Calibration of sealed HCl cells used for TCCON instrumental line shape monitoring

[摘要] The TCCON (Total Carbon Column Observing Network) FTIR (Fourier transform infrared) network provideshighly accurate observations of greenhouse gas column-averaged dry-air molefractions. As an important component of TCCON quality assurance, sealedcells filled with approximately 5 mbar of HCl are used for instrumental line shape(ILS) monitoring at all TCCON sites. Here, we introduce a calibrationprocedure for the HCl cells which employs a refillable, pressure-monitoredreference cell filled with C₂H₂. Using this method, we identifyvariations of HCl purity between the TCCON cells as a non-negligibledisturbance. The new calibration procedure introduced here assigns effectivepressure values to each individual cell to account for additional broadeningof the HCl lines. This approach will improve the consistency of the networkby significantly reducing possible station-to-station biases due toinconsistent ILS results from different HCl cells. We demonstrate that theproposed method is accurate enough to turn the ILS uncertainty into an errorsource of secondary importance from the viewpoint of network consistency.

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