## 2.25.4. Ebullition[¶](#ebullition "Permalink to this headline")
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Briefly, the simulated aqueous CH4 concentration in each soil level is used to estimate the expected equilibrium gaseous partial pressure (\\(C\_{e}\\) ), as a function of temperature and depth below the water table, by first estimating the Henry’s law partitioning coefficient (\\(k\_{h}^{C}\\) ) by the method described in [Wania et al. (2010)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#waniaetal2010):

(2.25.5)[¶](#equation-24-5 "Permalink to this equation")\\\[\\log \\left(\\frac{1}{k\_{H} } \\right)=\\log k\_{H}^{s} -\\frac{1}{C\_{H} } \\left(\\frac{1}{T} -\\frac{1}{T^{s} } \\right)\\\]

(2.25.6)[¶](#equation-24-6 "Permalink to this equation")\\\[k\_{h}^{C} =Tk\_{H} R\_{g}\\\]

(2.25.7)[¶](#equation-24-7 "Permalink to this equation")\\\[C\_{e} =\\frac{C\_{w} R\_{g} T}{\\theta \_{s} k\_{H}^{C} p}\\\]

where \\(C\_{H}\\) is a constant, \\(R\_{g}\\) is the universal gas constant, \\(k\_{H}^{s}\\) is Henry’s law partitioning coefficient at standard temperature (\\(T^{s}\\) ),\\(C\_{w}\\) is local aqueous CH4 concentration, and _p_ is pressure.

The local pressure is calculated as the sum of the ambient pressure, water pressure down to the local depth, and pressure from surface ponding (if applicable). When the CH4 partial pressure exceeds 15% of the local pressure ([Baird et al. 2004](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#bairdetal2004); [Strack et al. 2006](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#stracketal2006); [Wania et al. 2010](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#waniaetal2010)), bubbling occurs to remove CH4 to below this value, modified by the fraction of CH4 in the bubbles \[taken as 57%; ([Kellner et al. 2006](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#kellneretal2006); [Wania et al. 2010](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#waniaetal2010))\]. Bubbles are immediately added to the surface flux for saturated columns and are placed immediately above the water table interface in unsaturated columns.

