|
|
SPO789S30
-N2O-
| Observation |
| Frequency |
: |
Several times a month |
| Method |
: |
GC-ECD |
| Instrument |
: |
Shimadzu |
|
| Description |
: |
The flasks are of 6 types, 4 of which are the property of CSIRO (items a-d below) and 2 of which are the property of the Meteorological Service of Canada for air sampling at the Canadian sites, Alert, Estevan Point and Fraserdale (items e and f): (a) glass 0.5 litre, sealed with two stopcocks fitted with PTFE, PFA or Viton O-rings (flask identifier prefix "G050"), (b) glass 5.0 litre, sealed with two stopcocks fitted with PTFE O-rings ("G500"), (c) glass 0.8 litre, sealed with two stopcocks fitted with PTFE or PFA O-rings ("G080"), (d) electropolished stainless steel 1.6 litre "Sirocans" fitted with two stainless steel valves manufactured by either Nupro or Hoke ("S160"), (e) glass 2.0 litre sealed with a single stopcock fitted with a Viton O-ring ("F", "FF", "FA", "FE", "EP", ALT") or (f) glass 2.0 litre sealed with two stopcocks fitted with Viron O-rings ("M1", "S", "P2"). Experiments carried out to test for changes in sample N2O mixing ratio during storage have shown significant drifts in some flask types over test periods of several months to years (Cooper et al., 1999) and can be largely attributed to permeation through O-rings (Langenfelds, 2002; Sturm et al., 2004). Corrections derived from the test results are applied to network data according to flask type. Typical sample storage times range from days to weeks for some sites (e.g. Cape Grim, Aircraft) to as much as 1 year for Macquarie Island and the Antarctic sites.
Samples were analysed by gas chromatography with electron capture detection. One Shimadzu gas chromatograph, labelled "Shimadzu-1" (S1) was used over the length of the record. Further details are provided elsewhere of CSIRO's global sampling network, sampling and analytical techniques (Francey et al., 1996), and measurement uncertainty (Francey et al., 2003).
|
|
| Calibration |
| Scale |
: |
CSIRO Scale |
| Description |
: |
The scale maintained at CSIRO was established using six high-pressure cylinder standards (of a high purity N2O/CO2 mixture diluted with varying amounts of zero air) that were gravimetrically prepared by NOAA/CMDL in 1993. In 1995, two high-pressure cylinders were exchanged with NOAA/CMDL's Halocarbons and other Atmospheric Trace Species (HATS) group. However, further cylinder intercomparisons will be necessary to reliably quantify an observed scale difference and identify any time variation. Stability of the CSIRO scale is monitored with ~30 high-pressure cylinder standards, with lifetimes of 6-11+ years. Further details of calibration and measurement uncertainty are given by Francey et al. (2003).
|
| Data Processing |
| Unit |
: |
ppb |
| Description |
: |
Flask data are assigned flags to indicate whether they are classified as retained or rejected. Cause of rejection falls into three broad categories: (i) the sample is considered to be not representative of the atmosphere at the time and place of sampling due to identified or inferred sampling or analytical problems (eg. sample contamination, poor analysis), (ii) the sample is considered to be "non-baseline" as indicated by the meteorological conditions at the time of sampling and (iii) any remaining outliers are flagged on the basis of a 3-sigma filter (geographically fixed sites only). For completeness, all data are included here, regardless of whether they are retained or rejected. Please note that for routine "baseline" applications, any rejected data must be actively excluded from the provided data sets, while for "non-baseline" applications data flagged under categories (ii) and (iii) above may carry biogeochemical information (see DATA FORMAT section below). Also, further data selection may be desirable for those data sets that cannot be screened by the 3-sigma filter (e.g. AIA; aircraft).
|
| Average Procedure |
| Hourly |
: |
|
| Daily |
: |
|
| Monthly |
: |
For the geographically fixed sites, the monthly means are calculated as the mean of daily values from a smooth curve fit to the data using the curve-fitting routines described by Thoning et al. (1989). |
| Flag |
| Description |
: |
Flags: "..." indicates no flags, sample retained. Any entry other than "." in the first flag column indicates the sample is not representative of the time and place of sampling:
A = no sample taken
B = sample lost before analysis
C = identified sampling error
D = suspected sampling problem (eg. 2 or more species give anomalous values)
E = mixed samples (time/place not unique)
N = unacceptable analysis
* = no analysis data available
H = species-specific manually applied rejection flag
I = species-specific sample collection problem
J = irretrievable sample storage effect
. = not subject to any of the above flags
Any entry other than "." in the second flag column indicates the sample is non-baseline, rejected only on grounds of being an outlier or is excluded from this data set because of a non-standard sampling technique.
F = non-baseline meteorological conditions
G = marginal-baseline meteorological conditions
K = species-specific non-baseline meteorological conditions
L = species-specific marginal-baseline meteorological conditions
M = 3 sigma filter rejected
O = non-standard sampling technique
. = not subject to any of the above flags
|
|
|
|
