Flask sample measurements for CO2, CH4 and CO using cavity ring-down spectrometry
J.-L. Wang1, G. Jacobson2, C. W. Rella2, C.-Y. Chang3, I. Liu4, W.-T. Liu1, C. Chew3, C.-F. Ou-Yang1,5, W.-C. Liao1, and C.-C. Chang31Department of Chemistry, National Central University, 320 Chungli, Taiwan 2Picarro, Inc., Santa Clara, CA, USA 3Research Center for Environmental Changes, Academia Sinica, 11529 Taipei, Taiwan 4Jusun Inc., 231 New Taipei City, Taiwan 5Department of Atmospheric Sciences, National Central University, 320 Chungli, Taiwan
Received: 03 Aug 2013 – Accepted for review: 20 Aug 2013 – Discussion started: 22 Aug 2013
Abstract. In recent years, cavity ring-down spectrometry (CRDS) has been demonstrated to be a highly sensitive, stable and fast analytical technique for real-time in situ measurements of greenhouse gases. In this study, we propose the technique (which we call flask-CRDS) of analyzing whole air flask samples for CO2, CH4 and CO using a custom gas manifold designed to connect to a CRDS analyzer. Extremely stable measurements of these gases can be achieved over a large pressure range in the flask, from 175 to 760 Torr. The wide pressure range is conducive to flask sample measurement in three ways: (1) flask samples can be collected in low-pressure environments (e.g. high-altitude locations); (2) flask samples can be first analyzed for other trace gases with the remaining low-pressure sample for CRDS analysis of CO2, CH4 and CO; and (3) flask samples can be archived and re-analyzed for validation. The repeatability of this method (1σ of 0.07 ppm for CO2, 0.4 ppb for CH4, and 0.5 ppb for CO) was assessed by analyzing five canisters filled with the same air sample to a pressure of 200 Torr. An inter-comparison of the flask-CRDS data with in-situ CRDS measurements at a high-altitude mountain baseline station revealed excellent agreement, with differences of 0.10 ± 0.09 ppm (1σ) for CO2 and 0.9 ± 1.0 ppb for CH4. This study demonstrated that the flask-CRDS method was not only simple to build and operate but could also perform highly accurate and precise measurements of atmospheric CO2, CH4 and CO in flask samples.
Wang, J.-L., Jacobson, G., Rella, C. W., Chang, C.-Y., Liu, I., Liu, W.-T., Chew, C., Ou-Yang, C.-F., Liao, W.-C., and Chang, C.-C.: Flask sample measurements for CO2, CH4 and CO using cavity ring-down spectrometry, Atmos. Meas. Tech. Discuss., 6, 7633-7657, doi:10.5194/amtd-6-7633-2013, 2013.