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

F. Hase, B. J. Drouin, C. M. Roehl, G. C. Toon, P. O. Wennberg, D. Wunch, T. Blumenstock, F. Desmet, D. G. Feist, P. Heikkinen, M. De Mazière, M. Rettinger (+7 others)
2013 Atmospheric Measurement Techniques Discussions  
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
more » ... erence 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. 2011). However, the gradients in column CO 2 , for example, are small, requiring a precision and accuracy of < 1 ppm (< 0.25 %, Olsen and Randerson, 2004; Miller et al. 2007 ).
doi:10.5194/amtd-6-7185-2013 fatcat:dtd4xxrbgjgffe4nudgk5sbh5q