TARGAS-1 Operation Manual V. 1.02 158 support@ppsystems.com
=
In this case the value of / is calculated from a linear regression of the C and T data.
Correction for water vapor increase on CO
2
efflux
In addition to the influx of CO
2
from soil, a closed chamber system can also experience an increase in
H
2
O due to evapotranspiration from soil or plants. This added H
2
O dilutes the remaining CO
2
and
requires a compensation in a similar way to equation (A.13).
For total moles of air in the chamber of ,
(2.7) the moles of H
2
O added to the chamber is =
(
)
(
)
,
where
and
are H
2
O concentrations in mmol mol
-1
.
The initial moles CO
2
in the system =
× , where
is CO
2
concentration in mol mol
-1
.
Then, the final moles CO
2
in the system =
×
(
+
)
, where
is CO
2
concentration in mol mol
-
1
.
(2.8) The change in moles of CO
2
is (
×
(
+
)
(
× ) =
+
The term
is equivalent to the / term calculated above, and the
term is the
correction due to evapotranspiration.
(2.9) So, with the H
2
O compensation, we have
= +
where can be either from the quadratic or linear fit.
FCO
2
Units for measurement of Soil CO
2
Efflux
(2.10) To give the CO
2
flux in mass/unit area/unit time the following conversion is made:
(g m
hr
) =
mol
mol s
×
1013
×
273
273 +
×
44.009 g
22.414 L
×
m
m
×
mol
10
mol
×
3600 s
hr
×
10
L
m
Where
/ is from eqn 1.9 from linear or quadratic fit and with H
2
O compensation
is the correction for barometric pressure with P measured in mbar by the TARGAS-1,
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