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| 
Egbert
-VOCs-
| Observation |
| Category |
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Air sampling observation |
| Situation |
: |
ongoing |
| Time zone |
: |
UTC |
| Sampling |
| Sampling height |
: |
5 |
| Description |
: |
continuous |
| Sampling and analysis frequency |
: |
Every 3 hours |
| Sampling environment |
: |
The measurement site is located in a rural area approximately 70 km northwest of the city of Toronto (pop. ca. 4M). Predominant wind directions bring air either from the heavily anthropogenically influenced southeast or from the continental background regime (originating in the Arctic) of the northwest sector where biogenic contributions are substantial in summertime. |
| Description for sampling analysis |
: |
Custom-built sampling system with air periodically withdrawn from a continuously flushed sample line (ca. 500 ml/min, 6 mm X 4 m silca-lined stainless steel, 47 mm X 1.0 \&\#956\;m pore Teflon filter on inlet). Sample flow into the preconcentrator is ca. 50 mL/min for 20 minutes (ca. 1L sample volume). Sample line air is partially dried by a cold tube section held at 5\&\#730\;C then cryogenically concentrated on a silanized glass bead trap (80/100 mesh, 3 mm X 15 cm silica lined stainless steel tube) at a temperature of -188\&\#730\;C. Trap absolute pressure is limited to a maximum of 400 torr during sampling. Desorbtion follows at +125\&\#730\;C. Preliminary separation of analytes is on a pre-column (Supleco SPB-1, 45 m X 0.53 mm ID, 5.0 \&\#956\;m film thickness). Effluent from the precolumn is split to a GS-Q column set (J\&W Scientific, 2 @ 30 m X 0.53 mm ID PLOT in series) for analysis of C2 and C3 species and to an Alumina-PLOT column (J\&W Scientific, AlOx/KCl, 30 m X 0.53 mm ID) for analysis of C4 to C8 species. Temperature programming is from 35\&\#730\;C to 190\&\#730\;C with helium carrier gas flow rates of 10 mL/min for all columns.
Sampling and analysis is on a 3 hour cycle with daily automated secondary standard calibration and blank analysis.
Instrument performance has been assessed in interlaboratory comparison (GAW-2003), internal Environment Canada intercomparison (2005), and GAW-VOC audit (2008). |
| Instrument and Analysis |
| Measurement method |
: |
Gas Chromatography (FID) |
| Current status and history of instrument |
: |
GC-FID based on HP5890 GC (Agilent Technologies) with custom fabricated on-line sampling system
In use at this site since 2001, data available from March, 2001 |
| Description of instrument |
: |
About 33 C2-C8 hydrocarbons are analyzed on a routine base. Limit of Quantitation is between 2 and 20 pptv, depending on the individual hydrocarbon and corresponds to 10 \&\#963\; of the relevant integrated baseline noise. |
| Calibration |
| Current scale employed in the measurement |
: |
Scale is based on several gravimetrically prepared, certified mixtures of 6 to 22 hydrocarbons in N2 at mixing ratios of 10-15 ppm(v) prepared by Scott Specialty Gases (USA). Stated accuracies are 5%-10% . The following standards have been used:
1) 16 component mixture with approx. ½ the analytes measured. There have been two identical mixtures used over the 8 years of operation: cylinders nos. ALM005004 and ALM004956. Lab ID “SCA” and “SCC” for the first and second mixture respectively. These were extensively cross calibrated and found to be consistent within 5% for all compounds.
2) 16 component mixture with approx. ½ the analytes measured. This mixture has been in use since the beginning of the measurement period. Cylinder no. ALM010625. Lab ID “SCB”.
3) 22 component mixture containing the same compounds as mixture 2 (SCB) plus C6 to C8 aromaitc species. This was prepared by an second manufacturer (Polyscience/Messer) to cross check the standards made by Scott Specialty Gases (SCB). This cylinder was cross calibrated with mixture 2 (SCB) and mixture 4 (BTEX) and was found to be consistent within 10% for all compounds with the exception of acetylene and 2-methylbutane. This mixture has been in intermittant use since 2005.
4) 6 component mixtures containing C6 to C8 aromatic species. A number of these cylinders have been used over the period of operation and checked for consistency at each switchover point. Multiple cylinders have been required due to the small volume of gas in the cylinders and the short certified shelf life of mixtures containing these compounds.
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| Measurement calibration |
: |
In addition to the three hour samples, after every 7 samples (about once per day) a secondary standard (ambient air) is measured followed by a helium blank sample. These measurements characterize the performance of the system and are used for blank peak area determination, calibration verification, and compound identification. Each measurement takes about 1 hour. Peak areas are determined by use of chromatography software and peak baselines and peak identifications are carefully checked and adjusted if needed by trained operators or the PI.
Mixing ratio of a compound is calculated according to:
Mixing ratio = (peak area sample – average weekly blank peak area) / (response factor * Volume of sample)
Response factors are determined from periodic manual injections of the traceable gas standard mixtures which has been demonstrated to have a technique precision of 3% or better.
Values below quantition limit are reported as: -99 pptv. |
| Scale and calibration(treasability) |
: |
The scale is based on the NIST traceable, gravimetrically prepared gas standards supplied by the companies above. The standards are contained in passivated aluminum cylinders. Individual compound absolute response factors are determined several times per year and any adjustments needed are made to the response factors used in calculating sample mixing ratios. Deviation is typically within 5%. Measurements were tested in several international intercomparison experiments (NOMHICE, GAW-Rappenglück, and a GAW audit). Minor correction factors were applied to the data for acetylene and 2-methylbutane to correct for the differences observed between the Scott Gas standards in use and the NPL and NCAR/NIST standards used in the other studies. |
| Data Processing |
| Measurement unit |
: |
pptv |
| Data processing |
: |
Data are quality controlled. Hydrocarbons are identified by absolute and relative retention times. Nominally 33 analyte peaks are listed. |
| Processing for averaging |
: |
Processing for Hourly Data:
Each data point corresponds to a discrete measurement. Where column data consists of results from completely overlapping peaks from two compounds (co-elution), an averaged response factor of the two compounds is applied and the mixing ratio total for the two compounds is reported.
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| Data flag |
: |
Inserted in „compound, pptv“ column - Below Quantitation Limit: -99.0, Missing data point: -77.0 |
| Data remarks |
: |
Abbreviation for some parameters, http://ds.data.jma.go.jp/gmd/wdcgg/pub/data/documents/EC_VOCs_parameters.txt |
| Other Information |
| Scientific aim |
: |
C2-C8 hydrocarbons: Seasonal and diurnal cycles and trends, relation between hydrocarbon patterns and transport, anthropogenic versus biogenic origin, impact on local photochemistry and ozone formation, impact on growing local urbanization. |
| Reference |
: |
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| submitted by Environment Canada |
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