UC 10: Trace Gas Sampling Inlet Treatment

[gaochen-larc]

Context: The World Meteorological Organization (WMO) mandates that all atmospheric greenhouse gas (GHG) measurements be reported as a dry-air mole fraction. To achieve this, observing networks use one of two primary pathways:

1. Physical Drying: Physically removing water vapor from the sampling inlet prior to analysis.
2. Mathematical Correction: Measuring ambient (wet) air and applying a spectroscopic water-vapor correction algorithm based on simultaneous H2O measurements.
   While both pathways produce a compliant dry-air value, research and long-term record require exact documentation of physical sampling inlet conditions. Typical trace gas sampling inlet treatments include inlet heating (to prevent condensation), tubing passivation (e.g., SilcoNert/Deactivation coatings to prevent trace gas absorption), flow rate/residence time, and the drying technique itself.

Challenges:

1. Representing specific physical sample conditioning (Sample Treatment) versus post-measurement mathematical algorithms in the metadata layer.
2. Structurally recording common physical inlet treatments, including flow rate, heating, and passivation materials.

[gaochen-larc]

Gemini assessment:
wmdr2-bundled.json Limitation: Conflates physical drying with mathematical corrections into a single flat parameter declaration, while forcing all physical inlet treatments into unstructured, non-searchable text notes.

WMDR 2 Advantage: Explicitly separates mathematical correction algorithms (ReportingProcedure.dataProcessingAlgorithms) from physical hardware, while preserving changes in inlet setup across decades via time-bounded epochs (ObservingConfiguration).

Sampling Inlet & Treatment Requirement	Bundled GeoJSON Schema (wmdr2-bundled.json)	Proposed WMDR 2 Domain Model (WMDR2.pdf)
Physical Drying vs. Math Correction	Conflates pathways; cannot distinguish physical dryers from algorithmic water-vapor equations.	Formally captures math correction equations & software in ReportingProcedure.dataProcessingAlgorithms, but lacks a dedicated Sampling class for physical drying.
Inlet Heating & Passivation	No native fields; forces passivation material (e.g., SilcoNert) and heating into free-text notes.	Shared Gap: Lacks explicit Category 6 (Sampling) attributes in the PDF model; must attach parameters as generic notes/properties to ObservingConfiguration.
Flow Rate & Residence Time	Lacks flow parameters; machine-actionable flow metadata is lost.	Shared Gap: No structured fields for flow rate or residence time in the current PDF model.
Data Processing Transparency	Low; water-vapor correction algorithms cannot be formally declared.	High; explicitly records spectroscopic correction equations and processing tiers.
Long-Term Preservation (Epochs)	High risk of lost provenance when inlet hardware changes over a 30-year record.	Time-bounded ObservingConfiguration epochs preserve metadata versioning whenever physical inlet setups change.