ARM TR-049

> Precision Gas System (PGS) Handbook
>
> January 2005
>
> M. Torn
>
> Work supported by the U.S. Department of Energy,
>
> Office of Science, Office of Biological and Environmental Research

# Contents {#contents .Heading-Front}

[1. General Overview 1](#general-overview)

[2. Contacts 1](#contacts)

[3. Deployment Locations and History
1](#deployment-locations-and-history)

[4. Near-Real-Time Data Plots 1](#near-real-time-data-plots)

[5. Data Description and Examples 1](#data-description-and-examples)

[6. Data Quality 4](#data-quality)

[7. Instrument Details 5](#instrument-details)

#  {#section .Heading-Front}

# General Overview

This precision gas system (PGS) makes high-accuracy, high-precision
measurements of CO~2~ mixing ratio (ppmv dry air) in air sampled at 2,
4, 25, and 60 m above the ground.

# Contacts

## Mentor

Margaret Torn, Scientist

Earth Sciences Division

Mail Stop 90-1116

E.O. Lawrence Berkeley National Laboratory

1 Cyclotron Rd.

Berkeley, CA 94720

Phone: 510-495-2223

Fax: 510-486-7070

Email: <mstorn@lbl.gov>

Website: <http://www-esd.lbl.gov/ESD_staff/torn/index.html>

## Instrument Developer

Lawrence Berkeley National Laboratory (LBNL) staff built the system.

Li-Cor is the vendor for the infrared gas analyzer (IRGA), model LI-6252
CO~2~ Analyzer (see
<http://www.licor.com/env/Products/GasAnalyzers/li6262/6262.jsp> for
product description).

# Deployment Locations and History 

The precision gas system is located at the base of the 60 m tower at the
Central Facility at the Atmospheric Radiation Measurement (ARM)
Program's Climate Research Facility Southern Great Plains (SGP) locale.
The system operates continuously, except for occasional power outages.

# Near-Real-Time Data Plots

**Data stream 1**: Quick views of the precision gas system data for
yesterday are available at
<http://co2anal.lbl.gov/worldview/pgs-yest.html>.

**Data stream 2**: Quick views of the precision gas system data for the
past week are available at
<http://co2anal.lbl.gov/worldview/pgs-week.html>.

# Data Description and Examples

## Data File Contents

Data are reported as ppm (V) CO~2~ in dry air.

### Primary Variables and Expected Uncertainty

CO~2~ mixing ratio in dry air.

#### Definition of Uncertainty

Samples are bracketed by certified standards.

### Secondary/Underlying Variables

This section is not applicable to this instrument.

### Diagnostic Variables

The diagnostic variables are listed in the table for Data Quality Flags,
Section 5.1.4.

### Data Quality Flags

  ----------------------- -----------------------------------------------
  **QC flag name**        **Function (abbreviations defined below)**

  qc_co2mv_ch5            qc flag on co2mv_ch5 (reference channel)

  qc_co2mv_slope          qc flag on co2mv_slope

  qc_co2mv_slope_se       qc flag on co2mv_slope_se

  qc_co2ppm               qc flag on co2ppm

  qc_co2ppm_25m           qc flag on co2ppm_2m

  qc_co2ppm_2m            qc flag on co2ppm_2m

  qc_co2ppm_4m            qc flag on co2ppm_2m

  qc_co2ppm_60m           qc flag on co2ppm_2m

  qc_co2stor_25m          qc flag on co2stor_25m

  qc_co2stor_4m           qc flag on co2stor_4m

  qc_co2stor_60m          qc flag on co2stor_60m

  qc_coeff1_se            qc flag on coeff1_se

  qc_coeff2_se            qc flag on coeff2_se

  qc_coeff3_se            qc flag on coeff3_se

  qc_del_co2stor_25m      qc flag on del_co2stor_25m

  qc_del_co2stor_4m       qc flag on del_co2stor_4m

  qc_del_co2stor_60m      qc flag on del_co2stor_60m

  qc_flow_rate            qc flag on flow rate

  qc_pres                 qc flag on pres

  qc_pres_ctrlr           qc flag on pres_controller

  qc_pres1                qc flag on pres1

  qc_pres2                qc flag on pres2

  qc_pres3                qc flag on pres3

  qc_pres4                qc flag on pres4

  qc_q_25m                qc flag for q_25m

  qc_q_60m                qc flag for q_60m

  qc_t_irga               qc flag on t_irga

  qc_t_refrig             qc flag on t_refrig

  qc_temp_10m             qc flag on temp_10m

  qc_temp_25m             qc flag for temp_25m

  qc_temp_60m             qc flag for temp_60m
  ----------------------- -----------------------------------------------

Where:

heights are 2, 4, 10, 25, and 60 meters above ground level.

irga = IRGA, infra red gas analyzer

pres = pressure

q = humidity

refrig = cooling system for condensing water out of sample stream

stor = calculated C2 storage term

t = temperature

temp = temperature.

### Dimension Variables

This section is not applicable to this instrument.

## Annotated Examples

  ----------------------- -----------------------------------------------
  **QC flag name**        **Function (abbreviations defined below)**

  qc_co2mv_ch5            qc flag on co2mv_ch5 (reference channel)

  qc_co2mv_slope          qc flag on co2mv_slope

  qc_co2mv_slope_se       qc flag on co2mv_slope_se

  qc_co2ppm               qc flag on co2ppm

  qc_co2ppm_25m           qc flag on co2ppm_2m

  qc_co2ppm_2m            qc flag on co2ppm_2m

  qc_co2ppm_4m            qc flag on co2ppm_2m

  qc_co2ppm_60m           qc flag on co2ppm_2m

  qc_co2stor_25m          qc flag on co2stor_25m

  qc_co2stor_4m           qc flag on co2stor_4m

  qc_co2stor_60m          qc flag on co2stor_60m

  qc_coeff1_se            qc flag on coeff1_se

  qc_coeff2_se            qc flag on coeff2_se

  qc_coeff3_se            qc flag on coeff3_se

  qc_del_co2stor_25m      qc flag on del_co2stor_25m

  qc_del_co2stor_4m       qc flag on del_co2stor_4m

  qc_del_co2stor_60m      qc flag on del_co2stor_60m

  qc_flow_rate            qc flag on flow rate

  qc_pres                 qc flag on pres

  qc_pres_ctrlr           qc flag on pres_controller

  qc_pres1                qc flag on pres1

  qc_pres2                qc flag on pres2

  qc_pres3                qc flag on pres3

  qc_pres4                qc flag on pres4

  qc_q_25m                qc flag for q_25m

  qc_q_60m                qc flag for q_60m

  qc_t_irga               qc flag on t_irga

  qc_t_refrig             qc flag on t_refrig

  qc_temp_10m             qc flag on temp_10m

  qc_temp_25m             qc flag for temp_25m

  qc_temp_60m             qc flag for temp_60m
  ----------------------- -----------------------------------------------

Where:

heights are 2, 4, 10, 25, and 60 meters above ground level.

irga = IRGA, infra red gas analyzer

pres = pressure

q = humidty

refrig = cooling system for condensing water out of sample stream

stor = calculated C2 storage term

t = temperature

temp = temperature.

## User Notes and Known Problems

Datastreams are available through the ARM Data Archive.

## Frequently Asked Questions

**Where do I get more information?**

Contact the instrument mentor (see Section 2.1).

# Data Quality

## Data Quality Health and Status

The instrument has operated continuously since July, 2001. Occasional
loss of data has occurred due to loss of site power or other causes (ice
storm, pump failure). Please check data quality reports for specifics.

## Data Reviews by Instrument Mentor

ARM staff perform preventive maintenance checks weekly and
post-preventive maintenance reports on the internet. ARM carbon
scientists at LBNL check these reports each week. We evaluate the zero
drift (change in reference gas value) and specifications of all
instrument components every week.

Examples of variables that are diagnostic of instrument performance
include:

-   Temperature of IRGA

-   Pressure of gas in IRGA

-   Pressure of each air sample supplied to valve manifold

-   Temperature of the cooling (drying) unit

-   Flow rate of sample gas through the IRGA.

## Data Assessments by Site Scientist/Data Quality Office

Not available at this time.

## Value-Added Procedures and Quality Measurement Experiments

None at present.

# Instrument Details

## Detailed Description

### List of Components

  ----------------------- -----------------------------------------------
  **QC flag name**        **Function (abbreviations defined below)**

  qc_co2mv_ch5            qc flag on co2mv_ch5 (reference channel)

  qc_co2mv_slope          qc flag on co2mv_slope

  qc_co2mv_slope_se       qc flag on co2mv_slope_se

  qc_co2ppm               qc flag on co2ppm

  qc_co2ppm_25m           qc flag on co2ppm_2m

  qc_co2ppm_2m            qc flag on co2ppm_2m

  qc_co2ppm_4m            qc flag on co2ppm_2m

  qc_co2ppm_60m           qc flag on co2ppm_2m

  qc_co2stor_25m          qc flag on co2stor_25m

  qc_co2stor_4m           qc flag on co2stor_4m

  qc_co2stor_60m          qc flag on co2stor_60m

  qc_coeff1_se            qc flag on coeff1_se

  qc_coeff2_se            qc flag on coeff2_se

  qc_coeff3_se            qc flag on coeff3_se

  qc_del_co2stor_25m      qc flag on del_co2stor_25m

  qc_del_co2stor_4m       qc flag on del_co2stor_4m

  qc_del_co2stor_60m      qc flag on del_co2stor_60m

  qc_flow_rate            qc flag on flow rate

  qc_pres                 qc flag on pres

  qc_pres_ctrlr           qc flag on pres_controller

  qc_pres1                qc flag on pres1

  qc_pres2                qc flag on pres2

  qc_pres3                qc flag on pres3

  qc_pres4                qc flag on pres4

  qc_q_25m                qc flag for q_25m

  qc_q_60m                qc flag for q_60m

  qc_t_irga               qc flag on t_irga

  qc_t_refrig             qc flag on t_refrig

  qc_temp_10m             qc flag on temp_10m

  qc_temp_25m             qc flag for temp_25m

  qc_temp_60m             qc flag for temp_60m
  ----------------------- -----------------------------------------------

Where:

heights are 2, 4, 10, 25, and 60 meters above ground level.

irga = IRGA, infra red gas analyzer

pres = pressure

q = humidty

refrig = cooling system for condensing water out of sample stream

stor = calculated C2 storage term

t = temperature

temp = temperature.

Infra-Red Gas Analyzer (IRGA), LI-6252 (see <http://env.licor.com/>):

-   Sample is dried with a cooling unit and a Nafion membrane drier.

-   Flow is regulated with mass flow controller, pumps, and valves.

-   A 1-liter buffer volume is used to dampen very-short-term variation
    in CO~2~ concentration.

-   System is directed by a datalogger (Campbell 23x) that downloads to
    a computer every day.

Data collection system uses a 2.8 GHz Intel PC clone; operating system
Windows 2000.

### System Configuration and Measurement Methods

We measure one sample for 3 minutes at a time; the reported value is the
average of the last 30 seconds.

The IRGA is run in differential mode, with a reference gas (ca 360 ppm)
through the reference cell at all times. Every 15 minutes, we analyze
the reference gas through the sample cell as well, to correct for gain
(zero drift) in the system. Every 4 hours, we run four calibration
standards (National Oceanic and Atmospheric Administration Climate
Monitoring Diagnostics Laboratory (NOAA CMDL) certified standards at
approximately 330, 360, 390, and 420 ppm). Sample CO~2~ concentration is
calculated with the standards run before and after it.

We have followed protocols developed by the NOAA CMDL (e.g., Bakwin et
al.) for their high precision, continuous CO~2~ monitoring instruments.

### Specifications

This section is not applicable to this instrument.

## Theory of Operation

See Section 7.1, Detailed Description.

## Calibration

### Theory and Procedures

See above.

### History

Before deployment at ARM SGP, we did a blind comparison of a tank of
CO~2~ in air with the NOAA-CMDL standards lab. Our measurement agreed
with theirs to 0.05 ppm.

Currently the instrument performance is checked against weekly NOAA CMDL
flask samples collected from the 60-m air-sampling inlet.

## Operation and Maintenance

### User Manual

This section is not applicable to this instrument.

### Routine and Corrective Maintenance Documentation

ARM staff perform preventive maintenance checks weekly and
post-preventive maintenance reports on the internet. ARM carbon
scientists at LBNL check these reports each week. We evaluate the zero
drift (change in reference gas value) and specifications of all
instrument components every week. For examples of instrument operations
that we manage through the Routine and Corrective Maintenance documents,
See Data Reviews by Instrument Mentor.

### Software Documentation

There is none at this time.

### Additional Documentation

There is none at this time.

## Glossary

See the [ARM Glossary](http://www.arm.gov/about/glossary.stm).

## Acronyms

ARM: Atmospheric Radiation Measurement (Program)

CMDL: Climate Monitoring Diagnostics Laboratory

IRGA: infrared gas analyzer

LBNL: Lawrence Berkeley National Laboratory

NOAA: National Oceanic and Atmospheric Administration

PGS: precision gas system

SGP: Southern Great Plains

Also see the [ARM Acronyms and
Abbreviations](http://www.arm.gov/about/acronyms.stm).

## Citable References

Bakwin P.S., P.P. Tans, C.L. Zhao, W. Ussler, and E. Quesnell. 1995.
Measurements of carbon dioxide on a very tall tower. *Tellus Series
B-Chemical and Physical Meteorology*, V47(N5):535-549.

Bakwin, P.S., P.P. Tans, D.F. Hurst, and C.L. Zhao. 1998. Measurements
of carbon dioxide on very tall towers: results of the NOAA/CMDL program.
*Tellus Series B-Chemical and Physical Meteorology*, V50(N5):401-415.

Tans P.P., P.S. Bakwin, and D.W. Guenther. 1996. A Feasible global
carbon cycle observing system - a plan to decipher todays carbon cycle
based on observations. *Global Change Biology*, V2(N3):309-318.