Radiocarbon analysis of stratospheric CO 2 retrieved from AirCore sampling

• Published in: Atmospheric Measurement Techniques
• Main Authors: D. Paul, H. Chen, H. A. Been, R. Kivi, H. A. J. Meijer
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2016
• Subjects: Environmental engineering; TA170-171; Earthwork. Foundations; TA715-787; Sodankylä; Northern Finland
• Online Access: https://doi.org/10.5194/amt-9-4997-2016; https://doaj.org/article/09a8e396402b4419840a2f70537cc25b

Radiocarbon ( 14 C) is an important atmospheric tracer and one of the many used in the understanding of the global carbon budget, which includes the greenhouse gases CO 2 and CH 4 . Measurement of radiocarbon in atmospheric CO 2 generally requires the collection of large air samples (a few liters) from which CO 2 is extracted and then the concentration of radiocarbon is determined using accelerator mass spectrometry (AMS). However, the regular collection of air samples from the stratosphere, for example using aircraft and balloons, is prohibitively expensive. Here we describe radiocarbon measurements in stratospheric CO 2 collected by the AirCore sampling method. AirCore is an innovative atmospheric sampling system, which comprises a long tube descending from a high altitude with one end open and the other closed, and it has been demonstrated to be a reliable, cost-effective sampling system for high-altitude profile (up to ≈ 30 km) measurements of CH 4 and CO 2 . In Europe, AirCore measurements have been being performed on a regular basis near Sodankylä (northern Finland) since September 2013. Here we describe the analysis of samples from two such AirCore flights made there in July 2014, for determining the radiocarbon concentration in stratospheric CO 2 . The two AirCore profiles were collected on consecutive days. The stratospheric part of the AirCore was divided into six sections, each containing ≈ 35 µg CO 2 ( ≈ 9.6 µgC), and stored in a stratospheric air subsampler constructed from 1∕4 in. coiled stainless steel tubing ( ≈ 3 m). A small-volume extraction system was constructed that enabled > 99.5 % CO 2 extraction from the stratospheric air samples. Additionally, a new small-volume high-efficiency graphitization system was constructed for graphitization of these extracted CO 2 samples, which were measured at the Groningen AMS facility. Since the stratospheric samples were very similar in mass, reference samples were also prepared in the same mass range for calibration and contamination correction ...