Conversion of a Continuous Flow Cavity Ring-Down Spectrometer to Measure 13C in CO2 Using Static Analyses of Small Volume Grab Samples (Invited)
Abstract
Laser-based analyses of concentration and isotopic content allow unprecedented temporal resolution for a number of important atmospheric constituents. Perhaps overlooked is the potential for these tools to also provide analyses in a more traditional "mass spectrometric" mode that is readily deployable in a field setting. Certain sampling regimes (e.g. soil profiles) are not appropriate for continuous sampling due to their slow change and disturbance of gradients caused by frequent/continuous sampling. We have modified the inlet and plumbing system of a commercial continuous flow cavity ring-down spectrometer in a manner that allows for 13C analyses of CO2 from syringe samples at volumes as small as 25 ml of air with ambient concentrations of CO2. The method employs an external high vacuum pump and a series of programmable micro-valves that allow for evacuation of the long-pass ring-down cell followed by controlled filling, via syringe, of the cavity to optimal sampling pressure and subsequent static analysis of CO2 concentration and 13C /13C ratios. The set-up is field deployable with modest power requirements and allows for near real time analysis in a variety of sampling environments and on-the-fly determination of sampling protocol. In its current configuration, the system provides precision of 1% for CO2 concentration and 0.3 permil for δ13C in replicate analyses of reference air. We have deployed the system to a field laboratory in central New Mexico near a controlled tree mortality research site where post-mortality ecosystem CO2 evolution is being studied. Results from the first field season will be presented and discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B13E..07R
- Keywords:
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- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE / Biosphere/atmosphere interactions;
- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry;
- 0490 BIOGEOSCIENCES / Trace gases