¶ Precision Gas System (PGS)
¶ Instrument Description
Similar to the AOS Greenhouse Gas Monitor (AOSGHG), the Precision Gas System (PGS) is designed to measure the concentration of select primary greenhouse gases relevant to atmospheric study. Namely, the PGS measures concentrations of carbon dioxide (CO2) and methane (CH4). These measurements are made with high accuracy and precision. Unlike the AOSGHG, however, the PGS makes these measurements at a range of heights - 2, 4, 25 and 60 meters - through the use of the tall tower at the SGP C1 facility.
As of now, please monitor the a1-level pgs datastream for the PGS DQA assignment. When submitting DQPRs for the PGS, please use the PGS instrument class.
¶ Additional Information
For more information, please see the PGS Instrument web page.
¶ Expected Operations
¶ Metrics
In the metrics table below, the primary PGS measurements are outlined in red; all other measurements are diagnostic in nature. Those primary fields are:
- co2_dry_avg_corr - carbon dioxide (CO2) mixing ratio
- ch4_dry_avg_corr - methane (CH4) mole fraction
Note 1 that the PGS system performs twice- to three-times daily "zero" checks of a reference gas. These checks result in brief QC failures for the primary carbon dioxide and methane fields (see example above). You can simply ignore these instances; no need to take further DQ action on them.
Note 2 that although the PGS system also makes measurements of water vapor mixing ratios, these measurements are non-primary in nature. Rather, they are used to correct the primary CO2 and CH4 mixing ratios for water contamination.
¶ Plots
Daily and weekly greenhouse gas mixing ratios
The PGS's primary greenhouse gas m measurements are plotted on both daily and weekly timescales. These include carbon dioxide (CO2), methane (CH4) and water vapor (H2O), though the instrument mentor indicates that water vapor is more of a diagnostic field than of primary importance (used for water contamination correction). Different colors indicate the different height levels on the towers (2 - 60 meters).
You may notice some diurnal and vertical variation in the greenhouse gas mole fractions, especially carbon dioxide. From a physical and scientific standpoint, why might we expect these variations to occur?
Note: you will notice downward gaps in the mole fraction times series data that occur twice per day (~04:30 and 15:30 UTC). These are related to routine instrument calibration maneuvers, and do not need to be noted in your DQAs.
Daily and weekly diagnostic pressures
In addition to the primary greenhouse gas mixing ratio measurements, a number of diagnostic fields are also plotted to assist in monitoring overall instrument health.
The first set of plotted diagnostic fields include pressures associated with different components of the PGS instrument system. Many of these pressures are recorded at various height levels on the tower (2 - 60 meters), which are designated by different plotted colors. These include line pressures, calibration cylinder pressures, pressure control values, and pressures within the instrument cavities. It is not imperative that you focus so intently on these fields; rather, it is recommended that you monitor these fields for long-duration flatlines, QC failures, etc. that correspond to signatures in the primary mixing ratio fields.
Daily and weekly diagnostic temperatures
The second set of plotted diagnostic fields include temperatures associated with different components of the PGS instrument system. These include temperatures at the Nafion box, the pump box, within the instrument cavity and at the chiller. It is not imperative that you focus so intently on these fields; rather, it is recommended that you monitor these fields for long-duration flatlines, QC failures, etc. that correspond to signatures in the primary mixing ratio fields.
Daily and weekly Nafion diagnostics
The third set of plotted diagnostic fields include those associated with the Nafion - an instrument component responsible for drying the sample air. These include the Nafion purge pressure (usually negative) and the flow rate of dry air. Again, it is not imperative that you focus so intently on these fields; rather, it is recommended that you monitor these fields for long-duration flatlines, QC failures, etc. that correspond to signatures in the primary mixing ratio fields.
Daily and weekly auxiliary diagnostic fields
The final set of plotted diagnostic fields include auxiliary fields - something like the most diagnostic of the diagnostics! Many of these fields are recorded at various height levels on the tower (2 - 60 meters), which are designated by different plotted colors. These include liquid alarm states, tower line exhaust and front/rear fan flow rates, and a few diagnostic voltages. Especially here, it is not imperative that you focus so intently on these fields; rather, it is recommended that you monitor these fields for long-duration flatlines, QC failures, etc. that correspond to signatures in the primary mixing ratio fields.
¶ Known Issues
¶ Known Behaviors
List of the behavioral quirks of this instrument that DO NOT require DQPRs nor mentions in your DQAs:
Document some here
¶ Past Problems
List of the known past problems that DO need to be mentioned in your DQAs and/or DQPRs:
Document some here