Intercomparability of XCO2 and XCH4 from the United States TCCON sites

Other literature type English OPEN
Hedelius, Jacob K. ; Parker, Harrison ; Wunch, Debra ; Roehl, Coleen M. ; Viatte, Camille ; Newman, Sally ; Toon, Geoffrey C. ; Podolske, James R. ; Hillyard, Patrick W. ; Iraci, Laura T. ; Dubey, Manvendra K. ; Wennberg, Paul O. (2016)

The Total Carbon Column Observing Network (TCCON) has become the standard for long-term column-averaged measurements of CO<sub>2</sub> and CH<sub>4</sub>. Here, we use a pair of portable spectrometers to test for intra-network bias among the four currently operating TCCON sites in the United States (U.S.). A previous analytical error analysis has suggested that the maximum 2σ site-to-site relative (absolute) bias of TCCON should be less than 0.2&thinsp;% (0.8&thinsp;ppm) in X<sub>CO<sub>2</sub></sub> and 0.4&thinsp;% (7&thinsp;ppb) in X<sub>CH<sub>4</sub></sub>. We find here experimentally that the 95&thinsp;% confidence intervals for maximum pairwise site-to-site bias among the four U.S. TCCON sites are 0.05&ndash;0.14&thinsp;% for X<sub>CO<sub>2</sub></sub> and 0.08&ndash;0.24&thinsp;% for X<sub>CH<sub>4</sub></sub>. This is close to the limit of the bias we can detect using this methodology.
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