West Systems Portable diffuse flux meter, Руководство пользователя

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4 Measuring flux
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4.3 Quantifying the flux
As explained in the previous paragraph, the flux is proportional to the
concentration increase ratio ppm/sec. The proportionality factor depends on the
chamber volume/surface ratio as well as the barometric pressure and the air
temperature inside the accumulation chamber.
There are two methods to carry out the field work, in both cases for each
measurement you have to record the type of accumulation chamber used, the
barometric pressure, and the air temperature.
The variation of few mBar of the pressure and or few degrees of temperature
do not affect the evaluation of flux very much, then you can use a mean value
for both parameters. Of course that depends on the accuracy you want to reach
for the evaluation of flux.
The instrument measures the barometric pressure and the air temperature
inside the chamber.
Choosing the flux measurement unit
The first measurements made, 20 years ago, with the accumulation chamber
was expressed in cm/sec which is a speed, the speed of carbon dioxide flowing
out from the soil. During the last years several units have been used by
volcanologist and by geochemistry researchers. The most common unit is
grams/m
2 per day, but that requires using different conversion factors for each
gas species. Currently we use the unit moles/m 2 per day that has two
advantages: a single conversion factor for every gas specie and an easy
conversion of the flux in grams/sm per day simply multiplying the result
expressed in moles/m 2 per day for the molecular weight of the target gas.
The default unit in the FluxManager is ppm/sec , meaning that the
conversion to the flux unit is postponed to the post-processing of
the data.
Otherwise you can set it to moles/m 2 /day or µmoles/m 2 /day to
evaluate the flux extent directly in the field.