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Harvard Forest Symposium Abstract 2011

  • Title: High frequency measurements of Carbonyl Sulfide
  • Primary Author: Roisin Commane (Harvard Research Group)
  • Additional Authors: Steven Wofsy (Harvard University); Mark Zahniser (Aerodyne Research Inc.)
  • Abstract:

    Carbonyl sulfide (OCS) is the most abundant sulfur containing gas in the atmosphere. OCS is a surrogate for CO2 uptake by plants during photosynthesis, but, unlike CO2, is not emitted by plants during respiration. Recent studies have suggested that OCS may provide unique constraints on carbon assimilation by the biosphere that are independent of the influence of respiration. While the loss of OCS is thought to be dominated by vegetative uptake, OCS is also subject to significant loss through uptake by soils, the magnitudes of which is not known. Globally, OCS mixing ratios have been found to vary from 350 to 550 pptv (parts per trillion).





    Present measurement methods for measuring OCS rely on canister sampling followed by laboratory analysis using gas chromotography. While accurate and precise, this method is highly labour intensive, with limited sampling sites and global coverage. We have developed a method for the direct, continuous, measurement of OCS using an infrared laser absorption technique with a measurement precision (3 std deviation) of less than 10 ppt in 30 s. The instrument uses a continuous wave quantum cascade laser operated at near room temperature, allowing for long term unattended operation.


    Measurements of OCS gradients have been made at the EMS walk-up tower from October 2010 and will continue until October 2011. Before the winter snowfalls, OCS gradients were found to coincide with the night-time loss of H2 to soils observed at the nearby EMS flux tower. Winter gradients have been minimal but this is expected to change as the snow melts and the trees become active again in the spring.


  • Research Category:

  • Figures:
  • OCS_conc_201010_201101.png