AREA SOURCE SAMPLING PROTOCOL USING THE ODOFLUX™ SAMPLING
CHAMBER
A surface source is defined as a source of diffuse
emissions on a certain surface. Landfills, contaminated sites,
composts and manure, waste water treatment pools, spreading
fields and others are examples of area sources.
Gas sampling from surface sources is carried
out using TEDLAR© 1 bags or any chemically inert container.
The valves of the bag or the container must be chemically
resistant as well. Stainless steel or TEFLON© 2 are often
used. These bags or containers may vary in size from 5 to
80 liters. All piping, surfaces and connections in contact
with sampled gas are TEFLON©, TEDLAR©, stainless
steel, glass or acrylic resin.
For bags, sampling can be carried out using
a lung chamber. Gas can thereby be sampled from the surface
source without the gas coming into contact with internal parts
such as pump segments. The lung chamber consists of a tight
barrel in which the sampling bag is introduced. The flux chamber
consists of a cylindrical enclosure with a spherical top.
The flux chamber is supplied with a controlled flow of ultra
pure air coming from a cylinder (see Figure 1). The pure air
can also be generated in the field by a filtration system
and a compressor. The bag introduced in the lung chamber is
connected by a TEFLON© tube to the outlet of the flux
chamber. The air is sucked from the lung chamber using a pump
at a controlled flow rate. Due to negative relative pressure,
the bag is then filled with gas from the flux chamber (see
diagram bellow).
It is important to work under isokinetic conditions
between the gas introduced to the chamber and the gas withdrawn.
These isokinetic conditions insure that the gas is emitted
at the surface as if there was no flux chamber. This working
condition is essential to obtain a good measurement of the
real flux emitted from the surface. In most surface sources,
the emission flow rate is very small. A mass balance on the
flux chamber for O2 and N2 can then assume that all the volume
of air introduced in the chamber is coming from the pure air
source. In this case, the technician can set the inlet and
outlet flow rate at the same value to have the isokinetic
working conditions. In other cases the volume flow of gas
emitted at the surface source may not be insignificant. The
outlet flow rate will have to be adjusted in accordance to
obtain the isokinetic working conditions.
A : Ultra pure air (or any neutral gas)
B : Flux chamber
C : Lung chamber
D : TEDLAR© sampling bag
E : Pump
F : Rotameter
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