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Mt. Waliguan
-O3-
| Observation |
| Category |
: |
Air sampling observation |
| Situation |
: |
ongoing |
| Time zone |
: |
Local time +8 |
| Sampling |
| Sampling height |
: |
6 |
| Description |
: |
continuous |
| Sampling and analysis frequency |
: |
Ambient air is continuously sampled and analyzed. |
| Sampling environment |
: |
The station is located on top of Mt. Waliguan (WLG, 3810 m a.s.l), in Qinghai Province, China. Mt. Waliguan is situated at the northeast edge of the Qinghai-Tibetan Plateau and surrounded by highland steppes, tundra, desserts, salt lakes, etc. With very few population (about 6 persons per square kilometer) and nearly no industry within 30 km, the station is far from major anthropogenic sources. However, some impact of long-range transport of anthropogenic pollutants from the NE-SE sector cannot be excluded, particularly from the major cities Xining (about 90 km northeast of WLG, population ~2.13 millions) and Lanzhou (about 260 km east of WLG, population ~3.1 millions). Such impact, if any, may be significant only during the warmer period (May-September), as suggested by the airmass trajectories. |
| Description for sampling analysis |
: |
Air is sampled through PTFE Teflon tubing (OD 1/4", about 8 m) from the inlet (a Teflon filter-holder) at 1.8 m above the building roof. The flow rate is controlled at about 0.75 L/min. |
| Instrument and Analysis |
| Measurement method |
: |
Light absorption analysis (UV) |
| Current status and history of instrument |
: |
Two ozone analyzers are used for observation of surface ozone. A ozone calibrator is installed at the station for calibration.
1994 August - present, Model 49 (#47318-278), Thermo Environment Ins.
1994 August - 2011 May, Model 49 (#47307-278),
Thermo Environment Ins.
2011 May - 2012 July, Model 49i (#1031445280), Thermo Fisher Scientific Inc.
2012 July - present, Model 49i (#1031445279), Thermo Fisher Scientific Inc.
1994 August - present, Model 49PS (#47651-279), Thermo Environment Ins.
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| Description of instrument |
: |
Model 49
Range: 0 to 1000 ppb
Detection limit: 2 ppb
Precision: 2 ppb
Linearity: +/- 1 ppb
Response time: 20 seconds
Zero drift: <2% per month
Span drift: < 1% per month
Model 49i
Range: 0 to 1000 ppb
Detection limit: 0.5 ppb
Precision: 1 ppb
Linearity: +/- 1% full scale
Response time: 20 seconds
Zero drift: <1 ppb per day
Span drift: < 1% full scale per month
Model 49PS
Range: 0 to 1000 ppb
Detection limit: 2 ppb
Precision: 2 ppb
Linearity: +/- 1 ppb
Response time: 20 seconds
Zero drift: <2% per month
Span drift: < 1% per month
Ozonator output 25 - 1000 ppb at 6-8 LPM
Response: 1 min to 99% of final value in auto mode
Stability: +/- 4 ppb or 1%, whichever is greater |
| Calibration |
| Current scale employed in the measurement |
: |
NIST SRP |
| Measurement calibration |
: |
The analyzers are zero-checked every other day. Multipoint calibrations are made every three months by introducing at least seven span gases (e.g., 20, 35, 50, 65, 80, 100, 120 ppb) from the ozone calibrator. Each span is measured for 10 min. The mole fractions are determined by the linear regression line from zero level and spans. |
| Scale and calibration(treasability) |
: |
An ozone calibrator (Thermo Environment Ins. Model 49PS) is used. In 1994, 1995, 2000, 2004, and 2009, the calibrator was compared with the transfer standard from the WMO World Calibration Centre for Surface Ozone and Carbon Monoxide, EMPA, Switzerland. The transfer standard is traceable to the Standard Reference Photometer (SRP) in NIST, USA. |
| Data Processing |
| Measurement unit |
: |
ppb |
| Data processing |
: |
The raw data from the instruments are collected by a data logger (CR21X, Campell Scientific, Utah, UAS) and averaged and stored every 5 min. The 5-min averages are calibrated using calibration curves. Invalid data caused by instrumental malfunction are checked by comparing data from different instruments or with information from the station logbook. |
| Processing for averaging |
: |
Processing for Hourly Data:
Hourly data are generated by arithmetic means from the 5-min data without including invalid data. If an hourly mean value is an average of no less than 8 valid 5-min data, it is considered valid and flagged as “0”. If the number of valid data within an hour is less than 8, the hourly mean value is considered invalid and flagged as “1”. If all data within an hour are invalid, the hourly mean value is “-999” and flagged as "2".
Processing for Daily Data:
If more than 15 valid hourly data are available within a day, the corresponding daily mean value is considered valid and flagged as “0”. If less than 16 valid hourly data are available within a day, the corresponding daily mean value is considered invalid and flagged as “1”. If all hourly data within a day are invalid, the daily mean value is "-999" and flagged as "2".
Processing for Monthly Data:
If more than 66% of daily data within a month are valid, the corresponding monthly mean value is considered valid and flagged as “0”. If less than 66% of daily data within a month are valid, the corresponding monthly mean value is considered invalid and flagged as “1”. If all daily data within a month are invalid, the monthly mean value is "-999" and flagged as "2". |
| Data flag |
: |
0: Valid data
1: Insufficient number of averaging data
2: Invalid data |
| Data remarks |
: |
No remarks |
| Other Information |
| Scientific aim |
: |
To monitor the long-term trend of surface ozone at the Mt. Waliguan baseline station. |
| Reference |
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Xu, X., J. Tang, W. Lin, The trend and variability of surface ozone at the global GAW station Mt. Waliguan, China, in “Second Tropospheric Ozone Workshop Tropospheric Ozone Changes: Observations, state of understanding and model performances”, WMO/GAW report, WMO, Geneva, 2011, p49-55.
Zellweger, C., P. Hofer, B. Buchmann (2000), System and Performance Audit of Surface Ozone and Carbon Monoxide at the China GAW Baseline Observatory Waliguan Mountain (CGAWBO), WCC-Empa Report 00/3, gaw.empa.ch/audits/WLG_2000.pdf.
Zellweger, C., J. Klausen, B. Buchmann (2004), System and Performance Audit of Surface Ozone, Carbon Monoxide and Methane Global GAW Station Mt. Waliguan, China, October 2004, WCC-Empa Report 04/3, gaw.empa.ch/audits/WLG_2004.pdf.
Zellweger, C., J. Klausen, B. Buchmann, H.-E. Scheel (2009), System and Performance Audit of Surface Ozone, Carbon Monoxide, Methane and Nitrous Oxide at the GAW Global Station Mt. Waliguan and the Chinese Academy of Meteorological Sciences (CAMS), China, June 2009, WCC-Empa Report 09/2, gaw.empa.ch/audits/WLG_2009.pdf. |
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| submitted by China Meteorological Administration |
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