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Atmospheric Carbon Dioxide Dry Air Mole Fractions from 
quasi-continuous measurements at Barrow, Alaska; Mauna 
Loa, Hawaii; American Samoa; and South Pole, 1973-2012

National Oceanic and Atmospheric Administration (NOAA)
Earth System Research Laboratory (ESRL)
Global Monitoring Division (GMD)
Carbon Cycle Greenhouse Gases (CCGG)

Version: 2013-05-28
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CONTENTS

1.       Data source and contacts
2.       Use of data
2.1      Citation
3.       Reciprocity 
4.       Warnings
5.       Update notes
6.       Introduction
7.       DATA - General Comments
7.1      DATA - Sampling Locations
7.2      DATA - File Name Description
7.3      DATA - Hourly Averages
7.4      DATA - QC Flags
7.5      DATA - Daily Averages
7.6      DATA - Monthly Averages
7.7      DATA - All Mole Fraction Data
8.       Data retrieval
9.       References

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1. DATA SOURCE AND CONTACTS

These directories contain atmospheric Carbon Dioxide (CO2)
Dry Air Mole Fractions from quasi-continuous measurements 
at Barrow, Alaska (BRW); Mauna Loa, Hawaii (MLO); American 
Samoa (SMO); and South Pole (SPO), 1973-2012.

Correspondence concerning these data should be directed to:

Dr. Pieter Tans
NOAA ESRL Global Monitoring Division
325 Broadway, GMD-1
Boulder, Colorado, 80305 USA
Telephone: 303 497-6678
Electronic Mail: pieter.tans@noaa.gov

Kirk W. Thoning (kirk.w.thoning@noaa.gov)
NOAA ESRL GMD

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2. USE OF DATA

These data are made freely available to the public and the
scientific community in the belief that their wide dissemination
will lead to greater understanding and new scientific insights.
The availability of these data does not constitute publication
of the data.  NOAA relies on the ethics and integrity of the user to
insure that ESRL receives fair credit for their work.  If the data 
are obtained for potential use in a publication or presentation, 
ESRL should be informed at the outset of the nature of this work.  
If the ESRL data are essential to the work, or if an important 
result or conclusion depends on the ESRL data, co-authorship
may be appropriate.  This should be discussed at an early stage in
the work.  Manuscripts using the ESRL data should be sent to ESRL
for review before they are submitted for publication so we can
insure that the quality and limitations of the data are accurately
represented.

2.1 CITATION

Please reference these data as

   Thoning, K.W., D.R. Kitzis, and A. Crotwell (2013), Atmospheric 
   Carbon Dioxide Dry Air Mole Fractions from quasi-continuous 
   measurements at Barrow, Alaska; Mauna Loa, Hawaii; American
   Samoa; and South Pole, 1973-2012, Version: 2013-05-28, 
   Path: ftp://ftp.cmdl.noaa.gov/ccg/co2/in-situ/.

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3. RECIPROCITY

Use of these data implies an agreement to reciprocate.
Laboratories making similar measurements agree to make their
own data available to the general public and to the scientific
community in an equally complete and easily accessible form.
Modelers are encouraged to make available to the community,
upon request, their own tools used in the interpretation
of the ESRL data, namely well documented model code, transport
fields, and additional information necessary for other
scientists to repeat the work and to run modified versions.
Model availability includes collaborative support for new
users of the models.

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4. WARNINGS

Every effort is made to produce the most accurate and precise
measurements possible.  However, we reserve the right to make
corrections to the data based on recalibration of standard gases
or for other reasons deemed scientifically justified.

We are not responsible for results and conclusions based on use
of these data without regard to this warning.


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5. UPDATE NOTES

+++++++++++++++++++++++++++++++
Lab-wide notes:

2011-10-07

We have introduced the term "measurement group", which identifies
the group within NOAA and INSTAAR that made the actual measurement.
We can now have multiple groups measuring some of the same trace 
gas species in our discrete samples.  

Measurement groups within NOAA and INSTAAR are 

  ccgg:  NOAA Carbon Cycle Greenhouse Gases (CCGG)
  hats:  NOAA Halocarbons and other Atmospheric Trace Gases (HATS)
  arl:   INSTAAR Atmospheric Research Laboratory (ARL)
  sil:   INSTAAR Stable Isotope Laboratory (SIL)
  curl:  INSTAAR Laboratory for Radiocarbon Preparation and Research (CURL)

We have also changed the file naming convention (see section "DATA - FILE 
NAME DESCRIPTION").

+++++++++++++++++++++++++++++++
Project-specific notes:

===================================================================
2011-10-13

Quasi-continuous CO2 dry air mole fractions from 1980 to 2006 have all 
been recalculated to bring them into the WMO X2007 Mole Fraction 
Scale (X07). The data since 2007 were already on the X07 scale. 
WMO X2007 is based on repeated manometric measurements of the NOAA 
primary standards (Zhao et al. 2006) and comparison of those results 
to similar measurements made over a period of more than 10 years at 
Scripps Institution of Oceanography.  The difference between the X07 
and the previous scales propagated by SIO and NOAA (X83, X87, etc.) 
is ~0.2 ppm (X07-previous) in the 1980s, decreasing to ~0.1 ppm in 
the late 1990s, and to 0.0 ppm by 2006. The recalculation of individual 
measurements was accomplished by first determining the X07 values for 
the reference gases used to measure the air samples and then using those 
values with the raw data (NDIR voltages) to recompute mole fractions
for each sample. 

===================================================================
2003-11-28

Added year 2002 data for all sites.
Updated tar.gz files to include new data.

===================================================================
2003-03-13

The hourly average files now have a new format, which includes the 
standard deviation of the hourly average. See the README for details.
Individual text files also now have a .co2 extension on the file name.

===================================================================
2002-11-27

Revised Maunal Loa 2001 data.  There was a mistake in the
November 2001 data values, resulting in them being ~0.5 ppm to low.

===================================================================
2002-10-01

Added year 2000 data for Barrow, Samoa and South Pole.
Added year 2001 data for all sites.

===================================================================
2001-10-10

Added year 2000 data for Mauna Loa.
Updated mlo.in-situ.tar.Z files to include new data.

===================================================================
2000-10-05

Added data through 1999 for all sites.
Updated tar.Z files to include new data.
Updated tar.Z files to include new data.

===================================================================
1999-11-29

Added data through 1998 for all sites.
Updated tar.Z files to include new data.

===================================================================
1996-10-04

Changed the archive for the Mauna Loa data.

The formats of the Mauna Loa files are different from the other sites.
See the README for details.

Added Mauna Loa data for 1993, 1994, and 1995.
Updated tar.Z files to include new data.

===================================================================
1996-03-04

Changed the archive for all sites.

The formats of the files are different from before.
See the README for details.

Added data for 1993, 1994, and 1995.
Updated tar.Z files to include new data.

===================================================================
1994-05-18

Added data for Barrow, 1992.
Added data for Mauna Loa, 1992.
Added data for Samoa, 1992.
Added data for South Pole, 1991.
Added data for South Pole, 1992.

Changes to this data based on recalibration of reference gases
will occur in the future.

Updated tar.Z files to include new data.

===================================================================
1992-08-12

Minor corrections to Samoa and Barrow data were made.
Samoa:
	77-04-09   hour 00 	CO2 changed from 300.45 to 999.99
	77-04-09   hour 00 	Flag changed from SI to I
	81-11-20   hour 00 	CO2 changed from 861.97 to 999.99
	81-11-20   hour 01 	CO2 changed from 861.97 to 999.99
	82-01-07   hour 19 	CO2 changed from 902.43 to 999.99
	82-01-07   hour 20 	CO2 changed from 902.43 to 999.99
	82-01-07   hour 21 	CO2 changed from 902.43 to 999.99
	82-01-07   hour 22 	CO2 changed from 902.43 to 999.99
	82-01-07   hour 23 	CO2 changed from 902.43 to 999.99
	82-01-08   hour 00 	CO2 changed from 340.46 to 999.99
	82-01-08   hour 01 	CO2 changed from 340.11 to 999.99

Barrow:
	82-06-20   hour 09      CO2 changed from 99.99 to 999.99

===================================================================
1992-07-28

Compressed tar files are now available for transfer.
There are four files, one for each observatory.  Each tar file
contains all the files in the directory for that station, and
is named sta.in-situ.tar.Z where sta is the three letter station
code, 'brw', 'mlo', 'smo', or 'spo'.

===================================================================
1992-07-27

Preliminary data from Mauna Loa for 1991 is now available.
Changes to this data based on recalibration of reference gases
will occur in the future.

===================================================================
1992-07-27

Corrections to the Samoa data from January 1, 1988 to 
August 31, 1991 were made due to better determinations of the
reference gases used during this period.  Files affected were
smo88, smo89, smo90, smoday88, smoday89, smoday90, smomm.  The
data for 1991 were added to the archive. The new files are
smo91 and smoday91.  Data starting on September 1, 1991 are still
subject to revision.

===================================================================
1992-07-22

Preliminary data from Barrow for 1991 is now available.
Changes to this data based on recalibration of reference gases
will occur in the future.

===================================================================
1992-07-22

The types of flags used are currently under review.  Many
flags that were seldom used or were redundant in thier meaning 
will be replaced with more common flags.  The goal is to eventually
have only 8 base flags total; '  ', C, I, V, D, A, DN, and NC.
Any additional flags based on specific selection schemes for each
site will be noted in this file.

===================================================================
1992-07-22

The data selection for Barrow is not consistent for the
data set.  Data starting in 1981 has been given a more rigourous
selection than prior to this date, i.e., there are no D or A 
selection flags before 1981.

The data for Samoa from 1976 through 1987 have had an
additional selection based on wind direction and wind speed. 
(See Waterman et al., 1989).  A 'WD' code stands for data that
has been flagged because the wind direction was not from the clean
air sector.  A 'WS' speed is for data where the wind speed is
below a minimum value.  There are no 'A' flags in the data for
this time period.

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6. INTRODUCTION


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7. DATA - GENERAL COMMENTS


7.1 DATA - SAMPLING LOCATIONS


Carbon Cycle In Situ Observatory (ccg_obs).

The table includes the three letter code used to identify each
site; the site name; latitude, longitude, and elevation (meters
above sea level) of the sampling location; and country.

Note: Data for all species may not be available for all sites listed 
in the table.

To view near real-time data, manipulate and compare data, and create
custom graphs, please visit

http://www.esrl.noaa.gov/gmd/dv/iadv/.

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7.2 DATA - FILE NAME DESCRIPTION

Encoded into each file name are the parameter (trace gas identifier); sampling 
site; sampling project; laboratory ID number; measurement group; and optional 
qualifiers that further define the file contents.

All file names use the following naming scheme:

         1      2         3               4                   5                     6
[parameter]_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt

1. [parameter]

   Identifies the measured parameter or trace gas species.

   (ex)
   co2      Carbon dioxide
   ch4      Methane
   co2c13   d13C (co2)
   merge    more than one parameter

2. [site]

   Identifies the sampling site code.

   (ex)
   brw
   pocn30
   car
   amt

3. [project]
   
   Identifies sampling platform and strategy.

   (ex)
   surface-flask
   surface-pfp
   surface-insitu
   aircraft-pfp
   aircraft-insitu
   tower-insitu

4. [lab ID number]

   A numeric field that identifies the measurement laboratory (1,2,3, ...).
   NOAA ESRL is lab number 1 (see http://www.esrl.noaa.gov/gmd/ccgg/globalview/gv_labs.html).

5. [measurement group]

   Identifies the group with NOAA and INSTAAR that makes the actual measurement.
   See Section 5 (UPDATE NOTES) for details.

   (ex)
   ccgg
   hats
   arl
   sil

6. [optional qualifiers]

   Optional qualifier(s) may indicate data subsetting or averaging.
   Multiple qualifiers are delimited by an underscore (_).  A more detailed
   description of the file contents is included within each data file.

   (ex)
   event         All measurement results for all collected samples (discrete (flask) data only).
   hour_####     Computed hourly averages for the specified 4-digit year (quasi-continuous data only)
   day           Computed daily averages (quasi-continuous data only)
   month         Computed monthly mean values

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7.3 DATA - HOURLY AVERAGES

Hourly averaged data files are located in "ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2/in-situ/surface/[site]/"
and grouped by year (e.g., co2_mlo_surface-insitu_1_ccgg_hour_1998.txt).  

Files are named as follows (see Section 7.2 for details):

     co2_[site]_surface-insitu_1_ccgg_hour_[year].txt

(ex) co2_mlo_surface-insitu_1_ccgg_hour_1998.txt contains Mauna Loa 
     co2 hourly averages for 1998.

The data files contain multiple lines of header information followed by 
one line for each computed average.

Fields are defined as follows:

Field 1:    [SITE CODE] The three-character sampling location code (see above).

Field 2:    [YEAR] The sample collection date and time in UTC.
Field 3:    [MONTH]
Field 4:    [DAY]
Field 5:    [HOUR] The beginning hour is reported (e.g., hour 4 is constructed using measurements between 0400-0459).

Field 6:    [MEAN VALUE] Dry air mole fraction.
             Missing values are denoted by -999.99[9].

Field 7:    [STANDARD DEVIATION] Standard deviation of mean value (1 sigma).

Field 7:    [# OF MEASUREMENTS] Number of measurements used to calculate the hourly average.

Field 9:    [QC FLAG] A three-character field indicating the results of our
             data rejection and selection process, described in section 7.4.

Field 10:   [INTAKE HEIGHT] Intake height above ground level (m).

Field 11:   [INSTRUMENT] A multi-character code that identifies the instrument 
             used for the measurement.

Fields in each line are delimited by whitespace.

(ex)

   MLO 2004 01 01 02    376.380      0.150 231 ...      40.00    SU3-3

   MLO 2009 12 31 10   1807.443      1.290   3 ...      40.00    HP1-2

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7.4 QC FLAGS

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    INFORMATION 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.

SUMMARY OF SELECTION FLAGS

Missing data will have a value of -999.99 for the mole fraction.
Times are specified in Greenwich Mean Time. Hours are specified
as the beginning of the hour, for example, hour 5 corresponds to
5 AM to 6 AM GMT.

The selection process is done to distinguish "background" mole
fractions, that is, the values that we believe are not contaminated
by local sources or sinks of CO2.  The selection process depends
on the station (see references).  There are a large number of
possible codes, but the most common codes are:

   ... - No code applied. Data are considered 'background'
   *.. - Unable to compute a mole fraction or average
   C.. - Weekly calibration of reference gases, no data available
   I.. - Instrument malfunction, no data available
   .V. - Large variability of CO2 mole fraction within one hour
   .D. - Hour-to-hour difference in mole fraction > 0.25 ppm
   .A. - Automatic selection based on residuals from a spline curve
   .U. - Rejected, diurnal variation (upslope) in CO2 (Mauna Loa only)

Other codes may be used, but the main point is that missing data
will have a value of -999.99 for the hour, and "background" values
will be designated by a lack of a code.  See also the 'Update_notes'
file for information regarding other codes.

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7.5 DATA - DAILY AVERAGES

Daily averaged data files are located in "ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2/in-situ/surface/[site]/".
There is one daily mean data file for each site (e.g., co2_brw_surface-insitu_1_ccgg_day.txt).  
The file contains one row for each day in the reporting period. Daily
means are calculated from background hourly averages where the first two columns
of the QC flag are "..".  Days for which only one hourly value is used to
determine the average are assigned a default (-9.99) standard
deviation. 

Files are named as follows (see Section 7.2 for details):

     co2_[site]_surface-insitu_1_ccgg_day.txt

(ex) co2_brw_surface-insitu_1_ccgg_day.txt contains co2 daily 
     averages for the entire record from Barrow.

The data files contain multiple lines of header information 
followed by one line for each day.

Fields are defined as follows:

Field 1:    [SITE CODE] The three-character sampling location code (see above).

Field 2:    [YEAR] The sample collection date and time in UTC.
Field 3:    [MONTH]
Field 4:    [DAY]

Field 5:    [MEAN VALUE] Dry air mole fraction.
             Missing values are denoted by -999.99[9].

Field 6:    [STANDARD DEVIATION]  Standard deviation of mean value (1 sigma),

Field 7:    [# OF HOURS] Number of hourly averages used to calculate the daily mean.

Field 8:    [QC FLAG] A three-character field indicating the results of our
             data rejection and selection process, described in section 7.4.

Fields in each line are delimited by whitespace.

(ex)

   MLO 2010 11 29    389.380      0.140  11 ...

   MLO 1987 06 18   1699.857      4.177   7 ...

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7.6 DATA - MONTHLY AVERAGES

Monthly data files are located in "ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2/in-situ/surface/[site]/".
There is one monthly mean data file for each site, (e.g., co2_mlo_surface-insitu_1_ccgg_month.txt).
Monthly means are calculated from the daily averages.

The data files contain multiple lines of header information followed
by one line for each available month.

Fields are defined as follows:

Field 1:    [SITE CODE] The three-character sampling location code (see above).

Field 2:    [YEAR] The sample collection date and time in UTC.
Field 3:    [MONTH]

Field 4:    [MEAN VALUE] Dry air mole fraction.
             Missing values are denoted by -999.99[9].

Field 5:    [STANDARD DEVIATION]  The standard deviation is of the mean 
             value (1 sigma).

Field 6:    [# OF DAYS] The number of daily averages available.

Field 7:    [QC FLAG] A three-character field indicating the results of our
             data rejection and selection process, described in section 7.4.

Fields in each line are delimited by whitespace.

(ex)

   MLO 2009 12    387.230      0.620  21 ...

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7.7 DATA - ALL MOLE FRACTION DATA

Data files are available upon request.

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8. DATA RETRIEVAL

To transfer all files in a directory, it is more efficient to 
download the tar or zipped files.  

To transfer a tar file, use the following steps from the ftp prompt:

   1. ftp> binary                    ! set transfer mode to binary
   2. ftp> get filename.tar.gz       ! transfer the file
   3. ftp> bye                       ! leave ftp

   4. $ gunzip filename.tar.gz       ! unzip your local copy
   5. $ tar xvf filename.tar         ! unpack the file

To transfer a zipped file, use the following steps from the ftp prompt:

   1. ftp> binary                    ! set transfer mode to binary
   2. ftp> get filename.zip          ! transfer the file
   3. ftp> bye                       ! leave ftp

   4. $ unzip filename.zip           ! uncompress your local copy

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9. REFERENCES

Peterson, J.T., W.D. Komhyr, L.S. Waterman, R.H. Gammon, K.W.
   Thoning, and  T.J. Conway, Atmospheric CO2 variations at Barrow,
   Alaska, 1973-1982,  J. Atmos. Chem., 4, 491-510, 1986.

Herbert, G.A., E.R. Green, J.M. Harris, G.L. Koenig, S.J. Roughton,
   and K.W. Thaut, Control and monitoring instrumentation for the
   continuous measurement of atmospheric CO2 and meteorological
   variables, J. Atmos. Oceanic Technol., 3, 414-421, 1986.

Gillette, D.A., W.D. Komhyr, L.S. Waterman, L.P. Steele, and R.H.
   Gammon, The NOAA/GMCC continuous CO2 record at the South Pole,
   1975-1982, J. Geophys. Res., 92, 4231-4240, 1987.

Halter, B.C., Harris, J.M., and Conway, T.J., Component signals in
   the record of atmospheric carbon dioxide concentation at
   American Samoa, J. Geophys. Res., 93, 15914-15918, 1988.

Komhyr, W.D., T.B. Harris, L.S. Waterman, J.F.S. Chin, and K.W.
   Thoning,  Atmospheric carbon dioxide at Mauna Loa Observatory: 1.
   NOAA Global Monitoring for Climatic Change measurements with a
   nondispersive infrared analyzer, 1974-1985, J. Geophys. Res.,
   94, 8533-8547, 1989.

Thoning, K.W., P.P. Tans, and W.D. Komhyr, Atmospheric carbon
   dioxide at Mauna Loa Observatory, 2. Analysis of the NOAA/GMCC
   data, 1974-1985., J. Geophys. Res. ,94, 8549-8565, 1989.

Thoning, K.W. Selection of NOAA/GMCC CO2 data from Mauna Loa
   Observatory, In The Statistical Treatment of CO2 Data
   Records, NOAA Tech. Mem. (ERL-ARL-173), Environ. Res. Lab.,
   131 pp., 1989

Waterman, L.S., D. W. Nelson, W.D. Komhyr, T.B. Harris, and K.W.
   Thoning,  Atmospheric carbon dioxide measurements at Cape
   Matatula, American Samoa, 1976-1984., J. Geophys. Res. , 94,
   14817-14829, 1989.

Zhao, C., and P.P. Tans (2006), Estimating uncertainty of the 
   WMO Mole Fraction Scale for carbon dioxide in air, J. Geophys. 
   Res. 111, D08S09, doi: 10.1029/2005JD006003. 

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