Rescue of Climatic Change Data for Trace Gases
in the Atmosphere and Ocean from the RITS Program

[Overview] [RITS System Description] [Plan] [Progress]

Overview [Top of Page]

The Climate Monitoring and Diagnostics Laboratory (CMDL) of the National Oceanic and Atmospheric Administration (NOAA) operates four baseline observatories at Barrow, Alaska (BRW), Mauna Loa, Hawaii (MLO), American Samoa (SMO), and the South Pole (SPO). A fifth site at Niwot Ridge, Colorado (NWR) is operated cooperatively with the University of Colorado. Since 1977, pairs of air samples collected weekly in flasks at these sites have been transported to Boulder and analyzed for several compounds known to play an active role in the chemistry of stratospheric ozone.

In 1985, the Radiatively Important Trace Species (RITS) program was instigated to provide concurrent in situ monitoring of several of the same ozone-depleting chemicals measured with the flask program. Gas chromatograph (GC) systems utilizing electron capture detection (ECD) were installed at the five sites listed above for measuring the chlorofluorocarbons CFC-11 and CFC-12, the chlorinated solvents methyl chloroform (CH₃CCl₃) and carbon tetrachloride (CCl₄), and nitrous oxide (N₂O). Secondary calibration standards were prepared in the laboratory and shipped to the sites. Initially, samples were injected once every hour at the sites with environmental sampling occurring once every three hours (i.e. two calibration samples and an environmental sample every three hours). In 1991, the systems were modified for sampling every half hour. Calibration and environmental samples were alternated to increase the environmental sampling frequency from three hours to one hour.

Since the inception of these programs, many new compounds have been added to the list of those measured and analyzed by the HATS group. These include several hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) that have been developed to replace the CFCs banned by the United Nations' Montreal Protocol. Another compound that has gained considerable attention in recent years is Sulphur Hexafluoride (SF₆) due primarily to its greenhouse potency (25,000 times more powerful than CO2) and durability in the atmosphere (atmospheric lifetime > 3000 years). In response, the flask sampling program now analyzes over 25 gases, up more than eight-fold from the original three (i.e. CFC-11, CFC-12, and N₂O), and the in situ monitoring program is upgrading to the new 4-channel CATS system GCs.  After a period of concurrent RITS and CATS comparison measurements at the five sites, the RITS systems will be retired as has already occurred at Barrow, Alaska.

In the meantime, there may be considerable useful information held within the RITS data archive pertaining to some of the newer compounds that the RITS data were not originally analyzed for. In particular, small SF₆ peaks have been seen in the third channel of the RITS system for several years. A cursory examination of these data indicates that the small size of these peaks leads to a fair bit of noise in the data. Also, since the secondary calibration tanks shipped to the sites were not originally analyzed for SF₆, calibration will necessarily have to be done using non-standard methods. Nevertheless, with flask measurements of SF₆ from all five sites dating back several years, it is hoped that the in situ SF₆ data will prove useful and informative to some degree.

Elsewhere in the RITS data, contamination problems have compromised the analysis of some compounds. In the case of CFC-113 our secondary calibration standards shipped to the remote sites have suffered greatly from a lack of stability. Also, prior to 1990 a small peak interfered with the integration of the two chlorinated solvents, CH₃CCl₃ and CCl₄. With close to 5000 chromatograms arriving every week for integration analysis, humanpower resources at the time were devoted to system supervision and maintenance, routine analysis, and other ongoing issues. Analyses were concentrated on the least problematic data, putting off complex analyses of data with thorny problems until a later time. With the imminent retirement of the RITS systems, that time is arriving.

RITS System Description [Top of Page]

The RITS in situ monitoring system is a 2 or 3-channel GC/ECD. The first channel -- or A channel as it is known locally -- uses a Porasil B separation column and P5 carrier gas (Ar/CH₄ mixture) for the elution of N₂O, CFC-12 and CFC-11 in chronological order. The second (or B) channel uses an OV101 clone separation column and N₂ carrier gas for the elution of CFC-11, CFC-113, CH₃CCl₃ and CCl₄. Channels A and B are associated with a 2-channel Hewlett-Packard 5890 GC. Finally, the third (or C) channel (not installed at South Pole) uses a Porapak Q separation column, P5 carrier gas and a single-channel Shimadzu GC. It is dedicated solely to the measurement of N₂O. A simple schematic of the RITS system along with a description of the analytical technique and installation history at the four baseline observatories can be found at the in situ monitoring page. A photograph of the RITS system at Niwot Ridge is shown below.

The RITS system at Niwot Ridge. Shown from left to right are the data-recording system, analog-to-digital converter boxes, Hewlett-Packard GC housing channels A and B, and the Shimadzu GC housing channel C. On the wall above the system is the environmental stream intake manifold. The P5 and N₂ carrier gases, calibration gases, and pnuematic air tank (for driving the stream select valve) are out of the picture to the right.

A 3-channel RITS system sampling once every half hour produces 1008 chromatograms in a week. These chromatograms are recorded on site using an integer-differencing scheme and an internal (i.e. binary) proprietary format utilized by the Hewlett-Packard machines that were chosen in the mid-1980s for recording and manipulating the data. Transport of raw chromatograms to Boulder has traditionally been accomplished through the mail via floppy disk, although more recently in some cases -– and in all cases with the new CATS system -– raw chromatograms have been retrieved over the internet. As of December 1999 we continue to receive up to ~3700 RITS chromatograms every week, down from ~4700 before Barrow, Alaska went offline.

Integration of chromatogram peaks is performed on a Hewlett-Packard workstation using modified BASIC language software aquired at the time of the RITS program's inception. Binary format database files were designed and created in-house for storing the output generated by the peak integration software for later retrieval during the computation of mixing ratios. The volume of incoming data and the physical constraints and cost factors associated with the computer data systems technology of the mid-1980s made necessary the efforts taken to economize the amount of space required for data storage and the time required for integration and analysis.

Currently, the RITS raw data archive consists of several million HP-BASIC proprietary chromatograms stored on a few dozen magneto optical disks. A small percentage of the total number of chromatograms has been transferred, as is, over to CD-ROM. Those remaining also require transferal to modern storage media before the aging magneto optical disk drive is retired. The database files of integrated peaks are maintained on HP-UNIX workstations and backed up on a separate UNIX server as are the secondary standards measurements for the calibration tanks.  Finally, the notations of various station managers reporting on system status and performance over the years are stored on several pounds of paper.

Plan [Top of Page]

Using the current method, it takes one person ~3 hours to integrate one week's worth of trouble free RITS data from the five sites. When problems occur that slow down the integration process -- problems requiring extra user attention and input -- the time required for integration can increase dramatically. Thus, for a single person to reintegrate all RITS chromatograms generated during the course of just one year would require a minimum of four 40-hour work weeks or on the order of an entire year to go back through all of the data in the archive.  Troublesome data only adds to the amount of time required.

Given this situation, initial emphasis is being placed on generalizing and modernizing the database and raw data archive. This effort is motivated not only by the desire to save the data and facilitate further analyses and data recovery in the future, but also by the need to recover data that has been lost accidentally due to minor flaws in the current reduction process. A detailed look at several RITS database files has turned up three primary types of accidental data loss:

• Loss associated with chromatograms being incorrectly type-labeled;
• Loss associated with the misidentification of chromatographic peaks;
• Loss associated with defficiencies in the database structure.

Most of the various types of accidental data loss require the reintegration of chromatograms to correct. (Up to now the affected data have tended to be excluded as outliers during the computation of mixing ratios.) Furthermore, in order to prevent the type of accidental data loss outlined in the third bulleted item above, the database of integrated peak values will need to be restructured to include unique time stamps for each sample injection. Restructuring would also be required to make room for the addition of new peaks (e.g. SF₆) that have yet to be analyzed.  Given the current state of modern computer systems technology, these modifications can be easily accommodated.

A procedure is being developed to correct the problems detailed above during the transferal of the raw data to modern media. It is outlined as follows:

1. An entire year's worth of RITS raw chromatograms will be copied from magneto optical disk over to HP workstation hard disk for easier access. Any raw chromatograms with sample type labeling problems that have yet to be corrected will be fixed and reintegrated.
2. An inventory list will be built that holds information on every raw chromatogram saved for the year. Each listing will include the filename of a chromatogram, information about its internal time stamp (flagged if not consistent with its filename), its sample type, and a database record number which will be computed using the same algorithm currently used by the batch integration software. Information compiled in the inventory list will be used for running consistency checks on the integrated databases.
3. Metadata will be assembled for each station from handwritten notes using a program that allows a user to assign annotations to any of several common categories with the push of a button. These annotation flags will be time stamped for addition to the new database.
4. A series of diagnostic scans will be performed on the database to check for minor inconsistencies and data record time stamping problems. Trivial inconsistencies (e.g. integrated values exist in the database with no record of concurrent raw chromatograms in the inventory) can be corrected automatically. In other cases, diagnostic outputs will alert the user to areas where potential problems exits, and the user upon closer examination may elect to reintegrate chromatograms wherever appropriate.
5. The database will be scanned by a program designed to look for potential peak misidentification problems. Upon closer examination by a user, raw chromatograms will be reintegrated wherever appropriate.
6. A new database will be constructed from the cleaned up old-type database, the time stamped chromatogram inventory listings, and the annotation flags. Any chromatograms whose integrated values were overwritten in the old-type databases will be reintegrated and added to the new database.
7. When the old-type database has been cleaned up and a new database constructed, the raw chromatograms will be saved to CD-ROM and removed from the hard disk to make room for another year's worth of data.

Progress [Top of Page]

A new CIRES employee, David Nance, was hired over the summer of 1999 to handle the RITS data rescue and recovery project. Since his hiring, he has occupied much of his time familiarizing himself with the data system and reduction process through the ongoing analysis of RITS data which continues to arrive at a rate of ~3700 chromatograms every week. Along the way he has identified a few minor problems that were previously undetected. He has already written several programs and routines that have aided him in his search through the database for correctable errors. He has checked through almost the entire database compiling a list of chromatograms with probable sample type labeling errors that will need correction before they are saved to CD-ROM. He has been busy laying a software foundation of data structures, interfaces to those structures and other low-level routines upon which the larger programs he will use for accomplishing his outlined tasks will be built. He hopes to begin the methodical process of modernizing the RITS archive this winter, working backward through time, recovering data accidentally lost, and be well over halfway toward completion by the end of his first year. During his second year he will begin using the modernized archive in attempts to recover data that have been lost because of peculiar analysis complexities or because they were not originally analyzed for.

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