
: |
Raw data were visually inspected and quality assessed prior to zero-correction. The zero-correction involved computing the difference of valid ambient readings and the estimated zero air response. The zero-air response for time when ambient air was measured was estimated by applying a non-parametric (loess) fitting algorithm to the zero readings obtained between ambient measurements. |
| Processing for averaging |
: |
Processing for Hourly Data:
Average of 5-minute values. No criterion for minimum data-availability was applied.
Processing for Daily Data:
Average of 5-minute values. No criterion for minimum data-availability was applied.
Processing for Monthly Data:
Average of 5-minute values. No criterion for minimum data-availability was applied. |
| Data flag |
: |
Only data considered as 'valid' are submitted. |
| Data remarks |
: |
The column 'REM' indicates the estimated combined standard uncertainty of the aggregated values, estimated by considering the standard uncertainty of the 5-minute averages, as well as audit results. Standard uncertainties of higher aggregates were computed according to ISO 11222. Details will be provided in a forthcoming publication. |
| Other Information |
| Scientific aim |
: |
Assessment of Air quality, background concentrations, long-range transport of air pollutants, climate change, source apportionment |
| Reference |
: |
http://gaw.empa.ch/gawsis |
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| submitted by Agency for Meteorology, Climatology and Geophysics / Swiss Federal Laboratories for Materials Testing and Research |
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