Method of measuring the flux of a soil gas
A method for determining a flux of a gas contained in a medium through a boundary of the medium comprises 1) measuring at least twice with a probe a concentration C of the gas over a time interval Δt and 2) determining the flux of the gas using the following mathematical equation: (I) where F is the gas flux, D is the diffusivity value and ΔC is a variation in the gas concentration during the time interval Δt. The probe is placed proximate the boundary. The probe has a gas inlet, a cavity, a gas concentration sensor and a membrane. Each element is in fluid communication with each other so that the gas flows from the gas inlet through the membrane and contacts the gas concentration sensor. F = ( D ∂ C ( z , t ) ∂ z ) z = 0 = D Δ C πΔ t ( I )
1. A method for determining a flux of a gas contained in a medium through a boundary, the method comprising:
measuring at least twice with a probe a concentration C of the gas over a time interval Δt, said probe being placed proximate the boundary, said probe having a gas inlet, a cavity, a gas concentration sensor and a membrane in fluid communication with each other so that the gas flows from said gas inlet through said membrane and contacts said gas concentration sensor; and
determining the flux of the gas using the following mathematical relation:
F
=
(
D
∂
C
(
z
,
t
)
∂
z
)
z
=
0
where F is the gas flux, D is a diffusivity value of the gas and C(z,t) is said gas concentration as a function of both depth and time.
2. The method of claim 1 wherein said mathematical relation is the following mathematical equation:
F
=
D
Δ
C
πΔ
t
where ΔC is a variation in the gas concentration over the time interval Δt.
3. The method of claim 2 further comprising determining said diffusivity value of the gas.
4. The method of claim 3 further comprising determining said time interval Δt as a function of said diffusivity value of the gas.
5. The method of claim 4 wherein said diffusivity determining comprises imposing said diffusivity to the gas at a predetermined value with said membrane.
6. The method of claim 5 wherein said probe further comprises a gas exhaust in fluid communication with said gas inlet, said cavity and said gas concentration sensor.
7. The method of claim 6 wherein said gas exhaust is equipped with a second membrane, said determining comprises imposing said diffusivity to the gas at a predetermined value with said membranes.
8. The method of claim 4 wherein said determining of said diffusivity value of the gas comprises measuring a diffusivity of the gas through the boundary of the medium.
9. The method of any one of claims 1 to 8 , wherein said measuring occurs at a single location.
10. The method of claim 2 further comprising correcting said gas concentration measurement based on at least one of a temperature, a pressure, or an ambient atmospheric concentration of the gas outside of said probe.
11. The method of claim 2 further comprising conditioning said gas concentration measurement to remove undesired noise.
12. The method of claim 2 wherein said solving occurs simultaneously with said measuring.
13. The method of claim 2 further comprising resetting said concentration measuring of the gas.
14. The method of claim 13 wherein said resetting further comprises moving said probe away from said boundary and sequentially placing said probe back proximate said boundary so as to significantly influence said gas concentration measurement.
15. The method of claim 13 wherein said resetting further comprises purging said probe with a second gas substantially different from the measured gas so as to influence said gas concentration measurement.
16. The method of claim 13 wherein said resetting further comprises purging said probe with an ambient air surrounding said probe so as to influence said gas concentration measurement.
17. The method of claim 2 further comprising measuring an initial flux of the gas through the boundary of the medium.
18. The method of claim 2 wherein the medium is soil.
19. The method of claim 2 wherein the medium is water.
20. The method of claim 2 further comprising storing said data in an electronic memory.
21. The method of claim 2 further comprising sending said data over Internet.
22. The method of claim 1 wherein the boundary is a boundary of the medium.
23. The method of claim 1 wherein the boundary is a boundary of said probe.