Long-term Calibration Strategy for the Earth Networks CO2 and CH4 Sensor Network in Urban and Background Sites Using the Picarro CRDS Gas Analyzer

Friday, 19 December 2014
Lisa R Welp1,2, Tim Lueker1,2, Jooil Kim1,2, Peter Salameh1,2, Stephen Walker1,2, Ralph F Keeling1,2, Ray F Weiss1,2, Chrisopher Sloop3, William Callahan3, Donnie Bixler3 and Amanda Long3, (1)Scripps Institution of Oceanography, La Jolla, CA, United States, (2)University of California San Diego, La Jolla, CA, United States, (3)Earth Networks Inc., Germantown, MD, United States
The Earth Networks greenhouse-gas monitoring network initiated in 2010 has now expanded to nearly 35 stations across the United States. Building on this effort, the Megacities project funded by NIST has the goal of measuring CO2, CH4 and CO concentrations in the Los Angeles region to support quantitative emissions estimates. These efforts require precise concentration measurements that are internally consistent across the network so that small changes in concentration from one location to another are representative of emissions along the pathway. In this presentation, we examine the calibration strategy for these long-term monitoring efforts using data collected over the past few years. We will address the following issues as they apply to the Picarro G2301 CRDS CO2/CH4/H2O gas analyzer: (1) The frequency of calibration required. (2) The duration of calibration needed for the inlet system to stabilize. (3) The stability and linearity of the instrument span and options for monitoring with a high concentration tank or zero air tank in addition to an ambient concentration calibration tank. We will also outline the calibration tank overlap scheme employed to ensure a consistent long-term record of calibration.