Dissolved Methane

The data plots below are from an experimental dissolved methane probe developed for this project based on a Figaro TGS2611-C00 metal oxide semiconductor methane and LP gas sensor. See Probe Info. under Menu for more information on probe construction and calibration.

In the plots below, the solid line is the paritial pressure of dissolved methane, while the dotted line is the partial pressure of methane in the MC gas headspace.  Note, as currently calibrated, the dissolved methane concentration is higher than that in the gas headspace, which is not possible.  However, the methane sensor sensitivity at high methane concentrations (> 1%) is very low, so probe accuracy is poor at these concentrations.  These preliminary data do indicate that the MCs are not mass transfer limited.

Plots below are for the last 40 days.  Click on links below for plot of entire data.
MC 1 dCH4 
    Plot of all MC1 dCH4 data

MC2 dCH4
    Plot of all MC2 dCH4 data


MC 3 dCH4
    Plot of all MC3 dCH4 data


MC 4 dCH4
    Plot of all MC4 dCH4 data


Note, probes accumulate some water that causes the signal drop outs.  Water in the silicone tube causes decreased methane transport, but once it is removed, the probe seems to function as normal.  

Modifications

  1. Replaced 1/8" silicone tubing with 3/16" tubing (2 3/4" length) to see if these improve water accumulatin problem.  (17:00 3 May 2011, t = 256.7 d).
  2. Probes off-line for calibration with new tubing (10:00 5 May 2011, t = 258.42).
  3. Probes back on line (11:30 10 May 2011, t = 263.48 d).
  4. Probes cleaned, water removed (16:15 24 Jun 2011, t = 308.68 d)
  5. Probes cleaned, water removed (17:00 14 Jul 2011, t = 328.71 d).
  6. Probes cleaned, water removed (13:00  5 Aug 2011, t = 350.54 d).
  7. Probes in MC 2 and 3 cleaned, water removed (14:00 26 Aug 2011, t = 371.58 d).
  8. Probes cleaned, water removed (14:00  4 Oct 2011, t = 410.58 d).
  9. Probes cleaned, water removed (08:30  12 Jan 2012, t = 510.35 d).