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Izaña (Tenerife)
-O3-
| Observation |
| Category |
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Air sampling observation |
| Situation |
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ongoing |
| Time zone |
: |
UTC |
| Sampling |
| Sampling height |
: |
13 |
| Description |
: |
continuous |
| Sampling and analysis frequency |
: |
Continuous |
| Sampling environment |
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The Izaña station is located at 2367 m above see level, on the Island of Tenerife, Spain. The ground in the vicinity around Izaña is loosely covered with light volcanic soil. The vegetation in the surrounding area is sparse, consisting mainly of broom. A belt of pine forest grows between 1000 and 2000 meters a.s.l. During nighttime (20UTC-08UTC), in situ measurements are representative of free troposphere background conditions. This is due to the following facts: a) usually a strong subtropical temperature inversion layer is located at a lower altitude than Izana station; b) Izana station is located on the top of a crest, so during the night period downslope wind produces (by mass conservation) the arrival of free troposphere air to Izana. During daytime, small amounts of air coming from the forest can arrive to the station due to surface upslope wind produced by ground diurnal heating. Apart from this effect, there is no arrival of polluted air from the rest of the island, due to the presence of the strong subtropical temperature inversion layer. |
| Description for sampling analysis |
: |
The measurement technique used is the UV absorption method which is the preferred method in GAW-WMO programme.
The general ambient air inlet, which provides ambient air for all instruments is an 8cm inner diameter (ID) stainless steel pipe and has a high flow rate (2180 l/min). This inlet is situated on top of the building tower; the height above the ground has changed through the years: 13 m (1984-2000), 8 m (2000- May 2005) and 30 m (from June 2005). The Inlet is protected against rain by an upside-down stainless steel bucket.
Ozone instruments are installed at the 5th floor 20 m above ground.
Sampling-line ; Dimensions: length = ca. 4 m, inner diameter = 4 mm
Material ; PFTE Inlet-filter ; Teflon inlet filter before instrument, exchanged weekly
Flow rate ; ca. 2 l/min
Total residence time in the sampling line and the inlet ; ca. 3 s. Materials as well as the residence time of the inlet system are adequate for surface ozone measurements. |
| Instrument and Analysis |
| Measurement method |
: |
Light absorption analysis (UV) |
| Current status and history of instrument |
: |
UV Absorption |
| Description of instrument |
: |
May 87 - Jul 95 ; DASIBI 1008-AH #4283
Aug 95 - 21 Jul 96 ; DASIBI 1008-RS #5797
Apr 97-(O3 Calibrator) ;TEI 49-CPS#56085-306
22 Jul 96 - 31 Jan 99 ; TEI 49-C #55912-305
01Feb 99 - (Primary instrument); TEI 49-C #62900-337
12Dec 2001-(Secondary instrument) ; TEI 49-C #72491-371 |
| Calibration |
| Current scale employed in the measurement |
: |
WMO Standard Instrument |
| Measurement calibration |
: |
Internal Calibration with TEI 49C-PS Biennial WMO audits performed by the World Calibration Centre for Surface Ozone, Carbon Monoxide and Carbon Dioxide. The following EMPA's audits have been performed up to now: Nov 1996, Feb 1998, Jun 2000, Dec 2004, and Mar 2009. EMPA’s audit reports are available at http://www.empa.ch/gaw/audits/IZO yyyy.pdf, where yyyy is the year.
Automatic zero checks are performed as a daily check of the ozone analyzers at 16:00 GMT. These zero measurements are used later for data reprocessing and correcting the ambient air measurement values.
Time series are visualised and data is flagged as invalid in case of unexplainable values or based upon log book entries. All data is recalculated using the last calibration of the instrument. |
| Scale and calibration(treasability) |
: |
The audits were performed according to the “Standard Operating
Procedure (SOP) for performance auditing O3 analysers
at global and regional WMO-GAW sites”, WMOGAW Report No. 97.
The WCC-Empa traveling standard (TS) was compared with the Standard Reference Photometer before and after use during the field audit. |
| Data Processing |
| Measurement unit |
: |
ppb |
| Data processing |
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| Processing for averaging |
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Processing for Hourly Data:
Since July 1996, hourly O3 data is calculated from 1-minute O3 averages obtained, in turn, from continuous sampling.
Before July 1996, hourly data were obtained from 30-minute or 10-minute averaged data from continuous sampling.
Processing for Daily Data:
Daily data corresponds to the night period, which is representative of free troposphere conditions. So, the ozone valley breeze effect, as result of upslope winds (valley-to-mountain breeze), has been removed.
Nocturnal daily means correspond to the following period: from 20:00 UTC of the previous day to 08:00 UTC of the current day.
Processing for Monthly Data:
Monthly means are computed from nocturnal daily means as described above. |
| Data flag |
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| Data remarks |
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| Other Information |
| Scientific aim |
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Long-term surface ozone monitoring for trends detection.
Long-range pollution transport.
Atmospheric processes affecting tropospheric ozone (STE processes, Saharan Air Layer charcaterization...)
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| Reference |
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Cuevas, E., González, Y., Rodríguez, S., Guerra, J. C., Gómez-Peláez, A. J., Alonso-Pérez, S., Bustos, J., and Milford, C.: Assessment of atmospheric processes driving ozone variations in the subtropical North Atlantic free troposphere , Atmos. Chem. Phys., 13, 1973-1998, doi:10.5194/acp-13-1973-2013, 2013.
Available at http://www.atmos-chem-phys.net/13/1973/2013/acp-13-1973-2013.pdf |
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| submitted by Izana Atmospheric Research Center,Meteorological State Agency of Spain |
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