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Atmospheric Non Methane Hydrocarbons Mole Fractions
from the NOAA ESRL GMD Carbon Cycle Surface Network

Version: 2017-09-13
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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 - Event with single parameter
7.4      DATA - Event with multiple parameters
7.5      DATA - QC Flags
8.       Data retrieval
9.       References

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1. DATA SOURCE AND CONTACTS

University of Colorado
Institute of Arctic and Alpine Research (INSTAAR)
Atmospheric Research Laboratory group (ARL)

Correspondence concerning these data should be directed to:
Detlev Helmig and Jacques Hueber
INSTAAR, Univ. of Colorado
UCB 450
Boulder, CO 80309
U.S.A.

email: detlev.helmig@colorado.edu
       jacques.hueber@colorado.edu
ARL website: http://instaar.colorado.edu/arl/

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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 

   "Helmig D., Hueber J., Tans P. (2017)
   Non-Methane Hydrocarbons from the NOAA ESRL Surface Network, 2004-2016."

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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:

2016-08-26

Latitude and longitude were adjusted for 3 sites:
ALT
Old: 82.4508  -62.5056   205.00   200.00
New: 82.4508  -62.5072   195.00   190.00

TAC
Old: 52.5178    1.1389   236.00    56.00
New: 52.5177    1.1386   236.00    56.00

ZEP
Old: 78.9067   11.8889   479.00   474.00
New: 78.9067   11.8883   479.00   474.00

Collaborator name corrected for UTA:
Old: U.S. National Weather Service [NWS]
New: Beth Anderson/NWS Cooperative Observer 


2015-08-03

The 3-letter site identification code for Ushuaia, Argentina (TDF) was 
changed to USH to be consistent with the WMO GAWSIS. 

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 Species (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:

2015-11-20

Updated the content and format of event files to include elevation in 
meters above sea level (masl) and sample collection intake height in 
meters above ground level (magl). Elevation plus collection intake 
height equals altitude, which has always been included in the NOAA 
distribution. In adding these 2 fields, the event number column
has moved. The new format is described in Sections 7.3 and 7.4.

2013-08-27

Coordinates of some of the sample locations have changed.
These changes improve the specified location based on new
information.  Changes tend to be minor and do not necessarily
reflect a change in the actual sampling location.

2011-10-01

The data file format has been modified to include the measurement group
and, additionally, the sample collection and analysis times now include
second information (e.g., 2011 03 15 23 06 12).  See section 7.3 for
details.

2010-10-01

The format of the NOAA ESRL data records has been changed to include
an estimate of the uncertainty associated with each measurement.  The
determination of the estimate is trace gas specific and described in
section 6 (INTRODUCTION).

+++++++++++++++++++++++++++++++
Parameter-specific notes:


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6. INTRODUCTION

All samples in this archive were analyzed for light hydrocarbons at INSTAAR,
Atmospheric Research Laboratory (ARL) in Boulder, Colorado
by gas chromatography. ARL started NMHC measurements in samples from
the NOAA CMDL network in 2005, analyzing flasks from a dozen sites
at first and then rapidly extending the coverage to more than 40 sites.

ARL has also been running in-situ measurements at Pico (Azores)
and at Summit (Greenland) alongside the flask samples.

In-situ data from the Deutscher Wetterdienst in Hohenpeissenberg (HPB)
is also regularly compared to flask samples collected at this site.

The INSTAAR NMHC laboratory was audited by the World Calibration Center (WCC)
for Volatile Organic Compounds in 2008.  All measurement results passed
the quality criteria set by the WCC.

This NMHC monitoring is the centerpiece of the World Meteorological
Organization Global Atmospheric Watch Volatile Organic Compound program.

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7. DATA - GENERAL COMMENTS

Method:

The GC analysis involves drying of approximately 600 cc (STP)
of sample gas, then preconcentration of analytes on an adsorbent bed,
followed by thermal desorption onto a short capillary guard column
and main capillary column (HP-Plot AL2O3/KCl 0.53 mm x 60 m) for separation,
and finally detection by a Flame Ionization Detector (FID).
The gas chromatograph used is a HP-5890 series II.
Drying is accomplished by running the sample gas through a tube cooled
to -25°C. The custom-built preconcentration system is cooled to -35°C
and uses Carboxen 1000 and Carboxen 1016 as adsorbents.
Desorption is controlled at 310°C.  The flask analysis system is
completely automated, allowing analysis of up to 12 flasks in one sequence.

Calibration:

Analysis of air samples are compared to analysis of synthetic
and compressed air standards.  One compressed air standard is run
twice a day to check on the stability of the FID response, the other
standards are ran at least twice a month to determine the response of
the FID.  Blanks are prepared by running compressed air through a heated
bed of PtO.  Blank samples are analyzed twice daily.

Results:

Results are expressed as mole fractions (pmol/mol)

Uncertainty:

Reproducibility varies by compound and with mole fraction.
It is monitored routinely using the results of the paired flask sampling.
Reproducibility is typically better than 5% RSD.
Lower RSDs are obtained for the higher abundance compounds (ethane, propane).
Accuracy is determined by the calibration standard scale.
A minimum of three independently prepared and cross-referenced standards
is in use at any given time.  Deviations in the response factors
from these different standards are smaller than 5%, with results
for ethane and propane typically being equal or less than 2-3%.

Data correction:

After comparing the Isoprene (C5H8) flask data at the German Weather
Service Hohenpeissenberg (HPB) site with results from parallel sampling
and in-situ GC analysis at the site, a systematic correction was applied
to the whole isoprene dataset from 2007 to 2016, to scale the flask data
to the in-situ results. For mole fractions ranging from 8 ppt
(detection limit) to 450 ppt, a polynomial function was applied and
for mole fractions above 450 ppt, a linear function was applied.  These
correction functions adjust the original flask results for isoprene by
no more than the larger of 5 pmol/mol or 10%.

The Pacific Ocean Cruise (POC, travelling between the US west coast
and New Zealand or Australia) data have been merged and grouped into 
5 degree latitude bins.  For the South China Sea cruises (SCS) the 
data are grouped in 3 degree latitude bins.

Sampling frequencies are approximately weekly for the fixed sites
and average one sample every 3 weeks per latitude zone for POC and
about one sample every week per latitude for SCS.

Historically, samples have been collected using two general methods:
flushing and then pressurizing glass flasks with a pump, or opening a
stopcock on an evacuated glass flask; since 28 April 2003, only the
former method is used.  During each sampling event, a pair of flasks
is filled.

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7.1 DATA - SAMPLING LOCATIONS

For a summary of sampling locations, please visit

http://www.esrl.noaa.gov/gmd/dv/site/site_table.html.

IMPORTANT NOTES: 
1.  Data for all species may not be available for all sites listed 
in the table.
2.  The exact location of a sampling site recorded in our database
may change or become better defined over time.  The latitude,
longitude, and altitude of a sample event is based on the best
information available at the time of sample collection.  Differences
in sample position associated with a particular site may be due
to the site moving or changes in technology that permit a more
accurate location determination.

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            
[parameter]_[site]_[project]_[lab ID number]_[measurement group]_[optional 

         6           7
qualifiers].[file type]


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 sampling laboratory (1,2,3, ...).
   NOAA ESRL is lab number 1 (see http://www.esrl.noaa.gov/gmd/ccgg/obspack/labinfo.html).

5. [measurement group]

   Identifies the group within NOAA or 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).
   month         Computed monthly averages all collected samples (discrete (flask) data only).
   hour_####     Computed hourly averages for the specified 4-digit year (quasi-continuous data only)
   HourlyData    Computed hourly averages for entire record (quasi-continuous data only)
   DailyData     Computed daily averages for entire record (quasi-continuous data only)
   MonthlyData   Computed monthly averages for entire record (quasi-continuous data only)

7. [file type]
   
   We provide some NOAA Global Monitoring Division measurements
   in two unique file formats (netCDF and ASCII text). 

   (ex) 

   txt           ASCII text file
   nc            netCDF4 file

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7.3 DATA - EVENT WITH SINGLE PARAMETER

The event data files in ftp://aftp.cmdl.noaa.gov/data/trace_gases/voc/<parameter>/flask/surface/
scheme (see Section 7.2):

     [parameter]_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt

(ex) C2H6_brw_surface-flask_1_arl.txt contains C2H6 arl measurement 
     results for all surface flask samples collected at Barrow, Alaska.

The data files contain multiple lines of header information followed by one 
record for each atmospheric measurement of a single parameter or trace gas species.

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]
Field 6:    [MINUTE]
Field 7:    [SECOND]

Field 8:    [FLASK ID] The sample container ID.

Field 9:    [METHOD] A single-character code that identifies the sample 
             collection method.  The codes are:

             P - Sample collected using a portable, battery
                 powered pumping unit.  Two flasks are
                 connected in series, flushed with air, and then
                 pressurized to 1.2 - 1.5 times ambient pressure.

             D - Similar to P but the air passes through a
                 condenser cooled to about 5 deg C to partially
	              dry the sample.

             G - Similar to D but with a gold-plated condenser.

             T - Evacuated flask filled by opening an O-ring sealed       
                 stopcock.

             S - Flasks filled at NOAA ESRL observatories by sampling
                 air from the in situ CO2 measurement air intake system.

             N - Before 1981, flasks filled using a hand-held
                 aspirator bulb. After 1981, flasks filled using a
                 pump different from those used in method P, D, or G.

             F - Five liter evacuated flasks filled by opening a
                 ground glass, greased stopcock.

Field 10:   [TRACE GAS NAME] Gas identifier (e.g., co2, co2c13).

Field 11:   [MEASUREMENT GROUP] Identifies the group within NOAA and 
             INSTAAR making the actual measurement (e.g., ccgg, hats, arl).
             See Section 5 (UPDATE NOTES) for details.

Field 12:   [MEASURED VALUE] Dry air mole fraction or isotopic composition.  
             Missing values are denoted by -999.99[9].

Field 13:   [ESTIMATED UNCERTAINTY] Estimated uncertainty of the reported
             measurement value.  Missing values are denoted by -999.99[9].

Field 14:   [QC FLAG] A three-character field indicating the results of our 
             data rejection and selection process, described in section 7.5.

Field 15:   [INSTRUMENT] A 2-character code that identifies the instrument 
             used for the measurement.

Field 16:   [YEAR] The measurement date and time in LT.
Field 17:   [MONTH]
Field 18:   [DAY]
Field 19:   [HOUR]
Field 20:   [MINUTE]
Field 21:   [SECOND]

Field 22:   [LATITUDE] The latitude where the sample was collected, (negative (-)
             numbers indicate samples collected in the southern hemipshere).

Field 23:   [LONGITUDE] The longitude where the sample was collected, (negative (-)
             numbers indicate samples collected in the western hemisphere).

Field 24:   [ALTITUDE] The altitude of the sample inlet (masl). The reported altitude
            is the surface elevation plus sample intake height.

Field 25:   [ELEVATION] Surface elevation (masl).

Field 26:   [INTAKE HEIGHT] Air sample collection height above ground level (magl).

Field 27:   [EVENT NUMBER] A long integer that uniquely identifies the sampling
             event.

Fields in each line are delimited by whitespace.

(ex)
   LEF 2005 12 08 17 34 00 847-99 N C3H6 ARL 53.423 -999.990 ... v1 2006 03 14 00 13 
   00 45.9100 -90.2600 868.00 472.00 396.00 210595

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7.4 DATA - EVENT WITH MULTIPLE PARAMETERS

On special request we can distribute a "merged" file, which
includes for each sampling event, measurement results for muliple 
parameters or trace gas species.  A merged file does not include all 
information found in a single parameter data file.  For example,
merged files exclude measurement uncertainty, analysis instrument 
ID and date and time for each parameter.  Thus, the single parameter
data file is our most comprehensive data archive. 

The format of a merged file is slightly different from single parameter event file.
A "merged" file will have the word "merge" in the parameter field of the file name.  
The file name does not inform on the number of parameters included in the file.

Merged data files use the following naming scheme (see Section 7.2):

     merge_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt

(ex) merge_brw_surface-flask_1_arl.txt contains arl measurement results for two or more
     parameters for all surface flask samples collected at Barrow, Alaska.

The data files contain multiple lines of header information followed by one 
record for each atmospheric measurement of a single parameter or trace gas species.

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]
Field 6:    [MINUTE]
Field 7:    [SECOND]

Field 8:    [FLASK ID] The sample container ID.

Field 9:    [METHOD] A single-character code that identifies the sample 
             collection method.  The codes are:

             P - Sample collected using a portable, battery
                 powered pumping unit.  Two flasks are
                 connected in series, flushed with air, and then
                 pressurized to 1.2 - 1.5 times ambient pressure.

             D - Similar to P but the air passes through a
                 condenser cooled to about 5 deg C to partially
	              dry the sample.

             G - Similar to D but with a gold-plated condenser.

             T - Evacuated flask filled by opening an O-ring sealed       
                 stopcock.

             S - Flasks filled at NOAA ESRL observatories by sampling
                 air from the in situ CO2 measurement air intake system.

             N - Before 1981, flasks filled using a hand-held
                 aspirator bulb. After 1981, flasks filled using a
                 pump different from those used in method P, D, or G.

             F - Five liter evacuated flasks filled by opening a
                 ground glass, greased stopcock.

Field 10:   [LATITUDE] The latitude where the sample was collected, (negative (-)
             numbers indicate samples collected in the southern hemipshere).

Field 11:   [LONGITUDE] The longitude where the sample was collected, (negative (-)
             numbers indicate samples collected in the western hemisphere).

Field 12:   [ALTITUDE] The altitude of the sample inlet (masl). The reported altitude
            is the surface elevation plus sample intake height.

Field 13:   [ELEVATION] Surface elevation (masl).

Field 14:   [INTAKE HEIGHT] Air sample collection height above ground level (magl).

Field 15:   [EVENT NUMBER] A long integer that uniquely identifies the sampling
             event.


There is a group of 4 fields for each parameter and measurement group included in the 
merge file.

Field ##+1: [TRACE GAS NAME] Gas identifier (e.g., co2, co2c13).

Field ##+2: [MEASUREMENT GROUP] Identifies the group within NOAA and 
             INSTAAR making the actual measurement (e.g., ccgg, hats, arl).
             See Section 5 (UPDATE NOTES) for details.

Field ##+3: [MEASURED VALUE] Dry air mole fraction or isotopic composition.  
             Missing values are denoted by -999.99[9].

Field ##+4: [QC FLAG] A three-character field indicating the results of our 
             data rejection and selection process, described in section 7.5.

Fields in each line are delimited by whitespace.

(ex)
   LEF 2006 05 17 17 14 00 1382-99 N 45.9100 -90.2600 868.00 472.00 396.00 217438 
   C2H2 ARL -75.541 ... C2H4 ARL 76.617 ...

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7.5 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 assessed.

FLAGS DESCRIPTION:

'...' is a good sample

1st column flags:

'P..' flag: poor flask pair agreement

Since samples are collected in pairs, the pair difference is calculated.

If the mole fraction x falls between the below margins,
and the difference exceeds abs(dx) the flag is applied.

   x <= 10 and dx > |5|

   11 > x <= 25 and dx > |10|

   26 > x <= 63 and dx > |20|

   64 > x <= 156 and dx > |40|

   157 > x <= 391 and dx > |80|

   392 > x <= 977 and dx > |160|

   978 > x <= 2441 and dx > |320|

   2442 > x <= 6104 and dx > |640|

   6105 > x <= 15259 and dx > |1280|


'A..' flag: no data obtained

This flag is applied when there was an instrument failure or if the amount of air left
in the flask was too low for an analysis

'*..' flag:

This flag is applied when an unstable baseline made the peak integration impossible

'D..' flag:

This flag is applied when this particular compound was below the detection limit
of our measurement

'C..' flag:

This flag is applied when a contamination was found


3rd column flags:

'..C' flag:

This flag is applied when the amount of air left in the flask was too low for the
instrument to draw the standard volume for analysis. In that case an analysis
was performed with a reduced sampling volume.

Note:

We feel that this data set best represents hydrocarbons distribution in the remote,
well-mixed global troposphere. It is possible, and even likely, that some values
represent poorly mixed air parcels influenced by local anthropogenic sources.
Users of these data should be aware that further data screening is necessary.
We will provide advice in selecting the data that will best fit the goals
of user's particular investigation.

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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

Helmig, D., Bottenheim J., Galbally I. E., Lewis A., Milton M. J. T.,
Penkett S., Plass-Duelmer C., Reimann S., Tans P., Theil S. (2009)
Volatile Organic Compounds in the Global Atmosphere. Eos Trans. AGU, 90(52),
Feature.

Pollmann J., Helmig D., Hueber J., Plass-Duelmer C., and Tans P. (2008)
Sampling, storage, and analysis of C2-C7 non-methane hydrocarbons
from the US National Oceanic and Atmospheric Administration Cooperative
Air Sampling Network glass flasks. J. Chromatogr., 1188, 75-87.

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