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NO 2
Acronym NOAA
Name Earth System Research Laboratory, NOAA
Address 1 R/GMD1
Address 2 NOAA/ESRL
Address 3 325 Broadway Boulder, CO 80305-3337
Country/Territory United States of America
Website https://www.esrl.noaa.gov/gmd/index.html


Name Jocelyn Turnbull
Email j.turnbull@gns.cri.nz
Organization No 120
Organization acronym GNS
Organization name GNS Science
Organization country/territory New Zealand
Address 1
Address 2
Address 3
Country/territory New Zealand
Last updated date 2019-07-30

Name Scott Lehman
Email Scott.Lehman@colorado.edu
Organization No 34
Organization acronym INSTAAR
Organization name Institute of Arctic and Alpine Research, University of Colorado
Organization country/territory United States of America
Address 1 University of Colorado at Boulder
Address 2 1560 30th St
Address 3 Boulder, CO 80309-0450
Country/territory United States of America
Last updated date 2018-04-09

 Background observation
 9999-12-31 00:00:00 - 9999-12-31 23:59:59: Unknown(Mass spectrometry)
 [Monthly] Monthly means are produced for each site by first averaging all valid measurement results in the event file with a unique sample date and time. Values are then extracted at weekly intervals from a smooth curve (Thoning et al., 1989) fitted to the averaged data and these weekly values are averaged for each month to give the monthly means recorded in the files. Flagged data are excluded from the curve fitting process. Some sites are excluded from the monthly mean directory because sparse data or a short record does not allow a reasonable curve fit. Also, if there are 3 or more consecutive months without data, monthly means are not calculated for these months.
 NOAA ESRL uses a 3-column quality control flag where each column is defined as follows:
column 1 REJECTION flag. An alphanumeric other than a period (.) in the FIRST column indicates a sample with obvious problems during collection or analysis. This measurement should not be interpreted.

column 2 SELECTION flag. An alphanumeric other than a period (.) in the SECOND column indicates a sample that is likely valid but does not meet selection criteria determined by the goals of a particular investigation.

column 3 COMMENT flag. An alphanumeric other than a period (.) in the THIRD column provides additional information about the collection or analysis of the sample.

WARNING: A "P" in the 3rd column of the QC flag indicates the measurement result is preliminary and has not yet been carefully examined by the PI. The "P" flag is removed once the quality of the measurement has been determined.

If both the first and second column contain a period (e.g., "..." and "..I"), the sample is RETAINED.

At surface sites, 14CO2 measurements are typically obtained by combining the air from two flasks collected simultaneously. Thus at most sites, only a single 14CO2 measurement is made for each sampling date. However, for consistency with other NOAA/ESRL CCGG datasets, a 14CO2 result is reported for every flask measured, such that the same measurement may be replicated in the result list. We include a flag in the third column when multiple flasks were combined, and the set of flasks combined can be identified by the CURL number listed in the comments field. This CURL number identifies the unique AMS 14C measurement.

At some sites, four flasks are collected on some sampling dates, with first one pair of flasks collected simultaneously, immediately followed by collection of a second simultaneous pair. In this case, authentic replicate measurements are available (with differing CURL numbers).

For surface site time series, selection flags in the second column are automatically determined by use of CO measurements obtained in the same flasks. Samples in which the CO measurement is more than 15 ppb from the fitted seasonal cycle for that site are automatically flagged .F. In addition, manually flagged samples are indicated by .Z.
Flag Description
RETAINED ... Retained, no comments.
..M Multiple flasks were combined to obtain this measurement; retained
..I sample has also been measured by another lab as part of an intercomparison experiment

SELECTED .F. automatically flagged as non-background
.Z. flagged manually as non-background

REJECTED C.. rejected due to error in CO2 mixing ratio analysis
A.. rejected due to error in CO2C14 analysis
T.. sample collected as part of a methods test; not used in data analysis

The retained values comprise the data set that we feel best represents the 14CO2 distribution in the remote, well-mixed global troposphere.
These are the values we use to calculate long-term trends and interannual and seasonal variations in our studies of the global carbon cycle.
It is possible, and even likely, that the values flagged as not representative of background conditions are valid measurements, but represent poorly mixed air masses influenced by local or regional anthropogenic sources or strong local biospheric sources or sinks.
Users of these data should be aware that data selection is a difficult but necessary aspect of the analysis and interpretation of atmospheric trace gas data sets, and the specific data selection scheme used may be determined by the goals of a particular investigation.
1  Stuiver, M., and Polach, H. A.: Discussion: Reporting of 14C data, Radiocarbon, 19, 355-363, 1977.
2  Donahue, D. J., Linick, T., and Jull, A. T.: Isotope-ratio and background corrections for accelerator mass spectrometry radiocarbon measurements, Radiocarbon, 32, 135-142, 1990.
3  Turnbull, J. C., Miller, J. B., Lehman, S. J., Tans, P. P., Sparks, R. J., and Southon, J. R.: Comparison of 14CO2, CO and SF6 as tracers for determination of recently added fossil fuel CO2 in the atmosphere and implications for biological CO2 exchange, Geophysical Research Letters, 33, L01817, 2006.
4  Turnbull, J. C., Lehman, S. J., Miller, J. B., Sparks, R. J., Southon, J. R., and Tans, P. P.: A new high precision 14CO2 time series for North American continental air, Journal of Geophysical Research, 112, D11310, doi:10.1029/2006JD008184, 2007.
5  Turnbull, J. C., Miller, J. B., Lehman, S. J., Hurst, D. F., Peters, W., Tans, P. P., Southon, J. R., Montzka, S. A., Elkins, J. W., Mondeel, D. J., Romashkin, P. A., Elansky, N. F., and Shkorokhod, A.: Spatial distribution of D14CO2 across Eurasia: Measurements from the TROICA-8 expedition, Atmospheric Chemistry and Physics Discussions, 2008.