2.7. MAGICC Analysis Program
Though the CCG air sampling network has not expanded much in recent years, the number of people in the group has decreased, and the new MAGICC analysis system requires significantly fewer person-hours to complete measurements of all species. A schematic diagram of the system's plumbing is shown in Figure 2.21. The analyzers used, and the precision obtained from them, are summarized in Table 2.1. A Hewlett Packard (HP) UNIX workstation is interfaced to the all components in the analysis system by a VXI bus. Air samples are introduced into the system using a custom-made sample inlet system. The operator interface is through Netscape. Samples are analyzed in groups of up to eight. MAGICC makes efficient use of the analysis day; the operator can prepare a new set of samples for analysis before the previous set has finished. For species analyzed by a gas chromatograph (GC) (all but CO2), instrument signals are digitized using a 24-bit HP 35900 A/D and peaks are integrated by the MAGICC analysis program.
Fig. 2.21.Schematic diagram of the MAGICC analysis system.
A typical analysis day is as follows. The operator makes a preliminary check of all instruments and gas cylinders, then flushes the standard gas regulators four times each. A 48-min. pre-analysis check is started to "warm-up" the analyzers. During this time up to eight samples are connected to the 8-port sample inlet system. Once the pre-analysis check is complete, a separate flask analysis program is started, and MAGICC immediately begins the first measurement of standard gas for each species. During the time the standard gases are being analyzed, MAGICC asks the operator how many flasks will be analyzed (1-8) then begins evacuating the dead volumes at the gas-tight connections where the flasks attach to the manifold, and it checks for leaks. If no leaks are found, the operator is asked to open the stopcocks. Analysis of the first flask sample begins when the first round of standards is complete. The operator can then enter flask IDs into a table (this can be done anytime before the analysis is stopped) and record system parameters (signal levels, cylinder pressures, etc.) into an electronic daily work sheet. It is important for the operator to watch the progress of the analysis cycle. Near the end of the cycle, analyzed flasks are removed and unanalyzed flasks are added to the manifold. The first sample of the next set is started without delay. Mole fractions are calculated in real time. At the end of the day, the operator stops the analysis program, and the program immediately writes all analysis information to the appropriate site and raw data files.
Significant advantages that MAGICC offers over the previous systems are:(1) All analytical instruments and data acquisition systems offer the highest possible precision CCG is capable of. This is especially true of N2O measurements where a factor of three improvement in precision was obtained. (2) One analysis system and one operator replaces three systems and operators. Samples are handled only once for the complete set of trace gas analyses. (3) The system, and its user interface (written into Netscape), are easy to learn. Using Netscape also allows the system to be accessed remotely. (4) The analysis day is used very efficiently; the instruments are not sitting idle unnecessarily.