High resolution solar absorption Fourier transform spectrometry (FTS) is the most precise ground‐based remote sensing technique to measure the total column of atmospheric carbon dioxide. For carbon cycle studies as well as for the calibration and validation of spaceborne sensors the instrumental comparability of FTS systems is of critical importance. Retrievals from colocated measurements by two identically constructed FTS systems have been compared for the first time. Under clear sky conditions a precision for the retrieved xCO2 better than ∼0.1% is demonstrated and the instruments agree within ∼0.07%. An important factor in achieving such good comparability of the xCO2 is an accurate sampling of the internal reference laser. A periodic laser mis‐sampling leads to ghosts (artificial spectral lines), which are mirrored images from original spectral lines. These ghosts can interfere with the spectral range of interest. The influence of the laser mis‐sampling on the retrieved xCO2 and xO2 in the near‐IR has been quantified. For a typical misalignment, the ratio of the ghost intensity compared to the intensity of the original spectral line is about 0.18% and in this case the retrieved xCO2 is wrong by 0.26% (1 ppm) and the retrieved xO2 is wrong by 0.2%.

No abstract

No abstract

Abstract. The TCCON (Total Carbon Column Observing Network) FTIR (Fourier transform infrared) network provides highly accurate observations of greenhouse gas column-averaged dry-air mole fractions. As an important component of TCCON quality assurance, sealed cells filled with approximately 5 mbar of HCl are used for instrumental line shape (ILS) monitoring at all TCCON sites. Here, we introduce a calibration procedure for the HCl cells which employs a refillable, pressure-monitored reference cell filled with C 2 H 2 . Using this method, we identify variations of HCl purity between the TCCON cells as a non-negligible disturbance. The new calibration procedure introduced here assigns effective pressure values to each individual cell to account for additional broadening of the HCl lines. This approach will improve the consistency of the network by significantly reducing possible station-to-station biases due to inconsistent ILS results from different HCl cells. We demonstrate that the proposed method is accurate enough to turn the ILS uncertainty into an error source of secondary importance from the viewpoint of network consistency.

In this work, the behavior of a polymer electrolyte membrane ͑PEM͒ fuel cell with a Pt/Ru anode exposed to H 2 /CO mixtures is investigated. A compact, isothermal one-dimensional model is derived to address the phenomena occurring at the along-thechannel direction. Besides material balances for the anode channel and electrode, the model considers charge balances for the membrane ͑Laplace equation͒ and both the anodic and cathodic double layers. The model predicts the formation of complex spatiotemporal patterns for a wide range of technical relevant operating conditions. The system can be understood as a chain of coupled oscillators. The electrical coupling is influenced by the electrolyte conductivity. Furthermore, the system features coupling by the anode gas channel dynamics. Depending on the ratio of the characteristic time for CO transport in the gas channel and the characteristic time required for CO adsorption, two limiting cases with varying degrees of complexity exist. The qualitative theoretical results of the present contribution give a guideline for the design of a validating experiment and pave the way for a systematic experimental analysis.