A New Automated Extraction System for ¹⁴C Measurement for Atmospheric Co₂

Abstract

ABSTRACT. The radiocarbon content of atmospheric CO 2 ( 14 CO 2 ) has long been of interest to atmospheric and Earth system researchers. Recent improvements in 14 C measurement precision and reduction in sample size requirements have now made it possible to measure  14 CO 2 within existing trace gas sampling networks, most notably as a method to quantify recently added fossil-fuel-derived CO 2 in the atmosphere. At INSTAAR, in collaboration with NOAA/ESRL, ~600 atmospheric samples from around the globe are prepared each year, and that number is anticipated to grow in connection with various monitoring and data assimilation efforts. To accommodate the growing demand and reduce per sample costs, we developed an automated extraction system to quantitatively isolate CO 2 from whole air for AMS 14 C analysis. Twenty samples can be extracted in 1 fully automated run, taking 10-12 hr to complete and requiring only about 1 hr of operator time, a substantial improvement over the manual extraction system. CO 2 is extracted cryogenically by flowing the whole air over a liquid nitrogen trap, after first removing water in a trap at -85 °C. Large volume vacuum lines are used to extract ~30 µmol of CO 2 in less than 10 min, keeping contamination from leaks to a minimum and allowing rapid processing and greater throughput.  13 C measurements on the resultant CO 2 demonstrate that extraction is quantitative, and extractions of 14 C-free air show that no significant modern contamination occurs. Replicate analyses of standard materials indicate that both mean values and precision are comparable to those for the manual extraction system.

Strong regional atmospheric 14C signature of respired CO2 observed from a tall tower over the midwestern United States

“…Δ 14 CO 2 was analyzed by extraction of CO 2 from the whole air samples using cryogenic separation followed by reduction of extracted CO 2 to graphite for atom counting via accelerator mass spectrometry (AMS). Extractions of authentic samples, measurement controls, and process blanks were performed at the University of Colorado Institute for Arctic and Alpine Research (INSTAAR) Laboratory for AMS Radiocarbon Preparation and Research (NSRL) using an automated extraction system [ Turnbull et al ., ]. Graphitization and AMS analysis of the LEF samples were done at Lawrence Livermore National Laboratory's (LLNL) Center for Accelerator Mass Spectrometry (CAMS).…”

Allocation of Terrestrial Carbon Sources Using 14CO2; Methods, Measurement, and Modeling

“…Extraction, graphitization, measurement and normalization follow methods described in Turnbull et al (2007). Extraction occurs on either a manual or an automated extraction line ("CRex," as described in Turnbull et al 2010) and samples from individual observing sites are always extracted on the same line.…”

Assessment of fossil fuel carbon dioxide and other anthropogenic trace gas emissions from airborne measurements over Sacramento, California in spring 2009

“…For example, carbon monoxide (CO) is produced during incomplete combustion, and the emission ratio of CO to CO 2 ff (R CO/CO 2 ff ) varies from 0.1 to 100 ppbCO/ppmCO 2 ff, with the lowest values being associated with large, efficient power plants, and larger values observed from vehicles and domestic coal burning (e.g. Ohara et al, 2007;USEPA, 2009). Recent efforts to improve air quality have also resulted in a decrease in CO emissions from anthropogenic sources over the last decade (Hudman et al, 2008;Parrish et al, 2006;Warneke et al, 2006).…”