Long-term greenhouse gas measurements from aircraft

• Published in: Atmospheric Measurement Techniques
• Main Authors: A. Karion, C. Sweeney, S. Wolter, T. Newberger, H. Chen, A. Andrews, J. Kofler, D. Neff, P. Tans
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2013
• Subjects: Environmental engineering; TA170-171; Earthwork. Foundations; TA715-787; Arctic; Hercules; Barrow; Kodiak; Alaska
• Online Access: https://doi.org/10.5194/amt-6-511-2013; https://doaj.org/article/8a73dfd999644124bc91517737eaf955

In March 2009 the NOAA/ESRL/GMD Carbon Cycle and Greenhouse Gases Group collaborated with the US Coast Guard (USCG) to establish the Alaska Coast Guard (ACG) sampling site, a unique addition to NOAA's atmospheric monitoring network. This collaboration takes advantage of USCG bi-weekly Arctic Domain Awareness (ADA) flights, conducted with Hercules C-130 aircraft from March to November each year. Flights typically last 8 h and cover a large area, traveling from Kodiak up to Barrow, Alaska, with altitude profiles near the coast and in the interior. NOAA instrumentation on each flight includes a flask sampling system, a continuous cavity ring-down spectroscopy (CRDS) carbon dioxide (CO 2 )/methane (CH 4 )/carbon monoxide (CO)/water vapor (H 2 O) analyzer, a continuous ozone analyzer, and an ambient temperature and humidity sensor. Air samples collected in flight are analyzed at NOAA/ESRL for the major greenhouse gases and a variety of halocarbons and hydrocarbons that influence climate, stratospheric ozone, and air quality. We describe the overall system for making accurate greenhouse gas measurements using a CRDS analyzer on an aircraft with minimal operator interaction and present an assessment of analyzer performance over a three-year period. Overall analytical uncertainty of CRDS measurements in 2011 is estimated to be 0.15 ppm, 1.4 ppb, and 5 ppb for CO 2 , CH 4 , and CO, respectively, considering short-term precision, calibration uncertainties, and water vapor correction uncertainty. The stability of the CRDS analyzer over a seven-month deployment period is better than 0.15 ppm, 2 ppb, and 4 ppb for CO 2 , CH 4 , and CO, respectively, based on differences of on-board reference tank measurements from a laboratory calibration performed prior to deployment. This stability is not affected by variation in pressure or temperature during flight. We conclude that the uncertainty reported for our measurements would not be significantly affected if the measurements were made without in-flight calibrations, provided ...